I am building a sailplane that has a T tail with flexable pushrod inside. The problem is that the cable inside is too tight for my servos to move easily. I am considering putting bellcranks inside the Vertical fin instead of the flex cable. (the first bend is causing the problem it has to turn in 1/2 inch radius.).

Maybe it would be better to take the existing stab and turn it into a V-tail. Which I am happy to do if someone better than me thinks there is enough area to be effective.

The plane is a Bobcat.

Thanks[&o]

Mr. Mitchell what kinda of pushrod material are you using? you might consider going with a lighter more flexible pushrod, or a small cable. I would try Sullivan Gold-N-rod or the small cable in a rod system.

Soar dude

I am using Golden Rod. And I have tried the smallest cable I could find.

But seeing as how I was impatient I am building another fin, slightly thicker, with a 90 degree bell crank and solid music wire down to another 90 degree bell crank then foward to the servo.

Thanks for the quick response.

The Bobcat kit was purchased off Ebay for $8.00 so I can't complain.

Mike

Besides its 50 miles round trip to Hobby Town , plus 30 or 40 minutes "window shopping" there.
In that period of time I can build the fin.

I have used appx 1/32 dia stranded cable inside sheath by Sullivan for tight bend pushrod for flying stabs. I'm not sure it would make a 1/2 inch radius and be easy to move even this thin cable... The tightest I tried has been a 2 inch radius. (that works fine)

You may need to go to a pull-pull on pulleys... You can run Spider Wire fishing line using brass eyelets as pulleys on 2-56 screws for the axles. That's how I'm setting up the scale control system in a 8 ft span glow power model... Steel wire kinks with the scale size pulleys.

Why dont u locate your elevator servo in the tail. So u will have a short conection which wont bind and u will be able to use regular pianowires or 4-40.

Dont think complicated think easy.

Saludos

Landi

Thanks for the info. Like I said I went ahead with the linkages.

The Bobcat doesnt have room for the servo in the tail.

Thanks,
Mike

I just thought of something......

Have you done T-tail with flying stab before? (does that plane have the flying stab? or a fixed stab and hinged elevator?)

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Lets assume its a flying stab:

Why have you got 2 bellcranks?

The pushrod would go from the servo to the first 90. Then straight up to a clevce with the pin driven out or a brass tube soldered on and flattened and drilled

The flying stab pivots on the appx 25% line rod.

There should be another rod between the 2 flying stab halves that travele in an arc in a slot. That rod captures the drilled tube (or modified clevice). You get a VERY good loction to connect the pushrod at NO weight cost from having the control horn. (and the horn would be external... and thus adding drag...) you elimnate the second bellcrank (and its weight... and its control lnkage slop...)

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Did I uncover the reason for your binding too?

The servo is mounted in forward fuse. A pushrod goes aft ftom servo to first 90 degree bellcrank. A pushrod goes vertical in the fin to the second 90* bellcrank. A pishrod goes to elevator connecrtion (horizontal)