| Performance degradation of Black Hawk and Apache helicopters has resulted from weight growth associated with new mission equipment packages. Increased lift and range requirements are being sought to support future battle scenarios plus an increase in mission radius capability to 500km for both aircraft. A common engine for both would greatly reduce the operating and support costs associated with aviation systems. Thus there is a requirement for an advanced common engine programme (CEP) in the 3,000hp class to ensure both helicopters remain operationally effective well into this century.
A CEP will enhance the gas generator technology developed under the IHPTET/JTAGG phase I and phase II programmes. For 10 years US Army aviation and missile command at Fort Eustis has been working on the joint turbine advanced gas generator (JTAGG) programme. This is aimed at achieving the turboshaft engine goals of the integrated high-performance turbine engine technology (IHPTET) programme. JTAGG I goals included a 20 per cent reduction in specific fuel consumption (sfc) and a 40 per cent increase in shaft horsepower-to-weight ratio (shp/wt). These were exceeded, a 22 per cent reduction in fuel consumption and a 64 per cent increase in shp/wt being achieved. Phase II goals include a 30 per cent reduction in consumption, an 80 per cent increase in shp/wt, a 20 per cent reduction in production and maintenance costs, and a 20 per cent improvement in life.
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Increased lift and range requirements are being sought to support future battle scenarios |
The army requires improvements in both range and payload capability. Existing engines typically are enlarged by increasing airflow and/or turbine inlet temperature to meet larger horsepower demand because of increased weight. Assuming no significant improvement in sfc, aircraft fuel burn rate is increased, decreasing mission range capability. So, to get improved range and payload capability, a new centreline engine has to be developed.
The CEP will develop an engine applicable to Black Hawks, Sea Hawks and Apaches. Its goals include a 25-30 per cent reduction in sfc, a 60-80 per cent improvement in shp/wt, and a 20 per cent reduction in acquisition and maintenance costs.
Black Hawk
The Black Hawk will need increased range and payload capabilities to facilitate the modernisation plan. Presently it operates with two T700-GE-701C engines each providing 1,856hp installed at SLS, MRP. This power provides a huge capability of about 20,050lbs at 4k, 95F operating conditions. Assuming internal fuel load of 2,164lbs and a tog weight of 20,050lbs, the Black Hawk can carry about 5,000lbs of external payload over a radius of action of 135km. If the Black Hawk tog weight grows to 26,500lbs to provide for a 9,000lb external lift, the power required exceeds the capability of current engines. If tog weight grows as predicted an increase in engine capability also will be required.
Two options exist to develop a derivative engine or a new centreline engine. If a derivative engine were developed with the necessary horsepower growth at a current sfc level, the external 9,000lbs lift could be accomplished but the radius of action would be only 65km. However, a new centreline engine with a 25 per cent reduction in sfc and 60 per cent increase in shp/wt allows a radius of action of 135km, the threshold requirement for the emerging UH-60(X) ORD.
In a combat assault mission, the tog weight of the Black Hawk is about 18,600lbs whereas the modernised version has an assumed tog weight of 21,500lbs. A Black Hawk with 701C engines has a radius of action of 230km, a derivative engine provides a radius of action of only 185km. A new centreline developed under CEP with a 25 per cent reduction in sfc and 60 per cent increase in shp/wt, provides a radius of action of 275km, the threshold requirement for the emerging UH-60(X) ORD.
Considering self-deployment capability, the Black Hawk ferry range is now 1,260km. If a derivative engine with no improvement in sfc is selected for the modernised version, the maximum ferry leg is estimated at 1,055km. And that’s the problem: the primary European deployment route has a 1,150km leg, the first alternate a 755km leg; the second a 1,394km leg. For African deployment routes, the primary has a 1,150km leg; the alternate a 1,394km leg. The primary Latin/south American route is a 1,394km leg and the alternate 1,067km. The derivative engine will allow self deployment of the modernised Black Hawk using only the first alternative of the European deployment routes. The CEP approach, with 25 per cent reduction in sfc, provides a maximum ferry leg of 1,425km, so a new centreline incorporating IHPTET technologies allows self deployment capability on several routes.
Sea Hawk
The CEP could provide further benefits for the Sea Hawk. If the attack mission profile assumes a tog weight of 21,740lbs, incorporating two acoustic homing torpedoes and a fuel load of 5,100lbs, current engines allow cruising out to 93km with 187 minutes on station. Utilisation of the new centreline engine with a 25 per cent reduction in sfc would allow 273 minutes on station, 46 per cent better than current capability.
Longbow Apache
CEP also would provide superior mission capability for the modernised Longbow Apache. A combat mission tog weight of 17,500lbs and a fuel load of 375 gallons means current capability with 701C engines is 1,260lbs payload and a 220km mission radius. Assuming a growth derivative engine is installed, a 1,250lbs payload with a mission radius of 170km is achievable. But, a new centreline engine developed under CEP with a 25 per cent reduction in sfc and 60 per cent improvement in shp/wt, provides a 1,465lb payload with mission radius of 250km for the Longbow.
A deep attack mission with a tog weight of 22,500lbs and a fuel load of 835 gallons, including two external fuel tanks, equals a mission radius of 435km and a payload capability of 1,540lbs with a derivative engine. Utilising the CEP engine with a 25 per cent reduction in sfc and 60 per cent improvement in shp/wt will provide a 1,740lb payload with mission radius of 605km. A study conducted by McDonnell Douglas Helicopter Systems in 1994 underscored the benefits of incorporating JTAGG technology into modernised Apaches. It stated: “The decreased fuel flow and weight of the JTAGG engines, yielding greater mission radius and increased payload capability, made these engines the single most effective performance improvement”.
Propulsion system technology developed over the past 10 years will provide significant improvements in Black Hawk and Apache helicopters’ range and payload capability. Reduced cost make these engines an affordable opportunity. A derivative engine may have increased payload capability, but suffers loss of range. Are we willing to have users live with such diminished capability or is it worth the investment to provide a significant capability affordable to the user? Without incorporating new engine technology as proposed under CEP, Black Hawks and Apaches cannot meet desired performance levels now or in the future. © |
