How is this helicopter flying if the blades aren't spinning?

[BUFF]

typical chopper (don't know exact Mi-24 figure) main rotor RPM is 300-400 = ~5-6.67/s
but there are 5 blades on a Hind which gives you 5 chances of a blade being in the same place per rotation for each frame so 25-33 chances/ second.

typical camcorder fps ~29-30 so it's definitely in the right ball park nos. wise

[TeePee]

Another perspective.
Helicopters fly without power every day. It's called autorotating. The difference is they can't maintain altitude, but they are still flying.

But they have the blades spinning, and there is a reason for this. The helicopter uses it's forward motion to push against the inside part of the blade and make the blade spin. The outer part of the blade, turning, then provides lift. If you were to develop a helicopter which could fly without engine power, you'd want (and need!) the blades to turn, for this effect. The engine thrust would be directed backward to give you forward speed to drive the rotor disc, rather than downward, as the thrust from a turboshaft engine would not be nearly enough, even with the power turbine removed.

[BUFF]

If you were to develop a helicopter which could fly without engine power, you'd want (and need!) the blades to turn, for this effect. The engine thrust would be directed backward to give you forward speed to drive the rotor disc, rather than downward, as the thrust from a turboshaft engine would not be nearly enough, even with the power turbine removed.

you would then have a jet powered autogyro

[MaddAussie]

Another perspective.
Helicopters fly without power every day. It's called autorotating. The difference is they can't maintain altitude, but they are still flying.

But they have the blades spinning, and there is a reason for this. The helicopter uses it's forward motion to push against the inside part of the blade and make the blade spin. The outer part of the blade, turning, then provides lift. If you were to develop a helicopter which could fly without engine power, you'd want (and need!) the blades to turn, for this effect. The engine thrust would be directed backward to give you forward speed to drive the rotor disc, rather than downward, as the thrust from a turboshaft engine would not be nearly enough, even with the power turbine removed.

Nearest thing to this is an Autogyro think little nelly from You Only Live Twice

Edit: Beaten by Buff!!!

[YorkieBen]

They have this function as well. I think they started putting stub wings on helicopters for payload, and developed them into airfoils for speed increase.

You might be able to get a faster top speed by adding more blades to the main rotor, but I don't understand how, aerodynamically, the loss of lift from the wings could be contered by increasing lift from the rotors without the rotor drag increasing well beyond the drag the wings gave.

strange how the Britsh army Lynx, one of the fastest choppers in the world doesnt have them

as mentioned above its strange that this is not mentioned in any 'real' websites e.g. FAS etc

imo its a camera trick.

[Butuz]

I don't know whether its some kind of camera photoshop trick, or whether it's just a freak of rame rate and rotor speed but those rotors are certainly spinning at up to 500rpm - and the tail blades usually spin at 2-3x the main rotor speed so 1000-1500rpm.

As for the rotors changing in speed slightly, thats normal as even though the throttle is automatically gouverned to keep the rotors at constant RPM - its impossible to govern the rotor speed preciceley enough to achieve say a constant 473rpm - as you add more pitch, or less, the rotor speed will vary slightly, which in this context is enough to make the blades look like they are moving back and fore slightly.

The "wings" add a small amount of vertical lift but only at fast forward flying speeds. They certainly wouldnt be giving any lift in those hovering / slow aerobatic passes in those videos.

Interesting video, and thread!

Butuz

[Butuz]

Another perspective.
Helicopters fly without power every day. It's called autorotating. The difference is they can't maintain altitude, but they are still flying.

You also need to add negative pitch if possible (some helis can apply negative pitch, some can't). If you add negative pitch as your autorotating then the air effect of basically falling out of the sky will actually keep your rotors spinning fast enough for you to be able to land in a controlled manner.

One thing you do need to autororate is height - with out height, your screwed no mater how fast your going forward.

Butuz

[TeePee]

But you can still trade airspeed for altitude

[Nick]

Aye, but that does you no good in a chopper... you can go as fast forwards as you like but if you can;t get those blades spinning by getting an UPWARD draft through them, you're screwed.

You don't need negative pitch and in fact, thinking about it, neg pitch on the blades in an auto-rotation scenario would be disastrous, you want the blades to spin as fast as possible in the direction they're meant to spin, which, if using the upward flow of air, is only possible with positive pitch.

The whole idea of auto-rotation is to trade height for vertical airspeed to get the updraught to keep your rotors spinning... You disengage the clutch, let the rotor free wheel and then using skilful timing and dumb luck, you give the blades max pitch. The desired effect is to use the blades inertia and momentum to slow your rate of descent to something survivable... preferably close to the ground. If you can do it within ground effect too (so your downwash is bouncing back up to help cushion the chopper), then that's even better.

I've logged a few hours in helicopters... though I could never get the damn things to fly straight... hardest damn thing to fly after a bungalow or perhaps a rocket-powered bath tub...

[TeePee]

Can you not increase your pitch up, raising the nose and translating forward speed into updraft through the blades?

I'm definitely going to do a rotorcraft add-on at some point.

Have you considered flying in the US? An FAA rotorcraft PPL is valid in the UK and not restricted to a single type. Prices are significantly cheaper, even allowing for flights over and loss of income while abroad.

[JPreston]

Here's a very very good book:

Chickenhawk

...and he writes a lot about technical aspects of helicopters as well

[Nick]

Can you not increase your pitch up, raising the nose and translating forward speed into updraft through the blades?

The only control surfaces you have on a chopper are the two rotors... the tail does yaw and compensates the gyro effect of the main rotor while the main rotor is pitch and roll all in one.

If the main rotor has no power all you have is what inertia is in the weight of the rotor so you need the blades spinning fast enough to give some lift to pitch against... and if they;re spinning that fast already you won't want to worry about pitching up to increase the updraught.

Of course, flaring in an auto-rotation is crucial and I've been told that on the less robust types, like R22s, slamming the tail in to the ground the soften the crash is advisable.

[TeePee]

Wow... I'm definitely going to look into this..

I only need 50 hours for a commercial add-on, or 30 for private priviledges, so it shouldn't be that expensive, especially if I can do it over a few months. It takes longer for those without a fixed-wing commercial ticket.

Of course, I need my seaplane add-on first!

[Nick]

Dude, take it from me, with all your fixed wing experience, you might find helis a tad harder... you look at the instruments to check they're there more than actually read them.

Helis, the small ones, are very much seat of the pants, fly by feel and that's the hard part, re-learning to look at the horizon and trust what you feel and not what the dials tell you, if you spend longer than 2 seconds with your head inside the cockpit the damn thing runs off on you, espesh if you're ding hovering practice on a sloping hill!

[Lowe]

Nah, not convinced it's got vector thrust in the slightest.

The Hind is a really, really old chopper, and the other thing is - look at the angle of the blades. They're not drooping down, which a rotor would do if it wasn't spinning. They're being held up by drag, so the rotor definitely is spinning. There is no reason what so ever for a chopper to be able to halt its rotors and 'glide'.

I say a super FPS camera with selected frames pasted together to give the illusion of a static main rotor.

[Dreaming]

I'm no authority whatsoever but I did some googling and they said that the Mi-24 was so heavy that it couldn't even hover properly, it had to fly forwards in order to get the proper lift. Not sure how true that is or not but some people seemed very sure it couldn't maintain a steady hover behind trees like an Apache or something can.

It's either strings from god or it's camera trickery. Think of a fixed wing plane; with a body that size imagine the size of the wings for one minute? Are the rotors the right size and depth? No, they won't provide adequate lift.

Though on break the video 'maker' apparently says its cool how he synced it. So there we have it?