Bf-109 Elec. Propeller Pitch control, .. how it works?

[Anatoli-Kagari9]

I'll try again tonight leaving the prop governor automation ON before killing the engine, but this turn around starting at 25000'

[Art-J]

The windmilling prop behaviour is not so simple and depends on speed and rpm. As you have engine down the prop will rotate at the desired rpm because the prop governor decreases pitch to keep rpm. It's not hard because cranking engine creates evenly distributed resistance moment (compression strokes are compensated with extension (power) strokes), and rotating prop creates much torque.

 

At moderate speed a high solidity factor propeller that has high absorbed power will create more drag than at windmilling as it freezes at fine pitch.

 

Starting the stopped prop is not easy or impossible sometimes because of high resistance of first compression strokes and relatively low moments created with the stopped prop.

 

I don't quite understand it either. I thought windmilling prop always produced more drag than the stopped one (I assumed it's similar situation to autorotation in helicopters), especially when hydromatic prop goes full fine pitch after loss of oil pressure (engine off). What am I missing here?

[sobek]

I assume full fine stopped is worse than full coarse rotating.

[Yo-Yo]

I assume full fine stopped is worse than full coarse rotating.

 

Yes, right. And worse than full fine rotating...

[Yo-Yo]

I don't quite understand it either. I thought windmilling prop always produced more drag than the stopped one (I assumed it's similar situation to autorotation in helicopters), especially when hydromatic prop goes full fine pitch after loss of oil pressure (engine off). What am I missing here?

 

Compare total blade area/disk area ratio for helicopter rotor and Mustang prop.

 

I have to say two things: a) this effect for P-51 is not calculated - it is known from RL

b) windmilling and stopped props are quite complicated matter, especially windmilling

[IIIJG52_Otto_]

Compare total blade area/disk area ratio for helicopter rotor and Mustang prop.

 

I have to say two things: a) this effect for P-51 is not calculated - it is known from RL

b) windmilling and stopped props are quite complicated matter, especially windmilling

 

YoYo,.. which have you matching the Bf-109K4 windmilling behavior?? ... :unsure:

[Yo-Yo]

YoYo,.. which have you matching the Bf-109K4 windmilling behavior?? ... :unsure:

 

At least with the model that matches the real Hamilton Standard. But I checked some numbers though... so, the moment seems to be sufficient to rotate the engine,as I can see. Ok, we will check the slow model.

Edited March 31, 2015 by Yo-Yo

[IIIJG52_Otto_]

At least with the model that matches the real Hamilton Standard. But I checked some numbers though... so, the moment seems to be sufficient to rotate the engine,as I can see. Ok, we will check the slow model.

 

Thank you Yo-Yo .. I think that it ´s very necessary.

 

The actual way that Bf-109 engine windmillind, and engine stop behavior, (it´s like the crankshaft gripping all the times), with no vibrations, no misfiring, or premonitory noise, when engine is overheating, etc.. I think it´s not realistic.

[Yo-Yo]

Thank you Yo-Yo .. I think that it ´s very necessary.

 

The actual way that Bf-109 engine windmillind, and engine stop behavior, (it´s like the crankshaft gripping all the times), with no vibrations, no misfiring, or premonitory noise, when engine is overheating, etc.. I think it´s not realistic.

 

I disagree, there are at least two variants of carastrophic failure: heat jam from overheat - gradual with changing sound - and piston rod breaking. In the last case the engine will stop in moment, and yes, we have to add some effects like oil smoke or coolant vapours because of broken case.

 

Then the engine can fail due to fuel system, ignition, etc.

[Llucmk]

I disagree, there are at least two variants of carastrophic failure: heat jam from overheat - gradual with changing sound - and piston rod breaking. In the last case the engine will stop in moment, and yes, we have to add some effects like oil smoke or coolant vapours because of broken case.

 

Then the engine can fail due to fuel system, ignition, etc.

 

I've heard once from a friend who studied engines and once in class, one engine exploted by grip cause... He said that the engine obviously stopped and some some pieces of the engine almost hit him at really fast speed... Maybe if you guys take a look to some damage model effects, you could take a look at this. Some Sparks or pieces take apart from the plane when the motor is gripped would be a realistic effect if what my friend told me it's true.

 

 

If the video doesn't work...

Edited March 31, 2015 by NineLine

[Yo-Yo]

Waiting for new graphic effects :)

Edited March 31, 2015 by Yo-Yo

[IIIJG52_Otto_]

I disagree, there are at least two variants of carastrophic failure: heat jam from overheat - gradual with changing sound - and piston rod breaking. In the last case the engine will stop in moment, and yes, we have to add some effects like oil smoke or coolant vapours because of broken case.

 

Then the engine can fail due to fuel system, ignition, etc.

 

I have not seen engine failures in aircraft piston engine (although in a jet engine), but i had some serious engine breakdowns, in any of the 5 cars I´ve owned in the last 30 years.

From my own experience, a piston engine, not usually stop suddenly, without notice, when it has serious problem.

I suffered a breaking of the connecting rod bearing in my old car (15 years ago), and the engine began to jiggle and make a loud noise of hammering. I shut off the ignition key and the engine was not destroyed. The connecting rod bearing can be replaced later, and the engine came back to run properly.

Before stopping due to mechanical fault of alternative train (crankshaft, connecting rod, piston), a piston engine, always makes strange noises, vibration or hammering. In addition, the oil pressure decreases,and water temperature, or cylinder head temperature values, rise to red.

 

If the video doesn't work...

 

In the video shred by Llucmk, the sound changes at the minute 0:06, the engine begins to shake at the minute 0:25 , and exploded at minute 0:31.

The explosion is not immediately, but probably this can be an induced failure on a test engine.

Edited April 1, 2015 by III/JG52_Otto_+

[NineLine]

I have not seen engine failures in aircraft piston engine (although in a jet engine), but i had some serious engine breakdowns, in any of the 5 cars I´ve owned in the last 30 years.

From my own experience, a piston engine, not usually stop suddenly, without notice, when it has serious problem.

I suffered a breaking of the connecting rod bearing in my old car (15 years ago), and the engine began to jiggle and make a loud noise of hammering. I shut off the ignition key and the engine was not destroyed. The connecting rod bearing can be replaced later, and the engine came back to run properly.

Before stopping due to mechanical fault of alternative train (crankshaft, connecting rod, piston), a piston engine, always makes strange noises, vibration or hammering. In addition, the oil pressure decreases,and water temperature, or cylinder head temperature values, rise to red.

 

I don't think comparing a general street car engine in most cases is a good comparison to a high performance aircraft motor. Take a high performance dragster that is known to launch a piston into the next state on failure :)

 

Breaking a connecting rod during an intense flight in an aircraft like this, I would expect the internal damage to be much greater, and the internal forces much stronger... but I am no expert on blowing up engines ;)

[Pikey]

My old man kept a piston as an ashtray after he wrecked yet another Chevron engine. I saw the melted metal on the piston rod and often wondered about the forces involved in that...

[Yo-Yo]

I have not seen engine failures in aircraft piston engine (although in a jet engine), but i had some serious engine breakdowns, in any of the 5 cars I´ve owned in the last 30 years.

From my own experience, a piston engine, not usually stop suddenly, without notice, when it has serious problem.

I suffered a breaking of the connecting rod bearing in my old car (15 years ago), and the engine began to jiggle and make a loud noise of hammering. I shut off the ignition key and the engine was not destroyed. The connecting rod bearing can be replaced later, and the engine came back to run properly.

Before stopping due to mechanical fault of alternative train (crankshaft, connecting rod, piston), a piston engine, always makes strange noises, vibration or hammering. In addition, the oil pressure decreases,and water temperature, or cylinder head temperature values, rise to red.

 

The aircraft engine has very different load of mechanics. The car engine has 10000+ hours (if you recalc 600000 km before a full overhaul to hours). Fighter engine had 100-150 hours typically.

V-engine has different geometry, so the known piston rods failures usually led to instant destruction and jam.

[msalama]

V-engine has different geometry, so the known piston rods failures usually led to instant destruction and jam.

Not only the big aero V12s, but pretty much any engine throwing a rod can actually lead to an immediate seizure, because said snapped / broken conrod often exits right through the engine block side. Has seen this happen a couple of times myself when I worked on all kinds of beat-up junkers as a kid ;)

[Echo38]

This isn't exactly the type of engine failure originally being discussed, but here's an example of how a high-performance aircraft engine can fail catastrophically enough to shatter the propeller:

 

Yes, I know, this is almost the opposite of "stopping instantly" (because in this case, the failure caused the propeller to over-speed), but the point is, as Yo-Yo and others pointed out, there's little to compare with automobile engines and high-performance aircraft engines.

[IIIJG52_Otto_]

I don't think comparing a general street car engine in most cases is a good comparison to a high performance aircraft motor. Take a high performance dragster that is known to launch a piston into the next state on failure :)

 

Breaking a connecting rod during an intense flight in an aircraft like this, I would expect the internal damage to be much greater, and the internal forces much stronger... but I am no expert on blowing up engines ;)

 

The aircraft engine has very different load of mechanics. The car engine has 10000+ hours (if you recalc 600000 km before a full overhaul to hours). Fighter engine had 100-150 hours typically.

V-engine has different geometry, so the known piston rods failures usually led to instant destruction and jam.

 

Yo-Yo, I´m not agree, ..piston rods failures are very rare if the pilot have the engine parameters in view. Except damage by shooting in combat of course.

 

SiThSpAwN, ..the engines of today street cars, are more advanced than aircraft engines WWII.

The big V-engines, with 6 or more cylinders, can enduring hours, with 1 or 2 cylinder degraded, running at low power. (WWII engines included)

[NineLine]

Yo-Yo, I´m not agree, ..piston rods failures are very rare if the pilot have the engine parameters in view. Except damage by shooting in combat of course.

 

SiThSpAwN, ..the engines of today street cars, are more advanced than aircraft engines WWII.

The big V-engines, with 6 or more cylinders, can enduring hours, with 1 or 2 cylinder degraded, running at low power. (WWII engines included)

 

Exactly, you only prove my point, a 1940's something engine is going to detonate in a big way where when I lost the engine in my Escape it was drivable to the dealership to have it replaced.

[IIIJG52_Otto_]

This isn't exactly the type of engine failure originally being discussed, but here's an example of how a high-performance aircraft engine can fail catastrophically enough to shatter the propeller:

 

Yes, I know, this is almost the opposite of "stopping instantly" (because in this case, the failure caused the propeller to over-speed), but the point is, as Yo-Yo and others pointed out, there's little to compare with automobile engines and high-performance aircraft engines.

 

This is not piston rod failure, or overheating ...this is an aircraft overspeed case, according with video description.

"""the turbulence and G's ere too much for the engine and the oil filter housing broke off, dumping the oil, over-speeding the propeller""".

Today automotive engine are better in power/weight ratio and performances than any WWII engines.

 

This is a today automotive street car engine, The Volkswagen Group W16 engine as configured for the Bugatti Veyron EB16.4 is a 16 cylinder quad-turbocharged engine with four valves per cylinder. The engine is 71 centimetres (28 in) long, and weighs approximately 400 kilograms (882 lb). Maximum power output is 736 kilowatts (1,001 PS; 987 bhp) at 6,000 revolutions per minute (rpm), with a maximum torque of 1,250 newton metres (922 lbf·ft)

 

[Anatoli-Kagari9]

I'm going to be honest!

 

I prefer the way engines fail in A2A's p51d, Sptifire...

Depending on the type of damage inflicted, failure can be catastrophic or progressive.

 

It just feel more plausible, and Dudley Henriques, and experirnced p51d ( and other types ) pilot, confirms ;-)

Edited April 1, 2015 by jcomm

[IIIJG52_Otto_]

Some automotive piston engine from racing car equipped some WWII replicas, as this Thunder Mustang, with original P-51 performances.

There are not many differences between big inline piston engines from automotive, to aviation at present day

 

 

A shame .. They don't do it with a Bf-109 :smilewink:

Edited April 1, 2015 by III/JG52_Otto_+

[leafer]

From my own experience, a piston engine, not usually stop suddenly, without notice, when it has serious problem.

 

I had seen several high performance automobile engine with piston sticking out of its oilpan, and recently saw a hole on the side of honda cylinder block punched out by a piston. The Honda owner said he heard some sound and then his engine was ded.

[Kurfürst]

Whatever the case being argued, I always enjoy reading these discussions very much. YoYo's very through knowledge of appearantly every engineering detail behind ('how stuff works') and his willingness to explain it is simply awesome! :)

[msalama]

a hole on the side of honda cylinder block punched out by a piston

 

Exactly what I meant above. Happens more often than not, because the forces involved are huge. So I think we can safely assume a thrown conrod usually seizing, say, a 36-litre V12 ;)