Spit 1a

[furbs]

Been flying the Spit 1a this morning on the SYN server and been struggling to get it going more than 250MPH at sea level.
This is with a full load of fuel, 100 Prop pitch and boost on.

Anyone managed any better?

[Plt Off JRB Meaker]

Are you using complex engine management?I believe there is a bug in the non cem model making it slow.

If using cem,one small tip,presumably you're rad is are open,if not,it should be,but and it's a big but,you must ensure it's not fully open,as the drag with it being fully open totally kills you're speed,almost the same as an airbrake being applied.

To answer you're question,yes I have had my Mk1a well over 250mph.

[furbs]

Full real, Rad open 70%, boost on prop pitch 100.

Il give it a go at different rad settings.

Can you check your speed again and tell me you max at sea level?

cheers.

[skouras]

the spit is buggy in my opinion
only the spit II has the real speed

[ATAG_Snapper]

Been flying the Spit 1a this morning on the SYN server and been struggling to get it going more than 250MPH at sea level.
This is with a full load of fuel, 100 Prop pitch and boost on.

Anyone managed any better?

Hi Furbs,

I did a speed trial at Brealistic's request over on the other forum at the optimum alts (per manufacturer) using CEM : http://vimeo.com/26706198

Much of my Spit flying is at sea level/low alt and my experience mirrors yours.

[Ze-Jamz]

Are you using complex engine management?I believe there is a bug in the non cem model making it slow.

If using cem,one small tip,presumably you're rad is are open,if not,it should be,but and it's a big but,you must ensure it's not fully open,as the drag with it being fully open totally kills you're speed,almost the same as an airbrake being applied.

To answer you're question,yes I have had my Mk1a well over 250mph.


I doubt very much you've had it 'way' over...if you have it's news to me and I've probably sent 80/90 hours flying it online with CEM on

[ATAG_Dutch]

I concur.

Tried this with both mixture settings but couldn't sustain any more than 250-ish.

http://www.youtube.com/watch?v=OpT8Oh9aQPE

[furbs]

I might have missed it, but has Luthier ever spoken about why the aircraft perform this way?
maybe different engines? fuel?

How can they be so off?

[ATAG_Dutch]

I don't think there's been a statement regarding the performance of the aircraft, but 30mph at sea level and 10,000ft in altitude performance is a fair old chunk! :)

Here's a nice link;

http://www.spitfireperformance.com/spit1vrs109e.html

[furbs]

So its not 60MPH its 100 MPH off what it should be, same with the 109.

Just thinking thats why were not hitting the right heights as well.

Spit 1a should be getting 360MPH and 31.000 ft

Crazy stuff.

[Welshman]

also seems to have the 2 speed prop not the rotol , i tried the rotol hurry for a very quick test and held 280 easy , the 2 speed hurri was stuck at 250 .

[ATAG_Dutch]

According to the graph on the link I gave, the Spit1a with +6.25lbs boost should be 285mph @ zero ft, with 355ish @ about 19.000ft. But it does state @ 3000rpm, and with a Rotol prop.

The +12lb graph shows higher performance all round. I couldn't find a two-speed prop performance graph, but will have a hunt around.

Edit: The only reference I could find to DeHavilland 2-speed prop performance was in Alfred Price 'The Spitfire Story', but no figures are present for max speed at sea level. Max @ 18,600ft is 367, ceiling 34,400.

It does state that the original fixed pitch 2-bladed prop had max speed @ 2000ft (lowest shown) of 295mph. The 2-speed prop was much heavier, inhibiting the rate of climb, but you'd expect performance in coarse pitch to be similar to the fixed pitch.

[furbs]

Just used the FMB to start with a Spit 1a at 18,000 ft @ 300MPH

The spit then started at 200 MPH and wouldn't go any quicker.

Can someone else please test the same?

[Welshman]

spit IIa has the rotol prop and i just held 310 , without full trimming etc at sea level

so i guess we just need the rotol spit 1 not the 1938/9 version

[Plt Off JRB Meaker]

furbs,will check my settings properly tonight and get back to you,I'm sure I've had my Mk1a over 250mph.

Will confirm this later if I get the chance.

[furbs]

Welshman, well im sure the spit 2 should be quicker than that.

[ATAG_Dutch]

Can someone else please test the same?

Just done it.

Entered 500kph @ 6000m in FMB, and once the 'plane was trimmed out for straight and level, with boost through the gate and coarse pitch, after a bit of a wait and some re-trimming the airspeed indicator read 240mph, which allowing for IAS/TAS calculations, put the speed at about 350mph.

This looks about right to me. Unless my maths is wrong, I had to convert to metric and back also.

Which begs the question, when you enter speed in FMB, are you entering IAS or TAS? Does FMB calculate the difference?

Interestingly, she really wanted to climb so lots of down trim was needed. Might test the altitude again to see if anything has changed.
;-)

[Welshman]

starts loosing boost above 18000 too

[Welshman]

yes i know but no good for top speed ;)

[Plt Off JRB Meaker]

Just done it.

Entered 500kph @ 6000m in FMB, and once the 'plane was trimmed out for straight and level, with boost through the gate and coarse pitch, after a bit of a wait and some re-trimming the airspeed indicator read 240mph, which allowing for IAS/TAS calculations, put the speed at about 350mph.

This looks about right to me. Unless my maths is wrong, I had to convert to metric and back also.

Which begs the question, when you enter speed in FMB, are you entering IAS or TAS? Does FMB calculate the difference?

Interestingly, she really wanted to climb so lots of down trim was needed. Might test the altitude again to see if anything has changed.
;-)

Well done Dutch,got there before me,top job;-)

[IvanK]

I have spent hours in the National Archives chasing original source performance stuff. With respect to DH 2 Pitch prop there was little to find, though I am yet to exhaust the contents of the archives :). The only solid data I have found (so far) with regards DH 2 Pitch performance was some trial data of tests on a Spit IA with a "conformal" tank on the port wing. So obviously inferior performance to a clean IA. Even the Motherload document Avia 18/682 doesn't have much in this regard.

Here is the data for what its worth:

http://img813.imageshack.us/img813/6057/spit12pitchsml.jpg

http://img215.imageshack.us/img215/498/spit12pitchsml2.jpg

http://img828.imageshack.us/img828/703/2pitchsml.jpg

The interesting thing is Max Speed is being achieved at 2700 -2900RPM which implies Full Fine to me. its also 87Octane at 61/4Lbs Boost
At FTH 17,900ft its still getting 352MPH TAS at 3000RPM and 6.2Lbs Boost

[ATAG_Dutch]

Well done Dutch,got there before me,top job;-)

Thanks Meaks!

It doesn't explain the performance at sea level though.

If the 2-bladed fixed pitch prop achieved 295 @ 2000ft, 250 for the 2-pitch prop at sea level seems a bit dismal.

Can anyone find any figs/graphs? Most google references point to either 1C or Ultrapack!!:grin:

[Blackdog_kt]

Almost everything except the Spit Mk.II is slower than it should and that's what Luthier probably referred to when talking about FM fixes (i think he was replying to a thread about this very issue).

With that out of the way and without going into the octane/boost levels debate at all, the root cause of the problem is the fact that most people are not really familiar with how prop pitch works and are getting confused with the two-speed prop.

The trick is simple but a little time consuming, however it should be no big deal for any dedicated Spit drivers until we get a Rotol (constant speed) variant:
start a free flight mission and just fly for half an hour with the sole aim of seeing how much you can get away with without frying the engine.

I'm almost not flying the Spit at all but i have no problem getting 250mph IAS at medium altitudes (which would translate to about 300 mph) with very conservative cruise power settings: no over-boost, just maximum continuous power (the white triangle marker in the instruments red zone), coarse pitch and being careful to trim well and minimize radiator use.

The problem many people have is that they don't know much about how the propellers really work and what that means for ease of maintaining performance. It's no biggie, i didn't know either, there are a load of articles on the web and after some reading my handling with all aircraft improved considerably.

I've seen three excellent articles posted here some time ago, some of it might be too technical (actually the mixture article is mostly about modern civilian prop-aircraft from a point onwards) but it's a worthy read. Just take your time when reading it and don't rush through it, you'll see a lot of mysteries getting explained ;-)

Here are the links
manifold pressure: http://www.avweb.com/news/pelican/182081-1.html
propellers: http://www.avweb.com/news/pelican/182082-1.html
mixture: http://www.avweb.com/news/pelican/182084-1.html

[Al Schlageter]

How did these screwed up FMs get by initial testing?

[Blackdog_kt]

I think it's more due to the new engine modeling. The FMs feel fine in terms of handling, i can't quite put my finger on it but it feels like an improved IL2 experience, it just feels more fluid and less on rails.

The performance issues seem to be tied to power output from the engines (top speeds/ceilings/climb rates) so i guess the new CEM is where the tweaking needs to happen. The fact that the AI has to use simplified routines without cheating makes it all the more complicated (it costs about 10 FPS per aircraft to enable the new CEM, so it's only used for the player aircraft and the AI ones use simpler models), not to mention that most players are not up to it yet (lot's of variation between what each pilot can achieve).

That being said, i'd rather have this new feature with a couple of inaccuracies to be corrected as time goes by, rather than go back to IL2 style engine modeling.

[ATAG_Dutch]

Interestingly, she really wanted to climb so lots of down trim was needed. Might test the altitude again to see if anything has changed.

I thought the altitude capability may have improved, but tried this out this afternoon.

Started with the same 500kph@6000m in FMB, and kept the climb rate at 1000ft per min or below.

It took a long time, but got to 25,500ft. There may have been more to come, but progress was very slow by this point.

Here's a screenshot of the instruments for those who're interested in such matters.;-)