Maximum fall speed of a helicopter with disabled rotors

[eagle555]

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

[SASless]

Take a set of streamlined car keys and drop them......that would be pretty close I think!

[Hummingfrog]

The Vmax of a falling human body is about 120mph or 10560ft/min so a helicopter with rotors stopped will fall at around that speed assuming it falls from a height which allows it to reach terminal velocity.

HF

[ShyTorque]

120 mph for a human meat bomb, yes - but terminal velocity of a falling object varies with the individual item being dropped.

For example, Barnes Wallis designed a streamlined bomb that was designed to reach supersonic speed in free fall from 40,000 feet (it didn't because there was no suitable aircraft to lift it high enough to accelerate for long enough).

But even 120 mph with the rotors stopped will make the pilot's eyes water. :{

[SASless]

Would not most any velocity normally achieved in a rotors stopped free fall event be considered "terminal"?

[farsouth]

Be kind to the guy - he is obviously not a pilot and English may not be his first language. I would guess his question is really referring to autorotation (disabled rotors = disengaged rotors = autorotating ??? - he did not say "Rotors stopped")

I don't have a figure for Bell 222 but would guess at around 2 500 feet per minute in a stabilised auto ??? Sure someone will give you a more accurate figure:)

[SASless]

That would make better sense than what most of us thought he meant. Someone with a 222 or 230 manual handy?

[IFMU]

One test is worth 1000 expert opinions.

IFMU

[heli-cal]

But even 120 mph with the rotors stopped will make the pilot's eyes water.

I can assure you that in this scenario, the pilot wouldn't be in the least bit concerned about moist eyes... :{

[Flying Binghi]

eagle555 if yer a computer person there must be other flight sims around with a bell222 that you can get the numbers from ?






.

[griffothefog]

He must work for the Sun newspaper....;)

[ShyTorque]

One test is worth 1000 expert opinions.

Yes, any volunteers? Not me, I've got a bad leg. :p

[SASless]

Most Bell 206 comments i found doing a google search shows about an average 1800 Feet Per Minute Rate of Descent.

I would guess.....for the 222 it would be from about 1600-2500 fpm depending upon collective setting and main rotor RPM.

[Woolf]

I don't think he/she is asking for rate of descent in autorotation. My guess is that the question refers to helicopter drag (air resistance), in particular the drag created by the airframe shape itself. 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.

[farsouth]

Eagle555 - Nathaniel. Help us out here - can you make it clearer exactly what you are trying to find out

[SASless]

His initial question....which we should interpret as being authoritative descent rate....and from that ....he can do his calculations.

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...

[Colibri49]

"authoritative" ???

[SASless]

Awlrite......"a u t o r o t a t i v e".....down to one eye right now and sometimes I don't see what i actually typed....old age and Cataracts!:{

[ShyTorque]

Those predictive text brains are not always so user friendly... ;)

[Senior Pilot]

Eagle555 - Nathaniel. Help us out here - can you make it clearer exactly what you are trying to find out

He took 8 days before he returned to another forum for the replies to his query: he signed off from Rotorheads 1 minute after asking here, and hasn't been back since.

In the meantime you are talking to each other, as is so often the case with newbies who visit once in a blue moon and don't have the courtesy to return and acknowledge the advice they have sought :ugh:

[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]

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!:ok:

[eagle555]

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...