Just flew my new v-tail FlatBat. It has a 36" swept foam wing, and powered by an OS 40. Fast and manuverable, but has a noticeable "wobble" with power on. When I kill the engine, the Wobble stops. (The wobble is in the yaw axis, pitch is rock steady.
What causes this?

Is the wobble constant or do it "turn on and off", turning on at higher speeds?

The wobble in the yaw axis seems to get worse with an increase in airspeed with throttle open. You make an interesting point, I'll try a high speed dive with throttle off to see if prop vorticees are at work here. The wing, although swept, is flat bottom and I may be trying to push it thru the air to fast.. I'm still experimenting. Thanks for the reply. BalsaBum

Bum, I've probably built 25/35 combat planes in the past two years, all with v tails. I've found the tail wag in a lot of them, and used to fret about it. But, then I discovered it was not affecting their handling (turn and burn, yank and bank) so I quit frettting about it. The v tail is just a natural on the bat.

I have heard, but have not researched it, that the full scale Bonanza with a V tail has a little of this same tail wag.

Right on CAJUN, The Vee tail is a simple and strong installation for sure, and it looks better that a conventional tail I think. It is a little harder to maintain visual orientation with it, I did'nt realize how much looking at the tail of the model in flight contributed to this. I'll just have to get used to it. I am trying to figure out how to upload pics, when i do I'll post them.

Wobble in the yaw axis is a sure sign of insufficient vertical fin area.

I'm with mkirsch it's called Dutch Roll.

JESTER

Thanks for the tips guys! I am building a new bat with the grey flatbat fuse. It's not as sturdy as the black one, but should work out ok. CAUTION, the Spad web site does not show that you need to run the corrogations front to back when building a coro wing. I built my first one with them running spanwise, thus creating a triangular shape to the top of the wing when folding it over the spar, it flys ok but i'm sure there is more drag then I need with this shape. I have also increased the tail area by 25 % to dampen the "wobbles" on this one.

I should have made it a little clearer, sorry! It's mentioned on the picture with a small arrow, and in the first sentence under the red square about flashing coro.

http://www.spadtothebone.com/SPAD/Fl...ing_const.html

hey tattoo, i built two wings with the flutes running span wise before i read this.....can i expect some different flight characteristics???? i'm probably going to go ahead and use them til the're not usable anymore.....thanks, bill w.

At top speed you won't notice a difference, it's during slower flight and especially dead stick that the smooth airfoil makes more clean lift and you'll see the biggest difference!

Thanks TATTOO ! You are right, it's all there in the instructions...my bad... it just seems logical that the coro direction would run spanwise, providing increased strength to the wing, but subsequent observation on my part has proven my assumption to be incorrect. A good bud made his wing the same way, but avoided the top crease by installing several balsa ribs on the spar, but then we are getting away from the true beauty of these birds, which is of course thier simplicity.

There is one wing design, the Saturday Night Special, that purposely has the flutes running in the spanwise direction for simplicity. It's a 4mm wing and the real beauty of that is the ailerons are part of the wing and not seperately added. The drawback is that it does create a faceted airfoil that is not as effecient at lower speeds, but does do ok. I've been thinking that it just may be possible on a wing such as this to treat a group (4-6 flutes maybe?) of flutes like a hinge at the apex of the airfoil, cut them out, and get a beautiful airfoil out of it. Just may have to do some experimenting

But when working with 2mm coroplast the chordwise flute airfoil comes out so sweet...it just can't be beat!

In my early attempts at 2mm SPAD wings, I ran the flutes spanwise, and came out with a really smooth "Laminar flow" style symmetrical airfoil. However, the wing is very "mushy" on the surface. Running the flutes chordwise pre-stresses the surface, making a much more rigid wing.

I'm going to start putting my V tail flat bat together soon but have a slight problem. It seem the instruction sheet disappeared. Can anyone scan the instruction and email them to me? would appreciate it. Joe

Click on the link below for the instructions to build a Flatbat.

http://www.spadtothebone.com/SPAD/Flatbat/

Thanks for the comeback on the instructions for the V Tail F/Bat. I sure am getting a education while putting this critter together. I'm used to the measure and remeasure while assembling, not with this you don't. I'm going with a OS 20 for power with a 9x 4 prop or would a smaller prop be better? I do have a OS 25FX but I'm saving that for the Battlefloyd sitting in a box by my bench. Anyway, this V Tail is my first depature from pylon type airplanes and I don't want to get too crazy..........well, not yet anyway. I'll be watching this forum for tips because I think this combat thing is going to be a education and A REAL BLAST!!!!!!!!!!!!!!!!!!!!! :devious:

An OS .25 FX on a Battle Floyd? If I was in your shoes, I'd put the .25 on the bat, and the .20 on the Floyd. Not that the Floyd can't handle the power, I've seen several guys around here run .25s on Floyds. But built stock, a Floyd with that much power won't hold up when you run in to something going that fast.

I fly modified Battle Floyds in A class combat, with Mag .15xl engines, and they are very competitive.

If I could only get my B class planes to turn like my A class Floyds do.

Swept wing Bat