Ka-50 compared to Mi-24

[ThunderChief]

Interesting how accurately the ECU is able to maintain rotor RPM even when the heli is maneuvering. Thumbs up to Mil :thumbup:

 

In some parts of the video you can see that the rpm changes as the rotor starts to "move".

 

If the camera uses 24 - 30 FPS this would be equal to 100 1440 - 1800 rpm of the main rotor which is far to high.

Therefore the main rotor rpm can only be 1/5 (or 1/10) of the camera's FPS (because of the 5 blades).

 

This means that the small "movement" of the rotor is actualy multiplied by 5. So if you see a movement of ~5 rpm it means the rpm changed by 25rpm (= 5% - 10%).

 

But I think thats still quite good for the technology of the Hind at rapidly changing load of the rotor while maneuvering.

[ThunderChief]

The effect of anhedral has a negative effect on the stability of an aircraft... is that what you're trying to say because that would be correct. However "broad sweeping turns" has nothing to do with that. The radius of turn is not a function of stability. In the case of the Mi-24 I think it was done for other, possibly structural, reasons.

The Hind uses anhedral for the same reason as heavy lifter like A-124 use it. The rotor (or wings) is high above the center of gravity and this causes stability problems which lead to a combination of continues roll and yaw. This effect is reduced by the anhedral of the wings.

[chaos]

The Hind uses anhedral for the same reason as heavy lifter like A-124 use it. The rotor (or wings) is high above the center of gravity and this causes stability problems which lead to a combination of continues roll and yaw. This effect is reduced by the anhedral of the wings.

 

That's definitely not true. A high wing is positively stable. In general one uses anhedral to lessen stability (for a variety of reasons)...

Edited July 19, 2008 by chaos

[ThunderChief]

That's definitely not true. A high wing is positively stable. In general one uses anhedral to lessen stability (for a variety of reasons)...

I think we are both right but maybe I used the wrong words. ;)

It's stable but it will cause oscillations (yaw and roll). In fact the oscillation is caused by too much stability and anhedral is used to reduce this.

[Avimimus]

is..well.. hogwash :)

 

Point taken regarding maximum speed. I was wrong, the figures I had for the Ah-64 and Ah-1 were inaccurate (both are faster than the Mi-24).

 

I was also under the impression that lift generated by the passing of the air through the rotor disk and over the stub wings will reduce the torque on the rotor allowing the collective to be lowered and allowing more of the torque to be directed to the cyclic (thus increasing the forward thrust of the rotor relative to what would be possible if the rotor system had to generate equal lift to that required in a hover and the power for maintaining velocity at the same time). Is this correct?

 

 

The effect of anhedral has a negative effect on the stability of an aircraft... is that what you're trying to say because that would be correct. However "broad sweeping turns" has nothing to do with that. The radius of turn is not a function of stability. In the case of the Mi-24 I think it was done for other, possibly structural, reasons.

 

I looked this up. The anhedral was actually introduced for stability (the original prototype showed signs of going into a "dutch roll" at higher speeds). The anhedral does also have the additional effect of helping to introduce a natural yawing motion in response to a slight banking of the helicopter when at speed. This is supposedly one of the unusual characteristics of this aircraft. When considering its effects on stability and turning moment it is also a good idea to consider that the stub wings have a higher angle of incidence than in fixed wing aircraft.

 

At 20-30kph there's no appreciable amount of lift from the stubwings. It does have a negative effect on lift of the rotor-disc ("shadow" that you mentioned).

 

This was exactly my point. Not only do you lose the lift from forward flight but you also suffer from the swings "shadow". Sorry for any lack of clarity.

 

Thanks for the corrections,

Edited July 19, 2008 by Avimimus

[AlphaOneSix]

If the camera uses 24 - 30 FPS this would be equal to 100 1440 - 1800 rpm of the main rotor which is far to high.

Therefore the main rotor rpm can only be 1/5 (or 1/10) of the camera's FPS (because of the 5 blades).

 

The rotor RPM should be right around 240 for the Mi-24 (give or take maybe 5 rpm).

[zakobi]

The Mi-24's tail can break off in quick turns, something like that...

[arneh]

Wether it has stubwings or not has nothing to do with it. In fact, the fastest helicopter is a (modified) Lynx if I'm not mistaken.

 

 

It is indeed a modified Lynx which has the current helicopter speed record at 400.87 kph. The previous record holder though was a modified Mi-24 (called A-10) at 368.4 kph. Interestingly this Hind had its wings removed to reduce weight. It was also one of the earlier models with the greenhouse-cockpit, not the bubble-canopies.

 

It is (or was - didn't the F-117 looking helicopter (Commanche?) that the Americans built manage to beat its speed record?).

 

The Comanche wasn't particulary fast, but you're maybe thinking of the AH-56 Cheyenne, which at least on paper was capable of maximum speeds of over 400 kph. But it never ran for the speed record before it got cancelled, and in any case wasn't eligible in the helicopter class as it was a compound. It used fairly big wings and a pusher-propeller to give it higher top speed. In fact, at higher speeds only one fifth of the engine power went to the rotor, the rest going to the pusher propeller.

 

[ThunderChief]

The Ka-50 seem to be very slow compared to this. Producer Note #3 stated that you get warnings at 300 kph. I thought the koaxial rotor would allow higher speeds?

[arneh]

The Ka-50 seem to be very slow compared to this. Producer Note #3 stated that you get warnings at 300 kph. I thought the koaxial rotor would allow higher speeds?

 

Well, you're comparing to specially modified helicopters (in the case of the AH-56 the entire helicopter was built for speed). A regular Lynx is much slower. And even if the Mi-24 was built for speed, the regular models don't go much above 300 kph. 300 kph is in fact quite fast for a helicopter. More normal helicopters like a Huey or Jet Ranger are barely faster than 200 kph.

[Tango]

The Ka-50 seem to be very slow compared to this. Producer Note #3 stated that you get warnings at 300 kph. I thought the koaxial rotor would allow higher speeds?

I thought top speed was largely an aerodynamic restriction? For helicopters in general, I thought this was around 250 kph, due to the effects of retreating blade stall?

 

Best regards,

Tango.

[Esac_mirmidon]

Depende of the source but Ka-50 top speed is related to be between 310 kph to 390 kph. ( Different in horizontal or vertical flight).

[ThunderChief]

I thought the coaxial rotor wouldn't suffer from retreating blade stall as it would happen symetrically.

[Tango]

Maybe the whole rotor stalls then? Eventually you're going to require such an AoA on the blades, that they're no longer going to be able to generate lift.

 

When I wrote 250 kph in my previous post, I actually meant 250 kts. I thought this was a general maximum speed for helicopters?

 

I know the Bell JetRanger is limited to approx. 120 kts, but this is due to the problem of retreating blade stall.

 

To design for a higher top speed, do you require more blades that are larger and turning more slowly (generally) compared to smaller helis, or isn't it a function of size?

 

Best regards,

Tango.

[GGTharos]

How about the rotor discs touching? Think about it ...

 

I thought the coaxial rotor wouldn't suffer from retreating blade stall as it would happen symetrically.

[arneh]

Another limiting factor for helicopter top speed is that such high aspect ratio wings as a rotor blade cannot go supersonic. And as speed builds up (and the retreating blade reaches stall speed) the advancing blade tips reaches supersonic speed.

[Tango]

How about the rotor discs touching? Think about it ...

I already did, and I can't see how sheer forward speed would make the problem the worse...

 

To yaw the speeds between the two rotors is altered - that's simple. Is only the upper rotor tilted to get the aircraft moving, or does the whole head tilt?

 

I would expect that dropping the collective would simply result in loss of lift from both sets of rotors, so the relative gap between blades would remain the same I would have thought (noting however that the retreating blades are on opposite sides, flying head-on with the advancing blade above/below, relatively).

 

* Looks for detailed information on Ka-50 rotor system *

 

Best regards,

Tango.

[GGTharos]

Top rotor tilts down on the left, for example, because the blade is retreating so it droops. The rotor beneath it is counter-rotating, and RISES on the side because that side of it is producing lift ...

Edited July 19, 2008 by GGTharos

[ThunderChief]

Would you say that 40 - 50 kph more speed would make a real diffrence in combat? I mean its slow anyway compared to aircraft and missiles.

[GGTharos]

It can make a difference in operations planning/logistics, though who knows.

[Tango]

I guess like-vs-like it becomes significant.

 

Is there anywhere I can get some tech info on the Ka-50? I can't seem to find anything via Goooogle. I'm looking for specifics on the rotor system and power plant. I'm also interested in the flight controls.

 

Best regards,

Tango.

Edited July 20, 2008 by Tango

[Canada]

I remember a while ago I asked in the FAQ about how the Ka-50 yaws. AirTito posted some diagrams of the head.

Hope that helps.

 

http://forums.eagle.ru/showpost.php?p=458081&postcount=5

[sobek]

In some parts of the video you can see that the rpm changes as the rotor starts to "move".

 

If the camera uses 24 - 30 FPS this would be equal to 100 1440 - 1800 rpm of the main rotor which is far to high.

Therefore the main rotor rpm can only be 1/5 (or 1/10) of the camera's FPS (because of the 5 blades).

 

This means that the small "movement" of the rotor is actualy multiplied by 5. So if you see a movement of ~5 rpm it means the rpm changed by 25rpm (= 5% - 10%).

 

But I think thats still quite good for the technology of the Hind at rapidly changing load of the rotor while maneuvering.

 

You only see it turn when the heli itself turns, thus its only the helicopters superimposed turn, the rpm stays the same IMHO.

[sobek]

I remember a while ago I asked in the FAQ about how the Ka-50 yaws. AirTito posted some diagrams of the head.

Hope that helps.

 

http://forums.eagle.ru/showpost.php?p=458081&postcount=5

 

Holy sh*** i've been craving such a diagram for a long time now, thx for the link.:book:

 

Edit:

Can anybody tell me what the feathering hinge does?

Edited July 20, 2008 by sobek

[nscode]

And it eats a bucket of lubricant :)