P-factor and vibration at high angle of atack

[Dorsal]

I have been chasing down a few vibrations like reenforcing the lower cowl and securing the belly fabric which has made for smoother cruise. One small but noticeable vibration occurs only at high angle of attack which I am attributing to the asymmetrical loading of the prop (P-factor). Do others experience this during a steep climb?

[Dorsal]

Surely someone has an opinion on this?

[rosslr]

G'day Dorsal,

for the sake of letting know there are still people out in the ether I will respond! No, I don't experience that in a steep climb.
but I am interested in tracking down vibration sources. One interesting one I have been playing with is tyre pressure in the airstreaks - I was flying with 8lb in the them and felt a vibration - looked at the tyres and I could see them slightly distorting so I put 10lb in them on return and the vibration disappeared!?


good luch with tracking down the vibration - with differing engine and prop set ups I am guessing it will be hard to compare apples to apples.

cheers

ross

[Dorsal]

Thanks Ross, interesting observation on the tires. Various vibrations are inevitable but I would like to account for them where possible.
Anyone else observe an increase in vibration while in a steep climb?

Clearly the Beach Boys were not pilots, there is no such thing as a good vibration

[Slyfox]

sorry Dorsal, I can't help you. I on occasion will run flat prop and full speed and pull up hard and do about 1600 vertical with a nice smooth flight. what kind of prop do you have? I've done many a hammer heads with no ill effect. have done many turn back with a hard back pressure on the elevator at about 60mph with throttle, with no vibrations at all. I have done the same with no throttle and got a vibration or should I say a partial stall that was sort of rough but that was expected. still made the massive turn without falling out. ya, I know, maybe I should put smoke on my plane and be kyle.

[Dorsal]

Thats some aggressive flying, cool!
The vibrations I speak of are fairly subtle (no shuttering or shaking) and definitely related to AOA. I run a fixed pitch Warp Drive taper tip.

[PapuaPilot]

Have you checked your prop blade angles and prop balance?

[rv9ralph]

Wouldn't prop imbalance manifest itself at any AOA? Dorsal, I think Rossir may be onto something. If your wheels are starting to rotate at high angle of attack, that may cause the vibration. Next time you feel the vibration, push on the brakes. It could be the rotation of the wheels that is causing the vibration, I seem to think I have heard of that before.

Ralph

[Slyfox]

are you able to see your wheels or do you have the doors blocked on the bottoms. mine are clear and I can see the wheels if they are turning. mine also have a slight out of round but not too bad. on take off I generally hit the brakes, but than again with the p factor after take off I generally wobble a little when I do it. haha

one more thing, when I do my turn back I'm generally on a 90degree bank.

[Dorsal]

Good thought but wheels are still and stable at all points of flight. I believe P-factor should cause vibration similar to a slightly imbalanced prop as the descending blade is loaded differently the ascending one. Was hoping some others had observed this so can stop looking for the cause.

From an article on propeller dynamics

"P-factor also produces a vibration, because the loads on the propeller blades are constantly fluctuating. Three and four bladed propellers reduce the overall vibration due to P-factor."