Rahul M wrote:thanks, what do you think the service ceiling would be like ?
also up to what alt would it retain hover ability ?
Every country and every manufacturer defines Service ceiling with respect to helicopters in a different way. Some define it as the same as aircraft so that the climb rate must be maintained at around 0.5 meters/sec and the highest altitude at which the aircraft can do that is considered as its service ceiling. But the question then arises: at what weight of the system? The Normal TO weight? MTOW? or Operational Weights?
Another question which adds the combination of answers is whether in multi-engined helicopters whether one engine should be deactivated for these tests or is it both engines running? Maximum sustainable power or Emergency power?
As you can see, the combination of the above are aplenty. So each manufacturer tweaks these numbers to reflect better on their products.
So I wouldn't even try to put values here that people will try and compare brochure specifications with and come back and say "Hey, this site says this and that site says that" and so forth. All of these are true if we knew the context, which these sites will never mention.
So, what I will tell you is that I define helicopter performance into five criteria:
a) Flight performance (Forward flight at cruising speeds): defined at having full spec rate of climb and maximum sustainable power from both engines to carry the maximum payload for a given altitude.
b) Vertical Lift-off: defined at having a minimum rate of climb of 2.5 meters/sec (combat rate of climb) for a non-forward roll liftoff for maximum payload at a given altitude with calculations being made for OGE conditions.
c) Rolling-Take-off: defined same as above but for helicopters with landing wheels and availability of ALGs (Advanced Landing Grounds).
d) Hover IGE (In-Ground-Effect): calculated for a minimum rate of climb of 0.5 meters/sec for a vertical liftoff at maximum possible payload for a given altitude. This is your Hover ceiling by the way (as long as the design weight is capable of being lifted)
e) Hover OGE (Out-of-Ground-Effect): calculated same as for Hover IGE.
The last two are purely of academic use in the sense that a rate of climb of 0.5 meters/sec is meaningless to most Military forces. In reality, a rate of Climb of a minimum of 2.5 Meters/sec (~500ft/min) is required and is known as combat ceiling, and is the reference I try to follow when I do these calculations.
Now, coming to the issue of fuel/payload ratios, you need to fix that for a given range. So assuming we have a requirement of a combat radius (note: radius, not range) of around 100Km in the Aksai Chin region, and fixing the fuel for that, the LCH is capable of lifting (per my calculations) around 400Kg of weapons from an altitude of around 16000 feet under combat-ceiling conditions defined above and around 540 Kg of weapons from the same altitude for Hover OGE conditions.
These values are what remains after you remove the standard airframe weights, fuel, the weights of the flight crew, auxiliary weights, lubricants (which should not be ignored and can be substantial for heavier helicopters) and assuming a 10% reserve fuel for the said flight.
At 18000 feet, the LCH is capable of hovering with the above weapons load assuming that some fuel has been lost during the flight to that altitude. Very few peaks in the Aksai-Chin region are higher than 18500 feet, so I doubt the need to be hovering anywhere near them, but these are the engineering limits anyway.
But if the helicopter were cruising above the same region rather than hovering, then the LCH can in fact lift up to around 1000Kgs during forward flight for maximum rate of climb up to around 22000 feet and higher if you leave the condition of design ROC.
Note: Any suggestions to improve the above model are welcome. The results of the calculations can vary around 10-15% either way from actual data as far as I can tell. Sorry!
p.s. check mail.
Yeah, I got it. Thanks. Will get back to you on that pretty soon.