RCU Forums - T-tail woes

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So I don't see many t-tail planes at all, anywhere, ever. Are they actually that deficient and troublesome, or is just that they are a pain to build with any strength. I happen to like their looks,......am I asking for trouble?.

Just finished the 1:4 scale Beechcraft 350i King Air!!!

I have used T-tails a few times on my designs, but I always felt that support struts were needed.

The King Airs V-Stab is the same thickness all the way up, so it is easy to tie the spars of the V-Stab into the structure of the H-Stab. Plus I ha a CF rod on each side of the V-Stab runnig from a former in the Fuselage that is well secures the the root ribs in the H-Stab!

Quote:

Originally Posted by r ward (Post 12422008)

The original idea in the design of full scale traditional airplanes is to keep the horizontal tail surfaces as far from the turbulence of the main wing as possible (not a problem for canard types), specially for high angle of attack conditions.
The design compromise is to make the tail structural strong and the control linkages of the elevator reliable without much weight and manufacturing complexity-costs penalty.

Going back to full scale training days, Piper had a side by side 2 place low wing design w/T-tail called a Tomahawk. You don't see many of them around any more for some reason. Point being, they were nick named Trauma Hawks. Never had the pleasure myself, but thinking it safe to assume there were issues regarding low speed handling.....

I flew those Pipers back in the 80’s, as well as a T-tailed Arrow IV and Seminole twin. They had some different handling characteristics compared to conventional tailed Cherokees and Cessnas. But nothing really onerous. Stalls & spins looked & sounded scary in the Tomahawk, as there was quite a bit of flexing in the tail. In an aggravated stall you could potentially blank the elevators causing them to stall and the plane to pitch up.

in short, t-tail designs aren’t bad, just different.

I did a carbon fiber strut at the rudder hinge line, tied into the end of the fuselage and a another as the leading edge of the vertical stab (also tied into a former). ended up as stiff as a typical fuselage can resist twisting in the tail. built the vertical stab around the struts and set a pad on the top to screw the horizontal stab down with a couple nylon 6-32 machine screws, then made all my own custom designed carbon fiber internal linkage and bell cranks to minimize slop. turned out as tight as a conventional system with all the adjustability needed and although I never weighed it,...i'll bet it is lighter than a conventional tail empennage, despite all the extra pieces.

Quote:

Originally Posted by r ward (Post 12423060)

Sounds interesting. Do you have any photos during construction?
Like I said before, I have always felt the need for struts to stiffen the tailplane on a T-tail, but I am considering a scale model of a type without struts.
I can build a stiff fin, but I'm wondering how to make the top join onto the tailplane stiff. How did you cross the Tee? Any photos?

no photos,....don't know how to do that stuff and this plane was built 5 years ago. but I can explain clearly. sheet vertical stab is foil shaped by using a wider balsa strut internally, bisecting the fore and aft spans at root and tip of stab. about 1/4" space from balsa strut gives room for internal linkage. at the top of the stab, I epoxied a 3/4 in wide piece of 1/8 liteply the length of the stab. this forms the "T" platform that the horizontal stab gets screwed to. I epoxied a couple 6-32 aluminum t-nuts into this platform to accept the nylon 6-32 screws for the horizontal stab. you must dremel out a slot for the elevator linkage and control horn in the center of this platform. the control horn for the elelvator was custom made and lays horizontally off the elevator, and swings through this platform.. making a decent fillet of epoxy on the outside joint between platform and vertical stab will support the stresses fine. linkage is typical pushrod/ belcrank with a belcrank at the base of the vertical stab redirecting the pushrod up to the elevator's horizontal control horn. it uses a typical threaded pushrod and spring steel clevis at the control horn with the lower end doglegged into the belcrank. the 90 degree belcrank is mounted inside the tail end of the fuselage with the leg attatched to the servo rod pointed down abd the other leg pointed aft. make sure this arrangement is secure because it is unaccessable when the plane is covered. a small hatch at that belcrank location might not be a bad idea and if I ever have trouble with it, that is what i'll do. adjustment can be made by turning the vertical pushrod at the top of the vertical stab where it attatches to the elevator horn. sorry for the incapability of posting pics,....I hope this will help.

One Little trim thing comes with Everything above,or under the line of motor thrust.Resistance of air fow making nose up trim with increasing speed.This is possible to mix as negative elevator to throttle.
T-tail is mostly used for sail planes as the strains are gentle and turbulent flow from the wing ahead makes more brake if in line of the wing.

Quote:

Originally Posted by linesnrc (Post 12445693)

yes,...thought about that in design prep.. will watch for it and be ready to trim accordingly on maiden.