What is this? - Auxiliary Power Unit (APU)

I found two pictures of AA-1 F-35. But, I found one curious thing. Is that a new heat emission part? If so, doesn't it affect stealth?

Curious George, Newbie.

I found two pictures of AA-1 F-35. But, I found one curioous thing. Is that a new heat emission part? If so, doesn't it affect stealt?

Curious Goerge, Newbie.

That's the APU. The auxiliary power unit. A small turbine used for providing power when the F-135 engine is not running. It is only used on the ground. It doesn't output anything while in flight or even when the aircraft is taxiing with the main engine running.

On the production airframes (AF-1 and later) this is moved to the underside.

I found two pictures of AA-1 F-35. But, I found one curioous thing. Is that a new heat emission part? If so, doesn't it affect stealt?

Curious Goerge, Newbie.

That's the APU. The auxiliary power unit. A small turbine used for providing power when the F-135 engine is not running. It is only used on the ground. It doesn't output anything while in flight or even when the aircraft is taxiing with the main engine running.

Ah, I guessed it was APU. Sorry, I know APU. my background is avionics and design. Oh but not for mil planes.

On the production airframes (AF-1 and later) this is moved to the underside.

I see. That's why I got confused. AA-1 and earlier test frames showed no such APU. That will be moved to undersided?

If so, what Lockheed announced is true? Some articles said that the overheating issue is critical in terms of IR singnal. Is that the reason they changed the frame slightly?

The APU can supply power in the air but its not running but using ram air to do it.