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?
(L to R): The Indian HAL LCH, Chinese Changhe Z-10 and the Russian Mi-35 (in Indian colors)
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.
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.
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.
Dr. Vivek Ahuja
