Spit mkIX level speed inaccuracies

[Biggs]

Dont know why I haven't done this sooner but I finally decided to see if the LF mkIX (merlin 66) we currently have in DCS.

Phil Style posted a video on the SL top speed and could only achieve close to 330 IAS when it should be 343. My tests to match historical level speed at altitude fared even worse.

I set out to match IAS at 3 different altitudes 10, 18 and 22000 ft (21 being the alt where it achieves its top speed of 407 TAS or 300 IAS.

@ 10k the IAS should be 337, I could only manage 305-307 IAS - a 32 MPH difference
@ 18k the IAS should be 306.5, I could only manage just over 280 IAS - a 26 MPH difference
@ 22K the IAS should be 300, I could only manage just over 270 IAS - a 30 MPH difference

The average is 29.3 MPH lower than historical airspeed... A shockingly high discrepancy in airspeeds

I did 2 attempts at these test and found that with full power and rpm (as historically tested) the plane was kept in auto rad (the closest we will get to being able to hold the rads full closed as they were in the historical tests.) I watched Phil Styles' vid on the SL top speed test and how he modulated the RPM to achieve a higher speed than just holding it at full RPM. I tried this as well but it did not make any appreciable difference (maybe a couple MPH change at best). 3000, 2800 2600 RPMs were tried the differences were negligible. *all tests were carried out trimmed out as precisely as I could

I implore more of you to make tests at level top speeds, Im hoping Im just doing something wrong.

The data I used was taken from http://www.spitfireperformance.com/bs543.html scroll down to "TABLE V.
Spitfire IX BS. 543 (Merlin 66)
Level speed performance"

[Redeye]

You need to take this to the ED forums mate:) I think there is already a debate rolling on this. All input on this is gold. Keep in mind off course that it being early access this could change, for the better hopefully:)

[Coopes]

A few things of note. The DCS Spit IX is not the BS543. Yo-Yo has produced a curve for the DCS spit performance.
The BS 543, IX MA. 648 and Mk VIII JF. 275 were all used as references.
So to try and achieve the speeds on the chart you posted is pointless as it not the performance curve in game.

The DCS Spit actually outperforms the BS 543 above 16000 ft according to the graph.

Did you know that the BS 543 was a converted MkVc??

Also remember that this is not the Spit IX BS 543 simulator. Many sources would have been looked at and a mean average applied.

Soviet trials of a Spit IX out perform both the DCS and BS 543 from 16000 to 19000.

The DCS Spitfire matches the references within the real tests tolerance in the whole range from 0 to 10-11 km

[Biggs]

A few things of note .......

You're keep saying that the dcs outperforms BS543, yet my test says otherwise.

I started this whole thing out just trying to see if I could reach 407 mph at 21-22000 ft (as that is the top speed stated in every historical documents ever produced about the LF mkIX ever)... BS543 was just used because it had a full top speed chart.

And yes I know it was a converted mkvc... mh434 (dcs's spitifre) represents the early 1943 version of the mkIX which would put it in line with those that were mkVc conversions. So I'm not sure where you're going with that one.

I'd just like to see where they are basing their information off of to get a spit9 that seems to be ~25mph slower than documented.

[Coopes]

I don't keep saying it, I said according to the charts of which YoYo produced.

I found a historical document saying 404 not 407. So its not every.

I will see later if I can match YoYo's chart.

Post it in the bug forum if you think its too slow

[Dickie]

FWIW every IX was a converted V from a converted I, either by factory refit or from new design changes. The VIII was on the only actual new design, but it was constantly late.

[Sprite]

When did RAF switch to BAM100 Octane fuel? I wonder if maybe the tests that ED used were based on performance statistics using 87 octane as opposed to 100. However if RAF were almost exclusively using 100 Octane by the time they started rolling out merlin 66's then I dont see that being a factor

[Biggs]

I don't keep saying it, I said according to the charts of which YoYo produced.

I found a historical document saying 404 not 407. So its not every.

I will see later if I can match YoYo's chart.

Post it in the bug forum if you think its too slow

Ive read anywhere between 404 to 411mph as it's top speed... the difference is small obviously, but my point is I found that I came no where near that indicated speed... if it was 5-10 mph off I'd have been somewhat satisfied (human error and altitude modeling factoring into the discrepancy), but 30mph difference is significant.

I set my altimeter before taking off... Novo, is about 130ft above SL which is where I did my testing.

I will do more testing tonight.

[Coopes]

Yea 400 odd TAS.

The point i was clumsily trying to make earlier was i have seen the curve YoYo has modelled the DCS spit too which is close to the speeds your looking for.
So if its definately not happening something must have broken in the last updates, i dont know.

[Onebad]

Did same exact tests earlier today.

Was able to achieve just above 300mph @10 000ft & around 280 mph at 18 000ft.
Didn't bother to test at higher alts but I don't think I'd achieve any different results than Phil and Biggs did.

It's indeed quite dissapointing though I hope some changes and fixes will be applied as the module leaves Early Acces later on, because let's be honest, DCS Spitfire is far from perfect as it is right now.