Low & Slow Issue 23 1973

LOW & SLOW.-

#23

... the "fly yourself" magazine (large format start on i,s1i'~e 25 ) serving the world of self-soaring, skysurfing, hang gliding, kiting, and man-powered aircraft ...... and any manner of manned fu~/._/ess flight wherein the piloting crew and all device remain undetached launch .to landing. :··:,

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Dear Editor

The University of Liverpool

FROM THE DEPARTMENT OF MECHANICAL ENGINEERING P.O. 60~}47 Ll~RPOOL L69 38X

Eng lend

Thank you for sending around order forms for my book 'Man Powered Flight' with the last copy I received of 'Low If readers have any queries I would be pleased· and Slow•. to answer them.

Keep up the good work with this magazine, although I find it a bit confusing at times, not being familiar with the hang-gliding scene in the States, it provides the right atmosphere for creative thinking from which new ideas can spring both in hang-gliding and manpowered flight.·

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I.enclose a'..photograph of 'Liverpuffin' which commenced taxying trials·· before· Christmas.

Unfortunately a sudden gust (lSknots with as·- 8 knot 'steady' wind) turned it · over whilst: I was organising the necessary personnel.

This caused' some-· damage so it is back in the workshop till Easter when- .I. anticipate that the· weather will be kinder anyway.

Thi.s .also allows some modifications following feed back from the. t~xying,t;1:ials, the most important being that of making _it )l!O:te transportable (we have the 30ft. long trailer used · ·for t:he· Sc>'uthampton machine).

However, this incident c~osed 1971 M.P.F. scene in an appropriate way since the Weybridge aircraft·did the same earlier in the year, but flew 'in September, and Linnet IV was destroyed."

Here's hoping that 1972 is better.

At least this incident indicated that 'Liverpuffin' would take-off? and thoroughly proof tested the E.P.S. secondary structure of the wings, which passed the test with flying colours.

May I hope that groups in the Un-;ited States will attempt 'true' man-powered flight.

I hate to 'split hairs'·but I find the general reference to hang-gliding as man-powered flight in Low and Slow. as being inappropriate.

There is a world of difference between a simple hang-glider and say the Weybridge man-powered aircraft in terms of design, construction and control.

They estimate something like 10,000 man-hours of construction.time on that aircraft alone, although this is

at£

extreme example.

Sc may we get some sort

of order into low/slow flight activities.

Although a simple Rogallo hang glider and the Weybridge M.P.A are related, 1 fundamentally they are as different as an L /D ratio of 4: 1 Obviously one wants to make compared to 40: 1 can make them. the definition of man-powered flight as general as possible so how about 'that form of flight whereby a positive gain in · altitude can be achieved without atmospheric help by the expenditure of human energy along'.

This is obviously still very general and.would include simple man-powered aircraft or even gliders with.a man-powered take-off run provided that the aerodynamic design was sufficient to·a11ow take-off with some.excess speed in still air conditions.

However it would preclude hang gliders with. very low lift/drag ratios.

So why not simply accept that hanggliding and man-powered flight are two related but different aspects of Low-Slow flight.

From this you might actually be able to persuade groups in the Sta~es to have a go at manpowered flight.

We in Britain consider we are leaders in the field at the present time so come on U.S.A.J you can't allow this state-of-affairs to continue.

I enclose a report giving some ideas on simple M.P.A. that is to be published in full in the A.I.A.A. student journal.

However,.you might like to extract any details you want for 'Low and· Slow' readership and from it one would hope to get some creative feed-back of ideas.

How about the idea of an efficient saii wing with a flying wing cqnfiguration, swept~back for stability.

Monoplane of course?

K. Sherwin.

S-SA

President Message: Judgement is affected by the motives of our flying. Flying to meet someone's prescribed skill standard is a motivation that cloud's the beginner's judgement. The beginner will dci well to discover his or her own body, mind, environment, atmosphere, and flight system. The complexity of these variables makes it nearly criminal to urge movement newcomers to obtain prescribed skill-level badges. Rather, the leaders ought to urge fledglings to express how well the beginner is reviewing himself before attempting something beyond their known capabilities. At that point it is hoped that: we all extend to one another some time of sharing ideas.In that sharing we exchange praise and aid; recognition comes to bear and one's efforts receives social consolation. ' Only the self-soarer can define when he moves from Category 1 flying to the practice of Category 2 flying. No instructor or association wi 11 ever be able to define the transition; it must come from the aeronout himself. Al I competition flying, regardless of its apparent innocence, seriously ploys with judgement and therein reasonably demands of the self-soarer that he be a master Category 2 oeronout before entering any sort of competition.

In this light it is urged that all clubs throughout the world consider seriously any seeds of competition that may take root almost unknowingly.

The subject of this message concerns the potentials of physical injury to aeronouts, There is no intention to speak here to competiti6n of ideas, only to those acts that con immediately result in death should judgement be clouded, attention be diverted, memory be sluggish, or awareness be. du I.led. ~~~:if~····:.·.

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1904 hi!)h aspect ratio Rogallo flown in France.

All renewals ($6 or more) and correspondence to: S-SA

Box 1860, Santa Monica, CA 90406

Kremer prize, July, 1973, has been increased from $30,000 to $129,000 at the current exchange rate, reports member Grant Smith from Michigan (ref. see ad in the new format L&S 25). Many .new MPA projects ace being started with this new incentive. The MPA of MIT, MASS., a biplane, looks like a potential winner.

The NIT, CA., project has been changed and has gone into secrecy. A MP A is is intended to be moved on the ground by the pilot and moved in the air by the pilot --this is why we include MP A in self-soaring and why we do not include such craft as the Wright 1902 primary glider. There is so very much aircraft interest that your Self-Soar Association must stay close to the self-soar dream with as little compromise as possible. Should your interests carry you elsewhere, fine, but do not. give up your self-soar relationship. Keep dreaming and helping.

MAN

POWERED AIRCRAFT DEVELOPMENT

Dr. Keith Sherwin University of Liverpool Deportment of Mechanical Engineering This Teport is based on a lecture "The Development of Man Powered Flight as a Sporting Activity" presented by the author before the Royal Aeronautical Society on Fri<{ay, October 15, 1971.

Ten man-powered aircraft with wingspans of between 64 and 120 ft. have flown over the past decade. Experience gained with these indicate that at the present "state· of -the -art" it is impractical to construct afrcraft for a direct attempt at the Kremer Prize due to limitations of manpower, hanger facilities, and atmospheric conditions.

It is suggested that a more positive aim for manpowered flight would be its development as a sport. Practical machines of under 50 ft. wing span can be built, possibly by individuals within private workshops, that will fly short distances and could provide the basis for such an activity. Initially flights could be extended through the utilization of low - altitude up currents. Competitions would provide incentive for long term development that could ultimately result in the winning of the Kremer Prize.

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MAN POWERED FLIGHT AS A SPORTING ACTIVITY

Dynamometer test rig for evaluating candidates in the N.I. T.

MP A project. '

Photo by George Uvegef· I

Ir is now ten years since the first true man- powered flight cook place when. the Southampton Uni versicy machine covered a distance of 50 yards from cake· off. , That we should now be in a position to discuss practical manpowered aircraft suitable for sports flying is an indication of the many developments that have taken place Jince then. Ten aircraft of differing configurations ·and with wing spans ranging from 64 to 120 ft. have achieved ma~powered flights, see Table 1. ·

TABLE 1 Aircraft SUMP AC Puffin 1 Puffin II Linnet I Linnet II Linnet III Linnet IV Malliga Santa Meada OXl Weybridge

2 Span (ft.) Wing (ft. )

Empty Flying Wing Aspect Weight Weight Loading Ratio (lb.) (lb./ft.2) Country (lb.)

U.K. U.K. U.K.

0.90 0.81 0.78 0.80 0.80 0.72

15.6 17.9

111 119 113 122

269 267 290 230 225 232 237 239 245

0.91 0.85

Japan Japan Japan Japan Austria Japan

30.0

125

276

0.57

U.K.

80 84 93 73 73 83 79 64 73

300 330 390 288 280 325

2L3 21.4 22.0 18.5 19.0 21.2

262 290

120

480

[TI

128 118 140 105

99

None of these machines have complied with the requirements of rhe Kremer competitions that initially defined their performance requirements. There arc several reasons for this but the major one is tbe increase in power required for the climb. All the aircraft listed in Table 1 would need co fly at say 2- 3 ft. altitude for most of the course in order to cake advantage of the ground effect, then climb back co 10 ft. altitude required at che finishing point. Power for climbing can be related to the cruising power and the angle of climb O by the simple relationship :

t:CLtf118 = pcRu.ase

L 0

D

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57.3

so that with an L/D rntto of 50 · or over, as _achieved by che lai:ter aircraft, the climbing power would be approximately twice that for cruise with a I degree 'climbing angle.

In this respect che lacer 5,000 pounds Kremer competition in which flyers ,have to complete two "slalom" runs is in reality probably more difficult lhan the 10,000 Kremer competition which retained the initial figure ei_ght.

MAN POWERED AIRCRAFT DEVELOPMENT

It must not be inferred from the foregoing remarks that the Kremer competitions are an impossible dream, but there muse be further developments before they can be won, yec, che compecicio~s themselves do not provide the necessary encouragement for such developments.

The problem is chat all che aircraft have so far been designed for a direct attempt ac the competition where the crew are required to provide all the power for the flight, unaided by any of the atmosphere's help. In order to extend flights the aim has been to reduce power input, by increasing wing spans, so resulting in machines that are subject to the following restrictions.

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The planes can only be flown in .very calm conditions, either at dusk or early in the morning, so there is limiting flying experience. They can only be entrusted to expert pilots so the power available for propulsion is limited. Another drawback is that construction can only be attempted by large dedicated groups. ·(It is estimated that the Weybridge aircraft involved 10,000 man hours of construction time.) Such machines require that large workshop,. hanger, and flying field facilities be readily available.

The lasr two resrrictions obviously limit the number of such ai~craft that can be built and due to the present difficulties of the aircraft industry, future attempts at building aircrafr of the size of Weybridge of Toucan can nor be envisioned.

At the present time we have the Weybridge and Toucan machines with wing spans of 120 and 123 ft. respectively. They are designed co fly around the complete co.urse at an altitude of 10 fr. since the decrease in induced drag at lower altitudes is smaller. In the case of the Weybridge machine the power saved by reducing altitude fiorn IO to 3 Jc. is only 5%, ·so in theory these aircraft can zoom w IO ft. altitude from an increased .take· off speed and maintain altitude throughout the rem~nder of the course. However, in pea ctice these large aircraft require still air conditions in order to attempt flights and this will restrict the amount of flying that is necessary for the Kremer prizes.

Stemming from these arguments it is considered that designing and constructing manpowered aircraft solely for a direct attempt at the Kremer competitions is an impractical exercise at the present time. However, since there must be some pos itive aim in any endeavor, it is suggested that manpowered flight be developed as a sporting activity. This suggestion is based on the expected enthusiasm that would result from such an aim and also on the past history of gliding indicating that sporting competitions are a powerful incentive for improving the performance of the aircraft themselves. Therefore the change in direction of manpowered flight cowards a sport could eventually lead to winning of the Kremer prizes.

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TECHNICAL DEVELOPMENTS The performance of manpowered aircraft is a function of the aircraft weight co power ratio (w/p). le is possible to re- state this ratio in terms of performance parameters in order to assess the relevant design criteria:

wl .h_ ll -P a V

, o·

c,_

(c

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..!:L c~) c '"lo A L "L

cc ___!.'----::-7--,,Cn

_!!__ (.,_ lj-&.

-t-

K

(

'I~

A

L where Co is the overall profile· drag coefficient, C the life coefficient, K th~ induce~ drag factor due to ground effect and A islaie aspect ratio. Obviously to' improve the weight to power ratio the term needs i

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fc .

1r-

co: decrease.

I JI, (~ ' .. ,1 ) · , Plots of the terml'" P./(,_ • + I (4 ). against lift coefficients are pre semed in Figure l for Cv 0 of 0.015 and K/,rA equal to 0.01, 0.015, and O.b2 respectively. An overall pcofile drag coefflcient Co 0 = 0.015 is entirely

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realistic being approximately equal to that for SUMP AC , whilstK/'.'.: A. would be equivalent to rectangular wings working within the ground effec(r?fgion with aspect ratios of 20, 13 1/3, and IO respectively. ' The most notable feat11re of figure 1 is the improvemenc in performance that c~n be gained by increasing CL within the range of 1.2. For larger values of CL the improvements are very much smaller and with low aspect ra~ios are almost negligible. i The most important rechnical development of the pasr decade has been in the improvement of aerofoil sections for use at the low Reynolds appropriate to man pciwered flight. It is now possible co base che design of manpowered aircraft on I the certain achievement of a CL of approximately 1.2 with a corresponding aerofdil profile drag coefficient, CD, no greater than 0.010. SUMPAC utilized the NACA 65 - 818 aerofoil section with a design CL .8'5 and an assumed pro file drag coefficient Co 0.0083, which indicates the improvements char have taken place.

Puffin II incorporated the Wortmann FX- 63137 aerofoil section, sluwn 111 Figure 2, and was designed with a CL=l.15 and Cl) =0.0092. Experimental lifrdrng curves for the FX-63137 aerofoil section and upon which the design of Puffin II was based, are shown in Figure 3. The validity of these results has been partly confirmed by the good agreement between the actual performanc~ characteristics of Puffin II and chose estimated during its design. le is con sldered chat the accuracy of wind runnel results depends on the turbulence level I 8

of the wind runnel itself. Too high a turbulence level results in a low profile. drag coefficient but the Wortmann wind tunnel having a low turbulence level can be assumed to provide realistic drag results. The confidence the designer can now place on the use of the Wonmann FX-63137 section makesit possible to consider the. design of re~atively compact manpowered airer a£,. su1table for sports Uying. Little is to be gained by waiting for further developments in aerofoil sections since, _referring back to Figure I, any improvement in CL will result in very little improvement in the aircraft performance.

The main disadvantage with the FX-63137 is that with·a thickness chord ratio of only 13. 7% the depth of the main spar is restricted so that the necessary bending moment of such a spat requires larger, and therefore heavier, members than would be the case for a deeper aerofoil section. Later developments by Dr. Wortmann have resulted in the FX~6Sl60 section shown in Figure 2. No experimental data is available but this section is incorporated in the Weybridge aircraft, Figure 4 shown. This shows the estimated lift-drag curve upon which their design is based and flight trials with the aircraft indicate the data to be realistic, at lease near the design C.Iof 1.0.

The Malliga aircraft employs an aerofoil section created by its designer on the basis of "looking right." No performance data is available but its success can be judged from success of the aircraft which )1as already flown forcy times.

An estimated shape of this profile is shown in Figure 2 and the working CL would appear to be in the range 0.8- 0.9. The section would appear to require early transition to a turbulent boundary layer since Herr Malliga is certain chat an uncovered expanded polystyrene leading edge gave a better performance than a cov.ered one.

Stemming from the success of the Malliga aircraft one begins to doubt chat aerofoil sections are quite so critical at low Reynolds numbers as designers liad previously feared.

With regard to other aircraft performance considerations, experience with actual ~anpowered aircraft has indee.d indicated that fuselage design is not critical since the parasite drag is only a small part of the total aircraft drag. Care was exercised with many of the manpowered aircraft to minimize fu~alage drag by encasing the pilot in suitably streamlined fully enclosed cockpits. However, the Malliga aircraft has the pilot pedalling in a reclining position within an open cockpit with a streamlined fairing behind his head.

Open cockpits, although having some drag penalty, allow: the pilot co pedal in more comfort and so in practice may result in an improved performance.

Pedalling has proved to be the most suitable form of power input with either a choice of a cycling position or a reclining position. Earlier it was considered .that take -offs could only be achieved using manpower alone by having a driven undercarriage. This has been disproved by the Linnet and Ma!liga aircrafts that have rake-off distances comparable with the ocher aircraft but utilize propellor thrust alone, resulting in a simpler drive mechanicsm.

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EARLY TYPE GLIDER

The Passage of Time Improves Our Products 9

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OFF-ROAD USE OF THE INFERNAL COMBUSTION ENGINE

Ted Organ, May, 1972

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SAN GABRIEL ACADEMY 8th grade: The students completed tests on a well-made biplane man-powered craft. Wingspan:36 feet. Pilot Dave Zavas peddled. The right wing buckled under stress of initial trials. Class in· structor Ted Bauer was thanked for his guidance via the class naming ~he ship 1~;i:~ately • 'Bauer Bird'.

'111 the future we might look back and see

that the non-self-soar compromise of using off-road vehicles for high frequency repeated flights is the cause of much animosity from conservationists. It is recommended that pilots develop wings that require less and less use of the car.

We see it as a big loss for the movement chad Licher from Soaring Society has , actively encouraged chat cars be brought to aid the progress of repetitive flights at his coming meet. The first major Otto meet primarily promoted by Self-Soar Assn did not have any such vehicles. We now are getting close to wings that can soar up the slope in mild li~. But the giant commercial push behind the standard conical Rogallo brings us a movement that begs for the use of engines to aid repeated flights. Especially, the extra vehicle gives disquiet when the slope is of moderate height.

At normally quiet sites of moderate height, there is a kind of violence in seeking a second flight by the rush use of a car or truck. Not only does the act not give one rest from the car-world, but it is occurring that plants are being hurt by this. Use of existing roads is not so violent to our environment. But, surely, land owners will f~own on our sport if we come off with the image of using tow vehicles and back-up-hill vehides. We believe that there is to remain a pure movement that aims not to depend on the car for the flight repetition. Let's all be careful to carry the image we really want.

(Feb. Aerospace) Dec. 23,1972, made

its first flights at Radlett Airfield, Herts,

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England. Built by Hertsforshire Pedal Aeronaucs,, the longest of 3 flights that ~ day was 68 yards and max. alt. of 2 fr.

Bryan Bowan piloted and Derek May was was considered crew.

Span: 123 ft, begun in 1967, completed June I6th,1972. Length: 17 ft., empty wt.: e 210 lbs. Gross wt.: S20 lb. Balsa is used extensively; spruce and plywood also employed for the spars and some of the bracing. The wing leading edges and some sheeting over the front areas of the wing are of expanded polystyrene and the aircraft is covered with 'Melinex plastic' film.· As the turning moments produced by a rudder would be small, due to the short fuselage and high aspect ratio wing, control· is exercised through slot-lip ailerons.

An all -moving tailplane provides pitch control.

Feb. 8, 1973, Dr.Sherwin wrote and told us 'Toucan flew Dec. 23, 3 flights, one just over 60 yds.

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N7487S Not flown, but damaged, James Mc Avoy in 1963 N as pictured in Aug/Sep '63 Air Progress. Does anyone know if his idea has been followed by anyone?

Other pies of same can be found in the May, 1963, Popular Science.

Time Magazine August 17,1962, article on MPA. REFERENCES Scientific American: 1S0:2S8 May '34 148:274-6 May '33 148: 104 Feb. '33

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Popular Mechanics p. S86, Oct. '23: seven-winged affair was supposed to have flown for seven yards by foot power.

KANSA CITY Dave Jack son , student of K. C. Art Institute never became airborne in his bicycle powered.MP A-glider. He lives on 4014 Baltimore, K.C.

On the structural side weight constitutes the major part ot the total aircraft weight so that appreciable savings in airframe weight ~e neces • sary in order to make a worthwhile sav ~ ing in the power requirements. So that from the sporting aircraft aspect it is the robustness of the structure that is important. Whether it can be moved with ease, ·whether it will need repair after each flight, and whether it will stand a certain amount of mishandling, both on the ground and in the air are questions that must be ~swered. In this respect two interesting develop· ments over the past decad~ have been the Czerwinski laced joint for chin metal tubes and the use of expanded polystyrene for wing secondary struc • tures. The Malliga aircraft utilizesaluminum tube primary structure of 4" diameter for the wing and 1" thick expanded polystyrene for the leading edge covering. This provides a robust structure with minimum con· struction time.

Thin aluminum tubes jointed .by fibre glass tape and then coated with epoxy resin are used for the whole of the wing primary structure on the Weybridge machine. This has been loaded stacicaily and measured de· flections are in good agreement with· the estimated ones.

With regard to control of man• powered aircraft the position is no clearer than it was ten years ago.

Most of the aircraft that have flown employ directional, longitudinal, and later~! control- surfaces. SUMP AC incorporated an all - flying· tail plane that was difficult to control, so that the conventional elevator used for Puffin and Linnet could ap.pE'ar .t;o be a more suitable choice. With th.e increased wing span of Puffin II the rudder became ineffective· due to the variation of induced drag on each wing tip during a tum, Fully con· trolled turns could only be executed by the provision of wing ·tip. ~ag rudders in order to increase the drag of the lower wing tip.

Directional control of the Toucan is by means of wing tip drag rud• ders alone.

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WOMAN POWERED AIRCRAFT: WP A ?

The slow down of the Northrop MP A has encouraged Rose Marie Lieber to stay in trim for a WP A attempt to win the Kremer $129,000. She takes ·regular training ses· sions on the dynamometer connected bicy<::le. Her performance has shown that she could indeed maintain output to win.

Photo: Uveges

' \ I I I ·1

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Several systems for lateral control have been built. Con_ventional ailerons were used on SUMP AC and Puffin. Transverse wing tip ailerons are used on the .Malliga aircraft. Finally the Weybridge aircraft incorporates a mechanism.for varying the incidence of each wing half, a system that was originally used on the pre - war Haessler- Villinger machine. It is rumoured that Linnet. III and IV were built without ailerons, but had the dihedral angle increased to "6% to maintain lateral stability.

Certainly the elimination of any form of lateral controls would greatly simplify the · pilots task while also simplifying the wing construction.

'FHE FUTURE OF MANPO\VERED FUG/ff To design and build manpowered aircraft solely to make a direct attempt at the Kremer competitions is considered to be impractical at the present time. To continue with this as the only aim of manpowered flight would limit developments since the machines required for such attempts require extensive facilities and dedicated group who are prepared to spend several years on the construction. On the otherhand, to build more practical machines simply to prove the feasibility of manpowered flight is unnecessary following the flights over the past decade .. For any activity to develop there must be a positive aim and it is suggested that the only future for manpowered flight lies in its development as a sporting activity where competitions could provide the incentive for human interest and the improvement in designs.

From the design point of view the initial requirements for such a sporting activity are that the aircraft be simple and capable of being constructed by individuals or by small groups having limited workshop facilities. Such a craft should be easily transported and rapidly assembled for flight, while being able to sustain winds of 10 knots at least. Finally, it should be durable and strong enough to withstand some mishandling that would be inevitable during transportation and pilot training.

All these requirements lead to the need for manpowered aircraft of minimum wing span comp at able with the necessary low power input. It is now feasible to consider such aircraft due to the avail ability of suitable aerofoil sections with good CL values with the low drag range. Figure 5 shows a fam_i_ly of curves for manpowere_d aircraft

13

The 1973 Central California Self-Soar Meet led by Dave Kilbourne, Larry Maurro, Herman Rice, and Kent Trei:nble, had two special non-self-soar intrusions: one with a gasoline back-pack engine and the other, shown above, wherein husband and wife powered ( ?HWP A ? ) their own take-off, but could not decide who was pilot, passenger, or c~pilot. In this special "first" -a marital team flight-; a legitimate self soar system might have happened. However, Kilbourne points out tl:!~t the "two in one flesh" should not encourage non-couples to coupl!;! iii. the air because of the high probability of one ending as a pass·enger rather than as an equal partner (thus non-self-soar).

The English MP A 'Toucan' has 'two' who 'can' input power for flight. Control is the main responsibility of one of. the pilots.

The U.S.A., F.A.A. has strict regulations about carrying passengers. Kiibourne rec·~mmends that our ·movement _concentrate on reaching the dream of individual flight.

of different wing spans. The plot is of minimum pilot input pow er against wing height and is based on the use of the FX63137 aerofoil section workin,g at a design C'- of l.15. It has been assumed that the wing plan form is rectangular, the fusalage has the same parasite drag as the SUMP AC fusalage and that the weight is related to the wing span by the simple formula: W(lb.):o 190 + wing span{ft.), i.e.,.a wing span of 50 ft. would result in an aircraft weight of 240 lb.

It is therefore possible to consider a manpowered aircraft of 50 ft. span that would require a power input of 0.48 h.p. when flying with a wing height of 10 ft. above the ground. Such an aircraft would comply more closely with the requirements of a sporting machine than any of the machines that have flown. Although probably not ideal, the construction of machines of this size would allow the initial development of manpowered flight as a sporting activity and could provide the knowledge for future design improvements.

During take-off the power requirement wo_uld be less than 0.48 h.p. 'due to a decrease in the induced drag so rhat'an average fit man whose weight was not greater than 150 lbs. could be sure of at least short flights of say, 50 • 100 yards. Petfor •

14

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mance could be extended by the use of athletes as pilots or by utilizing low altitude convection up- currents. The former would be the obvious requirement for competition at national level and would be practicable since such a machine would be easier to control than any of the manpowered aircraft that have flown.

The utilization of up - currents would be the most preferable method of increasing performance since it would allow a much wider range of pilots to participate in sporting manpowered flight. Knowledge regarding very low altitude up- currents is limited but certainly there is evidence of useful lift being obtained above runways on warm sunny days. Rising air with a vertical movement of I ft./sec. would be adequate for manpowered aircraft and theoretically it is possible to get this velocity at IO ft. above a runway with only two degrees temperature difference between the runway and the surrounding grass. However, up-currents can only be maintained by downward flows in adjacent regions so that a great deal has to be learnt before extended rtips become reality, and this knowledge can only be gained by actual flights witl:µn these conditions.

MANPOWERED AIRCRAFT, FOR SPORTS FLYING All designers tend to have their own ideas so there is a danger in submitting a proposed design in that it may inhibit the creative pro,cess of others. With this in mind it is still considered to be preferable to present some ideas regarding manpowered aircraft design since it may ensute success than if no guidance was given.

A manpowered aircraft suitable for sports flying should be compact and simple to construct and Figure 6 shows a suggested configutation for.a simple sporting

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?

.

Proposed man-powered

aircraft configur~tion for spoi:ts flying.

Please tell us if you have received the

FIGURE 6.

Low & Slow 25 on a self-soar trust.

15

manpowered ::,ircraft with a 50 fr. wing span. The "pod and boom" type of fusalage facilitates rapid construction with the pod housing the pilot. The pilot- peddler is in a reclining position in an open cockpit. A screen in front of the pilot can house a twisted belt drive from the pedals co the propellor shaft. Drive to the undercarriage is unnecessary and the drive shaft would go over the pilot to the rear mounted propellor.

Wing construction could be similiar to that for the Malliga wing having a " diameter aluminum tube primary structure and expanded polystyrene secondary structure. The low wing configuration would minimize induced drag due to the effect of the ground, while the 6 degree dihedral angle would ensure good lateral stability so that lateral controls could be eliminated. During the take-off when the aircraft would be most suscepcable to gusts, stability could be maintained by help from the ground crew running alongside the aircraft.

Rudder and elevator controls would be necessary and the control wires for these could be housed within the boom. The pilot would exercise control by means of a conventional floor mounted stick with fore and aft movement for the elevator and side - to-side movement for the rudder.

Assuming an aircraft empty weight of 85 lbs., a pilot weight of 145 lbs., and the use of the Wortmann FX- 63137 aerofoil section at a working CL= 1.2, the power required for cruising at a 3 ft. altitude would be 0.52 h.p. at a forward speed of 29 ft./ sec. These values are entirely realistic judged from previous manpowered take - off and aircraft experience and indicates ·chat such a machine should be capable of flights of 100 yards, or more, from a manpowered take - off without any external help. Such flights would be suitable to initiate sports flying, while a machine of chis size and weight should withstand the handling it receive in this type of activity. · Figur.es ( ~ath-graphs) 1 to 5 could riot be put. in chis issue. Should your interest require these, then either wait for Dr. Sherwin's coming second book or References send $1 and get a photo copy of these graphs. Editor.

1.

2.

3.

4.

5.

6.

Sherwin, K., "Man Powered Flight," published by M.A.P., 1971 Spillman, J.J., "Design Philosophy of Man Powered Aircraft," J./fof Ae. S., Vol. 66, November, 1962, pp. 699 - 706 Conditions for the Kremer Competition, published by R.Ae.S., 1967 Pressnell, M. S., "Toucan Progress Report," J. of R.Ae.S. Shenstone, B. S., "Vncoventional Flight," J. of R.Ae.S., Vol. 72, August, 1968, pp. 655-660 Czerwinski, W., "Structural Trends in the Development of Man Powered Aircraft," ]. of R.Ae.S., Vol. 71, January, 1967, pp. 9-13 16

Joy Faust,7, has so helped in the attic production of early Low & Slow booklets.

Thank you, Joy. Membership renewal is due now for most of you. Please cell us if you received L&S 25 of the new large format,on crust.

We have now mailed 25,26, and have 27 and 28 ready for mail for you. The response on the new size and pictures and plans is very good. We are even catching up co dace so chat we will have 12 large issues mailed in 1973.

Retain your dream one day we all will be able co truly self-soar.

Pho10 hy WAA 0£ Self-Soor Associotio.o·~ TVTkcy Fly.

Tom Vulenrine·s biplon~ shown in Hight,

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I AM WHO FLIES Grant Smith here offers two types of certificate wordings . .we· encourage anyone to offer similar items. Those who have signed for membership will soon receive a special card made up from the best phrases possible. We are also on the hunt for the best expressions for a self-soar declaration certificate.

As pilot of this craft, I have inspected its structure, ' observed it~ 9peration, and determined that I may safely ope~ate said craft. I hereby waive all liability rights. against the owners of the equipment or flying area and hold. myself solely responsible for injury or damage to myself or other persons or property while in co.mmand of this ship.

Signed Date - - - - - - . Witnessed b y - , - - - , - - - - - - - - - - - - - -

· On this day of 197 _ _ , - - - - - - - . ·did successfully break all physical bonds with Earth, take off arid sustain controlled solo}light utilizing his · own physical· po~er without aid n~r assistance from others. · is hereby certified as So~lo .pilot and has demonstrated his. skill and control .in a~'-,,------,------..,.,..------------

Signed: - - - - - - - - - - - D a t e : - - , - - - Witnessed by: - - - - - - - - - - - - - - - - Signed: _ _ _ _ _ _ _ _ _ _ Date: _ _ __ Witnessed b y : - - - - - - - - - - - - - - - -

19

STEVE SLAUGHTER captured in the camera eye of George Uveges while Steve makes ready for winning the Kremer $129,000 ••. makes a picture quite unlike the scenic hillside hang gliding ones wc arc accustomed seeing. Maybe the lure is enough to have him be inside.

84ci cover photographer: George Uveges