Configuration Design part 3

Configuration Design Configuration Design part 3part 3

Engine Engine PlacementPlacement

ENGINE PLACEMENTENGINE PLACEMENT

Factors to be considered:Factors to be considered:Effect of power changes or power failures Effect of power changes or power failures

on Stability & Control.on Stability & Control.Drag of the proposed configuration.Drag of the proposed configuration.Weight & Balance considerations.Weight & Balance considerations.Inlet requirements and resulting effect on Inlet requirements and resulting effect on

installed thrust and efficiency.installed thrust and efficiency.Accessibility and maintainability.Accessibility and maintainability.

ENGINE PLACEMENT: Propeller-ENGINE PLACEMENT: Propeller-Driven ACDriven AC

Option 1:Option 1: Engines placed along fuselage Engines placed along fuselage centerline.centerline.

Pros:Pros:

1.1. No thrust asymmetry in the event of No thrust asymmetry in the event of engine failure.engine failure. Cessna SkymasterCessna Skymaster

2.2. High thrust line.High thrust line. Dornier CD-2 Dornier CD-2 SeastarSeastar

Important for amphibian ac.Important for amphibian ac.

Cessna SkymasterCessna Skymaster

Dornier CD-2 SeastarDornier CD-2 Seastar


Option 2:Option 2: Engines placed symmetrically Engines placed symmetrically on the wingon the wing King AirKing Air

Pros:Pros:1.1.Most attractive aerodynamically & Most attractive aerodynamically &

structurally.structurally. Prop slipstream has favorable effect on stall (built-in Prop slipstream has favorable effect on stall (built-in

safety against stall)safety against stall) Prop slipstream increases L, especially when TE flaps Prop slipstream increases L, especially when TE flaps

are employed.are employed.

Beech King AirBeech King Air


Option 2:Option 2: Engines placed symmetrically on the wing Engines placed symmetrically on the wingCons:Cons:1.1.Engine failure may cause high windmilling D before Engine failure may cause high windmilling D before

prop is feathered. Induced YM and PM present prop is feathered. Induced YM and PM present control problems especially during TO.control problems especially during TO.

2.2.Variation of engine power changes the downwash Variation of engine power changes the downwash on the tailon the tail

NB:NB: If props are placed behind the wing, prop plane If props are placed behind the wing, prop plane must be at least 0.5 c behind the TE to avoid vortex must be at least 0.5 c behind the TE to avoid vortex excitation from the flaps or the TE onto prop blades! excitation from the flaps or the TE onto prop blades! (GP-166, B-36 : prop fatigue, broken blades)(GP-166, B-36 : prop fatigue, broken blades)

Piaggio GP-166 AvantiPiaggio GP-166 Avanti

B-36B-36


Pusher vs. TractorPusher vs. Tractor

Pusher Pusher ProsPros::

1.1. Stabilizing tendency in both pitch and yaw Stabilizing tendency in both pitch and yaw when compared to tractors. This feature when compared to tractors. This feature can result in reduced tail surface can result in reduced tail surface requirements.requirements.

2.2. Lower cabin interior noise.Lower cabin interior noise.

ENGINE PLACEMENT: Jet ACENGINE PLACEMENT: Jet ACIntake requirementsIntake requirements::MustMust Provide const. airflow at different engine settings and flight Provide const. airflow at different engine settings and flight

conditions.conditions. Limit flow distortion and turbulence at the compressor face.Limit flow distortion and turbulence at the compressor face. Have short length, otherwise increased W and p-loss.Have short length, otherwise increased W and p-loss.

Must notMust not Change excessively the direction of the oncoming air at different Change excessively the direction of the oncoming air at different

aoa.aoa. Allow the wake of a partially stalled wing to enter the inlet duct Allow the wake of a partially stalled wing to enter the inlet duct

(i.e., wing LE is unsuitable for intake location)(i.e., wing LE is unsuitable for intake location) Generate unstable flow in sideslipping (air oscillating instead of Generate unstable flow in sideslipping (air oscillating instead of

entering the duct; problem with split intakes).entering the duct; problem with split intakes). Have pronounced curvature.Have pronounced curvature.

ENGINE PLACEMENT: ENGINE PLACEMENT: Single Single EngineEngine Jet AC Jet AC

engine mounted inside the engine mounted inside the fuselagefuselage

Problem: Problem: Intake & exhaust duct locationIntake & exhaust duct location

SolutionsSolutions

1.1 Pitot Type Intake1.1 Pitot Type IntakeFokker S-14, MIG-17Fokker S-14, MIG-17

ProPro: Provides the engine w. undisturbed flow : Provides the engine w. undisturbed flow for for all flight conditionsall flight conditions

ConCon: Requires long inlet duct, which generally has : Requires long inlet duct, which generally has to be divided at the level of the cockpit – low to be divided at the level of the cockpit – low intake efficiencyintake efficiency

Fokker S-14Fokker S-14 MIG-17MIG-17


1.2 Wing Root Inlet1.2 Wing Root Inlet Hawker HunterHawker Hunter

ConCon: Difficult to meet the intake requirements : Difficult to meet the intake requirements (i.e., supply the engine with the required (i.e., supply the engine with the required airflow at different intake velocities) and airflow at different intake velocities) and cope w. changes in aoa & aos. An cope w. changes in aoa & aos. An additional constraint is that the local airfoil additional constraint is that the local airfoil shape must not be modified excessively.shape must not be modified excessively.

Hawker HunterHawker Hunter


1.3 Side Inlets (Scoop Type)1.3 Side Inlets (Scoop Type) X-35 JSFX-35 JSF

ProblemsProblems: : 1.1. Additional D. To minimize this D, the airscoops must Additional D. To minimize this D, the airscoops must

not be too short and must be well faired. not be too short and must be well faired.

2.2. A divertor is needed to prevent the fuselage BL from A divertor is needed to prevent the fuselage BL from entering the duct but this also increases D.entering the duct but this also increases D.

3.3. The inlet opening must be located far ahead of the The inlet opening must be located far ahead of the wing to avoid interference and excessive variations in wing to avoid interference and excessive variations in the intake conditions.the intake conditions.


1.4 Top Inlets1.4 Top InletsMiles Student, North American YF-107AMiles Student, North American YF-107A

ProblemProblem::

The opening must be raised far above the The opening must be raised far above the fuselage to avoid BL and wake ingestion fuselage to avoid BL and wake ingestion at large aoa.at large aoa.

Miles Student Experimental Miles Student Experimental JetJet

North American YF-107ANorth American YF-107A


1.5 Split Bottom Inlet1.5 Split Bottom Inlet

North American Rockwell BuckeyeNorth American Rockwell Buckeye

ProPro: Attractive for mid-wing and high-wing ac: Attractive for mid-wing and high-wing ac

ConCon: Measures must be taken to avoid : Measures must be taken to avoid ingestion of debris during taxiing and TO.ingestion of debris during taxiing and TO.

North American Rockwell North American Rockwell BuckeyeBuckeye


Exhaust requirementsExhaust requirements::MustMust Be as short as possible; exhausts cause T-loss = 0.3% per ft-Be as short as possible; exhausts cause T-loss = 0.3% per ft-

length or 1% per m-length. 2 tail-booms can be used for this length or 1% per m-length. 2 tail-booms can be used for this purpose, offering the additional advantage of excellent engine purpose, offering the additional advantage of excellent engine accessibility.accessibility.

Must notMust not Not allow the hot jet efflux to impinge on the ac structure; for Not allow the hot jet efflux to impinge on the ac structure; for

M<1 in parallel flow, the expanding gases form a cone with M<1 in parallel flow, the expanding gases form a cone with semi-apex angle = 6 deg.semi-apex angle = 6 deg.


1.6 Rear End Exhaust1.6 Rear End Exhaust F-16F-16

ProPro: Keeps efflux away from the ac w/o any : Keeps efflux away from the ac w/o any special precautionsspecial precautions

ConsCons::

1.1. Structural problemsStructural problems

2.2. Complicated fairings must be used Complicated fairings must be used around the exhaust around the exhaust

F-16F-16


1.7 Split Exhaust1.7 Split Exhaust Hawker Sea HawkHawker Sea Hawk

ConsCons::

1.1. Structural problemsStructural problems

2.2. Complicated fairings must be used Complicated fairings must be used around the exhaust around the exhaust

Hawker Sea HawkHawker Sea Hawk

ENGINE PLACEMENT: ENGINE PLACEMENT: Multi Multi EngineEngine Jet AC Jet AC

2.1 Engines buried entirely within the wing root2.1 Engines buried entirely within the wing rootDe Havilland Comet, Avro Vulcan, Vickers Valiant, Handley Page Victor, Tupolev 104De Havilland Comet, Avro Vulcan, Vickers Valiant, Handley Page Victor, Tupolev 104

ProsPros: : 1.1. Low D.Low D.

2.2. Better maneuvering capabilities as a result of the low W/S (larger S) and Better maneuvering capabilities as a result of the low W/S (larger S) and low Clow CLL in cruise. Also, no compressibility problems such as buffeting. in cruise. Also, no compressibility problems such as buffeting.

3.3. Smaller nose-up pitching moment due to sweep angle because of the Smaller nose-up pitching moment due to sweep angle because of the low AR.low AR.

4.4. Better low speed performance due to the low W/S.Better low speed performance due to the low W/S.

5.5. Better from the aeroelastic point of view because the low R wing box Better from the aeroelastic point of view because the low R wing box structure offers greater stiffness.structure offers greater stiffness.

6.6. If LFC is used (ex. BL suction), low T engines integrated inside the If LFC is used (ex. BL suction), low T engines integrated inside the fuselage of the wing in combination with a low W/S may be used.fuselage of the wing in combination with a low W/S may be used.

De Havilland CometDe Havilland Comet

Avro VulcanAvro Vulcan

Vickers ValiantVickers Valiant

Handley Page VictorHandley Page Victor

Tupolev 104Tupolev 104


2.1 Engines buried entirely within the wing root2.1 Engines buried entirely within the wing root

ConsCons: :

1.1. AccessibilityAccessibility to the engines: Detachable skin panels to the engines: Detachable skin panels are necessary at a location where the wing is highly are necessary at a location where the wing is highly stressed.stressed.

2.2. SafetySafety: In the event of an engine fire the likelihood : In the event of an engine fire the likelihood that the fire will spread to the fuel stored in the wing that the fire will spread to the fuel stored in the wing is great.is great.


2.2 Pod-Mounted Engines2.2 Pod-Mounted EnginesProsPros::

1.1. Safety: in the event of an engine fire the likelihood Safety: in the event of an engine fire the likelihood that the fire will spread to the fuel is limited (main that the fire will spread to the fuel is limited (main argument for the choice of the B-47 configuration)argument for the choice of the B-47 configuration)

2.2. Optimum engine operation due to short intake & Optimum engine operation due to short intake & exhaust ductsexhaust ducts

3.3. Engine accessibility.Engine accessibility.

4.4. Current high bypass ratio engines together with the Current high bypass ratio engines together with the development of efficient HLS favor the use of high development of efficient HLS favor the use of high W/S (smaller S) and pod-mounted enginesW/S (smaller S) and pod-mounted engines

ConCon: Higher D penalty: Higher D penalty


2.2.1 Pod-mounted engines suspended below the wing2.2.1 Pod-mounted engines suspended below the wingB-47, An-225, AB-380, B-777B-47, An-225, AB-380, B-777

ProsPros::

1.1. Structural advantages: the mass of the engines & pylons Structural advantages: the mass of the engines & pylons lead to a reduction in the root BM, thus lightening the wing lead to a reduction in the root BM, thus lightening the wing structure. If engines are placed ahead of the wing flexural structure. If engines are placed ahead of the wing flexural axis, they also constitute a mass balance against flutter.axis, they also constitute a mass balance against flutter.

2.2. Easy engine accessibility for maintenance.Easy engine accessibility for maintenance.

3.3. Favorable aerodynamic effects of the pylons at large:Favorable aerodynamic effects of the pylons at large: Tend to counteract the nose-up PM of swept back wings.Tend to counteract the nose-up PM of swept back wings. Act as fences, which are often used on “clean” wings.Act as fences, which are often used on “clean” wings.

Antonov 225 MriyaAntonov 225 Mriya

Airbus 380Airbus 380

Boeing 777Boeing 777


2.2.1 Pod-mounted engines suspended below the wing2.2.1 Pod-mounted engines suspended below the wing

ConsCons::

1.1. Engines placed too far outboard increase LND Engines placed too far outboard increase LND impact.impact.

2.2. Engines placed too far outboard require a large fin.Engines placed too far outboard require a large fin.

3.3. Higher D.Higher D.

4.4. Large YM & PM in case of engine failure.Large YM & PM in case of engine failure.


2.2.2 Pod-mounted engines fitted to the rear of the fuselage2.2.2 Pod-mounted engines fitted to the rear of the fuselageSud-Aviation Caravelle, DC-9Sud-Aviation Caravelle, DC-9

ProsPros::1.1. ““Clean” wing.Clean” wing.

2.2. Low door level.Low door level.

3.3. Little asymmetric T in case of engine failure.Little asymmetric T in case of engine failure.

ConsCons::1.1. Large c.g. travel w. variation in loading conditions.Large c.g. travel w. variation in loading conditions.

2.2. Deep stall because of the T-tail.Deep stall because of the T-tail.

3.3. W increase due to required local “beefup” of the structure.W increase due to required local “beefup” of the structure.

4.4. Loss of useful space in fuselage tail; result = longer fuselage for same PL.Loss of useful space in fuselage tail; result = longer fuselage for same PL.

5.5. In general, OEW will be about 2% greater.In general, OEW will be about 2% greater.

6.6. Engines are not easily accessible for maintenance.Engines are not easily accessible for maintenance.

7.7. At full PL large download on the tail; result = lower L/D.At full PL large download on the tail; result = lower L/D.

Sud-Aviation CaravelleSud-Aviation Caravelle

DC-9DC-9


2.3 2.3 Mounting of a central engineMounting of a central engine

2.3.1 2.3.1 Engine buried in the fuselageEngine buried in the fuselage B-727, L-B-727, L-10111011

ConsCons::1.1. Long and curved inlet; loss in intake efficiency.Long and curved inlet; loss in intake efficiency.

2.2. Heavier.Heavier.

L-1011L-1011


2.3.1 Engine pod-mounted on top of the fuselage2.3.1 Engine pod-mounted on top of the fuselage

ProblemProblem:: Fin forms an obstruction.Fin forms an obstruction.

SolutionsSolutions:: Cigar engine (DC-10)Cigar engine (DC-10) Butterfly tailButterfly tail

DC-10DC-10

Date post:	03-Jan-2016
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Configuration Design part 3

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