Rod Machado's Private Pilot eHandbook · 2015-02-23 · Rod Machado’s Private Pilot Handbook O2...

“Cessna 2132 Bravo, this isDeparture Control, please squawkstandby. There’s a problem with yourtransponder,” said the controller.

“What’s the problem?” asked thepilot of the Cessna 152.

“Well, we show your airplaneclimbing through 19,500 feet doing320 knots,” replied the controller.

The quick thinking pilot with anexcellent sense of humor replied, “Ohno, that’s right. We just had ourengine overhauled.” Now that’s realperformance! Except, of course, thatit was unreal performance. The con-troller could easily predict that no152 on (or off) Earth was capable ofdoing 320 knots or climbing to 19,500feet.

Airplane performance is pre-dictable. Unlike psychics, pilots don’tneed crystal balls or Quija boards tomake performance estimates that arevery close to the mark. An airplane’stakeoff, climb, cruise and landingperformance is easily estimated froma variety of charts found in thePilot’s Operating Handbook (POH),which is as much a part of the air-craft’s equipment as the wings. (Ifyou don’t see either the wings or thePOH, better ask about it).

Your job is to know how to use theperformance charts. As you’ll soon

see, all airplane performance is basedon one very important item—air den-sity. That’s because the thickness ofthe air flowing over the wings or intothe engine determines how well theairplane performs (or fails to per-form).

Air DensityAirplanes are remarkably similar

to people in that both experiencedecreased performance in less-denseair. Anyone who’s ever hiked to thetop of a high mountain knows howhuman performance decreases. One

trip up El Capitan at Yosemite andyou feel like you’re the big, bad wolf,huffing and puffing as though youwere trying to blow a house down.

Airplanes, too, are air-breathingmachines, and they respond much asyou do to lowered air density. Themore air molecules flowing over theairplane’s wing, the greater the liftdeveloped. Anything that thins theair reduces the wings’ ability to gen-erate lift.

Airplane engine performance isaffected in the same way. Power-plants require air to run. Anything

Page O1

Chapter Fifteen

Airplane PerformanceKnow Before You Go

Twin 34Alpha, give me yourbest rate of climb to5,000 feet please!

Ha, ha!Yes, both are onand I’m climbingas fast as I can.

How canthere be a noiseproblem at this

altitude?

Whoa!She’s really

starting to climbnow!

OK Center,I’m trying!

Twin 34 Alpha,have you ever heard the

sound of two airplanes hit-ting one another?

Twin 34Alpha, are you usingboth of your engines?

Twin 34 Alpha,give me your best rate of

climb now or make animmediate right turn for

noise abatement!

Courtesy Cessna

Licensed exclusively for DeWayne Britton ([email protected]) Transaction: #0002858938

Rod Machado’s Private Pilot HandbookO2

reducing the amount of air the engineswallows diminishes its power output.Less power equals less performance. Nofancy mathematics here. It’s really quitesimple. To fly without understanding thisimportant relationship is about as wise ashaving the three little pigs invite the wolfin for a spot of tea, which would certainlygive new meaning to the term “pig out.”

Let’s take a closer look at the thingswhich affect airplane performance.

HeightAs we discussed in an earlier chapter,

the higher you go, the less frequentlyyou—or your airplane’s wing—will runinto air molecules, because they are fewerand farther between with increasing alti-tude. This is another way of saying thatthe air density is less. Fewer air moleculesare available to move past the wing, so liftis reduced and performance is decreased.Expect higher altitudes to provide youwith slower acceleration, longer groundruns, and shallower climb profiles, asshown in Figure 1.

HeatHeat is also notorious for reducing the

performance of airplanes. Heated air ismuch less dense than colder air. Expectslower acceleration, longer takeoff runs,and shallower climb profiles on hot days,as shown in Figure 2.

HumidityHigh humidity also reduces airplane

performance by thinning the air. Wait aminute, you say! How can adding mois-ture to air make it thinner? Moist air islighter (thus less dense) because watermolecules are actually lighter than airmolecules. Mind you, I said water mole-cules, not water, which is obviously a lotheavier because of the density. If you’veever tried to carry a bucket of steam (itrises because it’s lighter than air), you’vehad direct proof that moist air is lessdense than dry air. By itself, moist airisn’t much of a problem. This is why mostperformance charts make no correctionfor humidity. Nevertheless, in combina-tion with height and heat it could putyour airplane dangerously close to thosetrees at the end of the runway.

The very best way to think of all this isto remember that you should avoid joining

30 12

30 12

30 12

HEIGHT AND AIRPLANE PERFORMANCE

Ground Roll

15,000' MSL(air too thin for this airplane

to become airborne)

5,000' MSL(takeoff ground roll increased

and climb angle shallower)

100' MSL(fairly short ground roll andgood climb performance)

I hate itwhen thishappens.

An increase in altitude has an adverse effect on airplane performance. Higher alti-tude means thinner air, which reduces the wing's ability to develop lift as well as re-ducing the engine's power output. Higher altitudes are associated with a longerground run, a reduced rate of climb and a shallower climb angle. The likelihood ofclimbing over obstacles at the departure end of the runway diminishes at this de-creased air density.

HEAT AND AIRPLANE PERFORMANCE

Ground Roll

110 F(air too thin for this airplane

to become airborne)

90 F(takeoff ground roll increased

and climb angle shallower)

50 F(fairly short ground roll andgood climb performance)

Ahh! I'moutta here!

For examplepurposes only.This ATC towerwouldn't reallybe at the endof the runway.

(Honest!)

An increase in temperature has an adverse effect on airplane performance. Warmerair means thinner air which reduces the wings' ability to develop lift as well as re-duces the engine's power output. Warmer temperatures bring longer ground runsand shallow climb angles.

He's lookinggood!

I can seehis eyes!

o

o

o

Fig. 1

Fig. 2

Flare when you hear the crickets.Dave Rossi


Chapter 15 - Airplane Performance: Know Before You GoO3

aviation’s 4-H club. Because if youhave height, heat and humidity, youhave heck to pay (ahhh, those 4 H’s!).Any one or a combination of thesefactors can turn an airplane into acar by keeping it from becoming air-borne.

If you want to avoid ending up onthe Oprah Winfrey show, don’t doweird, strange things in your air-plane, like taking off with a lot ofheight, heat and humidity.

“OK, Rod,” I hear you saying,“how much is a lot?” Good question.The effects of height and heat are allcombined into one very importantcalculation called density altitude.

Density AltitudeTaking off at an airport near sea

level usually results in good accelera-tion and climb performance. The ele-vation has no effect on performance,temperatures are usually moderate,and the humidity is generally not toohigh. If we take off from an airportsituated at 100 feet MSL, the air-plane performs quite well.

Suppose, however, that it’s anextraordinarily hot day at our 100foot MSL airport. Will the airplaneperform well? No. Because of thehigh heat, the air might have a densi-ty equivalent to an altitude around3,000 feet. The term density altitudedescribes how dense the air feels tothe airplane, regardless of the air-plane’s present height above sealevel. Density altitude is an extreme-ly important term for you to under-stand.

In the previous example, eventhough the airplane was physically at100 feet MSL, in terms of airplaneperformance the airport has a densityaltitude of 3,000 feet.

In Chapter 5, I mentioned thatpressure altitude was the referenceto which airplane engineers calibratetheir performance charts. Pressurealtitude is what the altimeter indi-cates when 29.92 inches Hg is set inthe altimeter’s Kollsman window. Inaddition to the pressure altitude ref-erence, engineers also calibrate manyof their performance charts to a stan-dard temperature of 59 degrees F (15degrees C) at sea level.

Engineers call the conditions of29.92 inches Hg and 59 degrees F (15degrees C) at sea level standard con-ditions. Since you must have a start-ing point or reference when calibrat-ing the performance of airplanes (andtheir instruments), standard condi-

tions at sea level is a good startingplace. For example, when you ask theteacher how your son Bobby is doingin school, he or she normally com-pares his performance to that of aprevious year. The teacher might say,“Well, compared to last year, Bobbyis doing better.” If the teacher said,“Well, in reference to all forms of ani-mal and plant life on this planet, lit-tle Bobby is holding his own againstmost species of protozoa,” thenBobby is in trouble. Standard tem-perature and pressure conditions aresimply a reference point where abaseline of performance is estab-lished.

Of course, if standard conditionsexisted at sea level all the time, wewouldn’t have to worry aboutchanges in air density and its effectson airplane performance. Unfor-tunately, Mother Nature doesn’t likeconstant, standard conditions (that’swhy a tornado is similar to a divorceor an earthquake—one of them isgoing to get your house).

Let’s assume you’re at an airportat 4,000 foot MSL and standard con-ditions exist at sea level. Let’s alsoassume that temperatures decreaseat 3.5 degrees F (2 degrees C) per1,000 feet (by now you know thatwhile this is the engineer’s standardlapse rate and is used for instrumentcalibration, it is seldom the actuallapse rate found in the environment).Under these conditions, the tempera-ture at 4,000 feet should be 45degrees F (4x3.5=14 and 59-14=45degrees F). Suppose it’s really hot,

HIGH FRIGHTI was on a night, scenic VFR flight with a passenger.

After one hour my passenger was trying to eat popcornand talk, but it was all “gibberish.” My altimeter was indi-cating 11,500’ and holding steady. However, I noticed asteady rate of climb indication of 120 fpm, and an 11,000’mountain off the wing appeared unusually small. I con-tacted Approach and asked for Mode C readout. Theyinformed me that Center read me at 19,700’ MSL. Thecontroller recommended rapping on the panel. I began adescent for home airport and banged on the panel above

the altimeter. It immediately jumped to 16,400 and was moving again. I should havenoticed a shallow climb with the other instruments. However, I hadn’t had any sleepfor 36 hours and thought I was doing a nice job of maintaining my eastbound cruisealtitude of 11,500. ASRS Report

HUMIDITYAn increase in humidity produces an increase in density altitude, butit’s not often dramatic. Increasing the relative humidity of standardtemperature air from 50% to 100% often doesn’t increase the densityaltitude by more than 100 to 150 feet. Now, if the air is significantlyabove standard temperature, then the increase in density altitude canbe as high as 600 feet. For example, if the air temperature at 5,000 feet is 80 degrees F with

a 0% relative humidity, then the density altitude is approximately 7,445feet. Increase the humidity in the example above to 100% and thedensity altitude jumps to 7957 feet. That’s an increase in 514 feet dueto a 100% increase in relative humidity at these higher temperatures.If you’d like to see for yourself how humidity affects density altitude

take a look at Richard Shelquist’s density altitude calculator page at(http://wahiduddin.net/calc/calc_da_rh.htm).



say 100 degrees F (38 degrees C) at4,000 feet (this is definitely a non-standard temperature). Is the air-plane going to perform like it normal-ly would at 4,000 feet? Definitely not.In fact, the airplane is going to per-form more like it’s at 7,500 feet (I’llshow you in just a moment how Iarrived at this value).

Because of the higher than normaltemperature, the air has a densityaltitude—a performance altitude, ifyou want to think of it that way—ofapproximately 7,500 feet. Think ofdensity altitude as you do personaldebt. Whenever debt increases, badthings happen; when debt decreases,good things happen. Increasing den-sity altitude decreases airplane per-formance; decreasing density altitudeincreases airplane performance.

Density Altitude Example No. 1 –Finding the density altitude is easywith the density altitude chart inFigure 3. Along the bottom (horizon-tal) axis is a temperature scale withFahrenheit and Celsius markings.Rising diagonally upward from left toright are pressure altitude lines. Onthe left side of the chart is the densi-ty altitude reading along the verticalscale. If you know the pressure alti-tude and the air temperature foryour location, you can easily find thedensity altitude. Let’s see how thisworks.

Assume your outside air tempera-ture (OAT) is 80 degrees F (27degrees C) and the pressure altitudeis 7,000 feet. Referring to Figure 3,find 80 degrees F (27 degrees C) onthe bottom, horizontal scale andmove upwards until reaching the7,000 foot (diagonal) pressure alti-tude line. Make a mark at this point(position 1) and move horizontally tothe left. The number on the left handvertical scale is the density altitude.In our example the density altitude is10,000 feet.

Density Altitude Example No. 2 –What is your density altitude if thepressure altitude is 3,257 feet andthe OAT is 75 degrees F (24 degreesC)? First you must locate yourpressure altitude between the diag-onal lines on the density altitude

chart in Figure 4. Locating the pres-sure altitude value of 3,257 is easy ifyou draw the intermediate valuesbetween the 1,000 foot pressure alti-tude lines. Simply draw the 3,500foot pressure altitude value betweenthe 3,000 and 4,000 foot pressurealtitude lines, as shown in Figure 4.Now draw an intermediate valuebetween the 3,000 and 3,500 footpressure altitude line. This will rep-resent the 3,250 foot pressure alti-tude value. Move up the 75 degree F(24 degree C) line until reaching thepressure altitude line of 3,250, asshown by position 2 (this is very closeto the actual pressure altitude valueof 3,257 feet). Go across to the left tofind a density altitude value ofapproximately 5,000 feet.

At the end of this chapter inPostflight Briefing #15-1, I’ve includ-ed two different types of density alti-tude problems that show up on FAA

knowledge exams. Unfortunately,one of the problems is more test ori-ented than it is practical in the realworld. Don’t ask me why test cre-ators do this. It reminds me of some8th century monk-scribe insertingwords in an ancient text that eventu-ally becomes the foundation of ourmodern English language. As themonk is writing the official word forsharp instrument with a handle thatcuts your steak, he looks around,then mischievously inserts a K in theword knife. No one knows why he didthis, but it’s a done deed. We’ve gotto live with it. Study Postflight Briefing#15-1 carefully during your finalpreparation for the knowledge exam.

Let’s look at an even more mean-ingful example of how density alti-tude relates to airplane performance.Before we can do that we need tounderstand something known as ser-vice ceiling.

Fig. 3



Service CeilingMost POHs for individual air-

planes inform pilots of the maximumheight the airplane can be flown tobefore it ceases climbing (technically,the altitude at which the climb ratedrops to 100 feet per minute). Thisheight is known as the service ceiling(Figure 5). The service ceiling appliesto a brand new airplane with a newengine. You can expect older air-planes to have service ceilings lessthan the book value. Figure 6 shows14,700 feet as the service ceiling of a1980 Cessna 152. Of course, if thedensity altitude is close to or equal tothat of the 14,700 foot service ceiling,the airplane will only climb at 100feet per minute or less.

Density Altitude Problem No. 3 –Suppose you’re flying a new Cessna152 from an airport where the pres-sure altitude is 10,000 feet and theOAT is 95 degrees F (35 degrees C)(that’s hot for an airport that high—better be careful!). What is the densi-ty altitude at that airport?

Use the density altitude chart(Figure 4) to identify where the 95

THE SERVICE CEILING

5,000' MSL

10,000' MSL

14,700' MSL(Service Ceiling)

.

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An airplane reaches its service ceiling when its climb rate isreduced to 100 feet per minute or less.

Fig. 5

Fig. 4

Fig. 6

Pilot Operating Handbook Showing Service Ceiling

For Training Purposes Only!



degree F (35° C) line intersects the10,000 foot pressure altitude line(position 3). Moving horizontally tothe left you determine the densityaltitude to be 14,700 feet.

How will our airplane perform?Not well. Better get out your driver’slicense, since driving is what you’ll bedoing. The airplane, if it gets off therunway at all, will barely climb 100feet per minute. You’re going to scarequite a few people standing at theend of the runway. Take my word forit, if it’s an older airplane, you’llnever become airborne under theconditions in this example. And if it’sa tired old airplane you’ll noticesomething is wrong because it’ll takefull power to taxi (that’s a joke. But itdoes emphasize how much the perfor-mance decreases).

Here’s Machado’s Service CeilingCaveat: Never count on more than75% of an airplane’s posted serviceceiling. This is, admittedly, a conserv-ative estimate if the airplane is new,but a wise and realistic one if the air-plane is old. By my numbers, I wouldexpect a Cessna 152 to climb nofaster than 100 feet per minute at adensity altitude of 11,025 feet (75%of 14,700 feet).

Anything that makes the air thin-ner (lower pressure, high heat, highhumidity) increases the density alti-tude. Anything making the air thick-er (increasing pressure, low heat, lowhumidity) decreases the density alti-tude.

Machado’s Whammo DensityPredictor states: For a given pressurealtitude, the density altitude increas-

es by 1,000 feet for every 15 degree F(8.5 degree C) temperature increase.Given this, and knowledge of yourairplane’s service ceiling, you caneasily estimate the amount your air-plane’s performance will decrease.

Performance ChartsAs a kid, it was often difficult to

predict whether my grandfather wasbeing serious or just joking around.He was a card carrying prankster andproud of it. One time he called meover to his chair and said, “Did youknow you were adopted?”

I was crushed and sighed, “Youmean I was really adopted? Oh no!”

“That’s right,” grandpa said, “butthey brought you back.” Hah!

On another occasion (according tomy mom), whenever I cried as a kidmy grandfather would threaten to callTibet and tell the authorities that hesuspected I was the new Dalai Lama,knowing that they’d come and takeme away. Everybody had a big laughover that one, except me. To this day,whenever someone knocks at thedoor, I peep through the hole and yellout, “You aren’t from Tibet are you? Iwas adopted so leave me alone.”

Fortunately, while grandpa’santics were hard to predict, air-plane performance isn’t. That’sbecause airplanes have performance

What’s AGround Roll?

Aviation has lots of funny terms.Especially if you think about them.

Ground roll is one of those.Sounds like you fed a dinner roll toa CuisinArt, or maybe somethingyou order along with an egg roll atthe local Chinese restaurant.

In fact, ground roll is the distancethe airplane rolls on the ground dur-ing takeoff or landing. On takeoff,it’s the distance from the start of thetakeoff run until the airplane leavesthe ground. On landing, it’s the dis-tance from touchdown to where theplane can be brought to a full stop.

Next time you order from thatChinese place, ask for ground rolland see what happens.

This type of activity dramatically reduces airplane performance.

Nevertheless, credit must be given to the pilot who went out of his way

to entertain his passenger on those long flights.

TAKEOFF DEFINITIONS

The ground roll is the total distance required for the airplane to become air-borne. The point where the airplane reaches 50 feet above the runway is the to-tal distance required for the airplane to clear a 50 foot obstacle (supposedlyplaced at this precise point).

Ground roll

Total distance to clear a 50' obstacle

50'Obstacle

Litfoff orrotation point

AB

C

Fig. 7



charts for all facets of their normal activities:takeoff, climb, cruise, landing, etc. Your successat predicting what will happen during these con-ditions is a matter of your familiarity with thesecharts. Machado’s Ornithological Observationstates: All things that fly should use perfor-mance charts except birds—since they don’thave pockets.

Takeoff Concepts – Takeoffs are secondonly to landings for their excitement and chal-lenge. While a takeoff may not be as spectacularfor some pilots, in my view it requires just asmuch research and planning to do it well.Figure 7 shows a typical takeoff profile. At posi-tion A the airplane applies full power and accel-erates down the runway. It eventually reachesliftoff speed at position B and rotates, which is afancy word for raises the nose to climb. One timeI forgot to tell a student what rotate meant. Atthe appropriate point during the takeoff, Ilooked at him and said, “OK Bob, rotate, rotate.He looked really confused. He thought he wassupposed to twirl around somehow (perhaps as abizarre takeoff ritual similar to the secret hand-shake some flight instructors use). The takeoffground roll is the distance between A and B.

At position C, the airplane has attainedenough height to clear a 50 foot obstacle. Thedistance between positions A and C is called thetotal distance to clear a 50 foot obstacle (don’tyou wish all definitions were that easy?).Obviously, the taller the obstacle, the greaterthe distance required between A and C.

Best Rate and Best AngleOf Climb Speeds

After the liftoff is made, you normally want toclimb at a speed that will get you to your select-ed cruising altitude in the shortest possibletime. There is one and only one such speed. It is,as I hope you remember from the discussion inan earlier chapter, called the best rate of climbspeed—otherwise known as Vy.

Figure 8A shows how a climb at Vy mightlook. The best rate of climb speed will give youthe largest upward deflection on the verticalspeed indicator. In other words, you’ll be able togain altitude in the shortest possible time.

Sometimes climb angle instead of time is a concern during takeoff. Altitude gain for a given distance over theground is a concern when an obstacle looms at the departure end. Watching an obstacle grow in your windshield isexciting in the way it’s exciting to be a spotted owl at a lumberjack convention. If you want to gain the most altitudefor a given distance over the ground, then climb at the best angle of climb speed, otherwise known as Vx. Figure 8Bshows a climb profile at Vx. Notice that if the most altitude is gained by the time the airplane has arrived at the obsta-cle, this represents a very large angle of climb.

Even though the nose attitude is generally higher at Vx, the airplane won’t have as large a rate of climb deflectionon the VSI as it would at Vy (it will initially as you rotate, but then returns to a lesser value). The airplane still climbs

THREE CLIMBING AIRSPEEDS

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80KNOTS

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Vy: 79 kts 700 FPM

The best rate of climb speed (Vy) gives you the greatest altitude gain for agiven amount of time. In other words, it gives you the largest deflection onyour vertical speed indicator.

Climbing at the best rate of climb speed (Vy)

A cruise climb is done with the pilot's choice of airspeed. When no obstaclesare present, climbing at a slightly higher speed provides less climb rate yetprovides better visibility and good engine cooling.

60

100

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80KNOTS

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120 kts 400 FPM

Climbing at a cruise climb airspeed (pilot's choice)

Mostaltitude

The best angle of climb speed (Vx) gives you the greatest altitude gain for agiven distance over the ground. In other words, it gives you the largest climbangle possible.

Climbing at the best angle of climb speed (Vx)

For a given distance

BIG

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Vx: 69 kts 650 FPM

B

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Fig. 8



at a larger angle because Vx is slower than Vy.With a slower forward speed, it gains more alti-tude per foot of forward distance, making theangle of climb quite large. In many cases, theairplane’s POH recommends small flap settingsto facilitate a short-field climb over an obstacle.

The easiest way to remember the differencebetween Vx and Vy is to ask yourself which one,the Y or the X, has more angles? The X has moreangles making it the best angle of climb speed(Vx). By default, Y, with fewer angles, becomesthe best rate of climb speed.

Vx and Vy Change With AltitudeThe best angle and best rate of climb speeds

change slightly with altitude and weight. Sincethe airplane’s ability to climb is predicated onexcess thrust (power), changing altitude orchanging weight (or both) changes the amount ofexcess thrust (power) available for a climb. This,in turn, affects the speeds at which Vx and Vyoccur.

Figure 9 shows a typical rate of climb (ROC)vs. true airspeed graph under full throttle condi-tions. The curve identifies the ROC for differentairspeeds at a specific altitude. At full throttle(assumed to be maximum power) there is no rateof climb at point Z since all the airplane’s poweris used to achieve maximum forward speed.

As the airplane slows to point C, parasite dragdecreases and the excess thrust (thrust not used to overcome drag) has been converted into a rate of climb. Continuedslowing of the airplane further reduces the ROC because of the increasing induced drag. At point Y, the airplane hasno ROC since all the airplane’s power is used in overcoming an enormous amount of induced drag. (This is operating

behind the power curve, as described in Chapter 2.) The sea level, best rate of climb is found at point C. Dropping

directly downward to point D identifies the Vy speed for this particu-lar airplane. A tangent line from the bottom left corner of the graphcontacts the sea level ROC line at point A. At this point, the airplaneexperiences its best angle of climb. Dropping downward from point Ato point B identifies the airplane’s speed for Vx.

Why the tangent line? Mathematically, when the beginning of thisline is anchored at the graph’s origin (the 0 FPM, 0 airspeed point), ithas the steepest slope (largest angle upward) where it contacts theROC curve at point A.

As you can see, Vx is a little less than Vy. As altitude increases, theindicated airspeed for Vx increases slightly while the indicated air-speed for Vy decreases slightly, as shown in Figure 10. Think about itthis way: The smaller one (Vx) gets larger while the larger one (Vy)gets smaller as altitude increases.

Cruise Climb SpeedMost of the time, it’s preferable to climb at some speed slightly

above Vy. This is often called a cruise-climb speed and it provides youbetter forward visibility during the climb, as shown in Figure 8C. Onhot days it also keeps the engine cooler, preventing overheating andpossible detonation. The choice of cruise-climb speeds is a matter ofpilot preference.

100 FPM

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True Airspeed In Knots

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A600 FPM

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Vx - Bestangle of

climb69 kts

Vy - Bestrate ofclimb79 kts

The full throttle rate of climb (ROC) curve depicts a zero rate at point (Z)-- thepoint of maximum level forward speed and point (Y)--the power-on stallspeed. Where the tangent line contacts the ROC curve at point A, the air-plane attains the maximum altitude gain for a specific forward velocity, other-wise knows as the best angle of climb speed (point B at 69 knots). The maxi-mum rate of climb is achieved at point C. The speed for the maximum rate ofclimb is found at 79 knots at point D.

RATE OF CLIMB VS. TRUE AIRSPEED GRAPH

ROC Curve(Rate Of Climb)

Tang

ent L

ine

Vx AND Vy CHANGEWITH ALTITUDE

2,000'

0'

90 9560 65 70 75 80 85

4,000'

Indicated Airspeed In Knots

6,000'

8,000'

10,000'

Sta

ndar

d A

ltitu

de 12,000'

14,000'

16,000'

Bes

t Ang

leof

Clim

b(V

x)

Best R

ate of Clim

b (V

y)

The indicated airspeed for the best angle-of-climb(Vx) increases with an increase in altitude. The indi-cated airspeed for the best rate-of-climb (Vy) de-creases with altitude. The point at which they meet(point A) is the altitude where the airplane can nolonger climb. This is known as the .absolute ceiling

A

Fig. 9

Fig. 10



Figure 11 shows the rate of climb chart available for some airplanes. This chart is for a small two-place trainer.Notice that the rate of climb decreases with an increase in pressure altitude and that Vy is found at a slower indicatedairspeed (KIAS) at higher altitudes. (KIAS stands for knots of indicated airspeed.) Under the rate of climb column areseveral temperature columns with variable climb rates. Considering how airplane performance varies with air density,it shouldn’t come as a synaptic shock that the rate of climb varies with temperature.Many POHs don’t show the slight increase in the indicated airspeed for Vx with an increase in altitude because

the increase is usually small. These handbooks do often show the change in Vx with a change in airplane weight.Figure 12A is a short field takeoff distance chart. Section 1 (expanded) shows the variable Vx speeds under the 50FT column. Notice that these speeds decrease with a decrease in airplane weight (Vy also decreases with a weightdecrease). Remember, at higher altitudes your climb angle at Vx is going to be much less than it would at sea level despite the

fact that you’re at Vx. So give yourself plenty of extra margin if attempting to climb over an obstacle off thedeparture end of a high alti-tude airport.Also remember that the air-

plane is going to climb at lessof a rate or angle with thegear down. That’s why, onretractable gear airplanes, weretract the gear as soon as it’ssafe after departure (usuallywhen there is no runway lefton which to land). Flaps aresometimes used for takeoffwhen suggested by the POH.The important thing to keepin mind about flaps is thatthey usually shorten theground run but reduce theangle or rate of climb (notalways, but sometimes. Checkyour POH to determine if theydo). They should be retractedafter liftoff when the airplanehas accelerated to the recom-mended climb speed.

How Do They Figure Out All This Stuff?Having found out about the stork and babies, you are now per-

haps wondering where performance charts come from.

They come from actual flight data gathered by the airplane manu-facturers, using experienced test pilots and new airplanes. This issomething to keep in mind, because there are few mere mortalswho are as adept as a full-time test pilot at coaxing full performancefrom an airplane, and there are few airplanes that perform as wellas they did when they were new or nearly new.

Just so you don’t leave here with any illusions, they do not testto get the information for every single point on any chart. A certainamount of what’s there is by interpolation, the same way you’velearned to figure out what the winds are between altitudes wherethere are published data.

Always keep in mind that performance charts reflect a new air-plane, flown by a professional pilot, under optimal conditions. Yourmileage, as they say on the car stickers, may vary. So may yourlanding roll, rate of climb, and all the other things in the charts. Adda safety margin, especially when you are just getting to know anairplane.

Fig. 12A

The expanded portion of this short field, takeoff distance chart shows how the bestangle of climb speed (Vx) varies with a change in weight.

1

Fig. 11

For Training Purposes Only



Takeoff Distance ChartAll airplanes have some takeoff

and landing performance charts.Figure 12B is a typical example of atakeoff distance chart. With yourfirst glance at this chart, you proba-bly feel as confused as a farsightedVenus flytrap that’s just ripped thefly off someone’s pants. Not to worry!I’ll explain how to use it (the chart,not the flytrap).

This chart provides you with thetakeoff ground roll under variableairplane and airport conditions. Italso provides the best angle of climbspeeds based on various weight con-ditions. Learning how to use thischart is best done by example.A Hint When Using This and

Other Performance Charts –Many performance charts requirethat you slide up and down calibratedlines on the chart when moving fromone reference point to the next.

Movement along these lines shouldbe proportional, not parallel. Figure13 provides you with a good ideaabout how to do this. In those caseswhere a performance chart’s calibrat-ed lines are close together or appearparallel, then move parallel to theselines.Takeoff Distance Example No. 1 –

Using the takeoff distance chart inFigure 12B, what is your ground rolland distance to clear a 50 foot obsta-cle based on the following conditions:

OAT: 59 degrees F (15 degrees C)Pressure altitude: 5,650 feetTakeoff weight: 2,950 poundsHeadwind component: 9 knotsFirst, find 59 degrees F (15 degrees

C) on the bottom of the chart in sec-tion 1. Move directly up to the 5,650foot pressure altitude line (section 2).You’ll have to estimate where 5,650feet pressure altitude is, just like youdid with the density altitude chart in

Figure 3. Use the following method.The 5,000 foot pressure altitude lineis halfway between 4,000 and 6,000feet. Draw a hair-thin proportionalline between these altitudes. Itstands to reason that the 5,650 footpressure altitude line is a little abovea point halfway between the 5,000foot line and the 6,000 foot line. Nowmove horizontally to the right, direct-ly over to the dark, vertical referenceline in section 3. As you move hori-zontally on the chart simply followthe nearest grid line to avoid makingmistakes.

In section 3, we’ll correct forweight. Since our weight is 2,950pounds, and this is what the refer-ence line rests on, no correction isnecessary. Simply move right, hori-zontally, to the next reference line insection 4. If we did have a weight dif-ferent from 2,950 pounds, we’d moveproportionally to the diagonal linesuntil reaching our takeoff weight

Fig. 12B

1

87

2

3 4

5

6

6A2,300’

1,375’



shown on the bottom scale in sec-t ion 3 . Then we’d move r ight ,horizontally, to the reference linein section 4.

Now it’s time to correct for a head-wind or tailwind component. We havea 9 knot headwind component, sowe’ll move down, proportionally, tothe nearest diagonal line until reach-ing a 9 knot wind component value,shown on the bottom scale of section4. From this point we’ll move hori-zontally to the right, toward the nextreference line. If we had a tailwindvalue we’d move up and proportion-ally to the nearest sloping dashedline until reaching the appropriatewind component value. Then we’dmove horizontally to the right towardthe reference line.

At the reference line in section 5we can determine our takeoff groundroll by moving horizontally towardthe right. The numerical value ofapproximately 1,375 feet, listed atsection 6, is our takeoff ground roll.This is only our ground roll, not thedistance required to clear an obstacleat the end of the runway.

If an obstacle exists at the end ofthe runway, we can determine howmuch horizontal distance is requiredto clear that obstacle. Let’s assumewe have a 50 foot obstacle at the endof the runway. Move up and propor-tional to the diagonal line nearestsection 5 until reaching the 50 footheight mark on the bottom scale(obstacle heights are calibrated bythe scale at the bottom of section 5).When reaching the obstacle heightshown horizontally along the bottomof the chart (50 feet in our case), lookhorizontally to the right to find that2,300 feet of horizontal distance isrequired to clear that obstacle (sec-tion 6A). Keep in mind that this isjust to clear the obstacle. Your tiresshould just scrape the top of thatobstacle, possibly thumping somebird on the head (maybe that’s howbald eagles got bald?).

There are several other interestingthings you should know about thischart. First, in section 7, there is alist of takeoff speeds for differentweights. At 2,950 pounds we want tolift off at 66 knots. If there is anobstacle at the end of the runwaythen we want to climb at a speed of72 knots for that weight. Variableweights require different liftoff andobstacle climb speeds.

Second, section 8 lists all the asso-ciated conditions this chart is basedon. Machado’s Inverse Law of ChartConditions says: The notes on a per-formance chart will be of value to youonly when you forget to read them.Notes at the bottom of performancecharts are the fine print of aviation.Always make it a point to read all theconditions listed in this section of achart. There are many little variablesaffecting airplane performance listed

in this section. Notice that the enginemust be leaned to the appropriatefuel flow during takeoff. This assuresmaximum power is developed. Also,the gear is assumed to be retractedimmediately after a positive rate ofclimb is established. This is done,obviously, if there is an obstacle toclear. Normally, without an obstacle,you wait until there is no more run-way on which to land before raisingthe gear. (Of course if you areattempting to retract your landinggear on an airplane that isn’t of theretractable gear type, then I wantyou to reread those directions on theback of your cold medicine.)

Takeoff Distance Problem No. 2 –Refer to Figure 12B and determinethe ground roll and the total distancerequired for takeoff to clear a 50 footobstacle based on the following condi-tions:

OAT: standard conditionsPressure altitude: 4,000 feetTakeoff weight: 2,800 poundsHeadwind Component: calmFigure 14 shows how this problem

is solved. ISA stands for InternationalStandard Atmosphere and means thesame thing as the term standard con-ditions used by U.S. engineers. Justfind where the ISA line (standardtemperature line) intersects the4,000 foot pressure altitude line andmove right horizontally to the nextreference point. Approximately 1,050feet are required for the takeoffground roll and 1,750 feet of horizon-tal distance is required to clear a 50foot obstacle. Be careful when youare moving horizontally across thechart. Make sure you move parallelto one of the horizontal grid-lines,thus minimizing the chance of errorin chart reading.

Re

fere

nce

Lin

e

Re

fere

nce

Lin

e

When moving along the sloping line of aperformance chart, make sure you moveproportionally (up or down) the line. Inother words, don't parallel the nearestline as you move. Try to remain the same(proportional) distance between lines.

The line remains

proportionally

2/3rds from the

bottom as it

slopes down.

2/3

1/3

2/3

1/3

MOVING ALONG THEDIAGONAL LINES

OF A CHART

Fig. 13

Outside Air Temperature(OAT) ~ F

Weight in pounds Windcomponent

in Knots

Obstacleheight in

feeto

2,000

2,800

1,750'(to clear 50'

obstacle)

1,050'(ground roll)

4,0008,000

ISA

TAKEOFF DISTANCE COMPUTATION

Pressure altitudeFig. 14



Frankly, there is a time when youmight use the standard temperatureor ISA line when computing airplaneperformance. You may want to esti-mate how the airplane will performat a given altitude without knowingthe actual outside temperature (suchas when making rough estimates asto the amount of weight—fuel, pay-load, etc.—that you can depart with).Simply find where the ISA line inter-sects the elevation of the departureairport. Since you don’t know thetemperature and pressure altitude,this gives you a rough way to antici-pate airplane performance. Remem-ber, this is only used as an approxi-mation (I still have a feeling thatsome of those mischievous 8th centu-ry monk-scribes got loose from themonastery, became performancechart engineers and inserted theseISA or standard temperature lines inairplane performance charts).

Takeoff Distance Problem No. 3 –Refer to Figure 12B and determinethe ground roll and the total distancerequired for takeoff to clear a 50 footobstacle based on the following condi-tions:

OAT: 100°FPressure altitude: 2,000 feetTakeoff weight: 2,750 poundsTailwind Component: 5 knotsFigure 15 shows how this problem

is solved. The only significant differ-ence with this problem is that a tail-wind component exists. We mustmove upward, proportional to thedashed lines, in section 4 in Figure12B. From there we proceed to thenext reference line. A ground roll ofapproximately 1,300 feet is requiredand 2,150 feet of horizontal distancewill be used to clear a 50 foot obstacle.

At this point you’re probably won-dering why the Federal AviationAdministration puts up 50 foot obsta-cles at all these airports. All thesequestions make it seem like obstaclesare mounted on mobile dollies, towedto different airports (like the old MXmissile program) and placed on thedeparture end of runways to test theskills of a pilot. Well, this isn’t true,but it is interesting to consider thatmost of these obstacles are represent-ed as trees. If that were so, it wouldseem logical that those obstacleswould get smaller whenever pilots,ignorant about takeoff performancecharts, depart that runway. In otherwords, they’d be 50 foot obstacles atfirst, then, the following week they’dbe 46 foot obstacles, then 38 footobstacles and so on. Eventually, theFAA would have to tow in a newobstacle. Fortunately pilots do a goodjob in avoiding obstacles.

A Different Takeoff DistanceChart – Figure 16 shows a takeoffdistance chart for a small, two-placetrainer. As with all performancecharts, read the notes before doingany computations. Short field compu-tations are based on 10 degrees offlaps, full throttle then brake release,specific runway conditions, and zerowind. Note #3 states that distancesshould be decreased 10% for each 9knots of headwind. For tailwinds upto 10 knots, increase distances by10% for each 2 knots.

If we’re taking off on a dry, grassrunway, instead of a hard surface, weneed to increase distances by 15% ofthe ground roll. Grass creates dragand prevents acceleration of the air-plane. (If there are groundhogs hid-ing in the grass, this might also

inhibit acceleration. You’ll never seea chart that says to add 5% for eachsuspected groundhog). You’ll noticethere is no chart variation for differ-ent weights. That’s because a smalltwo-place trainer doesn’t have muchvariation in its payload compared to alarger, multiseat airplane.

Takeoff Distance Problem No. 4 –Using Figure 16, determine the take-off ground roll and distance to clear a50 foot obstacle based on the follow-ing conditions:

Pressure altitude: 3,000 feet

Temperature: 20 degrees C

Tailwind component: 4 knots

Without correcting for the tailwindwe obtain a ground roll of 1,000 feetand a distance to clear a 50 footobstacle of 1,870 feet according toFigure 16. Note #3 on the top ofFigure 16 states we need to increaseour distances by 10% for each 2 knotsof tailwind. Our calculated distancesneed to increase by 20%. Based onthe computations in Figure 17 ourexpected ground roll becomes 1,200feet and the horizontal distance toclear a 50 foot obstacle becomes 2,244feet.

Takeoff Distance Problem No. 5 –Using Figure 16, determine the take-off ground roll and distance to clear a50 foot obstacle based on the follow-ing conditions:


Temperature: 10 degrees C

Headwind component: 18 knots

Notice that the pressure altitude ishalfway between the 3,000 and 4,000foot values. There are several ways togo about solving this problem and alittle interpolation is necessary.Here’s one way, as shown in Figure 18.

Determine the ground roll and dis-tance to clear a 50 foot obstacle at3,500 feet by adding the 3,000 and4,000 foot values in the 10 degree Ccolumn together then dividing by 2.You should get 973 feet (rounded off)for the ground roll and 1,825 feet forthe distance over a 50 foot obstacle.

We could stop here if it were notfor the 18 knot headwind. Note #3 in


Weight in pounds Windcomponent

in Knots

Obstacleheight in

feeto

S.L.

2,750100

2,150'(to clear 50'

obstacle)

1,300'(ground roll)

2,0004,000

TAKEOFF DISTANCE COMPUTATION

Pressure altitudeFig. 15



Figure 16 says decrease dis-tances 10% for each 9 knots ofheadwind. This means wemust decrease both values by20%. According to Figure 18this gives us a 778 foot groundroll and 1,460 feet to clear a 50foot obstacle.

Be careful when applyingcorrections for headwinds ortailwinds. You must rememberto subtract takeoff distancevalues for a headwind and addthese values for a tailwind.Headwinds decrease takeoffdistances and tailwinds in-crease them.

Sometimes it will be neces-sary to interpolate for bothpressure altitude and tempera-ture when using these charts.If you find yourself close toany whole number value (fortemperature or pressure) andfeel it’s difficult to interpolate,then use the larger, wholenumber value. This gives you aslightly longer takeoff andobstacle clearance distance butat least it errs on the conserva-tive side.

Fig. 16


Fig. 17

Takeoff Distance Problem #4 Answer:20% of 1,000’ = (.20)x(1,000) = 200’1,000’+200’ = 1,200’ Ground Roll20% of 1,870’ = (.2)x(1,870’) = 374’1,870’+374’ = 2,244’ to clear 50’ obstacle.

Takeoff Distance ChartFor Training Purposes Only!

Fig. 18

Takeoff Distance Problem #5 Answer:Ground Roll at 3,500’ (925’+1,020’)/2 = 973’To clear a 50’ obstacle:973-(20% of 973’) = (973’)-(195’) = 778’ Ground Roll1,825-(20% of 1,825’) = (1,825’)-(365’) = 1,460’ to clear a 50’ obstacle.

Takeoff Distance ChartFor Training Purposes

Only!



Landing Distance Performance ChartsRemember as a kid watching movies in

school (on days when the teacher didn’t feellike teaching)? Sometimes the film would jam,and after straightening it out they’d run itbackwards a bit so you didn’t miss any morselsof knowledge.We’re about to do the same thing. A landing

chart is a takeoff chart in reverse. Instead oflaunching over a 50 foot obstacle, you’reassumed to be landing over one. Once againthere’s the distance over the obstacle to thepoint of touchdown, and there’s a ground rollto account for. Figure 19 shows a typical landing distance chart. Notice its similarity to the takeoff chart used in Figure 12B. This

chart is used in exactly the same way as Figure 12B. Remember, we’re just running the movie backwards.Keep in mind these distances for landing over a 50 foot obstacle assume that you barely clear the obstacle, as shown

in Figure 20. You may assume you will always clear an obstacle by more than just inches, but the chart doesn’tassume that. To be practical and safe about this, add a few more feet onto the values shown in the chart. In otherwords, you shouldn’t be landing with branches and twigs protruding from the wheelpants. Let’s try the followingproblems.

LANDING DEFINITIONS

During landing, the ground roll is the distance required to stop the airplaneonce the wheels have made contact with the runway. The distance to landover a 50' obstacle is the total distance to cross over that obstacle, touch-down and come to a stop.

Ground roll

Total distance to clear a 50' obstacle

50'Obstacle

Touchdownpoint

Airplanestopped

here

Fig. 20

Fig. 19

1

87

6

45

3

2



Landing Distance Problem No. 1 –Using the landing distance chart inFigure 19, and based on the followingconditions, determine the total dis-tance required to land.

OAT: 32 degrees FPressure altitude: 8,000 feetWeight: 2,600 poundsHeadwind component: 20 knotsObstacle: 50 feetBefore using any performance

chart, always read the conditions list-

ed on that chart. Section 8 in Figure19 lists the conditions under whichthe landing is conducted. Section 7lists the approach speeds you shouldbe using to obtain performance chartvalues for your landing. I also likehow it lists gear down as one of theconditions. (Remember, if you forgetto put the landing gear down, yourlanding distance will be cut byapproximately 99%, but your mainte-nance bill will go up considerably!)

Figure 21 shows how I computedthe answer. Notice the headwindcomponents require that you slidedown diagonal lines shown in section4 of the chart. Sliding downwarddecreases your final distance valuewhile sliding upward increases anylanding value. You need 1,400 feet ofhorizontal distance to clear a 50 footobstacle situated on or near the endof the runway. From the instant youcross the obstacle at 50 feet until thetime you come to a stop on the run-way, you’ll need 1,400 feet of dis-tance. Of course this assumes,according to section 7, that at 2,600pounds of weight, you cross theobstacle at an indicated airspeed of65 knots. Any faster and the landingdistance will increase.

Landing Distance Problem No. 2 –Using the landing distance chart inFigure 19, determine the total dis-tance required to land based on thefollowing conditions:

OAT: standard


Weight: 2,300 pounds

Headwind component: calm

Obstacle: no obstacle

According to Figure 22, you’ll needan 850 foot ground roll under theseconditions. This is the distancerequired to stop from the time theairplane touches down.


Weight in pounds

Pressure altitude

Windcomponent

in Knots

Obstacleheight in

feeto

6,000

2,60032

1,400'(to clear 50'

obstacle)

8,00010,000

LANDING DISTANCE COMPUTATION


Weight in pounds

Pressure altitude

Windcomponent

in Knots

Obstacleheight in

feeto

2,000

2,300

ISA

850'(ground roll)4,000

8,000

LANDING DISTANCE COMPUTATION

Fig. 21

Fig. 22

A LEAN MEAN FLYING MACHINE(Written as an ASRS report by a University flight instructor) One item that is

seldom mentioned in articles on fuel exhaustion and mismanagement dealswith student pilots or low-time pilots on cross-country trips. In local areatraining, the instructors keep the mixture rich because of the varied powersettings used and seldom mention or practice proper leaning procedures.So when the solo or low-time pilot is on a trip, under a relatively high work-load, they fail to remember to lean the mixture. (The fuel flow data used inflight planning always assumes a proper leaning of the mixture. Thus, theflight planned fuel consumption is often higher than expected and the resultis fuel starvation.) Also, since local area flights are brief, the instructor andthe student seldom (and sometimes never) switch fuel tanks. When thetraining is in an aircraft having a fuel selector with the option of “Both,” thereis even less incentive for the student pilot to develop the habit of switchingfuel tanks.

ASRS Report

Bob! You’re sup-posed to lean with themixture, not your body.



A Different LandingDistance Chart

There are certain things you justnever do. For instance, never put theword yes on a job application on theline that says salary expected. Whenbeing interviewed as a police officercandidate and asked why you wantthe job, you shouldn’t say, “Thelights man, I love all the lights.Whooo, whooo, whooo.” There’s onething you never do when workingwith a landing distance chart. Youshould never assume that all landingdistance charts are the same. Thesecharts come in several shapes andflavors.

The chart shown in Figure 23 isanother version of a landing chart.Once again, before using any chart,look at the notes and conditions list-ed on the chart.

Notice that note #1 says we mustdecrease distances by 10% for each 4knots of headwind. We must increasedistances by 10% for every 60 degrees F

temperature increases above stan-dard. Standard temperatures arethose listed next to the altitudes ineach chart column. Sixty degrees is arather large temperature jump. Iftemperatures are only 30 degrees Fabove standard, increase distancesby 5%.

Notice that in note 3, landing dis-tances on dry, grass runwaysincrease all calculations by 20%. Ifdry, grass runways increase our take-off distance, shouldn’t they alsodecrease our landing distance? Notreally. Braking is much less efficienton grass (even if you are conkinggophers on the head). Delicate brak-ing is required to slow the airplane,making stopping distances muchlonger. Read the note carefully! Let’stry a few of these problems.

Landing Distance Problem No. 3 –Using the landing distance chart inFigure 23, and based on the followingconditions, determine the total dis-tance required to land over a 50 footobstacle.

OAT: standardPressure altitude: 7,500 feetHeadwind component: 8 knotsRunway: dry grassBased on pressure altitude of 7,500

feet and a standard temperature of32 degrees F, our landing distanceover a 50 foot obstacle is 1,255 feet.With a headwind of 8 knots we needto decrease our distance by 20%according to the chart note #1. Thisgives us a ground roll of 1,255 - (20%of 1,255)=1,004 feet. Our last correc-tion is for a dry, grass runway. Note3 states we must increase all dis-tances by 20% of the total to clear a50 foot obstacle distance. This givesus a final value of 1,004 + (20% of1,004)= 1,204.8 or 1,205 feet.

Landing Distance Problem No. 4 –Using the landing distance chart inFigure 23, and based on the followingconditions, determine the total dis-tance required to land over a 50 footobstacle.

OAT: 101 degrees FPressure altitude: 5,000 feetHeadwind component: calmAccording to Figure 23, an altitude

of 5,000 feet and 41 degrees F pro-duces a distance over a 50 foot obsta-cle of 1,195 feet. Our temperature is60 degrees F more than standard forthat altitude. According to note #2,we need to increase our landing dis-tance by 10%. This gives us a 50 footobstacle clearance value of (10% of1,195)+1,195=1,315 feet.

Never forget Machado’s Calcu-lation Canon: The most importantpart of the body to use in calculatingtakeoff and landing distance is thebrain, not the wishbone.

Hmmm? For an obstacle this size the short field takeoff performance

chart says not to use Vx. It says use V911 and keep my eyes closed.

Fig. 23



Time, Fuel and DistanceTo Climb Chart

Another flavor of chart useful inflight planning is the time, fuel anddistance to climb chart shown inFigure 24. As always, read all thenotes before using the chart. Noticethat the columns provide you with aclimb speed (the best rate of climbspeed, Vy), an expected rate of climb,the time it takes to climb, fuel used ingallons and distance covered (assum-ing zero wind). The chart shows howVy decreases with an increase in alti-tude.

Climb Problem No. 1 – UsingFigure 24, estimate the amount oftime and fuel consumed to climb fromsea level to 5,000 feet pressure altitudeunder standard temperature condi-tions.

This is a relatively easy problem tosolve. First, look at the fuel used anddistance values for the 5,000 foot pres-sure altitude row. This gives you 8minutes and 1.2 gallons of fuel used.Adding .8 gallon of fuel per note #1,we find that we consume 2.0 gallons offuel while taking approximately 8 min-utes to climb once airborne. That’seasy, so let’s make it a little more prac-tical and challenging.

Climb Problem No. 2 – UsingFigure 24, estimate the amount oftime and fuel used to take off andclimb from an airport with a pressurealtitude of 2,000 feet to 6,000 feetpressure altitude, when the tempera-ture at the airport is 21 degrees C.

This problem requires us to subtractthe difference in time and fuel consumed from 6,000 feet to 2,000 feet. This gives us a time to climb from 2,000 to6,000 feet pressure altitude of approximately (10 minute - 3 minutes = 7 minutes). We also derive a fuel consumptionof approximately (1.4 gallons - .4 gallons = 1 gallon).

The last thing we do is make a correction for the nonstandard temperature. Since 21 degrees C at 2,000 feet is 10degrees C above standard temperature for that altitude, per note #3 we should increase both these values by 10%.Our time to climb value becomes (7 minutes + .7 minutes = 7.7 minutes). Our fuel-used value becomes (1.0 gallon +.1 gallon = 1.1 gallons). We do, however, need to add that .8 gallon according to note #1 for engine start, taxi andtakeoff. This gives us a total fuel consumption of 1.9 gallons.

This is a very handy little chart to use. You’ll find it very useful for cross country flight planning purposes.Although we didn’t compute the distances covered during the climb, this is easily done using the same methoddescribed in Chapter 14, page N32, under the section titled: A More Accurate Flight Plan.

To Trust or Not to TrustThe only way to accurately estimate your airplane’s actual fuel consumption is to observe what it does over numerousflights. Take note of how much fuel your airplane actually consumes under different conditions and compare this to thechart’s estimated fuel consumption. At least you’ll know how accurate your charts are.

Fig. 24




Cruise Performance ChartSo far we have charts for predict-

ing takeoff distance, landing dis-tance, and time and fuel to climb.Now let’s look at a chart to help com-pute enroute fuel consumption andexpected true airspeed. This chart isthe cruise power setting chart, shownin Figure 25.

Once again, Machado’s Fire andBrimstone Chart Principle No. 666says, Always read the notes beforeusing the chart lest you be visited byperdition’s dark and evil forces. Thenote at the top of the chart assumesthe engine operates at 65% maximumcontinuous power or full throttle.(Remember, at higher altitudes, eventhough you have full throttle applied,you might not be able to develop 65%power.) The 65% power figure isbased on the RPM and manifold pres-sure settings provided in the chart.Obviously, this chart is for an air-plane with a constant speed propellersince it has both manifold pressurefor power and RPM column for propspeed.

Three temperature sections existon the chart. The middle column isfor standard temperature, or ISA.The left and right columns are sec-tions for temperatures below andabove standard conditions, respec-tively. Within each section is an indi-vidual temperature column (listedunder IOAT—indicated outside air

temperature) for variable tempera-ture conditions enroute. When youare given a pressure altitude andtemperature, simply find the pres-sure altitude on the far left columnand proceed to the right until you arenear a temperature similar to thatfor your cruise altitude. If it’s notexact, that’s OK. Just get as close asyou can. Immediately to the rightwill be the RPM and manifold pres-sure settings required to develop 65%power with the associated fuel flowand true airspeed for those settings .

Cruise Performance ProblemNo. 1 – Using Figure 25, approxi-mately what fuel consumption andtrue airspeed should you expect for aflight under the following conditions:


Temperature: +22 degrees C

Manifold pressure: 20.8 inches of Hg

Wind: calm

Find the 8,000 foot pressure alti-tude line and follow it horizontallyacross until reaching a temperatureof or near +22 degrees C. This putsyou in section #3 of the charts (or inthe higher-than-standard tempera-ture section). To produce 65% poweran engine RPM of 2450 and a mani-fold pressure of 20.8 inch of Hg arenecessary. Under these conditionsyou can expect a fuel flow of 11.5 gal-lons per hour and an estimated trueairspeed of 164 knots.

Cruise Performance ProblemNo. 2 – Using Figure 25, determinethe approximate manifold pressuresetting with 2,450 RPM to achieve65% maximum continuous power at6,500 feet pressure altitude with atemperature of 36 degrees F higherthan standard.

A temperature of 36 degrees Fhigher than standard would put youin section #3 of the chart (the tem-perature of ISA+20 degrees C is 36degrees F above standard tempera-ture). Following the 6,000 foot pres-sure altitude value to the third sec-tion we find a manifold pressurevalue of 21.0 inches. Since 6,500 feetis slightly higher than this, let’sinterpolate. The 8,000 foot pressurealtitude line shows a manifold pres-sure of 20.8 inches. We can assumethat at 7,000 feet the manifold pres-sure required is 20.9 inches. Thevalue we want is halfway between6,000 feet and 7,000 feet or halfwaybetween 21.0 and 20.9 inches, so20.95 inches is the manifold pressurerequired at 2450 RPM to maintain65% power. Realistically, you’ll use21.0 inches of manifold pressuresince your power gauges (and youreyes) aren’t calibrated to read inhundredths. I suppose you could usea small magnifying glass but, underthe wrong sunlight conditions, youmight burn a little hole in the instru-ment (just kidding).

Fig. 25


Section 1 Section 3Section 2



Cruise Performance Problem No. 3 – What fuelflow should a pilot expect at a pressure altitude of 11,000feet on a standard day with 65% maximum continuouspower using Figure 25?

Standard day (ISA) conditions are found in section #2of the chart. Since there is no value for 11,000 feet, locatefuel flow values for 10,000 feet and 12,000 feet. The fuelflow for 11,000 feet will be halfway between these values.

Simple interpolation:10,000 foot fuel flow value: 11.5 GPH12,000 foot fuel flow value: 10.9 GPH(11.5+10.9)/2 = 11.2 GPH for 11,000 feet It’s hard to believe that people can run out of fuel in

airplanes. The fact is, they do. That’s why Machado’sAbove the Ground Fuel Rule says: Pilots coming close torunning out of fuel in an airplane can get a $200 advancefrom an undertaker any time they want.

Another Variety of Cruise Performance ChartsA different variety of cruise performance chart is

shown in Figure 26. This chart is for an airplane with afixed pitch propeller. Pressure altitudes are found onthe left side of the chart with variable RPM settings forvariable power conditions. Unlike our previous chart,this chart allows us to choose various percentage selec-tions of BHP (brake horsepower) with which to operate.In other words, if the airplane has a 100 horsepowerengine, this chart shows what percentage of those 100horses are being used. Similar to the chart in Figure 25,this chart has three temperature columns. Let’s try afew problems.

Cruise Performance Problem No. 4 – Determinethe expected fuel consumption and true airspeed for aflight at a pressure altitude of 4,000 feet at 2,300 RPMunder standard conditions, using Figure 26.

Find the 4,000 foot pressure altitude column, thenmove to the 2,300 RPM value. Directly across is ourexpected true airspeed of 95 knots and fuel consumptionof 5.1 gallons per hour at an expected power output of63%. Are you wondering why we want to know how muchpower our engine is producing? In many airplanes, lean-ing of the mixture is recommended when the engine isproducing less than 75% power. This chart lets you knowwhen it’s reasonable to lean the mixture for more effi-cient engine operations. It also provides information thatmight be required in computing values based on otherperformance charts.

Since this chart doesn’t have detailed calibrations forvarious temperatures, what do you do if the temperatureis only slightly different from the values listed in one ofthe three vertical temperature columns? The answer is topick the temperature column closest to the actual airtemperature.

Cruise Performance Problem No. 5 – Using Figure26, determine the expected fuel consumption for a flight

at a pressure altitude of 5,500 feet at 2,400 RPM underconditions 14 degrees C colder than standard for yourflight altitude.

We’ll use the first temperature column, since 14degrees C colder than standard is closest to its -20degrees C below standard value. Notice that we’re using5,500 feet, which isn’t shown on the chart. A little inter-polation is necessary here.

Fuel flow for 6,000 feet at 2,400 RPM: 5.8 GPHFuel flow for 4,000 feet at 2,400 RPM: 6.1 GPHFrom this you can find the fuel flow for 5,000 feet:(5.8+6.1)/2=5.95 GPH at 5,000 feet at 2,400 RPMNow, find the fuel flow for 5,500 feet at 2,400 RPMThis is the difference between the 5,000 foot and 6,000

foot values(5.95 + 5.8)/2=5.87 or approximately 5.9 GPHLet’s be real practical about this. Looking at the num-

bers, you can usually eyeball the correct value withoutmuch difficulty (even without interpolating). This ismade much easier when chart values don’t vary muchbetween conditions. In other words, at 4,000 feet in thisexample we had a fuel flow of 6.1 GPH and at 6,000 feetwe had 5.8 GPH. It’s fairly easy to see that the value for

Fig. 26



5,500 feet is closest to 5.8 GPH. In the real world this works fine. For FAAtesting purposes you want to be as precise as possible. There is nothingwrong with taking liberties at estimating values as long as you know howto be precise when the need arises.

Endurance and Range Profile ChartsFigures 27 and 28 are two additional charts you might see. Figure 27 is a

best-endurance chart and Figure 28 is a best-range chart. There are manytimes when knowing your endurance and range is of immense value. Forinstance, if I had to remain airborne until the weather cleared for landing,the endurance chart would be of immense value. I’d know how long I couldafford to hang around while flying in circles before heading to another airport.

To use either chart, you need to know the percentage of power devel-oped by the engine. Given that information, you can find your enduranceand range for various altitudes. Just where will you find the engine’spower output in percentages? From the typical cruise performance chartswe’ve already seen in Figures 25 and 26.

If we were using 65% power, what would our endurance be at 8,000 feet?Simply find 8,000 feet in Figure 27 and move across to the 65% powerline. Drop straight down and find an endurance of 3 hours and 36 minutes(5 divisions between hour marks=12 minutes per division). At 65% power,according to Figure 28, our range is approximately 354 nautical miles. Ofcourse, assuming you’ve read all the conditions in both charts you’ll knowthe range is based on no wind, and both charts yield numbers that includea 45 minute fuel reserve.


In the unfortunate event you

happen to conk a prairie dog

on the head during

takeoff, this could

affect your ground

run. This isn’t

good (espe-

cially for

the

prairie

dog!).

Fig. 27 Fig. 28

For TrainingPurposes

Only!

For TrainingPurposes

Only!


Crosswind ComponentChartThe only pilots who don’t have to

worry about crosswinds are aircraftcarrier pilots. They have a lot moreto worry about than crosswinds.Their runway is always moving.How would you like to take off,then return to find your airporthas moved to another location?And I bet you never have to worryabout rolling off the end of the run-way and getting run over by theairport. Compared to such chal-lenges, crosswinds pale. For therest of us, however, crosswinds area factor, so we’d better learn howto figure them out.Several of our performance

charts require us to determine theamount of headwind or tailwindcomponent in order to determineour takeoff or landing distance.You will also find in most POHs a value listed for the maximum crosswind component the airplane is capable of han-dling. This limit is usually a function of flight control limitations and pilot skill available for coping with the crosswind. The chart in Figure 29 allows us to determine the headwind and crosswind components. Crosswind Problem No. 1 – Assume you’re departing on Runway 30, as shown in Figure 30. The tower reports a

wind from 330 degrees at 40 knots. What are the headwind and crosswind components associated with this wind?Runway 30 is aligned in a direction of 300 degrees. A wind from 330 degrees makes a 30 degree angle with the run-

way. It’s reasonable to say that some of this wind imparts a headwind component and some a crosswind component(do you remember Bud and Ed from Chapter 2, the bottom of page B3? It’s the same principle). To find exactly howmuch there is of each, ask yourself what the angle is between the wind and the nose of the airplane. Obviously the wind is 30 degrees off

the right of the nose. The chart inFigure 30 shows degree calibrations inincrements of 10, in a right direction.Assume the zero degree mark repre-sents the nose of the airplane. Start theproblem there. Find the 30 degree diag-onal line (point A). This represents theangle the wind makes with the nose ofthe airplane. Slide down this 30 degreeline until reaching the 40 knot windvelocity arc (point B). Now all you needto do is drop straight down to point D todetermine the amount of crosswindblowing on the airplane. We have aright crosswind of 20 knots. To find theamount of headwind blowing on the air-plane, simply move left horizontally topoint C. This represents the amount ofheadwind blowing on the airplane. Wehave a headwind value of 35 knots. Thisheadwind value is what we would usefor any takeoff or landing performancecomputation.


0oo

10o

10

10

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50 o

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o

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90o

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o

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70o

HE

AD

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CROSSWIND COMPONENT

WINDVELO

CITY

12

30

Wind330 at 40 knots

Headwindcomponent

35 knots

Crosswindcomponent

20 knots

A

BC

D

THE CROSSWIND COMPONENT CHART

If the tower reports a wind from 330 degrees at 40 knots, you can find your headwindand crosswind components by finding the angle between the wind and the nose.That angle is 30 degrees. Find the 30 degree line (point A) and move downward to the40 knot wind arc (point B). Move horizontally to point C to find the headwind compo-nent (35 knots). Drop straight down to point D to find the crosswind component (20knots).

(300)o

30o

Fig. 29

Fig. 30

CROSSWIND COMPONENT CHART



Crosswind Problem No. 2 – Basedon Figure 29, what is the crosswindcomponent you can expect if landing onRunway 18 with the tower reporting awind of 220 degrees at 35 knots?

Use Figure 31. First ask yourselfwhat the angle is between the wind andthe nose. The difference between 180degrees and 220 degrees is 40 degrees.Find the 40 degree diagonal line (pointA) and slide down it until reaching the35 knot wind arc (point B). You’ll haveto estimate where 35 is between the 30and 40 arcs. Dropping straight downgives you a crosswind component ofapproximately 23 knots (point D). Aheadwind component of 27 knots alsoexists (point C). If your airplane wascertified to handle a maximum cross-wind component of 20 knots, would itbe safe to fly? Probably not. This isanother good reason to know how touse this chart.

Crosswind Problem No. 3. – Using Figure 29, determine the maximum wind velocity for a 30 degree crosswind ifthe maximum crosswind component for the airplane is 12 knots.

The solution is provided in Figure 32. This problem requires us to work backwards. First, we know our airplane hasa maximum crosswind component of 12 knots. Find this position along the bottom of the crosswind chart (point A).Move straight up until reaching the 30 degree diagonal line representing the wind’s angle with the nose of the airplane

HE

AD

WIN

D C

OM

PO

NE

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CROSSWIND COMPONENT

0o

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o

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o

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70o

A

BC

THE CROSSWINDCOMPONENT CHART

Suppose your airplane has a maximum dem-onstrated crosswind component of 12 knots.What is the maximum speed of a 30 degreewind that won't exceed this 12 knot limit? Wecan solve this problem by working backwards.Start with a 12 knot crosswind at point A andmove upward till reaching the 30 degree angleline at point B. The 24 knot wind arc runsthrough this point as seen at the end of the arc(points C).

WINDVELO

CITY

0o

o

10o

(180)o

10

10

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o

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WINDVELO

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18

Wind220 at 35 knots

A

BC

D

THE CROSSWIND COMPONENT CHART

If the tower reports a wind from 220 degrees at 35 knots you can find your headwindand crosswind components by finding the angle between the wind and the nose.That angle is 40 degrees. Find the 40 degree line (point A) and move downward to the35 knot wind arc (point B). Move horizontally to point C to find the headwind compo-nent (27 kts). Drop straight down to point D to find the crosswind component (23kts.).

40o

HE

AD

WIN

D C

OM

PO

NE

NT

CROSSWIND COMPONENT

Headwind

component

35 knots

Crosswind

component

20 knots

Fig. 31

Fig. 32Fig. 33



(point B). At this point, ask yourselfwhat wind arc you would be restingon if smaller wind-arc calibrationsexisted. Parallel this arc around tothe end of the scale (either direction).The maximum wind velocity shouldbe 24 knots.

Crosswind Problem No. 4 –Using Figure 29, find the amount oftailwind expected with a 30 knotwind from 135 degrees when landingon Runway 27.

The crosswind chart can also beused to find tailwind and crosswindcomponents quite easily. The sameprocedure applies, except that wemust find the angle between thewind and the tail (since we’re talkingabout tailwinds). Figure 33 showsthis problem. If you have troublefinding the angle between the windand the tail, draw (or find) a circularcompass rose with the four majordirections (N, E, S, and W) on it asshown in Figure 33.

Aligned with Runway 27 meansyou are pointed in a direction of 270degrees. With wind from 135 degrees(remember, wind always blow fromsomewhere), you have wind thatmakes a 45 degree angle betweenitself and the tail. Simply go to thecrosswind chart and find the windcomponents for a 30 knot wind offsetat a 45 degree angle. Point A shows a

crosswind of 21 knots. Keeping youroriginal picture in mind, you’ll recog-nize this as a left crosswind. Point Bshows a headwind component of 21knots; we know, however, that this isactually a tailwind component. Thecrosswind chart wasn’t necessarilybuilt to find tailwind components,but if you understand the principleinvolved, it can be done. This is notto encourage you to plan on takingoff with a tailwind. Such behavior israrely prudent unless the tailwind ispretty minor.

Making the ForcesBe With You

During my youth, many a schoolcounselor attempted to predict what Imight do with my life. One counselorsuggested life as a woodworker, thenrealized it meant handling sharpobjects. No go. Another felt I wouldsucceed at hubcap repair, but back-tracked once he thought about how

distracting all the bright, shinyobjects would be.

Fortunately, my counselors didn’tpredict well. This may be becausenobody ever predicts someone willgrow up to be a flight instructor.That’s an inherently unpredictableoutcome.

As a pilot, you can’t afford to pre-dict poorly when it comes to airplaneperformance. You need to becomevery familiar with the performancecharts—not only how to crunch num-bers, but what those numbers reallymean in terms of performance.Additionally, you need to understandthe limitations these numbers imposeon when and where flight can besafely undertaken.

Remember, performance charts areprediction charts. And good pilotsnever leave to chance what they canpredict.

A wise man says, “On theground it’s OK to say the fuel tanksare half full. In the air, it’s best to

think of them as half empty.Optimism is not useful when

calculating fuel consumption.”



Advanced Lesson in Density Altitude

Advanced Density AltitudeProblem #1

In the airplane, finding pressurealtitude is as easy as being a life-guard in a car wash. Simply place29.92 in the altimeter’s Kollsmanwindow and read what the handspoint to (the indicated altitude). Thisis your pressure altitude. Take theOAT and the pressure altitude andcompute the density altitude by usingthe chart in Figure 34.

But how do you compute densityaltitude for an airport if you aren’tthere to set the altimeter to 29.92inches of Hg and read the tempera-ture? In other words, if you’re read-ing the METAR for an airport andknow the temperature and altimetersetting, can you still find its densityaltitude? Yes. Here’s how. Let’s startwith a field elevation of 7,257 feet MSL.

To the right of the density altitudechart is a vertical column showingaltimeter settings vs. pressure alti-tude conversion factors. Simply findthe airport’s current altimeter in thealtimeter setting column and seewhat conversion factor must beapplied to the altimeter reading tofind pressure altitude. In otherwords, the altimeter should read thefield elevation of 7,257 feet MSL with30.20 inches of Hg set in theKollsman window. Moving the win-dow’s numbers down to 29.92 wouldsimultaneously move the handsdownward (make the indicated alti-tude read less). The conversion factorspecifies how much the hands wouldmove downward.

Figure 34, position 1, shows thatthe conversion factor for an altimetersetting of 30.20 is -257 feet (youwould add this value if it didn’t havea “-” sign next to it). Subtracting 257from 7,257 gives you 7,000 which isthe pressure altitude. Take the OATof 80 degrees F (27 degrees C) and apressure altitude of 7,000 feet and, as

shown by position 2 in Figure 34, thedensity altitude is 10,000 feet. Eventhough your airplane is at 7,257 feetMSL, it’s going to perform like it’s at10,000 feet MSL.


Notice the diagonal line labeled“standard temperature” runningdownward from left to right inFigure 34. Sometimes we want toknow the standard temperature for aspecific altitude when standard con-ditions exists at sea level. Find anyspot where the standard temperatureline intersects a pressure altitudeline and drop straight down to thetemperature scale. This reading isthe standard temperature for thatpressure altitude. For example, onFigure 34, find where the standardtemperature line intersects the 4,000foot pressure altitude line (position3). Drop down to find the standardtemperature of 45 degrees F (7°C) forthat altitude. The same process worksfor all other pressure altitude values.

Suppose I ask you to find the den-sity altitude if standard temperatureexists at 4,000 feet pressure altitude.Simply find where the standard tem-perature line intersects the pressurealtitude line on Figure 34 and movehorizontally left to read a densityaltitude of 4,000 feet. You’ll noticethat whenever standard temperatureexists at various pressure altitudes,the pressure altitude is always equalto the density altitude. I offer thisonly as an academic exercise, becausestandard temperatures seldom existat various pressure altitudes. I havebeen flying since 1970 and I have yetto see more than a handful of dayshaving standard temperatures at sealevel that stayed that way for any sig-nificant amount of time.

Another important reason foroffering this to you is because some-one decided to put this type of ques-tion on the knowledge test (don’t askme why either).


What is your density altitude if thealtimeter setting is 29.96 inches of

Hg and the airport elevation is 3,293feet with an OAT of 75 degrees F (24degrees C)? First, you must find thepressure altitude. With the altimetersetting in the altimeter window, thealtimeter reads the true altitude (afield elevation of 3,293 feet MSL).The pressure altitude conversion for29.96 inches of Hg is approximatelyhalfway between that for 29.92 and30.00, as shown in Figure 34, posi-tion 4. Since the correction factor for29.92 is 0 and 30.00 is -73, use avalue halfway between them, orapproximately -36. Subtracting 36from 3,293 gives us a pressure alti-tude of 3,257 feet.

Locating the pressure altitudevalue of 3,257 is easy if you draw theintermediate values between the1,000 foot pressure altitude lines.Simply draw the 3,500 foot pressurealtitude value between the 3,000 and4,000 foot pressure altitude lines, asshown by position 5 on Figure 34.Now draw an intermediate valuebetween the 3,000 and 3,500 footpressure altitude line. This repre-sents the 3,250 foot pressure altitudevalue. Move up the 75 degree F(24°C) line until reaching the pres-sure altitude line of 3,250, as shownby position 6 on Figure 34 (this isreal close to the actual pressure alti-tude value of 3,257 feet). Go across tothe left to find a density altitudevalue of approximately 5,000 feet.


Suppose you’re flying a new Cessna152 from an airport located at 9,702feet MSL. The altimeter setting is29.60 and the OAT is 95 degrees F(35 degrees C) (that’s hot for an air-port that high—better be careful!)What is the density altitude at thatairport?

Using the pressure altitude conver-sion table in Figure 34 you determinethat it’s necessary to add 298 feetonto the true altitude to obtain apressure altitude of 10,000 feet(298+9,702=10,000). Using the OATof 95 degrees F (35°C) and a pressurealtitude of 10,000 feet gives you adensity altitude of 14,700 feet.

Postflight Briefing #15-1



Fig. 34



Higher Knowledge: Cruise Performance (time and fuel planning)By Steve King

FAA regulations (FAR Part 91) require that you plan your VFR flight to include enoughfuel to get to the destination with sufficient reserve to fly for 30 minutes during the dayand 45 minutes at night. Realistically, you need to allow substantially more than thatto protect against running out of fuel. The following suggestions will help you makesafer decisions about how far you can safely go between fuel stops.

1. Assume 5% (x .95) less cruise airspeed than what is shown in the POH charts.Then, calculate actual TAS in flight to compare with your estimate. When you dothis comparison, note the aircraft weight, since it will affect the cruise speed a little,especially at higher altitudes/lower power settings.

2. Assume 20% (x 1.2) more fuel consumption (GPH) than what is shown in the POHcharts. Then, calculate actual GPH after a flight (using takeoff to landing time) tocompare with your estimate.

3. For fairly good conditions, plan on having 1.5 hours of fuel left when you land torefuel. For good to excellent conditions, less than 1.5 hours reserve might be ade-quate. If flying with a smaller reserve, compare your actual progress (actualelapsed time to checkpoints) with your flight plan. For adverse conditions, youshould have at least a 2 hour reserve, possibly more. Consider the following whenyou make decisions about fuel reserves:

· Day or night? It’s wise to add about 1 hour additional fuel reserve at night. Why? There are greater consequences associated with running out gas when it’s dark. Additionally, the extra fuel reserve helps in case you have difficulty with navigation (pilotage,for instance, is more difficult at night). And, since weather hazards are more difficult to detect at night, you might need the fuel to deviate to another airport. Finally, consider that fewer places sell fuel at night. You might need to travel to find a place that sells it.

· Ease of navigation? Is there any chance of being lost enroute, or of having difficulty in finding the destination?· How many airports are along the route so you can land if you are low on gas or are behind schedule?· How many of those airports sell gas? (See #5 below.)· How good is the weather? If the weather is somewhat marginal, it may become necessary to leave the planned route for things like

flying around clusters of thunderstorms. This could add significantly to the planned distance and time. Diverting from a plannedroute also increases the possibility of becoming lost, especially if the weather is poor. You really want to avoid the possibilitythat you might be lost (thus not knowing where you could go to land) and be low on fuel and in poor weather all at the same time!

· How hazardous is the terrain over which you are flying? For example, how does flying over water, over mountains or over veryremote areas compare to following a freeway?

4. To fly with as little as one-half hour fuel reserve (assuming that you have previously assumed 95% TAS and 120% GPH), you shouldhave ideal conditions including:· Daytime flight, planned to end well before sunset. (Watch for delays that could affect this.)· Very easy navigation, like following a freeway, with careful navigation planning—integrating pilotage, dead reckoning and

electronic navigation.· Many airports along the latter third of your route, with fuel available (you can use these as alternate fuel stops in case you fall

behind schedule, or the ideal conditions deteriorate). (See #5 below.)· Excellent weather, with essentially no chance of any weather problems. (Make sure you monitor the weather through Flight

Watch, etc., during flight.)· Non-hazardous terrain that’s within easy gliding distance of a freeway, airport, or dry lake at all times during the latter third of the flight.

5. Before planning to depend on an airport or an alternate fuel stop (especially the one during last third of the route), verify that youwill actually be able to get fuel at that location, by phoning ahead. Then, before descending from cruise to land at an airport whenyour fuel level is low, call on Unicom to verify fuel availability. If they don’t respond, you might be able to safely fly to a nearby air-port to refuel even though you wouldn’t have enough fuel to land at the first airport, then take off and fly to the second airport.When you phone, check the following:

· How late are they open? If you fall behind schedule and arrive late, what are the chances of getting fuel at that airport?· Do they have the type of fuel you need? Will they accept your form of payment? Some places only accept cash, traveler’s checks

(some don’t accept these, or only certain brands because of counterfeiting concerns), or their own oil company creditcard (often Phillips 66).

Steve King is professor and department head of the Professional Pilot Training Program at Long Beach City College locatedin Long Beach, California. He has been a pilot since 1965, an A&P since 1966 and is a certificated flight instructor.

Postflight Briefing #15-2

Steve King


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