Flat Spot in P51 Performance around 10,000ft. ?

[BlitzPig_EL]

Anyone notice that the Mustang kind of falls flat on it's face around 10 to 12 thousand feet or so?

Was flying with the Pigs last night and in that altitude range +/- and the manifold pressure just drops off, full throttle and 2600/2700 rpm.  I tried switching the supercharger between 1st speed and automatic, but it had no effect.  I've never had the Mustang feel like it was towing a drogue chute before.  Very odd.

[LuftManu]

35 minutes ago, BlitzPig_EL said:

Anyone notice that the Mustang kind of falls flat on it's face around 10 to 12 thousand feet or so?

Was flying with the Pigs last night and in that altitude range +/- and the manifold pressure just drops off, full throttle and 2600/2700 rpm.  I tried switching the supercharger between 1st speed and automatic, but it had no effect.  I've never had the Mustang feel like it was towing a drogue chute before.  Very odd.

Hey BlitzPig!

Don't know how much "perfromance loss" there is, but I think around 10k to 15k for the -7 isn't the best altitude.

 

You should expect some performance and MAP drop.

 

 

Extra:

 

From http://www.wwiiaircraftperformance.org/mustang/mustangtest.html

 

Edited December 11, 2021 by LF_Gallahad

[BlitzPig_EL]

Thanks.  

[ZachariasX]

8 hours ago, BlitzPig_EL said:

full throttle and 2600/2700 rpm.

Your engine wouldn‘t last long like that.

[BlitzPig_EL]

In the sim it doesn't seem to matter.  In real life, yes.

[NanashiAnjin]

20 hours ago, ZachariasX said:

Your engine wouldn‘t last long like that.

Thing is, I noticed too, on that alt, MP drops so much that on full throttle you might not even get into combat power on 2700 rpm.

[BlitzPig_EL]

Exactly.

[Guster]

Yes, it's kinda tricky from 10,000 and up until the supercharger kicks in at about 16,000. AFAIK, it's the way it's supposed to be, so you've got to either stay up high and do your escort and fighter sweep routine or hit the deck for your strafing runs.

[Toots_LeGuerre]

You might take a look at the Supercharger light in the low center panel.

Set up a button for it and when it glows red, press the button.

Not sure this works every time, but the times I tried it it worked.

There is a null zone I think to keep the Supercharger from cycling back and forth at around 10 to 12 K feet..

[ZachariasX]

13 hours ago, NanashiAnjin said:

Thing is, I noticed too, on that alt, MP drops so much that on full throttle you might not even get into combat power on 2700 rpm.

Yes, and it shows one more issue about our timer: You probably should be able to rev up to 3000 rpm without unduly effects on the engine at this MAP. As long as you have a reasonable MAP, you can (usually: must) have high revs. Much too little throttle at high revs causes the piston to have insufficient backpressure and you can kill an engine within the limits of what are in principle permissive rpm. You should be able to rev up and have most of your supercharger a tad above critical altitude. It was a common strategy to rev the engine higher than rated (for the respective power setting) at altitude to get better performance. They even did it in the 109. This of course at the price of the economy. It will depend on the respective engine construction and piston speed what the toleraces for this are.

[NanashiAnjin]

Do note that, if you are below stated combat power settings, the combat power timer will be longer too.

[I./JG52_Woutwocampe]

Quick question about 2 stages supercharging. Does each state have 2 gears? Is the second stage only activated at high altitude?

[BlitzPig_EL]

As I understand it low gear operates the low stage, and high gear operates the second stage.  So you couldn't have second stage operated in low gear, or vice versa.

Edited December 13, 2021 by BlitzPig_EL

[=420=Syphen]

2 hours ago, I./JG52_Woutwocampe said:

Quick question about 2 stages supercharging. Does each state have 2 gears? Is the second stage only activated at high altitude?

 

Superchargers can come in single or multi stage and also in single or multi speed.  Stage and Speed are two very different things. Most WW2 Aircraft we have in IL2 are single stage, two speed superchargers. The first speed / gear will be good up till a critical altitude where the performance falls off, then either manually or automatically depending on the aircraft you'll move into second speed which gives you further performance up to another critical altitude.  A multistage supercharger will have a supercharger or turbo feeding another supercharger (P47 or P38 can be considered two stage with a 'turbo supercharger').  

 

Calum Douglas and/or Greg's Airplanes have published on YT and in book form some great info about WW2 aircraft supercharging for further follow up.

Edited December 13, 2021 by =420=Syphen

[I./JG52_Woutwocampe]

42 minutes ago, =420=Syphen said:

 

Superchargers can come in single or multi stage and also in single or multi speed.  Stage and Speed are two very different things. Most WW2 Aircraft we have in IL2 are single stage, two speed superchargers. The first speed / gear will be good up till a critical altitude where the performance falls off, then either manually or automatically depending on the aircraft you'll move into second speed which gives you further performance up to another critical altitude.  A multistage supercharger will have a supercharger or turbo feeding another supercharger (P47 or P38 can be considered two stage with a 'turbo supercharger').  

 

Calum Douglas and/or Greg's Airplanes have published on YT and in book form some great info about WW2 aircraft supercharging for further follow up.

 

Yeah I know about single stage with 2 speeds and turbos etc etc I just want to understand more about 2 stages superchargers. For instance at low alt are the gears of the second stage at idle or not? Is the intercooler only used at high alt? Etc etc. 

[=420=Syphen]

18 minutes ago, I./JG52_Woutwocampe said:

 

Yeah I know about single stage with 2 speeds and turbos etc etc I just want to understand more about 2 stages superchargers. For instance at low alt are the gears of the second stage at idle or not? Is the intercooler only used at high alt? Etc etc. 

 

 

For the most part, they share a similar mechanism to a automotive manual transmission. With the dog selector will be hydraulically or mechanically driven to engage the next gear ratio of the supercharger.  Intercoolers will be used at all altitudes - they help cool the charge air.

 

Every installation will be a bit different so you'd have to deep dive into a specific model of engine for the details on how they work 

[I./JG52_Woutwocampe]

1 hour ago, =420=Syphen said:

 

 

For the most part, they share a similar mechanism to a automotive manual transmission. With the dog selector will be hydraulically or mechanically driven to engage the next gear ratio of the supercharger.  Intercoolers will be used at all altitudes - they help cool the charge air.

 

Every installation will be a bit different so you'd have to deep dive into a specific model of engine for the details on how they work 

 

Yeah I'll check Greg's channel to know more about the specs of the Merlin/Packard double stage supercharger. He most likely had that covered in previous vid I must only have missed it.