The effects of x-wind in ( powerful ) prop aircraft...

[Guest deleted@50488]

Guys,

 

among you I believe there are a few "operators" of RW powerful prop aircraft, so, I wonder if those could help in finding out more about an effect that was, until very recently, completely unknown to me...

 

- The effects of deflected propwash during takeoff, particularly with flaps, under a strong x-wind ( from the left for CW rotating props, from the right for CCW rotating props as some of the Russian fighters in BoS are... )

 

I also learned, from my RL ( glider pilot experience ) but also from years flying as a "co-pilot" of tug props, that a x-wind demands, as all of the aviation texts I have read point out, downwind rudder ( rudder opposite true x-wind component ) and aileron into the wind, to stay on the rw centerline, and keep the wings as level as possible as we get airborne...

 

Now, I've learned from my experience in another flight simulator, that when the x-wind component is strong ( let's say 12m/s or more ), from your left, on a CW rotating prop aircraft, the propwash deflected downwind will have an effect over the downwind wing and tail surfaces that can make, at least during the initial takeoff run, the aircraft "want to turn" it's nose downwind and even rise it's downwind ( starboard in this case ) wing, forcing the pilot to use left rudder ( into the wind ) and even aileron to the right, clearly opposing common sense on takeoffs under x-wind.

 

This means that under some circumstances, this deflected propwash effect can overcome the weathervaning tendency, at least during the initial stages of the takeoff run.

 

It depends also on the particular aircraft model, and the use of flaps on takeoff can magnify the effect.

 

Have you ever experienced this is BoS ?  Do you know about it from RL flying experience  ?

 

Any comments really welcomed ;-)

[unreasonable]

Experienced it? I can barely comprehend it! Actually after reading twice I think I get it.

 

"Un bon croquis vaut mieux qu'un long discours." Discuss.

[Guest deleted@50488]

@unreasonable:

 

It's an old subject at another forum... 

 

You can find here a sketch I made to explain it ...

 

http://forums.eagle.ru/showpost.php?p=2228726&postcount=3

[unreasonable]

 

Much easier! (Recycled picture....)

Edited July 22, 2015 by unreasonable

[Guest deleted@50488]

Thx a LOT unreasonable !

 

And, the "theory" behind this effect is based on the wash that the downwind wind and tail surfaces of the aircraft receive from the deflected propwash, creating that tendency to lift the downwind wing and also the yaw that counters the intuitive weathervane effect.

 

I still have some difficulties accepting that it can really account for a yaw away from the wind, requiring sometimes into wind rudder inputs! but I have a report of someone, from another forum, who had the chance to talk to a P51d pilot and he mentioned the effect as being real !

 

So far I was unable to reproduce it in BoS, but it's dificult, in the QMB, to set the wind and choose arw where it is blowing practically from left or right at 12 knot or more...

Edited July 22, 2015 by jcomm

[Dakpilot]

This tech demo shows effects of prop wash and other things

 

https://www.youtube.com/watch?v=o3tJlFsGRSE

 

Although from RoF and from 2010 the aero and physics model has only grown more sophisticated since then, I would be very surprised if the effect you are asking about is not modelled

 

anyway it's a cool vid if you are not familiar with it

 

Cheers Dakpilot

[Guest deleted@50488]

@Dakpilot:  Yep, I already knew about that video, and it was actually what made me buy RoF as well, although I don't even have it installed right now...

 

Thx anyway for the answer. I hope the effect is indeed modeled, and will keep testing and trying to find it's effects.