Sonic - like VTPR build

[Red]

Today I started building the stabs. They are fairly simple sheeted foam construction, but with a 3D printed root rib/socket. This uses a square carbon tube and with an elliptical pulley arrangement will allow for hopefully 180 degree travel.

I cut away some foam and epoxied the printed rib in place. Then I added some carbon over them to spread the load a little. The sheeting is 1/32 light balsa with a little bit of fiberglass at the TE for stiffness. I sheeted both halves in one piece, and I will cut them apart after.

So the whole affair is clamped/weighted in place. Once cured, I’ll add balsa LE’s and tips, sand to shape and they will be ready for covering. Next I’ll get the pulley arrangement and bearings in place and frame up a rudder.

 

[Stephane]

Hello Red,
Nice project!
I see your madstab will be with square joiner. The rib system and the elliptical cam look great! Did you use it before? I'm afraid about this system on a 100" glider.
You should have no float at all to avoid flutter.
But I don't know all the good solutions that have been used, this is why I ask if you built other madstabs before.
About the square rod solution, I can't remember about glider heavier than 1kg with this kind of madstab. Even the 2m Fluid was with this system but being quite light (<1kg).
Here is a onboard video of a flutter I had on a madstab on a Troll (2m, 1.7kg). It can appear very easily on madstab.

 

[Red]

Hello Red,
Nice project!
I see your madstab will be with square joiner. The rib system and the elliptical cam look great! Did you use it before? I'm afraid about this system on a 100" glider.
You should have no float at all to avoid flutter.
But I don't know all the good solutions that have been used, this is why I ask if you built other madstabs before.
About the square rod solution, I can't remember about glider heavier than 1kg with this kind of madstab. Even the 2m Fluid was with this system but being quite light (<1kg).
Here is a onboard video of a flutter I had on a madstab on a Troll (2m, 1.7kg). It can appear very easily on madstab.

Stefane,

Thanks for the vid, that highlights my flutter concern as well. I'm happy to hear it was easily repairable.

I have not used this system in an glider this large before, however I am aware of the issues that float will cause. I plan to bush the tube and reinforce it so there is very little slop. I will post my progress here, and if it doesn't work I can always cut it out and change it.

Cheers
Red

 

[Wayne]

As a little background Red is on the NASA payroll where he builds experimental RC models and flight tests them (among many other things). Has owned a hobby shop, and has also been a small kit manufacturer for what a decade or so? He is also building his own designed full scale Formula 1 race plane. He is a very skilled builder that likes to try new things as well as old things.

 

[Red]

Thanks Wayne. The only thing that matters is I love airplanes lol.

 

[Red]

I've got the stab separated and LE's and tips bonded on and shaped. I turned some Delrin down in the lathe o make a couple bushings, Heeding Stephane's advice, I'm aiming for as close to zero slop as I can get. The bushings are slightly too long, but I wanted as much shoulder area as I could get for stability. I'll have to final fit them still. So far though, everything fits real nice and I'm happy.
Next up is to get the bushings and cam mechanism fit into the tail and bonded in.

 

[Wayne]

Probably overkill, but what about a bit of balsa inside the tube to avoid the stress at the bearing edges crushing the pultruded? Only need a bit of balsa centered up in there.

 

[Red]

Probably overkill, but what about a bit of balsa inside the tube to avoid the stress at the bearing edges crushing the pultruded? Only need a bit of balsa centered up in there.

I'll look into it. I think the stresses there are pretty low.

 

[Wayne]

I'm not sure what your wall thickness is on the tube.. I've just seen so many tubes crush down and fail. It is almost an automatic for me to want to stuff them with a bit of wood.

Think about Stephane's video. Ack!

 

[Hawaii Sloper]

Why not use a solid Carbon rod? Is the weight that critical?

 

[Shoelace]

As a little background Red is on the NASA payroll where he builds experimental RC models and flight tests them (among many other things). Has owned a hobby shop, and has also been a small kit manufacturer for what a decade or so? He is also building his own designed full scale Formula 1 race plane. He is a very skilled builder that likes to try new things as well as old things.

This makes me feel a little better when I look at Red's builds and think to myself, "I could never do that..."

 

[Stephane]

Beautiful!
Will there be a square/circle adapter between the rod and the bushings? Or does the square rod just turn in the round holes of bushings?

 

[Red]

Beautiful!
Will there be a square/circle adapter between the rod and the bushings? Or does the square rod just turn in the round holes of bushings?

I sized the bushings so that the square rod rides directly in the round bushings. This is also why I made the bushings as wide as possible to spread the load.

 

[Red]

I was able to get the bushings for the stabs dry fit into the fuselage. The fit is pretty good. The cam sits higher than I would like, I may print a smaller one. I also built a rudder.

 

[Red]

I bonded the stab bushings in with E-6000 and they are curing. Delrin is pretty slippery stuff so fingers crossed it sticks.

 

[thenated0g]

I would leave that overnight at least. Looks great.

 

[Wayne]

I'm just realizing where your pull wire needs to run. Oh my.

 

[Red]

I would leave that overnight at least. Looks great.

Yeah it'll sit until tomorrow,

 

[Red]

I'm just realizing where your pull wire needs to run. Oh my.

Yes, well sort of. New smaller cams printing and it will be "cocked" to meet the cables square on. I'll be running Kevlar thread and running guide tubes to prevent chaffing.

 

[Stephane]

Nice work!
I guess you plan to have the cam horizontal with a return?
It is what François Cahour does on its Quartz and Sylphe, and what I did on my 7.5kg Bocian (picture attached ).