Why does it yaw right?

[kontiuka]

Maybe a noob question but why does the P-51 yaw right as it picks up speed? This is with a fixed RPM and manifold pressure. I know I have to apply left rudder trim before going into a dive in order to compensate but I'd like to understand the aerodynamic principle.

[Buzzles]

Try here for answers.

 

Also here.

[kontiuka]

Thanks. I took a look. Those explanations seems to explain left yaw. So, I'm still not clear what causes right yaw. I'm not banking so it's not adverse yaw. I'm just flying straight with constant MP and RPM.

[Merlin-27]

I believe the vertical fin of the P-51D is offset left (1 degree maybe) from the centerline as a design feature to counter the yawing tendencies of the aircraft. So, as more air flows around it, the greater the effect.

[kontiuka]

I believe the vertical fin of the P-51D is offset left (1 degree maybe) from the centerline as a design feature to counter the yawing tendencies of the aircraft. So, as more air flows around it, the greater the effect.

Would that cause a yaw to the right?

[Merlin-27]

Would that cause a yaw to the right?

 

Well if you think about the purpose of the vertical fin, it is to maintain directional stability. It wants to follow the path of least resistance (weathervane) and will be trying to move to that point and become parallel with the flight path. With it offset to the left it will cause the nose of the aircraft to move right.

[kontiuka]

Well if you think about the purpose of the vertical fin, it is to maintain directional stability. It wants to follow the path of least resistance (weathervane) and will be trying to move to that point and become parallel with the flight path. With it offset to the left it will cause the nose of the aircraft to move right.

So, you mean the leading edge of the vertical fin angles 1 degree to the left? In that case, ya I can see it causing right yaw.

[Anatoli-Kagari9]

Merlin already presented some good arguments.

 

Indeed, the default cant with which the p51 fin is assembled, and which is even visible in the remarkable 3d model in DCS, is there to help countering the prop effects at high power settings and / or high AoAs... When flight regime changes to reduced power, even idle, and descent / high speed descents, the purpose of that cant is no longer active, and indeed it starts creating the opposed effect of yawing, and due to yaw-roll coupling also rolling the aircraft Cw ( on a Cw rotating prop aircraft... )

 

Another effect that adds to this one is the "negative torque", because what is driving / pushing the prop on such descents is the airflow, and thus it transmits it's force to the manifold, and because of those strange ideas by that 17th Century guy named Newton, the opposing reaction will actually give you a right rolling moment which will add to the yaw-induced right roll caused by the canted vertical fin, asking for left aileron trim...

Edited April 12, 2015 by jcomm

[Blaze]

So, you mean the leading edge of the vertical fin angles 1 degree to the left?

 

Looks like one degree to the right, actually.

 

[Merlin-27]

[Ala13_ManOWar]

Maybe a noob question but why does the P-51 yaw right as it picks up speed? This is with a fixed RPM and manifold pressure. I know I have to apply left rudder trim before going into a dive in order to compensate but I'd like to understand the aerodynamic principle.

I think it's a mix of reasons. P factor when you lower your nose drives you to the right, but that's for a while. Also propwash as you get faster probably affects you less as it is "straighter". Uneven prop blades lift probably affects you as you lower your nose while diving. And governor tries to keep revs so coarse pitch makes lower propwash again and may be lower your engine torque. So a mix of everything, and may be more things I don't guess, makes you having overall less torque and as you were probably trimmed for a higher one you "feel" like drove to the right. My guess :smilewink:.

 

S!