Phil Nasskau looks at how Rolls-Royce is planning to design without a pilot in mind.
The longstanding argument between airframers and powerplanters, as to who designs its parts around the other is one that will likely never end.
But, for Rolls-Royce military engines division, it is clear the engine comes first – particularly that now with possibly the last manned fighter in development, the future will be in unmanned aviation.
An engine is not an engine anymore. It is an IPS or Integrated Power System, says the British OEM.
This is largely driven by the current demands and those of the future on aerial platforms that will be increasingly more complex, a need for autonomy and networked operations, an affordability and capability balance and a through life support.
“Once the pilot is removed from the loop there are going to be large power demands for any platform. Only a small percentage of that power will be engine thrust,” says Graham Hopkins, director of defence engineering and technology at Rolls-Royce.
Looking at UCAVs (Unmanned Combat Aerial Vehicles) the need to design around a human pilot has gone. “A UCAV does need to have stealth, loitering ability plus high-speed capabilities. One way to increase stealth is to decrease the size of the vehicle. Vehicle size is generally determined by the size of the engine,” says Hopkins.
The engine diameter determines the cross-section and the powerplant, intakes and exhaust determines the platform length.
Temperature
The platform length in turn determines wingspan. The question for Rolls-Royce is how to decrease the size of the engine without decreasing performance.
Typically the engine size is determined by the diameter of the fan, which is set according to the bypass ratio. The bypass of cold air allows the ability to use cold plume temperatures and not only reduce noise because the hot exhaust is shrouded by cool air but also increases thrust. However, high temperature core technology is changing and is something that will change the physical size of an engine.
Increasing the engine core temperature by 100°K (173°C) can allow an estimated 10% size reduction of the platform. An increase in core temperature (implied increase in efficiency) to maintain the same thrust means a smaller core is needed.
Currently jet engines operate in the range of 1,950-2,000°K – Kerosene has a stoichiometric limit of roughly 2,400°K (effectively the temperature at which the combustion process will burn all the fuel). Therefore, a smaller core can be used; a smaller core means a smaller fan diameter for the same bypass ratio. This allows for a smaller aircraft.
A smaller aircraft means a smaller radar cross section and an increase in stealth. The smaller an aircraft is the stronger or closer radar has to be to it to see it.
Rolls-Royce is working on high temperature core technology with its EFE (Environmentally Friendly Engine) technology demonstrator. However, with the limited export market that defence technology can offer is chasing funding from the British Ministry of Defence.
The EFE is more environmentally friendly because of the greater efficiency – in a UCAV application it is expected that specific fuel consumption will be improved by 15%, allowing greater range or longer loiter times.
Because the fuel is burning more efficiently, the exhaust temperature can be reduced by up to 200°K.
Technology
Although there are no civil applications yet, it is possible that this technology will feature on the Airbus A350XWB engines.
Another major project for RR is the TP400 turboprop for the Airbus A400M Airlifter, although the project is currently six months behind schedule it is due to deliver the first flight test engine to Marshalls Aerospace in the coming weeks.
“The TP400 is a challenging programme, and we are optimising the cruise propeller speeds. It is an 11,500hp engine – the western worlds largest and we all just need to do our jobs,” says John Boughton, director customer business, defence aerospace.
The engine has accumulated around 400hrs of running so far, the planned timeline has appeared a little too optimistic as it called for about 1,100hrs testing at this point in the programme.
The JSF F136 alternative engine has seen a recent stalling, although 50% of the funding for the entire programme has been spent, and it is still expected to have its first flight in 2010.
Source: Flight Daily News
