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flGLETHE ULTIMATE AIRFOIL FOR

SPORT AIRCRAFT

S,

By Michael C. Myal (EAA 7978)

28763 CunninghamWarren, Michigan 48092

S E L E C T I O N O F AN D recommendat ions fo r light air-craft airfoils have been the subject of many articles inSPORT AVIATION over th e past twenty some years. Arecent phone call to Jack Cox at EAA Headquarters con-f irmed that an update on new developments might proveinteresting to fellow E AA members. In looking back over

past issues, it is a reflection of our maturity that we

literally have progressed from yesterday's ". . . most anyairfoil constructed satisfactorily wil l fl y well..." to today's

penultimate answer ". . . based on your design parametersfor cruise, climb and landing, the computer program de-

veloped . . ." i— — — — — — — —Low Speed/High Lift Stuff (Vso = 19.75 V W/S* C L max

The lowest possible f lying speed of an aircraft equatesto the need for an airfoil with a high maximum lift coeffi-

cient, CL max or a large wi n g area or the appropriate

combination of the two. Early airfoils were thin and highlycambered, producing good lift but excessive drag. Struc-

tural and speed requirements evolved thick airfoils with

less camber. Flaps (plain , split, Zap, slotted, Krueger,

Fowler, blown, etc.) were then invented to increase the liftof thick shapes to those of the early days. Lift coefficientsof th e plain vanilla airfoil grew from about 1.5 with noflaps to 3.2 and better with these high-lif t devices, ulti-mately making it possible for the Jet Age to come to yourhome town. Today, there are a number of high-l if t , unflap-ped airfoils available to the amateur designer, whereas inthe 30's the 23015 was about the only choice if high cruise

speed and low drag were a specification.

High Speed/Low Drag Stuff

Once the principle of metal construction was accepted

in lieu of fabric an d flying wires, research w as focused onthe drag of the wing. Metal cantilevers of corrugatedaluminum soon gave way to even more efficient stressedskin surfaces. Rivets became invisible; sanding fillers wereon e solution. Conditions of airstream flow described asl am inar and turbulent were discovered which explaineddifferences in interaction between the wing and the sup-porting air.Attention was diverted to a new problemdealing with Mach numbers and the sound barrier. Wo rkon subsonic laminar flow problems essentially stopped

while the challenges of the Jet Agewerebeing answered.

32 AUGUST 1983

The LinkThe author of "Megatrends", John Naisbitt, observes

that our technological inventions become accepted and

commonplace through first use as novelties or toys. There

is mu ch truth to that conclusion when we look back at

barnstorming before th e advent of commercial flying, in -troductions of horseless carriages, radio, television and

project ourselves beyond today's 48k home computer to

year 2001.

FIGURE 1 — The shape of United States airfoil development

over some 40 years. Compare Eagle I to the Jacobs (P-51)

section.



In a very real sense sport avia t ion is part of this natura lprogression from uniqueness to ut i l i ty . The commercialaircraft designs of tomorrow (beginning with the Lear Fan)will owe much of thei r parentage to the fun ships of today.The link from sport flying to seat cents per mile is nowh eremore evident than in the history of sai lplane airfoil de -velopment. It was the European sai lplane builders whoprompted fresh approaches to the study of subsonic l i f t an ddrag and the use of analytic methods. The scientific com-

munity responded and the name of Wortmann soon becameknown in the win ner's circle. Modern airfoil concepts havethe i r roots in these endeavors.

The Computer

In his SPORT AVIATION article of June 1978, Dr.Robert T. Jones chronicled the achievements of a numberof airfoil pioneers. Each of these men also contributedmuch knowledge to the solid foundation which is the basis

fo r airfo i l design today. We are at the point of learning

where theory and experience are shadows of each other;the theory can predict results while experience furtherverifies the theory.

So where does the computer come in? It is merely the

"number cruncher" which does all the complex an d repeti-t ive computations in a precise, accurate, speed of lightmanner , in accordance with h u m a n instruct ions based onthe sum total of established theory and experience. Thistool is as good as its program of instruction and, in thecase of airfoil design, it is better than anything else around!

Th e Program

Fo r those of you w ho are interested ye t wonder whata computer program looks l ike, I have included a fewlines of instruction from the NASA program writ ten in

Fortran. The airfoil design program in use today totalssome 2600 lines of such program statements. Use of this

program is not the beginning nor the end of the solution. . . fo r intelligence must be applied in the form of specificinstructions to the program.

Airfoi l Engineering

Here is where experience enters the picture! Imagineas you begin the design of a new airfoil at a computer

console the unfolding pattern of pressure distribution lines,as recalled by you from some existing airfoil plot. Nowbegin to adjust these lines via keyboard commands tomainta in laminar flow along th e chord to the maximumextent possible, considering local airflow velocities. Mean-while, also vary th e angle of attack while maki ng adjust-ments to minimize separation. As you change an d manipu-late these variables, the computer program maintains acontinuing process of defining the upper and lower surfacesof an airfoil meeting your parameters.

The individual 's skills in aeronautical engineering,fluid dynamics and computer programming come together

intuitively to produce a product which in all respects sur-

passes th e former cut and try wind tunnel methods!

Since the majority of amateur designers/homebuildersdo not have the financial resources or ready access to awind tunne l , it is no big loss to realize that this airfoildesign process is also out of reach for the majority of us.However . . .!

A Solut ion!

Do yo u want an airfoil that has high lift an d very lo wdrag with a min imum amount of wing torsion (pitchingmoment)? Also, do you want an airfoil which will stall

gently? Well, look no further because courtesy of NASA

FIGURE 2 — Overview of lift and drag characteristics fo r selected airfoils at available Reynolds Numbers.

SPORT AVIATION 33



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FIGURE 3 — The Eagle I (NLF(1)-0215F) sect ion .

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FIGURE 4 — Eagle I coord inates. Note the high degree o f c o o r -dinate accuracy generated b y t h e co m p u t e r i n o r d e r t o m a i n t ai nlaminar f l o w .

F IG U RE 5 — A lg o r i th m o f t h e co m p u t er p r o g r a m , th e p a t h an doperat ions t o b e f o l l o w e d dur ing p r o g r a m e x e cu t i o n .

research, you now can have all of the above!I predict this airfoil will become the decade's workhorse

much as the Clark Y did its share for aviation when itwas needed. In my estimation it's even better than the GA

series covered previously in SPORT AVIATION, but yoube the f inal judge after examining the evidence.

First, let's give it a "handle" we can all remember:EAGLE 1. We are already burdened wi t h zip codes, SS #,ai rcraf t N # . . . also because a "handle" sounds far moreconversational and fr iendly than today's fancy airfoil nam-ing conventions (or do you think NLF(1)-0215F is hand-ier?). Eagle 1 was designed by Dan Somers, a researchaerodynamicist at the NASA Langley Research Center,author of several technical papers, a sailplane pilot and

aviation enthusiast. He has collaborated with RichardEppler on airfoi l research and used the Eppler Airfoi l De-sign and Analysis Program to develop Eagle 1.

This airfoil was designed in 1979 to meet high perfor-mance specifications for a single engine project. Although

34 AUGUST 1983

the ai rcraf t was never built, the legacy of this work is freefor all to use! The design parameters inc lude a 15% thick-ness, a minimal pitching moment coefficient of -.05, anda 25% chord simple f lap. Up to 50% of the chord w i l l sustainlaminar flow under smooth surface conditions! The mostunusual feature of Eagle 1 is its "split personality". Whendirty, this airfoi l perfo rms l ike the best of the GA series.It should be ment ioned that the contour promotes, ratherthan forces, laminar flow. Indiscriminate changes to th ick-ness by proport ioning around th e mean l ine wi l l l ikelyadversely affect laminar conditions. If the wing structurerequires a different airfoil thickness, it is probably best tobegin anew.

For those EAAmembers who wish to learn more about

the excellent characteristics of Eagle 1, NASA TechnicalPaper 1865 i s avai lable by mail order from AerospaceResearch Appl ica t ions Center, P.O. Box 647, Indianapol i s ,IN 46223. I ordered a copy by phone on 317/264-4644. The

price was about $19.00 which was billed later.



P R O G R A M P R O F I L E

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FIGURE 6 — A few lines of FORTRAN program statements f romth e program. Over 2600 lines of such instruct ions are needed.

Other Airfoils

For a comparison let us review the features of someother airfoils:

Whitcomb/McGhee — Shown is the latest 17% NASAturbulent-f low airfoil (LS(1)-0417) designed in 1981 for

general aviation aircraft of conventional metal construc-t ion. It has very high lift and a somewhat abrupt stal l .This airfoil represents a distinct improvement over th ewidely published GA series (GA(W)-2 shown) in that itachieves lower drag at climb lift coefficients while featur-ing a reduced pitching moment coefficient. The blun t t rai l-in g edge may present design and construction difficultiesfo r hinged control surfaces.

Peterson/Chen — A NASA 16% general aviation airfoil(GA(PC)-l) of 1978 vintage, incorporat ing a flap for controlof wing camber at climb and cruise at same deck angle(min imal fuselage drag). Non-lamin ar in concept, intende dto be used with commercial quali ty metal construction.Stall is of t ra i l ing edge type an d considered to be abrupt.

Jacobs — Identified by R. T. Jones as a significantcontrib utor to the understanding of laminar airfoil design,research which culminated in the famous P-51. Very lowdrag at high Reynolds numbers evidenced by the "bucket"shaped drag curve. The NACA 6 series generally is sensi-tive to surface roughness an d stall abruptly.

23015 — Still the most developed and tested airfoilaround having high l ift , near zero pitching mom ent, fairlylow drag and an abrupt stall characteristic. An excellentreference airfoil fo r unders tanding an d predict ing effectsof various flaps, slats, etc. on new airfoils. I flew a Minicab

in Canada years ag o which was a baby in stalls becauseof the wing's engineered washout. I'm satisfied its stallproblem can be eliminated through careful wing design.

Davis — The mystery airfoi l of World War II, used on

th e Consolidated B-24 heavy bomber. Derived by un iquemathematical formulae, th e Davis airfoil claimed highload/range efficiency. The contour appears to resemble the

NAC A 4415 section. Inc luded here as a curio. Wind tunnel

data missing from normal references; does anyone have

this data to share for the historical record?

Concluding Remarks

At this point it should come as no surprise that mydesign project incorporates Eagle 1 since it has been amplydemonstrated that typical composite construction doesprovide th e contours necessary to maintain laminar flow.Perhaps, it is final ly t ime to focus ou r collective EA Aingenuity to the solution of the bug problem.

Current NASA airfoil research is devoted to the ad-vancement of U.S. commercial transport technology. No

further investigation or cataloging of general aviationairfoils is scheduled (as done in the 1930's with the NACA4- an d 5-digit series). This status does not preclude newdiscoveries. Keep in mind work on supercritical airafoilsalso resulted in the GA series of the 70's; who knows,perhaps the current NASA effort will discover new ap-proaches useful to the homebuilder.

FIGURE 7 — Dan Somers, Designer of "Eagle I" (NLF(1)-0215F)and f requent lecturer at Oshkosh forums.

References

1. Somers, Dan M., "Design and ExperimentalResults

Fo rA Flapped Natural Laminar Flow Airfoil For GeneralAviation Applications", NASA Technical Paper 1865,NASA Langley Research Center 1981,(EAGLE 1) .

2. McGhee, Robert J. and Beasley, William D., "WindTunnel Results For A Modified 17% Thick Low SpeedAirfoil Section", NASA Technical Paper 1919,NASALangley Research Center, 1981,(LS(1)-0417 Mod).

3. McGhee, Robert J., Beasley, William D. and Somers,Dan M., "Low Speed Aerodynamic Characteristics of a13% Thick Airfoil Section Designed For General Avia-tion Applications", NASA TM X-72697 1875, (GA(W)-2) .

4. Barnwell, Richard W. et al, "Low Speed AerodynamicCharacteristics of a 16% Thick V ariable Geometry Air-

fo i l Designed Fo r General Aviation Applications",NASA Technical Paper 1324, NASA Langley ResearchCenter, December 1978,(GA(PC)-l) .

5. Becar, Noel, "Selecting A Suitable Airfoil", SPORT

AVIATION, EAA, June 1962, (N A CA 63g 615).6. Jones, Robert T., "Highlights From the History of Air-

foil Development", SPORT A VIA TION, EAA, June

1978.7. Abbott, Ira H. and Van Doenhoff, Albert E. , "Theory of

Wi n g Sections", Dover Publications, June 1958, ( N A C A23015).

8. Davis, David R. , "Fluid Foil", United States Patent2,281,272 (filed May 9, 1938,granted April 28 , 1942).

9. McCormick, Barnes W., "Aerodynamics, Aeronautics

and Fl igh t Mechanics", John Wiley and Sons, NewYork, 1979 (low speed airfoil data, winglets, etc. coveredin this fresh textbook).NASA reports are ava i lable from: N at i o n a l Technical

Information Service, 5285 Port Royal Road, Springfield,VA 22161.

SPORT AVIATION 35

0909_archives eagle 1 airfoil

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