Readers Comment On ...
LANDING GEARS HAVING NO SHOCK ABSORBERS ome months ago we invited readers to comment on the practicability of making small airplanes easier and Scheaper to build through omitting landing gear shock absorbers. By omitting them it is obviously possible to save weight, machine work, and hinged landing gear attachments, as well as material cost and some drag. The question was, how well do such gears work out in practice and what points should one take into consideration in trying to decide for or against an absorberless gear? Quite a few useful comments resulted, and from them one should be able to make a wise choice. "The planes I have had experience with that did not have shock absorbers worked fine. The gear structures did not seem to be any heavier than others having shock absorbers and I never encountered structural failure. Landing was a little more "solid" but certainly not difficult for students."—C. W. Lasher "When the first Aeronca C-2's came out they had a simple straight-axle landing gear that was lashed to the lower longerons with shock cord. Its shortcoming was that it was too narrow for ground stability what with that long, high wing, so they switched to an absorberless tripod gear of wider tread, using airwheels to take up the shocks. When this same gear was tried on the early and heavier two-seater C-3's, it was discovered that the trouble was not on landings but on take-offs. If the field was anything like the usual sod one, the wheels tended to follow the irregularities of the surface and transmit them directly to the plane. As speed built up this imparted a most annoying galloping action to the plane, somewhat like the porpoising of a seaplane. So a switch was made to a hydraulic shock absorber which contained bottoming springs to take the ship's weight on the ground and flex enough during takeoff runs to absorb unevenness. Perhaps on a later lightplane with enough power to pull it off the ground fast, this porpoising would not have shown up, but with only 36 hp the Aeronca naturally held its wheels on the runway for enough distance to allow porpoising to develop."—An Oldtimer "Shock absorbers are primarily designed to take the initial landing load rather than allowing the airplane's structure to take this load. Therefore, the prime consideration when leaving off shock absorbers is, will the structure take it? You have to consider what will happen at places such as the engine mount, the seat supports and the wing supports when the ship plops down hard. Large airwheels will act as effective shock absorbers on light, slow airplanes, but if I were going to design a ship with no shock absorbers I'd use heavier tubing in the forward end of the fuselage, just in case. The question then is whether any cost and weight would be saved as compared to fixing up some kind of simple shock absorbers."—Lt. Robert T. Smith
This one will puzzle about 99% of you readers, so to get everyone off the hook this ship is an Alexander "Flyabout", built in the early 1930's by the firm which made the famous Eaglerock planes. It had no shock absorbers but relied on airwheels for cushioning. How well such landing gears work out depends on a careful consideration of airframes stresses during landing, and of handling qualities during ground operation.
but not least, satisfactory ride while on the ground. You could deactivate the shock struts on a ship flown by a smooth pilot off a paved field and still give the ship less of a beating than it would get at the hands of a student pilot or out of a rough unprepared field even with very good shock absorbers. The present structural designs are satisfactory if the pilot just uses them with caution and the field is not too rough for the ship's
landing speed. If you know the ship will be operated by students or out of rough fields, either use shock absorbers or reinforce the supporting structure."—Paul E. Best "Last year I removed the shock struts from my Baby Ace and substituted rigid members, using the 8.00 x 4 tires at about 16 lbs. pressure. This change eliminated a tendency to wander on takeoffs and landings and gave positive ground control. I assume therefore that when an airplane is equipped with fairly soft shock absorbers, Crosswinds and centrifugal forces acting on the body and wings of a plane can cause the plane to sway and rock on its gear with predictable results on your ability to hold it straight. In this connection it may be significant that the landing gears of heavy, fast military and commercial planes are designed to give straight vertical shock strut travel and to minimize changes in axle camber, caster and alignment. The many hours on the ship since this change have disclosed no evidence of strain or failure. Thirty years ago my experience with many types of planes with rigid gears was satisfactory except for one design which had a stub axle welded directly to the longeron . . . it failed only on extremely hard landings. I feel that most of today's structures are able to support a rigid gear with low-pressure tires for landing speeds below 50. Over that I feel high pressure tires are needed and so shocks must be used. Remember that if tires run at very low pressure for shock absorption on landings, they will let the ship rock easier on the ground. During a fast ground run this can cause tire distortion and let the ship drift or slither around. Also, too-soft tires can slip on their hubs during hard braking and can even roll off the rims in an unusually fast turn. For training planes, I feel shocks are indispensible regardless of the tires."—James M. Wells "Without shock absorbers, the fuselage has to be stronger. Think of the airplane as coming down with
"Shock absorbers are only required for rough pilots,
some particular vertical velocity and forget the horizontal
very rough landing strips, high-speed landings and last
Continued on Page 29 SPORT AVIATION
13
THE STORY STORY . . .
Continued from Page 5 No. 2 with a three-sided flat glass frame taken from a PT-17 or a PT-19. Cockpit details also differed in instrument panel layout and in the fact that the throttle was on the left side on No. 1 and on the right side on No. 2. The purchaser of No. 1, Bill Rainey, modified it by building up the turtledeck behind the cockpit and adding a simple flat-wrap curved canopy hinged on one side. The present owners leave this off most of the time since it seriously restricts the headroom. No. 2 retains the original built-up steel tube headrest, but certain softies among the present owners added a tubular frame with flat plexiglass side panels and hinged it to the top of the
flat windshield. The rear portion of this hinged canopy frame is contoured to fit over the head rest.
obtained by Paul Weaver, also of Seattle, who will complete it with certain modifications found to be desirable from experience with No.'s 1 and 2, notably improved cockpit arrangement and a cleaned-up landing gear.
For all their old-fashioned features and oversize
dimensions, the two Storys have proved that there are many considerations other than good looks, small size, and speed that are of importance to homebuilts. These made a great impression on the author and influenced the design of his EAA contest entry, which is a ship with the Story's size, general proportions, and basic structural features. The major changes are low-cost all-wood construction and minor refinements of line and equipment. Beyond that, there just isn't much room for improvement in the Story design even though its prototype appeared over 25 years ago. A
No. 2 was sold to Dick Andress of Portland, who sold
it to a Seattle group consisting of Cecil Hendricks, Harold
LANDING GEARS . . . Continued from Page 13 speed. The kinetic energy to be absorbed by the landing
gear is therefore %mu2 where v is the vertical velocity
and m is the plane's mass, or weight. In a normal landing gear the tire will deflect about one-fourth of the shock leg stroke so deflection and stroke can be combined into one value, h. Then: i'vtnv2 = n m g h, where n is a load factor. Therefore;
ng =
mh 2h So if h is reduced it is possible to increase n. Of course, a pilot with a sensitive sitting muscle will do a
lot to alleviate the problem!"—Gorges Jacquemin
Photo
by
Pete
Bowers
Comparison with Tom Rich! (in cockpit) and Dave Gaothier (at prop) show that the Storys are not as small as the average single-seat homebuilt.
From all the above pointers, any amateur designer should now be able to make a considered choice about his landing gear struts and, fellows, isn't it really thrill-
ing to see how much information Sport Aviation is able
Clark, and the author in 1947. This sale turned out to be typical, with the license expiring a few weeks later and the ship needing a recover. Consequently, the group, organized as "The Story Flying Club", had to take in a fourth member to finance the dope and fabric and didn't get operating until early in 1958. When No. 1 was brought to Seattle by Rex Richards and Jim Clark in July, 1959, the owners of No. 2 tried to get them to call themselves "The Second Story Flying Club", but they didn't go for the idea. The fuselage that was started for a third Story, along with some ribs and wires, has been
to gather by calling upon the practical and engineering experience scattered among many thousands of members? To add frosting to this little cake, we should mention that member Art Bell, an FAA Maintenance Agent in Grand Rapids, Mich., calls to our attention the fact that in the May,
1955 issue of Aero Digest there is an article on
pp. 48-50, by Ken Coward, giving the mathematical computations used in determining the best dimensions for spring steel landing gear legs. Ken is vice-president of Bee Aviation Associates, developers of the Wee Bee, Honey Bee and Queen Bee.
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Rex Richards and Pete Bowers do a little tail chasing in Story Specials No. 1 and 2 (N1337N and N1338N).
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