Semi new, new to war birds.

[msdt74]

Sorry for the slight rambling, just giving you guys a small background check on myself and rc planes. Been back into rc planes for about 8 months. Self taught on a trainer. Moved up to a 1500mm low wing sport and then to a small(1100mm) war bird(P51). Bought a 1400mm P51 from Motion RC. Have ground launched it 4 times, crashed it 3 of the 4. Ripped the gear off on the second attempt, so I had a buddy hand launch it. Flies great, so I belly land it in tall grass, fix the gear and go again. Rough launch but I manage it keep it up this time. One main will not come down(yep, I cycled it several times to make sure it was working correct) so I belly land it again. Fixed the problem and tried to ground launch again. Crashed and really ripped up the main wing. New one on the way. I think I know what my problem is, but I am wanting to see if you guys and gals can confirm it. I have a huge place to fly, but my runway is narrow and less than 100ft. The plane gets off the ground about 5 ft, then noses over hard to the left and straight into the ground every time. Never had this problem on the small war bird. It is not my receiver(have tested it in another plane) nor my radio. After a few days of self debate, I am thinking its motor torque with me fire walling the throttle because of the short runway. Just to confirm what I am thinking and since I crashed it on its maiden flight and had to do alot of repair, I did a slow speed pass at very low altitude and fire walled the motor. As I suspected it did a hard left nose over and went into the grass. My thinking is that this is caused by motor torque, basically I think I am trying to get airborne to quick. Am I thinking in the right direction?? Thanks for any input.

Steve

[xviper]

I have a 1700mm FMS Corsair that did the same thing. Quite a few of these 1400mm and bigger warbirds have this tendency. When you have such a short runway, you usually have to "floor" it to get it off the ground before you run out of ground. These things almost always roll left and drop. I said "did" the same thing because I now instinctively apply some right aileron when rolling, apply some right rudder as the plane gets light and as soon as the plane lifts off, I try to NOT climb very fast so that the plane gains some airspeed. At this critical point in the take off, it can stall very easily, especially if it's rolling. It's better to counter the roll, skim the ground and keep the power on (IF YOU CAN). There is a natural tendency to back off the throttle when we see our plane heading for dirt.
Oh, and my 1450mm FMS P-51 used to do the same thing.

[msdt74]

I have a 1700mm FMS Corsair that did the same thing. Quite a few of these 1400mm and bigger warbirds have this tendency. When you have such a short runway, you usually have to "floor" it to get it off the ground before you run out of ground. These things almost always roll left and drop. I said "did" the same thing because I now instinctively apply some right aileron when rolling, apply some right rudder as the plane gets light and as soon as the plane lifts off, I try to NOT climb very fast so that the plane gains some airspeed. At this critical point in the take off, it can stall very easily, especially if it's rolling. It's better to counter the roll, skim the ground and keep the power on (IF YOU CAN). There is a natural tendency to back off the throttle when we see our plane heading for dirt.
Oh, and my 1450mm FMS P-51 used to do the same thing.

Thanks for the input! Its a private flying field right by my house. Other side has plenty of room for a "normal" take off. When this new wing comes in, my plan is to use that side to see if I am correct. Normal, tail up, roll out, slow lift off, then gas it once I have plenty of air and room to correct it. I think that is the problem, because, like I said, I have no problem with the 1100mm and 1200mm P51.

[xviper]

Thanks for the input! Its a private flying field right by my house. Other side has plenty of room for a "normal" take off. When this new wing comes in, my plan is to use that side to see if I am correct. Normal, tail up, roll out, slow lift off, then gas it once I have plenty of air and room to correct it. I think that is the problem, because, like I said, I have no problem with the 1100mm and 1200mm P51.

IMO, I believe this to be the biggest mistake. With these bigger warbirds, it's not just the torque that presents the problem, BUT rather, it's the sudden change of rpm that pours on the torque quickly when the plane can't handle it (low airspeed). Try this experiment and see for yourself. Hold the plane securely in your hands with the prop pointed away from you and everyone else. Have another flyer (not a non-flyer) briskly increase throttle to over half. Feel the torque. However, once the motor has reached it's higher rpm, the torque roll effect subsides even though the motor is still running very fast. My technique for getting off the grass quickly is to keep the tail on the ground and do a 3-point lift off. This accomplishes two things. 1. It keeps the big prop from mowing grass and possibly upending the plane. 2. It keeps this nose up attitude so that it will only take off once the airspeed is sufficient to initiate lift.
So, I keep full UP elevator from the start. Use heavy throttle to get the plane moving on the grass. Once moving, I increase throttle briskly, but not suddenly and not slowly. By the time the plane begins to lift off, I'm at about 3/4 throttle or more. This is also done with some right aileron stick and slight right rudder. As soon as the plane begins to lift, I neutralize the AIL and RUD sticks as needed to keep the wings level. Additionally, I'm letting off on the UP elevator so it doesn't climb right away but skims a few feet over the ground. Once it's got good airspeed, climb out and up comes the gear and flaps. If you're flying off short, smooth grass or a paved runway with good distance, you can lift that tail up all you like while rolling and build up speed the way you want.

[Alpha]

Your flying surfaces need to be flying before they can... well... fly. Insufficient airspeed will deprive your flying surfaces of authority, leaving the aircraft slave other forces, most notably the torque (P-factor) generated by the prop. As Xviper said, there's a threshold for every model that you'll need to explore and become comfortable with, below which the model will stall and above which you're inviting a stalled wing on takeoff. Find the sweet spot for your model, ideally on a paved surface to rule out rolling resistance caused by grass.

Ultimately, models cannot choose the surface from which they're flown, and the fixed size of their wheels, wing loading, etc mean We are the only variable variable.

Have fun!

[Aros]

Yep Alpha and xviper are correct. Get her up to speed so those control surfaces can do their jobs. But the best advice I heard was have fun!

[TiredIronGRB]

Like others have said, longer roll out...use some up elevator and rudder to keep it straight until you get enough speed to rotate.

[msdt74]

Thanks for all of the input. New wing should be here tomorrow......and as ya'll confirmed.....build up my speed and a longer roll out. Thanks again!

[F22trainer]

Actually torque and p-factor are not the same thing. There are 4 things at work with a rapid increase in power.
1.) Torque - acts in the direction of roll and opposite the rotation of the propeller.
2.) P-factor - is the descending propeller blades have a higher angle of attack than the ascending blade. Acts in the direction of yaw.
3.) Gyroscopic Precessions - come from a changing longitudinal axis, resulting in a force acting 90* to the direction of the applied force. With tail dragging aircraft that is more noticeable due to the downforce applied for a climb.
4.) Spiraling slipstream- the rotating propeller creates a stream of air with a circular flow, which pushes the tail left in airplanes with a clockwise rotating propeller.
:Cool: