Spitfire V Merlin 45 too fast?

[Panthera]

I've noted that the Spitfire Mk.V's top speed at SL as pr. the below calcuated chart was 515 kmh (318.5 mph) at SL with the Merlin 45 @ +16 boost, and not the 535 km/h (332 mph) we have ingame.

 

http://www.wwiiaircraftperformance.org/Spitfire_V_Level_Speed_RAE.jpg

 

The above chart also shows performance at 8,000 ft being 353 mph, or 4 mph faster than the flight tested speed of 349 mph: http://www.spitfireperformance.com/aa878.html

 

Thus it seems that the top SL speed of the Merlin 45 equipped Spitfire V should be in the order of ~510 km/h at +16 boost, and not the 535 km/h we have listed on the ingame datasheets.

[-=PHX=-SuperEtendard]

This was discussed when update 2.011 came (bringing the Spit). One of the devs, Gavrik, talked about the top speed in that thread. By comparing different tests for different Spitfire Mk V subvariants (Mk Vb, Mk Vc, with and without snowgard in the intake) they extrapolated more or less what our Spit Mk Vb with intake snowgard speed at +16 boost would be.

 

According to him it should be 526 km/h, and ingame the plane does 533 km/h at +16 with radiator opened at 40% (which I think it's what they used in the tests?). He recognises it's a bit too fast, but he considers the ~1.5% difference to be aceptable (at least for now, as Petrovich told us that the new Yak-7B had 1% speed margin, I look forwards for them to update the other flight models to this new standard, specially at high altitudes where some planes are too fast, and this will be specially important for Bodenplatte).

 

About Spitfire maximal speed in level flight.
First. About speed difference between +9 and +16 mode.
We have two sources for +16 engine mode.
That: http://www.spitfirep....com/aa878.html (Difference in speed between +9 and +16 below full throttle altitude is near 36 m.p.h.)
And that: http://www.wwiiaircr...l_Speed_RAE.jpg (Difference in speed between +9 and +16 below full throttle altitude is 28...32 m.p.h.)
In simulator, under ideal conditions, speed increases by approximatly 34.5 m.p.h. (below full throttle altitude). And it is close to both (36 m.p.h. and 28...32 m.p.h.) sources.
Ok, now second. About maximal speed at +9 mode.
If we compare that http://www.spitfirep....com/x4922.html , that http://www.spitfirep....com/w3134.html , and that http://www.spitfirep....com/aa873.html sources, we find that in all of them we have similar maximum speed in lewel flight (375 m.p.h., 371.0 m.p.h., 374 m.p.h.,).
In simulator top speed - 367 m.p.h., but we hawe a snowguard, which decrease top speed.
But in this report (which we already considered above, when talking about +16 mode) http://www.spitfirep....com/aa878.html top speed at +9 mode is only 359.5 m.p.h., and this is considerable slowly that top speed from other three reports.
And, finally, we have that http://alternathisto...9_0-640x330.JPG data for lend-lease Spitfire with Merlin 46 from NII VVS tests (left kolumn, in k.p.h.) And this data close to Spitfire in simulator with Merlin 46 (near 10 k.p.h difference, less that 2%).
So, after all, i think that Spitfire top speed in level flight in simulator close to real test flight data.

 

 

This is wrong point of view. It is necessary to take into account all available sources, not one "convenient".

Once again.

http://www.spitfireperformance.com/x4922.html http://www.spitfireperformance.com/w3134.html http://www.spitfireperformance.com/aa873.html

Different airplanes, but similar top speeds. So, this data and these speeds can be trusted.

http://www.spitfireperformance.com/aa878.html

Report with information about +16 mode. But, at the same altitude as the previous three aircraft ("reliable data"), this slower by about 12 mph. So, at the ground level should be the same thing - this airplane should be slower. If we extrapolate speed graph at +16 to ground level, we have near 315 mph. 315+12 = 327. In simulator - 331 (40% radiator). near 1.5% mistake.

Lets take a look at this graph. http://www.wwiiaircraftperformance.org/Spitfire_V_Level_Speed_RAE.jpg This plane a bit slower, that first three, but not so much as previous aircraft. And this airplane has a smaller speed increase, that previous aircraft (36 m.p.h. and 28...32 m.p.h.). Because of these circumstances, we can lose 4...8 m.p.h., depending on how to evaluate. But okay, let's say that 317 miles per hour from the chart is an exact figure and comparable to the simulator. 4% mistake, under ideal conditions in simulator (In the simulator, the aircraft can ideally withstand course and altitude). And it is still less that permissible error of 5%.

And do not forget that the +16 mode is not eternal. Three minutes later the brougham turns into a pumpkin. 2 min "cooldown" is an error, and should be fixed, of course.

https://forum.il2sturmovik.com/topic/29943-game-version-2011-discussion-spitfire-mkvb-blazing-steppe-ne/page-10?do=findComment&comment=488757

Edited February 4, 2018 by -=PHX=-SuperEtendard

[Panthera]

Odd how he arrived at 526 kmh when RAE graphs show 515 kmh.

[Holtzauge]

This summer I did a comparison of the in-game developer data and C++ simulation results and indeed it looks like the Spitfire Mk5 is a bit fast but then again I usually tune the C++ models Cdo based on a speed value and IIRC then the one I used in this case was from values I found at WW2aircraftperformance.org. Maybe there is other data indicating a higher value but so far the data I have used to tune with gives the result below which is pretty much in line with what you are saying Panthera.

 

 

[CUJO_1970]

How common was this engine on Eastern Front?

[Barnacles]

How common was this engine on Eastern Front?

 

Not very, most* LL Spitfire Vs had the 46 engine.

 

* Can't remember exact figure, in the dd maybe 80% was stated?

[Panthera]

I'm starting to fall in love with that C++ sim of yours Holtzauge :D But now that I know it can read my mind the important question becomes: Does it cook? :D

Edited February 5, 2018 by Panthera

[LukeFF]

Not very, most* LL Spitfire Vs had the 46 engine.

 

* Can't remember exact figure, in the dd maybe 80% was stated?

 

It was discussed here: https://forum.il2sturmovik.com/topic/25295-which-spitfire-engine-are-we-getting-our-mkvb/

[-=PHX=-SuperEtendard]

Would there be significant speed difference between the c type and b type wings? I guess the armored windshield (internal or external) would also affect. As the devs used data from both Vb and Vc.. maybe the drag difference was overestimated?

 

 

I did some speed tests with both engines.

With Merlin 45

At +9 boost and 3000 RPM, 40% rads top speed was 475 km/h, with 20% rads 478 km/h and fully closed was 481 km/h.

At +12 boost and 3000 RPM, 40% rads top speed was 501 km/h, with 20% rads 504 km/h and fully closed was 508 km/h.

 

At +16 boost and 3000 RPM, 40% rads top speed was 531 km/h, with 20% rads 534 km/h and fully closed was 538 km/h.

 

With Merlin 46

 

At +9 boost and 3000 RPM, 40% rads top speed was 453 km/h, with 20% rads 456 km/h and fully closed was 460  km/h.

 

At +12 boost and 3000 RPM, 40% rads top speed was 480 km/h, with 20% rads 484 km/h, and fully closed was 487 km/h.

 

At +16 boost and 3000 RPM, 40% rads top speed was 511 km/h, with 20% rads 514 km/h, and fully closed was 517 km/h.


Also in the ingame specs the standard weight is listed as 2979 kg, around 400 kg lighter than Holtzauge's simulation. Could this weight difference explain the extra speed?
 

Edited February 5, 2018 by -=PHX=-SuperEtendard

[Kurfurst]

Would there be significant speed difference between the c type and b type wings? I guess the armored windshield (internal or external) would also affect. As the devs used data from both Vb and Vc.. maybe the drag difference was overestimated?

 

B and C wing drag difference was not very significant, however, there were a couple of small drag changes like big/small cannon bulges. Snow guards and intake variantions could also play a significant role.

Edited February 5, 2018 by VO101Kurfurst

[303_Kwiatek]

Would there be significant speed difference between the c type and b type wings? I guess the armored windshield (internal or external) would also affect. As the devs used data from both Vb and Vc.. maybe the drag difference was overestimated?

 

 

I did some speed tests with both engines.

 

With Merlin 45

 

At +9 boost and 3000 RPM, 40% rads top speed was 475 km/h, with 20% rads 478 km/h and fully closed was 481 km/h.

 

At +12 boost and 3000 RPM, 40% rads top speed was 501 km/h, with 20% rads 504 km/h and fully closed was 508 km/h.

 

At +16 boost and 3000 RPM, 40% rads top speed was 531 km/h, with 20% rads 534 km/h and fully closed was 538 km/h.

 

 

With Merlin 46

 

At +9 boost and 3000 RPM, 40% rads top speed was 453 km/h, with 20% rads 456 km/h and fully closed was 460 km/h.

 

At +12 boost and 3000 RPM, 40% rads top speed was 480 km/h, with 20% rads 484 km/h, and fully closed was 487 km/h.

 

At +16 boost and 3000 RPM, 40% rads top speed was 511 km/h, with 20% rads 514 km/h, and fully closed was 517 km/h.

 

 

Also in the ingame specs the standard weight is listed as 2979 kg, around 400 kg lighter than Holtzauge's simulation. Could this weight difference explain the extra speed?

 

Speed at +9lbs and +12 lbs looks very accurate. Probably there were no sea level test data speed for +16lbs thats why devs calculated it.

 

Other thing is that VVS didnt use 100 octan fuel but their own lower octan fuel thats why all western planes serviced in VVS got lower performance then with 100 octan fuel. In one interview with Russian ace he mentioned these.

Edited February 5, 2018 by 303_Kwiatek

[303_Kwiatek]

I found some data for SPitfire MKVB with Merlin 45 +9 and +12 lbs and with Merlin 50M at +18 lbs

 

 

[Brano]

Other thing is that VVS didnt use 100 octan fuel but their own lower octan fuel thats why all western planes serviced in VVS got lower performance then with 100 octan fuel. In one interview with Russian ace he mentioned these.

Dont mislead the people with such generalisations. Soviets received plenty of Б-95 and Б-100 (octane nr.) via LL. They were not mixed with domestic fuels. On contrary,these LL fuels were used when domestic production was not available. It could be used for M-105PA/PF,AM-38,M-88,M-87 and even M-63 of late series Ishaks.

[Panthera]

Speed at +9lbs and +12 lbs looks very accurate. Probably there were no sea level test data speed for +16lbs thats why devs calculated it.

 

Other thing is that VVS didnt use 100 octan fuel but their own lower octan fuel thats why all western planes serviced in VVS got lower performance then with 100 octan fuel. In one interview with Russian ace he mentioned these.

There is data for SL though, an otherwise optimistic RAE calculation listing a top SL speed of 515 km/h at +16 boost.

[Kurfurst]

Speed at +9lbs and +12 lbs looks very accurate. Probably there were no sea level test data speed for +16lbs thats why devs calculated it.

 

Other thing is that VVS didnt use 100 octan fuel but their own lower octan fuel thats why all western planes serviced in VVS got lower performance then with 100 octan fuel. In one interview with Russian ace he mentioned these.

 

Unless they reduced to manifold pressure, there shouldn't be. Octane rating is completely irrelevant when it comes to actually producing power at a given manifold pressure (as long as knocking can be avoided), since the BTU (energy) of burning either fuel is the SAME. 

[Holtzauge]

<snip> Does it cook? :D

 

Not only does it cook: The stack can be uploaded into the sleeve of your choise Panthera.......

Edited February 5, 2018 by Holtzauge

[Panthera]

Not only does it cook: The stack can be uploaded into the sleeve of your choise Panthera.......

 

Well this sleeve is certainly ready

Edited February 5, 2018 by Panthera

[SCG_Fenris_Wolf]

The Japanese are building synthetic sleeves already?