PDA

View Full Version : Axi outrunner motors


Rosie
08-14-2006, 07:38 PM
Hi Guys ... I have been using several Axi outrunner motors which I find to be
extremely powerful, but I have had several crashes due to high speed left turn
takeoffs. I am beginning to think that these motors produce so much torque
that I should be putting in some right thrust. For example, on my SR X-250
I installed a small Axi outrunner and with the landing gear straight she goes
left to the point where I haven't been able to straighten it out. Once it is in the
air it flies great . Any comments on this problem ?

Happy landings,
Rosie

simibill
08-14-2006, 08:05 PM
A few degrees of right thrust can't hurt, and will probably help with your takeoff problem.

Dereck
08-14-2006, 08:47 PM
See above re right thrust - most model aircraft need some. Usually, things like pattern model aircraft, designed for faster, smoother aerobatics, need the least, things like WW1 biplanes need the most.

Take off technique. It's even more fun with a taildragger too! As you apply power and start the take-off roll, you start with a lot of mechanical power - the prop's torque trying to rotate the aircraft opposite to the prop's rotation, and little aerodynamic control to do much about it. This is from standstill to whenever the rudder has enough airflow speed over it to join in and work for a living.

Taildraggers - especially electrics which tend to much larger props compared to the model's wingspan. You start in that nose-high posture (the model, not you :eek: ) apply power, and soon after, the nose comes up. This causes something complicated called, I think, gyroscopic precession. This causes the model to yaw hard left in our case.

It's a real pain and hits the man-carrying world just as hard, so as you don't feel too bad. Many taildraggers start their take off run with full down ele to get the tail up as soon as possible before there's much speed on - I've even seen a pilot lift the tail with the aircraft stationary, to eliminate that torque induced swing.

If you ever get that good with a model, we have some questions for you ... He was a very good airshow pilot with about a zillion hours in his Piper Cub.

Try starting your take off runs into wind - every little helps - with a fair amount of right rudder held on. Open the throttle smoothly and steadily, so as not to hit the model with a whopping burst of torque all in one go. Our little, low inertia taildraggers will often pull their own tails up very soon after they start to move. Once you have her on the mains, use the left stick to hold take off heading, head up to full power, and then gently rotate off the ground with a smooth and steady pull on the elevator.

At that point, you raise the nose ten degrees and when at half wingspan plus twice the grass height, you half roll to inverted and push into a 45 degree climb before pulling back through for a long four point roll.

Sorry, that last bit's from lesson two ;)

Taking off is much trickier than flying around, but somewhat easier than landing. Both demand a lot of thought and practice, the reward is getting to take your model home the same shape it started the day more often.

Hope that helps

Dereck

ragbag
08-15-2006, 12:55 AM
A few degrees of right thrust can't hurt, and will probably help with your takeoff problem.

In the few months that I have been building, if it doesn't have 3-5 degrees of right and 3-5 degrees of down thrust I put it in. Then go from there.:D







.

DickCorby
08-15-2006, 01:54 AM
In the few months that I have been building, if it doesn't have 3-5 degrees of right and 3-5 degrees of down thrust I put it in. Then go from there.:D .

Too much right (or Left for that matter) is not a good thing as well. I think that starting at erhaps 1.5 degrees is a bit more realistic. I use the Robart guage on my planes and even the ARF's seem to have about that built in.

Then if the plane has the capability of vertical climb for any distance, My Hyperion goes vertical forever, you can tweak it to be what the plane needs. In theory, without any external forces (Wind, thermals etc.) a plane with the correct thrust on the motor will climb vertical with no correction required.

Something that will really help the most however is to put in some Toe In on the landing gear. Then once the tail lifts, it tends to go in the same direction as when it lifts the tail. I've had to put in a lot of toe in on some of my planes to enable it to work, but usually about 1-2 degrees is adequate.

If a plane does not track straight in level flight, most people correct with rudder. Sometimes a minor change in Thrust line will enable straight tracking with the rudder dead on.

Another thing that will help get rid of this problem, it to put in some toe in on the landing gear. Then once the tail lifts, the gear will tend to keep it on the same track that it had when the tail lifted.