The Exploration of Airfoil Sections to Determine the Optimal
Airfoil for Remote Controlled Pylon Racing
by
Michael R. DeRosa
A Project Proposal Submitted to the Graduate
Faculty of Rensselaer Polytechnic Institute
In Partial Fulfillment of the
Requirements for the degree of
MASTER OF SCIENCE
Major Subject: MECHANICAL ENGINEERING
Approved:
____________________________________
Ernesto Gutierrez-Miravete, RPI Thesis Advisor
Rensselaer Polytechnic Institute
Hartford, CT
Abstract
In remote controlled pylon racing, the Quickie 500 class of airplanes has 500 square
inches of wing area, and with a Jett 0.40 in displacement methanol fueled engine, has a top speed
of about 150 miles per hour. They are flown 10 times around an oval course marked by 3
pylons, for a total of 2 to 2.5 miles. These planes lose a significant amount of speed in the turns
due to drag from higher angles of attacks around the turns at 30G’s. This project will explore
several airfoils to find the optimal airfoil that will minimize the loss of speed of turns while
having low drag for the straight-aways. Airfoil selections include NACA, particularly the
popular 66-012, Martin Hepperle, Selig, Clark Y, and Eppler. Raw wind tunnel and analytical
data for each airfoil will be used to calculate the finite wing drag for level and turning flights.
The blending of 2 airfoil sections to obtain the best of both will be explored as well as flaps to
increase lift during the turns. Finally, using Maple and Excel, each airfoil section will be run
through a simulated race, and the airfoil section that completes the race in the shortest amount of
time is the optimal airfoil for Quickie 500 pylon racing.
Introduction/Background
Radio controlled pylon racing has been around since the 1960’s, and now there are 3
distinct classes: sport Quickie 500 (120 mph), AMA Quickie 500 (150-160 mph), and Quarter
40 (180-200 mph). The only difference between sport and AMA Quickie 500 is that the former
uses the 1.25 horsepower Thunder Tiger Pro .40 engine, while the latter uses a 1.7 horsepower
Jett .40 engine. Both are powered by methanol fuel. The .40 signifies the size of the engines, at
0.40 cubic inch total displacement. The Jett is able to gain a 0.45 horsepower advantage through
the use of advanced timing.
There is always a search for an edge to design these planes to fly as fast as possible,
while still being within rules. The official rules posted on the Academy of Model Aeronautics’
website impose the restriction on Q-500 airplane wings:



Minimum projected wing area of 500 square inches
Wingspan range of 50-52 inches
Minimum airfoil thickness of 1.1875 inches
The purpose of these rules is to enforce equality among each racer. It also keeps the
speeds down and to allow the planes to maintain structural integrity in turns. Only Jett .40
engines are allowed in the AMA class. There also are rules imposed on the fuselage size and tail
thickness, but they have been mostly optimized through years of experience. The tail is typically
a V-tail configuration, and they have been optimized for size and stability. Any further
optimization on the tail and fuselage will yield an insignificant speed benefit due to the reduction
of drag. The wing is the largest contributor of drag in all phases of flight, so there is room for
improvement there, particularly the airfoil section.
Hence, the Q-500 rules provide sufficient constraint on design that lends the airplane to
be an ideal airfoil test bed. The wing area is fixed at 500 square inches, and the minimum span is
50 inches, which leads to an aspect ratio of 5. With an aspect ratio of 5, the chord is 10 inches.
With a minimum airfoil thickness of 1.1875 inches, the airfoil thickness to chord ratio, t/c is
fixed at 0.11875. The chord and t/c are important inputs for the selection of airfoil design and
the lift and drag calculations. Figure 1 below shows a typical Q-500 racer, a Viper 500, which is
sold by Great Planes. Note the constant chord wing and the V-tail.
Figure 1: A typical Quickie 500 pylon racing airplane
In pylon racing, four racers take off at the same time, fly around a course ten times, and
the first plane that crosses the finish line wins. Pilot skill being equal, the fastest plane wins,
obviously. This isn’t a perfect world, and pilot skill does vary, but having a fast plane certainly
does help to win races. A typical racing course is laid out below in Figure 2.
475.5 ft
100 ft
Figure 2: A typical racing course
As seen in Figure 2, a typical course has 3 pylons, with 2 being 100 feet apart, while the
third is 475.5 ft. from the centerline of the 2. The perimeter is 951 feet, translates to 2 miles
when flown for 10 laps in a counter clockwise direction. Now, it is an inefficient flight path to
fly a triangular course as shown, but rather, an oval flight path is more typical, and the overall
distance covered is closer to 2.5 miles. The start/finish line is 100 ft. from the twin pylons. All
planes take off within 0.5 seconds of each other and immediately turn at the far pylon. The way
the course is laid out, there are 2 turns per lap, for a total of 20 turns between straight and level
flight. There are significant penalties if the planes turn inside the pylons, so this scenario won’t
be considered here.
Problem Description
While entering the 50 ft. radius turns at 150 mph, the airplane experiences 30G’s of
centripetal acceleration. This leads the wings to adjust to a higher angle of attack to create more
lift to keep the plane in place while turning. An increase of drag from a higher angle of attack
will significantly slow the plane down in the turns. The favorite airfoil for pylon racing, the
laminar NACA 66-012 (Figure 3), typically loses 15-20 miles per hour in the turns. This airfoil
is desirable for low drag in straight and level flight, at the cost of high drag in the turns. On the
other hand, a flat bottomed Clark Y airfoil (Figure 4) has a higher lift to drag ratio due to its high
camber. The high L/D ratio of the Clark Y reduce loss of speed in the turns, but its high form
drag will not allow it to attain sufficient speed in the straightway.
Figure 3 NACA 66-012 Airfoil
Figure 4 Clark Y Airfoil
There are several different newer airfoils created by Hepperle, Selig, and Eppler that may
have the benefits of both. Particularly, Hepperle and Eppler have design airfoils especially for
pylon racing, and they are good candidates. A formal evaluation of all possible pylon racing
airfoils has not been done to this date. A wing comprised of two different types of airfoils may
have the best of both worlds, as well as flaps deflected at small angles during the turns. Those
configurations need to be assessed as well. The anticipated speed benefit of using the optimal
airfoil over the NACA 66-012 for this application will be mostly likely small. Even then, a 5
mph speed benefit coming out of the turns is huge, which will allow the plane to jump ahead of
the competition while coming out of turns.
Methodology/Approach
I will select several airfoils created by NACA, Hepperle, Selig, and Eppler, and Clark.
The raw experimental data can be found in Theory of Wing Sections, the University of Illinois
online airfoil database, and from XFOIL. XFOIL is a program created by Dr. Mark Drela of
MIT, which uses viscous flow equations to estimate the coefficients of lift and drag of an airfoil
based on its shape. Next, I will use the raw data to determine the total lift and drag of each
airfoil in straight and level flight and in turning flight using equations from aerospace
engineering textbooks. Using engine performance parameters, I will determine the maximum
speed and amount of speed loss in turns for each airfoil. Once all of the airfoil data has been
calculated, I will determine the time to complete 10 laps while accounting for speed loss in turns.
I will derive the equations Maple and tabulate the result in an Excel spreadsheet.
To simplify calculations, several assumptions will be made. The fuselage and tail will be
the same for each wing of a particular airfoil, which will allow me to ignore form, parasite, and
interference drag of those parts. The only variable for each plane is the airfoil. The aspect ratio
and airfoil thickness has already been determined by the AMA rules. The engine/propeller
performance will be the same for each case as well. Standard sea level atmospheric conditions
will be assumed.
Resources Required
The raw airfoil data are readily available from books such as Theory of Wing Sections
and the University of Illinois online database. I will download the latest copy of XFOIL and
learn to use the program for this purpose. All required calculations are readily available in
aerospace engineering textbooks such as Fundamentals of Aerodynamics and Introduction to
Flight. Methods of calculation of performance can be found in books such as Aerodynamics of
Wings and Bodies and Theory of Flight. My model airplane reference is Model Airplane
Aerodynamics by Martin Simons. I also have access to Maple at RPI to assist me in calculation
the 10 lap time of each airfoil.
Expected Outcomes
The goal of this project is to obtain an airfoil(s) section that will yield the lowest 10 lap
time by finding an airfoil that has the least amount of drag in straight and level flight and in
turns. By only having the airfoil cross section as the only variable in the pylon racing airplane,
the performance benefit or loss of each airfoil can be easily be compared.
Milestone/Deadline List
The deadline list has been provided by Dr. Gutierrez-Miravete for RPI Master’s projects,
and will be adhered to. The schedule to complete this project by April 20th is as follows:
February 3: Submit tentative proposal draft
February 10: Final project proposal and PowerPoint presentation of project
February 24: First Progress Report, Airfoil data collected
March 9: Second Progress Report
March 23: Final Draft submitted to Dr. Gutierrez-Miravete, All calculations completed and
tabulated
April 6: Preliminary Final Report submitted to Dr. Gutierrez-Miravete for his review
April 20: Final project and PowerPoint presentation due for final approval
References
1. Abbot, Ira H, Von Doenhoff, Albert E, Theory of Wing Sections, Dover Publications,
1959.
2. Anderson, John D., Fundamentals of Aerodynamics, Third Edition, McGraw-Hill, 2001.
3. Anderson, John D., Introduction to Flight, Fourth Edition, McGraw-Hill, 2000.
4. Ashley, Holt, Landahl, Marten, Aerodynamics of Wings and Bodies, Addison-Wesley
Publishing Company, 1965.
5. Simons, Martin, Model Aircraft Aerodynamics, Fourth Edition, Special Interest Model
Books, 1999.
6. Von Mises, Richard, Theory of Flight, Dover Publications, First Edition, 1959.
7. AMA Pylon Racing Official Rules, website, http://www.modelaircraft.org/files/20112012RCPylonRacing2JAEdit.pdf.
8. University of Illinois Airfoil Database, website, http://www.ae.illinois.edu/mselig/ads/coord_database.html.