Why do helicopters "chop"?

[lamarbur]

Re: Why do helicopters \"chop\"?

I went up in the first new Eurocopter that Mass state police bought. They are a far cry from the old baling wire and chewing gum kept together Hueys that I flew in..

 

[Tractors4u]

Re: Why do helicopters \"chop\"?

Eurocopter had the biggest display at the show and all the helis on display were already sold and were being delivered at or after the show. They unveiled there newest model the EC145. It was an Air Evac that I think was heading to Florida. It's November # was N911LZ. How appropriate, 911.

 

[AMP762]

Re: Why do helicopters \"chop\"?

In 69 they new crewchiefs that Hueys and bumble bee operate on the same principal, niether can fly /forums/images/graemlins/confused.gif
FYI that big fan on top is just for cooling
if it stops,everyone starts to sweat /forums/images/graemlins/crazy.gif

 

[RobS]

Re: Why do helicopters \"chop\"?

Fascinating, thanks Dave. We had a bunch of air handlers placed on our roof at work a year ago by helicopter. They did it on a Saturday and I took my sons over to watch. It was amazing to see the rotor blades flex so much as the load increased. The other thing I noticed was the long lenth of cable between the helicopter and the load. I suspect this was to keep the helicopter out of the rotor wash that occurs close to the ground?

Any RC helicopter pilots out there? That's another item on my "life list". I was watching a guy fly one several years ago. He aluded to how difficult it was to fly with this analogy: "It's like balancing three balls on top of each other, on the end of a stick, with you holding the stick". Sure was cool to watch /forums/images/graemlins/smile.gif

 

[dmartin88]

Re: Why do helicopters \"chop\"?

I just started flying RC helicopters at Christmas-- still very early in the learning stage and it is hard but a computer simulator program helps.

I can hover and fly forward but having a lot of trouble with the helicopter flying nose in to me-- all the controls are reversed and have to make all you movements the opposite of tail in.

Having said this, it's a lot of fun and very expensive- kind of like tractors!

 

[MossRoad]

Re: Why do helicopters \"chop\"?

<font color="blue"> I prefer helicopters to small planes anyday. Those things just scare me to death. </font>

Helicopter engine dies, you get one chance to land it just right in narrow cone beneath you. Airplane engine dies, hopefully you got some altitude, you can at least have a few seconds to look around for a place to glide in to. Also, aforementioned special J nut... yikes! /forums/images/graemlins/tongue.gif

 

[Bird]

Re: Why do helicopters \"chop\"?

</font><font color="blue" class="small">( I would also add that I prefer helicopters to small planes anyday. Those things just scare me to death. )</font>

I'm just the opposite. Helicopters are fun, but small planes are even more fun to me, and I feel safer in a small plane. Flying a new Cessna 152 from the factory in Wichita, KS to Anchorage, AK in 4 days with my brother was one of the most fun trips I ever made.

Maybe I feel safer in a small plane because, though I never got a pilot's license, I've had a few lessons and handled the controls on both helicopters and small planes and feel fairly confident that I could get a small plane on the ground and walk away from it if I had to, but I'm not so sure about an egg beater. /forums/images/graemlins/wink.gif /forums/images/graemlins/laugh.gif

 

[TWINKLE_TOES]

Re: Why do helicopters \"chop\"?

Watch the copter over your left shoulder when you are flying towards you.

 

[MossRoad]

Re: Why do helicopters \"chop\"?

I saw a guy autorotate a bell jet ranger down hard on the end of a taxi way once after his engine lost power. He was white as a corpse and had to change his pants. I'm not making fun of the guy, either. He lived. A lesser pilot might not have. /forums/images/graemlins/shocked.gif Bent the heck out of the skids. It was bow legged after that landing. I'm surprised the rotor didn't smack the ground. I also saw the aftermath of a state police car that drove up too close to a jet ranger while it was running. The big whip antenna was promtly removed from the cruiser and sent a hundred yards through a hangar wall and into a small two seater inside the hangar. Helicopters are fun. What a weird feeling going straight up, back, sideways, etc.... but I still prefer a small plane. /forums/images/graemlins/laugh.gif

 

[RobS]

Re: Why do helicopters \"chop\"?

OK, for some reason my mind won't let this go...

If the chop is a blade related phenomena wouldn't it still be a steady state thing rather than say, a once per rotation event? For a constant pitch, the airflow should be relatively constant (neglecting turbulance) and shock waves produced would be constant throughout a revolution. This would account for a steady sound but not the chop, or discontinuous sound.

So that brings us to the variable pitch of a helicopter blade. To produce directional thrust the pitch is varied through the swashplate mechanism. The pitch will vary through a single revolution thus the shock waves will vary through that same revolution. I can see how this would produce the unsteady chop sound.

Using the same theory, a helicopter in neutral flight may not produce the chop as the pitch is constant throughout a revolution. I haven't paid that much attention but it does seem that a helicopter at "idle" is much quieter.

So, does any of this make sense? Also, can you tell our weather is still not suitable for tractoring? Fear not, by this weekend I'll be on the tractor working on a retaining wall project even if it's raining /forums/images/graemlins/smile.gif