Aerodynamics of Mi-24 wings

[AeriaGloria]

Hello I made a post in Sim Research about trying to use LUA figures to find the lift coefficient of the Mi-24 wing. I also linked a study that shows the amount of lift produced by the rotor at different speeds. It appears they attached transducers to the main and tail rotor of a Polish Mi-24, then did wind tunnel simulations to find certain forces involved or in flight stress testing, it’s hard to tell, but I compiled results from the study, converting Newtons to kilograms of force, and taking the rotor load, subtracting from the 11,500 kg weight of the study to find wing lift, assuming wing lift is constant for a given speed and AOA, and using that amount of wing lift to find the percentage of lift generated by the wing from empty weight to max take off weight.

I can only assume the study was done at ISA, as it does not mention, here is the post I made with the study 

And here are the numbers I generated from the study, my intent was to see if it was really true and under what conditions the aprocyphal number of the Mi-24 wing producing 20-25% of the lift was. The larger percentage is the wing lift compared to empty weight, and the smaller percentage wing lift compared to max take off weight 

I also added tail rotor thrust compared to main rotor, and the study includes all forces and moments on the main rotor during those three speeds and climbing and diving maneuvers. Interestingly enough, the main rotor in steady flight is always producing a pitch up and roll right force. I assume roll right is partly to fight tail rotor thrust, and the pitch up is for stability fighting the pitch down caused by the wing being behind the CG

I find the wing aerodynamics fascinating, it seems to make the pitch up during mushing more sever then other helicopters, since the 19 degree incidence wing would stall at nearly any positive AOA, and it’s behind CG, it’s stall would decrease the pitch down moment it create 

140 kmh: 

Wing: 500 kg Force, 6-4.3% of lift

Tail rotor: 3.6% of thrust

260 kmh: 

Wing: 2000 kg force, 23.5-17.4% of lift

Tail rotor: 5.2% of thrust 

300 kmh: 

Wing: 2,170 kg Force,  25.5-18.8% of lift

Tail rotor: 7% of thrust 

 

Edited March 30, 2022 by AeriaGloria

[Tiger-II]

Are the left and right wings symmetrical? Is the rolling tendency offset by the right wing producing slightly more lift than the left? i.e. not symmetrical?

The thrust due to the tail rotor is diminished at high forward speed, so seems a reasonable assumption that it would help cancel out the rolling force.

Quote

my intent was to see if it was really true and under what conditions the aprocyphal number of the Mi-24 wing producing 20-25% of the lift was.

Why would this be in doubt? The wing area is not insignificant, and clearly forms an aerodynamic surface.

Edited April 1, 2022 by Tiger-II

[AeriaGloria]

56 minutes ago, Tiger-II said:

Are the left and right wings symmetrical? Is the rolling tendency offset by the right wing producing slightly more lift than the left? i.e. not symmetrical?

The thrust due to the tail rotor is diminished at high forward speed, so seems a reasonable assumption that it would help cancel out the rolling force.

Why would this be in doubt? The wing area is not insignificant, and clearly forms an aerodynamic surface.

 

Sorry if I was unclear. The wings don’t produce the rolling force or pitch up force, the rotor does. And yes I’m sure the tail rotor offsets this, as it’s placement above the lateral CG means it’s probably also producing a small left roll moment on the airframe.

Just like an airplane the wing is behind the CG, so it produces a net pitch down force; which adds stability

The wings are symmetrical. They have 8.5 degree sweep, 19 degrees of incidence, 6.25 meters squared wing area, and have 12 degrees of anhedral. So yes they are large, but there are many that think their influence is over exaggerated. And that they are only really there for pylon space. You could say their incidence is even there so that at no point in fast forward flight is their AOA negative, for the reason that they have no negative impact on flying qualities they way other winged helcipters with less incidence in their wings have negative effects from the wings when they start going so fast that it requires so much negative pitch the wing is actually producing down force

The anhedral is only there to reduce the Dutch roll effect caused by the dihedral effect caused by the swept wings. The yaw dampener in the autopilot also helps eliminate the yaw caused roll oscillations that come from the swept wings 

[Tiger-II]

Quote

Sorry if I was unclear. The wings don’t produce the rolling force or pitch up force, the rotor does.

You were clear!   I wondered if the wings offset the right rolling force, but as you point out, with the tail rotor being above the CoG it could be enough to do this on its own (and an effect I hadn't actually considered).

I don't understand why people would think it is over-modelled? If you're flying with virtually flat pitch on the main rotor in high speed flight, sure, but I don't see that in any of the videos I've seen. The collective is far from "at the bottom".

Edited April 1, 2022 by Tiger-II

[AeriaGloria]

22 minutes ago, Tiger-II said:

You were clear!   I wondered if the wings offset the right rolling force, but as you point out, with the tail rotor being above the CoG it could be enough to do this on its own (and an effect I hadn't actually considered).

I don't understand why people would think it is over-modelled? If you're flying with virtually flat pitch on the main rotor in high speed flight, sure, but I don't see that in any of the videos I've seen. The collective is far from "at the bottom".

 

I don’t mean people saying it’s over exaggerated in DCS. I mean ever since Mi-24 entered service 50 years ago and people threw around that the wing produced 20-25% of the lift, people have argued of wether that’s an exaggeration or not. 
 

For 50 years 

[Tiger-II]

22 minutes ago, AeriaGloria said:

I don’t mean people saying it’s over exaggerated in DCS. I mean ever since Mi-24 entered service 50 years ago and people threw around that the wing produced 20-25% of the lift, people have argued of wether that’s an exaggeration or not. 
 

For 50 years 

That's insane!

Re-framing the question: why do people doubt the veracity of the claim? 50 years ago makes it the 1970s, and by then they understood lifting bodies, so I would doubt it is ignorance of the physics?

Is it a East vs. West thing, or were people within Russia also debating it? I think we were experimenting with wings on helicopters, but AFAIK in the 1970s we weren't flying anything with "wings". Pylons, yes.

I'm also thinking about helicopters such as the Sikorskis that have the protruding landing gear wells, and others such as the SH-3 and derivatives that had long, shaped nacelles either side of the fuselage, such as the CH-3 and later MH-53.

Edited April 1, 2022 by Tiger-II

[AeriaGloria]

1 hour ago, Tiger-II said:

That's insane!

Re-framing the question: why do people doubt the veracity of the claim? 50 years ago makes it the 1970s, and by then they understood lifting bodies, so I would doubt it is ignorance of the physics?

Is it a East vs. West thing, or were people within Russia also debating it? I think we were experimenting with wings on helicopters, but AFAIK in the 1970s we weren't flying anything with "wings". Pylons, yes.

I'm also thinking about helicopters such as the Sikorskis that have the protruding landing gear wells, and others such as the SH-3 and derivatives that had long, shaped nacelles either side of the fuselage, such as the CH-3 and later MH-53.

 

Idk, just not everyone trusted the 20-25% figure or that even if they did that it was a big deal. Even today wings on helcipters are unusual, and almost all wings are for military attack helicopters to put weapons on. Only a few like the Mi-6 and Mi-24 actually have them at such a huge angle that They produce lift throughout the entire flight envelope faster then ETL. 
 

Take a look at this Embry Riddle study on page 64.

This paper analyzes different compound helicopter concepts. They use the S-67 as the model for lift compounded helicopters. Which the Mi-24 is. The S-67 is also uniquely close to our Mi-24 in weight, and role, being an attack helicopter with troop transport capability, and even more wing area then Mi-24. It’s wing is at 8 degrees incidence. On page 64 is a diagram showing lift force generated by the wing compared to airspeed, greater then 40 knots the wing leaves the rotor wake and starts contributing significant lift, however past about 160 knots the nose of the helicopter is now titled at over a -8 pitch angle. This means that for a wing with a 8 degree incidence angle, it now has 0 AOA and any further speed increase requiring more nose down would cause negative wing AOA and negative lift. This negative lift hurts the helicopter performance at such speeds.

You can see this in DCS for Ka-50 and AH-64, at greater then medium speeds the wing is at negative AOA, and this creates negative lift hurting the flight performance. 

So helicopters like Mi-6 and Mi-24 with such high incidence wings that only hurt flight in slow speeds close to hover, are not the norm, and there is no western equivalent to such a design. So it is likely misunderstood that all wings on helicopters are not the same, and the high incidence of these two Mil helicopters wing designs give unique and rare benefits  

[Krez]

Make no mistake that once the Berlin wall fell and the "West" got their hands on a few Hinds in the 1990's, everything discussed here was tested. If that information is available is another story.

[AeriaGloria]

1 hour ago, Krez said:

Make no mistake that once the Berlin wall fell and the "West" got their hands on a few Hinds in the 1990's, everything discussed here was tested. If that information is available is another story.

Yes, unfortunetly I could not find any tests, they likely occurred behind closed doors. The test I posted earlier, where the forces the rotor and tail rotor produce in different phases of flight and maneuvers is actually a polish study. There are other studies by the same team using this data from the rotor force study to calculate new standards for structural integrity and overhaul limits for the airframe and load components. 
 

Interestingly, the wing is never mentioned in the study. It is clearly cited in the rotor load figure that rotor is only producing 9500 kg lift for the 11500 kg weight in level flight. So I assume to the people doing this study to find stress loads on the Mi-24, that removing the wings would only decrease the time period between over haul/flying hour times, as they are distributing and reducing the load of the lift from the main gearbox by anywhere from 0-25%, though I assume since becuase of vibration above 270 kmh, the 25% of lift is rarely ever met and 0-20% is closer to how much the wing helps lift in a usual flight