It's a pretty simple matter to lay up a set of skins for the wing stub much like the Diehl outboard wing skins. The ones on my KR were made in the same fashion as the Diehl skins using a simple rib profile cut out of plywood and lined with formica as a mold. The cord is constant on the wing stub, so the same mold works for both sides. They are stout enough to walk on. In fact, with the taller landing gear I always step up onto the non-slip pads on the wing stub to enter the cockpit.
Considering there has never been a failure in this area, I'm not sure I would call it a problem, and the fact that mine was re-enforced was only to satisfy my building techniques and desire to have a re-enforced step pad, not because of a perceived design deficit. -Jeff Scott Arkansas Ozarks > Sent: Monday, April 06, 2020 at 1:03 PM > From: "Dr. Feng Hsu via KRnet" <[email protected]> > To: KRnet <[email protected]> > Cc: "Dr. Feng Hsu" <[email protected]>, "colin hales" > <[email protected]> > Subject: Re: KR> Stress Calculations. > > Thank you CH for your critical safety information regarding the KR2 > structural design margin issues. Yes, I have been thinking of the strength > on that exact spot/area of the stub wing and have been very reluctant to > kneel or step on it whenever needed to get in & out of the cockpit.... I > used my fingers to push around that area several times and felt it was > pretty "soft" or lack of material strength.... > > Not sure if this problem existed only in the KR2S design or in the KR2 > design as well? How would you fix the issue without spending too much time > & efforts on tearing apart the skin of the stub wings completely? > > Also, I have been thinking of the best or easiest way to make something to > cover up the ugly opens on both sides of the KR2 wing joints or attachment > area? Of course, without using tapes or anything hard to remove...?! > > Stay safe & healthy, > > Dr. Hsu > > On Mon, Apr 6, 2020, 6:13 AM colin hales via KRnet <[email protected]> > wrote: > > > With respect to the strength of the KR2 and KR2S, we had a stress analyst > > carry out in depth calculations on the whole airframe many years ago. > > > > The stress analyst's report is intellectual property, but I'm sure by now > > the gent who paid for the calculations shouldn't mind if I release the > > information. The analysis was carried out to allow the KR2S to be accepted > > by the UK LAA as an approved design. The KR2 was built under what we call > > "Grand Father Conditions", meaning 'no one ever carried out any > > calculations and It was only allowed to be built and flown, because none of > > them had broken yet!' When the KR2S came along, it was deemed as having > > sufficient modifications to classify it as a brand new airframe design and > > therefore required its own individual approval. > > > > From memory, stressing to EASA VLA requirements, which is +6 -4 G and VNA > > of 175 MPH +10% the airframe was actually quite close in places to not be > > strong enough. But it wasn't the spars or longerons or wing attachment > > brackets, the weakest part of the aircraft or the part with the lowest > > safety margin was the top skin section between the front and rear spar on > > the stub wings. The one layer of glass leaves that area susceptible to > > failure in torsional loading. Who would have thought it? Hence we have a UK > > requirement to double up the skin thickness in that area to two layers of > > 92/125 bi-directional glass cloth. > > > > This skin having the lowest safety margin of the whole airframe is a fact > > and isn't open to comment or conjecture. We've done the maths. I'll see if > > I can publish the calculations which prove this fact. > > > > So don't worry about any of the structural strengths of the KR2 design at > > all. It is all perfectly acceptable. Some of it by over 200% The doubling > > of the top stub skin thickness is recommended and not compulsory. We do it > > though as that means you can kneel on it or put your foot on it when > > getting in and out. > > > > The calculations are complex and considerable. I'll ask the intellectual > > owner if I can publish all or just highlight some of the data. > > > > All good news. > > > > CH. > > _______________________________________________ > > Search the KRnet Archives at > > https://www.mail-archive.com/[email protected]/. > > Please see LIST RULES and KRnet info at http://www.krnet.org/info.html. > > see http://list.krnet.org/mailman/listinfo/krnet_list.krnet.org to change > > options. > > To UNsubscribe from KRnet, send a message to [email protected] > > > _______________________________________________ > Search the KRnet Archives at > https://www.mail-archive.com/[email protected]/. > Please see LIST RULES and KRnet info at http://www.krnet.org/info.html. > see http://list.krnet.org/mailman/listinfo/krnet_list.krnet.org to change > options. > To UNsubscribe from KRnet, send a message to [email protected] > _______________________________________________ Search the KRnet Archives at https://www.mail-archive.com/[email protected]/. Please see LIST RULES and KRnet info at http://www.krnet.org/info.html. see http://list.krnet.org/mailman/listinfo/krnet_list.krnet.org to change options. To UNsubscribe from KRnet, send a message to [email protected]
