Comparison of Loading Parameters For Various Single Engine Light Airplanes Curtiss JN-4D. Built by Andy Anderson, this plane has a square tube fuselage but many new Jenny parts. Powered

By Howard L. Chevalier EAA 31823 Texas A & M University Aerospace Engineering Dept. College Station, Texas

by OX-5.

I

N GENERAL, most homebuilders are building existing airplane designs which have been proven to have

certain

stability

and

performance

characteristics. However, for the individuals who are modifying existing

Original S.P.A.D. VII. Plane was owned for years by a school in Oregon until purchased by "Swede" Ralston who sold it to Wings and Wheels. Dummy twin machine guns since replaced by single, real Vickers.

ANTIQUERS . . . (Continued from preceding page)

The "Wheels" part of the collection includes such famous names as Buick (1911), Hudson (1912), Ford (Model T and A), Chevrolet (1927), Cadillac (1939) — and even a 1923 Fordson tractor! The stars will be a 1922 Anderson — the only car ever produced in South Carolina — and a 1931 Duesenberg, never before on pub-

lic display. The collection continues to grow — Al Williams'

Curtiss "Gulfhawk" is soon to be delivered, the nation's best-known Staggerwing Beech will be in on loan, and by early next year, a full-size, working reproduction of

America's first scheduled train, the "Best Friend of Charleston" will be completed and running on a track around the grounds!

Wings and Wheels is solely owned by Dolph Overton of Smithfield, N. C., a jet ace in the Korean War, who, in addition to collecting antique airplanes, is involved in several industrial pursuits. He is well along the

road toward realizing every antiquer's dream, "to own one of everything!" Wings and Wheels is open daily and on a year-round basis. If you fly in, the airport is on the 290 degree

radial about 3A of a mile from Vance VOR. The facili-

ty has its own restaurant, gas, oil, and repairs are available. Free transportation is provided to nearby motels and golf courses. If you are planning a trip to Florida this winter to escape those Yankee winter blasts, make Wings and Wheels a "must" stop. It's lots warmer in South Carolina and if you love old airplanes — it will

warm your heart. PAGE 40

NOVEMBER 1969

®

designs or designing their own airplane, the questions that arise are: how will it handle, how will it perform, and how can one improve on the current class of homebuilt airplanes? For some of us who have the technical background, the problem becomes one of many hours of calculations for any one design configuration. Those without the technical background are forced to make guesses (same as the engineer at the end of all the elaborate calculations). The writer, during the design of his airplane, which is currently under construction, found a wide variety of opinions from fellow homebuilders on the subject of engine size and airplane geometry. Also, the writer was admittedly confused as to why many homebuilt airplanes were termed as being "hot" with high landing speeds when the wing loading on these airplanes is relatively low as compared with current commercially manufactured airplanes. For example, general aviation airplanes have wing loadings approaching 20 lbs./ft.2 and commercial transports exceed 100 lbs./ft.2. This article presents a comparison of existing airplane data used by the writer to obtain an empirical approximation of the relationship between airplane weight, wing area, wing span, and engine size for desirable stability and performance. In view of the type

of comparisons made, the results also include an evaluation of the aerodynamic efficiency of homebuilt airplanes as a representative class of aircraft.

Values of airplane weight, wing area, wing span and engine size from published material were used to define three of the most frequent and important aerodynamic parameters found in stability and performance analysis of aircraft: wing loading, span loading, and power loading. As an example of the importance of these parameters, the following two equations of statics related to wing loading and power loading yield the major characteristics of airplane performance in unaccelerated flight:

Note:

AA

(—1

is functionally

equivalent to (——)

V hp/

Increases in span loading can result in high roll rates and directional and lateral instabilities such as a spiral instability. Generally, wings with large span loadings also have low aspect ratios resulting in high drag. Decreasing power loading can result in trim instabilities due to the location of the engine thrust line. The writer also is convinced that some homebuilt airplanes have speed instabilities (operating on the so-called "backside of the power curve") during the approach to landing, but cannot prove this point because of the lack of data. Figure 1 shows the variation of span loading with wing loading for current single and twin-engine light

airplanes. It should be noted that the data for special purpose airplanes, biplanes, and STOL aircraft were not used. The aircraft data used are identified by symbols to show the wing, engine, and landing gear configuration. Only U.S. design homebuilt airplanes are shown for comparison. Most data were obtained from Janes All the World Aircraft, 1965-66. Since

the objective was to compare a class of aircraft as a whole, manufacturers and designers are not identified on the figures. Since any straight line drawn through the origin in Fig. 1 is a line of constant aspect ratio, one obvious fact shown is that most aircraft are (Continued on next page)

SYMBOLS AND UNITS

1)

V =

2 Mr 'L

2)

R/C =

CL

b =

wing

span

5 = wino, arta AR = aspec-t

—Npte that increased wing loading will not result in increased rate of climb as implied by this equation due to the relation between required lift coefficient and resulting drag coefficient for a given airplane weight. Wing loading, span loading, and power loading can also be related in equation form to airplane stability. However, to show all the functional relationships of these parameters to stability and performance would be an involved subject and beyond the scope of this article. However, a few words of caution are inserted here to point out some of the critical changes that can occur as a result of changes in these loading parameters. Increased wing loading can result in the following aerodynamic changes:

W

—^

b

(s