No Go On The C20b!

[chopper doctor]

OK, here is whats up. FCU had been changed out about 15 hours ago. Pilot reporting minor compressor stall during start, and starting hot. Engineer tasked to adjust FCU, found it not responding as per usual. Did quick test flight and single engine power checks were ok ( its in a light twin helo) Next day all is well, starts good, pilot goes to take off and can only get 60% Q out of this engine before rotor rpm droops off. WTF i say? check out all lines and linkages, its all good. Decided that after all the probs adjusting this FCU, maybe its time for it to go. New FCU installed by myself......same problem...........engine is good until you pull pitch, 60% Q and 90.5% N1 is all you get, pull more pitch and rotor droops off. Hmmmm, fuel flow limited it seems.....very strange, well, we have a spare governor, lets try that. Same prob. New fuel nozzle, same prob, fuel pump from the other engine, same prob. All lines pneumatic leak checked, all ok. Rigging triple checked ( was not touched during original FCU change) all ok. Running out of ideas here. When you hit 60 % Q it just stops, and when you lower collective, the N1 goes down right away, the torque seems to stick for a second or two, then jumps down to follow the collective input. This A/C had been operating normally before the FCU change. Sorry for the long post, but trying to get all the info out here...............

Ideas? suggestions?

 

[chopper doctor]

One last thing, its a bendix system.....

[highbladedown]

Compressor case half liner or bleed valve? Company I worked for had a similar situation on a BIII, compressor liner was shot and new case halves cured problem. All else fails call 204-775-9711, ask for Neil hancock (Standard Aero tech rep) first thing in the AM, or Kevin Griggs RR CSR in Seattle, Office: 360-678-1154 Cell: 360-239-9081. We can all speculate till the cows come home, myself included, you need results and results now and it is only a quick call.

 

Tell'em Kim sent you, most people know me by my handle, but the choice is yours, either will give you some quick and accurate answers and save you time.

 

 

Hope it helps...

HDB

[ray]

Check the PC filter for contamination, or it's lines for cracks.

 

I know you say you've checked the rigging, but confirm that the throttle stop on the FCU is right on the stop at full throttle.

[Lunchbox]

We can all speculate till the cows come home, myself included, you need results and results now and it is only a quick call.

 

Agree. Phone tech support, rather than relying on us armchair engineers.

 

However.....

 

It's rare, but maybe you've got two consecutive bogus FCU's? Seen it before. Enough to drive one literally insane. Perhaps take the FCU from the 'good' engine, and swap it with the FCU from the 'bad' engine, and you'll know for sure if it's the FCU causing troubles (one advantage of working on a twin.....swap parts from the good side to the bad side!).

 

Also, perhaps check that the FCU fuel flow setting matches the requirement of the airframe type.

 

Please post the results/final story, as I'm sure there's someting we can learn from it.

[ktown]

I had a problem with a C20B it was stalling on start up and sometimes in flight. I turned the FCU down, no go, rigging check, no go, comp wash, wait, heard some rubbing. So I opened it up and what did I find but a hole one inch long by 1/8 wide in the rotor itself. The #1 bearing had .009 radial play. Well that solved that problem, and in six and a half hours one compressor later we were on our way. And yes I pulled the turbine. Just my thoughts.

[chopper doctor]

Talked to the Standard Aero guys, and they all figure its a PC air leak somewhere. Pulled the accumulator off, checked it in water, no problems. This engine uses those PC shut off valves for doing engine washes, so thought "maybe" as pretty well tried everything else. Put a standard scroll fitting in there, same problem! Getting pretty frustrated here. Just on a crap shoot tried the check valve thats in line, just before the line that goes to the fuel nozzle, and lo and behold, engine runs as per normal. Really strange, as this check valves purpose in life is just to prevent any fuel running into the burner can while engine is shut down. Needs more than boost pump pressure to operate. Well, for some reason this one was restricting fuel flow above 90% N1.

Anyways, problem solved, nobody i talked to has ever heard of this before, so its one for the " I remember one time" file..........

[T55]

good post!

It's always nice to have those tidbits stored in the back of the memory banks. Especially when someone doesn't have to go thru all the grief you did. Who would have thunk it?

It's amazing that you can be around a certain engine for 30 years and they can still throw a f**k at ya.

Thanks for the info!

[arctic_front]

I'd read in a CEB of a similar thing way back when. Have a gander at them one day when you are bored. Tons of really good info hiding in the CEB's. But like T55 says, good to hear the snag and then the eventual outcome.

 

Thanks... I'll be keeping that one in the mental tool box.

 

cheers

[highbladedown]

R U going to SDR it. If it is an AAI kit and it is not in the ICA's for troubleshooting let them (AAI) know as it is their STC and there PSE people jusy might have an interest in your findings, just a suggestion

 

 

HBD