KR2 style foam wing

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stanislavz

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Aug 21, 2016
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Somewhere in this forum, there is posts by a swiss (iirc) ultralight glider manufacturer explaining how they use a similar technique to make smooth skins without a female mould. It was pretty interesting, I shall put my search skill to the test again...
Flying wing or normal ?
 

wsimpso1

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Oct 18, 2003
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Saline Michigan
I feel a need to emphasize: Guessing is BAAAD.

We pretty much know that a KR or Long-EZ built to plans and flown within the known speed ranges for each are OK. Monkey-see, monkey-do is another deal - if you copy somebody else's design scheme, the only really safe move is copy everything - materials, proportions, dimensions, max g's, max speeds, etc. I doubt the KR is good to Long-EZ true airspeeds and Vdive at altitude...

Whatever design schemes you are considering for something less than an exact copy should be checked out. Nothing should break, bind, buckle. I suggest that nothing should deflect enough to trip laminar boundary layers to turbulent within the speed and g range for the intended mission (cruise for most of us, max level flight speeds for racers, Vne and Va maneuvering for aerobats). Put in all the aero loads, get the resulting shear, bending, torsion, and panel loads, and make sure that the strength gives enough FOS at limit loads (composite structures need 2.0, wood and metal need 1.5) and deflections are small enough for whatever level of laminar flow and for control clearance.

I must emphasize that slow airplanes can get away with a lot, but for an airplane that flies (or dives) faster, inflation loads on skins goes up faster - with the square of airspeed.

Last point to emphasize is the flight envelope includes max g to Vne. Decent aileron travel (or to standard aileron input forces) up at Vne are also normally included. All stressors can be combined in flight and so should be combined in analysis. If parts break anywhere within the envelope, the design still has problems.
 
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