Helicopter Performance Analysis

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vivek_ahuja
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Helicopter Performance Analysis

Postby vivek_ahuja » 15 Mar 2015 16:29

The Indian Light Utility Helicopter Procurement: where does HAL’s LUH bid stand?

Introduction:

An analysis is presented here to compare the various helicopters bidding for the Indian Light Utility Helicopter (LUH) procurement. In addition to the Bell 407, the Eurocopter Fennec and the Kamov Ka-226T, HAL’s own design, known by the generic title LUH, is also in the fight to win the contract. But where does the LUH stand amongst its competitors? For that matter, where do the competitors stand amongst themselves?

The procurement of any military aircraft or helicopter type is a complicated process. And this analysis will not attempt to cover all possible areas pertaining to geo-politics, economics or the like. Instead, the focus of this analysis is on a preliminary aerodynamic and propulsive standpoint, especially for the extremely high-altitude conditions encountered in the Himalayan Mountains. The analysis is done using simulation tools that integrate payload capacities and typical rate-of-climb requirements with a preliminary rotary aerodynamics model and a simple propulsion module. When coupled with an atmospheric simulator for the Himalayas, the performance of each helicopter type can be predicted and compared. The rotary-aerodynamics module is advanced enough to predict the different performances of a single main rotor plus tail rotor system, a tandem rotor system or a contra-rotating rotor system as found for the Kamov designs. Furthermore, the models allow for the performance analysis in Ground Effect conditions. The Ground Effect conditions are encountered when the helicopters are hovering very close to the ground and serves to work as a performance multiplier with regard to power needed in lifting a certain payload.

The models do not compensate for transmission limitations for the power, which means that the analysis is idealized wherein power generated is power available. This is, of course, not encountered in practice, but works well for high-altitude conditions where power available is almost always less than the transmission limits. At lower altitudes, the performance of the various designs must be assumed to be ideal, rather than restricted from transmission and structural limitations. For example, the maximum rate-of-climb (ROC) values obtained from this simulator for sea-level (SL) conditions will typically be higher than what is allowed by other limitations. However, such removal of limitations is required in order to compare the various contenders at the same performance benchmarks.

Data for this analysis is obtained from the manufacturers via open-sources. No proprietary information is shared here. Unless where cited, the analysis results are to be considered proprietary of the author. See remarks for details.

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General remarks on the LUH design:

Of the four helicopter types involved, three belong to the standard single-main-rotor design concept. These are the Fennec, LUH and Bell-407GT. All of these designs feature a main rotor and a tail rotor. The tail rotor designs all have a major power/aerodynamics drawback in that the tail rotor does not correspond to lifting payload and yet draws power away from the engines. This power requirement can vary in the range of 10-15% of total available power in some designs. The Ka-226T belongs to the contra-rotating design model and overcomes the tail rotor by having two contra-rotating rotors that cancel net rotor torque. Since both rotors contribute to vertical thrust, the losses from the tail rotor are theoretically recovered. However, two contra-rotating sets of blades in close proximity contribute to other losses that serve to negate some of the advantages of the design. Current analysis suggests that this loss is almost the same as tail rotor losses. However, the lack of the tail rotor serves additional practical advantages including a compact design, removal of a vulnerable boom, easier entry and exit of passengers (with less risk) and overall increase in maneuverability.

From the power standpoint, the LUH’s power-plant and drivetrain is the biggest variable at the time of writing of this article. While the Bell, Eurocopter and Kamov designs are essentially “stabilized” from a design standpoint, the HAL design remains a mystery in terms of performance. The first prototype has not yet flown. And varying sources at different times have quoted different power and weight numbers. To compensate for this, the analysis here will provide a spread of numbers for the LUH performance depending on what its final powertrain will look like and what its limitations are likely to be. The spread is distributed between three power output numbers from the single Shakti engine employed within the LUH: 750 KW (provided by HAL during a presentation on the LUH design; it is possible that this is not the rated engine output but rather the transmission limitation at sea-level), 825 KW (assuming that the powertrain will have similar limitations to the LCH) and 1,067 KW (assuming maximum powertrain efficiency using the Shakti engine output). The Shakti engine power output is well ahead of any of the equivalent engines in the competition, but the powertrain restrictions will decide how much potential of the engine has been extracted.

Similarly, another area of focus will be the overall weight of the LUH design. Numbers provided by the HAL during its presentations at Aero India 2015 point to an empty mass of the LUH to be 1,910 kg. When compared with the empty masses of its competitors, 1,220 kg (Fennec), 1,700 kg (Ka-226T) and 1,210 kg (Bell-407GT), the weight of the LUH is an immediate area of concern. One possibility is that the weight is a result of a much more powerful power system (Shakti engine) in the LUH. However, this is only balanced out if the resulting power from the engines transmitted to the rotors is much higher than the other designs. If only a 750 KW powertrain is extracted despite the 1,910 kg empty weight of the helicopter (as quoted by HAL in its official presentations), the resulting performance can be expected to be dismal at best compared with the other LUH bids. The HAL design team, drawing experience from the ALH and LCH efforts, will have to undergo a similar effort in weight-trimming and in improving the power-train restrictions of the LUH design. Further details will be obtained when the first prototype of the helicopter flies in 2015 or early 2016.

Performance results:

Two sets of hover performance numbers have been presented. The first set is for conditions where the helicopter is hovering out of the Ground Effect (OGE) and the other set is for hover performance in Ground Effect conditions (IGE). The IGE performance is evaluated for the various contenders for a hover altitude of 2 meters above the ground. The performance is evaluated for all the helicopters at empty weight conditions (no fuel and no passengers) and the maximum allowable payload is restricted to 1,000 kg (internal or external). The hover performance is evaluated at altitudes varying from 0 ft (SL) to 25,000 ft. Altitudes in the Himalayan Mountains regularly require flights above 10,000 ft and often up to 22,000 ft.

Image Image

The Bell-407 and Fennec models are virtually identical with minor differences in hover performance. This is not unexpected. Generally speaking, the Fennec (AS-550) model is found to perform slightly better at higher altitudes (greater than 10,000 ft). For example, at 20,000 ft altitude, the Fennec can lift ~50 kg more payload than the Bell design. However, considering the very close performance of the two designs, this minor difference should be accounted within the error margins of the analysis. For all practical purposes, the two Eurocopter and Bell models perform similarly under ideal conditions. Structural and transmission conditions may put one design above the other, however. Both these helicopters have a similar loss in performance versus altitude as ascertained from the slopes of their payload-altitude curves. The IGE performance is superior to the OGE performance for these two designs as seen above. Both helicopters can lift up to ~850 kg in Ground Effect conditions as compared to only ~450 kg out of Ground Effect conditions. Note, however, that this lifting capacity does not include pilots and fuel (> 400 kg overall) nor does it allow for any rate-of-climb capacity to allow flying in valleys and mountains. When these factors are accounted, the net payload capacity of the two helicopters is negligible beyond ~17,000 ft altitude.

The Kamov model has visibly different performance owing to its different design concept. A combination of high empty mass, contra-rotating rotors and higher available power means that the tail-off in performance for this design is different from the Bell and Eurocopter models. The performance of the Kamov design generally tails-off faster than its competitors at higher altitudes. There is a substantial difference in hover performance between the Kamov design and others beyond 15,000 ft altitude and this difference only increases as altitude increases. When similar pilot, fuel and rate-of-climb effects are added, the Kamov design’s payload capacity is negligible beyond ~16,000 ft altitude.

The HAL design’s performance varies between outstanding or dismal depending on what power transmission numbers are assumed. If HAL’s quote of 750 KW transmission is assumed, coupled with the 1,910 kg empty weight, the performance of its design is far below the others. Under such conditions, the LUH can have negligible payload beyond ~14,000 ft altitude in OGE hover. A powertrain similar to that of the LCH will bring the performance of the HAL design similar to that of the Kamov design. However, if we assume that the implied 750 KW is simply the transmission limitation and not the engine output (which is 1,067 KW), then the performance of the HAL design far exceeds the performance of its competitors and can haul usable payloads up to an altitude of ~21,000 ft despite the much higher empty weight.

Ground effect multipliers for the various designs are also different and offer differing improvements for the four designs (see below). Once again, the Bell and Fennec designs are near identical in their IGE performance effects. The LUH, with a slightly higher main-rotor blade radius performs better. The Kamov design gains the best effects in IGE conditions on account of its twin-rotor system with large blades. It is the result of this improved performance in IGE that allows the Kamov design to match the Bell and Fennec designs in IGE hover up to an altitude of 20,000 ft. Beyond 22,000 ft, the IGE performance gains for the Kamov tail off coupled with its general performance to bring it below its other competitors.

Image

Maximum rate-of-climb performance with a usable payload is of more importance within the context of a light-utility helicopter than it is for medium and large transport helicopters. A utility helicopter is expected to perform a variety of roles under tough conditions where the maximum payload is less important than the maneuverability in the vertical plane. For this to be compared, all of the designs were run through the simulations with a maximum payload of 500 kg in addition to 200 kg for crew and 300 kg for fuel (1,000 kg overall payload). The maximum ROC was plotted versus altitudes from sea level to 25,000 ft.

Image

For the max-ROC profile, the performance of the Bell, Eurocopter and Kamov designs are similar. The maximum vertical ROC obtained at sea-level is by the Fennec (10.28 m/sec). The worst performer for sea-level conditions is the Kamov design (8.41 m/sec). Assuming the 750 KW limitation proposed by HAL for its design, a dismal maximum vertical ROC is obtained (6.80 m/sec). The tail-off in max-ROC at high altitude is also of a similar trend, considering the near-linear variation in performance versus altitude (as expected theoretically). An HAL design boosted with a full 1,067 KW throughput puts the HAL design far in excess of its competitors (16.78 m/sec!). But this is an ideal that HAL itself has stated to be unrealistic considering their statement for a 750 KW restriction. A powertrain throughput on a single engine similar to that of LCH will put the HAL design within the spread of its competitor designs.

Conclusion:

The first-flight of the HAL design in 2015/16 will provide much insight into the successes (or failures) of the HAL design team to meet its competitors for the LUH contract. How much empty weight can be shaved off and how much more power can be provided to the main rotor will determine the performance of the design at high-altitude. Current numbers provided by HAL do not suggest that the first prototype of the LUH will be superior to its competitors from Bell, Eurocopter and Kamov. However, it is expected that the prototype will serve as a test-bed in which the HAL team can conduct a series of efforts to improve performance as confidence in its design builds up. How fast that effort can be undertaken, how long the process will take and whether it will be successful or not, remains to be seen.

-Vivek

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Re: Indian Military Helicopters

Postby Indranil » 15 Mar 2015 20:40

Thank you for the excellent work Vivek ji.

LUH will be powered by the Ardiden 1U which was bench tested and delivered to HAL in December 2014. Although, there is no credible information on its output power, there are a few pointers:

1. Safran's Tweet:
#DidYouKnow? #Ardiden 1U/#Shakti 1U on #LUH will allow the helicopter to fly at 6,500 m = 20,000 feet


2. HAL is developing its very own turboshaft, rated between 1000 kW and 1200 kW.

3. By the way, does anybody have a clear picture of the display board placed in front of the LUH?
Image

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Re: Indian Military Helicopters

Postby sankum » 15 Mar 2015 22:05

Image

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Re: Indian Military Helicopters

Postby vivek_ahuja » 16 Mar 2015 10:16

Why the LCH is a sports car compared to the lumbering Z-10


Introduction:

I often get asked the question: “Is the Indian LCH better than the Chinese Z-10?” An attempt to answer such a question verbally is difficult. It is preferable that one sees the numbers themselves. The Z-10 is two times heavier than the LCH when carrying the same payload in weapons, fuel and crew. The Z-10’s empty weight is 5,540 kg and the LCH even in its current overweight mode is about 2,800-3,000 kg. And yet the Z-10 is powered by the same net total power as the LCH (~2,000 KW for the Z-10 versus ~1,700 KW for the LCH). That’s a nasty combination in terms of performance, both at sea-level and at high altitudes. The effect of additional weight versus power required is non-linear for rotary flying machines.

But just how bad is it really for the Z-10?

To answer that question, I present here a comparison study. We will take the LCH and the Z-10 and put an identical payload of 500 kg on them. We will run both helicopters through a simulation model where we subject them to altitude variations and see how it affects their rate-of-climb capabilities while in hover, out of Ground Effect conditions. The rate-of-climb (ROC, measured here in meters/second) is a true measure of the maneuvering capability of an attack helicopter. Typically, a ROC of 0.5 m/sec is used to evaluate service ceiling conditions. A ROC of 2.5 m/sec is typically the bare minimum for combat conditions. For a helicopter in high mountains to be truly maneuverable, it may need somewhere in the range of 2.5 to 8 m/sec vertical ROC equivalent in power capacity. Of course, beyond a certain altitude, the helicopter may not be able to fly with the 500 kg payload, let alone providing additional power for high ROC. So we will also see where those limits are for the LCH and the Z-10.

The focus of this analysis is on a preliminary aerodynamic and propulsive standpoint. The analysis is done using simulation tools that integrate payload capacities and typical rate-of-climb requirements with a preliminary rotary aerodynamics model and a simple propulsion module. When coupled with an atmospheric simulator for the Himalayas, the performance of each helicopter type can be predicted and compared. Furthermore, the models allow for the performance analysis in Ground Effect conditions. The Ground Effect conditions are encountered when the helicopters are hovering very close to the ground and serves to work as a performance multiplier with regard to power needed in lifting a certain payload.

The models do not compensate for transmission limitations for the power, which means that the analysis is idealized wherein power generated is power available. This is, of course, not encountered in practice, but works well for high-altitude conditions where power available is almost always less than the transmission limits. At lower altitudes, the performance of the various designs must be assumed to be ideal, rather than restricted from transmission and structural limitations. For example, the maximum rate-of-climb (ROC) values obtained from this simulator for sea-level (SL) conditions will typically be higher than what is allowed by other limitations. However, such removal of limitations is required in order to compare the various contenders at the same performance benchmarks.

Data for this analysis is obtained from the manufacturers via open-sources. No proprietary information is shared here. Unless where cited, the analysis results are to be considered proprietary of the author. See remarks for details.

Image

LCH versus the Z-10:

The hover performance is evaluated at altitudes varying from 0 ft (SL) to 25,000 ft. Altitudes in the Himalayan Mountains regularly require flights above 10,000 ft and often up to 22,000 ft. The data is presented for the LCH and the Z-10 for payload and available maximum ROC capability versus altitude. A threshold ROC line is shown for the reference 8 m/sec combat ROC.

Image

Notice how the sea-level performance of the LCH and the Z-10 are significantly different. The Z-10, with a 500 kg payload (not counting weapons and fuel) is able to generate a maximum vertical ROC capability of 3.6 m/sec. By comparison, at sea-level, the LCH is able to carry the 500 kg and is able to provide a power excess for a theoretical max ROC of 21 m/sec! Of course, this will not be allowed in reality. The LCH powertrain transmission limitations will bring that max ROC to about ~10 m/sec for structural safety reasons. Both helicopters are able to lift the 500 kg requirement at sea-level.

Now consider how the change in altitude affects both helicopters. The Z-10, trying to maintain the 500 kg payload, begins to tail-off its ROC capability from 3.6 m/sec at sea-level to 0 m/sec ROC at ~8,000 ft. Beyond 8,000 ft altitude, the Z-10 also cannot carry its 500 kg payload and the tail-off in that capacity is dramatic. The Z-10 cannot operate beyond 10,000 ft under any conditions.

The LCH, on the other hand, utilizes its light-weight structure to great effect. It can not only maintain the 500 kg payload for all altitudes from sea-level to the Himalayan mountain tops, the tail-off in the ROC does not drop below 8 m/sec until ~12,000 ft. The tail-off does not drop below the minimum 2.5 m/sec until ~19,000 ft. The LCH can fly, and fight, at all altitudes in the Himalayas.

Z-10 versus the Mi-35: The Pakistani Insight

You will notice that I put the Mi-35 performance numbers in the plot above for identical conditions. The reason for doing so is to illustrate why the Pakistanis went for the Mi-35 option when the spanking-new Z-10s were on the table. The Mi-35 performance for high-altitude conditions is dismal. This is a fact known in Indian Air Force circles for many years and has led to the genesis of the LCH. But as bad as the performance for the Mi-35 is in the mountains, it is still better than the Z-10. At sea-level, the Mi-35 can completely outperform the Z-10 for ROC capability. Its ROC tail-off at high altitude is at ~9,500 ft. Its payload tail-off is at ~12,500 ft. Both these numbers are better than that of the Z-10. Coupled with lower operating costs and generally rugged reliability, the Pakistani decision to pursue the Mi-35 becomes clearer. Additional geo-political and economic constraints may also apply, but are not discussed here.

-Vivek

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helicopter performance analysis

Postby Singha » 17 Mar 2015 08:51

for the agyani asuric hordes to learn quietly from the gyanis.

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Re: helicopter performance analysis

Postby vivek_ahuja » 17 Mar 2015 20:55

Singha, Indranil,

Thanks for creating this thread for my ramblings. :)

-Vivek

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Re: helicopter performance analysis

Postby vivek_ahuja » 17 Mar 2015 20:59

Why the Apache is a brute and LCH is elegant
Last edited by Indranil on 06 Oct 2015 20:18, edited 1 time in total.
Reason: Post updated below.

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Re: helicopter performance analysis

Postby sohamn » 17 Mar 2015 22:49

Very good analysis and thanks for the detailed explanation. It would be great if you can compare Mi-17 configured as attack chopper vs LCH. This is because we used Mi-17 / Mi-8 during Kargil operations to great effect till the SAM threat became serious.

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Re: helicopter performance analysis

Postby Cybaru » 18 Mar 2015 01:08

Vivek,

Thanks for your writeup. I think the real performance of the D model is much lower than what you suggest. It has trouble high altitudes. A better comparision would be the Echo model with RR engines. That allows for higher performance and the performance we may demand for our forces. The D model does not have color feed from its sensors unlike the DoCompass EO sensor on the dhruv/lch combo. Could you add the E model with RR engines in this graph?

Question: What about environmental controls in the cockpit in these helicopters that operate at these high altitudes. Do they carry oxygen? Any real cabin pressurization? or as usual we carry 30 minute oxygen bottles?

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Re: helicopter performance analysis

Postby deejay » 18 Mar 2015 08:17

Vivek Sir, In your LUH comparison above a major evaluation factor (IMHO only) at the 'User' level could be the performance of existing Cheetah's for the same parameters (IGE/OGE; ROC; Payload; Engine Start Altitude; Range/Endurance etc). The expectation from this Light Helicopter will be to do better than the Cheetah on most factors if not all.

Maybe, you could include in the graphs the performance of the Cheetahs (If available) for a better understanding on the status of contenders vs. the existing platform. (Only a request from a jingo!!!)

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Re: Helicopter Performance Analysis

Postby ramana » 19 Mar 2015 00:14

Vivek, KiranM reported thinking the comments are visible to the poster. Its wrt Apache and LCH post.

KiranM wrote:
Couple of corrections might be needed.

"So we will also see where those limits are for the LCH and the Z-10. "
Looks like copy/ paste error. Needs to be AH64D instead of Z-10.

"The LCH, on the other hand, once again utilizes its light-weight structure to great effect. It can not only maintain the 1,000 kg payload for another 3,000 ft altitude (i.e. up to ~21,000 ft), the tail-off in the ROC does not drop below 8 m/sec until ~11,000 ft."
As per graph it is not 11000ft but ~7500ft?



Thanks,


ramana

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Re: helicopter performance analysis

Postby vivek_ahuja » 19 Mar 2015 10:18

Cybaru wrote:Thanks for your writeup. I think the real performance of the D model is much lower than what you suggest. It has trouble high altitudes. A better comparision would be the Echo model with RR engines. That allows for higher performance and the performance we may demand for our forces. The D model does not have color feed from its sensors unlike the DoCompass EO sensor on the dhruv/lch combo. Could you add the E model with RR engines in this graph?


Apologies. I should have mentioned that I had used the Apache E model engine (T700-GE-701D and not T700-GE-701C). Hence the improved performance in the high-altitude arena.

But the mass and other numbers are for the Apache D model. This is because I couldn't get reliable information for the E model mass values.

So just to confirm: this is the Apache E model for all practical purposes.

pandyan wrote:saar - minor typo:
>> So we will also see where those limits are for the LCH and the Z-10.
should read apache


Noted. Will Fix it.

KiranM wrote:"The LCH, on the other hand, once again utilizes its light-weight structure to great effect. It can not only maintain the 1,000 kg payload for another 3,000 ft altitude (i.e. up to ~21,000 ft), the tail-off in the ROC does not drop below 8 m/sec until ~11,000 ft."
As per graph it is not 11000ft but ~7500ft?


The LCH is the blue dotted line in that ROC curve and goes just above 10,000 ft. The red one is Apache which is about 7,500 ft.

ramana wrote:Vivek, KiranM reported thinking the comments are visible to the poster. Its wrt Apache and LCH post.


Ramana,

I see the typo. Thanks for pointing it out. I have corrected my document, but I can't edit the post because it has been a couple days. Is there any way I can get access to fix the typos in the post? Or should we just let it be and trust the readers to take it in stride?

-Vivek

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Re: helicopter performance analysis

Postby vivek_ahuja » 19 Mar 2015 10:22

deejay wrote:Maybe, you could include in the graphs the performance of the Cheetahs (If available) for a better understanding on the status of contenders vs. the existing platform.


Hmm. So like a Chetak, Cheetah and LUH kind of comparison? I think that can be done. But instead of modifying the LUH article, I will just post a new snippet on the Chetak, Cheetah and the HAL LUH. The relative performance plots should help everyone get an idea.

sohamn wrote:Very good analysis and thanks for the detailed explanation. It would be great if you can compare Mi-17 configured as attack chopper vs LCH. This is because we used Mi-17 / Mi-8 during Kargil operations to great effect till the SAM threat became serious.


The Mi-17 is something I am going to bring in during the transport helicopter analysis articles. Not sure I see the IAF using Mi-17s in the attack role now that the LCH and Rudra are on the scene...

-Vivek

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Re: Helicopter Performance Analysis

Postby vivek_ahuja » 19 Mar 2015 11:50

Why the Chinook is efficient and the Mi-26 is a heavy-lifting guzzler

Introduction:

So this one is something that’s been on all our minds for a while. The Mi-26 “Halo” versus the CH-47 “Chinook”. Boeing has been marketing the Chinook in India for years for the Indian Air Force’s heavy lift helicopter requirement.

This role is currently filled by the Russian Mi-26 in India. The Mi-26 is massive in bulk, mass and power. It is the largest helicopter in series production in the world. Its power capacity at sea-level is completely unmatched. And in Indian colors it has been a sight to behold when it takes the air under its massive main rotors. The Mi-26 has been associated with many firsts in the Laddakh area of the Himalayas, ferrying in large quantities of supplies, bulk construction equipment for the Army and so on in an area where no other helicopters, until recent years, could even fly. Elsewhere around the country, the Mi-26 has evacuated civilians, airlifted heavy equipment and has been a vital cog in the Indian airlift capabilities. On the face of it, the Chinook has little chance of doing well against this powerful competitor.

But for all that, operating the Mi-26 is not without woes. Lack of spares is a problem. In recent years, the Indian Mi-26 fleet (4 helicopters) has spent more time on the ground than in the air. It is not uncommon to find the Mi-26 sitting with panels open and requiring repair more often than they are seen flying. Operating cost is even higher. The Mi-26 is a massive machine that guzzles fuel at a huge rate. Operating this helicopter from main airbases (with their large fuel farms) is one thing. But out in the mountains, the fuel guzzled by this helicopter’s engines can sap the capacity of any forward-deployed unit to keep their helicopters flying. And if the Mi-26 is tasked with carrying its own fuel, just how much payload can it possibly carry? Boeing offers the Chinook as a cost-effective, albeit smaller, option. If it remains more efficient in the Himalayas and requires less fuel for similar payloads, then it has a chance to replace the Mi-26 in the Indian context.

To answer these questions, we will turn to analysis.

The first thing that strikes the casual observer is the vast difference in design and numbers for the two contenders. The Mi-26 is a massive beast compared even with the large Chinook. The Chinook weighs in at 10,185 kg when empty. The empty weight of the Mi-26 is 28,200 kg! The Mi-26 is almost 2.8 times as heavy as the Chinook when empty. But the Mi-26 is powered by the massive Loratev engines, providing a total of 17,000 KW of lifting power. By comparison, the Chinook is powered by ~7,000 KW of power in its twin rotor arrangement. The Mi-26 loses about 15% of its available power to the tail-rotor, but the Chinook has no such problem due to its tandem rotor design. So there is some recovery of power there in favor of Chinook, but not by much. We readily expect the Chinook to underperform on pure lifting capabilities. In terms of fuel rates, there is surprisingly little difference as well. The Loratev engines have a fuel consumption rate of 0.465 lb/shp-hr and the Chinook has a fuel consumption rate of ~0.5 lb/shp-hr. But because the Chinook weighs a lot less, it has to use a lot less fuel. We will see later how this works.

Since we are now comparing transport helicopters, we will shift focus from ROC capabilities to payload and more importantly, fuel consumption rates. The reasoning is simple: a helicopter can lift more than the other helicopter, but if it needs twice as much fuel to do it, it loses some (or all) of that additional payload to the extra fuel it must carry for the same range. The plots below will apply for hover conditions OGE.

The focus of this analysis is on a preliminary aerodynamic and propulsive standpoint. The analysis is done using simulation tools that integrate payload capacities and typical rate-of-climb requirements with a preliminary rotary aerodynamics model and a simple propulsion module. When coupled with an atmospheric simulator for the Himalayas, the performance of each helicopter type can be predicted and compared. Furthermore, the models allow for the performance analysis in Ground Effect conditions. The Ground Effect conditions are encountered when the helicopters are hovering very close to the ground and serves to work as a performance multiplier with regard to power needed in lifting a certain payload.

The models do not compensate for transmission limitations for the power, which means that the analysis is idealized wherein power generated is power available. This is, of course, not encountered in practice, but works well for high-altitude conditions where power available is almost always less than the transmission limits. At lower altitudes, the performance of the various designs must be assumed to be ideal, rather than restricted from transmission and structural limitations.

Data for this analysis is obtained from the manufacturers via open-sources. No proprietary information is shared here. Unless where cited, the analysis results are to be considered proprietary of the author. See remarks for details.

Image

Halo versus Chinook:

The hover OGE performance is evaluated at altitudes varying from 0 ft (SL) to 25,000 ft. Altitudes in the Himalayan Mountains regularly require flights above 10,000 ft and often up to 22,000 ft. There are two sets of plots provided. One set provides the “true-lifting capacity” plots where we compare the Mi-26 and the CH-47F on purely lifting performance regardless of mission profiles etc. This is done to necessarily drive home the difference between the two helicopter performances from an academic standpoint. The second plot then provides a comparison plot where the Mi-26 payload is reduced down to the maximum lifting capacity of the CH-47F and corresponding fuel rates are plotted versus altitude. The intent for the second plot is to compare the two helicopters on equal footing.

Image

At sea-level, there is virtually no comparison between the CH-47F and the Mi-26 for lift capacity. The Mi-26 can lift twice the maximum possible payload capacity (zero fuel and zero crew) of the CH-47F. But that capacity trails of with altitude. The maximum lifting capacity of the Mi-26 starts to drop off after about 3,000 ft altitude. And the drop-off is faster than that of the Chinook. The Chinook overtakes the Mi-26 lift capacity at ~21,000 ft in ideal terms.
Let’s look at the practical comparison plot for a mission profile. The requirement here is for the CH-47F and the Mi-26 to lift identical payloads of 12,495 kg (max possible payload for the CH-47F) under zero-fuel and zero-crew conditions in hover OGE. It is instantly clear that because of the large power difference between the two helicopters, the Mi-26 is able to maintain that payload limit far in excess of the CH-47F. The CH-47F starts losing payload capacity at ~3,000 ft altitude. The Mi-26 maintains payload capacity up to ~12,000 ft altitude. Note, however, that the CH-47F overtakes the Mi-26 at around ~21,000 ft as pointed out before. In terms of true lift capabilities, the Mi-26 comes out on top.

Now let’s look at fuel consumption rates. You will notice that the fuel-rates have a maximum point on the curves. This point corresponds to the location where each helicopter begins to lose off payload capacity. With reduced payload comes reduced fuel usage, even though the engines are operating at maximum power for that altitude. The assumption here is that both helicopters maintain their specific-fuel-rates with altitude. If this is not the case, the performance will be worse than what is predicted here. The CH-47F has a substantially lower (almost 50% lower) fuel consumption at sea-level even when it’s carrying the same payload as the Mi-26. It maintains that difference to about ~3,000 ft altitude where the payload capacity drops. Through all altitudes, the Mi-26 consumes fuel at a massive rate compared to the CH-47F.

A typical day in Leh:

The effect of increased fuel consumption on payload capacity can be explained with a simple example. For a flight that extends for 1 hour in the mountains where the mean altitude is 10,000 ft (for example in Leh, Laddakh), the Mi-26 will lift a maximum of 12,495 kg but will need a fuel of ~2,800 kg. The CH-47F will lift about 8,000 kg at that altitude but will need only ~1,000 kg fuel for the same flight. Let’s assume that both helicopters need about 500 kg of crew and other common items. This means that the Mi-26’s “true” payload will be only ~9,200 kg. The “true” payload of the Chinook will then be ~6,500 kg.

A validation of the model:

As an aerospace engineer looking for validation data for my models, I am like a squirrel looking for berries: always wanting more, never finding enough. But here is a rare example of information provided by Boeing on the Chinook that I would like to share with the reader. Back in 2012, the Boeing Company released a slideshow for the Indian media to highlight the performance benefits of the Chinook. Within those slides was one slide that I will share with you:

Image

Notice how Boeing claims that the CH-47F has a capacity to carry about 2,600 lbs (1,227 kg) of payload at 20,000 ft. We assume, as always about 300 kg of crew and other items and at least another 1,000 kg of fuel (considering a short flight, plus reserves etc.). So that gives us about a total of 2,527 kg of overall mass that the CH-47 will lift at 20,000 ft. Assuming that some spare power is reserved for climbing, that is effectively about ~3,000 kg of payload in the hover plots above. The models I use for my helicopter analysis predicted 3,013 kg at 20,000 ft altitude for the CH-47F.

Conclusions:

The Chinook is cost effective. A tandem rotor design has significant other advantages over a single rotor design in the high mountains, especially on ridges. The economical fuel consumption of the Chinook versus the Mi-26 helps it get closer to the latter in terms of payload capacities. But in acquiring the Chinook, the IAF will have to forgo some of the true payload capacities of the Mi-26. There will always be a difference in payload in favor of the Mi-26. But as outlined above, is that difference enough of an advantage to balance out so many performance disadvantages? The conclusion of this author is that the Chinook wins this competition on its merits. The end of the days of the Mi-26 in Indian colors could quite possibly be around the corner.

-Vivek

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Re: Helicopter Performance Analysis

Postby KiranM » 19 Mar 2015 18:09

ramana wrote:Vivek, KiranM reported thinking the comments are visible to the poster. Its wrt Apache and LCH post.

Apologies I was not aware of same. But perhaps that is a feature that can be enabled? Rather than point out nitpicks to the aam junta.

vivek_ahuja wrote:The LCH is the blue dotted line in that ROC curve and goes just above 10,000 ft. The red one is Apache which is about 7,500 ft.


Ahuja sir, I had not noticed the line indicating 8m/s ROC. But that does not correctly match with the y-axis on right side which I believe is ROC.

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Re: Helicopter Performance Analysis

Postby vivek_ahuja » 19 Mar 2015 18:23

KiranM wrote:Ahuja sir, I had not noticed the line indicating 8m/s ROC. But that does not correctly match with the y-axis on right side which I believe is ROC.


Ya allah! Joo are correct. That plot needs to get that line fixed to match the secondary Y axis. :shock:

How do I edit that plot on the post? Can the admins give me temporary access to go fix that line in the plot and other minor typos?

-Vivek

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Re: Helicopter Performance Analysis

Postby Singha » 19 Mar 2015 22:57

are you not able to edit the posts ? they still show up as under your name only.

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Re: Helicopter Performance Analysis

Postby vivek_ahuja » 19 Mar 2015 23:04

Singha wrote:are you not able to edit the posts ? they still show up as under your name only.


Nope. They show up under my name but I think the software has a 24 hour limit or something after which the post cannot be edited. You guys (admin) can go and do it, but not regular junta. So I can quote the post, but can't edit it.

Any thoughts? :oops:

-Vivek

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Re: Helicopter Performance Analysis

Postby Singha » 19 Mar 2015 23:15

admins can only lock and delete posts.
so only way seems you first quote the post and embed the correction.
then admin deletes the original post.

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Re: Helicopter Performance Analysis

Postby Indranil » 19 Mar 2015 23:18

OT

We have faced this problem before with Maitya saar and this needs to be sorted out. Because it was a one off thing, I used to modify his posts based on his inputs. Probably, with you also having a thread, and probably more some gyan threads to follow, we will have to find out a clean solution to this.

For now, let's do it the dirty way.

1. Please make a new post, and quote your entire last post that you want to modify. Make the modifications in the quoted part.
2. I (or any other moderator) will then replace your original post with the contents of your new quote, and delete the new post.

P.S. Singha sire wrote in concurrence. Singha sir, let's do it my method :D . This way, the sequence of the original posts are maintained, though it is slightly more work for us.

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Re: Helicopter Performance Analysis

Postby vivek_ahuja » 24 Mar 2015 10:46

Why the Apache is a brute and LCH is elegant


Introduction:

Following up on my previous article about the LCH versus its Chinese opponent (the very sluggish Z-10), the obvious question comes to mind: “How does the LCH compare with what AH-64E Apache that Boeing is offering to India?” Once again, we turn to analysis. The Apache is in the same weight class as the Z-10 and is also two times heavier than the LCH when carrying the same payload in weapons, fuel and crew. The AH-64E is 5,165 kg and the LCH even in its current overweight mode is about 2,800-3,000 kg. But where the Z-10 lost out to an acute lack of power, the Apache reigns supreme. Powered by engines that produce each produce one and half times the LCH’s net power, (an incredible ~2,980 KW for the AH-64E versus ~1,700 KW for the LCH), the Apache makes up for the extra weight by sheer brute power. This allows the Apache to get close to the LCH at both sea-level and high-altitude conditions.

But just how close does it get?

To answer that question, I present here a comparison study similar to that done previously for the Z-10. We will take the LCH and the Apache and put an identical payload of 1,000 kg on them. Note that we have increased the payload here from 500 kg to 1000 kg for this analysis as opposed to that done for the Z-10. The reasoning is simple: both the LCH and the Apache can haul 500 kg through the high Himalayas. However, to get an idea of different performances, we are getting more realistic and putting a higher payload. In reality, with about 200 kg of crew and around 300 kg of fuel, the effective payload of weapons is only 500 kg. We will run both helicopters through a simulation model where we subject them to altitude variations and see how it affects their rate-of-climb capabilities while in hover, out of Ground Effect conditions. The rate-of-climb (ROC, measured here in meters/second) is a true measure of the maneuvering capability of an attack helicopter. Typically, a ROC of 0.5 m/sec is used to evaluate service ceiling conditions. A ROC of 2.5 m/sec is typically the bare minimum for combat conditions. For a helicopter in high mountains to be truly maneuverable, it may need somewhere in the range of 2.5 to 8 m/sec vertical ROC equivalent in power capacity. Of course, beyond a certain altitude, the helicopter may not be able to fly with the 500 kg payload, let alone providing additional power for high ROC. So we will also see where those limits are for the LCH and the Apache.

The focus of this analysis is on a preliminary aerodynamic and propulsive standpoint. The analysis is done using simulation tools that integrate payload capacities and typical rate-of-climb requirements with a preliminary rotary aerodynamics model and a simple propulsion module. When coupled with an atmospheric simulator for the Himalayas, the performance of each helicopter type can be predicted and compared. Furthermore, the models allow for the performance analysis in Ground Effect conditions. The Ground Effect conditions are encountered when the helicopters are hovering very close to the ground and serves to work as a performance multiplier with regard to power needed in lifting a certain payload.

The models do not compensate for transmission limitations for the power, which means that the analysis is idealized wherein power generated is power available. This is, of course, not encountered in practice, but works well for high-altitude conditions where power available is almost always less than the transmission limits. At lower altitudes, the performance of the various designs must be assumed to be ideal, rather than restricted from transmission and structural limitations. For example, the maximum rate-of-climb (ROC) values obtained from this simulator for sea-level (SL) conditions will typically be higher than what is allowed by other limitations. However, such removal of limitations is required in order to compare the various contenders at the same performance benchmarks.

Data for this analysis is obtained from the manufacturers via open-sources. No proprietary information is shared here. Unless where cited, the analysis results are to be considered proprietary of the author. See remarks for details.

Image

LCH versus Apache:

The hover performance is evaluated at altitudes varying from 0 ft (SL) to 25,000 ft. Altitudes in the Himalayan Mountains regularly require flights above 10,000 ft and often up to 22,000 ft. The data is presented for the LCH and the Apache for payload and available maximum ROC capability versus altitude. A threshold ROC line is shown for the reference 8 m/sec combat ROC.

Image

Notice how the sea-level performance of the LCH and the Apache are similar. The Apache, with a 1,000 kg payload is able to generate a maximum vertical ROC capability of 12.77 m/sec. By comparison, at sea-level, the LCH is able to carry the 1,000 kg and is able to provide a power excess for a theoretical max ROC of 15.16 m/sec. It is instantly apparent how the Apache is able to use its outstanding source of power to lift its much heavier mass and still come close to the LCH performance. This heavier bulk involves greater armor and protection for the Apache pilots.

Now consider how the change in altitude affects both helicopters. The Apache, trying to maintain the 1,000 kg payload, begins to tail-off its ROC capability from 12.77 m/sec at sea-level to 0 m/sec ROC at ~18,000 ft. Beyond 18,000 ft altitude, the Apache also cannot carry its 1,000 kg payload and the tail-off in that capacity is visible, although less dramatic than the Z-10 from the previous articles. The Z-10 cannot operate beyond 10,000 ft under any conditions. The Apache, on the other hand, flies and fights up till ~15,000 ft altitude.

The LCH, on the other hand, once again utilizes its light-weight structure to great effect. It can not only maintain the 1,000 kg payload for another 3,000 ft altitude (i.e. up to ~21,000 ft), the tail-off in the ROC does not drop below 8 m/sec until ~7,000 ft. The tail-off does not drop below the minimum 2.5 m/sec until ~15,000 ft.

Conclusions:

The difference between the LCH and Apache at high altitudes is going to be in maneuverability. The LCH will turn out to be more agile and have higher performance in general because it is custom-designed to fight at higher altitudes. The Apache, on the other hand, is a brute-force machine, matching the LCH up to the Himalayas for payload, but losing out in agility. The Apache will be less agile than the LCH but will take more hits and keep flying. Where the LCH will look to evade and survive, the Apache will turn to its armor.

-Vivek
Last edited by vivek_ahuja on 24 Mar 2015 10:48, edited 1 time in total.

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Re: Helicopter Performance Analysis

Postby vivek_ahuja » 24 Mar 2015 10:48

Indranil, Singha,

Corrected the plots and the article typos for the LCH versus Apache. Can you delete the earlier one?

-Vivek

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Re: Helicopter Performance Analysis

Postby vivek_ahuja » 04 Apr 2015 21:21

Since I have received numerous requests to put these articles above on my blog (to make it easier to share), I have revamped my old blog to focus primarily on these analysis articles. You can now access the blog here:

thebetacoefficient.blogspot.com

Image

I will be adding some other articles on here about the Indian aerial tanker competition and so on.

Feedback is most welcome.

-Vivek

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Re: Helicopter Performance Analysis

Postby Austin » 04 Apr 2015 21:56

Vivek I wonder if you have taken into account the parameters for Mi-26T2 when comparing with latest model of Chinook ?

http://aviationweek.com/awin/rostvertol ... ed-mi-26-0

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Re: Helicopter Performance Analysis

Postby vivek_ahuja » 05 Apr 2015 16:41

Austin wrote:Vivek I wonder if you have taken into account the parameters for Mi-26T2 when comparing with latest model of Chinook ?

http://aviationweek.com/awin/rostvertol ... ed-mi-26-0


Austin,

I did not use the Mi-26T2. I went with the version of the Mi-26 in IAF service for three reasons:

1. Using the Mi-26 in IAF service was a good reference point to see what the CH-47 brought to the table relative to what is there now.
2. The IAF has made it very clear that it wants the CH-47 only.
3. I didn't know how far the Mi-26T2 design has made it in terms of being a viable option to the IAF. That is, has it entered production for any armed forces anywhere; what the user feedback has been etc. By comparison, we have loads of feedback on what the IAF thinks about the existing Mi-26. And we have similar user experience data for the CH-47 design as well.

That said, I want to say that the main difference in the analysis above (which focuses on the performance aspects) for the baseline Mi-26 and the Mi-26T2 is the improved engine, which outputs about 3% higher power per engine. So that will improve the results somewhat in its favor. The new engine also has FADEC so the fuel efficiency will be slightly better as well. So you can mentally adjust the numbers by a little bit in the new Mi-26T2's favor relative to the baseline Mi-26. But I ran the numbers through the code and the difference isn't much.

-Vivek

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Re: Helicopter Performance Analysis

Postby Aditya G » 03 May 2015 16:11

Hi Vivek, I was pondering a question, can any or LRMP aircraft operate in South China Sea? IL-38N, Tu-142 and P-8I?

Or what is the farthest extent these aircraft can reasonably operate? like you have done for IL-78 vs A-330.

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Re: Helicopter Performance Analysis

Postby ramana » 15 May 2015 05:09

From what I know Tu-142 does operate in SCS taking off from Madras.

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Re: Helicopter Performance Analysis

Postby Philip » 16 May 2015 14:39

An interesting site with the editor's ratings.
http://www.aircraftcompare.com/helicopt ... Sergei/274

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Re: Helicopter Performance Analysis

Postby Vriksh » 20 May 2015 10:59

Shiv saar mentioned a while ago that Tilt rotor A/C such as V22 have poorer performance in HOGE (hover above ground effect) as compared to Helicopters. Shiv also mentioned (my recollection) that the tilt rotors cannot hover above 15000 m AGL.

Are these statements true and if so why?

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Re: Helicopter Performance Analysis

Postby koti » 23 May 2015 23:10

Vivek Saab, can you give your insigh on the Ka-226 now that we are getting it. Can you compare its usefulness vis-a-vis Cheetak and Cheetah(In high alt/Land/Naval role) as it should replace them.

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Re: Helicopter Performance Analysis

Postby saumitra_j » 24 Jun 2015 05:15

Cross posting from the LCA Thread: For Jingos interested in learning the basics of Aircraft Performance, there is a new NPTEL course starting this July. Please check here. Enjoy the learning.

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Re: Helicopter Performance Analysis

Postby Indranil » 06 Oct 2015 20:29

Vivek, some calibration points for LCH high altitude performance.

The LCH fills in an important gap for intercepting and engaging UAV
Wg Cdr (retd) Unni Pillai, Chief Test Pilot (Rotary Wing) HAL
1. The LCH can carry a full load of weapons till 14,000 feet which is unmatched anywhere in the world. Essentially, the LCH can fly at heights of 4.5 km with a full weapons load.

2. The speed of LCH is 280 kmph and Dhruv is around 240 kmph. Because of its sleek design, you can maintain the speed and climb at faster rate.

3. Dhruv takes 6.5 minutes to climb to 20,000 feet. In the summer at Leh, there is the Khardungla Pass which is at 20,000 feet. When you take off from Leh, all the helicopters whether they are Cheetah, Mi-8/Mi-17, they start orbiting over the town of Leh to gain height and once they have reached the necessary altitude only then do they cross the pass. In Dhruv and LCH, you just have to take-off and turn, the helicopter rockets upwards then you have to level out.

4. Rudra has a top speed of 210 kmph, the LCH is able to achieve 280 kmph with all the external stores.

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Re: Helicopter Performance Analysis

Postby Aditya G » 10 Oct 2015 14:47

ramana wrote:From what I know Tu-142 does operate in SCS taking off from Madras.


One way distance from TN to Spratly Islands is 4,800 Km without overflying Thailand or Malaysia. You will have to pass through the narrow area between Singapore and Indonesia. Assuming a 11000 Km range for Tu-142, it is doable but there will not be any significant loiter time available on target.

One way from INS Baaz is signficantly less at 3,200 Km. Doable by Tu-142, but with added complexity of staging from a forward base.

P-8Is dont even come close.

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Re: Helicopter Performance Analysis

Postby negi » 06 Dec 2015 19:30

^ Bears are capable of mid air refueling .

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Re: Helicopter Performance Analysis

Postby Indranil » 31 Dec 2015 00:16

CROSS POST.

Nuggets of information about ALH flight envelop from HAL's tender for OBSTACLE AVOIDANCE SYSTEM FOR ALH.

Rate of climb : 740 m/min for ALH Utility(Mk III variant) and 670m/min for ALH WSI(Mk IV variant)
Rate of descent : 900 m/min for ALH Utility(Mk III variant) and 900 m/min for ALH WSI(Mk IV variant)
Image

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Re: Helicopter Performance Analysis

Postby Virendra » 26 Feb 2016 10:49

Has anyone studied VTOL drones like Airmule or V22 Osprey for Siachen feasibility?

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Re: Helicopter Performance Analysis

Postby Indranil » 13 Sep 2016 23:12

vivek_ahuja wrote:The Indian Light Utility Helicopter Procurement: where does HAL’s LUH bid stand?

General remarks on the LUH design:

From the power standpoint, the LUH’s power-plant and drivetrain is the biggest variable at the time of writing of this article. While the Bell, Eurocopter and Kamov designs are essentially “stabilized” from a design standpoint, the HAL design remains a mystery in terms of performance. The first prototype has not yet flown. And varying sources at different times have quoted different power and weight numbers. To compensate for this, the analysis here will provide a spread of numbers for the LUH performance depending on what its final powertrain will look like and what its limitations are likely to be. The spread is distributed between three power output numbers from the single Shakti engine employed within the LUH: 750 KW (provided by HAL during a presentation on the LUH design; it is possible that this is not the rated engine output but rather the transmission limitation at sea-level), 825 KW (assuming that the powertrain will have similar limitations to the LCH) and 1,067 KW (assuming maximum powertrain efficiency using the Shakti engine output). The Shakti engine power output is well ahead of any of the equivalent engines in the competition, but the powertrain restrictions will decide how much potential of the engine has been extracted.

Similarly, another area of focus will be the overall weight of the LUH design. Numbers provided by the HAL during its presentations at Aero India 2015 point to an empty mass of the LUH to be 1,910 kg. When compared with the empty masses of its competitors, 1,220 kg (Fennec), 1,700 kg (Ka-226T) and 1,210 kg (Bell-407GT), the weight of the LUH is an immediate area of concern. One possibility is that the weight is a result of a much more powerful power system (Shakti engine) in the LUH. However, this is only balanced out if the resulting power from the engines transmitted to the rotors is much higher than the other designs. If only a 750 KW powertrain is extracted despite the 1,910 kg empty weight of the helicopter (as quoted by HAL in its official presentations), the resulting performance can be expected to be dismal at best compared with the other LUH bids. The HAL design team, drawing experience from the ALH and LCH efforts, will have to undergo a similar effort in weight-trimming and in improving the power-train restrictions of the LUH design. Further details will be obtained when the first prototype of the helicopter flies in 2015 or early 2016.



Vivek,

I looked into these helicopters in some detail over this weekend. Actually the 1067 kW is the thermal power available for the Ardiden 1H1. 1 U may be about 5-10% more powerful. But, the maximum mechanical power available for the 1H1 is 741 kW(Take off) and 650kW (continuous). Therefore LUH's MGB which is capable of handling 750kW should be enough.
[url=Rolls-Royce 250-C47B/8]Click here[/url]

Similary, here are the numbers for the other helis:

Fennec
======
Engine: Ardiden 2D
Take off power: 632 kW
Continuous: 543 kW
Click here and here.

Bell-407GT
=========
Engine: Rolls-Royce 250-C47B/8
Take off power: 503kW
Continuous: 470 kW

You should go to this page. Find "aircraft literature" and chose Product specification to download. The pdf has great datapoints for you to calibrate the IGE and OGE performance of this aircraft.

Kamov 226T
==========
Engine: Arrius 2G1
Take off power: 2 * 537 kW
Continuous: 2 * 455 kW

The 226T brochures says that take off power is 432 kW per engine, and a press release from Kamov on 226T's first flight says a takeoff power of 500 kW per engine.

Regarding weight, the empty weight of the Ka-226T is close to 2590 kgs according to Avia-Russia. But I think that given that maximum underslung load is 1500 kg and that MTOW (underslung is 3800 kg), the empty weight is near 2,000 kgs.

Actually, it is unfair to compare the specifications of Bell 407 and Fennec to that of LUH. LUH is more in the category of Bell 429, and has similar dimensions and weight.

Also, I expect the rate of climb of LUH to be close to the Dhruv Mk 3(12.33 m/sec) and Rudra (11.17 m/sec).


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