Inner Plane Struts?
11-15-2002, 08:19 PM
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Inner Plane Struts?
It depends if they are load bearing or just cosmetic. If the wings are cantilevered and the cabane struts carry all the loads for the upper wing then you have lots of options to attach cosmetic interplane struts.
I built an S-1 Pitts model that simply used pairs of small plywood studs on the bottom and top of the upper and lower wing spars. The wooden I struts fit over them and were pinned and held in place with small screws. They were load bearing but not much. The only loads were primarily compression and shear loads and designed only to keep the wing from teetering on the cabane struts and to assist somewhat in keeping the wing tips squared fore and aft with the fuselage. All the other flight loads were carried through the cabane struts. The load bearing cabane struts were aluminum tube and were attached on either side of a much larger load bearing plywood stud on the bottom side of the upper wing spars with a screw going through the stud and struts for both the fore and aft set of cabane struts. The lower ends of the cabane struts were permanently attached to the fuselage structure.
If the interplane struts are structural, care needs to be taken to transfer the loads to and from the spars and not to the wing ribs as cracked and broken ribs will result. (A problem on some early models of the full scale Pitts)
Non structural interplane struts, or I struts not loaded in tension, can be held in place with a simple tube and wire arrangement with the tubes in the wing and the wires in the I struts. The major problem here is that care is required in getting them in place without poking holes in the covering.
When assembling the aircraft, the I struts can be set in the lower wings and then the upper wing can be placed on the aircraft. Different lenghts of wire on the strut on each side will allow you to line up one strut at a time (the longer wired one first). A balsa cover over the other shorter strut wires on the other side, will allow the wing to sit on the I strut without poking holes in the upper wing while assembling the other side. The cabane struts then hold both wings together and with proper dimensions the I struts will add carry just a little compression load which will again prevent any teetering. the pin and tube arrangement also assists in preventing the wing from rotating around the cabane strut attache points by carrying some shear loads. The advantage here is 100% scale looks with no screws, pins, nylon hardware, etc. showing.
The quick and dirty non structural method is to attach the I struts to screws in the upper and lower wing spars with 90 degree nylon brackets. These can either have screws on both ends of the bracket or be the snap-on type. The snap- on type are quicker to assemble but can also snap off in flight, which leads to the I strut either departing the aircraft or flopping around putting holes in the wing. Best advice for those is to leave them off in flight.
I built an S-1 Pitts model that simply used pairs of small plywood studs on the bottom and top of the upper and lower wing spars. The wooden I struts fit over them and were pinned and held in place with small screws. They were load bearing but not much. The only loads were primarily compression and shear loads and designed only to keep the wing from teetering on the cabane struts and to assist somewhat in keeping the wing tips squared fore and aft with the fuselage. All the other flight loads were carried through the cabane struts. The load bearing cabane struts were aluminum tube and were attached on either side of a much larger load bearing plywood stud on the bottom side of the upper wing spars with a screw going through the stud and struts for both the fore and aft set of cabane struts. The lower ends of the cabane struts were permanently attached to the fuselage structure.
If the interplane struts are structural, care needs to be taken to transfer the loads to and from the spars and not to the wing ribs as cracked and broken ribs will result. (A problem on some early models of the full scale Pitts)
Non structural interplane struts, or I struts not loaded in tension, can be held in place with a simple tube and wire arrangement with the tubes in the wing and the wires in the I struts. The major problem here is that care is required in getting them in place without poking holes in the covering.
When assembling the aircraft, the I struts can be set in the lower wings and then the upper wing can be placed on the aircraft. Different lenghts of wire on the strut on each side will allow you to line up one strut at a time (the longer wired one first). A balsa cover over the other shorter strut wires on the other side, will allow the wing to sit on the I strut without poking holes in the upper wing while assembling the other side. The cabane struts then hold both wings together and with proper dimensions the I struts will add carry just a little compression load which will again prevent any teetering. the pin and tube arrangement also assists in preventing the wing from rotating around the cabane strut attache points by carrying some shear loads. The advantage here is 100% scale looks with no screws, pins, nylon hardware, etc. showing.
The quick and dirty non structural method is to attach the I struts to screws in the upper and lower wing spars with 90 degree nylon brackets. These can either have screws on both ends of the bracket or be the snap-on type. The snap- on type are quicker to assemble but can also snap off in flight, which leads to the I strut either departing the aircraft or flopping around putting holes in the wing. Best advice for those is to leave them off in flight.
