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MSFS Double tail aircraft

Hi all,

I'm defining a flight model for an aircraft that has 2 vertical tails.
From what I understand from the SDK documentation, one can only define a single vertical tail.
I'm quiet new to this, so what is your common technique to get around that? I search the forum but no luck.

In order to get the same yawing moment I would define a single center tail with twice the size
But with the new MSFS flight physics, I understand that wing downwash/propwash/fuselage interaction are taken into account, so this could result in inaccurate behavior.

Any suggestion?

Thank you all.
In the past, I have created a Breguet Fauvette 905 which had a V tail, so you shoud create two rudders, each rudder will be defined by an empty, at this empty you associated one tail and two elevators, all theses elements will be the childs of this empty.
It is this empty which will be animated.

I am French people and I have some difficulties to explain it but :
for the elevators you should create 4 elevators:
- two are visibles and the others invisibles,
- two are visibles and "UP" steps together
- the others two were visibles for "DOWN" steps and the first invisibles

I will try to upload a MDL that I have created in 2015 if I find it.

Roy Holmes

Resource contributor
Normally, (ie pre MSFS), the model would have no effect on flight dynamics. You could make a box with no wings and it would fly according to the flight dynamics. In this case make your two Fins and rudders visible and have one rudder for flight dynamics purposes.
MSFS looks like it is different, but I'm no expert on that.
Normally, (ie pre MSFS), the model would have no effect on flight dynamics.
To the best of my knowledge, that is indeed the case with MSFS, too. (Even if marketing material might make you think otherwise.)

I assume @StellaEM is asking how to model it in the .cfg files (or perhaps even interactively in Aircraft Editor). I would do it with double the horizontal and vertical tail area compared to those of each tail of the actual aircraft. I.e. multiply the linear sizes of the actual tail surfaces by the square root of two.

Roy Holmes

Resource contributor
The pitch and yaw moments from elevator and rudder deflection have no area inputs in their computation. The moments are proportional to control surface deflection times a coefficient and the coefficient is independent of area. In fact you could have any number of surfaces of any size and it would change nothing. So for pitch you just need a reasonable value of=CMde R1541. There are other coefficients that play a part as well but my point is that area does not. For the elevator you need the following, values are just typical:
pitch_moment_delta_elevator =-3.60947
If you want a good guide to sim flight dynamics look for Flight Dynamics in Microsoft Flight Simulator Version 1 July 2012 by Yves Guillame.
The pitch and yaw moments from elevator and rudder deflection have no area inputs in their computation.
Umm, you mean that the size of an elevator or a rudder has no impact on how well it performs its function? Or something else?

Roy Holmes

Resource contributor
The effectiveness of all control surfaces, ailerons, elevators and rudders in the FSXA/P3D sim and earlier versions are a function of surface angular deflection and the appropriate coefficient. Same with flaps and speedbrakes. You choose the coefficient and the full deflection angle should come from what the actual airplane has. Clearly the pilot controls the deflection amount. Size should affect your choice of the value of the coefficient. Inertias will affect the onset times and rate of change of roll etc. In Prop planes you need to consider propwash effects, like giving a burst of power to get a tail-dragger to turn when on the ground. However there are no inputs for size in the calculations of control effectiveness. Area is used for lift calculations.
Merci @Lagaffe , as tml said my question was more about the flight dynamics. However thank you for the tip I'll keep that in mind when I'll come to animation.

Thank you for your answers. It may be the main difference between MSFS and FSX/P3D here. The MSFS SDK documentation says that it is now a surface base aerodynamics simulation. I am not sure what does it mean but I'll have a thorough read at the flight model physics page. The Yves Guillaume document looks really great but the .air file doesn't exist anymore.

When it comes to aircraft controls, SDK documentation tells to define at minimum the area, deflection, span, elasticity of the control surface.
I ran some tests with a single large tail, the aircraft looks balanced. At normal speeds, full rudder deflection can be compensated by full aileron deflection.

My aircraft has the engines mounted on the wings, both tails should encounter propwash. Which will not be the case with the single center rudder.
As for the fuselage interaction I'm still not sure how is this simulated.

I'll keep you updated guys, thank you very much!
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