What method does the F-22 use to start its engines?
In the video below, you can see a flap open and flame and steam shoot out as the engine starts to spin up. Is this an example of cartridge start? If so, could anyone explain how this works in greater detail?
Video of F-22 engine start:
It's a Jet Fuel Starter (JFS) system, used by the F-16 and other jet fighters. On-board compressed air (called Stored Energy System) is released onto a turbine, which starts a small gas turbine engine, which then mechanically engages with the engine's gearbox to spin it.
F-22 calls it Auxiliary Power Generation System.
On the F-16 the JFS allows two bursts/attempts, before needing to recharge (re-compress the air). And if I'm not mistaken, it can be charged after two failed attempts using hydraulic pressure from the brake accumulator, as the engine would not be able provide hydraulic pressure to charge the system yet.
Following the release of the high-pressure gas, the sudden expansion and subsequent cooling causes condensation, which is the smoke we see in the video. The two flaps that open prior to the compressed air release are the intake and exhaust doors for the small gas turbine engine.
The F-22 certainly doesn't use a cartridge start (Coffman engine starter). That's mainly for WWII-era reciprocating engines, and some old jet engines.
On an airliner, the equivalent system is an APU. It's started using the battery and then it drives the engine's gearbox using bleed-air. It's a slow process compared to releasing compressed air, especially when you are to scramble as quickly as possible. Technically, both systems are APU's.
This longer video gives us better clues: you can see the JFS's smoke, then see its heat haze, followed by each engine's heat haze. Each step accompanied by sweet music.
(YouTube) Smoke and heat haze from the JFS.
No, the F-22 has an Allied Signal APU in the port wing root opposite of the cannon installation, which is on the starboard wing root.
From GlobalSecurity.org (http://www.globalsecurity.org/military/systems/aircraft/f-22-fcas.htm)
Auxiliary Power Generation System (APGS)
The Auxiliary Power Generation System (APGS) for the F-22 is being developed, built, and tested by Allied Signal Aerospace for Boeing. The APGS consists of an auxiliary power unit (APU), and a self-contained Stored Energy System (SES).
The APGS provides secondary aircraft power for everyday main engine ground start, aircraft ground maintenance, and in-flight emergency power for aircraft recovery. The APGS uses the G-250 APU, a 450 hp turbine engine that utilizes state-of-the-art materials and design resulting in the highest power density APU in the industry (horsepower-to-weight).
It is possible the APU uses a cartridge to start it up, as opposed to electrical power. The video you posted is good evidence of that.
F-15s and F-16s use nitrogen pre-charged hydraulic start systems. There is no 'air' involved. The utility hydraulic system pumps fluid into the two accumulators against the nitrogen side of the chamber. When the handle is pulled for starting, NORMALLY one bottle is opened and the hydraulic fluid is released thru the hydraulic start motor on the JFS. After engine start, the hydraulic fluid is replaced under pressure. If both bottles are expended, there is a hand pump for the purpose of refilling the bottles - NOT THE PREFERRED METHOD!!!! In super cold weather, the use of both bottles together may be required.
