Could you push a hovering helicopter?

[Velocity173]

I read your post here and think, damn, it's amazing those things fly. I didn't think of the tail rotor and the opposing force of the main rotor, that would probably make it pretty hard to push. A helicopter lesson or two may get added to my bucket list.

I've had a few rides now, the best was from Las Vegas to the Grand Canyon. I was seated in front for W and B purposes, but had controls for my seat. So I said to the pilot, you get us a few feet off the ground and I'll take over, what does this do? He looked at me with a little fear in his eyes and said you can't touch the controls. I had to assure him I was just kidding with him, that I was a pilot and would never touch anything unless told to. Almost got myself kicked out of the best aviation ride of my life.

Yep, the aircraft is basically a delicate balance of conflicting forces.

Take the hover for example, you’ll notice helicopters (counter clockwise rotors) hang left skid low. That’s because the tail rotor is producing thrust towards the right. You need that thrust towards the right to counteract the torque from the main rotor that wants to spin the nose right. Problem is, that tries to push the helicopter right (translating tendency). To counter translating tendency, the helicopter either has a left tilt in the mast or a mechanical mixing unit that automatically tilts the disk left. That tilt, plus the fact that the tail rotor thrust vector is rarely perfectly aligned with the main rotor lateral thrust vector, the result is a left skid/wheel low hover.

Now, throw in a tail rotor like a Black Hawk that has a 20 degree tilt in it and you have a whole new can of worms.

 

[Clark1961]

Now, throw in a tail rotor like a Black Hawk that has a 20 degree tilt in it and you have a whole new can of worms.

Why have a can of worms if you aren't fishing?

 

[Velocity173]

Why have a can of worms if you aren't fishing?

Well, can o worms as in problems. Problems as in a vertical thrust component that has to be countered by another component (main rotor / horz stab) in order to be stable.

 

[Clark1961]

Well, can o worms as in problems. Problems as in a vertical thrust component that has to be countered by another component (main rotor / horz stab) in order to be stable.

Humor, funny, chuckle, laugh....

 

[Zeldman]

We are going fishing now..????

 

[Sac Arrow]

The helicopter just won’t drift in a frictionless state after the application of force though. Just the air pressure alone will help stabilize it but the primary factor will be “blow back” from the rotor.

If a helicopter at a hover develops any momentum, the rotor will want to tilt past it’s previous position because of blow back. That is, the unequal lift that will occur on the advancing side of the blades as the helicopter moves over the ground. That unequal lift acts 90 degrees later (phase lag) and will tilt the rotor in the opposite direction of movement.

So, if a strong lateral force is applied that accelerates the aircraft to say 10 kts, the helicopter will oscillate a few times and come to a stationary hover again. Depending on the helicopter and if it has stability augmentation systems (SAS), the amount of oscillation will vary.

It’s also not sitting there afloat like a balloon. Just to stay at a hover you have one force (main rotor) opposing another force (tail rotor). There are some thrust variations that will occur in lateral movement that would oppose a push.

Years ago doing sling load quals in the Black Hawk, I was told you could grab a tire and push the entire aircraft. Didn’t know if they were pulling my leg or not but I never bothered to test the theory.

I would think that if you pushed the helicopter by its skid or wheel, it will want to pivot about point where the rotors connect, having the net effect of applying the cyclic in the opposite direction. Or probably more accurately 90 degrees from the pivoting force, considering the gyroscopics of the rotor.

 

[Clark1961]

We are going fishing now..????

Must catch square three ounce fish for Sac.

 

[Lachlan]

What if it was suspended by a string?
If you had a 747 hanging from a rope, surely I could grab a wing tip and make it spin.

What if you had soap on a rope, but you still dropped it?

 

[Velocity173]

I would think that if you pushed the helicopter by its skid or wheel, it will want to pivot about point where the rotors connect, having the net effect of applying the cyclic in the opposite direction. Or probably more accurately 90 degrees from the pivoting force, considering the gyroscopics of the rotor.

Yeah just depends on the amount of force I guess. Like Flymy47 commented on earlier, if you’re trying to pick up 6,000 lb cement block and you’re not aligned, it’s gonna align you. Pick up a 60 lb cement block and you’re not aligned, the aircraft won’t feel a thing.

So, whether or not a human could move a helicopter laterally, would depend on type aircraft. Personally, I think I could take a little Robbie by the skid and push it all over the ramp at a hover. Then again, there’s dynamic rollover...

 

[Palmpilot]

Actually, hang around places where they're flying hot air balloons. It takes a LOT of effort to move one of these things, once they're aloft. Remember, you're not only moving the mass of the basket, burner, occupants, etc, you're also moving the mass of the air inside the envelope.

Don't know how much of a ground crew the Goodyear folks use, but you can find historical video of dirigibles and see dozens of guys on the ground-handling ropes.

Ron Wanttaja

I would also expect a balloon to have a lot of drag.

 

[FormerHangie]

You'd have to sneak up on it from behind. Somehow I think if the pilot saw you pushing on the helicopter he might just push back, and you'd find out why those things are sometimes called "choppers".

 

[James331]

 

[NoHeat]

What if it was suspended by a string?
If you had a 747 hanging from a rope, surely I could grab a wing tip and make it spin.

Sure you can.

The rate at which you can spin it up (angular acceleration) is the torque you apply divided by the Boeing 747’s moment of inertia. Unfortunately the latter quantity is very big, like maybe fifty million lb ft^2, so this project will take some persistence.

By the way, what kind of rope will you use?

 

[PaulS]

Sure you can.

The rate at which you can spin it up (angular acceleration) is the torque you apply divided by the Boeing 747’s moment of inertia. Unfortunately the latter quantity is very big, like maybe fifty million lb ft^2, so this project will take some persistence.

By the way, what kind of rope will you use?

Old soap rope.

 

[Brad Smith]

Perhaps the government will do a $2,000,000 study to discover the effects of pushing on the skid of a hovering helicopter. It would include pushing left, right, up, down, forward and reverse. The results would be available in approximately 3 years.