Quick question about prop aircraft

[Broadsword2004]

Okay, this question is just off of a basic thing about helicopters that I was thinking of in regards to single-engine prop aircraft. I am not sure, so anyways, with a helicopter, a counteracting rotor is needed to keep the helo from spinning out of control, since the engine turning the rotor in one direction causes the fuselage to turn in the opposite direction (Newton's law).

So anyhow, does the same thing apply to single-engine prop aircraft (i.e. the engine turns the propeller in one direction, so the fuselage tries to turn in the other direction)?

Or does it "try" to turn the fuselage, but since the aircraft only gets airborn once it is moving at a forward speed, does the wind on the wings prevent this?

The reason I ask is because I've heard that powerful enough aircraft (like certain aerobatics planes) can "hang" on their prop, so if they can do that, without turning in a circle opposite that of their propeller, is there something that prevents the engine from turning the plane around?

Oh, and BTW, I hadn't noticed the Apache thread got expanded on, so thanks for info on the rolls (aerilon roll, barrel roll, and the videos).

 

[x-wing]

it ends up causing a left turning tendency, but on some aircrafts they make the angle of attack on one wing higher than the other to counter the turning.

 

[handjive]

I've never heard of different AOA's on the wing (although it is certainly possible), but they do engineer in things to counter the twist. For example, the T-34 has asymetrical elevator trim and has a slight twist in the engine exhaust nozzels. However, anyone that has flown the TorMentor can testify on the amount of rudder required when making drastic power changes at slow speeds. At higher speeds, the trim becomes more effective.

In regards to helicopters, you also have to realize the incredible difference in mass and moment arm of the turning blades compared to a prop. Torque is force X distance, so the length of the blades make a big difference.

Most of the planes that I have seem that "hang" on their props only do it momentarily, so lateral control is not really an issue.

 

[SteveG75]

Vertical stabs can also be offset to counteract the propwash. The Bf-109 had this. Generally, rudder trim will depend on throttle setting.

Also, do a little research on torque roll and high performance fighters such as F4U and F8F. It very possible for a ham fisted pilot to flip an aircraft on its back by applying full throttle too fast while executing a waveoff at the boat.

 

[Fly Navy]

Widow makers. Ensign killers.

 

[Schnugg]

In single engine aircraft we call that torque force P-factor.

Below is from a google search...can't vouch for the exact techincal aspects.

P-Factor is an aerodynamic effect that causes propellor-driven planes to yaw when they are flown at high power and low speed (takeoff and climbout, for example.)


At low speeds, the plane flies at a substantial angle of attack, and so the airflow is not parallel to the plane's axis. Relative to the plane, the airflow is directed several degrees upwards. Now the prop axis is normally parallel to the plane's axis. As the prop rotates, on one side the blades are travelling upwards and on the other side they are travelling downwards. (On most planes, the prop turns clockwise, as seen from behind, so the left side goes up and the right side goes down.)

The upwards angle of the airflow causes the downward (right) side of the prop to have a greater airspeed and angle of attack than the upward (left) side. So the downward (right) side of the prop generates more thrust. Pull harder on the right side of the plane than on the left and the plane will yaw to the left.

This is one of the reasons why most real prop planes need a certain amount of right rudder to keep them straight during takeoff and climbout.

The other factor that requires right rudder on takeoff (in planes with clockwise props) is spiral propwash. The sideways component of the spiral propwash strikes the vertical stabilizer from the left (in conventional single engine configurations), also causing a yaw to the left. In general, the spiral propwash effect is a lot stronger than P-factor. You also need right aileron to keep the plane straight to counteract the rotational torque from the engine(s).

 

[Broadsword2004]

I see, thanks for the info.

 

[VarmintShooter]

Not to be difficult Schnugg, but I don't think that torque and P-Factor are the same thing.

P-Factor results (basically) from the upward moving prop blades taking less of a 'bite' out of the air than the downward moving blades, as the web excerpt suggests. This is due to the fact that the rushing air does not travel exactly perpendicular to the motion of the prop.

P-factor results in a yawing moment.


Torque on the other hand has to do with trying to rotate the propeller. For example, torque effects can be seen in space (no atmosphere) if an astronaut attempts to rotate a heavy object (whichever is lighter of the object and the astronaut will rotate faster), while P-factor does not exist in space (no air).

Torque results in a rolling moment.


I know it's picky, I'll go back to my corner now ...

 

[Schnugg]

No worries, good comment. Most likely you're right. For the newbies, it does get that specific when you're in flight school.

r/
G

 

[Fly Navy]

Thank God for jets.