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Design of a Light Sport Aircraft

Marc LeRoy

Dominic Contenza

Nathan Butt

Submitted to: Dr. Marquart

5/2/2014

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Table of Contents

1. Introduction pg. 3

2. Design Description pg. 4

3. Conclusion pg. 8

4. NACA 8-H-12 Airfoil Polars pg. 9

5. Engine Selection Chart pg. 12

6. EES Programs pg.13

7. References pg. 15

8. Parameter Calculations

Lift Analysis pg. 16

Thrust Analysis pg. 18

Turning Analysis pg. 19

Rate of Climb/Ceiling Analysis pg. 20

Landing/Takeoff Distance Analysis pg. 21

Fuel Weight/Range Analysis pg. 23

9. Preliminary Aircraft Drawings pg. 24

10. Project Description Handout pg. 27

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Introduction

The purpose of this report is to communicate an idea for a design of an LSA (light

sport aircraft). An LSA is a category of aircraft described by the FFA as a simple to

operate, easy to fly aircraft that follows certain specifications. For example, a few

constraints include a maximum weight of 1,320 lbs, a maximum speed of 138 mph, a

maximum stall speed of 51 mph, and maximum service ceiling of 10,000 feet. Other

constraints exist as well like fixed landing gear, a single reciprocating engine, a fixed

or ground adjustable propeller, and an unpressurized cabin. An LSA must be

designed so the average person can own an aircraft and enjoy flying. This means the

price of the aircraft cannot be astronomical, and the aircraft itself must have very

easy controls and be very stable in the air. In an ideal situation, an LSA should have

the capacity for a pilot and a passenger. The plane can be sold to a much larger

market if it can carry two people. This is an important design point for this project.

In the following sections, design parameters are summarized, assumptions are

stated, and justification for these assumptions and design decisions are explained.

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Design Description

This section contains the details of the preliminary design. The configurations and

parameters of the aircraft design are laid out in the following table:

Table 1: Aircraft parameters (all performance values @ sealevel)

Engine Direction tractor, propeller in noseWing low placement, dihedral of 3 degrees, straight with a

slight taper, chord at fuselage = 6 ft, chord at wing tip = 4 ft, NACA 8-H-12 airfoil, s = 125 ft2, wingspan = 25 ft. (tip

to tip is 30 ft. including the 5 ft. width of the fuselage

Fuselage Single boom with a width of 5 ft. at its widest part, needs to be this wide to accommodate 2 people sitting side by

side, 18.5 ft. in length, a bubble canopy for good visibility

Tail T-tail configuration, top of tail is 8.5 ft. off the ground

Landing Gear tricycle arrangement

Powerplant Information Engine model – Rotax 503 UL, rated at 50 hp, propeller efficiency = 85%, thrust = 266 lbs, max range of 1,580

miles on 30 gallons of fuel

Weight Max takeoff weight = 1215 lbs, 360 lbs, for 2 people, 182 lbs for fuel, 673 lbs. max weight for empty aircraft

Wing Loading 1215/125 = 9.72 lbs/ft2

Thrust to Weight Ratio 266/1215 = 0.219

Max Rate of Climb 13.7 ft/sec

Stall Speed 39 mph

Max Speed 300 mph

Takeoff/Landing distance

577 ft./1,140 ft.

Service/Absolute Ceiling

60,000 ft./63,200 ft.

Min Turn Radius 126 ft.

Max Turn Rate 36.9 degrees/sec.

The calculations for these values are shown in the Parameter Calculations Section.

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Aircraft Configuration

An LSA needs to be a very stable aircraft. A low placed wing with a slight dihedral of

3 degrees will help provide this stability. A straight wing will provide the maximum

lift, and slight taper will help to decrease the wing drag. The NACA 8-H-12 is a high

lift airfoil, normally used for helicopter rotary blades. The polar graphs for this

airfoil are shown in the Airfoil Polar Graph section. However, it can be used for an

aircraft wing as well. The high lift capabilities make it ideal for an LSA as the higher

lift can help reduce the stall speed of the aircraft. A planform area of 125 ft2 will

help with lift as well. The fuel will be held in two 15-gallon tanks, one in each of the

wings. Single Slot flaps on the wing will help to give the CLmax of 2 required for

takeoff and landing. These flaps also help to achieve the 39 mph stall speed. A T-tail

was chosen strictly for aesthetics purposes. It is just as effective as a normal tail

configuration. A single boom fuselage is the simplest type of fuselage, and simplicity

is important for an LSA. The tricycle landing gear will provide easy maneuvering on

the ground. Also, tricycle landing gears are safer and easier overall for novice pilots

to work with. It should be noted that in this analysis of this aircraft design, the drag

polar used (aka the CD,0 and k values) was that of just the wing of the aircraft, not the

entire aircraft.

Powerplant Information

The engine chosen for this plane is a Rotax 503 UL, with a rated maximum

horsepower output of 50 hp. An estimated propeller efficiency of 85% is used to

find the thrust available for the engine. This thrust available was used in all

subsequent calculations.

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Weight

In these initial design stages, the goal for maximum weight fully loaded is 1,215 lbs.

The two passengers are 360 lbs, and the fuel weight is 182 lbs. This leaves the

aircraft to weigh up to 673 lbs. This is reasonable when compared to other

successful LSA designs. The design should not be up to the limit of 1,320 lbs.

because then the passengers could bring some baggage (extra weight) with them

(another selling point of this design).

Rate of Climb

The rate of climb value of 13.7 ft/sec is reasonable for a preliminary design. Again,

the assumptions made with the drag polar effect the accuracy of this value. The

actual rate of climb for a given velocity can also be found in the rate of climb

analysis in the Parameter Calculation Section.

Max Speed/ Stall Speed

According to the max velocity analysis, the max speed for the design is 440 ft/sec

(300 mph). This is high for an LSA as the max speed allowed for an LSA is 138 mph.

Even thought the value is rather high, it is not unreasonable. Using the drag polar for

the entire aircraft would give a more accurate approximation of this max speed

value. For a first shot at design, this is an acceptable value, which will surely

decrease as the design progresses and become more accurate to the real thing. A

stall speed of 39 mph is well below the maximum stall speed of 51 mph. This is

excellent for the beginner pilots who want to learn to fly.

Takeoff/Landing Distance

The calculated takeoff and landing distance are found using a CLmax of 2. The

distances given in Table 1 are similar to that of other successful LSA designs. The

extensive calculations, again, are shown in the Parameter Calculations Section.

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Service/Absolute Ceiling

These calculated values are very high, too high in fact for an LSA. One explanation

for this error is the drag polar. Since it was only of the wing, technically it doesn’t

truly represent the aircraft. An LSA has a maximum altitude of 10,000 ft. This design

must be trimmed so the aircraft has a maximum altitude of around 10,000 ft.

Developing a drag polar for the entire aircraft would give more accurate CD,0 and k

values, which would allow for a more accurate calculation of the real service and

absolute ceilings for this design.

Min Turn Radius/Max Turn Rate

The value for minimum turn radius is a relatively small, but within reason. In reality,

the real turning radius might be 1.5 – 2 times larger than the calculated. The value

for Max Turn rate, 36.9 degrees/sec. seems to be very large. Normally, aircraft do

“rate” turns. For example, a Standard Rate turn is turning at a rate of 3 degree/sec.

Some low speed aircraft (an LSA is considered a low speed aircraft) can perform a 2

Rate Turn, or 6 degrees/sec. Again, using a drag polar of the entire aircraft would

give a more accurate Max Turn Rate value.

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Conclusion

The proposed design meets most the requirements for an LSA. For example, the

weight estimate is well within the required specifications and the engine is of the

correct type. There is no limit on the power output of the engine, just that it must be

single reciprocating. The 50 horsepower engine chosen for this design is small,

lightweight, and costs around $5,000. This is great when it comes to selling the

plane because it can be sold at a lower price. The stall speed requirement is fulfilled,

and landing and takeoff distances are normal compared to other successful LSA. The

rate of climb at sea level for this design, 13.7 ft/sec, is reasonable for an LSA.

It is very important to note that the drag polar used in all the calculations was for

the wing of the aircraft alone, not the entire aircraft. This is going to cause some

discrepancies in the parameters as they will differ from what they would actually be

if the aircraft drag polar was found and used. The service and absolute ceilings are

very high for an LSA. Since an LSA can only go to 10,000 ft. max, the performance

will have to be restricted in some manner. The drag polar for the aircraft would help

with this, but it would probably need to be trimmed back in other design ways as

well. The max speed of 300 mph is excessive as the max speed for an LSA is 138

mph. However, this could be trimmed back to make the max speed of the design

within range of LSA specifications.

With some refining, this design could easily produce a successful LSA. The

inexpensive engine in the design helps greatly to save on cost, and the two-

passenger capability is a great selling point for the design. The design could easily

be made so all parameters are within the LSA specifications. The low wing will give

better stability, and the bubble canopy will allow a better all-around view for the

pilot and passenger.

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Airfoil Polars for NACA 8-H-12 Airfoil

-The curves are from a Reynolds number of 1,000,000.

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Engine Selection Sheet

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EES Code and Plots

Rate of Climb vs. Elevation - plot and code

0 10000 20000 30000 40000 50000 60000 700000

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4

6

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10

12

14

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h (ft)

RC

max

(ft/s

)

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Maximum Velocity – Plot and Code

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References

1. J. Marquart, Final Aircraft Design Project Handout, Ohio Northern University,

2014.

2. Anderson, John D. Aircraft Performance and Design. 1st ed. McGraw-Hill

Companies, 1999. Print.

3. Airfoil Tools, “NACA 8-H-12 airfoil,” http://airfoiltools.com/airfoil/details?

airfoil=n8h12-il, April 2014.