Overspeeding engine in dive

[Awesomejlee]

Every time I've gotten into a good dive I end up overspeeding the engine. I pull the RPM level back but in the dive it seems like it still just forces the prop over the redline. What am I doing wrong? (prop settings are on auto).

[grafspee]

When you are overspending prop, doesn't matter what your rpm set are, if your set rpm is 2550 for example, and you notice that your rpm start increasing, this is the point when prop pitch reach it's max pitch angle, pulling prop lever farther back changes nothing.

Only solution is to switch to manual mode and increase prop pitch angle even more. looks like manual mode allow to farther the prop and automatic mode is limited to something like 45 degrees of pitch angle and this is easily overspeed able.

According to the manual, you can over speed engine to 3060 rpm for a short time, for example when diving 20-30 seconds of overspeed should have no adverse effects on engine.

Edited April 24, 2021 by grafspee

[Awesomejlee]

Thanks, I'll try it. Diving from 25k to sea level seems to trash it, but I'll try the auto adjustment.

[Diesel_Thunder]

I agree, once the prop is on the low pitch mechanical stops, the governor can do no more. At that point good ol’ physics takes over and the prop RPM is now a function of airspeed in the dive. 

[Nealius]

Honest question: In what situations would you need a prolonged dive that could induce overspeeding? In combat situations I have not yet found myself needing to dive any more than 7~8000ft, which with an entry at 200~250mph, MP between 32" and 52", RPM at 2550, has not resulted in any overspeeding.

Edited May 27, 2021 by Nealius

[Red_Pilot]

It's driving me crazy.   I can't accelerate more than 500 mph in diving because I'll break the engine. This is the most unreliable engine among the warbirds in this simulator! But ok, I have to trust the developers. But then why does this plane have recovery flaps? At a speed of 500 miles per hour, the aircraft is perfectly controllable and recovery flaps are obviously needed at a much higher speed. But who needs recovery flaps if you break the engine much earlier?   Is this some kind of mockery of the pilots?

Edited April 26, 2022 by Red_Pilot

[grafspee]

10 hours ago, Red_Pilot said:

It's driving me crazy.   I can't accelerate more than 500 mph in diving because I'll break the engine. This is the most unreliable engine among the warbirds in this simulator! But ok, I have to trust the developers. But then why does this plane have recovery flaps? At a speed of 500 miles per hour, the aircraft is perfectly controllable and recovery flaps are obviously needed at a much higher speed. But who needs recovery flaps if you break the engine much earlier?   Is this some kind of mockery of the pilots?

 

Recovery flaps are needed only above 17000 ft, below that alt elevator authority comes back and you can recover from dive with elevator.

According to manual you can over speed engine to 3050rpm for short period of time, for example in dive for couple of seconds w/o any damage to engine, and this must be fixed. There are couple examples where ED over modeled things, which made things harder then it was IRL, i think every one on this forum can name couple of things.

Edited April 27, 2022 by grafspee

[Art-J]

@Red_Pilot - you can dive faster if you switch to manual prop mode and keep adjusting the pitch yourself to keep the rpm in green range...

... which I doubt was a necessity in real life (Graf mentioned about incorrect engine redline already), but for the time being, it is what it is.

[Fortinero]

This is still be a thing, yersterday I did tested dive performance in all ww2 modules, diving from 30k ft at 60° dive angle, and non of the aircrafts except the Jug broke his engine due overspeeding the prop, keeping in auto de prop pitch, in manual does not happens.

Why only affects to the P-47 and not in the P-51, Spitfire, and so on?

[Art-J]

Because Curtiss Electric prop, as modelled here, has narrower pitch adjustment range compared do Rotol and Hamilton Standard props on other Allied warbirds in DCS and it reaches the coarse pitch stop in a dive sooner. Granted, I don't know if it's correct for the particular prop version simulated, but it is what it is.

[DD_Fenrir]

2 hours ago, Fortinero said:

Why only affects to the P-47 and not in the P-51, Spitfire, and so on?

It's a radial engine problem.

In the inlines the crankshaft essentially sits in an oil bath, this keeps the bearings lubricated.

Not so in a radial. Oil is fed directly through the bearing to the face of the bearing and crank interface - but this point is optimised to lubricate the bearing when under power. I.E. when the engine is driving the propellor.

When you allow the propellor speed to overcome that of the speed of the engine the bearing and crank pressure point is now reversed - this is sub-optimal lubrication, causing the crank/bearing interface to heat and ultimately, if left unchecked, resulting in main bearing failure.

Diving at a high RPM and low throttle setting and letting airspeed build will cause this condition. The propellor is driving the engine, not the other way round. For the reason listed above, this is not good engine management.

It is one of the compromises that comes with operating radial engines.

Edited October 14, 2022 by DD_Fenrir

[Fortinero]

3 hours ago, DD_Fenrir said:

It's a radial engine problem.

In the inlines the crankshaft essentially sits in an oil bath, this keeps the bearings lubricated.

Not so in a radial. Oil is fed directly through the bearing to the face of the bearing and crank interface - but this point is optimised to lubricate the bearing when under power. I.E. when the engine is driving the propellor.

When you allow the propellor speed to overcome that of the speed of the engine the bearing and crank pressure point is now reversed - this is sub-optimal lubrication, causing the crank/bearing interface to heat and ultimately, if left unchecked, resulting in main bearing failure.

Diving at a high RPM and low throttle setting and letting airspeed build will cause this condition. The propellor is driving the engine, not the other way round. For the reason listed above, this is not good engine management.

It is one of the compromises that comes with operating radial engines.

 

Why does not happens with the radial BMW engine of the A8 in DCS then?

[DD_Fenrir]

Because it has the autokommandgerat system that automatically adjusts propeller pitch based on speed altitude and manifold pressure and prevents prop driven engine conditions. 
 

For similar behaviour you need to look at the I-16 and possibly the upcoming F4U and La-7 modules.

 

[grafspee]

1 hour ago, Fortinero said:

Why does not happens with the radial BMW engine of the A8 in DCS then?

Reason why P-47 engine dies is that automatic governor is not able to increase pitch beyond certain value, despite that prop it self is able to do it, but you have to switch to manual to get higher pitch, why i have no idea.

I think it is some error in modeling, logically thinking if that was a problem, automatic system would get wider pitch range since prop assembly allow for that.

Second thing, according to manual P-47's engine can be over speeded to 3050rpm if engine dies below this limit, something wrong with modeling.

BMW radial engine is vulnerable exactly same as P-47, difference is rooted in engine managment.

Like @DD_Fenrir said fw190 has kommandgerat system, in simple terms it act like throttle-prop interconnector, if you shut throttle kommandogerat will reduce rpm to minimum and protect engine from damage, if you do this in P-47 MP will drop to near 0 but rpm will stay high this is dangerous, you can interconnect throttle with rpm lever in P-47 but is simple connection, in case of FW190 is quit complex system which is not simple interconnection.

[Fortinero]

1 hour ago, DD_Fenrir said:

Because it has the autokommandgerat system that automatically adjusts propeller pitch based on speed altitude and manifold pressure and prevents prop driven engine conditions. 
 

For similar behaviour you need to look at the I-16 and possibly the upcoming F4U and La-7 modules.

 

So in combat, I have to deactivate the propeller governor and manually, using the same switch that is in a non very ergonomically position in the meanwhile you're trying to dive away from an 109 at your six using a maneuver that mades, besides others things, the Jug famous as one, or, the best diver in the ww2, so I have to manually controls the RPM by that switch, but as instance, in the Fw-190A8 you don't have to disable the propeller governor automation switch, or kommandogerät, and you don't have to control manually the prop pitch using the rocker switch in the throttle in a step dive.

Also, what's the meaning of the air brake in the D-30 if even, after have been destroyed my engine and let the aircraft accelerate further more of the 500mph critical speed, and I still have plenty of control of the surfaces to recover it? like in almost all the ww2 modules in DCS...

I think that there is a few things that needs some reviewing.

 

[grafspee]

9 minutes ago, Fortinero said:

Also, what's the meaning of the air brake in the D-30 if even, after have been destroyed my engine and let the aircraft accelerate further more of the 500mph critical speed, and I still have plenty of control of the surfaces to recover it? like in almost all the ww2 modules in DCS...

It is not air brake it is device which allow P-47 exit compressibility, but it affect operations above 20k ft, below it isn't useful.  

When you extend those, they generate pull out force which decrease with decrease mach number.

P-47 can carry out dive with out it, but you would not be able to recover above 20k ft, elevator authority comes back below 20k ft.

Below 20k ft there is no way to encounter compressibility no matter how fast you are diving. 

Edited October 14, 2022 by grafspee

[Fortinero]

3 minutes ago, grafspee said:

It is not air brake it is device which allow P-47 exit compressibility, but it affect operations above 20k ft, below it isn't useful.  

 

I know what is his function, "compressibility recovery flaps", anyways, I dive steeply from higher altitudes than 30k ft, and still have plenty of control of the surfaces and I'm able always, of recover the plane.

I never in this sim, I never hit compressibility, it does not matter what I do.

[grafspee]

1 minute ago, Fortinero said:

I know what is his function, "compressibility recovery flaps", anyways, I dive steeply from higher altitudes than 30k ft, and still have plenty of control of the surfaces and I'm able always, of recover the plane.

I never in this sim, I never hit compressibility, it does not matter what I do.

To get to those you would need to dive straight down, like split S  from 40k ft, P-47 case was much much better case then P-38 which could enter compressibility at 35k at 10 degree dive.

[Fortinero]

34 minutes ago, grafspee said:

To get to those you would need to dive straight down, like split S  from 40k ft, P-47 case was much much better case then P-38 which could enter compressibility at 35k at 10 degree dive.

There are reports that below 15000 ft the Jug barely starts to get some control authority in order to recover the plane, and still, there are cases of pilot losts due compressibility, and, I insist, I ran many tests, and never in DCS I could reproduce compressibility effect.

In IL2 the compressibility effect is a factor, in DCS is not, even blowing the engine up in order to get the speed further more than 500 - 510 mph, cuz if I control manually the RPM and of course I keep the manifold on the limits, nothing happens even in a 90° dive to the deck...

Edited October 14, 2022 by Fortinero

[grafspee]

Pretty good explanation here, i haven't tried P-47 recently in DCS so i can't tell how it behave now.

I would not compare IL2 to DCS in that regard, DCS is not perfect to reality but IL2 has nothing common.

@Fortinero I just test it, agree with you, there is no compressibility issue in DCS, elevator authority is always available, cockpit shakes but no more effects.

Edited October 14, 2022 by grafspee

[Fortinero]

7 minutes ago, grafspee said:

Pretty good explanation here, i haven't tried P-47 recently in DCS so i can't tell how it behave now.

 

That's awesome, I already saw that video and many other, I love so much the Jug, I readed many of the NACA reports, and whatever could find about that beauty of plane. I really like the DCS module, but, I would love to see get it better, I know that seems that ww2 is not a priority for ED by now, so well, I guess we will have to have patience.

[grafspee]

5 minutes ago, Fortinero said:

That's awesome, I already saw that video and many other, I love so much the Jug, I readed many of the NACA reports, and whatever could find about that beauty of plane. I really like the DCS module, but, I would love to see get it better, I know that seems that ww2 is not a priority for ED by now, so well, I guess we will have to have patience.

I think it is time to report bug  I tested it just 1 min ago, it is true, no elevator authority control lost, i can pull out when ever i want in dive, which is not accurate at all.

Problem with P-47 was that at this high alt plane would loose control, and pilots would try to use trim to recover and this was a mistake, when plane descend to 17k elevator authority would come back and full force of trim would rip plane a part, that was dangerous about that.

But one thing is certain, if P-47 is operated below 20k it is no wat to enter compressibility, i remember in il2 not able to pull out from 10k dive and this in even more off.

Edited October 14, 2022 by grafspee

[Art-J]

22 hours ago, DD_Fenrir said:

In the inlines the crankshaft essentially sits in an oil bath, this keeps the bearings lubricated.

I'm pertty sure Merlins, Griffons and Allisons were all dry sump engines, so I kind of not agree about that part, but agree about the rest. 

As for the compressibility, I've never witnessed it in DCS Thunderbolt either, not in a dangerous way at least. A little bit of Mach tuck seems to be happening at high altitudes, so they've simulated at least that part, but at the same time elevator seems to be always fully effective indeed and that smells fishy.

[grafspee]

It is a little bit shame that P-47 is still missing proper high speed dive behavior, but nice thing is that DCS warbirds do not have this BS frozen stick behavior at low alt.

I have nice P-51 manual which describes compressibility problems of P-51 and say exactly how P-51 behave, and DCS P-51 behave exactly as manual says, so ED can do it but question is when?

[DD_Fenrir]

5 hours ago, Art-J said:

I'm pertty sure Merlins, Griffons and Allisons were all dry sump engines, so I kind of not agree about that part, but agree about the rest. 

Done some research and apparently the Merlin could be configured in both dry or wet sump as appropriate to each application; in aircraft dry sump is preferred.

In that case the crankshaft is hollow and used as the conduit for the oil feed with channels provided to feed oil to the big end bearing.