A Find

At one time I saw a bunch of pictures of an airfield where P51 flight training for the ROK Air Force was taking place. Lots of Mustangs screwed into the ground upside down doing go arounds.

 

How difficult is it, to take off with a P-51 ? What else is required besides full power, holding the stick all the way back, and keeping it centered on the runway with rudder inputs ?

 

Your question brings to mind a number of physical effects when applying high power to rotating propeller blades. (I borrowed this from the internet because I'm just not that smart to explain it on my own.)

1) Propeller torque effect

Torque effect is the influence of engine torque on aircraft movement and control. It is generally exhibited as a left turning tendency in piston single engine propeller driven aircraft.

According to Newton's law, "for every action there is an equal and opposite reaction," such that the propeller, if turning clockwise (when viewed from the cockpit), imparts a tendency for the aircraft to rotate counterclockwise. Since most single engine aircraft have propellers rotating clockwise, they rotate to the left, pushing the left wing down.

Typically, the pilot is expected to counter this force through the control inputs. To counter the aircraft roll left, the pilot applies right aileron.

It is important to understand that torque is a movement about the roll axis. Aileron controls roll. Prop torque is not countered by moving the rudder or by setting rudder trim. It is countered by moving or trimming the aileron.

This correction induces adverse yaw, which is corrected by moving or trimming the rudder (right rudder).

On aircraft with contrarotating propellers (propellers that rotate in opposite directions) the torque from the two propellers cancel each other out, so that no compensation is needed.

2) P-Factor

P-factor is the term for asymmetric propeller loading, that causes the airplane to yaw to the left when at high angles of attack.

Assuming a clockwise rotating propeller it is caused by the descending right side of the propeller (as seen from the rear) having a higher angle of attack relative to the oncoming air, and thus generating a higher air flow and thrust than the ascending blade on the left side, which at the other hand will generate less airflow and thrust. This will move the propellers aerodynamic centre to the right of the planes centreline, thus inducing an increasing yaw moment to the left with increasing angle of attack or increasing power. With increasing airspeed and decreasing angle of attack less right rudder will be required to maintain coordinated flight.

This occurs only when the propeller is not meeting the oncoming airflow head-on, for example when an aircraft is moving down the runway at a nose-high attitude (in essence at high angle of attack), as is the case with tail-draggers. Aircraft with tricycle landing gear maintain a level attitude on the takeoff roll run, so there is little P-factor during takeoff roll until lift off.

When having a negative angle of attack the yaw moment will instead be to the right and and left rudder will be required to maintain coordinated flight. However negative angles of attack is rarely encountered in normal flight. In all cases, though, the effect is weaker than prop wash.
** The P-factor helped the Blohm & Voss BV-141 observation airplane to fly in a straight line. In terms of thrust vs drag asymmetry, the countering of induced yaw was a more complicated matter. At low airspeed, it was calculated to be mostly alleviated because of a phenomenon known as P-factor, while at normal airspeed it proved to be easily controlled with trim. Yes it was a real and it flew..

3) Gyroscopic Precession

This is the tendency of a spinning object to precess or move about its axis when disturbed by a force. The engine and propeller act as a big gyroscope. However, gyroscopic precession is likely to be minimal in a typical aircraft.

Gyroscopic precession is frequently confused with p-factor.

*The above conditions probably contributed to what my Dad witnessed back in the late 40's at the end of the local USAAC airfield "One a day in Tampa Bay"
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This was a factor in a couple of well-known midair disintegrations of Lockheed Electra airliners in the 1960 time frame. Weakened outboard nacelle structure would allow the propeller/engine combinations to wobble in this fashion if the aircraft was excited by an event such as clear-air turbulence. When the frequency of the wobbling equaled the harmonic frequency of the wing, the entire wing would flap until it failed - typically less than 20 seconds. The phenomenon was known as whirl-mode flutter. It was more likely in turboprops because of the large spinning mass of the engine.

Lockheed rotated all Electras through its Burbank plant and beefed up the wing and outboard nacelle structure at its own expense, and the problem never recurred, nor has it with the many Orions around the world designed with the same wing and engines.

 

Induction of terminal pucker factor.......

 

I guess P-51 pilots will not be impressed with my Super Decathlon checkout (sad face).

 

A tail dragger is a tail dragger. My first td was a Citabria with a 150 hp Lyc. Seems like that little bugger was always wanting to follow the left turn lane. The 51 wants to do the same thing, just quicker, so its heads up all the way. Line up on runway.Take off is mash on the brakes. 30 in manifold pressure. Let the engine stabelize. One last check of fuel and oil pressure. Drop left hand down and check flaps up. Touch rudder and elivator trim for take off. Friction lock on t quad. Hyd pressure and t handle in. controls unlocked and free. Check that the canopy is locked. One last quick look around cockpit. Release brakes and slowly advance throttle to 40-45 in MP and keep it straight. Ease up on stick until tail wheel lifts about 1 ft then back pressure.Airplane accilarates quickly..hopefully...squeeze in more throttle up to 55 in MP and the howling little monster should be flying. Reach down with left hand and gear handle up and adjust trim for climb out. Should be going through 130 miles now. Keep nose down til 180 mph and climb out. Take off in a 51 is parallel to sex but without the nagging. Great little airplane. If I had as much money as Bob Parks and could have any fighter it would be the Mustang. Whew...

 

my preference for tail draggers is a performance take off ( if memory serves ), fewer transitions to adjust for...

 

What is a "performance take-off"?
I can guess, but...

A description?

 

performance take off is like short filed take off or non paved runway take off,

I always had more than adequate power, couldn't afford the laundry bills if the plane needed a bounce or two :=)

 

I remember hearing about a P-51 owner who would start his takeoffs pointed 45 degrees off the runway heading... I don't know how many takeoffs he actually did, to tell the truth. Maybe one...