Spirit T-tail mod help

[rick's fork]

Hi. Although I've lurked here for a while, this is my first post. I don't think this has been covered before, so I thought I'd ask.....

I have a Spirit 2M kit that I started several years ago and now I'm ready to pull it out of the closet and finish it. I've always liked the looks of T-tails. I've seen recomendations on enlarging the tail surfaces on the Spirit and V-tail mods, but I've never seen a T-tail mod. Has anyone here tried this? If you have ideas or suggestions I'd love to hear them. There are some things I've noticed and thought about:

- Most of the T-tails I've seen have a fairly vertical tail rather than the sloping/swept tail of the original Spirit. Is there a reason for this on T-tails? I'd like to keep the swept look of the original Spirit unless there's a reason not to.

- Since the tail will have to handle the forces of the elevator, it seems like it should be stronger than the original Spirit fin frame. I've thought of using thicker balsa stock for the leading and trailing edges of the fin. Thicker would also help with routing the elevator linkage through the fin.

- Similarly, it seems like the tail needs to be fastened to the fuselage in a stronger manner than just gluing to the top surface of the fuselage. I've thought about passing the leading and trailing edges of the fin through the top surface of the fuselage to the bottom (and gluing to both).

If anyone has built a Sophisticated Lady, how is this tail fastened to the fuselage? Thanks in advance for any suggestions you might have!

[Sparky Paul]

T-tails need a LOT of strengthening/support where the fin meets the fuselage.
And more where the horizontal sits on top.
And some kind of monkey-motion to get the elevator to move.
I tried one, didn't like it. :(

[Strawbalebob]

What, now? What kind of answer is that, Sparky Paul? "Monkey-Motion?" Not so!!

Rich's Fork: of COURSE you can do a T-tail on the spirit. I did and I LOVE it! (All mention of said Spirit will now be made in past-tense. It was lost two nights ago in an unfortunate accident involving an open window, a gust of wind, the floor, gravity, and things landing on top of it after it fell on the floor. I have learned my lesson - never store plane parts near open windows where gusty winds will have their ways.)

I enlarged the fin/rudder, but kept the LE of the fin fairly vertical 'cause I like 'em that way. The fin was balsa, nominally 3/8" thick, and the structure was similar to the original fin (ie diagonal "ribs"). I sanded an airfoil shape to it, and then covered it with 1/64" ply. The rudder was simply built up and monokote covered.

The elevator push/pull control was a Sullivan gold flex cable running through the fin. The elevator was built-up and had a chord of roughly 2-1/2"; the stab was solid 3/8" and had a tapered LE so that the chord was 2" in the center and 1-1/2" at the tip. The whole thing was sanded to an INVERTED flat-bottom airfoil shape. The control horn was FORWARD of the hingeline, and ABOVE the stab. I have a few pics of the finished plane at home; I'll bring them in Monday and post them and it'll all make better sense.

The stab was glued to the top of the fin, and the joints reinforced with triangle balsa on both sides. When the disaster occured, the stab was crushed but the joint remained intact. The fin was pretty much glued "on top" of the fuse, except that I had a solid rudder post that ran down to the bottom of the fuse, and I added micro-ballooned epoxy fillets at the base. When it was crushed, the fuse broke well below the fin/fuse joint. The Spirit has a couple of balsa doublers back there that add a bit of strength, and I think that it's quite enough.

I reduced the decalage (angle of stab relative to the wing) in the process, as recommended on the Charles River R/C website. I also had to add 1/4-1/2 oz of noseweight to make up for the added tail weight, but I was so thrilled with the performance that I didn't mind that so much. I had it trimmed very well, and had several flights that were one- to two hours long. I flew the plane VERY aggressively at times - dodging ticked-off hawks who didn't want me in their thermals forced me to fly sometimes VERY fast and maneuver VERY hard. At the same time, because of the monstrous elevator, I was able to fly very slowly and descent at a steep angle of attack without dragging the stab through the weeds - which is what prompted me to build the T-tail in the first place. Well, that and vanity.

I'm in the process of building a new fuse/tail, and I'll take construction pics for you and post them. I am such a fan of T-tails and I have no desire to participate in the presently-popular V-tail mania, so I'll build it the same. T-tails are heavier, and have to be built that way to be strong enough to survive. The added aerodynamic benefit is questionable on a design like the Spirit, but it looks SOOO much cooler.

So anyway, on to your question: you could keep the swept fin, but that will complicate the control routing some, and will compromise the structural strength a bit. One advantage of the more vertical LE on the fin is that there is simply less distance between the stab and the fuse. Longer fin (cause by a sweep) means longer cantilever, and that means more stress where the parts are joined. Don't let me stop you from doing it; I think it would look pretty cool!

Incidentally, I made a few mods to the wing: fully-sheeted D-tube and 1/4" of wash-out built in. With the T-tail, it turned on a wingtip with nary a tip-stall, fly supremely slowly at a high angle of attack, and it took extremely fast and aggressive maneuvering very well. It may not be a super-star sailplane, but it's sure a whole lot of fun!

I'll post pics Monday. I'm happy to have found another T-tail fan!

[ICTHRMLS]

T-tails have a great look to them and it is a natural to build one but Sparky is right on about needing strength. I built the Dynaflight Bobcat cuz the t-tail looked so cool only to have it snap off on the very first landing. It was built to supplied directions and there is A LOT of torque placed on the fuse at the fin attachment point. Even the Legend t-tail caused a lot of twisting and torquing on landings but then it has a fiberglass fuse. I don't want to dampen your enthusiasm for experimentation but if you think you might want to fly this bird in a contest with landing points at stake...... nix the t-tail. On the other hand... it would be unique and dress up the old Spirit lines. If you build it be sure to post pictures

[rick's fork]

Thanks for your coments and opinions! I'm just finishing the extra wing sheeting as suggested on the Charles River R/C website. The suggestion on this site to enlarge the rudder and fin surface areas is what prompted me to think "If I'm going to (re)build the rudder and fin larger, why not build it as a T-tail?"

Strawbalebob - Sorry to hear about your Spirit. I'd to see any pictures you have of it. The elevator sounds like it has a lot of authority and you hooked it up in an interesting way. I see what you mean about the sloping fin causing greater stress at the fuselage joint.

ICTHRMLS - How was the Bobcat's fin attached to the fuselage? -- was it glued on top or did it have any structure that went through the fuselage? I'd better use a stronger design.

[Ollie]

Sparky Paul,

Right on!!

[Ray Lowinski]

The Sophisticated Lady was probably the worst example of a T-tail ever made. Landings were always breaking it no matter how gentle they were. Mine is now a V-tail with no regrets.

OTOH my XL3200 is a T-tail with a glass fuse and it works/looks just great.

Go for it! You never know until you try. If it works you can bask in the glory, if not, at least you tried.

Ray

[ICTHRMLS]

ICTHRMLS - How was the Bobcat's fin attached to the fuselage? -- was it glued on top or did it have any structure that went through the fuselage? .
While the Bobcat's fin did indeed go into the fuse the biggest problem was the "lite-ply" used for the fuse sides that tapered down to a 1/2" x 3/4" box at the tail. Repairs included adding aircraft ply, carbon fiber and epoxy which added weight. It eventually flew - the t-tail LOOKED great - but the plane as a whole was a dog thermaler and when the wings finally blew on a launch nary a tear was shed.

Personally, I would reinforce the tail area with composites and strive for gentle landings everytime. ;)

[Strawbalebob]

Here are the pics of my t-tail Spirit. Am building a new fuse/tail now 'cause the one shown died when it fell off the bench and a bunch of other stuff fell on to it. I'm still not real happy about that...

The last pic (if they loaded right) was a little parasite-launch thing I was playing around with. Worked great!

[rick's fork]

Thanks for the pictures. It looks great! I hope the rebuild works and looks as good. With the "opportunity" to do it again, will you do anything differently?

[Strawbalebob]

This time I'm making the nose long enough that I hopefully won't have to add any noseweight at all. Also building it lighter, which isn't saying much 'cause the original used some pretty heavy balsa. I ran 3/8" triangle stock in the corners so I could round the corners. The triangle stock also adds quite a bit of material towards the back end, which helps quite a bit to stiffen things up. Hope it works as well as the first 'cause I really like the looks, and the first flew quite nicely.

[Soar_dude]

Strawbale Bob
Just a helpful hint the CG on the spirits are pretty conservative. I know a gentleman down in Seattle that has only like a 1/2 oz and standard gear in the nose. On my Spirit 100" I only have like 1 1/2 oz in the nose with standard size gear.

Soar Dude