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B-17: Queen of the Skies» Forums » General

Subject: If a runaway engine doesn't feather... rss

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Damo
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...why do the crew automatically have to bail out?

Now, you may say that it's obvious, that a heavily vibrating engine that has the potential to shear the prop off and into the cockpit or another engine would be a bad thing.

Well, you''d be right.

But the thing is, I've read several accounts by pilots who describe this event and there is no mention of them even thinking of bailing out.

Very badly scared yes, but bailing out? Nope.

So, has my reading been really selective or could it be that flying a B-17 with 3 good engines and fighting the 4th was preferable to bailing out?

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oystein eker
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As a rule of thumb, a dead non feathered engine will brake with as much power as it delivers. A 1000 hp engine will then brake with 1000 hp due to windmilling. Not very flyable aircraft. I guess they prayed for a quick propeller shaft shear and get rid of the propeller.

I guess the structural damage from a thrown prop will not be enough to down a B17. But stay away from from the tangential line of the prop disc!
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Damo
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A "runaway engine" operates at an increasing rate of speed until it mechanically fails or seizes due to lack of oil. Does one engine running faster then the other three create drag?

Successfully feathering an engine doesn't stop it from "running away", it just changes the pitch of the prop blades.

So, in game terms, if an engine "runs away" and the props are successfully featherd, at some point the engine would fail or sieze anyway.
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oystein eker
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Yes it runs faster due to lack of speed governor control. I do not know how to the prop pitch angle system works in B17. In a standard auto prop pitch the prop blade pitch will adjust itself to max brake - as it will in normal run, try to maximize prop pitch angle for best effect. In this case assuming that the pitch oil pressure will be obtained by windmilling, and the controls from cockpit is broken.

With no oil pressure the prop will aerodynymically try to move to fine pitch, worst possible position. As a backup you find counterweights on blade roots to force the pitch to move to coarse or feathered position. Do not know if this is implemented on B17.

It all boils down to how and when the feather system fails. If it fails and seize close to feather pitch, the problem may not be that bad. If the windmill does keep the oil pressure, you may have a problem. If the pitch is stuck in normal power range, you have a problem.

Successfully feathering an engine doesn't stop it from "running away", it just changes the pitch of the prop blades

In feather the engine does not rotate. because the pitch of prop blades are so coarse that there are no aerodynamic forces to create a windmill. With a successfull feather you cannot have a run away prop. The engine cannot fail, because it is already shut down.
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Jim P
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Damjon wrote:
A "runaway engine" operates at an increasing rate of speed until it mechanically fails or seizes due to lack of oil. Does one engine running faster then the other three create drag?

Successfully feathering an engine doesn't stop it from "running away", it just changes the pitch of the prop blades.

So, in game turns, if an engine "runs away" and the props are successfully featherd, at some point the engine would fail or sieze anyway.


Yes the runaway engine runs at a high rate and can’t be controlled by the pilots. Feathering it would probably make it vibrate more. As then the props would be paddles trying to torque the plane over on its back, I would think.

I just read about two planes in the 100th BG that flew on with runaway props. And yes they both sheared off after some time and yes the Pilots were praying for the prop shaft to shear, but one plane did have the sheared prop do damage all the way back even causing issues on landing IIRC.

I too question why the rules are written this way... But maybe we are only reading about the ones that survived a runaway prop. There may have been more incidents where the runaway prop was fatal to the crews. My reading hasn't had any information on this phenomenon. This is an interesting question though, anyone else with more information on this??

My 2cents!
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Jim P
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eker wrote:
In feather the engine does not rotate. because the pitch of prop blades are so coarse that there are no aerodynamic forces to create a windmill. With a successfull feather you cannot have a run away prop. The engine cannot fail, because it is already shut down.


Eker,
I think the question is for a runaway engine not a runaway prop. The rules allow for continued flight with a runaway prop (windmill) but not a runaway engine.

My take with the runaway engine, is that the prop is still under power and the pilots can't control the rpm rate anymore. So my guess is that the prop would still turn if the props were feathered or not, unless the mechanism disengages the prop when it becomes feathered. I don’t know how it works that well to be sure.

Jim
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oystein eker
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B-17: Queen of the Skies » Forums » General
Re: If a runaway engine doesn't feather...
You use the prop pitch for engine RPM control. Except around idle when taxiing on ground.

I just found a nice manual on Hamilton Standard. A safe bet this is used on B17.

http://www.connecticutscorsair.com/hamilton_standard_manual....
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Jim Rose
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I remember this picture from the B-17 "General Ike". Although flak did the damage to the engine you can see where the propeller blade sliced through behind the flight deck. Nasty close call!

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Damo
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I've just read another account of a non-feathering engine in Truman Smiths "The Wrong Stuff".

He was a copilot on a B-17 which had a runaway. They couldn't feather the engine due to low oil pressure and Smith relates that there was very heavy vibration before the engine welded itself together. The process took some time, certainly enough for the crew to bail out.

Yet they didn't.

Jasta6 is right that we only hear the stories of the ones that returned to tell the tale, yet none of other survivors tales relate to a non-feathering engine bail out (NFEBO). Now I'm not claiming to have comprehensively read all survivors accounts, but somewhere I would have expected to read a NFEBO story.

So I'm beginning to assume that the SOP for a non-feathering engine wasn't to bail out, but to suck-it-and-see. From the accounts I've read, apart from the heavy vibration, the B-17 was not made unflyable by a non-feathered engine.

If that's the case then perhaps the below variant rule could be enacted if a "6" is rolled when trying to feather an engine.

Roll a further D6:
1-3 engine fails without further damage to the B-17, treat as "feathered".
4-6 engine fails catastrophically. If the engine is #2 or #3 roll 3 hits (one for each prop) on both pilot compartment and neighbouring engine. If engine is #1 or #4 roll 3 hits on both relevant wing and neighbouring engine.


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David Lanphear
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All well and good, but remember this game is an abstraction. When you have a runaway engine, you have a 5/6 chance that things will be okay anyway. That 1/6 chance represents (to me anyway) that things didn't work out and in the captain's view it would be best to bail out and not just the fact that there is a continued "runaway" engine.

Yes we all want to make 25 missions, and as the game plays now, it's tough, as it was in real life. That's what makes getting those 25 for a plane or crew member so memorable (something I've never done).

Anyway my two .

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