Planeurs moches

[Stéphane]

Citation

vincent jouvet

 

• a écrit dans un autre sujet : 

 

Tiens, il n'y a jamais eu de sujet sur les planeurs moches ?

Pas mal pour l'hiver...

Alors, voici un cas assez intéressant pour commencer ce sujet: 

Ce planeur sans nom (mais surnommé entre autres "unidentified falling object" a bel et bien volé ! Voir un article dans "Soaring" de juin 1967.

Citation

ADVENTURES ON AN AERIAL SURFBOARD

PHIL LAMSON

 

 

There was a time when the most detestable thought to cross my mind was the possibility of becoming a glider pilot. This was in 1944 when raids were being made into the ranks of fledgling fighter pilots to supply crews for the troop-carrying gliders that would invade France on D-day. Having escaped this involuntary assignment, my next association with gliders grew out of an admiration for the various large birds that can often be seen soaring up the slopes of the Sierras. While trudging up a trail under a 50-lb. pack, I would dream of my reincarnation as a bald (this part of the dream has arrived) eagle. Being equipped with a light brain, but lacking feathers and hollow bones, I concluded that I could emulate the birds only by assembling some sort of artificial structure.

The practical result of this philosophizing is a very small prone-position glider. People who look at my unorthodox creation often ask, "Why do you fly that thing?" I could borrow a phrase from a mountain climber and reply profoundly, "Because it is there." However, since it hasn't been "there" for very long the answer is more involved.

First of all, glider pilots are frequently asked why they prefer to fly without an engine. We often reply by drawing a parallel between boats and aircraft. Whether it be on the sea or in the air, sailing we say, is more esthetically pleasing and more challenging than being dragged along by a thundering package of canned horsepower.

Why the prone position? Before I tried it myself, I had heard of several other prone gliders. Horten made a series of prone flying-wing gliders in Germany before WW II and in Argentina after the war. In the late 1940's Dr. August Raspet designed a (28-ft. span) all-wing prone glider which was built by Franklin Farrar at Vanderbilt University. Farrar invited me to lie down in the mock-up which I found quite comfortable. During the early flights, I understand that the removable tail cone had a habit of removing itself on take-off, leaving the pilot's legs dangling. This flustered the pilot because of both embarrassment and abrasions. Those Nashville flyers must be pansies if every minor operational difficulty flusters them.

Having now flown prone in my glider for about 70 hours (in 112 flights) I have nothing but praise for this position. It is a fantastic feeling and an enjoyable one. Simply gliding along in a straight line becomes an extraordinary experience because of the unexcelled view of the landscape below. It’s almost hypnotic — as spellbinding as the luminous dial becomes to the variometer watcher. If you are a surfer you can get an inkling of what it is like by lying on a surfboard that has a transparent nose. You will not be bored if there are no waves to ride because you will be captivated by the fascinating view beneath you. Anyone trying to convince me that I "should fly sitting up” would have as much luck as they would have in convincing a sky diver that he should free-fall in a sitting position. I will concede that prone flying might make map reading difficult on a long cross-country flight, but who makes long flights in a 20-ft. span glider?

Why the small size? Back to our boat analogy. Many sailors feel that sailing a small boat is more fun than sailing a large one. True, the small boat can’t beat the large ones to Honolulu but its quicker response and its ability to react to a shift in the sailor's weight make it a delight to sail. Response and reaction to weight shift increase another order of magnitude when the sailor jumps off his small boat onto a surfboard. The relationship between man and machine becomes rapidly more intimate as the size of the machine approaches that of the man. Now suppose we continue to reduce the size of the machine to the point at which the surfboard is of zero size and the rider becomes a bodysurfer. Similarly in the air, we can imagine reducing the size of a glider indefinitely. When the glider reaches zero size the pilot becomes a sky diver. But just as the surfboard rider has more freedom of motion than the bodysurfer, the pilot of a small glider has more freedom than the sky diver. Thus, if we are seeking the exhilaration of free motion, it would appear that we should look for an optimum rather than a minimum size.

My attempt at finding this optimum consists of a fuselage of surfboard length (about 10 feet) and a wing of adequate area (60 sq. ft.?) to allow reasonable (60 m.p.h.) take-off and landing speed. The center of gravity of my body is approximately at the center of gravity of the glider, so that when I perform a wing-over, for example, I can feel my feet still going up as my head starts down. Some other maneuvers which also provide unique sensations are loops, barrel rolls and spins. I tried a loop without ever having done one in any other kind if glider and was therefore not aware of the fact that to make it over the top, one must pull several G's at the bottom. As I gathered speed, I had notions of casually flying around a vertical circle, nonchalantly polishing my nails during the loop, I happened to glance at the airspeed. There wasn't any. The prone position had now become a standing position, so I just stood there admiring the view and waiting for something to happen. My patience was I rewarded. Coming down tail first, the glider tipped into an inverted attitude from which I did the second half of a loop.

Barrel rolls are really fun. A complete roll takes something less than two seconds. From the ground these rolls appear to be snap-rolls but my conservative nature has kept me from trying a snap-roll (i.e. I haven't thought of it while in the air).

Spins are steep, tight and wild. I entered one accidentally while unwinding from a barrel roll. To stop the rolling I suddenly (it has to be sudden or you've done another roll in the delay time) applied full opposite aileron. The glider whipped over the top and into a very steep spin which I think was inverted but can't be sure, as I was hanging head down in my shoulder harness. I can remember the Joshua trees whirling around under me. It was like peering into a giant washing machine (or peering out of one).

Having never spun in a head-down attitude, the situation was confusing. My recovery technique consisted of a mélange of control combinations. The first thing I tried included opposite aileron, but this was like taking a poorly aimed swat at any angry hornet. Things got angrier. Eventually I began fooling with the rudder while holding neutral stick. The rotation slowed and finally stopped, but then immediately resumed. Over the intercom I alerted the flight crew. The tail gunner suggested a committee be appointed to look into emergency bail-out procedure. But at that moment I pushed (or pulled) something with my hand (or foot) and the ground stopped turning. Since this has been my total spinning experience in this ship, I am unable to say whether it has poor recovery characteristics or whether the trouble was wholly pilot ignorance. Certainly I'll not again antagonize a spin with opposite aileron. (Coincidentally this experience occurred on the same day that Dick Johnson had spin trouble.)

Even routine landings are a thrill in this glider. Although exciting, landing is really quite easy because the pilot's eye level at touch-down is so close to ground level that correct flare-out is simple to do. The flaps are fairly effective, but I can't hold full flaps all the way to the ground. There is not enough elevator moment to allow flare-out with more than 30 or 40 degrees of flap. My first full-flap landing was a surprise. I considered making a second landing pattern from the summit of my bounce.

At any airfield there is never a shortage of armchair designers. Before I poke fun at any of them, I hasten to say that now and then I've been given an extremely helpful suggestion (e.g., "Now that you are set up, why is there a main spar pin still in your tool box?") so I am always a willing listener. Most of these consultants fit into a few well-defined categories. For example, there is the Grandfather-Would-Have-Done-It-This-Way category. They come up with ideas like: "It wouldn't take too much altering to fix your glider so that you could sit up in it." "If you would extend the fuselage a few more feet it would look a lot more like a regular glider."

The Repent! — The-End-Is-Near group informs me: "One off-field landing and you're dead," "You could never get out of that death trap in the air," "In that headfirst position, what happens if you hit a brick wall at 80 m.p.h.?"

The Alice-In-Wonderland category is more enlightened: "How about equipping your glider for in-flight movies?" or "Wouldn't it be nice to fix up the interior like a medieval castle, with banquet rooms on the main deck and a damp dungeon or two below?" or "Why not paint dozens of windows on the sides of the fuselage, park on the ramp at the L.A. International and wait for a stewardess to come aboard?"

That I didn't name the glider, left me wide open to the We've-Got-To-Give-It-A-Name group. Some sample names: The A-bomb, The M-balm, Marsh Gas West, The Super-Scenic Transport.

 

Some Design Details and Flight Tests

It is very easy for the home builder with no previous glider design experience to be occasionally careless about design details. Usually, errors will be caught by the FAA inspector but sometimes even serious ones can go unnoticed simply because there are so many individual parts in a glider. For example, I originally attached rudder cables not with standard sleeves and a swaging tool but by hammering on sleeves cut from copper tubing. During a taxi test one of these cable terminals failed. Had this happened in the air at low altitude and in particular in a spin the result could have been a nasty bump on the head. My original landing gear is another example of flimsy design. The wheel didn't always go in the same direction as the glider.

Taxi tests proved the vertical tail to be too small for directional control. First, a larger rudder was added. The new rudder extended a foot or so above the vertical fin. The first aerotow (January 10, 1965) showed that the part of the rudder which is above the fin stalled long before full deflection was reached. This was a harrowing experience. I found myself in a steep sideslip over El Mirage Dry Lake and the glider wanted to stay in that condition. I recovered in time to land but just as I touched down a yellow blur flashed past my nose. It was a dragster making a speed run. The tow pilot had been watching the car and me racing toward the same spot and from the air it looked as though it would be a tie. I went home and increased the size of the vertical fin.

The next test flight also had some unexpected moments. I had sanded the wings just prior to the flight, unaware that this could do anything but benefit the flying characteristics. Feeling peculiar on tow, I got lots of altitude before release. I released, slowed down and then a funny thing happened. Pulling back on the stick made the nose go down! Puzzled, I fumbled around for my booklet, "Flying, Self-Taught" and turned to page one. A little diagram illustrated lesson: "Stick back = nose up." So again I brought the stick back, again the nose went down. I pushed the stick forward, the nose came up. I threw the booklet over the side. On my descent I learned to fly a new way, being careful not to bank more than a needle's width.

Later, on the ground, I diagnosed the ailment as a laminar separation bubble at the wing leading edge. The lower the speed, the higher the angle of attack and the larger the bubble. The increasing bubble size meant a rearward shifting of the center of pressure making the glider nose-heavy. An obvious remedy was leading edge roughness, so I glued sand to the leading edge. It worked, no more control reversal! Since then, I've been able to eliminate the sand (with no ill effects) by reworking the leading edge contour. Cleaning up the leading edge also got rid of tail buffet which had occurred in tight turns. Apparently my airfoil section (NACA 8-H-12) is usually sensitive to changes in pressure distribution near the leading edge. (Have read that the NACA also had trouble with it and did not use it beyond tunnel tests?) Even now this sensitivity shows up in an adverse way. In smooth air my minimum sink is about half that in turbulent air.

 

Wing Extensions

How much soaring can one do in a glider of AR = 6.5 and wing loading 7.5 lbs./sq.ft.? The answer, of course, is very little. On one exceptional day I was able to climb at 1100 f.p.m. for four minutes; another day I remained aloft for more than an hour. But on a typical flight, the time spent in the air after release was about equal to the time on tow. So in order to stay up longer I built wing extensions which increased the span from 20 to 30 feet, construction is similar to that used in surfboards. Polyurethane foam was poured over an aluminum frame, then sanded down to the aluminum ribs and fiber-glassed.

I've now flown about ten hours with the extended wing. Considering the weak thermal conditions, the results have been quite satisfying. (An ear operation in May kept me grounded during the summer of 1966). Measuring L/D max on two different days has given two different values, 25 and 21 (at 70 m.p.h. TAS). One explanation is that the high value may have been obtained in a rising air mass. Another theory is that the low value was obtained on a very humid day and humidity may affect L/D. I favor the second explanation, but only further flight tests can illuminate this discrepancy.

I would like to obtain a small jet engine for self-launch. Several companies have shown an interest in such a device but would like to be assured of some money first. Would any of you millionaires out there in the audience like to get involved in this?

 

SPECIFICATIONS

                                                                       20-ft. span                    30-ft. span

Wingspan (ft.)                                                20                                  30

Wing area (sq.ft.)                                           60                                  75

Length (ft.)                                                     10.5                               10.5

Empty weight (lbs.)                                        —                                  270

Wing loading (Ibs./sq.ft.)                                7.5                                 6.5

Stall speed with flaps (m.p.h.)                       53                                  44

Measured L/D @ 70 m.p.h.                           15.5                               21/25

NOTES: Construction of the inner wing is of spruce and fir plywood; the 1.5 X 7.5-ft. extensions are of foam and fiberglass. Fuselage is of molded fiberglass. The prototype first flew on June 5, 1964; the modified version, with wing extensions, on Sept. 30, 1966.

 

Pour ceux qui ont besoin d'une traduction, je suggérerais l'emploi de DeepL... 

[Pierre]

Allez, je me lance avec quelques modèles américains :

- Duster BJ-1B (http://www.fiddlersgreen.net/models/aircraft/Duster-Sailplane.html)

- Woodstock

 

- HP 14 Schreder Club

[Stéphane]

Trop élégants encore ! Quid du Javelot ?

 

[Stéphane]

Ou le Doppelraab ?

[CPT]

Le 18/10/2023 à 15:27, Stéphane a dit :

Trop élégants encore ! Quid du Javelot ?

 

Le WA 21 n'était pas mieux et l'aile moins souple !

[Etienne]

Le Wa21 a son esthétique... a lui! Mais c'est très agréable aux commandes Par contre les AF son inutiles ! Si tu veux descendre il suffit d'accélérer au delà de 95km/h. Le taux de chute devient vite astronomique

[vincent jouvet]

Bonsoir,

celui relevé dans un autre sujet fait parti des "choses" que je considère "moches"

Merci à "CPT" pour le partage : http://bleu-ciel-editions.over-blog.com/pages/Piloter_couche_une_solution_pour_aviateurs_fatigues-4547909.html

[vincent jouvet]

Et voilà mon outsider que je trouve particulièrement gratiné

En plus, il est en vente sur https://www.flugzeugmarkt.de/segelflugzeug-kaufen/rubik/r-26su-gb-gebraucht-kaufen/2394.html

par contre, son papa est très connu ! https://en.wikipedia.org/wiki/Rubik_R-26_Góbé

 

[Bre901]

Citation

par contre, son papa est très connu !

C'est surtout son frère qui est universellement connu

[Stéphane]

Celui-ci n'est pas mal non plus. Il y en a eu quelques-uns importés en Belgique, e.a. à Courtrai et à Saint-Hubert.

Biplace Z-03A Ifjusag (Hongrie)

Pour une raison ou pour une autre, le lien ci-dessous ne fonctionne pas pour insérer une image plus nette :

http://gliders-fega.freeweb.hu/HA-5176.jpg