That is almost certainly a CG problem, with the CG being too far back.

You want the CG forward, rather than backward for the first flights. As far forward as 25% which ought to be pretty nose heavy but still controllable. My rule of thumb is between 1/4 and 1/3 of the chord at the root.

Check your CG as suggested, I think 28-30% is more stable, but 33% should still be within the acceptable range. After watching the video a couple times, I think it's more of a yaw issue. I think those are rudder induced rolls, and they are in different directions. This would lead me to think its a trim issue, combined with over correction.
I just flew yesterday, after a repair and was way out of trim. This combined with my excessive throws, it was everything I could do to bring it back down safely.

I agree with Jack . COG incorrect and to much throttle . fix both those and it will be good .

Originally Posted by sir_clive

jack, you are much more experienced then I am, but wouldn't 33% also be pretty far back? I think mine is somewhere at 28-30% and I felt very comfortable with that (kfm3 wing)

It is a classic rule of thumb and generally pretty safe. The KFm wings usually shift a CG point back a little more so it is on the conservative side.

I didn't look at the plans so I'd certainly defer to anyone that had first hand experience with that particular plane.

Jack

hah yeah. on the second throw in the vid i forgot to turn back the pot im using for variable throw.

also the horiz stabler isnt in 90deg relative to the fuse (band saw isnt cutting straight ) relative to the pilot, it is tilted ~<10deg to the right.

Originally Posted by sirbow2

hah yeah. on the second throw in the vid i forgot to turn back the pot im using for variable throw.

also the horiz stabler isnt in 90deg relative to the fuse (band saw isnt cutting straight ) relative to the pilot, it is tilted ~<10deg to the right.

We've all done that. It should work fine. It is a variation on the "V" tail concept, call it a "virgule" tail or "back slash" tail if anyone questions it.

I never have landing gear on my planes so I always do test glides or low power test glides over deep soft weeds before a first flight. You can see so much in the few seconds that takes.

Just give it a not too hard, level, full arm push launch into the breeze and watch first second or two from directly behind. It should start settling to the ground staying level. If it falls off to one side or the other a little, you can just ignore that for now. If the nose pitches up it is tail heavy and if it does a "lawn dart" out of you hand it is nose heavy.

Sometime a low power test launch will look good and you can just add a couple of clicks of throttle and it is flying straight away from you. I usually leave the throttle alone and let it continue a slow climb as I make any necessary rudder and elevator trim adjustments.

Good luck with it!

Jack

Sirbow2
You state the motor is tilted down and to the left, should it not be a little to the right? Secondly what happened in a test glide? Seems to me the left wing is heavier than the right in both flights? Along with the motor angle and the CG I would put a small weight on the tip of the right wing and test glide with that. My build was accurate as well but for some reason had to put 2 lead fishing shots about 1/4" round (flattened) on the wing tip. I agree with less power as these planes once balanced require very little power to function correctly and even when they are flying correctly over powering seems to get mine a little squirrely ..Lee

oh hah sorry, it is to the right but i was in a hurry to get it posted thanks for the test guide tip as i forgot about that. it might have been the wind as i couldn't throw exactly into it because of the field. ill do a roll "cog" test too.

so if i move the battery right behind the motor (either above or below fuse), i get a perfect 30% cog, so, once i get a rediciously expensive prop form my LHS i will do a test flight.

oh, and thanks for all the help guys. you almost make me fell bad for all the posts

Aaaand 1337 posts :P

ok test flight again. better but it always goes to the left like it did before, but with no stall. thrown into the wind and is pushed away, was it not going fast enough(ii was at 50%)? even with ailerons which jackerbes said would make this thing pretty agile, it didnt move.

blu-baby fail 2 (0 min 24 sec)

i did a roll COG test and it seemed to be pretty balanced. held onto the motor and then the back end of the fuse.

EDIT: i think it was because i didn't have enough power. then there wouldn't be as much air flow over the ailerons so they wouldn't do anything. then the wind jsut pushed it away.

Looking much better . A little more throttle and a little right rudder and try it again

I agree with Wilfor.

Does it look like maybe the rudder is pointing a little to the left with the stick centered?

Are you using left stick for throttle and rudder and right for elevator and ailerons?

Jack

Jack i was thinking that to but maybe it was the wind pushing it around as well . Maybe try on a day that isnt as windy . Makes learning to fly much easier . It looked as though it should fly

If the ailerons are level and the rudder not deflected to the left some, I guess it could be the wind.

It is always hard to remember what corrections you made or what was being applied when try to remember after the ship hits the sands...

Jack

Originally Posted by sirbow2

mine isnt going so well:
http://www.youtube.com/watch?v=ddBOsy0hlJ0

what do you think? i followed the bb42 plans pretty much exactly. motor is tilted a few deg down + left. the CG is pointing up slightly when held at 50% of the wing. sorry for the vid. someone else made it. does the same thing each time.

To the left? ? ?
I'm thinking this is either one of the probs here or a simple typo.........normal build will have a few degrees down and equal RIGHT built into the motor mount on a high wing trainer like this. Left angle will exaggerate the whole P factor and may cause just what he's experiencing.

we already discussed this i was in a rush and said left instead of right. fixed in post

anyways, i did some no motor glides, and i still got the issues. even with full right rudder and ele trim. these were straight into the wind.

a few ideas:
could a wing not perpendicular to the fuse cause this? same for rudder/elevator. i know my ele and wing are angled a bit to the left because the band saw wasnt straight when cutting. (pilot view). also, could different polyhedral angles on L vs R tips of the wing cause this?

yes, i have mode 2 TX (thr and rudder on right, ele/ail on right). i had it going full right aileron and it didnt have any roll affect. elevator seemed to have the only affect.