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Discussion in 'Tube and Fabric' started by blane.c, Jul 28, 2019.
I agree with Fritz; Bud Evans knew what he was doing. Go with his design.
I am not sure that the control stick/center section design was finished on the VP-3? My question is does the 7/8" tube just ride tight in the wood holes? The wood expanding and contracting around the metal tube concerns me. This area is different structurally from the other VP's?
It looks like it was finished. C-11 shows the torque tube riding in the Nylon/Micarta (Phenolic) fairlead on the back of the rear spar. On C-2 it does look like the torque tube is riding on the wood on the front spar. If that bothered you, you could make a bushing out of a 1.25" piece of 1"x0.065 tube and polish it out to the OD of the torque tube. (drilling the 7/8 hole out to 1" wouldn't make any difference). Both spars look like they have ply face doublers but I don't see them in the wing drawings.
CSI Las Cruces: I cleaned up the drawings a little so they're easier to read.
Having you look at it makes feel a lot better. Thank you.
Here it is with the holes and the fairlead but no ply doublers yet, I still can't find those in the drawings.
I'd like to draw the PtP stick assembly and see what that looks like.
EDIT: ...and of course the version 2 fairlead that weighs 1/2 as much
I know the push-pull will work. The push pull tube inside the torque tube is just a piston that goes thru a bushing at each end to keep it in alignment. the bushings are about a 0.012" loose sliding fit over the piston. That leaves a lot of clearance (relatively) for the rivet heads that hold the tube onto the reduced dia. ends that go thru the bushings. A rod on the stick end enables the swinging up and down lateral motion to be transferred to straight lateral motion thru the tube. Spherical rod ends at the aft end of the piston and the aft end of the first push-pull tube to bell-crank connection isolate the rotation of the torque tube from the push pull tube. I am thinking to keep that first push-pull tube after the control stick in as straight a line as possible so the spherical rod ends have little more to do, or the least extra to do although they will have to accommodate a slight up and down swing on the bell-crank. My only question about the motion now is if the piston inside the tube needs to be fixed in regards to rotation or if the connections on the rod ends are sufficiently strong on there own. And then there is all that engineering and strength of materials and magic stuff.
I don't know how clear this is, but if the piston needs to be fixed from rotation I was going to do this.
So square off the aft piston were it goes thru the bushing and make the aft bushing four (4) flat on one side round on the other side combination nut plates to hold the aileron crank as well.
This shows three positions of the rod and how it fits into the tube easily. I made a mistake and only put the control stick center 2 inches from the thrust washer when it should be three inches but I left it because it just further exemplifies that there is plenty of room for a nice long rod so as not to have an excessive angle.
Are you just trying to avoid holes in the spar or do you really like the idea of the co-axial tube? (both are very valid reasons)
Both. First it was just an exercise to see if it could be done. Then I got very interested in it. I like it.
I probably won't be able to build a second airplane if I am able to finish this one, and one at a time but if I could build a second one I would make it a two place and run the rudder controls as push pull tube up the port side so that they could be tapped into and used as hand controls. So stick for elevator and aileron in the right hand and the rudder would be controlled with the left hand. It would be fun to give kids rides and people without the use of there legs can fly an airplane just fine if the controls are in place for them.
The 3/4" aluminum tube inside the center section of the Torque tube ends up being about 12 11/16" long riveted to the two solid steel ends. I think it can be eliminated. Just make the entire piston from 1 piece of 1/2" O.D x 1/8" wall steel tube end to end the two ends can be tapped for threads this will weigh within grams of the other. Then the Torque tube can be reduced to a 1" O.D. with 7/8" I.D. This will further simplify. There appears to be clearance left for the rod.
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