How are tails attached?

[Brian Jackson]

Greeting all.

For non all-flying tails (a separate V fin and rudder), what structure holds them to the tailboom? I've seen many examples of such tails and they appeared to be held on by short straps at the base that bolted through the tail. Since the tail is mostly foam, that leaves the fiberglass skin to take the stress from those bolts. Clearly my thinking can't be right.

The Watson's Tail plans border between vague and... well I won't say out of politeness. I'll just say they weren't very intelligible to me in this area. Perhaps I missed something... don't know.

What is the rigid, structural bond between a composite tail and the tailboom? What keeps the tail from flying off into oblivion?

Thanks for any feedback.

Regards,
Brian Jackson

[StanFoster]

Brian: My horizontal stab is fiberglass...but it has an internal wooden cross piece to bolt through.

Stan

[RICK MARTIN]

Brian,
I used the Honeybee design for my V-Fin. The fin is offset with the leading edge to the right as far as it will go. I figure it's about 10 degrees. I'll try to describe the mounting and then take a close up for you tomorrow. Basically you make two cheek plates the length of fin (along the keel). These plates will be about 5" tall so that they will rise 3" above the top of the keel. At that 5 " height, the plates bend horizontally outward to create a 2" "shelf" along the length of the plates. The "shelves" will hold the inside edges of the two-piece H-stab. So if you had the plates installed, and were looking from above, you would see a channel formed by the plates and the top of the keel. Into this channel goes the V-fin sandwiched between a pair of opposite-facing tapered spacers. Then you just through-bolt the sandwich. Now for the H-stab. On a Honeybee, the H-stab is all one piece with a couple of slots cut in it so that it interlocks with the tabs cut in the V-fin. As I said before, mine is a two-piece. Both systems have support arms running from the outer areas of the H-stab to the bottom of the keel. Then there are also cables from the outer areas of the H-stab to the upper area of the V-fin. I understand that the later Honeybee tails did not require the upper cablesbut I don't know why.
My tail is foam and glass and I was also very concerned with the pressure points on the glass. You'll see that I used plates to disperse the pressure. Here are a few shots.

[KDOG]

Nice bird!!! I like the tail offset idea. Are you worried at all about the low H-fin?

[Doug Riley]

Brian: Look more closely at the Watson plans. Doc calls out circular plywood inserts that serve as hard points for each bolt that passes through a strap through the glass. The inserts are installed by scraping a matching depression in the foam core with a razor blade before glassing over. In my experience flying Doc's own prototype, this system works very nicely. I saw no evidence of hole enlargement, cracking or yielding of the laminate.

John Landry bought the prototype tail and continues to fly it. He may chime in here.

Have faith in the design as you find it on the Internet. These things have been flying, just as you see them in the plans/narrative, for years. Honest!

[Alan Coats]

Brian,

There are also braces that go from the tail boom up to the horizontal, for additional support.

Alan

[RICK MARTIN]

KDOG,
Thanks. I've worked very hard on it. No I'm not worried. It is bigger and higher than the prototype which flew very well.