The P-Factor Ballet :)

[Anatoli-Kagari9]

Now that I have finally started to understand why my Bf109 wants to pitch up when, from level flight but with a sideslip to the left I add right rudder to coordinate, or whenever I add right rudder when flying Straight & Level, I believe I finally also understood why sometimes I noticed a dance of the p51d nose when falling from the skies, my engine broken and even with the prop frozen....

 

Sometime ago, when the p51d was the only flyable prop aircraft available for DCS World, whenever my engine got broken, and even the prop got stop frozen, I pitched down ( almost 90º ) to pick speed and head towards the closest landing site... Sometimes I noticed the nose "designing" a circular movement, and never really understood it very well...

 

Then, from flight school, most of us learn that P-Fcator is a rather secondary effect, only affecting aircraft at high power and low speed situations, for instance during takeoff, and specially taildraggeers where the prop disk does show a much more pronnounced angle to the relative wind during the initial takeoff run...

 

But, some good books and aerodynamic sources, like for instance "See how it Flies" that I refer many times at the forums, specially at the end of the section named "8 Yaw-wise Torque Budget" shows a diferente reality, and even ends now in the revised version with a reference to a subject that was discussed at the forums sometime ago - why the rudder input required to fly coordinated in na aerobatic aircraft switches from right to left when we transit from flying upside to inverted...

 

Well, I understand the cycle, cal it "P-factor cycle" and it goes... for a CW rotating prop...

 

- yaw right ---> pitch up

- pitch up ---> yaw left

- yaw left ---> pitch down

- pitch down ---> yaw right....

 

Curiously, if you follow the cycle, it "rotates" CCW for a CW rotating prop, and the way around...

 

I guess this kond of stuff can only be noticed on high power prop aircraft, but I wonder if any of you with RW experience on such types have had the chance to notice it.... Probably not, because of the many forces / moments that perturb na aircraft during it's flight IRL :-)

 

I also still wonder if the effect should be noticeable on a p51d diving at high speed with it's engine and prop stopped ? The prop blades although static still act as "wings" generating asymmetric lift but... could this cause that dancing ?

Edited December 16, 2014 by jcomm