P-51D Speed Observations in Network Play

[USARStarkey]

This is a repeat/update of a previous thread. This one is intended to be definitive.

 

Right now in game the Best level speed attainable with the Mustang is 430mph. You should be able to hit about 440, or 442. The worst speed Ive ever seen listed for the D model was 437 at 24,000ft. Manifold Pressure of 67" is non sustainable past 24,700ft. IRL, it could be maintained to 26k. The Manual, both DCS and real, states 28000ft as the altitude where 67" can no longer be sustained.

The AI can reach 440mph at 28000ft at 61inches. I cannot even sustain 61inches at that height, much less hit 440mph. I can barely hold 425mph. I have included tracks on this. I know my flying isnt perfect, so feel free to test yourself.

 

The Following is Real Life data on the P-51D-With Wing Racks.

 

 

 

 

 

speed run.trk

speed run24000.trk

speed run26000.trk

[Yo-Yo]

The speeds in the reports never are results of one test - if you take a look at some reports there are a "cloud" of points and the resulting line is plotted through them. The gauges has their own erors - systematic and stochastic.

THis is the result of my measurements

http://forums.eagle.ru/showpost.php?p=1577405&postcount=7

 

the error is about 2-2.5%, I think it's less than gauges had in that time.

 

Technical reports are not banking reports, so you never have the numbers correspond up to 1 cent.

 

By the way, what temperature was set for your test?

Edited August 27, 2014 by Yo-Yo

[USARStarkey]

Temp was the default in DCS, which is like 5 C higher than a standard day. Also, your chart shows 61inches not 67. Is there one for WEP?

 

Also regarding tests there also differences in air-frames etc: no two planes are the same. That being said, The worst speed quoted for the 51D is 437mph. The variations in the tests are the reason I posted more than one data point. As best I can tell, The Dora in game is running about where the Green Line is. This is why this matters, as it makes a difference in the relative performance of the planes, even if the difference is only 2%. Someone one here earlier stated that 5% was a good standard for sims, which is crazy, as for a plane like the 51 or 109K that would be a +-20mph difference.

When the other DCS WW2 planes are added this will be even more critical. The top speed of the 109K is about 441mph. Ive also seen it quoted at 445, and 442. Getting a +- 2-3% bump will matter, regard its performance relative to other planes. Same goes for the P-47 etc.

 

Also why is the AI capable of going 10mph faster at 28k? I know its SFM, but In straight level flight they should be performing almost identically no? At the very least the AI shouldn't being getting higher MP.

 

Edited August 27, 2014 by USARStarkey

[USARStarkey]

many factors come into play within the sim

 

weather = wind speeds

= aircraft weights fuel payloads.

 

maybe I overlooked but I didn't see in your tests aircraft configurations. did u match the charts?

 

fuel loads in test? payloads , ammo in wings?

 

weather set in editor?

 

I matched the charts as best as I could tell. Radiator set to auto, but I did not have the wings racks, which only would have detracted anyhow. I was lighter, but about 200lbs, again a bonus. Ammo was loaded, as in tests.

Edited August 27, 2014 by USARStarkey

[Narushima]

And were those historical test corrected for error due to compressibility?

 

At that hight that error could be as big as 8mph.

 

See here for example. It's a FW 190 A-5, but it shows the effect of compressibility error. Obviously, higher the speed and altitude, higher the error.

 

Left line - corrected for compressibility error

Right line - without correction

 

[Yo-Yo]

Temp was the default in DCS, which is like 5 C higher than a standard day. Also, your chart shows 61inches not 67. Is there one for WEP?

 

Also regarding tests there also differences in air-frames etc: no two planes are the same. That being said, The worst speed quoted for the 51D is 437mph. The variations in the tests are the reason I posted more than one data point. As best I can tell, The Dora in game is running about where the Green Line is. This is why this matters, as it makes a difference in the relative performance of the planes, even if the difference is only 2%. Someone one here earlier stated that 5% was a good standard for sims, which is crazy, as for a plane like the 51 or 109K that would be a +-20mph difference.

When the other DCS WW2 planes are added this will be even more critical. The top speed of the 109K is about 441mph. Ive also seen it quoted at 445, and 442. Getting a +- 2-3% bump will matter, regard its performance relative to other planes. Same goes for the P-47 etc.

 

Also why is the AI capable of going 10mph faster at 28k? I know its SFM, but In straight level flight they should be performing almost identically no? At the very least the AI shouldn't being getting higher MP.

 

 

I am trying to say again - in real life as well as in real online or offline this 2% does not matter. I have no time but try to find the report with REAL points shown at the graph - even for the same plane the deviation is higher than 2%. One can barely maintain steady trimmed level flight to hit the maximal speed. Do you think that in real online you will be able to do it? In the real world the things were worse because of different engine conditions, airframe conditions, etc, it played a role.

 

For example, Erich Brunotte told us that he used to trade his schnaps and cigarettes to his ground technician manpower to have his plane polished as a mirror. It gave him an advantage in speed comparing to his fellow pilots.

[NineLine]

Well, seems we need to have schnaps and cigarettes added to the warehouse supply system....

[USARStarkey]

Right, and I mentioned those differences in passing. The thing is though, we dont have those variations in a sim. I dont jump out of one plane and into another one that is faster or slower by 10mph. That is why the baseline performance is so important. And as a note, in that first test the plane is flying WITH wing racks, and is still going over 440mph.

Second, whether or not i can maintain perfect level flight in combat is irrelevant. The 190D is extremely hard to fly level, even when trimmed, and the mere 5mph advantage it has on the deck is enough to escape the mustang given it starts out far enough to not be gunned down as it makes its escape. This absolutely matters.

Also it seems rather contradictory to spend all this time and money trying to make PFM's just to disregard any performance discrepancies as meaningless.

Also why is the AI faster?

Edited August 27, 2014 by USARStarkey

[NineLine]

You do have variations in the sim, you probably cant fly the same results each time. As with another pilot, might do worse or better than you.

 

As for the AI? Well they are perfect pilots...

[USARStarkey]

You do have variations in the sim, you probably cant fly the same results each time. As with another pilot, might do worse or better than you.

 

As for the AI? Well they are perfect pilots...

 

That was not the sort of variation we were discussing. We were referring to minute differences between specific air frames and changes in performance due to wear and polishing etc.

[NineLine]

That was not the sort of variation we were discussing. We were referring to minute differences between specific air frames and changes in performance due to wear and polishing etc.

 

You wont get those of course, and as such you might not get the performance boost of a buffed or losses of a worn aircraft, the data that Yo-Yo used is what you get...

Edited August 27, 2014 by NineLine

[Yo-Yo]

We even do not know now whether or not compressibility error was taken in account.

And what do you think about the measurements error of the gauges? It's not a rhytoric question. Do you know, for example, what is the error of old-school voltmeters, ampermetres, etc? It's only very simple one-parameter indoor measurements. (And it's not just a rhytoric question again - i'd like to have an answer from you).

If you have read "Dambusters" you must remember what it was a problem to measure accurate TAS at the certain conditions - TAS depends on the air temperature, real altitude is not barometric and depends on temperature too, measured temperatue depends on IAS, etc.

Physical measurements IS NOT AN ACCOUNTIST'S WORK. They always have errors or uncertain range.

By the way, you are trying to nail the FM errors but did not use standard atmosphere - is it right?

[Narushima]

I suspect that those graphs are without corrections for compressibility error.

 

The calculated graph for the P-51D on the other hand shows the top speed as 703 km/h (436mph). I assume they took compressibility error into consideration when doing those calculations.

[Yo-Yo]

I suspect that those graphs are without corrections for compressibility error.

 

The calculated graph for the P-51D on the other hand shows the top speed as 703 km/h (436mph). I assume they took compressibility error into consideration when doing those calculations.

 

I'd prefer not to take the calculated graph as a Bible. Any calculations have their own errors, simplifucations and assumptions.

[USARStarkey]

I suspect that those graphs are without corrections for compressibility error.

 

The calculated graph for the P-51D on the other hand shows the top speed as 703 km/h (436mph). I assume they took compressibility error into consideration when doing those calculations.

 

The calculated graph shows 440mph. Read the Report Text.

[USARStarkey]

I'd prefer not to take the calculated graph as a Bible. Any calculations have their own errors, simplifucations and assumptions.

 

Just like Flight Models.

[Yo-Yo]

Just like Flight Models.

 

I am waiting for the answers about gauges and their accuracy.

[USARStarkey]

We even do not know now whether or not compressibility error was taken in account.

And what do you think about the measurements error of the gauges? It's not a rhytoric question. Do you know, for example, what is the error of old-school voltmeters, ampermetres, etc? It's only very simple one-parameter indoor measurements. (And it's not just a rhytoric question again - i'd like to have an answer from you).

If you have read "Dambusters" you must remember what it was a problem to measure accurate TAS at the certain conditions - TAS depends on the air temperature, real altitude is not barometric and depends on temperature too, measured temperatue depends on IAS, etc.

Physical measurements IS NOT AN ACCOUNTIST'S WORK. They always have errors or uncertain range.

By the way, you are trying to nail the FM errors but did not use standard atmosphere - is it right?

 

This is a completely moot point. No, I don't know the exact variation of the old school guages, and based on your previous statement about percentages and what you "believe" neither do you. Furthermore this exact same point would apply to all the data gathered from the times ie: wind tunnel testing. I'd imagine the instrumentation used in the wind tunnel testing that you almost certainly had to use at some point to make the FM's had to have also used measurement tools from the same time period. More to the point, wind tunnel testing of the 40's is subject to error due to the variations in the tunnel itself, the composition and accuracy of the model being used, and the absence is most cases of various turbulent effects such as prop wash. For example, it was explained to me some time ago that you have to factor out things like tunnel ground effects--from which even more error can arise based on the measurements regarding the properties of the tunnel. This means that CL, Cdo, etc are all subject to some error for anyone making a FM. I'd imagine at some point that you, like every other sim maker, had to use data like this at some point in making the FM. This means that even the calculated values, whomever they are done by, are also subject to similar errors due to inaccuracy in test data used to make them. Essentially, all of these errors, testing or otherwise, are a virtual wash unless someone has all the data on every test, which probably doesn't exist.

 

If it helps, those tests I posted are corrected to a NACA standard day to answer the question regarding temperatures and pressures etc.

[NineLine]

So what is your end game here at this point? Yo-Yo has charted out the FM and is happy with it, it has been flown by real P-51D pilots and they are happy with it... what are you getting at? You said even your tests might not be correct because of poor flying... so what are you trying to say? Not being critical... just not seeing your point.

 

This is a completely moot point. No, I don't know the exact variation of the old school guages, and based on your previous statement about percentages and what you "believe" neither do you. Furthermore this exact same point would apply to all the data gathered from the times ie: wind tunnel testing. I'd imagine the instrumentation used in the wind tunnel testing that you almost certainly had to use at some point to make the FM's had to have also used measurement tools from the same time period. More to the point, wind tunnel testing of the 40's is subject to error due to the variations in the tunnel itself, the composition and accuracy of the model being used, and the absence is most cases of various turbulent effects such as prop wash. For example, it was explained to me some time ago that you have to factor out things like tunnel ground effects--from which even more error can arise based on the measurements regarding the properties of the tunnel. This means that CL, Cdo, etc are all subject to some error for anyone making a FM. I'd imagine at some point that you, like every other sim maker, had to use data like this at some point in making the FM. This means that even the calculated values, whomever they are done by, are also subject to similar errors due to inaccuracy in test data used to make them. Essentially, all of these errors, testing or otherwise, are a virtual wash unless someone has all the data on every test, which probably doesn't exist.

 

If it helps, those tests I posted are corrected to a NACA standard day to answer the question regarding temperatures and pressures etc.

[Yo-Yo]

2 USARStarkey

They corrected only systematic errors not random errors.

 

Ok, as you do not want to answer, I can tell you - most of electric gauges that were used as multimeters and had dimensions approx. 4 x 3" - they generally had 2.5% accuracy OF THE MAXIMUM reading. The 1% accuracy required bigger mechanics, mirror scale, etc. Common type gauges had more than 4%.

 

I can not catch the point of your speech, though... what do you want to declare? Are you complaining about the FM inaccuracy regarding inaccurate test results?

Just to clear things up - I do not want to say that they were deeply wrong, no. But ANY measurement has its inaccuracy or error. Even if you measure a matchbox with a ruler you can not get accuracy, say, more than 0.5 mm, If you begin to use a slide calipers you could get 0.1 or even 0.05 mm accuracy but the board matchbox is not rigid, so sliding the caliper you will deform it... it will be another source of inaccuracy.

 

Do you know, what test pilots wrote about getting and measuring the top speeds in Mustang?

Edited August 27, 2014 by Yo-Yo

[Double_D]

Or some people over annalize , and see something that may not be there...nothing is perfect even perfect is not perfect...:music_whistling:

[hattrick]

I am consistently able to reach 440-445 MPH TAS at 26000 in game given standard atmospheric conditions. The Mustang is actually VERY closely modeled to the first chart you posted. Here's my data collection.

 

Edited August 27, 2014 by hattrick

[USARStarkey]

2 USARStarkey

They corrected only systematic errors not random errors.

 

Ok, as you do not want to answer, I can tell you - most of electric gauges that were used as multimeters and had dimensions approx. 4 x 3" - they generally had 2.5% accuracy OF THE MAXIMUM reading. The 1% accuracy required bigger mechanics, mirror scale, etc. Common type gauges had more than 4%.

 

I can not catch the point of your speech, though... what do you want to declare? Are you complaining about the FM inaccuracy regarding inaccurate test results?

Just to clear things up - I do not want to say that they were deeply wrong, no. But ANY measurement has its inaccuracy or error. Even if you measure a matchbox with a ruler you can not get accuracy, say, more than 0.5 mm, If you begin to use a slide calipers you could get 0.1 or even 0.05 mm accuracy but the board matchbox is not rigid, so sliding the caliper you will deform it... it will be another source of inaccuracy.

 

Do you know, what test pilots wrote about getting and measuring the top speeds in Mustang?

 

My point in my last response is that the validity of any FM is just as flawed as any real test based on what you are saying. Sure, the gauges have inaccuracies, although without knowing exactly which gauges we cannot say how much. However, the flaws in 1940s instrumentation would be an issue for any raw data as well. When making the FM, I am sure you had to use raw data. That raw data would also be subject to the errors based on the stuff I listed earlier. So essentially, neither is perfect. Given that this is a virtual wash, a nod in the direction of the RL tests is necessary since the errors were discussing would have effected all nations aircraft testing. Right now, this might not be an issue. Ultimately this is a game, and within certain limits what counts is RELATIVE performance. So right now we have a Mustang that does 430mph. As best I can tell, we have a Dora that does 430mph. Given that there are curves showing both these planes doing 440 or higher, this is proportional. But will it remain so for the aircraft that are to come? If we get a BF-109 or P-47 or spit that clocks in at the more liberal interpretations of their performance where does that leave us? the 190, 51, and 109 all had top speeds of 440ish mph-estimated and real. If in game they all go 430mph, then it could be argued no big deal. But what if we get a 109 thats only doing say 420mph or perhaps it 440-450mph and is on the ideal side of things? Same goes for all the planes in game. Perhaps you already have and haven't said so, but now that 51 and these other planes will no longer being flying in vacuum, I dont think its all the unreasonable for the FM of the 51 to be re-looked at now that the details of its performance matter more than ever.

 

At the very least it would be nice to see a in game curve of the DCS P-51 at 67"

Edited August 28, 2014 by USARStarkey

[hattrick]

My point in my last response is that the validity of any FM is just as flawed as any real test based on what you are saying. Sure, the gauges have inaccuracies, although without knowing exactly which gauges we cannot say how much. However, the flaws in 1940s instrumentation would be an issue for any raw data as well. When making the FM, I am sure you had to use raw data. That raw data would also be subject to the errors based on the stuff I listed earlier. So essentially, neither is perfect. Given that this is a virtual wash, a nod in the direction of the RL tests is necessary since the errors were discussing would have effected all nations aircraft testing. Right now, this might not be an issue. Ultimately this is a game, and within certain limits what counts is RELATIVE performance. So right now we have a Mustang that does 430mph. As best I can tell, we have a Dora that does 430mph. Given that there are curves showing both these planes doing 440 or higher, this is proportional. But will it remain so for the aircraft that are to come? If we get a BF-109 or P-47 or spit that clocks in at the more liberal interpretations of their performance where does that leave us? the 190, 51, and 109 all had top speeds of 440ish mph-estimated and real. If in game they all go 430mph, then it could be argued no big deal. But what if we get a 109 thats only doing say 420mph or perhaps it 440-450mph and is on the ideal side of things? Same goes for all the planes in game. Perhaps you already have and haven't said so, but now that 51 and these other planes will no longer being flying in vacuum, I dont think its all the unreasonable for the FM of the 51 to be re-looked at now that the details of its performance matter more than ever.

 

At the very least it would be nice to see a in game curve of the DCS P-51 at 67"

 

Again.... I just posted my speeds above in DCS which do not agree with your claim that you can only get 430MPH in the Mustang. It's simply not true. As for the Dora.. it needs major work especially above 20000 feet with MW50 on. But that's for another thread/discussion.

Edited August 28, 2014 by hattrick

[USARStarkey]

Again.... I just posted my speeds above in DCS which do not agree with your claim that you can only get 430MPH in the Mustang. It's simply not true. As for the Dora.. it needs major work especially above 20000 feet with MW50 on. But that's for another thread/discussion.

 

Hattrick I admitted earlier that my flying my not have been the most straight. Your charts are interesting and I'm not sating they are wrong. Could I see a track or Tacview to verify that you were flying level? I appreciate you taking the time to make the charts, If i see verifiable evidence that its flying those speeds in sustained level flight I will drop this.

Edited August 28, 2014 by USARStarkey