Ailerons and Their Effect on Turn Performance Sebastian C. Kaser 1 University of California, San Diego, La Jolla, CA, 92093 The aim of this experiment is to observe the effect installing ailerons onto a lightweight RC airplane has on its turn performance, and compare this to the performance of the rudder. Specifically, the course heading over time, or turn rate, is measured for each case to quantify the results, which support the addition of the ailerons. In addition, the feel of the turn performance has been observed by the pilot, which has been noted as an improvement over the baseline configuration. Nomenclature L = Lift ρ = density of air V = airspeed, or velocity S = wing reference area C L = lift coefficient C D i = induced drag coefficient 1 Aerospace Engineering Student, Mechanical and Aerospace Engineering Department, 9500 Gilman Dr. MC 0411 American Institute of Aeronautics and Astronautics 1
Transcript
Ailerons and Their Effect on Turn Performance
Sebastian C. Kaser1 University of California, San Diego, La Jolla, CA, 92093
The aim of this experiment is to observe the effect installing ailerons onto a lightweight RC airplane has on its turn performance, and compare this to the performance of the rudder. Specifically, the course heading over time, or turn rate, is measured for each case to quantify the results, which support the addition of the ailerons. In addition, the feel of the turn performance has been observed by the pilot, which has been noted as an improvement over the baseline configuration.
NomenclatureL = Liftρ = density of airV = airspeed, or velocityS = wing reference areaCL = lift coefficientCDi
= induced drag coefficientK = induced drag correction factorψ = heading or azimuth angleφ = roll or bank anglep = pitch rager = yaw ratep = roll rate
I. Introductionhe design problem is to add ailerons to the wing of a small remote controlled aircraft to allow the plane to roll and assist it with turn performance due to the added maneuverability. The objective is to determine how well T
1 Aerospace Engineering Student, Mechanical and Aerospace Engineering Department, 9500 Gilman Dr. MC 0411
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the ailerons will improve the turn rate (degrees/second) versus using only the rudder to maneuver yaw. The airplane will be able to roll slightly and deflect the elevator upward, resulting in a more stable turn than using only a rudder.
To verify the ailerons’ performance, one or more flight tests will be performed to analyze each of the turning methods. A set number of turns will be conducted using the ailerons, and another set using the rudder. Each will be able to be tested during the same run since both will be configured to connect with the transmitter. In these flight tests, the airplane will perform turns consisting of either a banked turn while rolling or a turn using only the rudder. Using a GPS unit attached to the mounted breadboard, the turn rates can be calculated from the differential of heading angle (relative to North) over time, and these can also be compared to each other to demonstrate the ailerons’ improvement over the baseline rudder.
II. TheoryWhile a rudder can be used to produce yaw, it is not as effective as ailerons. Ailerons are control surfaces which
are utilized by all commercial, private, and military aircraft, but are not always common on small hobby remote controlled planes, as these smaller planes sometimes go for simpler designs. However, adding ailerons to these planes can be greatly beneficial to the performance of the aircraft.
In commercial airplanes, using only the rudder to generate yaw produces unfavorable circumstances for the passengers. “As the airplane rotates about the vertical axis, the passengers in the rear seat are forced from side to side, much like the passenger in the back seat of a car when it is turning on an unbanked road” due to the centripetal acceleration, and this can cause motion sickness.1 Rudders are also not very effective during high speed flight, as they do not have enough surface area to completely rotate the plane. Ailerons are used to generate a horizontal force when the airplane is banked, and this is what causes them to turn.
While these points are not applicable for slower RC airplanes, the turns produced with the rudder are not as coordinated as those produced by the ailerons. For lower speed aircraft, i.e. RC airplanes, the rudder also produces a banked turn when deflected. As it is rotated, say, to the left, the velocity V of the wing on the right hand side moves faster than that on the left, which slows down as you turn to the left. This produces more lift L on the right hand side, which causes the plane to bank. This can be seen in Eq. (1) below (where ρ is air density, S is wing reference area, and Cl is the lift coefficient). The extent of this effect, however, is not as predictable as a bank with the aileron. Using the ailerons instead, one can perform a much more controlled bank into a turn with the help of the elevator as well as the rudder to counter the adverse yaw.
L=12
ρ V 2 S CL (1)
Adverse yaw is the result of an aileron deflection, shown to the right in Fig. 1. Because both ailerons are deflected in opposite directions, the result in lift is different for each side. The down-deflected aileron creates more of a camber, increasing the pressure differential between the top and bottom of the airfoil, generating more lift while also producing more induced drag (parameterized by the induced drag coefficient CDi
; see Eq. (2) below, where K is the induced drag correction factor). The up-deflected aileron causes the opposite effect, reducing the pressure differential which produces less lift. This causing the up-deflected side to rotate down while the down-deflected side goes up, inducing a roll, the angle of which is denoted by ϕ. Due to this difference in drag, the down-deflected wing’s airspeed slows down in relation to the other side, producing a yaw in the opposite direction of the desired turn the
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Figure 1. Adverse Yaw. During a banked turn, the difference in lift between the two wings due to the aileron deflection causes a yaw in the opposite direction.2
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plane is banking into. Because of this, a pilot is able to pull off a more coordinated turn by also using the rudder to turn in the desired direction.
CDi=K∗CL
2 (2)3
While it is difficult to quantify a “coordinated turn”, it is possible to calculate ψ̇ , the change in course heading over time (also referred to as the “turn rate”) using two Euler angles (course heading ψ and the roll ϕ) and the rotational rates in a body-fixed frame (pitch rate q, yaw rate r, and roll rate p). This is shown in Eq. (3) below.
ϕ̇=p+ tan θ∗(q∗sin ϕ+r∗cosϕ) (3)4
These values require both an accelerometer and a magnetometer4, neither of which were used for this experiment. However, similar results can be obtained with the use of a GPS logger. This is explained further in the experimental procedure.
III. Experimental Procedure
A. Parts Used • (1) Weekender eEyeHawk, by HiTec, containing: fuselage assembly [with vertical stabilizer], main wing, horizontal stabilizer, brushless outrunner motor, 6-amp ESC, folding propeller, nano servos,• (1) Minima6S, 2.4GHz, 6-Channel Aircraft Receiver, by HiTec ,• Radio transmitter, • (1) or more 2S, 7.4V, 350 - 360 mAh LiPo battery,• (1) charger for battery,• (1) Arduino Micro,• (2) Micro Servos (Adafruit 169),• (1) Ultimate GPS Breakout v3 (Adafruit 1032),• (1) I2c FRAM Breakout,• (1) Adafruit Breadboard,
• wires,• receiver / servo connecters,• soldering tools,• foam board of various thicknesses to make wings and wing box,• X-Acto knife,• razor and 45 degree razor, • music wire for servo connection with aileron,• aluminum tubes for semi-spars, • glue gun and hot glue, super glue, and quick setting epoxy,• fiber glass tape,• (1) Cheetah 2204-14 brushless motor,• (1) 8 x 3.8 APC propeller.
B. The First AssemblyMy first assembly used the KFm-4 airfoil configuration, shown in Fig. 2 below, using three pieces of foam
board, one half mm thick, and two quarter mm thick. I also added a piece of balsa wood to the leading edge for extra support. By drilling holes into the root sides of the wings and into another piece of foam to fit into the fuselage, I configured the wing to be attached from both sides using two cut aluminum rods to position them and act as semi-spars. I attached the servo, music wire, and the servo clip to the ailerons using hot glue, and used a 2-to-1 “fork” wire to connect it to the receiver to properly direct ailerons. To help reduce drag, I put a piece of paper over the servos. I could then test my assembly.
C. The Second AssemblyAfter the results of the first flight test, shown above, I decided to use a different method for my second
assembly. I made larger wings to account for the lift needed due to the added weight of the servos. Using the lift equation (see Eq. (1)) and an estimated lift coefficient from the original wing, I determined the wing size needed. This time, I constructed the new wing with .5 cm thick foam with paper on both sides. To do this, I first cut the ends with a razor at 45 degree angle for streamline purposes, making a parallelogram shape. I then made a slice along
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Figure 2. KFm-4 Airfoil. The airfoil used for my first design. This uses a 6-12% thickness, with top and bottom steps at the 50% chord. It is “fast, maneuverable, and gives a steady flight profile across a wide speed range [making it a] great choice for aerobatic plans.”5
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foam at about half-way to one-third down the middle, leaving the paper on the opposite side. I cut out a square on the shorter “half” for the servo to fit into, and then folded the short end over to make an airfoil shape. Using some extra pieces of foam, I created camber in the airfoil and a spar. I fitted in the servo and wires before gluing the airfoil together with hot glue, minimizing usage to preserve the foam’s low weight. I then cut out ailerons from the wing and used the 45 degree razor to make a triangular edge at the hinge, and attached it back to the wing using fiber glass tape. I attached the servo clips to aileron and used bent music wires to connect it with the servo. Finally, I pushed two aluminum rods through center of the wing to connect them with fuselage, as before.
D. Reducing Weight and Increasing PowerBefore I collected any data, I ran a few flight tests to make sure the airplane would fly. Because the wing was
too heavy with the added servos, I had to reduce the weight of the wing. To do this, I cut out square all along the wing, leaving at least 1 cm lines horizontally and vertically to act as ribs and spars. I also left space where the wing attached to the aluminum rods, as well as close to the main root and the main internal spar to maintain structural stability. To finish it off, I put packaging tape along the openings to enclose the wing and maintain aerodynamic effectiveness. In addition to removing parts of the wing, I had to upgrade the motor and propeller to generate enough lift. The old motor was removed and the new one placed on the nose of the fuselage, using pins to keep it in place. Since the larger propeller did not fit the motor exactly, elastic bands were used to hold it onto the rotating portion.
E. Collecting and Analyzing the DataTo collect precise data on turn rate using the GPS logger, I specified in the Arduino “record” code to make the
GPS only send the GPRMC message, which identifies the course heading, ψ, in degrees from true North, (in addition to other values such as global position and ground speed). I also changed the update rate to 5 Hz as opposed to the 1 Hz default.
To analyze the data, I post-processed it with Matlab to determine ψ̇ , the change in course heading over time, using the forward finite difference method, and graphed these results accordingly.
Finally, I could test the final configuration. I observed the airplane’s turning and rolling performance, as well as gathering input from the pilot. I then compared results of the turning rate using the ailerons with that of the rudder baseline.
IV. ResultsThese results consist of data from two separate tests to record the heading φ, or flight path angle, from the GPS
logger. One test uses the baseline airplane configuration with the original wing, using only the rudder to change course, and the second uses the wings and ailerons I constructed. While testing conditions for each experiment were attempted to remain constant, variations in wind speed, power input, and wing used could affect the comparison between the two results.
Figure 3 to the left displays the turn rate during a steady turn using the rudder-only baseline configuration. As seen in the graph, the change in flight path angle over the course of the turn varied in an oscillating fashion, ranging from 23.5 to 51.8 deg/s, and averaging at 36.7 deg/s. Disregarding the lowest data point, this average improved to 38.6 deg/s (this will be explained further on). This test was performing during the day with moderate to high wind conditions.
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Figure 3. Turn rate using the rudder. This graph displays the turn rate (deg/s) of a steady turn performed using the baseline airplane’s rudder. This produced an average turn rate of 36.7 deg/s, with a maximum rate of 51.8 deg/s over the course of the test. The average of the four highest rates is 43.46 deg/s.
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Figure 4 below represents the GPS data retrieved from the final aileron flight test, displaying the calculated turn rate (deg/s) and the heading angle (deg) relative to true North. The heading angle is included to indicate which time ranges the airplane was performing a well-defined turn, and to allow comparison to the turn rate. These data also displays an oscillating pattern in the turn rate, despite a seemingly consistent change in heading angle. Another point to note is that the GPS was sampled at a rate of 5 Hz compared to the 1 Hz of the previous test. This test was conducted during the night, where wind speeds were low.
The turn rate varied (during a well-defined turn) from 11.4 to 63 deg/s, though due to the oscillation, simply averaging the rate over the entire range was not optimal. Table 1 below and to the right attempts to alleviate this problem, displaying the average turn rates over a variety of time ranges. The first few rows are averaged over the entire range, or most of the indicated samples, while the last few rows are averages of the peak turn rates seen in Fig 4. These peak turn rate averages omit the lowest data points which varied the greatest from their neighbors. These data were then averaged all together to produce an average peak turn rate.
While the wide time range turn rates are all lower than the turn rate of the rudder configuration, the peak rates are mostly higher, indicating an improvement over the baseline. This will be explored more in-depth in the discussion section.
V. Discussion and Data AnalysisComparing these two sets of data, it is obvious
that there is some variability in the turn rate, especially so for the aileron test. The oscillation pattern can be seen in both graphs. In the rudder data, this has a period of a few seconds, while in the aileron data, the period is closer to one second. This could possibly be due to the way the turns were
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Figure 4. Turn rate using ailerons. This graph displays the change in heading, or turn rate (deg/s) (shown as circles, quantified by the left-hand vertical axis), during a flight test using the fabricated ailerons and the heading angle relative to true North (degrees) (quantified by the right-hand vertical axis with
Table 1. Average turn rates using ailerons over a variety of time ranges. This data table seeks to avoid the discrepancies in the turn rates calculated from the change in heading.
coordinated. A constant jig of the stick might push the airplane over too far, while short little movements could allow for smoother turns. This is the reason I decided to separate the peak turn rates to determine the fastest observed turning performance. The average of the peak turn rates allows for some normalization of these maximum values to achieve a more accurate result.
The turn rates of the rudder test were much less affected by this effect, as they remain somewhat steady over the given interval, while the aileron turn rates reached down to 10 deg/s in some cases (which is quite low compared to 40 deg/s). To remain consistent, removing the lowest data point in the rudder case results in an average turn rate of 38.6 deg/s, still a bit lower than the average rate of the aileron test, 41.1 deg/s. Though by a small margin, this supports my original hypothesis that ailerons would improve turn performance. However, discrepancies could have been a major factor to my final results.
The only way to successfully fly the plane with the second assembly was to reduce the weight and increase the power. Without the additional power, the wing was still too heavy to fly with the instrumentation package—it was only able to glide shortly before either crashing or landing. After my continuous struggles to reduce the weight of the wing (as well as the airplane fuselage itself) without any success in flying the plane (with the instrumentation package), I deduced that the only other option was to increase the power and thrust. As described in the procedure, the base configuration was fitted with a more powerful motor and wider propeller to allow the airplane to fly with instrumentation package attached.
Due to these variations in the airplane configuration, these results could have discrepancies, as the test conditions were not entirely optimal. First of all, the wing I constructed in addition to the motor and propeller used were not identical to those of the original airplane used during the rudder-turn test. This could have caused variations in aerodynamic performance, though according to the ground speed received from the GPS, the two configurations were flying at relatively the same speed, around 10-12 m/s. In regards to the aerodynamics, I had wanted to test my final configuration by turning with only the plane’s rudder under the same conditions (such as wind speed) as the aileron test to ensure a reliable control for my experiment. However, due to unfavorable conditions and a time constraint, this was not possible at the time.
Despite these discrepancies, there is still the matter of how an aileron turn feels compared to that of a rudder’s. According to the pilot, another group-mate by the name of Elioth Freijo, the airplane was much easier and smoother to fly using the ailerons to roll and turn, rather than with the rudder, supporting my hypothesis. This could be due to the more natural flow of an aileron induced turn, while a rudder turn might feel a little forced.
VI. ConclusionOverall, my experiment produced favorable results in support of my hypothesis: adding ailerons to a remote
controlled airplane’s wing would improve its turn performance. This was displayed in terms of raw data by comparing turn rates of ailerons versus rudders, which showed an improvement of 2.5 deg/s. In addition, according to the pilot, the feel of the airplane’s turn was much more natural and fluid.
However, as stated previously, improvements could be made to both ensure a better control and receive more accurate data. A future test would involve testing both turning methods using the same airplane configuration, consisting of wing, motor, and propeller, in addition to testing under the same weather conditions.
Another change that could produce more accurate results would be to use an accelerometer and magnetometer or a gyroscope to calculate the Euler angles and body-fixed rotational rates. While the GPS produced reasonable heading data, the variability in its output is questionable, especially due to factors such as noise and distance from the satellite. On-board instruments would provide more real-time data to analyze, and therefore, likely more accurate results.
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Appendix
Figures A/B. The original foam wing with balsa wood, and the failed test flight (note the pertruding aluminum rods).
Figures C/D The first assembly, installed with the aileron and servo, covered up by a piece of paper to reduce drag.
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Figures E/F. The second assembly, before and after the weight reduction.
Figure G. The semi-final assembly with packaging tape covering the holes in the wings.
Figures H/I. The final assembly, installed with an 8 in propeller and a Cheetah 2204-14 brushless motor to increase the thrust and power.
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AcknowledgmentsI would like to thank Professor Mark Anderson, Karcher Morris, and Kaylee Feigum for their hard work and
commitment to helping our class succeed. The author would also like to thank the Department of Mechanical and Aerospace Engineering at the University of California, San Diego, and Elioth Freijo, Nayelli Mondragon, David Renteria, and Alex Akopian for their teamwork and cooperation throughout this project.
References1McLain, John E, “Understanding the Use of Rudder: Its Most Important Use is Preventing Yaw”, Empire Aviation [online
website], [published June 2001], URL: http://www.empire-aviation.com/flight-instructors/john-e-mclain/ understanding- the-use-of-rudder.html [cited 05 June 2015].
2Davisson, Budd, “Technique: The Basic Turn”, Flight Training, AOPA [online website], [originally published in the magazine Flight Training, April 2011], URL: http://flighttraining.aopa.org/magazine/2011/April/technique.html [cited 06 June 2015].
3Anderson, Mark, “Level Flight Performance”, MAE 155 Aero [online website], [posted online during Winter 2015], URL: https://sites.google.com/site/mae155aero / [cited 07 June 2015].
4Anderson, Mark, “Angular Rates”, MAE 142 Aero [online website], [posted online during Winter 2015], URL: https://sites.google.com/site/mae142aero / [cited 07 June 2015].
5Kline, Richard, "Kline–Fogleman Airfoil", Wikipedia [online database], URL: http://en.wikipedia.org/wiki/Kline%E2% 80%93Fogleman_airfoil [cited 05 June 2015].
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