Mooney tail

[carusoam]

Question for @M20Doc... does the Comanche have airleron/rudder interconnect...? ^^^^

question came up in the post above...

Best regards,

-a-

[Guest]

5 hours ago, PT20J said:

I understand, but that's why I compared the Mooney and Comanche -- because they are about as similar as two different airplanes can be. Similar airfoils, almost the same wing area, same MAC, same wingspan, dihedral within 1/2 degree, same forward sweep, essentially the same fuselage length.

Hmmm. I hadn't thought of that. Maybe that's one reason for adding the aileron rudder interconnect. I wonder if the Comanche has one?

Skip

Skip,

The 400, late model 260’s have rudder /aileron interconnected controls and some twins when modified by a Piper S/L and a Canadian AD, 180’s and 250’s do not.

Clarence

[Blue on Top]

@PT20J @carusoam @M20Doc  I would have guessed that, but ...

The lateral-directional regulation is .. ridiculous.  "Unreasonable" is probably a better word.  We (ASTM) is looking at a way to redefine the required testing … which will eliminate the need for rudder-aileron interconnects.  This is why I started that thread earlier.  Lateral-Directional stability by the way we test it is not necessarily good.  In fact a slightly unstable airplane is more controllable, which is what we want.  The original regulation was written to make sure the airplane could be flown home with any flight control disconnected.  In this case the rudder or aileron can be disconnected and the airplane can be flown to a runway.  Sweep and/or dihedral takes care of this normally.

BTW (and as a funny note), the new regulation states, "The airplane must have stability."  LOL .  What the hey?  Negative is "stability", too!  Also pitch phugoid mode doesn't need to be damped (positive) either.  Go figure! 

[0TreeLemur]

On 2/25/2020 at 9:50 PM, Blue on Top said:

@0TreeLemur and all.  These aerodynamics are actually a complicated subject (especially when talking about spin aerodynamics … it is not as easy as the books (so far) have stated, but we are getting closer with CFD … what one can trust of them.

On the simplest portion, the vertical flying with attached airflow, the most effective surface will be the one with the 25% chord most perpendicular to the airflow.

Spin characteristics and airflow are a completely different animal and depends on many, many other factors, such as: the horizontal surface - shape and location, the aft fuselage - shape, location, edges, etc., horizontal/rudder interface, fuselage/rudder interface, etc., etc, (meaning there's a lot more!  We have proven that the NASA formula for spin recovery is incorrect … or at least not complete.  This is why we are still required to spin the airplanes in all configurations.  We just don't know enough yet.

You are correct, aerodynamics of spins are very messy.   But, since we don't spin Mooney's intentionally , I'm not really thinking about the effect of forward-swept rudder on spin recovery.   It is much easier to make he case that at high angle of attack (e.g. landing flare) a forward swept rudder will have more effective area per unit deflection and length than an aft-swept rudder because the forward sweep minimizes spanwise flow.   That point is easy to make from geometric concerns, right?    Any data on that?

[Blue on Top]

14 hours ago, 0TreeLemur said:

1. It is much easier to make the case that at high angle of attack (e.g. landing flare) a forward swept vertical surface will have more effective area than an aft-swept surface because forward sweep decreases with increasing AOA and aft sweep increases with AOA.

@0TreeLemur  You can see how I slightly modified what you stated, but please use your own words to say this.

(additional information)  1. The vertical surface is more effective because the 25% chord line is more perpendicular to the oncoming airflow.

(additional point) 2. In addition, the rudder, which is also forward swept, is also more effective because when deflected, the airflow is forced downward into higher pressure and not upward and off the tip of the vertical surface.

I hope this makes more sense.  There are 2 reasons: 1) forward sweep being removed with increasing AOA on the entire vertical surface and 2) rudder hinge line forcing the incoming airflow down, into higher pressure (against its will).