I think the V-tail is glued on wrong

[Rwilkinson]

This is a lanier arf pylon racer I know it shoud be 0 0 0, I did everything in my power to make sure the tail was glued on at "0". This is the first bird I have set up with a v-tail, it is powered with a TT .46. When I am at 1/4 to 1/2 throttle it is fairly well behaved (little mushy) but when I go past 1/2 to WOT it wants to climb now. What I have done for now is mix in a little down elev. with the trottle stick. When the throttle is advanced the elevator goes down. I have set this at 3/4 throttle to fly straight and level because if I go to full throttle the bird is a little fast for me. I have limited the throttle to only go to 3/4 when the stick is all the way forward. (you pylon racers pilots are good!!!) What is the best way to set up a V-tail. I understand I am will have to dig out the epoxy at the tail.

Rick

[sayno2glo]

Try adjusting little down trust in motor mount

[J Klenske]

Try adjusting little down trust in motor mount


I agree.

As the plane gains speed the main wing makes more lift and thats whats making it climb. Add a spacer in the form of a wedge to the back or the engine mount to point the engine down a few degrees (2 or 3) and see what that does.

Now if you were to get serious about racing, you might not want to do this because it would actually slow it down slightly from a loss of forward thrust. But for sport flying, I think its your best bet.

[dwbebens]

Rick;

Something is absolutely wrong with your plane. I race this general type of plane in 424 racing. They are they are very pitch neutral, regardless of speed or throttle setting when everything is 0-0-0. This 0-0-0 setup is VERY important. Also the CG must be set in the suggested range.

As to how to set the plane up to be 0-0-0, I'll describe how I do it.

I first set set entire plane on a level flat surface. You may want to remove the landing gear. I then shim the fuselage so that the wing is at zero degrees incidence - - that is, the distance from the center of the trailing edge to the table is equal to the distance from the center of the leading edge to the table.

Then I check that there is no down thrust by laying a small square against the firewall down to the table surface. I then check that there is no side thrust by fastening a straight edge horizontally to the firewall and measuring back to the point of the tail equal distances out from the center of the firewall. When the firewall has no side thrust, the two measurements to the tail will be equal. A tapered shim of plywood glued onto the firewall can correct any non-zero thrustline problems you find.

Measuring the incidence of the tail is a little more complicated. Get or make a stick of of wood 3/4" thick by about 3-1/2" wide by about 6" long. It is very important that stick be very parallel in the 3-1/2" dimension and that it be of very uniform thickness in the 3/4" dimension. I lay this piece of wood onto the "V" of the tail with the long axis fore-and-aft and having the flat surface laying horizontal. Now I lay a small torpedo level onto the top of the wood with its long axis fore-and-aft (see the photo). Now you can see if the tail incidence is at zero degrees.

I suspect, from your description, that your tail is at negative incidence and/or your CG is way too far rearward. If the tail is at negative incidence, you can slice a small sliver out of each side of the fuselage directly under the tail, starting at the leading edge of the tail and going all the way back out the end of the fuselage. Then you can pull the trailing edge end of the tail assembly down and re-glue it in place. I've used this method and it is easy and quick. This way is much easier than digging out the tail epoxy and trying to re-mount the tail.

I would never try to live with a plane that flies as you described yours does. I couldn't race it - - it would be too much work. Adding such things as mixing and making thrust line changes may be expedient, but are only bandaids. The plane will still fly goofy.



Doug Bebensee

[ciressarg]

I think dwbebens is right. I have a predator 1 with the same problem. I think it is negative incidence on the v-tail. I have heard of guys putting a shim under the front of the v-tail. I havn't chopped into mine yet. I moved the cg forward just to see if I can live with it. but I havn't tried it yet.


Eric

[dwbebens]

deleted message

[daven]

Doug, that is a nice looking Quickie, what is it?

The tail looks great with its skinned hinges.

[dwbebens]

Daven;

It's a fuselage of my own design and a wing I found in the trash barrel after a previous race. I think the wing is from one of Marcus Blanchard's 424 Vortex kits, but I'm not sure. The tail was finished and hinged mostly according to Bill Vargas's instructions on the NMPRA site. The idea for coating the torque rod with Crisco shortening to prevent the epoxy sticking works better than any other method I've tried.

Doug Bebensee

[daven]

I've actually gone away from crisco for the most part and now use brass sleeves. I think I can get a little smoother action doing that over crisco, although I built many planes with that method that worked fine. Now that all of my tails are composite, the brass sleeves are easier.

Another suggestion on the bubble level method. It does work, but is not perfect. I have been testing a smaller digital level, and I can get close to a 3 degree difference compared to looking at the bubble alone. On a 424 plane 1-2 degrees diff is not a big issue, but at 428 speeds thats quite a bit.