climbing under power.

[omega blood]

I saw in an other thread that some models are designed to climb under power.I thought this was a bad thing and was why you added down thrust so the plane wouldn't balloon. Why would you want this in a model and what type of model would you put this in? I'm building a curtis jenny and the plans make NO mention of thrust angle. The plans call for a 2 degree pos. incidence on the top wing. Is this a case for wanting the plane to climb under power and why?

Here is another example the wattage sukoi and sporty. Almost the same plane the sporty has down/right thrust and the sukoi has none. Why?

[Quacker]

Hi omega blood,

It's not so much the climb as the pitch up when throttle is added or down when it's removed that is such a disturbance. Looking at a high-wing model from the side, it's easy to see that the center of thrust (the prop axle) is below the center of drag (the wing). When power is applied there is s strong tendency for the nose to rotate up around the center of drag. This makes sense. Adding some down thrust compensates for this annoying force. A low wing aircraft needs little or no down-thrust because opposite forces exist, tending to lower the nose when power is applied. Even if the pitch of the nose remains the same, there will be an increase in lift causing climb. This can be a problem in an aerobatic craft so a little added down-thrust is a good thing. A biplane usually has a wing above and below the thrust line. This helps balance the force and may explain why yours does not call for the offset. Side thrust compensates for torque. A little offset in the way the rudder is built can go a long way toward correcting it. I don't know the Sukoi and Sporty, but if you study them, you may find the rudder compensation is built into one of them.

Regards,
Q

[Sparky Paul]

If the plane won't climb under power, how can it take off, or climb at all?

[omega blood]

Thanks Quaker that clears it up and answers a lot of other questions. :)

[Majortomski]

"Side thrust compensates for torque. "


AAARRRGGGGHHHHH!!!!!!

It compensates for P factor not torque!!! ONLY ailerons can compensate for torque!:rolleyes:

[Sail 'n Soar]

P Factor?

[Quacker]

If a plane has dihedral, the rudder can compensate for torque, and so can side-thrust.

Q

[Ninjak2k]

P factor is the prop wash striking one side of the rudder - think of the prop wash as a corkscrewing motion with the stream corkscrewing right into the side of the rudder. This causes the plane to yaw.

Torque is caused by the engine and is related to the force of spinning the prop. I'm not sure how side thrust would affect torque as the same amount of torque is generated by the engine in any position.

Cheers,
Dan

[Quacker]

Anything that yaws a wing with dihedral will cause a rolling force due to uneven lift (forward wing has increased angle of attack, etc.). Thus, side thrust or rudder offset can be used to cause a roll force that counteracts torque.

Q

[omega blood]

Originally posted by Quacker
Anything that yaws a wing with dihedral will cause a rolling force due to uneven lift (forward wing has increased angle of attack, etc.). Thus, side thrust or rudder offset can be used to cause a roll force that counteracts torque.

Q

This is true, I've seen it.