KR2

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PiperCruisin

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For perspective, the Glasair-II has a single piece spar attached with an AN-6 in double shear on each side, plus an AN-3 in single shear on each side at the rear spar.

Six g, 260 MPH Vne.

BJC
The Glasair attachements are only taking the vertical shear loads (and some wing pitching moment) while the KR-2 mounts are reacting the vertical plus the dominating bending moment.
 

David L. Downey

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This is very important ^^^^^^^^^^^^^^^^

If you look at ANY cantilever wing that is designed to fold or be removable (gliders, powered aircraft, shipboard carrier-based aircraft) you will notice that the bolts or pins or shafts that are used for this are much much much larger than regular bolts.

Why do you suppose that is?
and, if you ever look at the bolt holes, any/all scratches that are on teh surface of the bores will be parallel to the axis of hte bore! the most perfect starting place for fatigue cracks! I have looked at several bore sets using taper pins and never saw the same degree of (micro) damage. I think people are afraid of them because of the reaming of the tapered hole, but it is very easy to do progressively with a dry fit between cuts to assure proper engagement of the pins.
 

ronp987

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Aug 11, 2021
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About a week ago, I removed the wings from a KR2 that I had recently acquired, this one has 4 AN6 bolts and 4 AN3 bolts per wing, nylock nuts and associated washers, along with the aileron attachment bolt (nylock w/washers, but it should take a castle nut and pin because of the rotation is sees). Pitot tube disconnect as well (tubing over a tube for the splice). The bolts were difficult to access, a ratcheting wrench was helpful, and I'd consider grinding a wrench down to fit better if I had to do it often. Wing attach fittings seem to fit well (snug), you will need a helper to wiggle the wing slightly to take the pressure off the bolts to move them in or out. Wings are relatively small and light weight, easily handled with two people. This plane did not have any covers over the wing attach fittings, so things might be different for your situation.
Plans may call for longer bolts, that go all the way through the front to back of the WAF, but this one doesn't have clearance to fit those in. That would reduce the number of bolts and sync up with kr2pilot's post earlier.
My friend's Sonerai has wings that pivot very easily, and fold back along the fuselage. It seats two in tandem. Both aircraft seem to have tight seating if you are a large individual.
KR2 is a pretty small plane, you may be able to fit it under the wing of a Cessna if hangar space is tight. If you put it on Harbor Freight moving dollies you could snake one in on an angle. If you take the wings off, they are about 8 feet wide, and not very tall. I think the folded Sonerai may be a little bit narrower, but will be longer. I'm not certain on the horizontal stabilizer width comparison. I hauled a KR2 project, on its belly, underneath a Sonerai, in an enclosed trailer. The KR2 is definitely a smaller airplane.
Thanks very much for the info. It appears that the Sonerai might be a better fit for me due to the folding wings. Good luck with your KR2 project.
 

Victor Bravo

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To clarify, what I was pointing out is that when a cantilever wing is designed to be removed often (gliders), or folded often (carrier-based), the designers very often seem to go to much larger pivots (larger pins, thick wall tubes, etc.) than they would otherwise use if the wing is not designed to be removed or folded on a daily basis.

So if the Glasair had been designed for the owner to fold outer wing panels upward at the end of the day, and store it in a one-car garage... AN6 bolts would likely not have been used. NOT because the AN6 bolt can't take 6G (obviously it can), but because the wear and movement and wiggling that happens when you fold the wings every day will result in excess wear, clearance, and looseness.

As an example (in the glider world where I came from), the typical fully certified 6G American gliders designed in the 1950's use AN 4, 5, or 6 bolts, and they either are not often taken apart or when they have to be taken apart they're a bigger PITA. The certified 6G European sailplanes (from the late 1970's on) use very large thick wall tubes as the "wing pins", and they assemble/disassemble in 5 minutes with very little trouble.

I can absolutely assure you that the reason the European aero engineers went to the thick wall tubes was not laziness or lack of engineering efficiency :)
 
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PiperCruisin

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I don't really disagree with VB, but just to clarify that if the wing was "removable" (but the same attachment config and not foldable because that would be a different load path and magnitude) then I might consider larger bolts (more margin) to avoid any significant wear due to normal ops and handling.

Never had to take a glider apart so just guessing. Using single pins, I would wonder how one might minimize the composite buildup required to take potentially large bearing loads. A hollow pin might fit the bill which would reduce the bearing stress for almost the same shear (have to be careful of shear inside the tube vs simple V/A). I'm sure they got it right though I have seen it screwed up (fortunately not on something that flew).

Out of curiosity I ran the number on a G3 AN6 (assuming 6g * 1.5 FoS for hardware):
(1625 lbs GW)*(9 g)*1.15/(2 wings)/(2 for double shear) = 4205 lbs. The shear stress is tau = (4/3)(V/A) = (4/3)*(4205 lbs/0.11 in2) = 51 ksi. AN shear allowable is 76 ksi. For an AN6, I think the shear (single) rating is 8280 lbs or about 75 ksi if you use V/A (used more typically for simplicity I think). For the bolt only, the MS = 76/51-1= +0.49. I'm guessing bearing could control, I don't have the geom or matl info. 125*0.577 = 72.1
 

Erik Snyman

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Oct 9, 2019
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I don't really disagree with VB, but just to clarify that if the wing was "removable" (but the same attachment config and not foldable because that would be a different load path and magnitude) then I might consider larger bolts (more margin) to avoid any significant wear due to normal ops and handling.

Never had to take a glider apart so just guessing. Using single pins, I would wonder how one might minimize the composite buildup required to take potentially large bearing loads. A hollow pin might fit the bill which would reduce the bearing stress for almost the same shear (have to be careful of shear inside the tube vs simple V/A). I'm sure they got it right though I have seen it screwed up (fortunately not on something that flew).

Out of curiosity I ran the number on a G3 AN6 (assuming 6g * 1.5 FoS for hardware):
(1625 lbs GW)*(9 g)*1.15/(2 wings)/(2 for double shear) = 4205 lbs. The shear stress is tau = (4/3)(V/A) = (4/3)*(4205 lbs/0.11 in2) = 51 ksi. AN shear allowable is 76 ksi. For an AN6, I think the shear (single) rating is 8280 lbs or about 75 ksi if you use V/A (used more typically for simplicity I think). For the bolt only, the MS = 76/51-1= +0.49. I'm guessing bearing could control, I don't have the geom or matl info. 125*0.577 = 72.1
Unrelated, but also related: I am not a glider pilot, though I have been up with friends a couple of times. The question: Why do glider pilots, and passengers, wear parachutes when flying? I am not pulling legs here, but a glider seems to me the one aircraft where a parachute is really NOT needed. Can anyone give me a reason that makes sense? Mid-air collisions in the same thermal, perhaps?
Erik in Oz.
 

JimCrawford

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Unrelated, but also related: I am not a glider pilot, though I have been up with friends a couple of times. The question: Why do glider pilots, and passengers, wear parachutes when flying? I am not pulling legs here, but a glider seems to me the one aircraft where a parachute is really NOT needed. Can anyone give me a reason that makes sense? Mid-air collisions in the same thermal, perhaps?
Erik in Oz.
Unless made impracticable by the design of the cockpit - generally only vintage types - it is usual in the UK to wear a parachute. Indeed the seats are designed to accept a backpack and would need a substantial cushion to fill the space.
The reason is to provide a plan B in case of collision. as correctly surmised in the quote the risk is higher in crowded thermals. There have been several escapes by parachute over the years for this reason in the UK but I can only recall a couple of in-flight structural failures, one almost certainly loss of control in cloud resulting in overspeeding and one fin post failure caused by an undocumented and poor repair.
An interesting note is that it used to be the only thing you were required to have to cloud fly in a glider under the old UK rules, was a serviceable parachute.

Jim
 
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