I’ve been busy t’day visiting back n’ forth with long-time aviation pal, Captain Ernie Lingren. We share a lot of common interests having joined the original Frontier Airlines within a few months of one-another.
The subject of the mystique that shrouded the venerable North American P-51 ‘Mustang’ came up. This led me on a trip down memory lane. So, I thought I would share a Nazy story with you.
Ernie, suggested that I should write a book. Here’s my reply:
Nazy had a lot of money. He didn’t always have money. Born in South Africa, Nazy came to America from Canada with few dollars. He worked hard and he was smart. He was a very sharp businessman.
“The misunderstanding of an un-commanded left roll appears to be widespread. It is hoped that the following information will promote thought and understanding and maybe help prevent another loss of control P-51 accident.
Engine torque at maximum power is not sufficient to torque roll the P-51D to the left during a go-around if the pilot does not allow the left wing to stall and maintains heading with the rudder and wings level with the ailerons.
An un-commanded left roll can occur if the pilot does not control yaw with the rudder. However, the roll is primarily caused by yaw-roll coupling and stalling the left wing, not torque.
The Mustang will not roll out of control to the left without first stalling the left wing. At airspeeds slightly above stalling speed, the Mustang has enough right roll authority to prevent an un-commanded left roll. Furthermore, at airspeeds slightly above stalling speed, with maximum engine power, the P-51D has enough right roll authority to perform a 360-degree right roll even with the flaps and landing gear fully extended.
The ascending propeller blades redirect the relative wind upward ahead of the left wing. The redirected relative wind increases the angle of attack over the left wing during high power settings. If the wing is already near the critical angle of attack, the additional angle of attack induced by the propeller slipstream can cause the inboard section of the left wing to stall and allow an un-commanded left roll to ensue.
The inboard portion of the wing behind the propeller stalls first. When the left wing stalls behind the ascending propeller blades, the un-commanded left roll begins. The angle of attack near the wingtip increases as the un-commanded roll progresses. The increase in angle of attack near the left wingtip results primarily from the induced relative wind opposite to the downward movement of the wingtip. The rate of roll increases dramatically when the critical angle of attack is exceeded near the left wingtip.
The Mustang has a pronounced pitch-up characteristic following a landing bounce. If the pilot does not take prompt corrective action, the nose may continue to pitch-up. When the nose has pitched up to the point that a stall is imminent, the application of power and the associated increased angle of attack induced by the propeller slipstream can stall the left wing.
Yaw-roll coupling, i.e. nose yaws left and left wing loses some lift, can cause an un-commanded left roll. The pilot must prevent the left yaw of the aircraft with right rudder to prevent an out of control left roll during a go-around. Asymmetric propeller thrust and other propeller factors cause the left yaw. The left yaw spoils some left wing lift and initiates the un-commanded left roll and the roll can stall the wing.
It is extremely important to reduce the angle of attack during a bounce recovery and go-around by lowering the aircraft nose. A reduction in angle of attack and the application of right rudder proportionate to the amount of power applied is essential to provide an acceptable margin of safety.
A nose high deck angle during a go-around and failure to maintain heading with the rudder during a go-around are ingredients for disaster.
Managing angle of attack, i.e. deck angle and maintaining heading with the rudder during a go-around or bounced landing recovery is crucial. It is much more important than the amount of power applied. The amount of power that can safely be used during a go-around is somewhat proportional to how skillfully the pilot controls angle of attack with the elevator and heading with the rudder. Of course, judicious use of engine power is recommended.
While we are discussing “torque” it may be good to talk about tire wear. Say what? Some folks say that the P-51 has so much torque that it causes the left main landing gear tire to wear faster than the right tire. It makes a good story, but the very small amount of extra weight on the left tire during takeoff, produced by torque, contributes very little to tire wear. Actually, deflection of the rudder to the right during takeoff, not torque, produces a horizontal left force on the aircraft. This left force, sometimes called translating tendency, causes more slippage and more wear on the left tire.
Many Mustang pilots have lost directional control during takeoff, swerved to the left and ran off the side of the runway. Again, torque is most often blamed. In almost all cases, the cause of the left swerve was gyroscopic precession, not torque. Gyroscopic precession is proportional to the rate of pitch change during transition from a three-point attitude to a tail up attitude. Pilots sometimes raise the tail too rapidly in an effort to see the runway over the aircraft nose and gyroscopic precession yaws the nose to the left with great enthusiasm! At that point, the pilot may have a great view of the runway out the right side of the canopy. Pilots who accept the lack of visibility over the aircraft nose until the tail has been raised very gradually do not have problems with gyroscopic precession. In fact, with no crosswind, a knowledgeable and skillful Mustang pilot can maintain runway heading during takeoff by varying the rate of pitch change and with almost no rudder pedal input at all. If the tail is raised slowly enough, the normal right rudder trim may yaw the nose to the right. Raising the tail a little more rapidly will compensate and yaw the nose to left. Reducing the rate that the tail is raised may allow the right rudder trim do the work for the pilot and bring the nose back to the right.
Understanding characteristic FACTS about this honest, wonderful airplane is essential to flying it safely, but much of what we hear about torque and “torque rolls” is FICTION.”