King Air Fuel Heat [Archive]

balaton

13th Nov 2008, 20:04

The B200 has an oil/fuel heat exchanger to prevent fuel filter ice. But there are two 7.5 Amp C/B's labeled "FUEL CONTROL HEAT" on the RH CB panel. Is there an electric component in the fuel heter system? No clue in the AOM not even in the FSI training manual. Any ideas?
(These C/B' are refered only in the Emer Checklist: DUAL GEN FAILURE where you should pull them to conserve batt life.)
Many thanks King Air pros.
balaton

inbalance

13th Nov 2008, 20:26

The Fuel Control Units are electrical heated. The Oil / Fuel heat exchanger are located in front of the FCU. So there should be warm fuel running throu the FCU as long as the Engine Oil is hot.
So why needs the FCU beeing electrical heated ?

I believe to prevent it from freezing as long as the oil is still cold ( start up)

Inbalance

bfisk

13th Nov 2008, 20:30

The FCU is partially controlled by P3 bleed air. There is a bleed line running from the forward to the aft part of the engine, to the FCU, and this is electrially heated to prevent moisture accumulation AFAIK. This could be it.

balaton

13th Nov 2008, 20:46

So, I understand there is a resistance type heater element around/in the FCU to heat it up which is all the time on when the batt swc is on and pulls approx. 7.5 amps per side.
Many thanks.

bfisk

13th Nov 2008, 21:15

Well, the element doesn't actually heat the FCU, it heats the airpipe from the P3 bleed to the FCU :--)

ahramin

14th Nov 2008, 15:33

No fuel is electrically heated. As bfisk said it is an air line to the FCU which is heated. This is the "Fuel Control Heat".

This circuit is energized any time the condition lever for the respective engine is in low idle or above. Basically on from engine start to engine shutdown. Older King Airs have switches in the anti-ice section for this circuit which are turned on after start.

barit1

14th Nov 2008, 20:17

Some other engines (non-PT6) have the P3 tube routed so there is a low point or "trap" before reaching the FCU. There is a small "weep" hole there to drain any water from the line.

Of course, the weep hole induces a small error in the sensed P3 signal due to the pressure drop caused by lost air. The FCU schedules have to compensate for this pressure loss. :cool:

balaton

15th Nov 2008, 19:54

Many thanks guys for the in-depth info. Impressive knowledge!

balaton