Sunday, March 22, 2015

Chinook 47 Vs Mi 26 HALO

Chinook 47 Vs Mi 26 HALO 

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

Typical Comparison of CH 47 and Mi 26


      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.

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.

      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 feet 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:

      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.


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.
Article By Vivek Ahuja BRF

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