LCH and other Helicopters Discussion Thread

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Hari Nair
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Re: LCH and other Helicopters Discussion Thread

Postby Hari Nair » 08 Sep 2010 22:05

rad wrote:Dear Hari Nair

Please explain what is control saturation , how and in what mode of flight can it occur and what we should do to avoid

getting into that situation . I have 6 hrs on Robinson R-22 but that that was nearly 20 years back , cheers

rad

Well – Rad, you just talked yourself into one torturous session of helicopter aerodynamics! I’ll keep it as short as possible and if you have the patience to read it till the end and still make some sense of it
…. so here goes-

The term 'Control Saturation' is totally inaccurate - actually nothing (neither the control nor the rotor gets 'saturated'). The helicopter is very much controllable.

Due to the fact that a helicopter’s main rotor is going ‘sideways’ through the air, it experiences dissymmetry of lift. That is – the advancing rotor blade going into the direction of flight experiences a faster relative airflow (due to the rotation of the rotor) and the retreating blade experiences a slower relative airflow. A perfectly rigid rotor would thus be unable to keep going and would ‘flip over’ due to the resulting imbalance of lift between its advancing and retreating sides.

To alleviate the lift imbalances, rotor blades are flexibly attached to the rotor hub, allowing the rotor blade to ‘flap’ up and down. Earlier technology required a flapping hinge to be built into the hub at the point of attachment of the rotor blade. Typical examples being the Russian Mi-8/17/24 series of helicopters. A variation of that theme was two diametrically opposed rotor blades attached with a see-saw type gymbal joint at the hub – The AH-1 Huey Cobra and the UH-1 are examples. Then there are newer ‘hinge-less’ rotors which have flexible ‘quasi-hinges’.

Whilst manoeuvring a helicopter, the pilot using the controls, tilts the main rotor into the desired direction. Thereby, a portion of the total rotor thrust is vectored into that direction. The helicopter’s body suspended pendulously below, responds with some delay to the changed direction of rotor thrust.

Now, if the flapping hinges (or quasi-hinges) are placed some distance away from the centre of the rotor hub, there is an additional force couple available to tilt the helicopter. The further out these flapping hinges are, the more powerful the force couple and the more instantaneous the helicopter’s response.

The advantages of high-offset flapping hinges are that even below zero ‘G’ flight condition, the pilot retains control over the rotor and can manoeuvre the helicopter to extreme flight attitudes. Now in certain conditions of extreme manoeuvres due to the fundamental issue of dissymmetry of lift of a single main rotor and certain other aerodynamic effects that also then kick in, the pilot may experience the cyclic control column at an extreme limit with the helicopter still in the manoeuvre. This depends on direction of rotation of the rotor - for a rotor turning to the left, the limit is reached during extreme manoeuvres to the right and vice-versa for a rotor turning to the right.

Recovery from this condition can be immediately affected by application of another control. However, the point is during hard manoeuvring in low level flight, the combination of factors may be such that the recovery control application is a tad too late or the height above ground is inadequate and the helicopter then impacts the ground. If adequate clearance is available above ground, recovery can be affected.

Therefore to answer your question, since the R-22 has a teetering head (no flapping hinge offset at all) and if you attempted some seriously severe manoeuvres, you would hit other rotor limits first (such as ‘mast bumping’) with perhaps more disastrous consequences, even before reaching cyclic stick limit. Which means that even if adequate clearance was available above terrain, you may not be able to recover! The R-22 being a trainer machine and having a teetering rotor has a modest flight envelope. That's defined in your Flight Manual - stick within those limits and you are safe.

So given the choices available with today’s level of technologies, I’d rather throw my hat in with the more manoeuvrable high-offset flapping (or quasi-flap) hinge rotor.

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Re: LCH and other Helicopters Discussion Thread

Postby vina » 08 Sep 2010 22:25

Now in certain conditions of extreme manoeuvres due to the fundamental issue of dissymmetry of lift of a single main rotor and certain other aerodynamic effects that also then kick in, and the pilot may experience the cyclic control column at an extreme limit with the helicopter still in the manoeuvre. This depends on direction of rotation of the rotor - for a rotor turning to the left, the limit is reached during extreme manoeuvres to the right and vice-versa for a rotor turning to the right.


So does that mean in a dual rotor copter (Kamov , Chinook , Kaman etc), you really dont have this "problem" because the rotors spin in opposite directions and any asymmetry of lift is canceled out?

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Re: LCH and other Helicopters Discussion Thread

Postby chetak » 08 Sep 2010 22:29

vina wrote:
Now in certain conditions of extreme manoeuvres due to the fundamental issue of dissymmetry of lift of a single main rotor and certain other aerodynamic effects that also then kick in, and the pilot may experience the cyclic control column at an extreme limit with the helicopter still in the manoeuvre. This depends on direction of rotation of the rotor - for a rotor turning to the left, the limit is reached during extreme manoeuvres to the right and vice-versa for a rotor turning to the right.


So does that mean in a dual rotor copter (Kamov , Chinook , Kaman etc), you really dont have this "problem" because the rotors spin in opposite directions and any asymmetry of lift is canceled out?


The Kamovs have a tiny problem of blade rendezvous. :)

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Re: LCH and other Helicopters Discussion Thread

Postby Drishyaman » 08 Sep 2010 22:39

Dear Hari Nair Sir,

I have a very small question. I will be delighted if you can answer that. I remember seeing Comanche Helicopter on Discovery TV a few years back. Comanche was able to move side-wise. I would like to know if LCH has also been designed for similar kind of side-wise movement.

Thank you in advance

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Re: LCH and other Helicopters Discussion Thread

Postby shiv » 09 Sep 2010 06:14

B_Ambuj wrote:Dear Hari Nair Sir,

I have a very small question. I will be delighted if you can answer that. I remember seeing Comanche Helicopter on Discovery TV a few years back. Comanche was able to move side-wise. I would like to know if LCH has also been designed for similar kind of side-wise movement.

Thank you in advance


Shows the power of Discovery channel programs, India really should pick up the art of showing simple things which are unknown to most. I don't think there is any helicopter on earth hat cannot move sideways or even backwards for that matter.

I am unable to find any video clip of the ALH flying sideways - but at 1'02'' the armed ALH in the video below can be seen flying backwards. I wonder if Hari Nair did that demo at Aero India

http://www.youtube.com/cybersurg#p/a/u/1/ADdxH7oChXA

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Re: LCH and other Helicopters Discussion Thread

Postby rad » 09 Sep 2010 11:46

Dear Hari Nair
I really appreciate the time and effort you take to explain helicopter aerodynamics to half baked people like me , it shows your patience and will to teach .It is one thing to be a TP and another thing to teach.I recall seeing a video series on "THE EMPIRE TEST PILOT SCHOOL" how students TP`s are made to work and what are the qualities required to pass the Course , could you give me your views wether our TP school is as good as theirs
i never doubt the quality of our graduates but i do feel they have better equipment and later aircraft to teach on , am i right .

Coming to the explanation you gave for control saturation I will be lying if i said i understood in toto what you said but i did take time to recall what i was taught 20 years back and understood to a large extent what you were trying to explain , never the less i will be asking you some doubts. As i dint progress far enough to come to learn terms like this , i thought it reffered to a situation where in the R-22 we could not give sudden inputs to the collective without twisting the throttle to get more RPM on the engine which had a time lag after throttle input , we were supposed to wait for the engine to pick up and then apply collective or other wise there will be a mismatch of torque applied to the rotor blades and the engine will stall , the last thing we want to happen in a low altitude.
So we had to keep monitoring a dial that had 2 needles crossing each other , if i recall correctly.
Compared to fixed wing flying experience that i had ,cessna-152 and microlights i found it very demanding to control a heli in slow flight and needless to say i was sweating profusely all the time , The brit instructor told me to visualize all the time what i had to do even when on the ground 24x7. That paid off for i started hovering around the 4th hr and
he was shocked pleasantly as students usually attain that after 10 hrs plus according to him and thought i was lying that i was a novice to Heli flying and insisted i complete the ppl coure , but not having the money at that time i had to call it quits , He had so much confidence in me that he let me fly 50 ft AGL in between small hills buzzing cows and farm land while videoing me with one hand and keeping one hand on the cyclic just in case!!
I am putting forth my experience so that you can place me .
Can our ALH and LCH do a barrel roll as the Tiger , lynx and the B105 given our rotor head technology ? , is it different from the Lynx, Tiger , ??? and I hear that it is the ultimate manouver to test the maturity of a heli design . Do we have it in our test shcedule .?.
Cheers

rad

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Re: LCH and other Helicopters Discussion Thread

Postby Philip » 09 Sep 2010 11:48

In VAYU's latest issue,there is a pic in the feature on helos,showing "ALHs" at HAL.There is an interesting pic of a naval ALH 910 sqd.,with a "beaked" nose/chin,carrying a maritime radar,unlike the circular under-cockpit installation on most foreign helos,plus lightweight TTs carried on outboard pylons.The "beak" adds about a metre extra in length to the helo,probably m,aking it too large for the hangars aboard IN warships (a major fault according to the IN).The Q is whether this is a prototype or a production version of the ALH for the IN.

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Re: LCH and other Helicopters Discussion Thread

Postby vina » 09 Sep 2010 13:00

i thought it reffered to a situation where in the R-22 we could not give sudden inputs to the collective without twisting the throttle to get more RPM on the engine which had a time lag after throttle input , we were supposed to wait for the engine to pick up and then apply collective or other wise there will be a mismatch of torque applied to the rotor blades and the engine will stall


Hmm. I guess that in this day and age, FADEC is implemented precisely to address this kinds of things. BTW do the engines in the ALH and LCH have FADEC ?

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Re: LCH and other Helicopters Discussion Thread

Postby rad » 09 Sep 2010 13:44

Yes i think they do have them , and also an auto hover flight control mode as well.

Hari nair correct me if i am wrong

rad

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Re: LCH and other Helicopters Discussion Thread

Postby Hari Nair » 09 Sep 2010 20:06

chetak wrote:
vina wrote:So does that mean in a dual rotor copter (Kamov , Chinook , Kaman etc), you really dont have this "problem" because the rotors spin in opposite directions and any asymmetry of lift is canceled out?


The Kamovs have a tiny problem of blade rendezvous. :)


Vina has guessed & Chetak’s hit the nail right on the head quite nicely. Check out my earlier post on the Ka-50/52. Notwithstanding this blade rendezvous problem thing, I do believe the future really requires a bit more of symmetry. Which means co-axial rotors, without the tail rotor. However with some very important differences from the Kamov layout.
The way forward, perhaps, may be Sikorsky’s ABC (Advancing Blade Concept) – check out how the Sikorsky X-1 prototype is doing to see what I mean. Even the Russki's have declared their official intent to hop on to the ABC bandwagon for their production helicopters after 2020-25.

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Re: LCH and other Helicopters Discussion Thread

Postby negi » 09 Sep 2010 20:39

^ Hari sir regarding 'blade rendezvous' does this happen only during landings/take offs ? Also is it correct to assume in case of Kamovs once the rotors are engaged they always rotate at '0' relative RPM (with respect to each other) hence chances of blade rendezvous are very low as long as they remain engaged (as the blades of rotors are out of phase) ?

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Re: LCH and other Helicopters Discussion Thread

Postby nachiket » 09 Sep 2010 20:45

negi wrote:^ Hari sir regarding 'blade rendezvous' does this happen only during landings/take offs ? Also is it correct to assume in case of Kamovs once the rotors are engaged they always rotate at '0' relative RPM (with respect to each other) hence chances of blade rendezvous are very low as long as they remain engaged ?


correct me if I'm wrong but I always believed that conventional helicopters use change in tail rotor speed to turn about the axis. In Kamovs, if the rotors always rotate at 0 relative RPM, how will the helicopter turn?

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Re: LCH and other Helicopters Discussion Thread

Postby Hari Nair » 09 Sep 2010 20:51

rad wrote:Dear Hari Nair
I really appreciate the time and effort you take to explain helicopter aerodynamics to half baked people like me , it shows your patience and will to teach .It is one thing to be a TP and another thing to teach.I recall seeing a video series on "THE EMPIRE TEST PILOT SCHOOL" how students TP`s are made to work and what are the qualities required to pass the Course , could you give me your views wether our TP school is as good as theirs
i never doubt the quality of our graduates but i do feel they have better equipment and later aircraft to teach on , am i right .

Coming to the explanation you gave for control saturation I will be lying if i said i understood in toto what you said but i did take time to recall what i was taught 20 years back and understood to a large extent what you were trying to explain , never the less i will be asking you some doubts. As i dint progress far enough to come to learn terms like this , i thought it reffered to a situation where in the R-22 we could not give sudden inputs to the collective without twisting the throttle to get more RPM on the engine which had a time lag after throttle input , we were supposed to wait for the engine to pick up and then apply collective or other wise there will be a mismatch of torque applied to the rotor blades and the engine will stall , the last thing we want to happen in a low altitude.
So we had to keep monitoring a dial that had 2 needles crossing each other , if i recall correctly.
Compared to fixed wing flying experience that i had ,cessna-152 and microlights i found it very demanding to control a heli in slow flight and needless to say i was sweating profusely all the time , The brit instructor told me to visualize all the time what i had to do even when on the ground 24x7. That paid off for i started hovering around the 4th hr and
he was shocked pleasantly as students usually attain that after 10 hrs plus according to him and thought i was lying that i was a novice to Heli flying and insisted i complete the ppl coure , but not having the money at that time i had to call it quits , He had so much confidence in me that he let me fly 50 ft AGL in between small hills buzzing cows and farm land while videoing me with one hand and keeping one hand on the cyclic just in case!!
I am putting forth my experience so that you can place me .
Can our ALH and LCH do a barrel roll as the Tiger , lynx and the B105 given our rotor head technology ? , is it different from the Lynx, Tiger , ??? and I hear that it is the ultimate manouver to test the maturity of a heli design . Do we have it in our test shcedule .?.
Cheers

rad


Rad,
The R-22 is a piston trainer designed with an objective of building skill level (and keeping op costs low). Even the 1960's vintage Alouette-III with its 1st or 2nd gen turbine can run rings around the R-22, in terms of power margin and engine governing.
But the point really is– the R-22 being a trainer, also has an objective of building skill levels and all that stuff about flying and maintaining the engine+rotor within limits would definitely have honed your skill level – which is the actual thing required, really.

A couple of other interesting points here--
How are you so sure we haven't cleared aerobatic manoeuvres for the ALH? :mrgreen:
A barrel roll is more of an airshow manoeuvre with perhaps little practical relevance in the military environment- with also a fair possibility of mis-handling during recovery - in that context- barrel roll by choppers have been banned by some airshow authorities.
An over-the-top manoeuvre is what's required, in my opinion, to prove the chopper's credentials for aerobatic manoeuvrability.

And did you just say “test schedule” – HMMMM - 8) could you explain further?
Last edited by Hari Nair on 10 Sep 2010 10:50, edited 3 times in total.

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Re: LCH and other Helicopters Discussion Thread

Postby negi » 09 Sep 2010 20:52

Nachiket that's an interesting point, again the question is is the RPM varied or the PITCH ? :-?

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Re: LCH and other Helicopters Discussion Thread

Postby chetak » 09 Sep 2010 20:58

nachiket wrote:
correct me if I'm wrong but I always believed that conventional helicopters use change in tail rotor speed to turn about the axis. In Kamovs, if the rotors always rotate at 0 relative RPM, how will the helicopter turn?



nachiket ji,

Here's the deal.

The tail rotor RPM remains constant but the pitch (or blade angle) is changed to make the helo turn via the rudder pedals.


The KAMOVs use a mechanism known as the CDPCM -- collective differential pitch change mechanism.
Last edited by chetak on 09 Sep 2010 21:20, edited 1 time in total.

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Re: LCH and other Helicopters Discussion Thread

Postby Hari Nair » 09 Sep 2010 21:04

rad wrote:Yes i think they do have them , and also an auto hover flight control mode as well.

Hari nair correct me if i am wrong

rad

Right on Rad!!

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Re: LCH and other Helicopters Discussion Thread

Postby nachiket » 09 Sep 2010 21:05

chetak wrote:nachiket ji,

Here's the deal.

The tail rotor RPM remains constant but the blade angle is changed to make the helo turn.


The KAMOVs use a mechanism known as the CDPCM -- collective differential pitch change mechanism.

Ah, so changing the pitch basically changes the AoA at which the blades cut the air, thus increasing/decreasing the thrust produced by the propeller. Much better (and quicker) way than increasing/decreasing the RPM. Am I right?

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Re: LCH and other Helicopters Discussion Thread

Postby chetak » 09 Sep 2010 21:50

nachiket wrote:Ah, so changing the pitch basically changes the AoA at which the blades cut the air, thus increasing/decreasing the thrust produced by the propeller. Much better (and quicker) way than increasing/decreasing the RPM. Am I right?


nachiket ji,

No offence but.......

Some basic reading up on the net would do you the world of good, no?

Basic aerodynamics in great detail and good books on the subject are available from the usual shady sites as also the net.

Do be a good sport and do some preliminary homework. :)

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Re: LCH and other Helicopters Discussion Thread

Postby Kartik » 09 Sep 2010 23:08

finally seeing some excellent discussions on BRF !! Hari Nair sir, please make your way to the Indian Aviation and MRCA threads as well !

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Re: LCH and other Helicopters Discussion Thread

Postby rad » 10 Sep 2010 00:08

Dear Hari Nair

Thanks for clearing the barrel roll importance , when you talk of over the top manouver is it like a stall turn in a fixed wing aircraft ,or in a heli where your nose is pointing straight up and nearly zero airspeed and then stomping on the rudders to swing the nose of the heli to point downwards and picking up airspeed subsequently , am i right .
I have seen the ALH do great aerobatics , a lay man seeing seeing a roll in a heli invariably draws oooohhs from the crowds so thats why i asked questions about the barrel role . Am i right in saying the tiger heli is the most manouverable heli around today , if not what in your opinion in is the most manouverable heli in the world.
cheers

rad

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Re: LCH and other Helicopters Discussion Thread

Postby rad » 10 Sep 2010 00:20

Dear Hari nair
When i talked about test schedule i was refering to wether doing a barrel role was a test point to be achieved ,
Is the hardware and software of the auto hover mode made in india or is it imported?
also there was some talk of active vibration cancellation system , is it also incorporated ?

rad

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Re: LCH and other Helicopters Discussion Thread

Postby Hari Nair » 10 Sep 2010 10:49

nachiket wrote:
chetak wrote:nachiket ji,

Here's the deal.

The tail rotor RPM remains constant but the blade angle is changed to make the helo turn.


The KAMOVs use a mechanism known as the CDPCM -- collective differential pitch change mechanism.

Ah, so changing the pitch basically changes the AoA at which the blades cut the air, thus increasing/decreasing the thrust produced by the propeller. Much better (and quicker) way than increasing/decreasing the RPM. Am I right?


Almost all helicopters use a near-constant rotor RPM. The main and tail rotors usually have a fixed ratio drive from the Main Gear Box. Rotor thrust is varied by altering pitch angles of blades, which results in variation of torque required to drive the rotors. The required torque is supplied by the powerplant.

This might just change in the future with high-speed helicopters with configurations such as the ABC, that will need to vary the rotor RPM to cope with high speeds and hover.

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Re: LCH and other Helicopters Discussion Thread

Postby vic » 10 Sep 2010 11:04

Mr. Hari Nair

Can you tell us something about the Medium Lift helo being proposed by HAL?

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Re: LCH and other Helicopters Discussion Thread

Postby vina » 10 Sep 2010 12:22

negi wrote:^ Hari sir regarding 'blade rendezvous' does this happen only during landings/take offs ? Also is it correct to assume in case of Kamovs once the rotors are engaged they always rotate at '0' relative RPM (with respect to each other) hence chances of blade rendezvous are very low as long as they remain engaged (as the blades of rotors are out of phase) ?


No. The rotors are spinning in opposite direction so the the relative angular velocity is not zero but actually 2*omega (angular velocity).

So I guess that blade "rendezvous" can happen at any speed under conditions where the clearance margin at the blade tips exceed the design clearance!.

If as you postulate the relative speed is zero, then it is very easy to fix the rendezvous problem. You can offset one rotor disk relative to another by a few degrees so that the blades will never strike each other how much ever they flap. That is simplicity itself and a piece of laddoo to do it. But now since each blade crosses the a particular one (assuming a single one sided blade... not real world, coz balancing that would be a b*tch, but as a thought experiment, fine, so 2 single blades one on top of the other) at a frequency of 2*omega and the oscillations are white noise random, all you can do is set the vertical offsets between the rotors so far apart that they can never clash for a given blade length.

Problem is that it limits the disc size (longer blades flex more). From basics we know that as much as practically possible, you want a large slow spinning rotor disc rather than a fast spinning slower one! That said, the Kamov type has 2 rotor discs, so each disc can be half the size theoretically of a single disc copter!.

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Re: LCH and other Helicopters Discussion Thread

Postby neerajb » 10 Sep 2010 13:14

Below is the main rotor of H-19. Can someone help me to locate the flapping hinge?
Hari Sir, I tried searching for high res pics of ALH rotor but found none. If it's not classified, can you please upload one? Thanks in advance.

Image

Cheers....

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Re: LCH and other Helicopters Discussion Thread

Postby Hari Nair » 10 Sep 2010 13:15

rad wrote:Dear Hari nair
When i talked about test schedule i was refering to wether doing a barrel role was a test point to be achieved ,
Is the hardware and software of the auto hover mode made in india or is it imported?
also there was some talk of active vibration cancellation system , is it also incorporated ?

rad


The most manoeuvrable helicopters in the world are the RC (Radio Control) models!!

This is partly because the models manage a higher rotor Lock number (ratio of aerodynamic to inertial forces). When the Sarang partook in the Al Ain Aerobatic Show under the FAI, there were some RC helicopters and after a couple of days of watching us, the RC choppers imitated and even bettered our manoeuvres! The little bu**ers were actually following our profile and even doing it better with stuff like reverse tail slides, inverted flat turns and they also had tiny smoke generators for effect.

In the full-scale world, the honours will need to go to MBB’s (Messerschmitt-Bölkow-Blohm) BO-105. It has a rigid titanium rotor head and fibre-glass rotor blades and a high flapping hinge-equivalent offset. The main rotor called “System Bolkow” was pretty revolutionary when introduced. It’s a smaller machine at 2.5 tonnes AUW (comparable to the Chetak) and is capable of some very extreme and amazing aerobatics – beats even fixed wing aircraft with some of those manoeuvres. There are a whole lot of You-Tube videos in the ‘net - check them out.

The Germans then went on to make the next gen ‘FEL Rotor’ –which is used on the Tiger. With MBB being design consultants in the early days of the ALH programme, the ALH’s rotor design is based on the ‘FEL Rotor’, with several important changes that were incorporated during the in-house development. MBB /Eurocopter Deutschland were also consultants on the US Commanche stealth helicopter program, which used a five-blade variant of their ‘FBW Rotor’, derived from the Bo-108 /EC-135.

Unfortunately now, with the Commanche program having been terminated and perhaps due to their merger into Eurocopter, the old MBB focus on hinge-less rotors with manoeuvrability seems to have been diluted.

Re- your question on a test point to achieve / clear the ALH for a barrel roll – read in conjunction with my earlier post on the utility of a barrel roll for helicopters. Test programmes are expensive and involve teams of specialists with prototypes, all doing their stuff to achieve defined objectives – which are towards meeting the defined requirements. All of that is an on-going process and one needs to interrupt and divert resources for anything else. It’s not a question of wanting to prove whether the ALH is capable of a barrel roll because another helicopter demonstrated it in an airshow – the more important question you need to answer is – why do you want to do the test if it doesn’t even remotely contribute towards mission capability? And in that context keep in mind that helicopter missions are invariably at low level over terrain and carrying out a barrel roll is perhaps, an interesting way to attract the attention of every weapon system in the neighbourhood!

The auto-hover function is obviously software driven (what hardware element were you referring to?) and its been developed in-house.
Last edited by Hari Nair on 10 Sep 2010 14:09, edited 1 time in total.

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Re: LCH and other Helicopters Discussion Thread

Postby Philip » 10 Sep 2010 13:35

Good news in today's papers that an additional 50-60 medium utility helos,MI-17Vs are being acquired (decision finalisedat highest levels) from Russia in additional to the 80+ already acquired.These meant to replace the older MI-8s,which have been soldiering on for an incredible 40+ years-a testament ot the maintenance capabilities of the IAF's heo corps,will prove immensely useful in the High Himalayas.

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Re: LCH and other Helicopters Discussion Thread

Postby Hari Nair » 10 Sep 2010 13:52

neerajb wrote:Below is the main rotor of H-19. Can someone help me to locate the flapping hinge?
Hari Sir, I tried searching for high res pics of ALH rotor but found none. If it's not classified, can you please upload one? Thanks in advance.

Cheers....

Neerajb - check out my earlier post on hinge-less rotors. The ALH does not have a flapping hinge. Check out the pic of the rotor head at:
http://www.b-domke.de/AviationImages/Ro ... #Hindustan
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Re: LCH and other Helicopters Discussion Thread

Postby Hari Nair » 10 Sep 2010 14:03

vina wrote:
No. The rotors are spinning in opposite direction so the the relative angular velocity is not zero but actually 2*omega (angular velocity).

So I guess that blade "rendezvous" can happen at any speed under conditions where the clearance margin at the blade tips exceed the design clearance!.

If as you postulate the relative speed is zero, then it is very easy to fix the rendezvous problem. You can offset one rotor disk relative to another by a few degrees so that the blades will never strike each other how much ever they flap. That is simplicity itself and a piece of laddoo to do it. But now since each blade crosses the a particular one (assuming a single one sided blade... not real world, coz balancing that would be a b*tch, but as a thought experiment, fine, so 2 single blades one on top of the other) at a frequency of 2*omega and the oscillations are white noise random, all you can do is set the vertical offsets between the rotors so far apart that they can never clash for a given blade length.

Problem is that it limits the disc size (longer blades flex more). From basics we know that as much as practically possible, you want a large slow spinning rotor disc rather than a fast spinning slower one! That said, the Kamov type has 2 rotor discs, so each disc can be half the size theoretically of a single disc copter!.


Check out Chetak's post regarding a bit of background reading ! :)
There's no now way you can make both rotors turn the same way and still fly the beast - you need to deal with torque reaction - which means the rotors need to be contra-rotating.

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Re: LCH and other Helicopters Discussion Thread

Postby negi » 10 Sep 2010 19:33

Wow just wow , my yesterday's post can easily give a 'charsi' a run for its money. :oops: Apologies for creating the confusion.

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Re: LCH and other Helicopters Discussion Thread

Postby Austin » 10 Sep 2010 19:47

Philip wrote:Good news in today's papers that an additional 50-60 medium utility helos,MI-17Vs are being acquired (decision finalisedat highest levels) from Russia in additional to the 80+ already acquired.These meant to replace the older MI-8s,which have been soldiering on for an incredible 40+ years-a testament ot the maintenance capabilities of the IAF's heo corps,will prove immensely useful in the High Himalayas.


Quite surprising they went for additional 50 plus Mi-17V , I remember reading Russia had proposed a version of Mi-38 as JV for HAL 12 T Medium Chopper project.

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Re: LCH and other Helicopters Discussion Thread

Postby shiv » 10 Sep 2010 19:57

Hari Nair could I ask if the Chetak the HAL helicopter academy lost has been replaced temporarily or permanently with an Mi 17?

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Re: LCH and other Helicopters Discussion Thread

Postby sumshyam » 10 Sep 2010 21:48

Sry If reposting..!

Scientists working on smart material for ALH

The project, funded by HAL, aims to build an “active trailing edge flap” and a “controller” that will make the flap, mounted on the aircraft’s rotor blades, respond in such a way to the aircraft’s vibrations that they will be reduced.

Reducing vibrations, apart from making the flight more comfortable for passengers, puts less strain on the aircraft’s structures, making them durable.

HAL’s Rotary Wing Research and Development Centre is collaborating with IISc’s department of aerospace on the Rs 6 crore effort.

IISc’s scientists said there are five different parts of the project. “Some of them are at the fabrication and prototype stage, at both the institute and HAL, following which there will be wind tunnel and other tests. Others need more work. An initial prototype, to demonstrate the concept, will be ready in two years. After that, to actually build an ALH-ready system that can get certification will take till 2010.”

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Re: LCH and other Helicopters Discussion Thread

Postby neerajb » 10 Sep 2010 22:39

sumshyam wrote:Sry If reposting..!

Scientists working on smart material for ALH



It's eerily similar to EADS Blue pulse. The date of the article suggests that HAL is working on it since 2005. So finally we are reaching the bleeding edge stage (at least in ALH).

Cheers....

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Re: LCH and other Helicopters Discussion Thread

Postby Hari Nair » 12 Sep 2010 08:53

shiv wrote:Hari Nair could I ask if the Chetak the HAL helicopter academy lost has been replaced temporarily or permanently with an Mi 17?

Replace with an Mi-17? :eek: That's a big fella at 13 tonnes, a 22 metre rotor, two powerful engines and a whole heap of systems on-board, very difficult for a newbie to learn to fly. The Academy was doing fairly well and this accident is very unfortunate - However, I am sure they will come out of this setback. You could ask their CFI about the future plans.
Last edited by Hari Nair on 12 Sep 2010 09:01, edited 1 time in total.

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Re: LCH and other Helicopters Discussion Thread

Postby Hari Nair » 12 Sep 2010 08:57

Austin wrote:
Philip wrote:Good news in today's papers that an additional 50-60 medium utility helos,MI-17Vs are being acquired (decision finalisedat highest levels) from Russia in additional to the 80+ already acquired.These meant to replace the older MI-8s,which have been soldiering on for an incredible 40+ years-a testament ot the maintenance capabilities of the IAF's heo corps,will prove immensely useful in the High Himalayas.


Quite surprising they went for additional 50 plus Mi-17V , I remember reading Russia had proposed a version of Mi-38 as JV for HAL 12 T Medium Chopper project.


The Mi-38 is a heavier 15 tonne aircraft.

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Re: LCH and other Helicopters Discussion Thread

Postby Singha » 12 Sep 2010 08:59

EADS also has a new design rotor with a oar type fat section at the end to reduce noise. could compromise on other things for noise
though. for attack and SF insertion helis quieter the better.

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Re: LCH and other Helicopters Discussion Thread

Postby viktor » 12 Sep 2010 09:54

Sorry to interrupt ongoing discussion, but I had this question in mind and feel that some guru will be able to answer it.

From what I understand, Denel has shutdown AH-2 Rooivalk project after supplying South African AF with just 12 birds. Denel has stopped the funding but they would still have the tech. Why can't we take their inputs for LCH project? Moreover we can rope in Mokopa for the work they have done on ZT-6 ATGM. I know Rooivalk is a heavier helo that LCH but it would save us lot of trouble and build relationship between our industries. I understand that Denel is blacklisted, but there are always loopholes in govt. policy.

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Re: LCH and other Helicopters Discussion Thread

Postby chetak » 12 Sep 2010 10:40

http://www.economist.com/node/16990748

Faster helicopters
More rotors, more speed
A new type of helicopter breaks speed records

Sep 9th 2010


The X2 is an experimental helicopter being developed by Sikorsky, an American company, at a test-flight centre in Florida. It recently flew at more than 430kph (267mph), according to a report in Spectrum, published by the Institute of Electrical and Electronics Engineers. The present record is held by a souped-up Westland Lynx helicopter, which managed 400kph in 1986. But most helicopters can’t fly at anything like these speeds and are typically flat out at 270kph.

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Re: LCH and other Helicopters Discussion Thread

Postby shiv » 12 Sep 2010 12:07

Hari Nair wrote:
shiv wrote:Hari Nair could I ask if the Chetak the HAL helicopter academy lost has been replaced temporarily or permanently with an Mi 17?

Replace with an Mi-17? :eek: That's a big fella at 13 tonnes, a 22 metre rotor, two powerful engines and a whole heap of systems on-board, very difficult for a newbie to learn to fly. The Academy was doing fairly well and this accident is very unfortunate - However, I am sure they will come out of this setback. You could ask their CFI about the future plans.


Ah then I was mistaken in assuming that the Mi 17 circling around might have been doing that job. It did seem unlikely even to my basically ignorant self. I did not think of the factors you have mentioned but felt the cost of fuel would be high 8) . But I thought I'd ask anyway.


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