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 <krnet@list.krnet.org> 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/krnet@list.krnet.org/. > 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 krnet-le...@list.krnet.org > _______________________________________________ Search the KRnet Archives at https://www.mail-archive.com/krnet@list.krnet.org/. 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 krnet-le...@list.krnet.org
