Flying the torque roll

Model Airplane News, Jul 2001 by Wolanski, Dan

IMAC Aerobatics

The torque roll is probably the single most impressive freestyle maneuver you can perform; it is also the most difficult to master. A torque roll requires that the aircraft, in a nose-up attitude, balance its weight with the propeller thrust while it slowly rotates about its roll axis. The airplane rolls in reaction to the engine's torque.

Torque rolls are even more impressive when executed close to the ground. During the last few years, this freestyle maneuver has been aided by the use of gyros. Gyros greatly help in maintaining a perfect nose-up attitude. But if you ever want to enter a freestyle competition such as one sanctioned by IMAC (International Miniature Aerobatic Club), you will need to master the maneuver without the aid of a gyro. There are several tricks to performing a torque roll correctly:

* Setup. Proper setup is essential. First, be sure your control surfaces are capable of 3D throws. Set up your rudder and elevators for at least 45 degrees of deflection. You will rarely need this much deflection, but when you do, you will need a lot of it. Quicker servos also help, since the faster you can input the correction, the less correction you will need. I use the Futaba 9402 servos, which provide lightning speed (0.09 second/60 degrees) while producing 111 oz.-in. of torque. Also make sure that your aircraft is not nose-heavy; a tail-heavy airplane will torque roll significantly more easily than a nose-heavy one. (Insider tip: many of the Tournament of Champion pilots add several pounds of weight to their planes' tails for freestyle events.) A good indicator that your model is tail-heavy is that when you roll it inverted during straight and level flight, it requires little or no down-elevator to maintain level flight.

Finally, you will need a large, light prop that will spool up very quickly and generate a lot of thrust. I use a Menz 32x10 wooden prop on my Desert Aircraft 150cc engine. This combination gives instant throttle response with enough torque to yank my 36-pound plane around like a yo-yo.

* Engine. You must have a reliable engine that is capable of instant throttle response. One little miss from your engine can spell disaster if you are close to the ground. Be sure your lowend idle is set up properly and gives immediate transition response. To perform low torque rolls, use the best fuel and engine you can afford.

* Flying the maneuver. The key to doing a torque roll properly is a good entry. It really doesn't matter whether you enter it upwind or downwind, but a torque roll is very difficult to perform in wind of more than 10mph. Your goal should be to enter the maneuver with the model in front of you, at a comfortable height and in a perfectly vertical attitude. For your first time, start with an entry that is at about 100 feet high. Throttle back to idle to bleed off speed, switch your transmitter to the 3D control rates, and point the plane straight up. Now do a 1/4-roll, so that you see the top of the plane. Seeing the top of the plane will help you sort out the initial inputs. (Hint: a common mistake is not getting the plane perfectly vertical; it should look as if its nose is pitched backward slightly toward the canopy).

Now, while pointing straight upward, let the plane come to a complete stop with the engine at idle, and begin to advance the throttle but not enough to gain altitude; in fact, you want the plane to slip backward ever so slightly. Once you are very close to equilibrium (where the thrust equals the model's weight), "rock the throttle," i.e., rev the throttle back and forth a few clicks around the point of equilibrium. The plane should then begin to rotate. If it doesn't, it isn't completely vertical. Once the plane does begin to rotate, you will need to be on top of every little correction.

During the torque roll, corrections should be made only with the elevator and rudder. Try to time your inputs for when your engine is at maximum rpm during your throttle "rocking." You will not need any aileron to get the plane to roll. You will need an almost instant reflex to make elevator and rudder inputs in every direction. If everything looks as if it is going perfectly, it isn't! Don't stop adding inputs or your model will fall out of the maneuver; in fact, a perfect torque roll requires constant "jabs" of up-elevator and right rudder to keep the model pointing straight up. Keep in mind that when you see the bottom of the plane as it rotates, rudder input will be reversed (just as the aileron inputs are when the model is coming toward you). This will take a little time to get used to.

* Recovery. Nothing lasts forever; even a perfect torque roll eventually stops. When you notice that your model is beginning to fall out of the torque roll and you can't save it, advance the throttle slightly past the point of equilibrium and let the nose fill, or advance to full throttle and recover by going straight upward. If your plane falls out and heads toward the ground, be sure to gain sufficient airspeed before you try to pull its nose up. If you have a chance, switch from the 3D rates back to your low rates so you don't suddenly, in a panic, give the plane a huge deflection of elevator. If you don't switch to low rates, be very careful while pulling out.