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#1 Falko

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Posted 22 July 2009 - 18:11

I think it was two years ago when this happend.

It was the first engine start of the day and my chief pilot was gonna teach me some bambi bucket work in the huey.

At that point I was just introduced to the 204b and wanted my boss doing the start up.
We all agree that, if the engine gets too hot we roll the throttle off into idle and keep cranking to blow the burning fuel out und keep doing this until the TOT goes down low enough.

So he started the engine and the TOT went obove the limits, but instead of rolling off the throttle he rolled it all the way on to full throttle and to my surprise the TOT came down again.

After the flight i asked him why he did that and he said, if you roll the throttle all the way on, there is too much fuel but not enough oxygen and thats what gets the TOT down again.

Whats your opinion on that guys?

------------------------------------------------
normal & hotstart

Edited by Falko, 22 July 2009 - 18:35.


#2 PhotoFlyer

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Posted 22 July 2009 - 18:43

While that is technically true, it probably isn't the smartest way to deal with the problem. There are to many variables to make this a feasible procedure.

First, what if (I know, I know, what if...) the engine was turning fast enough to sustain the flame with the starter turning. Now you just took an engine that might not have had ANY problem and turned it into a puddle of molten metal. Now that your engine is melting, and the aircraft is catching fire, was that an appropriate response? (obviously this is a worst case scenario)

Second, you've already hot started (possibly damaging/destroying the engine) do you REALLY want to respond with a home brew procedure that could cause more damage?

Edited by PhotoFlyer, 22 July 2009 - 18:45.

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#3 67november

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Posted 22 July 2009 - 19:07

before second guessing what should have been done,what is the procedure in the Lycoming T53 manual for hot starts?

It's not what was done but what should have been done.


anyone have a manual available?
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#4 Eric Hunt

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Posted 22 July 2009 - 19:29

Certainly not the standard procedure.
The T53 is started with the throttle already at idle, and the light-off is normally quite benign.

If it starts going hot, depress the solenoid plunger, roll throttle closed, keep cranking the engine.

The RFM doesn't have any home-made procedure like adding more fuel to the potential fire. If your theory was correct, then removing your finger from the start trigger would stop any more air from being drawn in and your temperature would go down. In reality, the temp would go through the roof, turbine wheel, combustion chamber and firewall.

#5 delorean

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Posted 22 July 2009 - 21:26

Kinda the same question.......

What if the throttle isn't closed (full, idle, or anywhere in between), and you hit the starter? The TOT will go up rapidly and technically you are suppose to roll the throttle off and keep the starter on to blow the flame out. But at that low of a N1, if you let off the starter and the air is gone! Keep on the starter and you're just giving all that extra fuel more flame and pressure to light off.

I've always wondered if that would work. I had a C28 light off on me the second I hit the starter once. The throttle was closed and the temp got up into the low 900s and just stayed there for about 3-4 seconds until I passed 20% N1. I was really lucky it didn't get over the limit. I think it I would have let off the starter it may have stopped and flamed out long before it hit 900. Couldn't take the risk of not following the set procedure though. Plugged drain or bad fuel nozzle--both were replaced.

#6 Eric Hunt

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Posted 23 July 2009 - 05:37

The real problem with low N1 on ignition is the lack of air to shape the flame and cool the combustion chamber - only 25% of the air that is induced is used in burning, the rest is cooling and shaping. Without the shaping, the flame touches the burner can and then the trouble begins.

I was just kidding about letting go of the starter switch. Any student who did that would get broken fingers because mine would be clamped over his like a vice.

#7 Gomer Pylot

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Posted 24 July 2009 - 00:43

If the engine lights immediately upon pressing the starter, I would release it immediately, then make sure the throttle was completely off. With less than 5% N1, which should be the case, the fire should go out immediately, no matter what the shape of the fireball is, because there isn't enough air to complete the combustion. I've had it happen, and the temp never even got into the green range. You do have to get off immediately, though.

Rolling the throttle to full open is something I wouldn't even consider. If you hotstart a T53, either something is badly out of adjustment or you weren't paying attention.
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#8 Wally

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Posted 24 July 2009 - 09:00

"Hot starts" are 'too much fire' an in inadequate air flow situation, adding 'oxygen' would only make that worse. My guess, and it's completely a guess as I've not flown the 204/short fuselage UH 1 in 40 years, is that the reduction in temp and opening the throttle in the event related by the OP was coincidental.

There are at least two fuel control set ups for engine starts in turbines: pilot modulated, throttle position controls amount of fuel (you control energy to the starter and amount and timing of fuel); And automated start schedules- which I remember the UH1/204 standard set up as having.
The automated starts assume adequate starter power and use some engine rpm signals to initiate events, ie so much fuel at such and such rate. The throttle is pretty much a switch, open, it allows fuel flow; close it, no fuel and only the starter keeps the engine turning. That's what I remember the UH1 as having, and that's why the SOP was to have the throttle below the ground idle detent so you could shut the fuel off with low battery voltage.
I'd guess that throttle position would affect automated starts. I'd never brag about having tried to modulate automated starts, but it has happened, with mixed results, usually unhappy. I wouldn't do it again unless I had expert advice or nothing to lose, it's fools game.
With all due respect the OP's Chief Pilot, his explanation doesn't have the technical detail to be convincing. I think that procedure worked by coincidence and the happy outcome was an accident. I would recommend against drawing any conclusions from that other than sometimes random events do end well.

Edited by Wally, 24 July 2009 - 09:03.

Just a pilot...

#9 BOATFIXERGUY

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Posted 24 July 2009 - 12:46

Kinda the same question.......

What if the throttle isn't closed (full, idle, or anywhere in between), and you hit the starter? The TOT will go up rapidly and technically you are suppose to roll the throttle off and keep the starter on to blow the flame out. But at that low of a N1, if you let off the starter and the air is gone! Keep on the starter and you're just giving all that extra fuel more flame and pressure to light off.

I've always wondered if that would work. I had a C28 light off on me the second I hit the starter once. The throttle was closed and the temp got up into the low 900s and just stayed there for about 3-4 seconds until I passed 20% N1. I was really lucky it didn't get over the limit. I think it I would have let off the starter it may have stopped and flamed out long before it hit 900. Couldn't take the risk of not following the set procedure though. Plugged drain or bad fuel nozzle--both were replaced.


The most common from what you describe is that the throttle was moved with the fuel valve on. It could have been bumped, mechanic inadvertently rolling on doing a daily with fuel valve still on, etc.

Obviously you're experienced, since a ton of new turbine pilots would have totally freaked if the TOT went that high.
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#10 Linc

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Posted 25 July 2009 - 11:02

There is some questionable language in the op. The TOT went "above the limits", and then when the throttle was full-opened the TOT came down...So, the chief pilot continued the flight on an overtemped engine?
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#11 rotorrodent

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Posted 26 July 2009 - 12:48

I think it was two years ago when this happend.

It was the first engine start of the day and my chief pilot was gonna teach me some bambi bucket work in the huey.

At that point I was just introduced to the 204b and wanted my boss doing the start up.
We all agree that, if the engine gets too hot we roll the throttle off into idle and keep cranking to blow the burning fuel out und keep doing this until the TOT goes down low enough.

So he started the engine and the TOT went obove the limits, but instead of rolling off the throttle he rolled it all the way on to full throttle and to my surprise the TOT came down again.

After the flight i asked him why he did that and he said, if you roll the throttle all the way on, there is too much fuel but not enough oxygen and thats what gets the TOT down again.

Whats your opinion on that guys?

------------------------------------------------
normal & hotstart


Been flying turbine engines for 30+ years. That procedure runs contrary to every bit of training I have ever had. Perhaps your chief pilot knows something "unique" about the fuel control unit that doesn't apply to the general rule....that being, fuel off and continue motoring. I certainly don't want to buy a new engine! Garrett engines and some other P&W engines used water injection to cool down the TOT's.

Probably is not the best habit, or motor skills (pun intended) to develop. Stick with the your training and POH. Let the Chief Pilot buy the next motor.

Cheers

Rotorrodent
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#12 Rob Lyman

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Posted 27 July 2009 - 05:52

There is some questionable language in the op. The TOT went "above the limits", and then when the throttle was full-opened the TOT came down...So, the chief pilot continued the flight on an overtemped engine?


It could be that he knows the engine manual and whether additional checks were required before flight. Personally, I would have to break out the manual and see what maintenance actions were required, if any. When I was at the MTP course they had a Chinook engine that had just experienced a moderate overtemp. I was suprised to see how many cracks they found on the power turbine blades. There were about 5 to 7 cracks per rotor, at various clock positions. They were found visually, but it is doubtful anyone could have seen them without an engine tear down.

I don't know that chief pilot's technical expertise, but if he couldn't point me to the spot in the engine manual that said it was OK, I would get out of the aircraft. Real damage could have been done. If damage was done, hopefully it will be found on the next inspection and not during the investigation following the accident 6 months later.

#13 Gerhardt

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Posted 27 July 2009 - 11:23

Yep, in one of Tropical Ed's last columns for Private Pilot he talks about pilots fessing up to ham-fisting so that someone else doesn't suffer from the mistake down the road.

#14 West Coaster

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Posted 27 July 2009 - 15:25

I honestly wouldn't be surprised if the chief pilot was looking at the wrong gauge for a moment, and then pulled this story about it being a legit technique just to cover is arse. It sounds unlikely, but I'll admit I've hit the starter and had a total brain fart as to what I should be monitoring and in what order. I aborted the start, went back inside and had another cup of coffee to get my head back in the game.




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