Merlin engine in Ace's

[dtango]

Okay I guess. The reports I read made it sound as if steep dives pushed more air past the propeller forcing it to rev beyond limits and wreck the gearing. If the only thing to worry about is failed governors then I can see why its not in the game like that but if steep dives do in fact cause this sort of problem I would like to see that in the game just to make things a little bit tougher.  

Yes this can definitely happen in a dive as well as you've described.  I could quibble with EDO about terminology of runaway props vs. overspeeding props, but no matter in either case the prop and crankshaft are spinning too fast that it wrecks the engine.  For a propeller with a working governor you can conceptually overspeed the prop in a dive.  This occurs though when blade pitch can longer be increased because it has hit the mechanical stops e.g. the oil piston driving the pitch is at it's maximum.  

Before it reaches the mechanical stops however the governor will continue to adjust to keep RPM constant.  As the airplane increases in velocity, the loading on the propeller lessens due to a lower relative blade aoa thanks to the increasing forward velocity.  Lower blade aoa means lower torque loading on the propeller therefore it spins faster.  This increases RPM on the crankshaft which changes the centrifugal force on the fly weights in the governor which causes the governor to pump more oil to increase blade pitch to increase the propeller loading.  More loading on the propeller makes it harder for the engine to turn the prop thus slowing the RPM back down to the desired setting.  That's what John Deakin's article that kvuo pointed out talks about.

Here's a schematic of the Hamilton Standard Hydromatic that many of our airplanes in AH used in real life and how it addresses the overspeeding I was describing in the paragraph above.



There is some increase in forward velocity however where we reach the mechanical stops.  When this happens the governor can't increase the pitch of the propeller anymore to adjust for the lower propeller loading.  Since the power loading keeps decreasing in this case with increasing velocity the prop and the crankshaft spins faster and faster.  At some point the engine can't handle it any more and blows chunks .  As to modelling this, I have no idea if AH has an RPM limit on planes before the engine fails.  Bear in mind though that in this particular case you can easily avoid ovespeeding the propeller by simply closing the throttle.

[BulletVI]

Ahem what type of merlin engine is in the MkVIII Spit in game as from reading this web page i hope its the Spitfire LF VIII

With the merlin 66 engine capable of

1720bhp @ 5750 feet
1595bhp @ 1600 feet   

It sounds powerful SLURP    

http://www.spitfireperformance.com/spitfire-VIII.html

[Masherbrum]

....and to think someone said "Goodbye" in this thread and is still posting.   

[BulletVI]

....and to think someone said "Goodbye" in this thread and is still posting.   

I was angry and have now vented it

[RTHolmes]

Ahem what type of merlin engine is in the MkVIII Spit in game as from reading this web page i hope its the Spitfire LF VIII

it is indeed a 66 in our LF VIII

[Chalenge]

There is some increase in forward velocity however where we reach the mechanical stops.  When this happens the governor can't increase the pitch of the propeller anymore to adjust for the lower propeller loading.  Since the power loading keeps decreasing in this case with increasing velocity the prop and the crankshaft spins faster and faster.  At some point the engine can't handle it any more and blows chunks .  As to modelling this, I have no idea if AH has an RPM limit on planes before the engine fails.  Bear in mind though that in this particular case you can easily avoid ovespeeding the propeller by simply closing the throttle.

Yes but the point is there are quite a few that dont so if Hitech returns to this thread...

+1 Please invoke the governor of dweebs for us all!  

[BulletVI]

You know what would really hurt people and thats if the wep wouldnt automatically cut out after 4 minute's. I mean imagine it all the wep dweebs suddenly go clonk clank pur pur pur stop

[SIK1]

There is some increase in forward velocity however where we reach the mechanical stops.  When this happens the governor can't increase the pitch of the propeller anymore to adjust for the lower propeller loading.  Since the power loading keeps decreasing in this case with increasing velocity the prop and the crankshaft spins faster and faster.  At some point the engine can't handle it any more and blows chunks .  As to modelling this, I have no idea if AH has an RPM limit on planes before the engine fails.  Bear in mind though that in this particular case you can easily avoid ovespeeding the propeller by simply closing the throttle.

I've never lunched an engine in AH by over speeding in WW2 planes, but have done it in the WW1 planes.

[EDO43]

Yes this can definitely happen in a dive as well as you've described.  I could quibble with EDO about terminology of runaway props vs. overspeeding props, but no matter in either case the prop and crankshaft are spinning too fast that it wrecks the engine.  For a propeller with a working governor you can conceptually overspeed the prop in a dive.  This occurs though when blade pitch can longer be increased because it has hit the mechanical stops e.g. the oil piston driving the pitch is at it's maximum.  

Yes, what you say is fact.  No disputing that.  I believe (but I may be incorrect) that in real aircraft such as those modeled in AH, the dive speed (Vne?) is partially determined by the prop loads/forces and airframe loads/forces (not including compressability).  We do not have such an airspeed restriction on the airplanes in AH, save the fact that some aircraft will experience structural failure when the airspeed gets too high (usually in a dive and without pulling G).  In oher words, there is no Pilot's Operating Handbook for the aircraft in AH telling us what airspeed restrictions and such....  That's too much info for the game dynamic. 

Regarding the overspeeding propelllor/runaway propellor... I don't follow but suffice to say that in my understanding of a constant speed prop, an overspeed only results in governor flyweights raising the oil valve due to the increased centrifugal force on said flyweights (provided the prop is in the constant speed range).  As you've said, it is a temporary condition that results in blade angle increase and more load on the engine, slowing the rpm back to where it's been set to.  Runaway prop is, in my minds eye, a propeller that cannot be feathered after an engine is shut down (multiengined aircraft) and consequently the torque and rpm's get to the point where the reduction gearcase bolts yield under the shear forces and there goes your prop/reduction gearcase off into the wild blue...not to mention what it does to the rest of the engine.

[Krusty]

WW1 has fixed pitch props, that's why. The more airflow pushes the engine past its limit, vs. adjusting pitch to keep the spin rate constant. Hence "constant speed" propellor....


P.S. AH has over-speeding sort of built in. I've noticed many times in many different planes an inability to reduce RPM at certain speeds, until the airspeed has slowed enough that it takes effect.

[dtango]

Regarding the overspeeding propelllor/runaway propellor... I don't follow but ........Runaway prop is, in my minds eye, a propeller that cannot be feathered after an engine is shut down (multiengined aircraft) and consequently the torque and rpm's get to the point where the reduction gearcase bolts yield under the shear forces and there goes your prop/reduction gearcase off into the wild blue...not to mention what it does to the rest of the engine.

Usually the context I see runaway props described is when the governor fails with the engine still running vs. how you described engine shut off and prop windmilling.  For instance here's the procedure out of the P-51D manual: (mentions the POH overspeed rpm's)



But I've also seen "runaway prop" used in other ways too.  Anyway just ignore my mumbling about the meaning of the terms .  Totally unimportant!  It's holdover from my work- infact today we were debating the precise definition of the meaning of "facility" vs. "plant" as information objects.  Is a facility a plant or a plant a facility?  Is a plant always a facility, but not all facilities plants?? etc. etc.  

[SlapShot]

You know what would really hurt people and thats if the wep wouldnt automatically cut out after 4 minute's. I mean imagine it all the wep dweebs suddenly go clonk clank pur pur pur stop

What is a WEP dweeb ?

[SlapShot]

It's holdover from my work- infact today we were debating the precise definition of the meaning of "facility" vs. "plant" as information objects.  Is a facility a plant or a plant a facility?  Is a plant always a facility, but not all facilities plants?? etc. etc.  

UGH ... a plant cannot be a facility ... a plant in something that grows in the ground !!! ... bunch of dummies !!! ...

[horble]

And here I was thinking that aircraft engines worked on magic and dreams  

[Soulyss]

And here I was thinking that aircraft engines worked on magic and dreams  

I've always assumed they worked on magic smoke just like modern electronics.  Ever let the magic smoke out of your computer or surround receiver? Stopped working didn't it?