[RESOLVED]P51D's speed underperformance

[Solty]

This issue was corrected. I have checked it and MIL/WEP is 361/375 mph.

 

The test must be perfromed at MSA conditions and be sure that the throttle is calibrated properly.

Can you (or anyone realy) tell us what are MSA conditions? I assume that is minimal safe altitude. It is supposedly 1000ft above the airdrome... but that is hardly SL... right?

 

Is it also possible that it is already fixed in 2.0 but not yet in 1.5?

 

I just made another flight.

 

I know my rudder coordination is not the best (I have a new stick and it has twichy rudder :() but still I am oscilating around 580kph. If anyone can make their own tests that would be great.

 

Thx.

 

EDIT: I just did a flight at 1000ft=304m. I was capable of 362mph or 582kph at 67'hg. IAS conversion to TAS gave me 368 mph 592kph.

Can somone double check my "math"? xD

Edited February 29, 2016 by Solty

[Yo-Yo]

Can you (or anyone realy) tell us what are MSA conditions? I assume that is minimal safe altitude. It is supposedly 1000ft above the airdrome... but that is hardly SL... right?

 

Is it also possible that it is already fixed in 2.0 but not yet in 1.5?

 

I just made another flight.

 

I know my rudder coordination is not the best (I have a new stick and it has twichy rudder :() but still I am oscilating around 580kph. If anyone can make their own tests that would be great.

 

Thx.

 

EDIT: I just did a flight at 1000ft=304m. I was capable of 362mph or 582kph at 67'hg. IAS conversion to TAS gave me 368 mph 592kph.

Can somone double check my "math"? xD

 

First of all, I must bring my aplogies - I mispelled ISA (International) with Russian МСА abbreviation :)

it means 760 mm Hg and 15C at sea level.

Then, the speed is TAS (corrected) and the better way to get it - to use F2 view. Looking to the gauge you must realise that it's only IAS even not CIAS.

Moreover, the longest part of your track you climbed...

[Solty]

Ohhh... so F2 does show TAS? But it is labeled as IAS... I am confused. Is it a typo in the game?

 

I'll try to make my flight more coordinated.

[Yo-Yo]

Ohhh... so F2 does show TAS? But it is labeled as IAS... I am confused. Is it a typo in the game?

 

I'll try to make my flight more coordinated.

 

It is switchable IAS/TAS... but I do not remember what keys exactly... :)

[cichlidfan]

Ctrl+Y, IIRC.

[rel4y]

Yes, press Ctrl+Y twice and you will have TAS. I just recently camo to know as well.

[saburo_cz]

Let me show you (or some from you) several picture which make this debate in fact pointless.

means "tuning" 5-10km/h if we does not know exact condition (or calculations) for real tests which we try to catch

Not mean it as a offence, please.

 

These pictures were taken during three test performed the same way :

take off from RWY at Batumi with coolants AUTO and I flew straight at altitude from 5 to 15 meters with engine setting 61" 3000RPM, all flights took 5 minutes (see watch in cockpit).

I only changed temperature and season, QNH was 760 in all three cases.

 

Summer - 1st June - temp +20° - 552km/h (it is stock map setting)

Spring - 1st May - temp +15° - 562Km/h

Winter - 1st February - temp +5° - 572km/h

 

btw. i have found note from test for previous version 1.5.2 and speed for stock map was 547km/h

 

I never tested Pony with 67"inHG, because I do not use it, 61 is enough to kill LW enemy at most time :).

 

IMHO speed is not problem, or i do not see nothing bad with it but there is some issue with oil coolant automatic.

If I fly with max. continuous setting (under 10000ft) oil temperature is same at is it at all cockpit pictures, too hot, and only way to get it to "green" is open manualy oil coolant for at least 5sec.

Please ED testers can you check it.

[Solty]

So you basically want to confirm that in fact it is too slow.

 

If you hit with 61'hg only 562Km/h (349mph) at 15C. You should be doing 580kph/360mph acording to Yo-Yo's chart.

 

I am doing my test now...

 

Thx for advice on TAS.

[Solty]

OK.

So I did my two tests. +15°C, 760mm

 

At 61'hg I was capable of 578kph (359mph) / reference data speed 363mph

 

At 67'hg I was capable of 595kph (369mph) / reference data speed 375mph

--------

But I still can't reach those reference speeds.

 

What I want to mention though is that the reference data states that bomb racks under wings were installed. That would impact the performance a bit and it was still faster than our P-51D in the game with clean configuration.

 

But yes it is closer to the data than it was before. And it was my testing conditions that made mostly the difference. But as I said, I can't reach the reference speeds.

 

 

@Saburo. I don't know how were you able to fly slower than me and slower than reference data and Yo-Yo's chart xD.

 

PS. And thank you guys again for the TAS indicator. It makes it sooooo much easier to mesure stuff xD

Edited March 1, 2016 by Solty

[Hummingbird]

The 109 is also too slow compared to reference speeds (does ~580 with 3/4th open rads when it should do 595) by about the same amount as the P-51 actually.

 

In other words in terms of speed we are given aircraft which reach the minimum requirements. But at least its the same across the board, so the RL balance should stay the same.

[Kurfürst]

OK.

So I did my two tests. +15°C, 760mm

 

At 61'hg I was capable of 578kph (359mph) / reference data speed 363mph

 

At 67'hg I was capable of 595kph (369mph) / reference data speed 375mph

--------

But I still can't reach those reference speeds.

 

Depends on what your reference data is... there is a lot of spread in P-51D measured performance, 375 mph is probably the best figure obtained only once a specially prepeared plane.

 

NA Inglewood, based on experience of numerous previous trials, which seem to make a good reference, calculated the P-51D speed as 355/368 mph at SL (61/67").

 

There are trials of P-51D that yielded 354 mph at 67" Hg map, so I do not quite see how exactly 369 mph counts as slow. If anything, it seems to be a quite a bit faster than your avarage Mustang.

Edited March 1, 2016 by Kurfürst

[Solty]

Sure there is a lot of different tests with different results. But I am focused on the reference data in this thread as it was taken into account by Yo-Yo

This issue was corrected. I have checked it and MIL/WEP is 361/375 mph.

 

The test must be perfromed at MSA conditions and be sure that the throttle is calibrated properly.

Also this data is based on:

Flight Test Engineering Branch

Wright Field, Dayton, Ohio

15 June 1945 Flight Tests on the North American

P-51D Airplane, AAF No. 44-15342

 

As I said, I was wrong about the asumption that nothing has been done, and in fact the P-51D is faster than it was when this thread was created. Nevertheless I was unable to reach desired speeds. :dontgetit: Thank you Yo-Yo for your time though.

 

That might be connected to the issue that Saburo mentioned, which is the engine overheating which causes the radiator to open too much which results in higher drag and worse max speed. That is just my theory though.:detective:

 

EDIT: @Kurfurst The plane doesn't seem to be specifically prepared for the tests, as even bomb racks are not taken down and the weight seems in order of a standard P-51D (9760 pounds)

Edited March 1, 2016 by Solty

[Friedrich-4B]

Sure there is a lot of different tests with different results. But I am focused on the reference data in this thread as it was taken into account by Yo-Yo

 

Also this data is based on:

Flight Test Engineering Branch

Wright Field, Dayton, Ohio

15 June 1945 Flight Tests on the North American

P-51D Airplane, AAF No. 44-15342

 

As I said, I was wrong about the asumption that nothing has been done, and in fact the P-51D is faster than it was when this thread was created. Nevertheless I was unable to reach desired speeds. :dontgetit:

 

That might be connected to the issue that Saburo mentioned, which is the engine overheating which causes the radiator to open too much which results in higher drag and worse max speed. That is just my theory though.:detective:

 

This is a transcript of the Wright Field tests;

 

http://www.wwiiaircraftperformance.org/mustang/p-51d-na-46-130.html

 

the chart:

 

http://www.wwiiaircraftperformance.org/mustang/na-46-130-chart.jpg

[rel4y]

Considerable effort was expended to achieve agreement between flight test and calculated results, and the data presented represent good agreement with most of the flight test results.

 

Quote from the document. I am guessing they didnt have to make it slower to fit the calculations.. ;)

 

I have posted this before, in some speed tests NA covered wings with paper on startup to not risk dead insects and dirt disrupting airflow over the wing. Also surfaces were specially prepared including filling rivets and sanding the whole thing to perfection. In the end it was covered with special smooth paint and off you go. Problem was that wind tunnel performance of the wing was a lot better than real world performance, since laminar flow could not be achieved in a real world environment and thus the desired drag reduction was missing. I can quote a lot of sources on this if you wish. Now I am not going to argue if its fast enough or to fast, because I dont really care.

Edited March 1, 2016 by rel4y

[Solty]

I just wanted to say that I do undestand how big of an impact many factors like weather and plane condition have and change the whole picture. Nevertheless, I was not looking for new data, just referencing the one that Yo-Yo based his model off.

 

I do understand that my tests are very well within margin of error and I might be able to get 1 or 2mph more if my rudder was more compliant :P

 

Again, thank you for your time Yo-Yo.

Edited March 1, 2016 by Solty

[Yo-Yo]

OK.

So I did my two tests. +15°C, 760mm

 

At 61'hg I was capable of 578kph (359mph) / reference data speed 363mph

 

At 67'hg I was capable of 595kph (369mph) / reference data speed 375mph

--------

But I still can't reach those reference speeds.

 

What I want to mention though is that the reference data states that bomb racks under wings were installed. That would impact the performance a bit and it was still faster than our P-51D in the game with clean configuration.

 

But yes it is closer to the data than it was before. And it was my testing conditions that made mostly the difference. But as I said, I can't reach the reference speeds.

 

 

@Saburo. I don't know how were you able to fly slower than me and slower than reference data and Yo-Yo's chart xD.

 

PS. And thank you guys again for the TAS indicator. It makes it sooooo much easier to mesure stuff xD

 

So, I am sure now that you have the same version of the program... :) but you can not get the values I can get every time.

First af all, regardless of our tests difference, I have to say that even you have 359 and not 361 mph, IT MEANS NOTHING.

As I was a Teaching Professor for a while I was tired explaining to the students what a great mistake they had made dividing, for example, measured value1.25 +- 0.01 to 2.221 +- 0.005 and writing 0.5628095

as a result simply copying their electronic calculator indicator....

 

Techincal measurements are not bank operations - up to 1 cent.

 

So, as you see 361 at the table it means 361 +- X, where X is not 0.00001%. If you take a look to the measuring means of that time (the same is actual even for modern time means) you can see that the tests give a cloud of points and the resulting line on the graph is plotted through this cloud.

 

So, the bank accountist's view to the problem never works for an engineer...

 

Anyway, presuming the stated 361 mph as a MEAN value we can try to fine adjust the DCS model to this value regardless of the fact that 20 Mustangs from the same batch would hit 20 different max speed values due to their differencies in geometry, surface, engines and engine adjustment.

 

And in my ACCURATE tests P-51 in DCS now is very close to 361 mph...

 

There are two main reasons explaining the difference in your tests and mine:

first of all, as the radiator shutter is controlled with the relay regulator, its actual position can be DIFFERENT depending on pre-history of the flight, i.e. in the worst case the regulator stopped the shutter in the position where the coolant temperature is minimal and in the best case - where the temperature is maximal (I mean that in both cases the temperature stays within regulator dead zone).

 

The second reason can be in your handling - any vertical speed during your test can cause this 2-3 mph difference. And not only vertical speed - if you do not keep 1 g flight trying to keep level flight you will bleed this mph.

[Yo-Yo]

2 All

Oil temperature gauge green part of the scale does not correspond to oil temperature regulator settings according the maintenance manual, so the temeperature automatics keeps is not too high.

[Solty]

Thank you YoYo as I said I am sure I just can't reach it and that is probably fault of my twitchy rudder. Today I have trimmed the plane to keep level at 67hg and hit 600kph.

 

It is probably my handling that pushes me away from the max speed.

 

Again. Thank you for your time. I was wrong with my assumption that nothing has changed.