KR> RE: re wing tip slop .. Wear mechanism and proposed fix ......
Hi Joe, Glenn, Patrick and Robin . Thank you for your comments and just to clarify, I didn't mean to justify slop, quite the opposite.I have wing tip slop on my aircraft and am not happy with it. I also believe that, with the standard parallel bolt system, it is not possible to eliminate all wing tip slop due to the necessary assembly clearance and the large forces that oppose and perhaps overcome friction between the WAF blades in flight and during taxiing. We are talking a few thousandths of an inch movement at the WAF which I'm not sure that you could discern with paint marks, IMHO. The sure way to discover any loose fit is to slacken the nuts off and check your wingtip movement. By way of comment, I can't detect any movement either with the bolts tight, but have play of several thousandths of an inch at the bolt holes giving me 1 inch of play at the wing tip when the bolts are loose and friction is not confusing the issue My goal is to get closer to the perfection of which you speak, if I can, with an improvement in the design of the WAF area and to make my flying safer! I'll let everyone know if I come up with a suitable design . Cheers Martin Martin Pearce - KR2 with Subaru EA81 + KR2 S with GMH Saturn - Both in my garage, neither registered or flying in Au ---yet! rocketdri...@optusnet.com.au
Fw: KR> RE: re wing tip slop .. Wear mechanism and proposed fix ...... long
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 citys best! http://thirdpartyoffers.juno.com/TGL3141/4dd66d37a88e758f058st04duc
KR> RE: re wing tip slop .. Wear mechanism and proposed fix ......long
On 5/20/2011 6:15 AM, Patrick and Robin Russo wrote: > Now if you have a new and improved design for wing attach fittings, put > it on the table. Many of us think that there is room for change there. If I were to make any change to the WAF, and it would be mostly for those who need to remove and reattach their wings often, the redesign would be to add bushings to the attach point holes, so they could be replaced whey they wear out, thus keeping the attach point tight. -- Glenn Martin, KR2 N1333A, Biloxi, MS
KR> RE: re wing tip slop .. Wear mechanism and proposed fix ......long
Wow Martin, after that dissertation I wouldn't dare make a comment! It is much like saying 2 plus 2 equals 4, does anyone want to refute this or make comment? My answer remains the same to your original question regarding wing tip movement. There should be NONE when you have finished installing all of the WAF bolts. Now if you have a new and improved design for wing attach fittings, put it on the table. Many of us think that there is room for change there. >" Your thoughts and comments would be appreciated ."..
KR> RE: re wing tip slop .. Wear mechanism and proposed fix ...... long
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. Correcting the problem Fixing the wear on the standard design is not that straightforward ... you need to jig the wings into the correct position and incidence and then drill / ream out the WAF fitting to the next size up, a procedure that seems to need some cutting out and subsequent repair of the wing leading edge. And you are still left with a joint that will wear. With this in mind, unless anyone knows of an existing design, I have determined to design a taper pin and spacer system that will allow for easy assembly of the wing to the aircraft and that will accommodate any wear that does occur. As a bonus, With this system, wear is likely to be much less because the inner and outer wing WAFs will not be moving relative to each other as both tapered pins will be firmly located into their tapered holes with all clearance taken up. Recommended annual inspection One last thought .. I would recommend that every KR owner should loosen the WAFs annually and check / measure any wing tip movement. This will indicate the presence of wear and enable the owner to monitor its progress. Your thoughts and comments would be appreciated ... Cheers Martin Martin Pearce - KR2 with Subaru EA81 + KR2 S with GMH Saturn - Both in my garage, neither registered or flying in Au ---yet! rocketdri...@optusnet.com.au -Original Message- From: krnet-boun...@mylist.net [mailto:krnet-boun...@mylist.net] On Behalf Of krnet-requ...@mylist.net Sent: Friday, 20 May 2011 6:34 AM To: kr...@mylist.net Subject: KRnet Digest, Vol 353, Issue 138 Send KRnet mailing list submissions to kr...@mylist.net To subscribe or unsubscribe via the World Wide Web, visit http://mylist.net/listinfo/krnet or, via email, send a message with subject or body 'help' to krnet-requ...@mylist.net You can reach the person managing the list at krnet-ow...@mylist.net When replying, please edit your Subject line so it is more specific than "Re: Contents of KRnet digest..."
