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Upshift / Downshift


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Hey HerkyWorld

Got an unusual situation here. Engine starts normal, LSGI torque set correctly. When

the LSGI button is pulled to upshift to Normal Ground Idle, torque stabilizes for a

moment at +-1200"lb ........ then increases to +-6000"lb, rpm decays to 94%, and

TIT increases. Also prop noise indicates the engine is labouring. When LSGI button

is pushed in, everything returns to normal. Standing on the blade line, you can see

the pitch change occurring.

Changed out valve housing, pitchlock regulator, and low pitch stop. Also removed all

cannon plugs to remove electronic influence - no good! Stays the same .....

Anyone out there seen this before? any ideas, theories ........ anything?

Have a great day

PJ

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Since the valve housing had been changed with no effect:-

1- De-activate NTS bracket by keeping the gap at maximum, and check your engine.

2- Check your NTS bracket on the valve housing cover assembly for bending.

3- Remove the electrical plug (the one for the feather solenoid valve) and recheck.

Hope those steps will help isolating the affected area of the NTS system.

GOOD LUCK.

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I have heard about this problem happening about three times on Little Rock aircraft over the years, and every time it seems the Valve Housing fixed it, so since you have already changed that, I'd have to say my condolences on having to work a crazy problem. The NTS system sounds like a good lead, but also, just for kicks, I'd start the engine null and see what happens. Remember the engine changes to Normal limiting during upshift. I could also guess internal leakage in the prop, but that would be a shot in the dark, and there is always the possibility of a malfunctioning fuel control, but I'm sure you've already considered that as well. Like Skip and tenten said, the NTS system looks likely, but I'd be lying if I said I knew for sure where to look next if that doesn't fix it. Good luck.

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Since the valve housing had been changed with no effect:-

1- De-activate NTS bracket by keeping the gap at maximum, and check your engine.

Done - no change

2- Check your NTS bracket on the valve housing cover assembly for bending.

Done - also changed out covers

3- Remove the electrical plug (the one for the feather solenoid valve) and recheck.

Hope those steps will help isolating the affected area of the NTS system.

Done - removed all 5 cannon plugs. Ran a purely mechanical prop, no anti-icing, no aux

feather motor, no pressure cutout, no low light, no synchrophaser, no feather solenoid

just for kicks, I'd start the engine null and see what happens

Did that - no difference

I could also guess internal leakage in the prop

Looking into that

always the possibility of a malfunctioning fuel control

Removed from equation by installing a known good prop

Thanx for the feedback so far. When/if we find out what it is, I'll get back

PJ

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Very strange indeed…

So the issue is when shifted to HSGI the torque increases to +-6000"lb, rpm decays to 94%, and TIT increases.

You stated there is a blade angle increase and RPM decrease…

The TIT increase is to what value?

Do you suspect it is due to the speed sensitive valve opening the bleed valves (rag check them) or ?

Just to set the stage...

Once the engine is stable at HSGI the only way to change blade angle is NTS action or by moving the throttle.

(Sounds like you have eliminated NTS as your issue.)

To troubleshoot NTS, remove the NST bracket….or select valve and have some one watch the NTS light as you shift to HSGI. Or you could select NTS which will hold the light on and you will see if the linkage is moving.

IMO, if the NTS is “sticking†it should drive the prop to feather and the engine would not continue to run. (Which is not your case)

Run the engine (Check to see what the valve housing is reading prior to and after), shift to HSGI after the torque increase to 6000 go to ground stop and see what the blade angles do. See if they return to ground idle blade angle (prior to reading). I think they will…

You are doing lots of unusual things to find the issue, cannon plus off ect… you may want to (watch the prop input) to see if it changes (moves) when you shift to HSGI.

If the engine is “rotating†inside the nacelle due to torque it may be inducing a blade angle change (and fuel schedule) input to your rigging... (engine mounts, QEC disconnect bracket?)

That’s why I think they (blade angles) return to normal (LSGI) there is less twisting in the nacelle and you have lost the increase blade angle input so the blades go back to the (throttle commanded) blade angle (and fuel schedule) not the twist induced position.

Last effort maybe “pin†the valve housing to see if your issue stops…. Then pin the rigging (work your way out) to find where it is malfunctioning.

Just make sure you have the fire handle shutdown system enabled as the feather position will be rendered useless.

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Last effort maybe “pin†the valve housing to see if your issue stops…. Then pin the rigging (work your way out) to find where it is malfunctioning....

Installed one of the last props we ran, engine is perfect. This is the only thing we didn't

do because we were out of time - priority engine. We will be doing more troubleshooting

in the next few days, then this will be checked also. I did move up close to the engine to

see if there was any linkage movement on the controls - nada. Also shutting the engine

down from NGI didn't show anything as the blades go back as soon as the engine slows.

Will post a vid later today ......

PJ

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Good luck this is very strange indeed!!!

Guys... The blade angles are changing when the engine is shifted to HSGI...

Acc bleeds will cause the TIT to go up but the blade angle is "set" by the throttle (in the ground range). The bleed valves will only cause the TIT to increase (less cooling air) not the "power"...

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th_VIDEO0295.jpg

Vid as promised. Don't worry about the odd movements, it's the way my HTC

captures the movement. Sound is not recommended, except to determine up-

and downshift. Starts of in NGI then goes to LSGI, back to NGI, and finishes

at LSGI. +-1minute, 8MB on Photobucket

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Very cool video!!!

Have you used a different pump housing?

The increase in speed would directly affect the pressure output of the main and standby pump. The standby (twice as much voulme) may be suppling pressure when not needed...normally only provides "extra" pressure/volume to get faster response. If it thinks the system wants more due to a bad check valve it may be driving the blade angle without any input other than speed.

In HSGI if you retard the throttle towards reverse does the RPM increase or overspeed or does the fuel flow and blade angle change?

What happens if you leave the engine at HSGI for an extended time?

TIT?

RPM?

Tq was/is 6000.

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I like this kind of thread. It's been a long time but!!...I would first check the rigging. Then I would do a complete run up, high power run, check for throttle splits,... Auto, manual..... TD amp. sync on, off..... cause it costs a lot of money to replace components........................Shit it's so long ago. I used to be hot!!...but I forgot a few things I beleive. I keep an eye on this thread........Bye Bye for now boys. You've got to be keen and know your systems!! It could be something simple and stupid!! Go for it!! Find that little bastard problem!! Take your time!...........and have a coffee...............John Boy

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Thanks pj for the video.

After seen the video, no doubt (to me) that an increase of blade angle is taking place during shifting up.

To my knowledge (CAUTION) limited :mad:

1- To increase blade angle, a controlled hyd. Fluid should get its way through transfer tube to the fwd. side of the piston.

2- The (simplified) normal rooting of the hyd. fluid to increase angle is:-

Pumps output →Transfer ports (on barrel extension)→ Pilot valve→ Back to Transfer ports →Transfer tube→ Fwd. side of the piston.

What if, something wrong on transfer ports (or around) causing the output of the pump -which is increase during shifting up- to get its way direct towards the transfer tube.

I believe that: “The truth is lying on the belly of pump housingâ€.

“Indeed corrections and inputs are appreciated from prop guys.â€

tenten

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You missed that they switch out the prop with a known good prop, that would (normally) eliminate the prop and bring it down to engine, rigging or cosmic rays.

By the video I am assuming that this is taking place on the test stand as well? If so that pretty much eliminates truss mounts and wing structure cracks.

At this point I would say call Anton LaVey and sacrifice the goat

goatST010606_175x125.jpg

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Very cool video!!!

Have you used a different pump housing?

Next on the 'to-do' list

In HSGI if you retard the throttle towards reverse does the RPM increase or overspeed or does the fuel flow and blade angle change?

What happens if you leave the engine at HSGI for an extended time?

TIT?

RPM?

Tq was/is 6000.

Moving to reverse is not a problem, torque, ff, rpm normal. Got to be very careful coming

back as the torque picks up very quickly. If left long enough the rpm will decrease

below 94%, risking flameout. TIT rises some

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Just to chew the fat, in Ground Idle, are we temp limiting or temp schedulling. How's the fuel flow compared to the other engines. How's the rigging from flight deck to QEC !! And how's the ground run !! Maybe I should go back to my coffee!!......................John Boy:)

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Just to chew the fat, in Ground Idle, are we temp limiting or temp schedulling. How's the fuel flow compared to the other engines. How's the rigging from flight deck to QEC !! And how's the ground run !! Maybe I should go back to my coffee!!......................John Boy:)

Ground idle below 65°, thus temp limiting. Fuel flow 700 - 800pph. Test cell uses

electric servo to run throttle, but rigging on engine was spot on. Ground run was

perfect after prop was changed. I'll take a coffee too - 1 sugar and milk, thanx

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