YEAR AROUND INCREASEDUTILIZATION * ECONOMY

IF YOU WANT MORE ENJOYMENT FOR LESS COS T

FLY A POWERED SAILPLAN E

Type Span

SFS31

L/D Cost* Delivery Seats HP

RF 5 B

Engine Rt . Sink

RF-4D 37 ft 20 DM 33,600 6 month Single 36 VW 4 .0 ft/se c

SFS-31 49 ft 29 DM 37,800 6 month Single 36 VW 2 .8 ft/sec

RF-5 46 ft 22 DM 50,400 6 month Dual 68 VW 4 .6 ft/sec

RF-5B 57 ft 26 DM 52,390 6 month Dual 68 VW/Frank 2 .8 ft/sec

Standard equipment includes : Airspeed indicator(s), Altimeter(s), Variometer(s )Magnetic compass, Gear warning light and horn, Safety harness(s), Seat cushion(s) ,Tail antenna, Cabin vent(s), Recording tachometer, Oil pressure gauge, Battery ,

Oil temp . gauge, Ammeter, Starter (elec .), Exhaust silencer(s) .

* Ex-factory

MOTORGLIDING

Elena Klein, Editor

Vol . 3, No . 6

Published by The Soaring Society of America, Inc .

June 1973

Contents Page

B I RDWATCHER 2

LETTERS TO THE EDITOR 2

SELF-LAUNCHING SAILPLANE D-39 ,by Wilhelm Dirks 3

THE HIGH PERFORMANCE MOTORGLIDER ANDITS APPLICATION IN COMPETITIONFLYING, by Ian Strachan 6

SO WHAT ELSE IS NEW?

by Elena Klein 7

DESIGN STUDY, by Dick Henderson 9

MOTORGLIDER M-17 UNIVERSAL 13

Cover : SF-25B, by Dr . Joseph H . Lorber

Material for Motorliding should be mailed to Elena Klein, 326 Elwood Street, Red -wood City, Calif . 94062 . Subscription to Motorgiiding is $5 .00 ($6 .00 outside o fU .S .) for 12 issues, beginning with the current issue . Subscriptions and adver -tising material should be submitted to the Soaring Society of America, P .O . Box66071, Los Angeles, California 90066 . Make all checks payable to The SoaringSociety of America, Inc .Back issues are available at $0 .50 each . All of 1971 are available except forJuly, September, and December ; only March and May of 1972 are available . (Noissues were published between May, 1972, and January, 1973 .) All of 1973 ar eavailable .

ADVERTISING RATES, CONDITIONS, AND SIZES

Display ads : $15 for ¼ page ; $25 for a page and $40 for full page . Prices arefor full-size, photo-ready copy . Extra charges for make-up, $3 .00 to $5 .00 ; re -ductions, $2 .00 ; and photos, $2 .50 . Sizes : 4-page, 3-3/8 x 4-5/8 ; z-page, 7 x4-5/8, or 3-3/8 x 9-1/2 ; full page, 7 x 9-1/2 . Classified ads : 50 per line(40 characters) or portion thereof .

Circulation of the May 1973 issue was 1090 .

1

There are (roughly) two approaches t othe proposition of designing a powere dglider--the scientific and the intuitive .Birdwatchers tend to be intuitive . (Whycan't you . . .? and There must be a way . . . )Institutions like M .I .T . are scientific .(Formuli . . .data . . .wind tunnels . . .statis-tics . . .) This month we are presenting bot happroaches in the hope of generating feed -back . We suspect Dick Henderson of usingthe intuitive approach and putting th eburden of proof on whoever decides t oimplement his proposals . M .I .T . uses thescientific approach . And we leave it upto the reader to evaluate both and send us

your evaluations .

SOMETHING TO LOOK FORWARD TO : STANHALL OF CHEROKEE fame has promised us anarticle on building a motorglider . JACKLAMBIE reports that--"We've done som eexciting motorgliding," and has promise dus another episode of The Adventures ofJack and His Flying Machine . Goody! IanStrachan's presentation to the M .I .T . Pro-ceedings, The HIGH PERFORMANCE MOTOR GLIDERAND ITS APPLICATION IN COMPETITION FLYING ,is complete (24 pages) in the second edi-tion of the Proceedings . We are reprintinghis Introduction .

Two of the pioneers of motorglidin gare old friends of the Birdwatcher so w ecouldn't resist bragging a little and be-sides we thought that for all you have readabout the HUMMINGBIRD you might like t oknow a little more about the men who dreame dit up, (intuitively?) and then applie da gread deal of scientific know-how t omaking it a reality .

LETTERS TO THE EDITOR

April 22, 1973Dear Ed :

Your latest issue of MOTORGLIDING i sindeed worth the price, (excluding th efront and first inside page) . It has moremeat and potatoes than some of the pre-vious issues . It seems that we are in asecond stage of the self-launching sail-plane movement . Things are starting t otake shape, the movement is starting totake hold, we start being mature and accept -ing the concept . Beware! We have a longway to go . (We love Jack Park who startedthis fine magazine . )

It is not the intention of this write rto again dare to upset our purist ; we merelyintend to bring out the facts as we hav eexperienced them in the last six years .We feel we do not want to express any royalclaims as distributor or dealer of theproduct line but state the facts and thu sgive sound information on the state of th eart to the reader and perhaps the prospe c-tive buyer .

First and foremost how does the FAAlook at the movement? My impression i sthis : The FAA is there to serve the people ;it is an institution and a government bod yto protect and serve the flying and non-flying populace . Rules and regulation swill only be issued then if the trend s odemands . I sincerely believe we will hav eacceptable rules and allowances within 1 2months of this date . At present we havehad no unacceptable restrictions or limita -tions in development, interest, and growt hof this self-launching sailplane movement .

With forty units now in the U .S .A . andCanada, single seat, two seat, tandem ,side-by-side, open class, standard class ,training, we can speak with some authority .

One needs to start somewhere ; we foundthe RF-4D to have the right concept . Itis mobile, self-contained, economical ,docile, reliable, responsive ; not only alittle of everything, but a little more

than everything . I made a 128-mile cross-country soaring flight without shaking th ewhole trip . Outclimbed my friend's 125 H P

(continued on page 11)

SELF-LAUNCHING SAILPLANE D-39

By Wilhelm DirksAkademische Fliegergruppe,T .H . Darmstadt, W. Germany

Introduction

A powered glider should fulfil th efollowing demands :1. Soaring performance should be nearl yas good as that of similar sailplanes .2. Under power it should have a shortt .o . distance, a good climbing speed, an da good cruising speed .3. It should make little noise .4. It should feature simple handling .

Configuration choic e

Some examples already constructe dand flying will now be discussed .1. Engine installed in the front, fitte dwith a feathering propeller (SFS-31, AS-K14) .The cooling air intake is at the nose .

2. Retractable engine and propeller (SF-27M ,D-37) .3. Ducted-fan in the rear fuselage (Sirius) .

4. Tailless aircraft with a propeller be-hind the trailing edge (AV 36, FS 26) .

Critical examination of these con-cepts gives the following results :

1. A front engine installation yieldsrelatively simple construction and hand-ling . The cooling is good and an effec-tive exhaust system can be fitted . The

propeller diameter can be as large a snecessary when a retractable main wheelis used . Fitting of a drive is possible .Using all these possibilities optimum per -formance under power and low noise ca nbe obtained . However, having the coolingair intakes and the propeller in front-even when it is feathered-produces s omuch drag that the gliding performance i sunsatisfactory .2. Retractable engine types guaranteegliding performance as good as those ofsailplanes of similar configuration, butperformance under power is comparativelypoor . The drag increase of the D-37, for

instance, is 40% when the engine is swungout . Problems arise for the engine section ,which has to be quite small and of verylow mass . A propeller of optimum diameter ,a drive, and an effective exhaust systemcan hardly be accommodated in the fuselageof a high-performance sailplane . Becauseof the complicated mechanism of this con-figuration the reliability of operatio nis unsatisfactory .3. The static thrust of a ducted-fan i stoo small . The gliding performance i spoor because the duct adds drag .4. Soaring performance of a tail-lessglider is always smaller than that of asimilar aircraft with a tail-plane . Lon-gitudinal stability is often unsatisfactory .

We can see, after this discussion ,that a configuration with the engine infront might be optimal for a powered glider,if, during gliding, the propeller is folde daway and the cooling 'air inlets are closed .Thus the D-39 powered glider will have apropeller which folds completely into th efuselage through openings closed by cover-

ing flaps . The engine (36-hp Hirth 01 7snowmobile engine) has a cooling fan s othat it can take the cooling air from thepropeller openings, which remain open i npowered flight . No further openings ar enecessary . Thus it is possible to con-struct a fuselage of high aerodynamic qual -ity as shown in Figure 1 .

The D-39 will be of fiberglass con-struction, with 15-m wing span, aspectratio 20 .5 and Wortmann laminar flow pro-file sections FX61-184 / FX61-126 . Pro-peller speed is reduced by a cog-belt t ohalf engine speed . The propeller diameteris 1 .25 m (Figure 2) .

Calculation of gliding performanc e

Gliding performance of the D-39 ha sbeen calculated using a digital computer .The results of this calculation may be com -pared with that of the high performanc esailplane D-38 which has the same wingsand tailplane as the D-39 : The drag o fthe fuselage (Figure 3) will be only 7%

larger than that of the smaller D-38 fuse-lage, if it is possible to have a laminar

3

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D- 39 cov e

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Figure 4

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Figure 1 cruising speed Vc [km/h)

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D-3 9find s

100- 38

D-3 9ASW 1 5

wide upwi

75

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D- 3 950 -

3

25

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Figure 5

Figure 2

4

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n- 45 ,1/

n

481/s

48

climb

V . 27, 8x ' &6 8

cruiseV=

n

48 1

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1/ e

/ s

V= 51, 6( max . c

m/ sruising ,P

mmz27 kW

V° 55,6 m/s speed )

10

15

20

25

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Figure 6

Figure 7

7 5

5o

25

Figure 8

boundary layer on the front part . However ,it is probably not possible to keep lamina rflow beyond the spinner . Thus further cal-culations are done assuming a turbulen tboundary layer . The drag is 25% greaterthan that of the D-38 fuselage . However,the air speed versus sinking speed chartsshow that the performance of the powere dglider is nearly as good as that of th esailplane (Figure 4) .

The best method to compare the per-formance of sailplanes is to calculate thecross-country cruising speed . This wasdone using a digital computer . Figure 5shows the cruising speed calculated fo rthe D-39, the D-38 and the standard classsailplane AS-W 15 . The cruising speed ofthe D-39 is only 3% to 5% lower than thatof the D-38 and as good as that of th eAS-W 15 . If lift is very weak the D-3 9is inferior to the sailplanes becuse ofthe minimum wing loading of 29 kg/m . (Inthis case sailplanes normally cannot con-tinue their cross-country flight and haveto land . Then the powered glider, ofcourse, is superior . )

Design of an optimum propeller

Using Reference 1 it is possible t ochoose the optimum propeller diameter ,speed, and blade loading for static thrust ,climb and cruise . Using these results apropeller for optimum climbing speed wa sdesigned using Theodorsen's propellertheory (2) . The result is a C L vs b dis-tribution, which completes the blade dat arequired . Clark Y profile sections werechosen for the D-39 propeller .

Calculation of performance under power

The calculation of the thrust forvarious airspeeds was done using the theoryof Betz (3, 4) . This calculation was als odone using a digital computer . The resultsare plotted in Figure 6 . The cruisin gspeed is 51 .6 m/s at a propeller speed o fn = 2880 rpm . Rate of climb is ws = 3 .60m/s at an airspeed of V = 27 .8 m/s and apropeller speed of n = 2810 rpm . Stati cthrust is T = 925 N at a propeller speed

5

of n = 2810 rpm . This performance unde rpower is better than that of current powere dgliders of similar configuration .

Design of the propeller blades andfolding mechanism

The propeller blades will be made ofthe fiberglass reinforced plastics . Theadvantage lies in the smaller weight b ycomparison with wooden blades . The fiber-glass rovings of the blade are used fo rthe connection to the hub also, withou tneed for additional material . Figure 7shows the connection . Figure 8 shows th econstruction of the blade . Torsion istaken by a fiberglass laminate with th eweave directed at 45 degrees to the center-line of the blade .

The blade folding mechanism (Figure 7 )is operated by the pilot when the propellerhas stopped rotating . In operational po-sition the propeller blades are fixed b ya knee joint . Centrifugal forces add tothe kneeing action .

References

1. Hartmann, E ., Biermann, D . ; NACA ReportNo . 640 . The aerodynamic characteristicsof full-scale propellers having 2, 3, and 4blades of CLARK Y and R .A .F . 6 Airfoi lsections .

2. Crigler, John L . ; NACA Report No . 924 .Application of Theodorsen's theory to pro -peller design .

3. Betz, A . ; Schraubenpropeller mit ger-ingstem Engergieverlust, Gottinger Nach-richten 1919 S . 193 .

4. Just, W., Jaeckel, K . ; Bericht 3 Aero-dynamik der Hubund Tragschrauber Tell 2Berechnung des Rotors, Bericht der Deut-schen Studiengemeinschaft Hubschrauber e .V .

(From Proceedings of the First InternationalSymposium on the Technology and Science ofMotorZess Flight, Massachusetts Institut eof Technology, October 18-21, 1972 . )

THE HIGH PERFORMANCE MOTORGLIDER AND IT SAPPLICATION IN COMPETITION FLYIN G

By Ian Strachan

Introduction

The author argues that the pattern o fhigh performance motorgliding in the futurewill be set by the next generation of de-signs reaching the gliding movement . Thismay in no small measure be influenced b ythe contest rules approved by the CIW forthe first world Motorglider championshipwhich will define whether engines will b eallowed to be used extensively, or whethe rthey will be regarded simply as aids t oprevent field landings . This paper give sa design specification for a high perfor-mance single seat motorglider (HPMG), asuggested draft for CIVV Motorglider contes trules, and a list of the additional Britis hGliding Association (BGA) rules that atpresent enable motorgliders to take par twith gliders in BGA contests . Perhaps thebiggest factor which presently holds up

HPMG development is the lack of a suitabl eengine . All motorglider enthusiasts shoul dscan the lists of commercial engines fo rthose with power outputs of 35-50 bhp a thigh power/wt ratios, and write to theirsoaring magazines (and the glider manu-facturers) with details of likely units .

All glider pilots who find themselve sinterested in owning the HPMG of the spec-ification described in the paper shoul dmake their views known loud and clear tothe glider manufacturers . Similarly CIVVshould receive as many inputs as possibl ethrough national representatives beforefinal decisions are made on contest rules .The author argues that we must ensure tha tmotorglider contests are won by soaringin high performance sailplanes, and notby indiscriminate use of engine in 'com-promise aeroplanes' that do not soar ver ywell but have superb engine-on performance .(From Proceedings of the First InternationalSymposium on the Technology and Science o fMotorless Flight, Massachusetts Institut eof Technology, October 18-21, 1972 . )

6

SO WHAT ELSE IS NEW ?

by Elena Klein

The mourning dove's plaintive hroo-hroo, the rustle of wind in the tops o fthe eucalyptus trees, the whistle of ahoming glider on the downwind leg-thes eare the gentle background noises punctuate dby friendly voices and the occasional bus yrattle of the little tractor or the rumbl eof sliding hangar doors . Then the calmis shattered by a piercing whine . Is i ta monster model airplane engine? A spee dboat? People come out of the hangar o rlounge to watch an old familiar show . TheHummingbird is taxiing up to the line . Itrolls briskly under power, rotates int oposition as its wing-tip wheel draws asmooth arc on the hardtop . The Nelsonengine revs to a fiercer whine and the shipstarts its brief takeoff run, lifts offand diminishes audially and visually int othe distance . The watchers drift back t ohangar, lounge, and glider trailer .

To the members of the Northern Cali-fornia Soaring Association the above scen eis a familiar one but one they seldom fai lto observe . I have watched the scene forover fifteen years but-to my own embar-rassment-without realizing that I wa swatching the wave of the future . Not unti lI became associated with MotorgZiding di dI become aware that Ted Nelson and HarryPerl had accomplished twenty years ag owhat so many engineers and designers wer ecurrently attempting-a self-sufficient ,glider! No Women's Libber, I have stil lnot reconciled myself to a sport, the sportof soaring, that is enjoyed by one perso nat the expense of so many, the expense o ftime, energy, and equipment to the exclu-sion in many cases of most other forms o fentertainment . I could be reconciled b ythe Nelson Hummingbird .

The Hwrnningbird gave its name to Hum -mingbird Haven situated at the foot o fAltamont Pass east of the town of Liver-more, California . There is the most com-fortable and accommodating glider site Ihave ever visited. With its swimming pool ,barbecue pit, picnic tables, swings, an dcomfortable lounge and clean bathrooms it

deserves a story of its own . All these ofcourse, besides the well-drained, well-surfaced runway, tow plane, and tractor ;and ridge, thermal and occasional wav esoaring .

But my story today concerns motor-gliding and the two men who solved th eproblem of soaring sans crew and launchfacilities . Motorgiiding readers haveseen the Hummingbird or read about it andknow its history . (See July 1971 Motorgliding) . Members of NCSA and PaSCo hav elong been familiar with it . Two Humming-birds are at home at Hummingbird Haven .Les Arnold nests his Hummingbird at Browns-ville in the Sierra foothills .

Any weekend morning at HummingbirdHaven Ten Nelson ambles down the lane fromhis home on the northeast corner of th efield .

"Guess I'll go upstairs and see what' scooking," he says, squinting at the sky .He is a tall lean man, fair as his Scan-dinavian forebears, affable and easy t otalk to once you have earned his respec tand trust ; formidable if you are careles sabout rules . After discussing the weather ,how it was yesterday, and what might b eexpected today, Ted goes to the hangar ,pulls out his ship and inspects it . Noneed for any assistance as he prepares fo ra flight . He climbs in, fastens harnes sand belts, pushes the starter button andtaxis to the flight line for takeoff. Teddoes this almost daily . His wife Alicewaves him off morning, noon, or evening .Perhaps she watches out the kitchen windowwhen she hears the Bird taxiing up to theline . She won't hear him land unless i tis a quiet weekday when she might catchthe rustle of the landing wheel on th ehardtop .

Ted can tell by the sound of the win dduring the night, the temperature, and thecolor of the sky whether there is likel yto be a wave off Mt . Diablo . Or he may gohunting down on Cedar Ridge to the southend of Livermore Valley . He'll chuckle ashe tells you that yesterday he got t o17,500--or even 19,000 on rarer occasions .

Ted was reporting such a flight oneday in the lounge when a young glider stu -dent innocently asked, "How many times did

7

you use the engine?" Ted fixed him with awithering glance . "You don't understan dgliding or you wouldn't ask that kind o fquestion," he answered . If Ted wants t ofly under power he flies an airplane .

Ted keeps in radio contact on hishunting expeditions . If he has found awave he directs other pilots to the site .If there's "nothing up there" he lands ,rolls up to the hangar, and shoves th eBird into its slot . No sweat, no assis -tance needed . He stops to chat and reporton conditions then goes off up the lan eto check in with Alice .

Harry Perl doesn't live at Hummingbir dHaven . It justs seems like it . He i sthere before anyone else Saturdays, Sundaysand holidays, and among the last to leave .Harry lives in Livermore . He stops of fat the Rad Lab to collect weather data .He makes up a profile of the weather ,soundings, winds at different levels, andpins it on the bulletin board in th elounge . He is a day ahead of the weathe rmaps . He checks out the towplane-an deverything else-and if it seems worth -while pulls out his Hummingbird and testsout the area or confirms his earlier find -ings .

Harry designed and built the Pene-trator (20 years ahead of its time, saysome glider guiders) and worked with Te ddesigning and building the Hummingbird andits forerunners, the Bumblebee and th eDragonfly . Harry is energetic, vigorous ,forthright . Like Ted he is intolerant o fcarelessness and rulebreaking but he i sgenerous with technical advice and counsel .For many years he was field manager o fHummingbird Haven. It is a measure of hi sindefatigable capabilities that it tookfive members to replace him as field mana -ger when he relinquished the title .

Harry does not readily commit himselfabout the new motorgliders . He talks aboutlight power planes, the costs of jet-assisted gliders, and performance figures ."As to the future," he wrote in Motor-gliding, "The big problem is economic ,not technical, in providing a satisfac -tory self-launching sailplane . The tech-nology to produce a high-performance machine

is well within the state-of-the-art . Themajor problem is to provide a sound, prop -erly financed development and productionproject . "

As often as I had seen the Humming-bird, I had never thought to ask for a rid ein it . Several years ago my husband tookoff from Hummingbird Haven in the firs tflight of his homebuilt HP-14 . We watchedhim until he released at about 2000 fee tover the field. Harry had given the Four-teen two auto-tows just a couple feet offthe deck before clearing it for an aero -tow .

"D'you want to go up and wave t oSherb?" he now asked .

"Sure!" I answered . "What in?""The Bird . "Great! Harry's Hummingbird was sit -

ting alongside the hangar . I climbed int othe back seat . Not roomy, by my claustro -phobic standards, but more comfortablethan the Pratt-Reed or the TG-3 . Harrydid some checking and climbed in . I re-member seeing him pull a string . Therewas an explosion of noise from the Nelso nengine behind me . The taxi and takeof fwere quick and smooth . Conversation impos -sible . We circled Sherb at .a comfortabl edistance, close enough to see his delighte dsmile inside the shining bubble of the -1 4canopy . We circled again then we headedsouth . I had become adjusted to the hig hdrone of the engine when suddenly it stop -ped. We were airborne-no longer unde rpower .

We flew for an hour . It was a "good"day but not "spectacular" . We caught acouple of thermals, enough to fly over thereservoir and back to the field with aroun d3,000 feet to spare . It was the most com -fortable and longest soaring flight I hadever made . The best part of it, of course ,was being able to share at least some o fSherb's elation . We entered the pattern ,dropped smoothly onto the runway and rolle dgently up to the hangar .

That all happened two years before Ibecame involved with Motorgiiding. Sowhat else is new? Well, it seems to thi sinveterate birdwatcher that surely motor -gliding isn't .

8

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LETTERS . . .(continued from page 2 )

Swift, passed up many a 150, 140, verywell known trainers-not to name our powere dbrothers . Flew in all kinds of weather ,VFR preferred, did my soaring during lunchhour and after 5 pm . I went to see howthe soaring was in other places and coul dstill be home for supper and take out myex-crew for dinner . Why was all this pos -sible? Well, utilization, the only wa yto reduce costs . This was only the star tof things to come, for me as well as fo r40 other satisfied pilots .

The SFS-31 showed a fast improvementin soaring ability over the RF-4D . TheRF-5 again gave a little more of everything .It showed the non-believing power pilo twhat soaring was all about ; it showed th enot-so-hep glider pilot that soaring cross -country does not need to take risks no rinvolve a lot of commotion .

Then there came the RF-5B which ha sreal total utilization of soaring flightand power flight . There is good to verygood soaring performance, good to very goo dto very good cross-country ability, powe ron or power off . It will allow you to ge tout of the high-density areas and enjoyflying as you used to . The family is stil lable to participate and enjoy it more thanever . Training is practical, economicaland justifiable for both fields of flying .Motorgliding will allow the power pilot t oventure into soaring without losing hi smobility . It will allow the new soarin gpilot to venture on a cross-country- athing of sheer terror in the past . TheRF-5B can be considered the total concept .Its folding wings make it easy to hangar ,it can be flown when the soaring is not sogood, it gives total utilization year round .A sink rate of 2 .8 ft/sec is not all bad ;it has allowed us soaring flights of 3 t o4 hours in this part of the country alread ythis year .

Ann Welch always does an outstandingjob on reporting the new things as well asstaying fair in comparing the apples an doranges-or whatever she is reporting on .I have flown both the AS-K16 as well a sthe SF-28 . Naturally we have more experi -ence with RF-5B and therefore a direc tcomparison is not available . Neither didwe count the bugs on the leading edge .

We will attempt to give a description o fthe RF-5B only along the same lines asreported on the SF-28 and AS-K16 by Ann

WelchThe RP-5B is an excellent 2-seat motor -

glider; it was so designed and it has live dup to its expectations . It is fitted withthe Sportavia-Limbach SL 1700 E 68 HP a t3400 rpm VW engine . The propeller is afeathering Hoffman with additional posi -tions for climb and cruise . The singl e600-6 tire and wheel with hydraulic-over -air shock gives very fine landing contro land is fully retractable . The fuselageand main wing spar are protected by tw osmall ski-runner type slats which preven tall damage when landing gear-up (we hav eproven this already) . The handling i sexcellent, also the 36 00 omni cockpit view .Takeoff and climb are at 500 ft/min an dthis with two people aboard at 1150-fee televation . (Note : we had our unit inColorado Springs at 7200 Ft . elev . Wenoted about 320 ftjmin climb at 40° F .The runway has some downhill slope andtakeoff roll was not measured .) The elec-tric starter produces instant inflightrestarts and with our 200 hours there ha snever been any problem hot or cold . TheRF-5B is a really delightful machine an dprobably one of the nicest and safest air -craft a club or private owner could own .It is, however, expensive to purchase com -pared to a regular sailplane . We feel itis not at all too complicated for a basi cschool trainer . Gear-up landings are no trecommended but ours have cost nothing butpride . (They occurred with engine off an dprop in horizontal position .) The gearwarning system is more than adequate an dworks independently from the throttle andthe airbrakes .

The airbrakes are very effective .Instruction from the back is very effec -tive and full control over the unit i spossible since all controls are duplicated .The folding wings of the RF-5B are an out -standing feature . The unit can be handledcompletely with one person on the groun dinside or outside close quarters .

. . .If there is anything we can do t ohelp you please let us know . . .You will hearmore from us . . .Thank you again for you rfine February issue .

Sincerely ,H . G . A . Buytendyk

11

May 23, 1973Dear Ed :

I suspect one reason that self-launche dsailplanes are not numerous is that fewpilots have seen them in operation, an dthat even fewer have flown one . Such i smy case .

I first saw one fly at Estrella, o nApril 17, this year . The pilot (I assumehe was Col . Barrett) simply wheeled hi sship out of the hanger, cranked it up, andleft . This may have been preceded by hour sof preparation, but "locals" told me th egentleman did this almost every day .

Very impressive . For the last 20years, soaring has always meant about fou rhours of panic on the ground for ever yhour in the air . Most older sailplanershave willingly paid the dues - trailering ,waiting for mysterious towplanes which neve rappear, crazy off-field landings, boringretrieves, etc .

I live 200 miles from the neares treliable towplane . Competition and badge sno longer interest me . A self-launche dsailplane is an obvious answer, but I doub tI will ever get to own one .

Purchase cost is a real bummer, bu tsoaring has never been cheap . I have neve rdared calculate the cost per hour for con -ventional soaring, but I suspect self-launching would be much cheaper, if every -thing is considered .

Getting hands on a self-launched shi pcan easily be done by inheriting a larg emess of money . Financing an approved-type ship is almost impossible ; who wil lput up the loot for an "x-rated" machine ?No one I know .

Almost any really-determined nut cansomehow get a well-used 1-26, or equivalent ,but I have seen very few self-launched ship sfor sale . Ten years from now, the situa-tion may be different ; I hope I am stillaround and flying .

Every "grass roots" level FAA inspecto rI have ever met has treated me well ; I cannot praise these men enough. But the bosses ,way up on the "policy" level, seem to em-body the worst features of the Gestapo ,the S .D., and Attila's Huns . No doubt theycan make the sum of restrictions on powere dsailplanes exceed the total on power and

sailplanes .The normal airport operator woul d

probably welcome more an Aero-Commander

fresh from Mexico with 1,000 bricks ofAcapulco Gold . Sailplanes don't use muchgas ; they are just useless clutter . Self-launchers don't even use towplane gas .

This "Jeremiad" is probably brough ton by age (geriatrics arise!) . Every momentspent actually soaring is worth more no wthan it used to be .

I remain an outsider on self-launching ,but I hope the various schemes fulfill thepromise they now seem to offer .

SincerelyAllison StoutBox 162Hurley, N.M . 8.8043

Dear Al :I know, I know . . .I know how you mus t

feel 200 miles from a towplane . Somethinglike a loyal crew wife feels on a dead-en ddirt road in an overheated car with fou rhungry thirsty quarreling children and aglider-trailer on her tail and a squawkin gunintelligible radio drowning out the soundsof a hot desert wind . Is home-building theanswer? It'll keep you busy for a fewyears during which a towplane might mov ecloser. How about winch or auto-tow? Mean -while keep an eye on Schreder's HP-17 .--Ed .

May 15, 1973Dear Ed :

Bennett's idea that the barograph wil lprove whether a starter went under the gat eis of course correct . Also consider howyou will feel after "winning" or even plac -ing high, to be told "Sorry old boy, yo udidn't quite get under the gate ." Sad .And slightly too late .

RegardsS . du Pont160 Long Meadow Rd .Fairfield, Ct . 0643 0

Dear Ed :Many thanks to you, George Uveges ,

and MOTORGLIDING for publishing so manyfine pictures of "N-SOAR" . It really madethe 4,000 mile round-trip worthwhile . Nowthat the weather here is nice, I am flyin gevery weekend and I am working to get m ySilver Badge down here in New Orleans . Ihave made the altitude here several times ,but without the barograph . Now I carryit at all times . We now have a commercia l

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and club sailplane operation here at Abit aSprings, 25 miles N . of Lakefront Airport ,so I am able to soar with other glider soften, seeking out thermals together .

Dick Schreder's article in the Marchissue was very exciting in that the nee dfor even smaller engines than the one Ihave may be very feasible in light of mor eefficient and lightweight sailplane designs .I was also pleased to read that he plans toretract the propeller (and/or engine? )perhaps similar to the SF-27M . In some200 flights and other hundreds of "demo "retracts, I have never had a problem withthe retract system, except one, when Ifailed to check it down and "locked" . Iwish the best of luck to Dick with his HP-17 .

I just tried a couple of new propeller smade for me by TM Development, Box 183 ,Darby, Pa. 19023, and they were fantastic .

The Hirth was overspeeding 300 rpm wit hthe present prop, and the new props by TM(of 120,000 tensile strength) limit themax . rpm to 5,000 as planned with a 10 0fpm or more increase in climb . At cruise ,(which I could not do without much banging -about and 4-cycling) the new prop puts asufficient load on the engine, yet is s oefficient the rpm minimum at full throttle -back is up 300 rpm . Fully throttled back ,she will still climb slightly previous t oa 100-fpm sink with the old prop .

I am working on a brand new Engine /reduction/prop combo and I will let yo uknow how it works out .

Good SoaringBill Mouton2113 Cleary Ave .Metairie, La . 7000 1

MOTOR GLIDER M-17 UNIVERSAL

NEW from Czechoslovakia is the M-1 7two-seater motor glider which had its firs tflight at Brno on October 17 last . JiriMatejcek, the designer of the Standar dClass Orlice, is in charge of the project .

The seating in the M-17 is arrange dside-by-side and there is a centrall ymounted Y-shaped control column . Thesingle spar ply-covered wings have a lin-ing of sandwich polyester foam ; it i sfitted with a T-tail and has a retractabl eunder-carriage .

The power unit used for the prototyp eis the 42hp Stamo MS 1500, and the pro -peller can be feathered for gliding flight .For further development and production ,however, it is intended to use the 65hpWalter-Mikron 3 engine . The report inDer Flieger, from which this extract ha sbeen taken, also mentions performanc efigures for the M-17 while towing a 15 msingle-seater VSO-10 (no details avail -able) ; the report does not state whethertows have in fact been carried out . Thedata given suggest that this really uni -versal aircraft would fall within our Red -hill definition of 1969 for self-launchinggliders . (The definition neither include snor excludes motor gliders capable o ftowing) .

42 hp 65 hpTechnical data Stamo Mikron

Span (m) 17 1 7Wing area(m2) 17 .5 17. 5All up weight (kg) 580 58 0Takeoff distance (m) 200 150Takeoff to clear 15m (m) 330 260Climb Rate (m/sec) 2 .5 4Maximum speed (km/h) 180 21 0Cruising speed (km/h) 150 200Ceiling (m) 5000 6000Range (km) *at 120km/h 450 500Fuel consumption ltr/ph 10 9

Calculated glider performance : Glideratio 95km/h over 28 :1 . Minimum sink a t80km/h below 0 .85m/sec . Landing speed65-70km/h .(Reprinted from June-July 197 3Sailplane & Gliding .)

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