206 L1 C28B question

[LRinDislands]

Hi all,

anyone had the following go-on with a C28B

Had the unit overhauled last year or so, worked fine 14% N1 introduce fuel - bingo off she goes. Stayed like this for approx 25hours then refused to light off at 14-12- even 10%. Spoke with RR they say that the compressor is so efficent (it was re-worked and set up in test cell) that it pushes so much air at lower N1 speeds, advised they did some C30's that light off at 5% - they sugested we try 6-8% . Since then if starts everytime at this range, peak TOT 790- 800c then quickly drops (have to be very careful when cracking the throttle though also quick re-starts as the TOT can get all outta hand real quick) one other issue is we cannot get it to stay in the 740-800C range for starting, dos'nt matter how we try the TOT always drops off to 680 ish in the 38-50% N1 range. Messed with the fuel settings and its the best we can get from her. I've got to ask this question caus it sometimes drives me nutz, pax on board, hit the starter miss 6-8% and sit there all the way to 18% trying to coax a light off - nothing. Wait for the N1 to go all way to zero - do it again - but now with added pressure of unburnt fuel in the can! All in a days work right!

Other than that she's a cracker + 9 at the last power count

Do we have a duffer or is RR onto something?:cool:

[RVDT]

Tried shimming the fuel nozzle back? Or try another nozzle?

[LRinDislands]

Yeah already tried that one without much change to be honest :ok:

[canterbury crusader]

This sounds like a nice problem to have :ok:

[bugdriver]

I have a friend who has an L1 C28 and he has always had to light off at 8%. The outfit I work for has two of them and I have never had a problem at 15%. Go figure.
But we had one that, under high power settings, would droop to 94%NR and not recover. Changed everything they could think of(fuel control, governor, injector, rigging) and it still did it. It has been undergoing some paint and a bunch of other improvements so i wait to see if it still behaves the same way. Any ideas?

[rotorrookie]

As long as your C-28 keeps on smoking like hell I guess it is working fine:ok:

[ricksheli]

I've had my L-1 about 14 months now approaching 300hrs flown. I'm the only one to have ever started it since I purchased it. Early on, felt it was a bit of a "fire cracker", has always required max attention to keep in the 740-800 band, but starts have always been achieved in under 30 seconds ( with a good battery ). I'm either getting used to it or since we fixed a problem with the wiring to the inlet temp sensor it feels more controllable. I've been lighting off at about 12% N1. Absolutely hate having to do a series of starts for say tail rotor balancing etc., but must say that it's always possible to modulate, it's just that on occasions it's easy to "over modulate". There was a week when it became slow to light off, but that cleared. Your power checks are good, what altitude you doing them at, I only get good results at + 3000 ft. Just fitted a new bleed valve, which I feel could be a bit sluggish in fully closing ( well I wish it had been calibrated to close sooner), it appears to close at N1 91-92%, Tq 80% (OAT 15 ) sometimes you can see the TOT coming down as it closes(normally from around 690 to 675ish). Hope my ramblings help, certainly good to hear your findings, not many people to turn to for advise on C28 in NZ.:)

[that chinese fella]

I had to smile when RR said the C28 compressor was so efficient - yeah, it was so efficient they only made 500 or so of them before bringing out the C30!

If it was so efficient why did the first 25 hrs TSO not need the abnormally low N1 light-off? I think this is a red herring.

Was the fuel nozzle was replaced with a recently spray pattern checked item? If so, and the shimming is correct per the MM then I would be suspecting something has changed in the FCU and would send it back to the shop. Like you said, it had been working as advertised post overhaul. It was quite a few years ago now but the FCU bellows caused major start issues in the C28/30 series.

Re the nozzle shimming, IMHO, once a shimming stack up has been worked out IAW with the MM, there should be no need to change it IF (and I put this important caveat on it) your nozzle pattern does not change.

Of course what happens in the field is that the pattern changes for whatever reason, and the old 'lets reshim the nozzle' is sprouted and it invariably works, hey presto, we have light-off. Problem is that you are correcting the shimming to allow for a non-standard pattern, one that could be torching 1 side of your NGV. Worse is the 'lets put the ignitor on the other side' fix, for the same reasons.

I maintained and flew 206L1/3's for 4 years and never adjusted the shimming, only the nozzle. Keep a rotable stock nozzle and pay the extra to get them pattern checked regularly. It's cheaper than NGV's and 1st stages.

[LRinDislands]

Chinese fella and all - thanx for the responce. When the unit was in OH it had a new nozzle fitted, I agree with you though - for what ever reason things do change in the field hence we are where we are at! I hear ya they soon came out with the 30P right !

I guess we try shimming again or like you said have another nozzle to try it out, the red herring seems very likely as they did not want the unit back under warranty and just gave us this great excuse - :mad:

Bug driver - Its ma good self, need to change location from De Bahamas mate, having fun yet?