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-64D 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-64D 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-64D 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 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 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.
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 ~11,000 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.
Excellent analysis from br
