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.
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.
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.
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.
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.
Aq to vivek ahuja analysis k226 had lowest performance at high altitude
no idea how it will perform in actual scenario.
Aq to psg k226 will be used by ndrf and bdo
To make roads
...... Looks like you hate for Modi has clouded your intelligence, or maybe you are just too used to the UPA Stupidity and way of doing business. Or should I say, way of NOT doing any business ?
