RR 250-C20B start

[tajmahara]

Have a C20B that fails to light off on first start at 15%, but will light at 8-10%
Then after light off will quit at +/- 40% and throttle needs to be open wide to keep start going. Installation in a 500D. Warm starts are fine.
When N2 set at 102% experiences large torque changes with small collective inputs then stabilizes. Are we looking at bellows problem ??? Governor ???? FCU ?????

[Agaricus bisporus]

Woah!!!

May I ask whether an engineer (for haven's sake tell us you're not a pilot) thinks this is the right place to be asking such questions. No doubt you have problems operating in Zim but this is a matter for Allison or your C20 support organisation, not unattributable opinion on the net!

fails to light off on first start at 15%, but will light at 8-10%

How the **** would you know that????
The flight manual clearly states "A start should not be attempted with N1 below 12%"
Do you mean to say you tried this????

after light off will quit at +/- 40% and throttle needs to be open wide to keep start going

Open wide at 40%? You've tried this too? Bejasus! Give us a clue on the TOT you saw or couldn't you bear to look? The results if the thing suddenly started operating correctly at that point with the throttle full open don't bear thinking about.

My opinion, purely surmise you understand, is that if the exhaust doesn't smell of roasted Troll then your hot section probably resembles the cheese on top of a pizza. And that smells like burning paper. ie a small mountain of $100 bills...

[tajmahara]

Ok . . . Ok . . . . yes I am an Alison trained tech ! ! the start is monitored throughout and haven't exceeded 830 on any starts. The first start at 8-10 is stopped at 750* and allowed to coll to 150* before 2nd start. After 1st start all starts after that are 20 -24 sec from initial to 58% and max TOT of 770 - 810 ?????? Anyone got some help on where to start looking ????? I think its probably fuel pump ???? Any boffins out there ???:ugh:

[helicopterray]

Start with your fuel nozzle, see if it's plugged. Check your spray pattern. (Use compressed air at the inlet and see.)

Check your rigging on the FCU, make sure the needle is right at 30 degrees when the throttle is at idle, although if it starts well at subsequent starts, it is probably fine.

Bleed the fuel system.

Check the fuel flow. With the throttle open, motor the engine, (with the ignitor circuit breaker pulled) and check the flow in 15 seconds. I don't recall the numbers off the top of my head, but the Rolls Royce 250 Maintenance Manual in chapter 71 will tell you what the number is supposed to be.