Aircraft peformances, is this joke ?

[CWMV]

Still waiting on a proper Emil as well.
Sadly this has all already been said. Many, many times.

[ATAG_Snapper]

Originally Posted by CWMV

Still waiting on a proper Emil as well.
Sadly this has all already been said. Many, many times.

+1

[FS~looksharp]

also... are you switching to rich mixture at sea level ????

i can get 290 mph out of the spit 2a at sea level with boost cut off enabled and rich mixture just as it should be

[ATAG_Snapper]

Originally Posted by looksharp

also... are you switching to rich mixture at sea level ????

i can get 290 mph out of the spit 2a at sea level with boost cut off enabled and rich mixture just as it should be

Yep. And when you do that, pull your mixture lever back to Full Lean and see what happens.

[Redroach]

oh, and: Isn't Lean <==> Rich in the current (latest) beta incarnation? At least on the SpitMkIa?

(I mean that I am of the opinion that the lever works the wrong way around)

[ATAG_Snapper]

Originally Posted by Redroach

oh, and: Isn't Lean <==> Rich in the current (latest) beta incarnation? At least on the SpitMkIa?

(I mean that I am of the opinion that the lever works the wrong way around)

Hi Redroach,

Yeah, that's been so since Cliffs of Dover was first launched and never corrected:

http://www.il2bugtracker.com/issues/18

But that's not what I'm referring to in my reply to Looksharp.

[Blackdog_kt]

Generally speaking, all piston aircraft checklists that i've seen specify rich mixture for high power settings.

The engine runs a bit more powerful on auto-lean but it also runs quite hotter, so for all high power regimes of flight auto-rich is used. Lean is just for cruising at reduced fuel consumption.

In short, going flat out and switching from rich to lean might cook the engine in short order.

I was lucky enough to have access to a friend's PC with a quite a few FSX add-ons that do extensive engine management and that's where i practiced before CoD was released.

At some point we were flying a Catalina add-on by Aerosoft that is modeled after the one they have restored in the Lelystad airfield museum in the Netherlands. We even did a 10-hour flight in it across the Caribbean, taking turns at the controls.
What we noticed right away was that flying at economy settings on auto-lean would result at the same cylinder head temperatures as when flying at higher power on auto-rich. The lower demands on the engines were completely offset by the leaner mixture.

The main gain was that we were burning less fuel because of running the engines at lower manifold pressure/RPM. Going to maximum continuous power resulted in the exact same cruising speed (an abysmal 100 knot IAS, that's slower than many cars ), but we had to go to auto-rich mixture instead. Then, after 2-3 minutes we also had to open the cowl flaps fully and the result was that at max continuous power we had to compromise so much in drag that our speed was lower and our fuel consumption much worse.

So why don't people fly like that (on lean/economy) all day long? Because higher power means better acceleration and climb. The difference here is that we were just cruising, but in a combat scenario it's different.

You can also see this in CoD to an extent. There are times when i am cruising at 1.1 Ata and the 109 does 380km/h IAS, there are other times when i'm pushing emergency power and it barely does 350km/h because i just exited a maneuver.

What we need is someone who can extract the data files to tell us which way for the in-game controls and levers corresponds to lean and which to rich for all of the flyable RAF aircraft, so that we can deduce with some accuracy if and what is wrong.

[jf1981]

Originally Posted by looksharp

also... are you switching to rich mixture at sea level ????

i can get 290 mph out of the spit 2a at sea level with boost cut off enabled and rich mixture just as it should be

No I don't think it was this way, the engine is rated with its full boost of 6,25 psi, going over that should give you an extra margin on top of the normal performance.

That's what I have understood from the sources I could cross.

Also if you note that the military power was only to be used for short time, I don't think it was the meaning to level the aircraft and apply more than its rated power in order to determine its maximum speed. You have to take into account that it was leveling up for a relatively long time before a stable reading could be obtained, say between 5 and 10 minutes most probably.

If you find informations supporting that it shall have its performance with the boost cutout open and applying the full available boost, I think it'd be worth to share.

In my opinion, we should have the right performance without use of bost cutout, up to my understanding. Octane grade 100 was probably also not available in 1938 for the Mk I prototype. The prototype itself fit with a wooden fixed pitch propeller reached 349 mph TAS at 17'000 ft.

I'll try to get more accurate datas from one of the big books I have related to Spitfire, a very good and complete one indeed. Those are interesting lecture.

Edit
I find no information supporting that the max speed of Mk I & II were measured with more than the rated power at 6 psi of boost.
Apparently the Mk I had 1030 bhp at altitude (either 16,250 or 17,000 ft ?) and Mk II 1150 bhp at 14'500 ft, source "The story of the spitfire" book.

[winny]

Originally Posted by jf1981

In my opinion, we should have the right performance without use of bost cutout, up to my understanding. Octane grade 100 was probably also not available in 1938 for the Mk I prototype. The prototype itself fit with a wooden fixed pitch propeller reached 349 mph TAS at 17'000 ft.

I'll try to get more accurate datas from one of the big books I have related to Spitfire, a very good and complete one indeed. Those are interesting lecture.

Edit
I find no information supporting that the max speed of Mk I & II were measured with more than the rated power at 6 psi of boost.
Apparently the Mk I had 1030 bhp at altitude (either 16,250 or 17,000 ft ?) and Mk II 1150 bhp at 14'500 ft, source "The story of the spitfire" book.

I can add some more to this, the figure that is usually quoted for a MK I Spitfire is 362mph at 18,500. This was referring to K9787, the first production Spitfire, in 1938.
Between then and the BoB there were some substantial modifications that lowered the top speed. A 73 lb armoured plate, bullet proof windscreen, 3mm of light alloy covering for the top of the upper fuel tank, installation of the IFF etc..

The AUW of K9787 was 5,819 lb, the AUW of a BoB period Mk I was around 6,115 lb.

There were also aerodynamic penalties, the IFF aerial was reckoned to cost 2 mph, the windscreen cost upto 6 mph. The top speed of a fully equipped Spitfire in Battle of Britian trim was closer to 350 mph at the same altitude.

Sources - Spitfire The History and Alfred Prices Spitfire in Combat

[jf1981]

Originally Posted by winny

I can add some more to this, the figure that is usually quoted for a MK I Spitfire is 362mph at 18,500. This was referring to K9787, the first production Spitfire, in 1938. [...]

This is right

Prototype K5054 1050 bhp at 16'000 ft at 3000 rpm 6 1/4 psi boost reached nearly 350 mph.

Merlin II engine was 1050 bhp at 6.25 psi boost (octane 87) and 1300 hp at 12 psi boost (octane 100) but shortening lifetime by a factor of 10 (100 hours to 10 hours).

-------------
Mk I

Martlesham Heath, 6 january 1939. K9787. Merlin II performance trials.
Cruising 318 mph @ 15'000 ft
Max spd 362 mph @ 18'500 ft
6.5 min to 15'000 ft (2300 fpm mean)
22.4 min to 30'000 ft

-------------
Mk I
May 1939
295 mph @ 1'000 ft
276 mph @ 20'000 ft
(I assume this is IAS)
-------------
Mk II

Spitfire serial K9788 was tested with merlin XII (the Mk II engine) with following results :

Boost 7 lb 366 mph @ 18,900 feet
Boost 9lb 369 mph @ 16,700 feet
Boost 12 lb 372 mph @ 13,450 feet