How do I achieve max speed?

[NoJoe]

Oh, hmm then I'm not sure what he's referring to either.

 

Is your issue that you can make 67 inches only up to 24,000 feet, while the manual (and other sources) say 26,000-28,000? You've got the carburetor air set to ram, not heat, right? (I know, I know, simple questions, but sometimes it's little things that get missed).

 

As for the propeller: Hitman, I think you're describing a "controllable pitch" propeller. The P-51 has a "constant speed" prop, so the RPM will remain constant by varying the blade angle. The pilot simply sets the desired RPM and the governor does the rest. I think Starkey's understanding is correct here.

 

And the reason the MP goes down at lower RPMs is because the supercharger is mechanically driven off the crankshaft of the engine. Lower RPM means the supercharger is running slower and, uh, supercharging less (assuming high power settings where the regulator may be already at maximum).

[USARStarkey]

Yep you understand my issue precisely now NoJoe. RPMS are at 3000, Throttle is to max, and Im at the specified critical altitude of 26000 or 28000ft. RAM is on. I even tried screwing with the carburetor just to see what would happen and as you might expect, it caused me to lose performance if i turned ram off or use hot air.

 

So yeah, I don't know what is causing this. IMO this is a big bug however. a 2000ft or 4000ft difference in critical altitude is not a small one. It is almost certainly the reason that I cannot achieve historical speeds as a result of not getting more power up at 26,000 where there would be less drag etc. Right now I'm stuck at 63 inches and 430mph. I should be getting 67inches and somewhere in the area of 437-442. I would hardly go any slower anyhow. How do we go about getting the attention of the people who could fix this?

[hitman]

Oh, hmm then I'm not sure what he's referring to either.

 

Is your issue that you can make 67 inches only up to 24,000 feet, while the manual (and other sources) say 26,000-28,000? You've got the carburetor air set to ram, not heat, right? (I know, I know, simple questions, but sometimes it's little things that get missed).

 

As for the propeller: Hitman, I think you're describing a "controllable pitch" propeller. The P-51 has a "constant speed" prop, so the RPM will remain constant by varying the blade angle. The pilot simply sets the desired RPM and the governor does the rest. I think Starkey's understanding is correct here.

 

And the reason the MP goes down at lower RPMs is because the supercharger is mechanically driven off the crankshaft of the engine. Lower RPM means the supercharger is running slower and, uh, supercharging less (assuming high power settings where the regulator may be already at maximum).

Constant speed prop means that it stays set at the prop speed you set it at when you adjust idle. For example - increasing the throttle and engine rpm will not change the propeller speed, the speed stays constant. Adjusting the pitch on the propeller blade causes the angle of the propeller to flatten against wind resistance, which increases the load on the propeller, which increases the load on the engine, which will decrease both engine rpm AND blade rpm. All changing pitch of the propeller does is increase the load on the engine. At full forward, the load on the propeller is minimized. At full back, its maximized. The throttle controls engine rpm. The prop pitch controls prop rpm AND engine rpm.

[USARStarkey]

Hitman you are misunderstanding how this works. Also, Can we please be back on track this is more about MP.

 

That being said, a constant speed prop allows the pilot to set a desired RPM. The prop governor then adjusts the prop pitch dynamically to maintain that RPM at whatever the throttle is set to. IE: The RPM remains the same regardless of throttle setting by adjusting the pitch to be less aggressive. The governor will automatically adjust pitch to be as aggressive as the throttle setting allows. For Example, Mil power in the P-51 is 61in 3000rpm. WEP is 67in aslo at 3000rpm. So why does the plane go faster? because at the same rpm the 67in allows for a more aggressive pitch and therefore more thrust. There is no pitch control in a P-51, only a rpm setting and throttle setting.

[hitman]

Hitman you are misunderstanding how this works. Also, Can we please be back on track this is more about MP.

 

That being said, a constant speed prop allows the pilot to set a desired RPM. The prop governor then adjusts the prop pitch dynamically to maintain that RPM at whatever the throttle is set to. IE: The RPM remains the same regardless of throttle setting by adjusting the pitch to be less aggressive. The governor will automatically adjust pitch to be as aggressive as the throttle setting allows. For Example, Mil power in the P-51 is 61in 3000rpm. WEP is 67in aslo at 3000rpm. So why does the plane go faster? because at the same rpm the 67in allows for a more aggressive pitch and therefore more thrust. There is no pitch control in a P-51, only a rpm setting and throttle setting.

What does the throttle control? Because it doesnt control propeller rpm. It carries a Hamilton Standard variable pitch propeller, which adjusts the pitch via a hydromatic piston that pushes the nose of the propeller forward or aft, which rotates the propellers on a geared transmission connected to the crankshaft. The rpm control controls propeller rpm. The throttle controls engine rpm. In lieu of engine rpm, you have MAP, which is just another instrument, but a more important instrument than engine rpm.

 

All of this translates to which transfers how much power to what. At full throttle, the engine will produce 1400bhp. Adjusting the propeller rpm tells you how much of that power it transfers into the blades to bite the air. At 3000rpm, you are losing hp and efficiency because the propeller tips are spinning faster than the speed of sound...which is amplified at higher altitudes. The speed of sound at 26k isnt the same speed of sound at sea level. Which is why I said 3000rpm at 26k isnt 3000rpm at sea level. What I am getting at is that you probably arent putting a big enough load on the engine, maximizing the amount of horse power to transfer to the propellers. You can do that by adjusting the pitch of the propellers (or you can call it adjusting propeller rpm, same thing) to a lower engine rpm. Anytime you put a load on the engine, you will see a drop of MAP.

Edited April 17, 2014 by hitman

[NoJoe]

Yep you understand my issue precisely now NoJoe. RPMS are at 3000, Throttle is to max, and Im at the specified critical altitude of 26000 or 28000ft. RAM is on. I even tried screwing with the carburetor just to see what would happen and as you might expect, it caused me to lose performance if i turned ram off or use hot air.

 

So yeah, I don't know what is causing this. IMO this is a big bug however. a 2000ft or 4000ft difference in critical altitude is not a small one. It is almost certainly the reason that I cannot achieve historical speeds as a result of not getting more power up at 26,000 where there would be less drag etc. Right now I'm stuck at 63 inches and 430mph. I should be getting 67inches and somewhere in the area of 437-442. I would hardly go any slower anyhow. How do we go about getting the attention of the people who could fix this?

 

 

I suppose you'd need Yo-Yo to chime in. Maybe the engine model could use a little tweaking to get the published critical altitude, or maybe there's some other legitimate reason it's behaving as it is. But without Yo-Yo's input we're just guessing.

 

I'd suggest submitting a bug report and see where that goes. Worth a shot. :)

 

I'll save the constant speed prop discussion for a different thread.

[USARStarkey]

How do i submit a bug report? If you mean a thread in the bug section I already did that and got no notice.

[hitman]

Out of curiosity, what blowers were on? Were they high or low?

[USARStarkey]

High.

[hitman]

http://www.spitfireperformance.com/mustang/mustangtest.html

 

According to these charts here, at those altitudes, these blowers only produce 60.5" @ 1260bhp. I just tested this myself, wasnt able to exceed 60.5, which is per spec on this data.

[NoJoe]

http://www.spitfireperformance.com/mustang/mustangtest.html

 

According to these charts here, at those altitudes, these blowers only produce 60.5" @ 1260bhp. I just tested this myself, wasnt able to exceed 60.5, which is per spec on this data.

 

Though they also show 60.5 at lower altitudes too, suggesting it's the regulator limiting it.

 

But check out most of the way down the page, there's a graph with a bunch of green and blue lines showing true airspeed versus altitude. The light green line is for our P-51D with V-1650-7 at 67" MP. The true airspeed shows a sharp decrease starting just above 24,000 feet.

 

Perhaps the other manuals are suspect, Starkey, and 24,000 feet is indeed the correct critical altitude? Interesting that the P-51Bs with the same engine show a critical altitude more like the 26,000 and 28,000 that you expected.

 

[EDIT] Wow, there are data in there for 75" and 90" MP. That's a lot of manifold pressure...!!

[EDIT2] That's a great page, Hitman, thanks!

Edited April 17, 2014 by NoJoe

[USARStarkey]

The other manuals are not suspect. Furthermore, hitman is looking at test for the V-1650-3, not the 7 which is where the 60.5 is coming from. You are looking at performance calculations, not tests. Report No. NA-46-130, are not actual flight tests, they are estimates. Once again, here are the actual real world tests:

[NoJoe]

You are looking at performance calculations, not tests. Report No. NA-46-130, are not actual flight tests, they are estimates.

 

Ah, fair point.

 

I see your thread in the bug reports section. You probably could have titled that better; "Multiplayer not working" is probably how most will read that. ;) Maybe something like "Critical altitude appears too low" would have been better. But there really hasn't been much activity in that section for a while, looks like. It may just take some time for one of the testers to check it out.

[USARStarkey]

I tried PMing yo-yo about it, but his message box is apparently too full. The good thing is that as it stand right now, I can run down the 190D even still. What concerns me is that the 109K will come blistering in at its estimated 441mph and be faster than everything else when in reality it should be equal. (P-51-442mph or 437) I realize there is some margin of error in FMs, but I would hate to see the relative-to-each-other performance get messed up as a result of this. Although technically, there are no surviving real-world flight tests of the 109K, so perhaps it wont be able to crack 440mph.

[hitman]

Just to throw this out there, this chart states even at 67" @ 26k, should be around 435. Its still fairly close to your tests...maybe the MAP gauge is reading incorrectly at altitude?

[USARStarkey]

Dude you didn't read the chart right man. It says 440 or 442. It goes by 10s not 5s

[hitman]

Been reading charts like this since A&P school, and it says 435kts @ 26k. Now at around 24,500 to 25k, it does intersect 440kts before it loses power sharply. I think you are looking at the chart for the -15NA. Specifically, this aircraft.

 

http://www.wwiiaircraftperformance.org/mustang/p51d-15342.html

Edited April 17, 2014 by hitman

[USARStarkey]

First off, this chart is in MPH not knots. 435 knots would be 500mph!.

 

It states 440mph for the calculated results and 442mph for the RL flight tests. There is no 435mph anywhere for a P-51D. Yes, the plane on the page you linked does 442mph....and is also the same plane shown in dark green on the chart.

Just look at the chart man. the last value is 450mph not 440. The Previous listed value is 430mph. That means the line in the middle is 440mph. And it is MILES PER HOUR, not knots.

Edited April 17, 2014 by USARStarkey

[hitman]

Lets try this one more time.

 

This - is what is currently modelled. The DCS P-51 is NOT aircraft 44-15342. The light green line represents the DCS P-51 very closely to performance with regards to this chart.

Edited April 17, 2014 by hitman

[USARStarkey]

Lets try this one more time.

 

This - is what is currently modelled. The DCS P-51 is NOT aircraft 44-15342. The light green line represents the DCS P-51 very closely to performance with regards to this chart.

 

 

You just proved your self wrong. You drew a line through 26,000ft, that doesn't even intersect the 440mph you sold boldly highlighted.....

 

allow ME to try this again.

 

The 440mph is slightly above 24,000ft. Not 26,000. It also isn't a real flight test. it is a CALCULATED ESTIMATE. the 442mph test DOES INTERSECT 26,000ft, which was the WHOLE POINT OF THIS POST.

 

ON TOP OF THIS, You cannot get close to hitting 440mph at that altitude in DCS P-51. The best you can do at 24,000ish feet is 374knots, or 430mph. If I could hit 440mph at 24,000ft I wouldn't have even made this post. 440mph would be so close to IRL it would not matter. BUT YOU CANT.

 

 

Check it out, I can do this too.

Edited April 17, 2014 by USARStarkey

[hitman]

You just proved your self wrong. You drew a line through 26,000ft, that doesn't even intersect the 440mph you sold boldly highlighted.....

 

allow ME to try this again.

 

The 440mph is slightly above 24,000ft. Not 26,000. It also isn't a real flight test. it is a CALCULATED ESTIMATE. the 442mph test DOES INTERSECT 26,000ft, which was the WHOLE POINT OF THIS POST.

 

ON TOP OF THIS, You cannot get close to hitting 440mph at that altitude in DCS P-51. The best you can do at 24,000ish feet is 374knots, or 430mph. If I could hit 440mph at 24,000ft I wouldn't have even made this post. 440mph would be so close to IRL it would not matter. BUT YOU CANT.

 

I didnt prove myself wrong, I stated earlier that the best speed came at 24,500 - 25k it DOES get to 440. And following that same line, at 26k altitude, it drops to 436. The only contradiciton between this chart and your performance tests only indicate an incorrect reading on the MAP gauge. And FWIW, I just tested again, and managed to hit 64" at 26k. It took a while, but I watched that needle slowly creep up from 58" to 64 in the span of 10 minutes.

[hitman]

You just proved your self wrong. You drew a line through 26,000ft, that doesn't even intersect the 440mph you sold boldly highlighted.....

 

allow ME to try this again.

 

The 440mph is slightly above 24,000ft. Not 26,000. It also isn't a real flight test. it is a CALCULATED ESTIMATE. the 442mph test DOES INTERSECT 26,000ft, which was the WHOLE POINT OF THIS POST.

 

ON TOP OF THIS, You cannot get close to hitting 440mph at that altitude in DCS P-51. The best you can do at 24,000ish feet is 374knots, or 430mph. If I could hit 440mph at 24,000ft I wouldn't have even made this post. 440mph would be so close to IRL it would not matter. BUT YOU CANT.

 

 

Check it out, I can do this too.

All of these lines do not represent a single aircraft. The two D models are either a block 15 or a block 20, and from what Ive read so far, they both have dissimilar superchargers. I am saying that you are reading the wrong information.

[USARStarkey]

I already stated some time ago that you could hit 64-63 at 26000. They do not use different superchargers. Both planes use V-1650-7. There are almost no major performance differences between the different marks of D model Mustang, save for the dorsal fin. Most of the changes between D model mustangs are electrical or other misc nonsense. In addition, the P-51 in DCS is a later mark D, as it has the dorsal fin. And once AGAIN, the 440 at 24k is AN ESTIMATE NOT AT REAL LIFE TEST. This is not an incorrect MP gauge. At 24,000+ The best speed you can get is 430mph. That is 10mph short of 440. At 26,000, it drops to 429. Also, why in hell are you looking at the estimated performance at 26,000ft when in that test it reaches max speed at a lower alt. In case you haven't noticed, were talking about max speed and MP at critical altitude.

 

Just to reiterate: "Just to throw this out there, this chart states even at 67" @ 26k, should be around 435. Its still fairly close to your tests...maybe the MAP gauge is reading incorrectly at altitude?"

 

Nowhere on these charts does it show a plane using 67 inches at 26,000 and getting a speed of 435mph.

 

And as to the differences in D model Mustangs.

 

 

nope, no change in supercharger

Edited April 17, 2014 by USARStarkey

[NoJoe]

Maybe Eagle Dynamics based their P-51D performance on what had been calculated in general (the light green line), instead of a single test with one specific aircraft. [shrug] Besides, what's the difference in percent between 440 mph and 430 mph.. Within 2.5 percent; that's pretty darn close.

[USARStarkey]

That isn't all that close. You can just apply a percentage to it piecemeal like that dude. Given how closely match the planes were getting are going to be, every little difference matters. I mean at what point would we consider something a large difference? For example, if I was going only 420mph, that would be only 5%. But 20mph would be a huge difference in speed! 10mph may not be huge, but it is significant-especially when weighed against that fact that its competitors 190D and 109K have almost exactly the same top speed. 442(51) 441(109K) 442(190D) For example, let us assume that the the 190 we get is a more historical variant with 2100bhp and 1.8 ata. That would give us a top speed of about 430mph at 18000ft. Imagine if something similar happens and it only does 420. But the 109 comes into the game and for whatever reason achieves its estimated top speed of 441. The 109k is now the fastest plane in the game for exactly no reason what-so-ever beyond disproportionate FM errors. Granted, some error must be expected, but not to such a degree that it significantly effects the performance of the aircraft relative to each other. For planes that are this close to each other in performance, it is crucial that the performance deviation be marginal. Otherwise one or more planes will start to look significantly better than the other in the speed department. If the Mustang were clocking in at 450mph Id be saying the same thing. ultimately however it will depend on how the other planes are modeled. Maybe they will all max out around 430mph- who knows.