The Exploration of Airfoil Sections to Determine the Optimal Airfoil for Remote Controlled Pylon Racing

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Nov 18, 2013 (3 years and 9 months ago)

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The Exploration of Airfoil Sections to Determine the O
ptimal
Airfoil

fo
r Remote Controlled Pylon R
acing





b
y

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 eng
ine, has a top speed
of about 15
0 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 3
0
G’s. This project will explore
several airfoils to find the optimal airfoil that wil
l 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 b
e 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 sectio
n 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 196
0’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, wh
ile 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 advant
age 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 al
low 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 dr
ag 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 rati
o, 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 wi
ng 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

th
at 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 certai
nly
does help to win races. A typical

racing course is laid out below

in Figure 2.



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 fligh
t 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 ot
her 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
475.5 ft
100 ft
flight. There are significant penalties if the planes turn inside the pylons, so this
scenario
won’t
be considered here.

Problem Description


While enteri
ng the 50 ft. radius turns at 15
0
mph, the airplane experiences 30
G’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 pla
ce 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 a
irfoil
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 li
kely 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, He
pperle, 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 equa
tions 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
engi
neering 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 accountin
g for s
peed 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 Aerodynami
cs

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 strai
ght
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 20
th

is as follows:

February 3: Submit tentative proposal draft

February 10: Final project proposal and PowerPoint presen
tation 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 Aer
odynamics
, 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 Aircr
aft 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/2011
-
2012RCPylonRacing2JAEdit.pdf
.

8.

University of Illinois Airfoil Database, website,
http://www.ae.illinois.edu/m
-
selig/ads/coord_database
.html
.