tazzrassinIDA
Posts: 32
Joined: Sun Jun 03, 2007 3:00 pm

In Theory, Could A Jet Engine Do This?

Tue Jun 26, 2007 11:13 am

Ok, the searches did not pull anything similar to this, so here it goes. (not that I am proficient at using the searches yet either.)

For some odd reason, I started thinking about this today. Who know maybe I had too much time on my hands. I am familiar with scenes in movies, like in Castaway, where it shows a jet running under water, threatening to eat the stars. There is no way this could happen I know. What if a plane crashed into water in such a way that the engine stayed attached to the wing, and it's fuel supply. The intake is clear of the water, sucking only air, and the safeties that should shut it down have failed. Would it be possible for it to keep running if the exhaust end were under water?

In my pondering, given the "perfect" conditions for the engine to run, except that the tail end is submerged, I would say no it would not. I would think it is kind of like plugging the tail pipe of a car, the engine would eventually not be able to sustain its self.

I hope to stir up some good natured conversation about this, express a question I have been pondering in hopes that my hypothesis is confirmed by others, and see how things go.

Tazz
Tazz
 
airfoilsguy
Posts: 3485
Joined: Sun Oct 09, 2005 7:28 am

RE: In Theory, Could A Jet Engine Do This?

Tue Jun 26, 2007 11:39 am

It's not a near miss it's a near hit!!
 
fr8mech
Posts: 6672
Joined: Mon Sep 26, 2005 9:00 am

RE: In Theory, Could A Jet Engine Do This?

Tue Jun 26, 2007 12:44 pm

Using your assumptions, I see no reason why it woud not continue to run. Performance may suffer a bit, but water at a depth of about 12 feet, assuming the engine is vertical, would be easily pushed away by the high speed exhaust.
When seconds count...the police are minutes away.
 
tazzrassinIDA
Posts: 32
Joined: Sun Jun 03, 2007 3:00 pm

RE: In Theory, Could A Jet Engine Do This?

Tue Jun 26, 2007 3:46 pm

Wow, that video is pretty amazing. I guess it is possible... Thanks for sharing.
Tazz
 
User avatar
SEPilot
Posts: 4970
Joined: Sat Dec 30, 2006 10:21 pm

RE: In Theory, Could A Jet Engine Do This?

Tue Jun 26, 2007 7:53 pm

As long as the engine has fuel and sufficient air and appropriate electrics (I'm not sure what jet engines require by way of electrical signals; piston aircraft engines require none) it will continue to run, regardless of whether the exhaust is under water or not. What would probably cause it to stop (assuming it doesn't run out of fuel) is water getting into the fuel, as the tanks have to be vented and if the vents are under water they will suck water instead of air, or if the engine settles into the water enough to suck enough water to drown it. It can actually suck a fair amount of water and still run, but there is a limit, of course.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
3MilesToWRO
Posts: 258
Joined: Sun Mar 12, 2006 2:08 am

RE: In Theory, Could A Jet Engine Do This?

Wed Jun 27, 2007 6:54 am

Quoting SEPilot (Reply 4):
I'm not sure what jet engines require by way of electrical signals; piston aircraft engines require none

Well, not "signals" maybe, but sparks are useful, I suppose.
 
User avatar
SEPilot
Posts: 4970
Joined: Sat Dec 30, 2006 10:21 pm

RE: In Theory, Could A Jet Engine Do This?

Wed Jun 27, 2007 9:20 am

Quoting 3MilesToWRO (Reply 5):

Well, not "signals" maybe, but sparks are useful, I suppose.

An aircraft piston engine has magnetos, which require no outside input, and so I consider them part of the engine. No outside signal is required for them to keep running; there is a grounding wire to short them out to prevent them from firing, but they will run happily all day long with no external connection.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
Fly2HMO
Posts: 7207
Joined: Sat Jan 24, 2004 12:14 pm

RE: In Theory, Could A Jet Engine Do This?

Wed Jun 27, 2007 1:05 pm

If you somehow isolate the engine core from the water, and give it some kind of a snorkel for the intake and exhaust, then yeah, it could work (I'm talking about a turbofan here). I don't think it would work too well though, it takes thousands of HP produced by the turbine section to make the fan turn in air, and water is only *slightly* more dense and heavy than air Big grin

In a pure turbojet, or turboprop, hell no, there's no way that could work. While they can sustain extreme rain intake, they are not submersible.

Quoting Airfoilsguy (Reply 1):
Here is a close one.

http://youtube.com/watch?v=TYhrpA0tmBQ

Very close indeed, but if you look closely, the waterline barely goes into the exhaust, and I really I doubt the last turbine stage is in contact with the water at all, the waterline is just too low.

[Edited 2007-06-27 06:10:45]
 
Analog
Posts: 1193
Joined: Fri Jul 14, 2006 3:24 am

RE: In Theory, Could A Jet Engine Do This?

Wed Jun 27, 2007 1:40 pm

Quoting SEPilot (Reply 6):

An aircraft piston engine has magnetos... they will run happily all day long with no external connection.

That's a bit scary to this engineer, but ON is a better default than OFF for this application, I guess.
 
User avatar
SEPilot
Posts: 4970
Joined: Sat Dec 30, 2006 10:21 pm

RE: In Theory, Could A Jet Engine Do This?

Wed Jun 27, 2007 8:10 pm

Quoting FLY2HMO (Reply 7):

In a pure turbojet, or turboprop, hell no, there's no way that could work. While they can sustain extreme rain intake, they are not submersible.

The situation was that the intake was out of the water but the exhaust was under water. As long as the engine was running when it went in I believe it could continue running until it sucked too much water in the intake. I totally agree that any substantial submersion (meaning a couple of inches) of the intake would drown it.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
User avatar
moriarty
Posts: 172
Joined: Tue Jan 10, 2006 1:05 am

RE: In Theory, Could A Jet Engine Do This?

Fri Jun 29, 2007 8:06 pm

Never the less, that video is quite remarkable! It is not too common to see crashes and their aftermath up close like that. Glad everyone seemed ok. Amazing the guy filming the whole thing kept shooting instead of assisting. I guess he made the decision that there was no need for more helping hands.

What I failed to understand was if the engine spooled up due to some technical reason or if there actually was a pilot left trying to do something (heroic or stupid, I'm not the person to judge that if so)...
Proud to part of www.novelair.com.
 
airfoilsguy
Posts: 3485
Joined: Sun Oct 09, 2005 7:28 am

RE: In Theory, Could A Jet Engine Do This?

Fri Jun 29, 2007 9:17 pm

Quoting Moriarty (Reply 10):
What I failed to understand was if the engine spooled up due to some technical reason or if there actually was a pilot left trying to do something

No one was left in the plane. I believe the engine restarted when they were trying to tie off the jet to the boat using some of the jets wiring. By the way the guy got a new jet with an ironic registration.  Smile



View Large View Medium
Click here for bigger photo!

Photo © Regin Krøigaard

It's not a near miss it's a near hit!!
 
User avatar
moriarty
Posts: 172
Joined: Tue Jan 10, 2006 1:05 am

RE: In Theory, Could A Jet Engine Do This?

Sat Jun 30, 2007 12:13 am

Quoting Airfoilsguy (Reply 11):
By the way the guy got a new jet with an ironic registration. Smile

That is absolutely hilarious!  bigthumbsup 
Proud to part of www.novelair.com.
 
User avatar
Starlionblue
Posts: 17117
Joined: Fri Feb 27, 2004 9:54 pm

RE: In Theory, Could A Jet Engine Do This?

Sat Jun 30, 2007 1:57 am

Quoting Moriarty (Reply 10):
Amazing the guy filming the whole thing kept shooting instead of assisting. I guess he made the decision that there was no need for more helping hands.

I would like to think so. But he probably just thought: "This will be great on YouTube"...
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
airfoilsguy
Posts: 3485
Joined: Sun Oct 09, 2005 7:28 am

RE: In Theory, Could A Jet Engine Do This?

Mon Jul 02, 2007 4:21 am

Quoting Moriarty (Reply 10):
Amazing the guy filming the whole thing kept shooting instead of assisting. I guess he made the decision that there was no need for more helping hands.

I am one of the first to criticise people for filming and not helping but what could this guy have done? All the action was in the water and I don't think he had a boat. He was also the first person to call 911.
It's not a near miss it's a near hit!!
 
VC-10
Posts: 3546
Joined: Tue Oct 26, 1999 11:34 am

RE: In Theory, Could A Jet Engine Do This?

Mon Jul 02, 2007 5:49 am

On a modern engine you would have to keep the EEC & the control alternator dry.
 
F14D4ever
Posts: 306
Joined: Sat May 07, 2005 3:20 am

RE: In Theory, Could A Jet Engine Do This?

Mon Jul 02, 2007 11:14 pm

Quoting TazzrassinIDA (Thread starter):
What if a plane crashed into water in such a way that the engine stayed attached to the wing, and it's (sic) fuel supply. The intake is clear of the water, sucking only air, and the safeties that should shut it down have failed. Would it be possible for it to keep running if the exhaust end were under water?

Absolutely not.

Quoting VC-10 (Reply 15):
On a modern engine you would have to keep the EEC & the control alternator dry.

The EEC is the least of the concerns in this scenario. With the exhaust under water, there would be insufficient pressure drop across the turbine to sustain compression, which in turn means insufficient pressure and temperature for combustion. At some point as the combustor inlet p & t spiraled down, the compressor would surge violently, at which point it's all over.
"He is risen, as He said."

Who is online

Users browsing this forum: No registered users and 16 guests