I'm having problems launching my 36" Guillows Cessna. It weighs in wet at 14 oz and is powered by a Norvel 049. I'm getting a lot of "reactionary torque" on the fuselage, and the plane rolls and wants to bank sharply to the left. (Just like when a rubber powered plane blasts off) I'm having problems correcting this with right rudder.

How many degrees of right thrust would be appropriate? Is there any other way to solve this problem?

Thanks

George,

Your weight at 14 oz. wet is good, should be a good flyer. 1 1/2 degrees of right thrust is the usual norm. I take it this plane has no ailerons, right? What does she do on a glide test into tall grass? The cg on small airplanes like this have a tendancy to slip aft so recheck the cg and move it forward a little just until you get the airplane trimmed. Also, check all of the surfaces to be sure you have no warps and your incidences are right. I'm betting you'll find the problem above, good luck... Jeff

Jeff has covered most of the ground on this one but what prop are you using? Torque REACTION is the issue,, and the larger the prop, the more reaction you'll get in response to the greater drag and inertia of a larger prop. Adequate dihedral helps. If all else fails, launch it with a pronounced bank to the right but then again, it could also be that you're not getting up enough airspeed on the launch.

I'm using a Tornado 6 X 3. It was my first launch of a gas-powered model. It reacted just like a rubber-powered plane during the initial burst of energy at release.

I'll do some more test gliding and see what happens. Should I launch with some right rudder??

Andy is right.

If the plane flies well after it gets airspeed, anything you do to correct a launching problem will lead to in-flight problems.

Just launch it in a pronounced right bank.

I've had some that took around 45 degrees for a good launch.

One more thing, with a banked launch you also have to toss the plane upward instead of level. Again, experiment for amount. Usually about ten degrees up is fine.

Bill.

Bill,

This is starting to make sense. I take it that there are 2 phases of flight during launch: the "pre-airspeed" and full airspeed phases.

During pre-airspeed the correcting dihedral forces are not strong enough to correct the reactionary torque. Once the model reaches flight speed, however, the dihedral kicks in.

(With rubber power I thought it had to do with the huge burst of energy at release, but I imagine airspeed is also a factor with rubber power)

So, I'll change the thrust angle by about 2 deg (the model is only 14 oz) and launch with a bank-- we'll see what happens.

By-the-way, why do you need to launch with an upward angle when launching into a bank?

Thanks,
George

George,

Thanks to Bill for elaborating. Your conclusions are correct.

It sounds like you had no right thrust at all though. Two degrees overall (not in addition to) ought to be more than enough. This will make the plane behave better on launch AND at airspeed. Launching with a right bank, though, is still a good idea till airspeed is achieved. Leave the rudder at neutral. It will be effective at launch but very quickly it'll be too effective.

But, why hand launch? No runway? No throttle? What engine are you using? Having a throttle allows you to back off on power if the launch gets hairy. I'd NEVER fly without a throttle.

If you've got a snorting Norvel doing 18K on the Tornado, that might be part of the problem too. Way too much power for a Cessna type with such a low weight. My Stik was 14 ounces and with the Norvel, I could go vertical from a grass takeoff. Nothing wrong with going vertical with a Cessna but you've got to be ready for it. If you're doing something like 16K that ought to be plenty.

George:

Launched in a bank, the airplane will circle a bit before it steadies into the climb. With the plane banked the effective wing area, or projected area, will be less than it will be in level flight. Combine the lower effective area with the low initial air speed, the plane will sink more, at the same angle of attack, until it acellerates.

And the up angle on launch is the "Up elevator" you need to counter the added sink.

You would have figured it out for yourself, and probably already had, before this response.

Bill.

Andy,

You comments are really helpful. I'm using a Big Mig 049-- no throttle, sorry. I don't have a tachometer, but I think the engine is doing well at a moderate lean setting.

On the initial flights, should I flip the prop around to lower thrust? Or, maybe run the engine rich? Or, should I just try an ROG without throttle??

George