Q-500 Racing Discuss AMA 428, AMA 424, and any other variants of Quickie 500 racing

Joining a V-Tail

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Old 01-03-2011, 10:45 PM
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HighPlains
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Default Joining a V-Tail

I've always hated the simple butt joint on a wood V-tail, while it is fairly weak, it was just too simple to do......sand the angle in and then glue it together.

So to actually make the simple assembly more difficult and stronger at less weight, I tried this throwback technique that I actually stole from a 1950's model airplane magazine. I find that model magazines that are 20 to 60 years old are much more interesting than the paid advertisements that are so prevalent today.

The pictures tell most of the story (saving thousands of words), but we are going to do a basic "box joint" to add a bunch of glue area to a standard 120 degree V-tail.

First thing is to make the flat version of the tail. Here it has the 1/64 plywood on the edges, and the hinge slots are already cut in. The elevators are tack glued to the stab with little 1/64" plywood tabs inserted into the hinge slots. Then it was sanded to shape and glassed. After it is joined, the elevators will be cut free and very little shaping will be required for an exact fit.
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Old 01-03-2011, 10:49 PM
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Default RE: Joining a V-Tail

The next step is to lay out the center line, and the cut lines for the "teeth" of the joint. These are 3/8" apart. Then to the band saw to cut in half.
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Old 01-03-2011, 10:50 PM
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Default RE: Joining a V-Tail

Love the posting giant picture problems that are currently on RCU.
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Old 01-03-2011, 10:52 PM
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Default RE: Joining a V-Tail

At this point, you need to trace the airfoil onto a stiff piece of cardboard.
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Old 01-03-2011, 10:57 PM
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Default RE: Joining a V-Tail

Here shows the relationship of the airfoil pattern to the cutout of the teeth of the box joint.
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Old 01-03-2011, 11:02 PM
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Default RE: Joining a V-Tail

When you cut out the teeth, you hold each half up at the angle you want the V-tail to have. I use 120 degree, so I just tape a 30-60-90 triangle to the backside. The triangle holds the angle while I push the tail into the bandsaw to remove the wood where the X's reside.
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Old 01-03-2011, 11:07 PM
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Default RE: Joining a V-Tail

When you have cut the angled notches in both half's, just slide them together. One thing you will notice is that while you might think we were marking up the topside (due to the angle of the cut), it goes together upside down of what you thought it would.
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Old 01-03-2011, 11:13 PM
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Bottom side looks like this. All that is left to do is to push everything tight, do the final adjustment of the angle, and hit it with some CA and baking soda. It has taken far longer to take the photos and type this up than to do the actual cutting. After it is glued, you can remove the excess material from the underside of the tail with a bit of sanding. Sorry for the out of focus picture. It's late, and the batteries for the camera are being recharged. Crappy NiMh self discharge.[:@]
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Old 01-04-2011, 04:29 AM
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Default RE: Joining a V-Tail

Very nice.
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Old 01-04-2011, 05:37 AM
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Default RE: Joining a V-Tail

That looks great. It appears that it is necessary to make the flat layout slightly longer in span to account for the overlap that will occur. I suppose I could work out the math myself, but from having already done it, how much overlap is needed? Thanks!
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Old 01-04-2011, 07:50 AM
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Default RE: Joining a V-Tail

Overlap - If you look at the pictures in post 2, you can see that the initial layout pattern is squares that are 3/8 wide and 3/8" long. In post 6 picture, the arc of the airfoil is added to the length and drawn with the leading edge and trailing edge aligned with the layout squares. The overall length is dependent on the thickness of the airfoil primarily and somewhat with the angle of the cut for the V.
(it's actually the Cosine of 30 degrees, but since that is 87% of the thickness of a very thin surface - what with the pen line thickness (twice) and cutting errors, I just added half the thickness of the airfoil.)

So the answer is that you cut out of the center (2 x 3/8") plus the thickness of the stab (1/4"). So in my case 1.0 inches is added to the initial span of the flat stab.

BTW, stab area is not all that critical anyway since we fly light weight models with the tank on the CG with almost no control throw. We get away with it since the center of lift and the CG are practically on top of each other.
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Old 04-01-2013, 06:44 PM
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Default RE: Joining a V-Tail

I was going to add the post crash picture to this thread for full documentation of this method of joining a V-Tail. But I guess I threw the remains away before the picture session. However, the mid-air that destroyed both aircraft broke the tail a couple inches from the joint. It has also survived another mid-air that took out the other airplane. So I think this method is quite strong, ie, stronger than the wood used to make the tail. I pulled up this thread because I couldn't remember what pitch I used for the teeth, as I am joining a couple more tails tonight.
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