Martin,While this is a disortation that follows some logic it is flawed in that the result should be 0 slop in the attach points. And backing into a reason to have slop is not the way to go. I have 0 movement and am able to pick the tire off the ground from the wing tip. I have not found any other KR that I have personally checked that had any movement at the tip. Yes friction may play a roll in the final juncture but accurate holes that are reemed to the actual size is the key. I did have one hole that I was not happy with and reamed it to the next size in metric. The wing attach fittings on my plane have paint marks to indicate if there has been any movement or change on the locations. If the builder does not strive for profection in his work he may never acheive something that is even adaquite.Joe Horton,Coopersburg, Pa. ---------- Forwarded Message ---------- From: "Martin Pearce" <rocketdri...@optusnet.com.au> To: <kr...@mylist.net> Subject: KR> RE: re wing tip slop .. Wear mechanism and proposed fix ...... long List-Post: krnet@list.krnet.org Date: Fri, 20 May 2011 12:13:34 +1000
Thanks to everyone who has chipped in so far with advice and assistance. This is a bit long, for which my apologies, ...... Bolt to bolt hole clearance and the effect at the wing tip As far as I can see, if parallel bolts and bolt holes are used, there has to be some clearance in order to fit the bolts. Given that the two WAfs on the main spar (on my a/c at least) are 145 mm apart and the tip is 2.38 metres from the bolt holes (again, my aircraft), 0.1 mm clearance (4 thou approx) at each main spar bolt will result in about 3mm vertical movement at the tip and .8 mm (31 thou) will give close to the 25 mm (1 inch) I am seeing. Standard average location fit tolerances For comparison, an average location fit for this size bolt will have a maximum clearance of 1.5 thou and is unlikely to be achieved in practice using 3/8 drills and aircraft bolts (an AN6 3/8 inch bolt has a diameter tolerance of -1 to -3 thou and then there is the drilled hole tolerance to add in as well.) Likely wear mechanism and applied loads True that KRs have been flying for 30 years now with little evidence of WAF failure in normal service, but it's also true that everyone speaks of WAF bolt hole wear as a "need to carefully inspect" if buying a used one. I suspect that the wear mechanism is that, with the WAF bolts tightened up, the friction between the WAFs of the stub wing and its outer panel makes the fit appear to be tight when a "casual" wing waggle test is done by hand, and no tip movement is detected. However, when G loads are applied, I believe that the WAFs will move one to the other due to the necessary assembly clearance and the G force overcoming the friction, thus causing wear on the bolt and fitting. Note that a 2 G load on a 1000 lb aeroplane will be applying about 3,800 lbs across each WAF fitting on each wing (being 500 lbs vertical lift plus about 3800lbs spanwise reacting the wing bending moment.) And then there are the significant and high frequency inertial loads imposed by taxiing over uneven surfaces .... especially if you have wing tanks. ____________________________________________________________ Groupon™ Official Site 1 ridiculously huge coupon a day. Get 50-90% off your city's best! http://thirdpartyoffers.juno.com/TGL3141/4dd66d37a88e758f058st04duc
