Indian Multi Role Helicopter (IMRH)

THESIS THORON

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But will it be feasible for a heavy helicopter ,the one you quoted is for light helis , i think tail rotor is better but the one like next gen US army chopper
WHY STEALTH IS NOT INCORPORATED IN DESIGN
 

Lonewolf

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WHY STEALTH IS NOT INCORPORATED IN DESIGN
Imrh ??? , Cause it's not attack helicopter nor for that purpose , we will need dedicated stealth transpot helicopter in future ,imrh can provide base for that
 

UnderFingy

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Hey is a NOTOR system better then having a tail rotar?

In case of military helicopters, the main problem for helicopters, the infra-red detection, is improved in case of NOTAR only if the engine exhaust (or part of it) is routed through the fan, as the South Africans did with the Aérospatiale Alouette III III in their Cirstel (Combined Infra Red Suppression and Tail rotor Elimination) project.

 

Starlight

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Imrh ??? , Cause it's not attack helicopter nor for that purpose , we will need dedicated stealth transpot helicopter in future ,imrh can provide base for that
He's trying to say why not like the stealth Black Hawks... we can retrofit the entire HAL helicopter fleet from Dhruv to the upcoming IMRH by the way.
 

CentralPoint

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NOTAR is a good system as long as it 'works'. A key challenge is the need for the 'tube' where you have to use an additional fan (blower) or use gases from the engine to blow air through the 'control' vanes at the back. If you use the air from the engine - temperature management also needs to be done.
Any military system also has to be 'robust' - take the case of the F22 - the turn around time after a flight will put WW2 aircraft to shame and needs a high level of maintenance.
Vanes can get blocked by dust, dirt, debris etc. On forward bases it adds an additional maintenance requirement esp. in our Hot, dusty environment. Control systems for the vanes will add additional complexity - to a critical part of the helicopter.
There is also a weight penalty - you have to counter the downwash of the main rotor - meaning a stubby tail wont work.
Maybe, we can try it on the ALH or LUH to solve for the shipborne chopper problem (easier stowage) but on the IMRH - overkill and just something that is not required IMHO.
 

Starlight

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NOTAR is a good system as long as it 'works'. A key challenge is the need for the 'tube' where you have to use an additional fan (blower) or use gases from the engine to blow air through the 'control' vanes at the back. If you use the air from the engine - temperature management also needs to be done.
Any military system also has to be 'robust' - take the case of the F22 - the turn around time after a flight will put WW2 aircraft to shame and needs a high level of maintenance.
Vanes can get blocked by dust, dirt, debris etc. On forward bases it adds an additional maintenance requirement esp. in our Hot, dusty environment. Control systems for the vanes will add additional complexity - to a critical part of the helicopter.
There is also a weight penalty - you have to counter the downwash of the main rotor - meaning a stubby tail wont work.
Maybe, we can try it on the ALH or LUH to solve for the shipborne chopper problem (easier stowage) but on the IMRH - overkill and just something that is not required IMHO.
Yes you are right, the only point here is maintenance ease and as you said a great turn around time. The vane system is a fixed unit easily cleaned once designed for an easy turn around compared to the tail rotor design complexity. That is the only reason the notar system is far better for the naval and airforce choppers. Design for the entire notar system is perfected already. I don't think we shouldn't make notar versions for all the HAL helicopters and make an entire range of notar helicopters.
 

CentralPoint

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Yes you are right, the only point here is maintenance ease and as you said a great turn around time. The vane system is a fixed unit easily cleaned once designed for an easy turn around compared to the tail rotor design complexity. That is the only reason the notar system is far better for the naval and airforce choppers. Design for the entire notar system is perfected already. I don't think we shouldn't make notar versions for all the HAL helicopters and make an entire range of notar helicopters.
Woah! - I never said 'great' turn around time - the F22 probably has the worst TAT of any 4+ gen aircraft in service today!

Okay, let me explain.

Airflow in tubes is very different from that in a 3 dimensional space which is open. The major challenge is 'predictability' of the flow.

Inside the tube - the fluid flow will be like a 'vortex' with a constant speed in the centre of the tube due to the continuous flow of the air. As it reaches the 'vanes' - there the flow will 'break' into turbulent flow which will be based on the flow of the air outside the tube - which will in this case be in 3 dimensions (the rotor downwash - predictable to a certain degree, the 'backward flow' - helicopter moving forward and the residual flow due to the Coanda effect on a curved surface. So, now your vanes will have to move in a direction perpendicular to the axial flow of the air to counteract the main rotor torque. This will create a turbulent layer which will induce parasitic drag - reducing efficiency.

Add to this the need for ensuring that the 'pipe' remains free from any debris inside (as it will disturb the flow adding more unpredictability).

Often you will hear the word 'trade-off' being used. The trade off for a 'slightly more' silent helicopter is higher maintenance, unpredictable or complex flow, requiring more complex surfaces.

A major part of the 'noise' of a helicopter is the blade slap when the succeeding blade enters the vortex created by the preceding blade. The tail rotor creates a higher frequency noise (at it rotates at a slightly higher RPM). One way of reducing the noise from a tail rotor is to house it in a duct (called a fenestron) with higher blade count where the tip vortexes are absorbed into the fenestron reducing the 'b;ade slap' and frequency attenuation that automatically happens due to the higher blade count. The other is using a 'non cruciform' tail blade design like that seen on the Apache.

Hope this helps.
 

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