Crashing Helicopters

goofball · #1 07-02-2005, 11:17 AM

I've never seen a helicopter crash in person or even on TV for real, but I've seen them in movies/TV shows, and here's what always seems to happen.

The rear propellor is blown off (the one that counters the spin from the top one) and the helicopter slowly spins as it crashes to the ground.

Here's my question:

I know why it spins, that's simple physics. But, why does it have to crash to the ground? The top propellor is still working, that's the one that provides the lift. I see no reason that the helicopter can't hold or even gain altitude.

Where have I gone wrong?

vulturesrow · #2 07-02-2005, 06:56 PM

You are basically right in that it wont necessarily make the helicopter crash. However there also no reason to keep trying to fly the thing. Also if the transmission fluid line is broken than you are going to be out of fluid soon and then your main rotor is going to be useless as well. So while it may not lead directly to a crash, the pilot is not going to try and keep flying if he can land it right there.

FNHinVA · #3 07-02-2005, 07:54 PM

When the main body of the craft starts spinning (in the same direction as the blades), the air speed of the chopper's blades (effectively, wings) is slowed because the engine is turning more weight (the entire craft). Since blade airspeed is a fairly delicate balancing act with gravity, the chopper is doomed without the rear prop to counter the spin.

It sure sounds like I know what I'm talking about but I don't. I'm guessing.

vulturesrow · #4 07-02-2005, 08:03 PM

[ QUOTE ]
When the main body of the craft starts spinning (in the same direction as the blades), the air speed of the chopper's blades (effectively, wings) is slowed because the engine is turning more weight (the entire craft). Since blade airspeed is a fairly delicate balancing act with gravity, the chopper is doomed without the rear prop to counter the spin.

It sure sounds like I know what I'm talking about but I don't. I'm guessing.

[/ QUOTE ]

You may be right. My experience is all with fixed wing aircraft. I'll have to ask one my buddies that flies helicopters the next time I talk to one. At any rate, with the tail rotor gone, most helicopters are essentially unflyable even if they dont immediately crash.

SmileyEH · #5 07-02-2005, 08:07 PM

You could only really control altitude without the rear prop. Pitch, and yaw is justing going to [censored] you. I'm sure all the pilots when this happen can think only of getting onto ground as quickly as possible.

-SmileyEH

vulturesrow · #6 07-02-2005, 08:13 PM

[ QUOTE ]
You could only really control altitude without the rear prop. Pitch, and yaw is justing going to [censored] you. I'm sure all the pilots when this happen can think only of getting onto ground as quickly as possible.

-SmileyEH

[/ QUOTE ]

I may be wrong, but I think the Apache is still flyable with a damaged/missing tail rotor. But other than that, I cant think of any others.

goofball · #7 07-02-2005, 09:14 PM

Ok, I understand what you all are saying. No reason it can't hold altitude but no reason to keep flying. However, in shows when they crash they always crash. They hit the ground with a decided lack of control, is this just theatrics?

(also, i'm pretty sure the body of the chopper would spin opposite the rotor)

FNHinVA · #8 07-02-2005, 10:07 PM

"(also, i'm pretty sure the body of the chopper would spin opposite the rotor)"

You are correct. Newton's third law: "For every action, there is an equal and opposite reaction." (duh!)

This actually does a better job of explaining the chopper's descent. When the counter force of the rear prop is eliminated and the body of the craft begins spinning opposite the lifting blades, the force spinning the body is essentially stolen from the force spinning the blades and lowers their air speed and lift. In other words, part of the total energy used to lift the chopper is now being wasted spinning the body of the craft.