The X-47B unmanned combat air system (UCAS) carries unique engine requirements, which the Pratt & Whitney F100-PW-220U engine meets.
How is the X-47B's engine novel?
If you stand in front of the X-47 and try to see the engine, you can't. The inlet is offset; as a result, the air that arrives at the engine is in some cases distorted, meaning it's not a smooth column of air. The engine has to accommodate that and it does.
It also has to be able to accommodate steam ingestion that you sometimes get at the end of a catapult stroke. If you don't have an engine that is very tolerant of that, it's the wrong time to have a stall. Picking the right engine was critical for Northrop [Grumman] and for us.
Aircraft engines are growing more complex with advanced electronics. Is that true of the F100?
The X-47 has a tremendous amount of sensor information on the air- plane, but the engine's predominant role is to provide thrust. It provides shaft horsepower to drive generators; it provides sensor inputs; and the engine's control system is built on the engine. The airplane and engine talk different languages; the airplane has a more current communications protocol. The F100 uses F-16 protocol, so we have a device called the engine interface unit, a translator that sits between the airplane commands and the engine response.
Is it difficult designing an engine to meet the needs of the U.S. Navy?
The Navy has a very unique set of requirements. They are at sea all the time, so this engine has to be able to accommodate a very harsh environment. If you've seen pictures of waves pouring over the front deck of a ship and bathing the airplanes and engines in seawater, that's bad enough, but think about...coming in to land on this ship, which is moving at 30 knots relative to the Earth. As we come in, we have to fly through something called a burble, a big air bubble that the carrier causes. You've got that perturbation and you've got to touch the deck, you've got to drop the hook, you've got three or four wires to catch-but what if you don't?
You're landing at near full power, because if you don't catch the wire, you've got to be ready to take off. These engines have to have thrust responses typical of fighter engines. You move the thrust from idle to full power, and it has to be there in a second or less; it can't be like a commercial engine that rolls up at the end of a runway because it would still be rolling up as you enter the water.
What challenges currently exist?
Avionics engineers can help. I give you 100 kilowatts (kW) [of electrical power] and you give me 70kW of heat back. I need that efficiency up; you can't dump the heat overboard on these new advanced systems because it attracts too much attention. I keep looking for the laser or radar that's 90 percent efficient. In the meantime, I am providing a lot of electrical power and getting a lot of it back as heat. It's our job to absorb and accommodate it, and many times that becomes the challenge.
NAME: Jimmy Reed
TITLE: director of advanced engine programs
CO.: Pratt & Whitney
ROLE: Creating, developing, and validating all the propulsion technologies that will be required in the future