The Development Of The First Practical, Full Scale,Test Method For Real Drag And Propulsive Efficiency

On Propeller Airplanes

D,"rag and propulsive efficiency arethe two most fundamental pieces ofdata in aeronautical engineering, and,most amazingly, for the nine decadessince the Wrights mastered flight bysuccessfully combining lift, controland power, these two fundamentalfacts have remained unreachable un-knowns on propeller-driven airplanes!There has simply never been a practi-cal, accurate, accessible test for realairframe drag and real propulsive effi-ciency on propeller-driven airplanes inflight.

Level flight speed/power tests giveapparent drag, but that hides the realt ru th , the real propuls ion losses,lumping them in with basic airframedrag and leaving them inseparableand indistinguishable. It turns outthere is much to be learned and un-derstood here.

Simply stated, despite billions in re-search, no one ever figured out how todevise an accurate, practical drag teston a propeller airplane, other than pro-pellerless glides, which are rarely done.As a result, real drag and propulsive ef-ficiency have remained unavailable.Propulsive efficiency is the ratio of thepower (drag x true airspeed) that theairframe actually requires to the powerthat the engine must actually provide.For 90 years the aeronautical engineerhas been forced to work around and as-sume the missing data with apatchwork of methods and assump-

By Jack Norris and Andy Bauer

tions . . . and the conclusions have notbeen correct. Indeed, aeronautical en-gineers tend to not recognize how basicand important , how downright badpropeller/engine propulsion efficiencycan be, because they've never had apractical test or factual data.

In addition to propeller losses(nominally 80% efficiency), there canbe a very negative interaction betweenthe propeller and the airframe that canbe better or worse than another 80%factor . . . 64% combined . . . depend-ing on design and power applied, andcooling losses on top of that! Propul-sion losses can be much bigger thanrecognized, particularly on the olderand poorer aircraft designs.

Drag and propulsive efficiency arethe prime unknowns because airplanesare flying machines that convert en-ergy, fuel energy, into flight. Poundsof drag times trip distance in feetequals "foot pounds" of mechanicalenergy, BTU's of fuel energy required,considering the all important (in)effi-ciency of the propulsive system:propeller efficiency, propeller/air-frame interference and cooling drag.(There are 778.26 foot pounds of me-chanical energy per BTU, nominally19,000 BTU/lbs, in avgas.)

Once you have a real test and startseeing the real truth of the matter, youfind airplane drag can be better (lower)than has been realized, but propulsiveefficiency can be much lower than hasbeen realized. Happily, it is much bet-

ter on the best new designs today.Overall engine thermal efficiency,combined with propulsive efficiency isa technological disaster, a gaping pit ofinefficiency crying for appropriate at-tention in order to provide us with animprovement in the next century, onlya nominal 18 to 24%.

Once you have a way to get to thereal truths of the matter through prac-tical, accurate testing, the whole gamechanges for pilots and design engi-neers alike. Once it's possible to put areal drag curve in front of the pilotand that 18% overall efficiency num-ber, the pilot begins to realize that it'sworth paying attention, worth learn-ing the thinking person's way of flyingan airplane efficiently and not fly onthe too vertical part of the drag curvewhere the payoff in speed vs. cost ispoor - because fuel use is already 4 or5 times the real energy requirement!

Put an 18 to 24% efficiency numberbefore the airplane and engine engi-neers and they immediatelyunderstand they have their marchingorders for now and for flight in thenext century as fuel becomes morescarce and costly . . . and real test datagives them the insight to get there,starting now. We deserve better!

Amazingly, our most competentfield, aeronautical engineering, hasgiven us personal flight, near millionpound transports for business menand grandmothers alike, supersonicflight, fly by wire controls, satellite

SPORT AVIATION 53

Jack Norris' 1947 Luscombe 8E . . . used for the firstzcrn thrust experiments.

weather and navigation and has takenus to the moon and back, but has suf-fered the indignity of the lack of themost fundamental of tests to checkand refine the most basic calculations.As a result, our insight has been ham-pered. That sick 18% number I'llexplore further for you shortly is am-ple evidence of that. Jets are great,but at max range, a 900,000 poundplus 747 uses over 360,000 pounds offuel. That's almost seven 8,000 gallondouble tank truck loads, just about a19.5 foot cube per night!

We've all had the great gift of beingborn at the right time, in the right cen-tury, in the greatest country ever. I'vebeen most fortunate to have the greatfun of working on some of our mostinteresting technology; in flight, jets,space and other diverse fields as engi-neer, entrepreneur, business founder,executive and high tech managementconsultant . . . but flight was alwaysmy fun, my avocation. Technologycan be great fun, but there are alsodays with huge problems and plenty ofpressure. I bought my now Classic1947 Luscombe 8E at Christmas 1950for $1,225, using my winnings inmodel airplane competition. I was asenior in engineering school at OhioState at the time. The Luscombe hasalways been my simple, reliable, nodemand R&R escape vehicle. No mat-

ter how lough and burdensome thetechnical or business problems had be-come in the crunches, an hour in theLuscombe rendered the week's oppres-sive problem a mere detail to be solvedas a challenge. Perspective is a won-derful thing, and there's nothing likeflight to get perspective on the world.

As a kid of 15, I had to solve thegraveyard spiral dive and crash prob-lem before I could succeed and winagainst the really high performancefree flight models that all the big kidswere building. Flight and how it reallyworks became a lifelong interest.

By 1982 I had a lifetime of experi-ence that included jet servo fl ightcontrol packages that really did fail-safe . . . absolutely never failed,because there was no further backup.Over 100 of my own spacecraft rocketcontrol products are on the spacecraftin the central hall of the National Airand Space Museum in Washington.With more time, financial indepen-dence and fewer professional andtechnical headaches, I looked at myclassic R&R vehicle and decided toquit flying it like an unaware driverand, as a fun project, figure out thereal logic, how it really worked . . . topick up professionally where I had leftoff as a modeler at age 21.

Boy, did I get a fast education and arude awakening! I found essentially

nobody could give me a proper educa-tion on flight mechanics, the logic offlight. The best pilots didn't have aclue, the proficient engineers didn'tknow what to explain or how to do it,lacking the grasp of what a pilotneeded to know. I was quickly intoAerodynamics for Naval Aviators, agreat reference, putting together myown logic of flight. There is a beauti-ful logic and it all comes out soamazingly simple and interesting thateveryone should know about it.

I found I could not test my Lus-combe to get a real drag curve, realpropulsive efficiency. Propulsive effi-ciency and accurate drag calculationswere an empty hope based on multipleassumptions. The classic tome ondrag by Hoerner targeted an 80%propulsive efficiency (based on an80% efficiency of a prop in a freestream), then went through a calcula-tion drill to make the sum of all theparts match that number. I wasn'tsure I believed that, after learning timeand again that assumptions are notthe way to a sound bottom line in en-gineering. If you don't have a test, youare at big risk!

Real airplanes have small to grossleaks at control surfaces and skin cor-rugations, major cooling drag, rivets,antennae, angular joints, less thanwonderful sheet metal work, pumping

54 MARCH 1995

losses roaring from holes at the ta i l . . .to leaking, low pressure cockpits,doors and canopies. Small tractor pro-pellers on less than sleek planes trypulling themselves forward by theirbootstraps, blowing back on the air-f rame whi le a t t empt ing to thrustthemselves forward. Pushers havegarbage in, if not garbage out. After alifetime in the engineering profession,I didn't need anyone to tell me calcula-tions or scale wind tunnel tests werenot going to yield the truth on all thatreal world complexity.

Refurbishing my Luscombe prop, Ithrew it on the granite inspectionplate, after hours, at one of my con-sulting client's plants. A layout checkand a little trig produced the shockingfact that it was almost within .1 de-gree of perfect helical pitch outboardof the structural inboard segment. Iwas told McCauley shop tolerance isonly .2 degrees. Impressive, but Iwould learn that you really don't wantpure helical pitch. You want to matchthe slowing layered airflow at the nose(or rear).

Occasionally getting my hands on acopy of Soaring magazine, I knew ofthe technically elegant glide testingwork that the soaring fraternity hadbeen doing for years to evaluate dragand performance. The basic physics ofgliding flight is that the potential en-ergy of height is converted to thekinetic energy and the power require-ment of the flight path, an elegantdirect tap on the basic physics. Theymeasure the conversion as shown be-low. Richard Johnson, many timesnational soaring champion, had raiseddrag and performance testing to an artform. His March 1983 evaluation ofthe ASW 22 shows incisive bumps onthe drag curve as laminar flow con-verts locally to turbulent! Real worldtesting doesn't get better than that.

Flight path power = vertical sinkpower

Dragff x TAS = GW# x sink ratesink rate (ft/sec)

Dragff = GW# x ————————TAS (ft/sec)

The light bulb lit. I could calculatean rpm for that accurate prop for anear zero thrust, minus 4 degree angleof attack, for several true airspeedsand go glide test the Luscombe with(almost) no prop there. Viola! In oneweekend I had a moderately good ballpark drag curve, a ton on insight . . .and conclusions that never basicallychanged over 10 years of ever more re-fined work . . . that did not agree withHoerner's book at all!

Look closely and you will see the wire thatrubs on the back of the prop hub to triggerthe zero thrust light.

The drag curve of the classic highaspect ratio Luscombe was surpris-ingly low, but that calculated out toridiculously low horsepower require-ments, which said the propulsiveefficiency was terrible, nominally 60%or a few percent above, worse if Iwould have added tight, closable cowlflaps, cut out the cooling drag and re-moved that propulsive penalty for theairframe. Now hold that grasp for amoment before we proceed with thedevelopment of Zero Thrust GlideTesting and I'll go back and tie in that18% overall efficiency number I knowyou're curious about.

Separately, I was playing with cruisecontrol, the logic of flight, a thinkingperson's way to fly ... real, intriguing,easy smarts for the pilot. The high as-pect ratio Luscombe can be made to gofaster by burning extra fuel, but withthat long wing, by design, it's really a100 mph cruiser. Purposely flying at acalibrated 85 IAS, 100 TAS at 8,500feet, hot, 10,500 density altitude, 2,280rpm, leaned at low power (45 hp) formax economy, I can fly non-stop fromLA to McCall, Idaho or Rick Springs,Wyoming on my Deluxe 8E's 30 gal-lons. That's only 3-3/4 gph vs. the 5 to5-1/2 gph that the manual says. That's26.66 mpg, but still at 100 mph TAS.

The fuel burn sounds way too low,doesn't it? People tend not to believesuch a low fuel burn at the Luscombe's100 TAS. Here's the shocker. Usingthat th inking person's way to flybrings the overall efficiency way up toa miserable 18.2% That low compres-sion heat engine without sparkadvance, with a big cooling load anddumping exhaust at nearly 2,000 de-grees has a nominal 30% thermal

efficiency. Multiply that by a nominal60% propulsive efficiency and you geta terrible 18% overall (only 24% at80%). Energy calculations yield a pre-cise 18.2% as an independent overallcheck that our test data is correct.

Knowing that number, incidentally,allows me to figure out that it takesjust about one gallon of fuel to hoist a1,400 pound gross weight Luscombe to10,000 feet, an insight I'd never beenable to nail down before. The gamethen becomes recovering as much aspossible of it on a letdown when theengine is throttled, thus even more in-efficient ... and you can't recover morethan the 18%! The 82% was lost heat-ing the atmosphere. Gone.

Having fallen into being the rare ex-pert on the subject of intelligent flight,on a chance visit I fell into being theTechnical Director on the VoyagerWorld Flight in 1986 and ended upwriting the official book, log, analysisand explanation of the flight for theNational Archives, an interesting, sep-arate story. Copies are still available,if you'd like to see the real inside factson that great feat (see sidebar).

There are limiting thermodynamicsproblems, but bet on the fact that inthe next century the game will be bet-ter than 18 to 24%.

Back to Zero Thrust Glide Testing.As an engineer, I knew I was onto theright track for some real breakthroughprogress on testing for drag, coolingand propulsive efficiency, but I alsorecognized I was a rank amateur in thevery sophisticated analytical capabilitythat the great aeros have developedand specialize in. By great good for-tune, a chance meeting in a class atOhio State had developed into a life-long friendship with Dr. Andy Bauer,also a modeler from those youthfuldays of the 1940's. Andy was a fullycompetent aero at Douglas LongBeach, had a Master of Science degreefrom Ohio State and a doctorate fromStanford. Rare in this jet age, as amodeler he could calculate a propellerwith great insight and had just com-pleted a test program on flow aroundbodies, both blunt and refined.Putting our two lifetimes of experiencetogether, we had the potential forsome real progress.

Andy quickly educated me to thefact that though the air had to speedup to get around my fuselage, the Lus-combe's relatively blunt cowl and theproximate windshield had the propflying in a layered bed of air signifi-cant ly slower than flight speed(ultimately about 8.5% slower). We

SPORT AVIATION 55

quickly teamed up and soon Andy hadme set up for a more sophisticatedglide test that took into considerationthat slowdown of the air. We wouldlower the calculated Zero Thrust rpmand increase the test drag somewhatfor a more refined answer with everbetter insight and accuracy over thesucceeding 7 years. We both saw wewere working on the most fundamen-tal testing and basic data gap in flight,and it became a multi-year part timechallenge effort, with ever more so-phisticated analysis and test insightinto the problem.

Along the way, we learned of other,often wild efforts to find a test solu-tion for "real" drag. Bill Lear did glidetests on his Lear Star with both recipsoff and feathered! That was nothingcompared to the early efforts atNorthrop on the then secret BlackWidow. Max Stanley, now a goodfriend and fellow QB, at the request ofhead aero Dr. Bill Sears, had tried ver-tical with both engines off and theprops feathered! Max, the final testpilot of the original Northrop flyingwings, chuckled at the classic simplic-ity, the elegance of our sailplane-likefinal solution: using a simple mod-eler's zero thrust switch.

August Raspet, Dick Johnson' pro-fessor and mentor at Mississippi State,and George Lambros came closest in1954 with propellerless glide tests of aBellanca Cruisair towed to 12,000 feetwith the cooling ducts sealed and un-sealed. They got excellent insight,despite being harried by dead sticklandings at the end of every test. See-ing terrible propulsive eff ic iency(58%), as we did, comparing the sealedduct glides with level f l ightspeed/power tests, they were moreshy than they should have been be-cause they were actually onto the realtruth of the matter that is still notwidely understood.

Our m u t u a l testing, confirmingeach other by independent arm'slength work, gives the confirmation,the corroboration that good sciencedemands. Raspet also tested theCessna 120 and reported a 60%propulsive efficiency; and Jack Cox,right on the ball, supplied us with acopy of the testing of Steve Wittman'sshort wing Tailwind, reported in theOctober 1956 issue of the EAA's Ex-perimenter. It showed the typicaldrop off in propulsive efficiency aspower was increased as our Luscombetesting did.

By 1989, with time off for the Voy-ager effort, we had the best data that

sophisticated analysis and paralleltesting could produce. Andy is a jewel!We offered a paper for the January1990 Reno AIAA Conference and wereaccepted. Even after 7 years of work, Ipanicked a bit, however. The originalobjective was a free standing, indepen-dent test, not dependent on analysis.With dues fully paid, we now had won-derful insight into every minute aspectof the problem, with Andy's excellentwork, but we were also off the originaltrack . . . encumbered, inhibited fromthe creative spark that was needed fora free-standing test after 90 years ofaviation history.

Recognizing that, I backed off, putthe minutiae out of mind, let the realproblem . . . how to physically do aZero Thrust Glide Test . . . gurglearound in my brain, and my subcon-scious spit out the answer like thefaucet was suddenly opened. Ilaughed. It was a classically simpleanswer, but one that only a pilot of asimple plane would see, and only if hehad all the necessary objectives andquestions in his head. Understandingthat there is a problem is necessary toinvent a solution. It's indeed true: in-vention is 90% prior perspiration,then 10% inspiration.

When you go to prop a small plane,you yank on the prop to be absolutelysure the guy in the cockpit really hasthe brakes on. The prop goes "klunk"because there is a small axial clearancein the thrust bearings, about .010" to.020". The same small klunk happensin flight on loose engines when youtransition from either thrust or drag.An engineer knows that in most casesthere are no bevel gears and no pres-sure bias, and a rotat ing shaft isessentially, absolutely friction free inthe axial direction . . . so that zerothrust can be detected! (Therewould be one final challenge to be en-countered and solved in ourEAA/CAFE program.)

With a grasp of dynamics, you knowyou do not want a micro switch, whichis a rat's nest of vibration problems, asa sensor. You know intuitively that asimple, light, short, stiff piece of 1/16"model airplane music wire set up as anelectrical switch to kiss or miss theback of the propeller hub makes theperfect vibration proof sensor. Stiffand light, it will have a very high nat-ural frequency of vibration, becompletely invulnerable to the low en-gine frequencies. Mounting it on aphenolic block for insulation on thefront of the crankcase allows you touse a simple flashlight bulb on the in-

strument panel as an output to visu-ally indicate when zero thrust wasoccurring.

To accomplish accurate Zero ThrustGlide Testing, you simply need to "fly"the prop accurately at zero thrust,with no axial friction, no bias, using avibration proof sensor. Nose down ornose up, the weight of the prop/crankwill try to slide forward or back, butthat one very accurately definable biascan be easily and accurately handled ineither of two separate ways.

Method 1: Fixed Pitch Prop -With a simple level in the cockpit(prop vertical), you can glide at thespeed where the crank is perfectlylevel and find the accurate ratio ofrpm/TAS for zero thrust. Yes, there isan accurate ratio and it stays accurate.Of interest, that's 14.94 rpm/mphTAS on my Luscombe with a 71" x 51"cruise prop, just under 1,500 rpm at100 mph; and precisely 747 at 50 mph,an easy to remember mnemonic. Thatratio can be used accurately (a digitalTAG is handy, ideal) at any true air-speed, any altitude, and there is noslope angle correction with thatmethod. In high speed glides, at alower angle of attack, a precise analyt-ical investigation will show less wingflow circulation, a tad less slowing ofthe airstream at the prop disc (highwing), a tad of prop drag amounting toa 1% or less erroneously high drag.Pros have to work smart to get to 1%data but you can apply that small cor-rection if you decide to get thatprecise.

Method 2: Constant Speed orFixed Pitch Prop - With Method 2,temporarily ignoring the "downhill"prop/crank weight error, you simplygo out and do glide tests holding thepower or rpm at the point where youjust get a "false" zero thrust indica-tion. False by the inclination errorcaused by the prop crank weight x thesine of the inclination angle. The biaserror on the Luscombe is O pounds to6 pounds excess indicated drag with a47 pound prop/crank. The inclinationangle can be measured with an incli-nometer or calculated. The glideangles are less than you think.

The prop has always been a hugeproblem . . . a big power absorbingwindmill, a thruster, an unsolved roadblock preventing drag testing of thereal a i r f rame, interference, warts,leaks, et al.

Dr. Thomas M. Weeks, editor of theAIAA Journal of Aircraft, recog-nized the method as the basic,significant piece of progress that it is

56 MARCH 1995

and can be and requested that we pre-pare it for publ icat ion in theprestigious AIAA Journal of Aircraft.Now, not hurried, we carefully reranall tests, refined the test for publica-tion, went through peer review andpublished in in the May-June 1993 is-sue.

No "cold fusion" nonsense here.We didn't rush out to beat our chestsin public. Engineering is a demandingbusiness that cuts down the promot-ers. We checked, cross checked, talkedwith other experienced pros and hon-ored the i r good insights beforepublishing in the professional journal.The Physics Book only knows truth,and to rush forth with mouth in gearbefore brain is engaged is to absolutelyguarantee getting cut off at the knees.Good engineers learn to be verystraight, honest folks.

There are very important, practicaladvantages to Zero Thrust Glide Test-ing. Obviously, it's safer and easier todo than the towed glide method andmuch, much more convenient. Aneven more important advantage is thatyou have the engine available so youcan climb and run several tests, check-ing and proving when you do and don'thave good repeatable data, and aver-aging the best. The final advantageand the biggest of all is that you cango find really good air for really pro-fessional test results. You don't haveto do it right over the airport with po-tential updrafts and downdrafts, witha subsequent forced, dead stick land-ing. A huge advantage! What you

find is that stable air is the mainfactor in data accuracy.

We found that at dawn, four milesout to sea off Ventura, California, wehad air so good you could literally lockyour controls, let the plane sink andessentially fly itself down through the3,000 to 2,000 feet test segment toproduce data that you just knew was agood as any ever taken. Zero ThrustGlide Testing is genuinely practicaland accurate. The fast high energytests take more skill and practice, butpractice brings competence. I've hadthe fun of watching others learn andfind that they too can be test pilots!Precisely calibrated instruments anddoing the necessary careful data cor-rections for temperature andbarometric pressure differences are re-ally where the labor is. The gliding isfun and an interesting challenge toyour flying skill.

That brings us to the final reallygood news. The CAFE Foundation inSanta Rosa, California, under the cre-ative leadership of Dr. Brien Seeley andwith the "go gettum" sponsorship ofTom Poberezny and the EAA, has beensetting up and refining equipment andprocedures to do the most completelycomprehensive, wide ranging test pro-gram in the history of aviation. It willamount to nothing less than the profes-sional caliber acquisition of completeand fundamental aerodynamic, perfor-mance and handling quality data on allclasses and types of homebuilt air-planes and, ultimately, almost certainly,all the other private aircraft.

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SPORT AVIATION 57

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FLYING THE THINKING PILOT'S WAYLUSCOMBE 8E

Drag - Power 1250# GW

JRAG * Cd x(Wing Area, S) x (pV2/ 2) (Ram Dynamic Pressure =

Parasite, Cdo + alpha sensitive Profile + Induced, Cdi[Cd = .0325 + .009444(CL - ,4)2 + CL

2/(7tAre)

INDUCED = CL2/(7r Ar e) x Wing Area, S x "q"

" also ' = (Span Loading, W/b)2 / (n e q)

PARASITE DRAG = FPA x "q"

MAX L/DDRAG*IAS MPH 68

40 50 60 70True IAS (CAS) MPH

Parasite -*- Di Theo.Profile a -©- Total DragEngine HP -a- Efficiency

100 110

Di ActualReqd.HP

58 MARCH 1995

Picture - worth a thousand words!The intelligent way to fly an airplane isat low drag, which is at low indicatedairspeed. Then go high to get free trueairspeed, get your engine wide openand lean for maximum thermal effi-ciency, all of which maximizes milesper gallon. Look at the graph: at 85mph IAS, at high altitude and the en-gine at maximum efficiency, I haveonly 82% of the drag I would have at100 mph. This is at a favorable "knee"in the propulsive efficiency line, whichis terrible at 100 mph. This is how I go800 miles nonstop in my Luscombe 8Eon cheap auto gas, beating the socksoff the guys trying to go fast down lowand stopping in the summer heat tobuy $2.00 per gallon 100 LL. Workyourself through the "short course" inaero engineering contained in thisgraph and fly smarter!

The standard leaning "lazy J" totaldrag curve results from an essentiallyconstant parasite drag coefficient, pro-ducing a (V2) parasite drag curve thatswoops up as speed increases (twice asfast, 4 times the drag), and a highlyvariable induced drag coefficient, de-pendent on CL2, that produces exactlythe opposite effect, a (1/V2) curve thatswoops down as speed increases (twiceas fast, 1/4 the induced drag). Noticethe combined total drag curve goesvertical very rapidly. It's just notsmart to fly way up on the verticalpart of the drag curve!

A significant part of the parasitedrag is the profile drag of the wettedwing surfaces. A small part of that isangle of attack, which we've been ableto separate out here, due to the sensi-tivity of the method and extremelygood test conditions found out over theocean at dawn. As shown here, it actslike induced drag, a function of CL2,and is usually lumped in with induceddrag rather than being shown sepa-rately.

These parts of the drag coefficientare combined, then multiplied by thewing area and the ram dynamic pres-sure, "q," measured by your pitot tube.That produces the J-shaped total dragcurve . . . in pounds vs. indicated air-speed, or its components which areshown here so you can see and graspthe whole subject. Fly low indicatedairspeed . . . high!

Since the constant parasite drag co-efficient is multiplied by the wing area,which varies from plane to plane, it isnot proper to compare drag coefficientsof two planes. However, Cdo times thewing area gives a quasi equivalent flatplate area that is a legitimate compari-son between planes that is easy tograsp. Flat plate area does not includeinduced drag.

In our test of the classic Luscombe,we found an airspeed system that lied,which is not at all unusual, a 4.55 ft.2flat plate area and an Oswald factor, e, of.74, a simple fudge factor to get Prandtl'sclassic theoretical formula for the in-duced drag coefficient up to its realvalue. (Cdi = CL2/K Ar e, where Ar isthe aspect ratio, span/average chord)

Pounds of drag multiplied by trueairspeed in feet per second gives footpounds per second, the units of power(550 foot pounds per second per horse-power), so a power required curve canbe calculated directly once you have adrag curve. If you run a standard speed-power test and curve for the plane, youcan plot both the power required andthe actual power input curves, and, di-viding, get the propulsive efficiency forthe plane at various speeds. The greatinsight you will gain is that the Lus-combe, like most of the planes of itsday, has a poor and degradingpropulsive efficiency. August Raspetfound that out in the '50s, but no oneseems to have caught on. The Lus-combe and its contemporaries are speedlimited as much by poor propulsive effi-ciency as by drag!

Notice how the engine horsepowercurve increases noticeably faster than the

power required curve, due to the fallingpropulsive efficiency. Also notice thatthe engine power curve did not proveto be smooth like the drag curves.With miles per gallon dependent on in-dicated air speed, low drag and highpropulsive efficiency, do you see why Ifly at only 85 mph indicated airspeed,at low drag, at the favorable knee inthe efficiency curve, but up high at100 + true airspeed with my enginewide open and leaned for maximum ef-ficiency to fly 800 miles from LA toIdaho on only 30 gallons of fuel? For agiven gross weight, drag (thus milesper gallon) is constant at constant in-dicated airspeed at any altitude, butpower increases as true airspeed in-creases, so I fly up high at about 45horsepower... flying faster, not hurt-ing the miles per gallon and actuallygaining engine efficiency by runningwide open.

Our best new homebuilts, a newleading edge of flight, will prove farsuperior. Next month we'll showyou the great insight that comesfrom directly comparing an RV-6and a Luscombe . . . lower drag,better propulsive efficiency, bettermiles per gallon, faster . . . win,win, win, win!

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Cruiser TR-4Cruise SpeedStall SpeedUseful LoadPowerplants

4-Place185 mph55 mph

1100 pds160-200 hp

Build Time 1200 1500 hrs

KIS TR-1Cruise SpeedStall SpeedUseful Load

2Place170 mph55 mph610 pds

Powerplants 80-125 hpBuild Time 800-1000 hrs

KIS two and four place all composite kitbuilt aircraft are designed toKeep It Simple. Pre-molded high temperature composite andprewelded metal parts make KIS assembly easy. Both KIS aircraftwill perform well with many different engine options. .'BHfiifc-

INFO PACK $10 • VIDEO $15 • OVERSEAS ADD 50%TRI-R Technologies, Inc., 1114 E. 5th St., Oxnard, CA 93030 USA

Phone (805) 3S5-36SO • FAX (805) 483-8366 • VISA/M.C. Accepted

SPORT AVIATION 59

That's where the story picks upnext month, and we'll even tell yousome of the problems and challenges,some of the very interesting insightsthat are beginning to emerge. TheCAFE group is a remarkable fortu-itous gathering of the right people,each just about perfect for his part ofthe task. The EAA chipped in someserious money to equip the test pro-gram, but without the unique team ofvolunteers, you couldn't do what'shappening in Santa Rosa withoutaerospace megabucks.

What will come out is scientificproof that homebuilt airplanes arethe new leading edge of flight. Nomore of this 60% propulsive effi-ciency nonsense. What we will see isremarkably lower drag, far better effi-ciency than the previous generationof aircraft. . . just artistically, aero-dynamically superior aircraft. The21st. Century is upon us and as in1903, homebuilt aircraft are at theleading edge. It was homebuilders,former modelers who did the VoyagerWorld Flight, the most recent "mis-sion impossible" major milestoneaviation feat. What a great time tolive, fly and appreciate!

VOYAGERThe Voyager, The Last Great

First, was a stellar product of thehomebui l t movement, the firsthomebuilt major milestone since theWright Flyer. Voyager was just likea home-grown Moon program, onlydone with a very small, tight groupof very competent people . . . withno bucks, rather than the aerospaceindustry standard of thousands withbillions. The work was every bit asgood as the Moon program. I knowbecause I was right in the middle ofboth of them! The Voyager's ac-complishment could not have beeneasier than Apollo because it came17 years later. It couldn't happenuntil people were smart enough, so-phisticated enough to do it. BurtRutan used the best new structuralmaterials to the max, was smarterand more gutsy than the industry.The 938 pound structural weightwas less than 10% of the airplane'sgross! The distance record was ac-tually doubled! In these high tech

days, when do you hear of a worldor Olympic record being doubled?

Voyager flew 26,358.6 miles. Ithad a nominal transcontinental re-serve, indeed much more if flownprecisely in August when the weatheris friendly. When it's not, as in De-cember when the flight was actuallymade, the crew was in for an adven-ture thriller to end them all!

If you'd like a copy of Voyager,The World Flight, with all the realfacts and insights, you can get acopy identical to that in the Na-tional Archives for $12.95,Personally autographed by Dick andJeana, it's $20.00. That's not asales pitch. Profits go to Dick andJeana, who worked so long and sohard, six years, to actually do "mis-sion impossible." It's a greathistorical record to have. Copies areavailable from: Jack Norris, Techni-cal Director, Voyager MissionControl, 11613 Seminole Circle,Northridge, CA 91326.

60 MARCH 1995