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Max Weight of Non Lift Producing Components
On Friday, December 8, 2017 at 1:45:06 PM UTC-8, James Thomson wrote:
At 01:59 08 December 2017, Dan Daly wrote: On Thursday, December 7, 2017 at 7:27:02 PM UTC-5, Jim wrote: I admit I am baffled by "max weight of non-lifting parts". I understand = the issue of spar bending moment limits, and I think I understand that weig= hing a glider without its wings will give the current non-lifting (i.e., no= n-wing) weight, but I have a feeling there are subtle things here that I do= not understand. I've rigged an ASK-21 and its wings are HEAVY! I haven't weighed them so= I don't know just how heavy they are though. Certainly felt like more tha= n 100 lbs each. Ask me how I know. I'll guess (I know, don't guess) each = wing weighs 150 lbs. Likely more. If I subtract 300 lbs from 780 and then= subtract that result from 1320 I'm still short of 902 - which I suppose is= a good thing. =20 Glider cockpit load limits are set by the lowest value determined by: Max AUW Seat strength limits Max wt of non-lifting parts Forward CG limit For a ASK21 for which I have the actual weighing results: Max AUW 1320 lbs Empty weight, fully equipped, 884 lbs Therefore disposable load is 436 lbs Seat strength limit is 242 lbs, so with a max weight pilot the other pilot cannot exceed 194 lbs Each wing weighs 219 lbs, max weight of non-lifting parts is 904 lbs. Fuselage, tailplane, etc wt is 884 - 438 = 446 lbs. Hence max load considering only non-lifting parts limit is 904 - 446 = 458 lbs. The AUW limit takes precedence. On this aircraft forward CG limit did not determine max cockpit load. Min cockpit load is set by aft CG limit. This whole issue has to do with the design limits of the airfoil design. The non-lifting parts impart a bending moment at the wing root. This is, of course, anticipated by the designer, but has a design limit imposed upon it. Hence, the limit on the non-lifting components. Tom |
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