Hi all! I did a scratch build job on a I-153 biplane and am having the following problems!

At take off the model will sway to the left (looking from behind) I have 4 degrees of right thrust and 2 down thrust. No mater what corrections I give it it will go in to a left banking turn and end up on its back or nose if I persist with the take off.

After checking for wing twists and etch I could not find anything.

Specs are!

wing span 72.5 inch (top wing)
weight is at 13 lbs
Power source is a G-26 Used 16x8 prop up to 18x8 (smaller was better).
Top wing is a + 2 degrees bottom is 0.0 VS is -1.0

Did try to change the top to 0.0 but nothing did change.

CG is at 15% based on the Tail volume calculations.

I have tried to take off 2 times and after a 2nd rebuild (Minor damage to the top wing) I am not considering to to rebuild this model. (Pity as it looks great)

Any one have any tips and comments on this type of phenomenon I would greatly appreciate it!

Kindly Regards

Kaptain_YAK.

Is this all going on on the ground or is the plane doing this after lift off? I had a bipe which on lift off had "0" aileron responce and had only rudder control until the plane got some speed up, tail up and got moving. Quite nerve racking. It did not last long, but your post reminds me of the situation I had. Something to consider is during takeoff you may be getting into the rudder on throttle transition a little which will cause fits with a shorter coupled plane. Hope this helps, Walt

the fix -- more thrust - not just the prop - more power .
typically - this type craft is "stalled" during much of the takeoff run (run?)
Old approaches -- add a long tailwheel setup which places th model at about 8-10 degrees aoa .
this lets you get into takeoff speed earlier as the combind drag is lessened.
- keep it on the ground till it is skimming --then gently lift off.
anotherhepl- move main gear aft to apoint that the model is actually "tippy" on the gear -
this lets the drag on the gear move aft and decreases the steering effect it can produce.
really nice looking model -
all of the fussing with wing AOA is wasted time - set both panels equally .
I would guess-from looking at the pic - that the wing loading is on the high side - which means that LOTS of takeoff speed is required to take off at a lower AOA.
If you lift off early - the tail group is simply blanked out and yaw control is reduced to nothing.
don't give up -

What Dick says.. I've done that on several poor groundhandlers quite successfully.

The landing gear looks like it is too far foreward. You could also toe the tires in a couple degrees for better tracking. Tailwheels require a differnent approach to directional control on the runway... you have to use quick rudder responces to the swirve, but don't hold the rudder too long or it will just swirve the other way... when you first add power and start to accelerate be prepared to use full rudder to correct for swirves... as it picks up speed you can reduce the rudder inputs to partial rudder. One more thing, make sure you are not using any aileron during takeoff... opposite aileron just makes them swirve harder. It would help if you gave a more detailed description of the last crash... for example did the model only swirve one way, or did it go in both directions... you said it banked to the left and ended up on its back... usually they bank to the left after swirving to the right, was that the case?

Ty

Kaptain, here's what occurs to me.

1. The wing incidence, I believe, should be zero on the bottom wing, or perhaps positive a degree, and negative on the top wing, perhaps a degree. That way, the last surface to stall would be the top wing, rather than the first. After reaching flying speed, if you don't pitch the plane up too quickly, you should not stall as you continue to build speed. But you must hold off on pulling it off the ground, until flying speed is reached.

2. The pull to the left will go away when the tail lifts off. When the thrust line is level, the prop won't pull you to the left. So, you need a longer, more gradual buildup of speed, to keep that big prop from yanking you to the left. Then, lift off slowly, after building lots of speed.

Those are the things that jump out at me. Beautiful plane, I hope it flies soon!

Best wishes,
Dave Olson

Didn't a lot of these types of layouts in full size require a LOT of right rudder during takeoff? Are you running out of right rudder and it's still doing the swing and flip thing? How much rudder travel do you have?

Normally our models have such little toothpicks for props compared to the originals that it's not really an issue but in this case you may be suffering from P effect and trying to lift off too soon as Dick and the others suggested. You may need to get the tail up and let it get up to a higher speed before trying to lift off at a shallower angle. This sort of thing was common with the higher powered fighters. I read one story about the Mustang in particular that the P effect was horrendous and flipped more than a few planes that tried to lift off too soon. The cure for them was lots of right rudder and lots of speed before liftoff.

Thanks boy's! will try to use all of this information and see what I get.
Well .......... here is a more detailed description.

Take off is accomplished at 50% throttle as full throttle makes the model swivel violently to the left like made and no amount of rudder stops it.
The model will not lift the tail 1st it will simply Jump into the air and fly at a strait line for a few meters . Then when power is applied it will start to clime but will then start a banking left turn. At this point the down elevator is not much use as I am already at a vertical situation and the unavoidable is evident.

2nd flight was different Take off was accomplished in a strong head wind. Again take off at less than 1/2 throttle flight at a strait line only this time it was a lot shorter. The left banking turn was again evident but this time it was more of a roll and no amount of right aileron (which would make things worse) fixed it. However the original right swinging to left swinging motion was not evident to this flight. I had added another 2 degrees right thrust (total of 4 degrees & 2 down).

Wind loading is not bad it is only 23 oz top wing has a 73 inch span (Some of my other warbirds are over 30oz and fly great).

The CG was calculated by the Tail volume method and I started at 15% or the top wing LE. This required an additional weight of 200grams to get this CG. So during taxi I had the occasional tip over.

Well at least I am now thinking of repairing the model (after 2 rebuilds I am getting a bit tired building for a week or 2 and crashing in under 5 seconds) but this time I will try a different setup Top wing will be at -1.0 , bottom at +1.0 Will try to keep it on the ground until I run out of active runway (Will try not to hit the fens at the end of the runway _ Or will find a bigger field to test fly it).

Keep it coming!

Regards

Kaiptain_YAK

another thought then - -if applying power makes it climb --which translates into a left yaw - you possibly are tailheavy and or need more "down" control in the horizontal stabilizer -either reset the stab (LE up) or increase down throw on the elevator(s).
Bipes can be critical to stall - especially short coupled small tailplane setups .
The full scale stuf like that can be a handful also .
for a really easy to fly bipe - something like a Bucker Jungemann setup is far easier - not as interesting perhaps but far more stable .

You may have multiple issues here, but the first thing you need to do is get the takeoff under control. My guess is the fin and rudder is getting blanketed some and is hence not effective. That problem is compounded by the gear being too far forward. Finally, the wing's lifting you off too soon and is probably very close to stall. My suggestions are to move the gear back some and drop the incidence in both wings. You need to try to get the tail to come up in the takeoff run before the plane simply leaps off the ground. If the tail hasn't come up then something is wrong whether it is balance or incidence. You need to resolve that because the plane is not ready to fly and it will stall. Once you get the tail to come up during takeoff you can run on the mains until you have sufficient flying speed.

From the description of your takeoff it sure sounds like it's tail heavy. But on the other hand with a 15% CG located on the upper wing it can't possibly be so. It may be worth redoing the tail volume coefficient again. I think you may have gotten something messed up with a term or the MAC or some other issue.

From what you describe in the second takeoff with the ailerons making things worse is a classic pre stall adverse yaw problem. In those conditions you need to use rudder to help the ailerons. I also really think you are trying to lift off too fast or have too much up trim and that is causing it to lift off with the wing in a near stall condition. If ever there was a candidate for differential throw in the ailerons this model sounds like it.

How about trying a LOT of down trim so that the tail will lift up on the takeoff run to the point where you need to use a bit of back pressure to lift off? If you overdo it and suffer a prop strike then reduce the down trim and try again. The goal is to strongly avoid the nose up to a stall situation that seems to be the main problem. Be sure to rotate slowly with very light back pressure. The idea is to see the model's tail come up as it accelerates and then SLOOOWWWLY add back pressure until it's skimming and then add just a hair more to lift off. It's wise to let it accelerate at the skimming point for a moment before lifting it up. Once in the air but still in the ground effect to let it accellerate a bit more. It should then be safe to climb out at a shallow angle and then re trim the pitch from a safe altitude for level flight. A helper to reach over and add the trim for the first flight would be helpful since this one is obviously a handful and you may not want to take your thumbs off the sticks. A few clicks of right rudder trim for the first flights to help hold it away from the left spiral would not be a bad idea either.

Also, somebody had it backwards, the top wing should have positive incidence compared to the bottom because you DO want the top wing to stall first on a possitive stagared wing Bip. but 0-0 would also work

you could also try some aileron differential, more up than down

4 degrees right thrust sounds like a ton to me

what are your throws for your rudder elevator and ailerons?

does it taxi straight?

could be nose heavy also if the rudder and elevator is ineffective
you got alot of 2 cents to go with here
good lookin model, dont give up!

It may be an optical illusion, but in the picture you posted it looks as though the left wheel is toed-out. This would definitely make the plane go left on take-off.

I had a similar problem with a Tiger Moth (of all things... they normally have no probelms) turned out to be a VERY minor warp in a wing. Check the incidences in several places along the span of both wings with a meter.

Mine was a hard right turn... full left rudder and full left aileron needed to level it with as minor a warp as I had... was unbelievable... (1/2 deg at the outer 1/4 of the left lower panel) Straightened the wing... trims were centered.

Thanks for every ones input!

Valued and interesting views! But for now I will freeze this project! As I need to get ready for the Annual SCALE AIR RACES I will be entering with my LA-7 .......... However I will return to this project and try to apply all of these thoughts and make the CHAIKA! FLY!

Regards

Kaptain_YAK