bananaboy
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Could a human stop an engine start?

Sun Dec 15, 2019 2:28 pm

This is a totally pointless question but I'm on a long train journey and my mind was wandering!

Disregarding all safety implications, could a person stop an engine start by holding on to the fan blades or props assuming the engine was totally stationary? Or, are the forces involved greater than an average human could overcome?

Mark

(Told you it was pointless :lol: )
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ParkFSI
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Re: Could a human stop an engine start?

Sun Dec 15, 2019 2:34 pm

Don’t know if it’s a urban legend but I’ve heard it could be done with a PT-6 turbo prop, but I wouldn’t want to try it !
 
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Starlionblue
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Re: Could a human stop an engine start?

Sun Dec 15, 2019 2:54 pm

Just as a total guess, I think you could stop the prop or fan from turning at least for a bit. Just not for very long.

The engine would still start, because you're not stopping the gas generator. You're just stopping the first spool (N1, the fan or prop), and I think the first spool turbine would really rather spin what with all that exhaust gas hitting it.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Tristarsteve
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Re: Could a human stop an engine start?

Sun Dec 15, 2019 4:04 pm

On the old RB211-22B on the Tristar we used to have lots of problems with the air flow control start bleed valves. (four of then, open at start, and closed at idle) The easiest way to check their operation was to tie the fan up with rope, and start the engine. A piece of ribbon tied to the bleed valve inlet showed when it was open or closed .
Probably not allowed in today's health and safety world, to have your head up the fan duct with the engine running, but it did the trick.
So rope held the fan at idle, but I would think it would need a very strong person, or three.
 
VSMUT
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Re: Could a human stop an engine start?

Sun Dec 15, 2019 4:14 pm

ParkFSI wrote:
Don’t know if it’s a urban legend but I’ve heard it could be done with a PT-6 turbo prop, but I wouldn’t want to try it !


Heard the same for the PW121 and 127. It's essentially the same that the propeller brake does on the ATRs hotel mode.
 
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SheikhDjibouti
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Re: Could a human stop an engine start?

Sun Dec 15, 2019 4:38 pm

1) If the engine had FADEC that included a check on whether the propeller or fan was impeded in some way, you might cause it to trip out at low torque in order to prevent possible engine damage.

2) Principle of levers; if you are allowed to extend the radius of the propeller by adding something (e.g. enclose it within a long length of 5" or 110mm drainage pipe), you could multiply your stopping power.

Otherwise, probably not.

I once worked on a site that included eight huge 1950's diesel generators of around 1500hp each. To protect maintenance crews working on them, when they were taken out of service, they were physically locked down using a thick iron bar. Very occasionally somebody attempted a restart without remembering to remove the safety lock. When that happened, everybody on site knew about it. :rotfl:
Nothing to see here; move along please.
 
CosmicCruiser
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Re: Could a human stop an engine start?

Sun Dec 15, 2019 5:11 pm

ParkFSI wrote:
Don’t know if it’s a urban legend but I’ve heard it could be done with a PT-6 turbo prop, but I wouldn’t want to try it !


saw it done on a PT-6 once but it was a free turbine and not geared.
 
Flow2706
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Re: Could a human stop an engine start?

Sun Dec 15, 2019 11:31 pm

SheikhDjibouti wrote:
1) If the engine had FADEC that included a check on whether the propeller or fan was impeded in some way, you might cause it to trip out at low torque in order to prevent possible engine damage.

On the CFM equipped A320 the FWC will generate an ECAM if there is not fan (N1) rotation during engine start, requiring a aborted start (unlike most of the other start malfunctions the FADEC will however not initiate an automatic aborted engine start in this case, in this case it has to be done manually). No such warning is provided for the IAE engine on the A320.
 
Yikes!
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Re: Could a human stop an engine start?

Mon Dec 16, 2019 3:56 am

CosmicCruiser wrote:
ParkFSI wrote:
Don’t know if it’s a urban legend but I’ve heard it could be done with a PT-6 turbo prop, but I wouldn’t want to try it !


saw it done on a PT-6 once but it was a free turbine and not geared.


It's not urban legend. I have done it. During extremely cold starts (< -40C), there is virtually no lubrication in the PT6 reduction gear box (RGB). Holding the propeller until the engine is running is the best way to reduce the wear and tear within the RGB at those extreme temperatures. This works on aircraft like a Twin Otter or a King Air but not on the larger (-50 engines) PT6's.

Back to the original question, regarding holding on to a fan on something like an RB211, once the engine is running, there is NO WAY a human can hold onto the fan. Had a human tried, he/she would then be integral with the engine exhaust.
 
spacecadet
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Re: Could a human stop an engine start?

Mon Dec 16, 2019 8:38 am

bananaboy wrote:
Disregarding all safety implications, could a person stop an engine start by holding on to the fan blades or props assuming the engine was totally stationary? Or, are the forces involved greater than an average human could overcome?


Seems to depend on the plane. I know that with even the little plane I'm currently flying (Diamond DA-40), there is no way to hold the prop to prevent its starting. Plenty of hands, arms, backs and other body parts have been shredded in the process of trying, some of which I have at least secondhand knowledge of.
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fr8mech
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Re: Could a human stop an engine start?

Mon Dec 16, 2019 11:56 am

There was a leak check procedure on the JT9D-7 that allowed you to tie the fan to the fan exit vanes.

Never saw it done, but it was there.
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Starlionblue
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Re: Could a human stop an engine start?

Mon Dec 16, 2019 1:59 pm

spacecadet wrote:
bananaboy wrote:
Disregarding all safety implications, could a person stop an engine start by holding on to the fan blades or props assuming the engine was totally stationary? Or, are the forces involved greater than an average human could overcome?


Seems to depend on the plane. I know that with even the little plane I'm currently flying (Diamond DA-40), there is no way to hold the prop to prevent its starting. Plenty of hands, arms, backs and other body parts have been shredded in the process of trying, some of which I have at least secondhand knowledge of.


A bit different. The prop on a piston like the Da-40 is mechanically connected to the enginecrankshaft. However, the fan on jets and the prop on most modern turboprops is not mechanically connected to the gas generator. The fan or prop is driven entirely by exhaust gases through the turbine.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Aircellist
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Re: Could a human stop an engine start?

Mon Dec 16, 2019 4:35 pm

spacecadet wrote:
Plenty of hands, arms, backs and other body parts have been shredded in the process of trying, some of which I have at least secondhand knowledge of.


That wins the prize for dark humor this morning!
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bananaboy
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Re: Could a human stop an engine start?

Tue Dec 17, 2019 6:03 pm

Thanks all for the responses!

Mark
All my life, I've been kissing, your top lip 'cause your bottom one's missing
 
strfyr51
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Re: Could a human stop an engine start?

Wed Dec 18, 2019 5:04 am

ParkFSI wrote:
Don’t know if it’s a urban legend but I’ve heard it could be done with a PT-6 turbo prop, but I wouldn’t want to try it !

the PT6 could be cranked with the prop held and as long as the engine was idle power? It could be held though you would quickly overheat the power section of the engine as that is where the exhaust escapes the engine. I worked at an airline that flew the Dash 7 with the PT6-50 engine and another mechanic started an engine with a power section shaft Bearing failing. the Gas Generator started but the Prop didn't move, later we found the gearbox section turbine bearing Failed locking the power section up
 
Swampfoot
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Re: Could a human stop an engine start?

Sun Dec 22, 2019 6:06 am

I have been in the hangar when a crew needed to generate some oil pressure to drive a prop to either flat pitch or feather on a Q400, don't remember the exact scenario, but it involved two people holding the prop still (by hand) while making sure no fuel or ignition would operate while someone motored the starter for maybe 20 seconds. This was a PW150, a free-turbine engine.

Seemed really dangerous to me. If the people holding it lost their grip, I think it would spin up to lethal speeds very quickly.

Anyone else done this or seen it done?
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WesternDC6B
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Re: Could a human stop an engine start?

Mon Jan 06, 2020 3:18 am

SheikhDjibouti wrote:
I once worked on a site that included eight huge 1950's diesel generators of around 1500hp each. To protect maintenance crews working on them, when they were taken out of service, they were physically locked down using a thick iron bar. Very occasionally somebody attempted a restart without remembering to remove the safety lock. When that happened, everybody on site knew about it. :rotfl:


My curiosity is heightened: how did everybody know?

1) Broken starter or starter gears, thus bringing forth loud and strong language from Those in Charge?

2) A tremendous “Clang!”, the iron bar being launched very high, then dropping to the ground, thus bringing forth loud and strong language from Those in Charge?

3) The person doing this being razzed and poked fun at, and who also brought forth loud and strong language from Those in Charge?
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SheikhDjibouti
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Re: Could a human stop an engine start?

Mon Jan 06, 2020 6:30 pm

WesternDC6B wrote:
SheikhDjibouti wrote:
I once worked on a site that included eight huge 1950's diesel generators of around 1500hp each. To protect maintenance crews working on them, when they were taken out of service, they were physically locked down using a thick iron bar. Very occasionally somebody attempted a restart without remembering to remove the safety lock. When that happened, everybody on site knew about it. :rotfl:


My curiosity is heightened: how did everybody know?

1) Broken starter or starter gears, thus bringing forth loud and strong language from Those in Charge?

2) A tremendous “Clang!”, the iron bar being launched very high, then dropping to the ground, thus bringing forth loud and strong language from Those in Charge?

3) The person doing this being razzed and poked fun at, and who also brought forth loud and strong language from Those in Charge?

I confess I don't know the specific answer to your question, but I was on site on one of the rare occasions it happened - and answer #2 is closest, in that there was a huge bang, amplified by the fact the engines were housed in a classic engine house that was built with cathedral-like proportions.
I am very glad I was ½km away at the time. If I had been inside the cathedral, I probably would have been knocked off my feet.

I cannot imagine that the metal bar would have been launched anywhere, and neither would it have snapped, but it may have rattled around in it's housing.

As for starting - IIRC these engines would have been turned over by compressed air, so no stripped starter gears either.

FWIW the engines were made by Mirrless Blackstone, at one time part of the Hawker Siddeley Group.
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DALMD80
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Re: Could a human stop an engine start?

Mon Jan 06, 2020 11:27 pm

bananaboy wrote:
This is a totally pointless question but I'm on a long train journey and my mind was wandering!

Disregarding all safety implications, could a person stop an engine start by holding on to the fan blades or props assuming the engine was totally stationary? Or, are the forces involved greater than an average human could overcome?

Mark

(Told you it was pointless :lol: )

Eventually any jet I know of would turn and then they would be sucked in. I guess it would stop the engine from starting, though.
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DarkSnowyNight
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Re: Could a human stop an engine start?

Tue Jan 07, 2020 6:52 am

Swampfoot wrote:
I have been in the hangar when a crew needed to generate some oil pressure to drive a prop to either flat pitch or feather on a Q400, don't remember the exact scenario, but it involved two people holding the prop still (by hand) while making sure no fuel or ignition would operate while someone motored the starter for maybe 20 seconds. This was a PW150, a free-turbine engine.

Seemed really dangerous to me. If the people holding it lost their grip, I think it would spin up to lethal speeds very quickly.

Anyone else done this or seen it done?


I have done a similar thing, but with a Dash8-300, with the PW123s, over at Piedmont, quiet a while ago. You do need two people to hold the blades, and about thirty seconds was also what we needed.

In more modern times, it is not at all unheard of to motor a turbofan for similar reasons. Most common, to bring the oil gauges to an accurate read. On a lot of engines, like the V2500, it is important to not over-service the oil. And after an hour or so of sitting, the reads and sight glass will both sag somewhat, necessitating this action if the oil has not already been serviced.

No need to hold the Front Fan Blades still in that case though.
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m1m2
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Re: Could a human stop an engine start?

Tue Jan 07, 2020 10:43 am

Regarding the PW150 on the Q400, I've motored that thing dozens of times on the starter to generate oil pressure to either unfeather, or feather the prop. There is no need to hold the prop from turning, but it can easily be done by one person if so desired (probably done if there's a ladder or maintenance stand near the prop). If that person let it go, it would spin very slowly as the hydraulic pump is driven by the same gearbox as the prop and generates quite a resistance to the prop turning. It wouldn't turn fast enough to generate an NP indication in the cockpit. You are correct in that you want to pull the ignition breakers and make sure the condition lever remains at "fuel off" during the motoring. Otherwise, noise will be heard from the exhaust and...well, you know the rest. lol

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