FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1944
1944 - 1810.PDF
238 FLIGHT AUGUST 31ST, 1944 Pre-Rotatioii of U/C Wl Some Interesting Results qj DetrefiypmeTH. Tests Vanes Light and Effective) Bv HENRY F. SCHIPPEL hdded F ^OR many years it has been the tesire of aircraft designers and operators to pre-rotatVlanding wheels in order to effect economies in desigrr^nd mainten ance. The mere physical operation of rotating a very simple matter indeed, but when additional weight is involved the problem can become very complicated. In a paper on this subject presented by colleagues of mine almost exactly a year ago, the various reasons for removal of Aircraft tyres from the service, the ways in which pre-rotation would help to prolong tyre life, and a weight-cost study of the problem were ghfen. But the most interesting part was the presentatkW*of results obtained by the Boeing Aircraft Co. on a pair of 19.00 x 23 tyres equipped with flexible vanes. Here at last was the first indication that we were on the right track. By the addition of only 5 Jb. of material to the aircraft weight, we had succeeded in obtaining a pre-rotation of 68 per cent. This figure represents a ratio of surface speed of the tyre to indicated airspeed at the moment of contact with the ground. In level flight the tyies would spin at only 58 per cent, of the I.A.S., but as the final portion of a landing approach is made with the airciaft decelerating, and the wheel deceleration is less than that of the aircnffi, the resulting effectiveness is much higher. Self-acting Vanes The report concluded that the vanes were generally satis factory in producing pre-rotation before landing; that they reduced severe cutting of the tyre due to sharp objects encountered during ground contact; but that if the wheel assemblies were not accurately balanced, they would pro duce resonant vibrations at the higher airspeeds. The dis tinctive feature of the vane design was that they were flexible, normally lying flush with the surface of the tyre, and only opening when the air stream impinged upon their leading edge. The vanes on both sides of the tyre were so arranged that they were opened by the air stream on the lower hair of the tyre, but on the upper half they closed and caused little more drag than that of the normal tyre surface. Thus, shielding of the upper half of the tyre, apparently so essential for rigid vane constructions, became of much less importance. * Abstract of a paper read before the Society of Automotive Engineers in New York. Mr. Schippel is manager of the Aeronautical Section, Field Engineering Department, of the B F. Goodrich comrany Next Confine t 25 vane 2,000 fa stq ist T5y Trans thjrdevelopment was a tes ^5 Trans- Wjftern Airlines on two 17.00 x 16 tyres on glas DC-3 machines. These tyres had nted on each side wall. At an altitude of eral level test flights were made, the landing gear being extended at 150 m.p.h. After one run of 142 seconds, the vaned tyre was revolving at 54 m.p.h., and on another run at 32 m.p.h. On an actual landing, the tyre was revolving at only 17 m.p.h., when the last read ing was taken over the end of the runway at an I.A.S. of 80 m.p.h. This signified that the tyre was decelerating faster than the aircraft, and was believed to be partlgjis/ due to the slight airscrew power used during approach, the upper part of the tyre being in the slipstream. It was observed, however, that even with this somewhat low degree of pre-rotation, the tyre screeched less than usual upon contact with the runway, and the drag force due to inertia of the wheel assembly was noticeably reduced. No conclusions were drawn from these tests, but the tyres were left on the aircraft to study tread wear. It was later Ve Number lb 18 18 18 9 9 nes Type Radial Angular • H I.A.S. at Gear Exten sion 140 130 140 150 130 150 Max. Tyre Speed 55 52 54 64 55 62 Time to reach Tyre Speed. Sect. 48 70 50 54 70 72 Tyre Speed 43 44 49 52 51 52 Landing I.A.S. 80 70 69 75 64 65 Per cent. pre* rota- . tion 54 63 71 69 80 60 Time from Gear ext. to Ground Contact 82 112 74 110 103 120 One of the 19.00x23 tyres equipped with radial flexible vanes which were the subject of the Boeing tests. A 17.00x16 tyre fitted with angular moulded vanes. These tyres were tested against those with radial moulded vanes. Summary of pre-rotation test on DC-3 aircraft 17.00 x 16 tyres with moulded vanes. observed that because the tyres on the DC-3 are not fully retracted, they slipped continually against the flight brakes which were not strong enough to resist the driving force of the vanes on the Tower part of the tyre. These brakes wore grooves in the tyre treads and the test was discon:y tinued. «*• The next phase of development was a study of vane design and improvement in the method of attachment. It had been found on previous tests that the cemented vanes tended to strip from the tyre side wall. Accordingly, on all vaned tyres of later manufacture, the uncured vanes were attached to the uncured tyre, and the whole assembly then cured in the normal tyre mould, adhesion of the mov able part of the vane being pre vented by the interspersion of holland cloth. This change greatly improved the appearance of the finished product, as well as the streamlining, by providing recesses for the vanes to retract flush with the tyre side walls. Wind tunnel tests were also made to determine the effect of varying the size of vanes and their angular position on the tyre side wall, and a stroboscope was used in conjunc tion with these tests to observe the vane action. As a result of this study, two pairs of 17.00 x 16 tyres were made, one pair having radial
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
