Overspeeding engine in dive

[grafspee]

16 hours ago, DD_Fenrir said:

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.

 

Dry sump or not, crank shaft has drilled lines to feed connection rod bearings. Wet sump was used in applications where engine want's exposed to extreme Gs like tanks, torpedo boats, in planes wet sump won't cut it because even small bank may starve oil pump.  

Main crank shaft bearings are feeded by in block oil lines, then oil is transferred through crank shaft further to connecting rod bearings and piston bearings.

Edited October 16, 2022 by grafspee

[303_Kermit]

On 4/26/2022 at 10:58 PM, grafspee said:

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.

 

Never happened. Even if you try from 35000ft

[grafspee]

14 hours ago, 303_Kermit said:

Never happened. Even if you try from 35000ft

Agree, i tested it lots of times, in DCS P-47 does not loose elevator control in high speed dives. I did drop from 40k and going straight down i didn't loose control in that dive.

Only thing what i achieved  was deadly engine over speed.

[Reflected]

On 4/27/2022 at 4:58 AM, grafspee said:

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.

 

Can you please post a screenshot of a manual that explicitly states this 3050 RPM? That's also not an 'N' manual. thx

[Art-J]

For example, it's in the B, C, D, G manual you've added to Wolfpack campaign :>. Page 32, top right section of the engine flight chart.

Edit: D-25 to D-40 manual for the Brits also has it, on page 36, listed as 3060 RPM.

Edited September 22, 2023 by Art-J

[grafspee]

12 hours ago, Reflected said:

Can you please post a screenshot of a manual that explicitly states this 3050 RPM? That's also not an 'N' manual. thx

Those are from older versions but we can safely assume that maximum permissible diving rpm didn't go down during engine improvements.

Edit: I found chart from P-47-25 through P-47-35 in which max permissible diving rpm wen up to 3060rpm. (last chart)

Based on those charts we can safely assume that over speeding engine to 3000rpm should not end up with imminent engine catastrophic failure. 

 

Edited September 22, 2023 by grafspee

[Art-J]

Yes, these were referred to in the other thread in bugs section, which was closed today despite Reflected posting two tracks showing engine failures when performing dives as requested by closing party - literally as per real manuals, ie. throttle pulled back to avoid overboosting, but not completely back to avoid dive getting steeper. Granted, the dives were steep enough for the engine to briefly go into 3050-60 range, but If the thread wasn't closed, I could post similar tracks showing more shallow dives with the same catastrophic outcome, below 3000 RPM, which contradicts the manuals.

If Reflected tracks, despite being as literal as can be, "failed to be acknowledged", then I would at least like to know please what the dev's position is on the second discussed matter, that of Curtiss Electric prop coarse pitch limit in governed mode. Kablamoman's photos posted in the aforementioned thread suggest the prop should have the same governed and manual coarse pitch limit, but in DCS it doesn't. What's the reason for that?

It's worth noting If the DCS prop in governed mode could increase the pitch past the current coarse limit, we wouldn't have the whole 2800-3050 discussion at all, and there would be no need for yet another damage simulation developer review. That's because the engine would just not rev above manual-"recommended" values, or at least not rev beyond that limit so early in a dive. Thus, prop pitch limit is a separate issue, which, IF ammended, could in turn potentially make the max RPM a non-issue in the end.

Edited September 22, 2023 by Art-J

[grafspee]

@Art-J

I posted also NACA documents which include high speed glide and dive testing of P-47. Which shows that P-47 could be operated with throttle closed and near close even in diving conditions.

Other topic is indeed automatic prop governor range, in DCS P-47 very susceptible to overspeed engine completely apposite to P-51 in which you can climb to 48k or so, point nose straight down and level out at 5k ft with not even 10rpm over speed.

[kablamoman]

30 minutes ago, grafspee said:

Other topic is indeed automatic prop governor range, in DCS P-47 very susceptible to overspeed engine completely apposite to P-51 in which you can climb to 48k or so, point nose straight down and level out at 5k ft with not even 10rpm over speed.

Worth mentioning the governing range on the P-51's Hamilton Standard prop gives a bit more leeway at higher speeds with 65 degrees for the high-pitch stop. The Jug's in the sim only governs to 48 degrees. Nevertheless, with any power on above 400mph in the jug it is next to impossible to keep the engine from overspeeding and causing trouble without manually reducing RPM by selecting a coarser setting with the manual mode. This is pretty silly that the entire range above 400 - 500 mph indicated (the number the 47 manual lists as the highest recommended dive speed below 25,000') requires the use of manual prop governing, lest you pull off all power and run the risk of MEB failure due to windmilling.

As an aside, the P51 also has a higher-than-redline allowable RPM overspeed for diving (3240 RPM) as per page 81 of the training manual:

[grafspee]

@kablamoman Very interesting thing is when we look at available over speed rpm. P-51 has 240 excess rpm and P-47 has 350-360 excess rpm available. Despite the fact that P-47's supposed to be more volnurable to excessive rpm. Maybe R-2800's MEB is volnurable but if we stay within permissible limits we should not encounter those engine problems, this is not the first time when ED makes things harder then irl, i will remind only one example, P-51 and famous WEP with logic "you touch it you dying"

I remember first iteration of this overdone MEB failure, back then even landing was almost impossible because you could not drop MP below 25" if you did slow process of grinding engine to death had begin. And at 25" slowing this plane down was problematic. 

Edited September 23, 2023 by grafspee

[peachmonkey]

when I dive I pull the throttle all the way back, although I'm usually diving from 10k feet or so, and by the time i'm deck the speed is around ~450mph, and the engine is still turning at the 2700 rpm.

Does the manual state you need to pull the throttle all the way back during the dive?

[grafspee]

5 hours ago, peachmonkey said:

when I dive I pull the throttle all the way back, although I'm usually diving from 10k feet or so, and by the time i'm deck the speed is around ~450mph, and the engine is still turning at the 2700 rpm.

Does the manual state you need to pull the throttle all the way back during the dive?

Manual states that during loss of elevator control in high speed dive throttle can't be pulled all way back because it will steep dive even more.  But last time i checked in DCS P-47 does not experience compresibility elevator loss of authority this not apply to DCS P47. Even if you start dive from split-s which is also forbidden in manual above certain alt. High speed dive happens when plane mach number is above 0.7 so diving from 10k ft you are completely safe. Elevator control comes back usually at 17k ft of alt. P38 was the plane which brought real pain because this one at 30k power on and 15 degree dive was entering compressibility elevator authority control loss and horizontal stabilizer loss of efficiency. That resulted in immediately dropping nose and entering lethal dive in wich pilot should do all things to not accelerate plane beyond structure integrity speed limit, unfortunately many died. P38 enters compresibility at mach 0.65 or so, very early comparing to P-47, at first trial tests they were afraid that P47 will be another P38 but compresibility in P47 turned out to be much mildly. 

Dive recovery in P47 out of my mind, Keep power on, do not try pull out by elevator trim, keep ailerons centered , P47 experienced ailerons reversal at high speed, and wait until elevator authority comes back then pull stick to level flight you can use trim to help pulling out of dive.

Edited September 24, 2023 by grafspee

[ShadowFrost]

6 hours ago, peachmonkey said:

when I dive I pull the throttle all the way back, although I'm usually diving from 10k feet or so, and by the time i'm deck the speed is around ~450mph, and the engine is still turning at the 2700 rpm.

Does the manual state you need to pull the throttle all the way back during the dive?

There's also good reason, besides the aerodynamic concerns, not to go to idle, especially with radial engines. (It can apply to all engines) Allowing the prop to drive the engine (and not the other way round) puts significant stress on the crankshaft + rods, and other components in a way it wasn't precisely designed for. Likely a non-issue for DCS, but a no-no for real life. The major issue is engine dependent as to how critical it will be, when the prop drives the engine, it slides marginally backwards away from the thrust bearing and can significantly alter or prevent oil from getting to certain places. This can, if applicable to the engine, cause catastrophic damage in a hurry. 

I do not have time in a P-47, or T-28, but for the friends I do have that fly T-28s. The interruption to oil distribution to a key component is reportedly something they are majorly concerned about, moreso than most warbirds, but obviously not the same engine. 

Edited September 24, 2023 by ShadowFrost

[grafspee]

P47 was tested in dives at 15' and 2550 rpm and glides with power off.  Engine used with care will score more hours but immediate engine failure during permissible engine over speed is not right.

[ShadowFrost]

23 minutes ago, grafspee said:

P47 was tested in dives at 15' and 2550 rpm and glides with power off.  Engine used with care will score more hours but immediate engine failure during permissible engine over speed is not right.

Oh agreed.

A lot of items done IRL are to make an engine last many more hours than were needed to per wartime. 

[Reflected]

On 9/23/2023 at 4:50 AM, Art-J said:

Yes, these were referred to in the other thread in bugs section, which was closed today despite Reflected posting two tracks showing engine failures when performing dives as requested by closing party - literally as per real manuals, ie. throttle pulled back to avoid overboosting, but not completely back to avoid dive getting steeper. Granted, the dives were steep enough for the engine to briefly go into 3050-60 range, but If the thread wasn't closed, I could post similar tracks showing more shallow dives with the same catastrophic outcome, below 3000 RPM, which contradicts the manuals.

If Reflected tracks, despite being as literal as can be, "failed to be acknowledged", then I would at least like to know please what the dev's position is on the second discussed matter, that of Curtiss Electric prop coarse pitch limit in governed mode. Kablamoman's photos posted in the aforementioned thread suggest the prop should have the same governed and manual coarse pitch limit, but in DCS it doesn't. What's the reason for that?

It's worth noting If the DCS prop in governed mode could increase the pitch past the current coarse limit, we wouldn't have the whole 2800-3050 discussion at all, and there would be no need for yet another damage simulation developer review. That's because the engine would just not rev above manual-"recommended" values, or at least not rev beyond that limit so early in a dive. Thus, prop pitch limit is a separate issue, which, IF ammended, could in turn potentially make the max RPM a non-issue in the end.

 

I agree that it’s weird that the auto governor doesn’t use the full range of movement of the blades. It may still be how it was, I don’t know.  
 

But:

if they explicitly put it in the P-47D manual - and not even in a hidden place -  that the engine can take 3050RPM in a dive for 30 seconds, that means IRL it was possible to reach it. 
 

and you don’t get more clear and black and white than having an original manual stating a number and a DCS track showing our Jug can’t do that. 
 

Then there is the question brought up above: no one ever puts a hard limit in a flight manual, there is always a lot of safty buffer left. But I see how we always get new planes so we can abuse these limits, so I wouldn’t mind not having a whole lot of safety buffer as long as the DCS Jug could produce the official numbers at least, which it currently cannot. 

Edited September 24, 2023 by Reflected

[Hobel]

Am 22.9.2023 um 22:50 schrieb Art-J:

It's worth noting If the DCS prop in governed mode could increase the pitch past the current coarse limit, we wouldn't have the whole 2800-3050 discussion at all, and there would be no need for yet another damage simulation developer review. That's because the engine would just not rev above manual-"recommended" values, or at least not rev beyond that limit so early in a dive. Thus, prop pitch limit is a separate issue, which, IF ammended, could in turn potentially make the max RPM a non-issue in the end.

Here is all the information you need. 

 

In short that the Dcs manual gives automatic 56° max pitch limit and ingame it as far as I can observe 48°.

https://forum.dcs.world/topic/286094-question-about-manual-vs-automatic-prop/#comment-4828821

[grafspee]

35 minutes ago, Hobel said:

Here is all the information you need. 

 

In short that the Dcs manual gives automatic 56° max pitch limit and ingame it as far as I can observe 48°.

https://forum.dcs.world/topic/286094-question-about-manual-vs-automatic-prop/#comment-4828821

Unfortunately fixing prop governor still won't solve 3060 rpm dive limit which can be used in case prop governor loss due to battle damage and if engine revs up above 2800 rpm at that moment engine is lost which is not true.

[Art-J]

1 hour ago, Hobel said:

Here is all the information you need. 

 

In short that the Dcs manual gives automatic 56° max pitch limit and ingame it as far as I can observe 48°.

https://forum.dcs.world/topic/286094-question-about-manual-vs-automatic-prop/#comment-4828821

Thanks, forgot about that thread. Will analyze it later. 

That's the whole point. Even if devs don't feel like touching the RPM limits for whatever arbitrary reason and reprogramming master bearing for the third time, ammended pitch limit would at least move the onset of overspeed towards higher IAS.

Look at the Anton. It had bearing failures imlpemented and tweaked later at the same tima as the Jug. For all we know it might have "glass" bearing issue and questionable high RPM limit as well, but we just never experience it, because Kommandogerat and VDM prop on it keep the RPM in check no matter how fast you dive.

Edited September 24, 2023 by Art-J