Francis Donaldson's thoughts on Evans Volksplane VP-2

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BBerson

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Look again at the VP-2 structure. It is a complete space frame and does not lack bracing. It resists deflection in the direction of the blue arrows, and consequently, can transfer torsion--if the fuselage is stiff.
scan_1888.jpgscan_1888-2.jpg
Cool drawing!
Yes, it does not lack bracing, but a single additional brace across the struts would effectively double the torsion load paths, I think.
Regarding the fuselage, I don't see a lack of torsional load path. The plywood side is a rigid beam diaphragm. No problem.
Of course, the cockpit opening allows the fuselage to twist, but each wing is attached to its fuselage side. The wings don't necessarily need to be torsionally connected across to each other if that is your concern.
 

Twodeaddogs

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You could end up like the Rans S9 (i think) with tubular braces running from the side of the cockpit and joining at the centre of the front bulkhead. Alternatively, build a VP-2 with a Jodel 112 wing, if it were possible.
 

Sockmonkey

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I know I keep saying this, but using a min max type strut arrangement on the VP just makes so much more sense to me.

It could still be a low wing, and even easier to get into.
 

cluttonfred

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I agree that a VP-2 with a MiniMax strut and gear arrangement would be interesting, but that's a major redesign not a minor modification. A "MiniMax V2" with side-by-side seating and a 2180cc VW would make even more sense.
 
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Tiger Tim

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I know I keep saying this, but using a min max type strut arrangement on the VP just makes so much more sense to me.

It could still be a low wing, and even easier to get into.
I was just thinking that the other day, and also wondering how nobody has made a two seat TwiniMax
 

blane.c

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So imagine that from the VP-2 you removed everything except the wing. So it is a complete wing from wingtip to wingtip with no wing parts missing. So now I can imagine that if I twist the wing in opposite directions like with the ailerons deflection, the twisting action from the tip through the area where the fuselage would attach and on to the other wing tip would be relatively uniform . So if I stiffen each tip the resulting twisted wing is going to be overall less twisted at the tips than previous before the modification. But what about in the middle the area where the fuselage usually resides why can't it be stiffened? It is a pair of carry through spars? Couldn't the spars have four cables crossing between them in the area under the seat? Or four rods with rolled thread ends? I suppose there might need to be a clever arrangement to get past the control cables but they may just naturally make it past as well not knowing without further study. Any way stiffened in the middle and at both ends it seems to me that although the wing would still twist it would be to a noticeably lesser degree and no longer uniformly but most of the twist in the areas outside of the center box and inboard of the tips? Considering the struts land in this area are we better off or have we created a new problem?
 

blane.c

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Torsional stiffness doesn't work that way. See post #22.
That doesn't make sense to me. If we remove all the other parts of the wing and only have left the wing tip and I can twist it and then I beef it up and it is noticeably more resistant to twisting when I attach the rest of the wing to it the wing is going to be more resistant to twisting closer to the tip?
 

cluttonfred

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There does seem to be an aspect here where both theories apply. With the two essentially rigid solid spars, clearly anything that holds the two ends fixed in the same plane is going help reduce distortion due to torsion somewhat over not having anything at all.

There is zero torsion/moment at the wing tip. Maximal at the root.
 
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