Maximum fall speed of a helicopter with disabled rotors

[Svenestron]

Hello,

Does somebody know the maximum falling speed of a heli like a bell222, with engine off and disabled rotors? If I have this variable I can calculate the air resistance for the heli flight simulator I'm making...

Regards,
Nathaniel

I think he is actually going for the "free-fall" velocity..
If you return, Nathaniel, it is exactly 348,582km/h. I just had a 222 dropped from 18.000ft to verify it for you..

[henra]

Originally Posted by Woolf

I'm not sure if any of the helicopter manufacturers publish such data but in any case it would really depend on which way the airstream is hitting the fuselage.

Exactly. And this is the big unknown.
If the Helicopter would shed its entire head I would expect it to go down Nose first.
For that particular case one could do a very rough guestimate which should give you an idea.

Let's try it for fun's sake:
Let's assume the helicopter weight is 3000kg. (Moderately loaded B222).
Frontal area ~5 m^2.
cw I don't know for a B222 but let's take 0.2 (Slender geometry).
Altitude close to Sea Level (Rho=1,2kg/m^3)
So let's see: gravitational force: Fg = 3000kg x 9,81 m/s^2 = 29430 N
drag force: Fd = Rho/2 x cw x A x v^2
Terminal velocity means drag force equal to gravitational force, i.e.
v=sqrt(29430N x 2/(Rho x cw x A) = 220 m/s or 42000 fps, i.e. ~ 440kts.
That's indeed eye watering.
But it's pure theory.

In reality it is likely to rather tumble to some extent so effective RoD will be less even when shedding the entire Rotor assy.
If the rotor is still on the heli and just fully stalled and thus stationary the attitude is even much harder to predict. but it will likely be much more flat with much more drag, so not nearly as fast.

[Soave_Pilot]

Are u serious there is tpoic about this? This dude must be bored as hell!

[eagle555]

Thanks for the replies

It's not about the specific attitude of the helicopter. I'm calculation air resistance for each surface (top,front,back,bottom) with local speed for that surface. I need to know the estimated speed if the fuselage is straight and the nose pitch at 0 degrees horizon. With the rotors not turning (disengaged).

[eagle555]

I think a helicopter would fall faster because it has more weight in volume. And it's the air resistance that slows down the object. F = M X A, A higher weight means more force is needed to stop it's direction...