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Ka-50 vs Mi-8 engine power performance question


Mobius_cz

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Hey guys!

I haven't played Ka-50 for a long time but i managed to get back to it. I was fyling Mi-8 a lot so i know it performance quite well. After some hours i still just feel Ka-50 is lack some power against Mi-8 mainly in howering. I tested some high altitude takeoff with Ka-50 and Mi-8. The hight was about 2500 m and takeoff weight for Ka-50 was 11 600 kg and 11 500 kg for Mi-8. I had almost no problem with Mi-8 but it was really hard to keep Ka-50 flying.

 

Ka-50 has TV3-117VMA engines which are rated at 2200HP each and Mi-8 uses TV3-117VM engines rated at 2000HP. Does anyone have the same feeling or it is just my oponion?

 

Also in an document about Ka-50 i read that power loss in gearbox is lower than in convencial type rotor system.

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Maximum take off weight, rotor diameter and area for both helicopters according to the manuals:

 

Ka-50: 10,800 kg, 14.45 m , 164 m^2 (x2)

Mi-8 : 13,000 kg, 21.29 m , 356 m^2

 

So the Ka-50 is supposed to be less powerful in that regard, probably because a high MTOW is not the primary goal when designing an attack helicopter - it should be faster and more maneuverable though.

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Maximum take off weight, rotor diameter and area for both helicopters according to the manuals:

 

Ka-50: 10,800 kg, 14.45 m , 164 m^2 (x2)

Mi-8 : 13,000 kg, 21.29 m , 356 m^2

 

So the Ka-50 is supposed to be less powerful in that regard, probably because a high MTOW is not the primary goal when designing an attack helicopter - it should be faster and more maneuverable though.

Well, what does the rotor area really say about the performance? It is, afaik, just the area that the blades cover when they are spinning. More interesting to know would be probably the blade surface area. The wider the blades, the more lift they can produce, right? But I haven't found any information about that so far ...

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Maximum take off weight, rotor diameter and area for both helicopters according to the manuals:

 

Ka-50: 10,800 kg, 14.45 m , 164 m^2 (x2)

Mi-8 : 13,000 kg, 21.29 m , 356 m^2

 

So the Ka-50 is supposed to be less powerful in that regard, probably because a high MTOW is not the primary goal when designing an attack helicopter - it should be faster and more maneuverable though.

 

That would explain that although Ka-50 has better engine power longer blades of Mi-8 does actually gives more cushion for the pushin` :)

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How can you compare a dual rotor configuration with a single rotor configuration, and hope to get any kind of meaningful comparison?

 

Surely the physics of one will be utterly different to the other, with efficiency of the lower rotor on the Ka50 seriously reduced due to the wash from the upper rotor? Also, there will be a need for extra power to drive the tail rotor of the Mi8 which isn't a factor in the Ka50.

 

Common sense really!

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How can you compare a dual rotor configuration with a single rotor configuration, and hope to get any kind of meaningful comparison?

 

Surely the physics of one will be utterly different to the other, with efficiency of the lower rotor on the Ka50 seriously reduced due to the wash from the upper rotor? Also, there will be a need for extra power to drive the tail rotor of the Mi8 which isn't a factor in the Ka50.

 

Common sense really!

 

Are you serious? I am glad we have an expert like you here, your post is such helpfull.

 

I am trying to understand something here lol i am not aviation expert but even me i really understand difference between these rotor systems. The point is: In my oponion Ka-50 in hower mode feels less powerfull than Mi-8 under the same conditions.

 

Is it due to simulation? (not enough data or maybe it is not possible to simulated as detailed as it should be) or it is the same in real life? if yes i WANT to know why.

 

"Is dual rotor system more suitable for higher speed flight than howering?" This is what is it all about. :pilotfly:

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Are you serious? I am glad we have an expert like you here, your post is such helpfull.

 

 

Yes, I am serious. The comment was made regarding the figures posted, not your question. Of course knowing how the two aircraft compare is very relevant.

 

Raw data stating the rotor areas, take off weights etc is utterly spurious however when two very different designs are compared. Or maybe you know better?

 

Your sarcasm does you no credit.

 

The real advantage of dual rotor systems is that they have much more efficient use of power. In a single rotor/tail rotor arrangement, a proportion of the enrgy has to be wasted to counteract torque. In a dual rotor design, the contra-rotating blades cancel out the torque. The down side is the complex rotor head assembly, and the lower rotor is less efficient due to the disturbed air from the top rotor.


Edited by NeilWillis
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In general I'd say the coaxial design is more efficient and should be able to generate more lift out of the same engine power if you design your rotors accordingly.

 

With the Ka-50 they chose to trade in some of that lifting capacity for higher speeds and smaller footprint.

 

"Is dual rotor system more suitable for higher speed flight than howering?"

 

Not necessarily. It does eliminate some problems in (fast) forward flight like asymmetric lift and interference between main and tail rotor though.

It's also yields a better maneuverability and is generally more efficient.

Check out the BS2 flight manual chapter 5 for some more information.

 

How you use that efficiency is up to the designers: Do you want a small, fast and agile helicopter? Then you have to sacrifice some lifting capacity. Do you want to lift more? Then you won't be able to fly that fast.

However those decisions are not limited to coaxial designs.

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Raw data stating the rotor areas, take off weights etc is utterly spurious however when two very different designs are compared.

 

Not sure why you consider comparing MOTWs spurious - it is after all the maximum weight the aircraft is supposed to take off with, regardless of design.

Yes, rotor areas won't tell you everything but still are an indicator for the helicopters performance.

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No one disputes the relevance of take off weight, but how the two aircraft compare. This isn't a good comparison, but let's just use it as a rough example. Would you directly compare the performance of a biplane and monoplane aircraft by comparing just wing area, take off weight and engine power? There is a huge amount of drag associated with biplanes, and without that, all the other data, while meaningful, is meaningless when the comparison between the two is made, without other highly relevant factors included. The fact that the two helicopter designs are fundamentally different renders any direct comparison very difficult.

 

Does that make my point any clearer?

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And I'm not saying that you can deduct all flight parameters by just looking at those stats.

 

However the original questions was concerning the Ka-50 feeling underpowered compared to the Mi-8 hovering in 2,500m and 11,500kg load.

Since I don't have first or second hand experience with either aircraft, all I can do is look at the relevant numbers.

 

The Ka-50 has a 17% lower MTOW (which was actually exceeded in this test) and a smaller rotor area, which makes me think that the observed behavior is plausible.

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I ask again ... what does the rotor area tell someone when comparing helos? I still think, the more relevant information would be the total blade surface area (and blade profile).

 

Example: two helos with the same rotor diameter - i.e. same disc area - but different number of blades - which will more likely perform better?

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And I'm not saying that you can deduct all flight parameters by just looking at those stats.

 

However the original questions was concerning the Ka-50 feeling underpowered compared to the Mi-8 hovering in 2,500m and 11,500kg load.

Since I don't have first or second hand experience with either aircraft, all I can do is look at the relevant numbers.

 

The Ka-50 has a 17% lower MTOW (which was actually exceeded in this test) and a smaller rotor area, which makes me think that the observed behavior is plausible.

 

So comparing a large, 5 bladed helicopter with a tail rotor with a small, twin rotor design that felt underpowered when it was flown above it's maximum advised takeoff weight is plausible under ANY circumstances?

 

This thread is simply going nowhere. Even a straight comparison of power to weight ratios would tell you nothing unless you factored in the efficiency differences.

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I can see that it is much more complicated than i thought it can be. I did not know the maximum take-off weight is 10 800 kg because maximum weight in game is displayed 11 900 kg. That makes sence when it is overloaded that it feels underpowered. In matter of fact everytime i fly combat mission with my standard load of 12 AT-9 and S-8 rocket pods it is over 11 000 kg with full fuel tanks.

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I did not know the maximum take-off weight is 10 800 kg because maximum weight in game is displayed 11 900 kg.

 

Yeah, that's a bit weird.

Wikipedia also lists 10 800kg and cites kamov.ru as source (only available via internet archive now)

 

There it says "takeoff weight: 10800kg" - possibly meaning typical tow? Or perhaps it was adjusted later?

Maybe someone with better connections (or better google skills) can shed some light on this.

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No one disputes the relevance of take off weight, but how the two aircraft compare. This isn't a good comparison, but let's just use it as a rough example. Would you directly compare the performance of a biplane and monoplane aircraft by comparing just wing area, take off weight and engine power? There is a huge amount of drag associated with biplanes, and without that, all the other data, while meaningful, is meaningless when the comparison between the two is made, without other highly relevant factors included. The fact that the two helicopter designs are fundamentally different renders any direct comparison very difficult.

 

Does that make my point any clearer?

 

Wing Area and engine power is, apart from a coeffiecient depending on the distribution of lift over the wing, almost everything you need for a comparison. To stick with your biplane example:

Assuming you have a similar shaped wing (same lift distr.), but the double wing area you are producing double the lift at the same speed and altitude. This leads to ~4x the drag at that speed.

 

To get back to the Mi8/Ka50 issue:

I'm not that fit in rotary wing dynamics, but if you take it simple (and the MTOW figures are correct) the Mi8 has better performance for takeoff as long as the takeoffweight is the same. I'd compare them at the same percentage of MTOW. If the MTOW is roughly the same I'd be a bit surprised aswell. The high momentum on takeoff would lead to quite a lot performance on the rear rotor... But again, I'm not very fit in rotary wing aerodynamics, especially when it comes to coaxial rotor systems


Edited by Maverick-X
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  • ED Team
I ask again ... what does the rotor area tell someone when comparing helos? I still think, the more relevant information would be the total blade surface area (and blade profile).

 

Example: two helos with the same rotor diameter - i.e. same disc area - but different number of blades - which will more likely perform better?

 

The rotor area is the main parameter that define rotor efficiency. It's an analogue of the wingspan as the blade area is more like wing area. If you compare a superglider and a plane with the same weight, same wing area but different wingspan you can see that L/D (efficience) ratio is much more for the glider.

 

THre reason is that the more air you use to accelerate the less speed you must add to get the same lift. THe power you have to spend is proportional to V^2.

 

When Mi-24 was derived from Mi-8 the rotor diameter was reduced, so Mi-24 became very underpowered on hovering. Ka-32 having the same engines and coaxial rotors are better than Ka-50 as it has larger rotor area.

Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

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The rotor area is the main parameter that define rotor efficiency. It's an analogue of the wingspan as the blade area is more like wing area. If you compare a superglider and a plane with the same weight, same wing area but different wingspan you can see that L/D (efficience) ratio is much more for the glider.

 

THre reason is that the more air you use to accelerate the less speed you must add to get the same lift. THe power you have to spend is proportional to V^2.

 

When Mi-24 was derived from Mi-8 the rotor diameter was reduced, so Mi-24 became very underpowered on hovering. Ka-32 having the same engines and coaxial rotors are better than Ka-50 as it has larger rotor area.

Thank you!

 

I think, I understood it now ... the width of a wing is not (really) relevant for how much lift it produces - more relevant is the profile. And when we assume that the profile is in both cases already optimized, there is no need to examine this factor in our comparisation. Therefore only the wing span is the deciding factor.

 

So, this is then the explanation of why the Ka-50 seems to perform less effective than the Mi-8 in regards to hovering? Mainly because of the slightly smaller disc area?

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Wing Area and engine power is, apart from a coeffiecient depending on the distribution of lift over the wing, almost everything you need for a comparison. To stick with your biplane example:

Assuming you have a similar shaped wing (same lift distr.), but the double wing area you are producing double the lift at the same speed and altitude. This leads to ~4x the drag at that speed.

 

To get back to the Mi8/Ka50 issue:

I'm not that fit in rotary wing dynamics, but if you take it simple (and the MTOW figures are correct) the Mi8 has better performance for takeoff as long as the takeoffweight is the same. I'd compare them at the same percentage of MTOW. If the MTOW is roughly the same I'd be a bit surprised aswell. The high momentum on takeoff would lead to quite a lot performance on the rear rotor... But again, I'm not very fit in rotary wing aerodynamics, especially when it comes to coaxial rotor systems

 

Simply ignoring the 15-20% greater efficiency of coaxial rotors quoted in the Black Shark manual?

 

The key word was MEANINGFUL, and if you fail to factor in the differences inherent in the two entirely disparate designs, how can any of the data resulting from the comparison have any meaning at all?

 

According to the Black Shark manual, the coaxial rotor has a higher total overall airflow due to the way the upper rotor wash narrows. If that adds the equivalent to an extra 10% to the rotor area, can you ignore that? Tail rotors on single rotor designs can soak up as much as 10% of the available power simply to overcome incipient torque. Can you ignore that too?

 

Isolated figures mean nothing without context, and in this case the context is that the figures apply to two very very different designs. Sure, you can take a rough guess, and make a hell of a lot of assumptions, but that is why the results are basically flawed, and utterly meaningless.

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in ka-50, there is a problem with the electronic control engine speed. This device does not work properly to a height of 2000-2500 meters.

 

Here are charts for the Ka-50 to climb speed depending on the weight of the helicopter.

 

57ec7475f857.jpg

 

So: to make it clear.

Terms of schedule: wind calm, the temperature 15 degrees Celsus, pressure 760 mm.

The left and right graph: according to the vertical axis - the height from the ground in kilometers along the horizontal axis - vertiklnaya speed in meters / second. Graphs for helicopter mass 8.5 tons, 9.2 tons, ........ and so forth.

The left diagram - this is when the helicopter flies with forward speed. for the Ka-50, this rate adopted 120-150 km / h. Mode of operation of the engine must be takeoff.

Right scheme - this climb without forward speed. Mode of operation of the engine must be takeoff.

 

 

 

Check - testirute - discuss. For developers simply silent on this issue.

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Simply ignoring the 15-20% greater efficiency of coaxial rotors quoted in the Black Shark manual?

 

The key word was MEANINGFUL, and if you fail to factor in the differences inherent in the two entirely disparate designs, how can any of the data resulting from the comparison have any meaning at all?

 

According to the Black Shark manual, the coaxial rotor has a higher total overall airflow due to the way the upper rotor wash narrows. If that adds the equivalent to an extra 10% to the rotor area, can you ignore that? Tail rotors on single rotor designs can soak up as much as 10% of the available power simply to overcome incipient torque. Can you ignore that too?

 

Isolated figures mean nothing without context, and in this case the context is that the figures apply to two very very different designs. Sure, you can take a rough guess, and make a hell of a lot of assumptions, but that is why the results are basically flawed, and utterly meaningless.

 

How about you step on the brakes a bit...

I simply said that isolated figures are quite meaningful for comparison of two different systems. This is the way you would try to compare them, as they are f***ing different! MTOW is MTOW, no matter what kind of propulsion system you use or whatever. I NEVER said you could utilize something like the pure engine power to spot a difference! But I'm the one who's ignorant???

 

And as I already said, I'm not that fit in rotor dynamics. ESPECIALLY WITH COAXIAL ROTORS. Read the whole post before getting back at me in a tone like that!

And still the ~20% better efficiency of a coaxial rotor as you mentioned it, would not explain the experience of the op, that the helicopter with the more powerful engines (which is not wasting power on a rear rotor, which I also mentionend in my post... what you ignored) seems to perform worse

 

 

EDIT:

In case you misinterpreted my continued example of your biplane-monoplane problem: if you have the engine power, the wing area, the air density and the weight you can compare these two very different designs because the fact that the doubled surface of the biplane leads to double the lift, and most of the drag is induced by lift...


Edited by Maverick-X
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Here are charts for the Ka-50 to climb speed depending on the weight of the helicopter.

 

Thank you.

The 11.9 and 10.8 ton graphs seem to indicate that the in-game MTOW of 11.9 is correct while the widely quoted 10.8 is not - so much for the Internet ;)

 

Also in 2500m at 11.4t you're pretty much stuck at 0m/s while hovering, so the in-game observation appears to match the real world performance. :D

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