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eye_spi t1_ixbh9w1 wrote

Reply to comment by DLBaker in When a military helicopter fires thousands of rounds while hovering still, does the operator have to slow the rotor to compensate for weight loss? by Legitimate-BurnerAcc

>If you're on the ground with one engine and a rolling liftoff is not available you won't get off the ground unless you jettison some or all your ammo.

How does a rolling lift off help a helicopter?

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TinKicker t1_ixcdm9q wrote

It’s called “translational lift”.

By moving forward, clean (undisturbed) air begins flowing over the rotor blades, greatly increasing their efficiency.

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eye_spi t1_ixci2nw wrote

Thanks, that's a very clear explanation.

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GarbageTheClown t1_ixbozcq wrote

Rough guess is that in a hover you are fighting your own prop wash / ground effect, which would reduce lift.

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tim36272 t1_ixc5rzp wrote

The rotor acts as a wing in forward flight, providing some of the lift. That was actually wrong: it’s because the vertical speed of the “fresh” air you’re flying into during forward flight is 0 (in the absence of external forces) whereas in hover the air above and below the rotor is already moving down, thus it takes more energy to accelerate that air further.

Same reason it takes less power to fly forward than to hover.

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