Originally Posted by Kwiatek (Post 390643)

Dont belive that 2-pitch prop cause such huge difference like in data tou posted.


Here is RL analys between Spitfire MK1 with 2-pitch metal prop DH ( plane without aditional armour - so much lighter) and with Rotol constant speed prop ( plane with aditional armour, armoured windshield etc - so much heaveir)

" Conclusions.

1. This aeroplane has a much better take-off and climbs faster than other Spitfires fitted with wooden fixed pitch or metal two pitch airscrews.

2. There is a drop of 13 m.p.h in maximum level speed compared with the 2-pitch airscrew aeroplane but of this, 8 m.p.h. can be attributed to sources other than the airscrew.

3. Below full throttle height an increase in speed of about 4 m.p.h. can be attained by controlling the engine R.P.M. at 2800 instead of 3000.

4. The limiting diving speed can be reached much more rapidly with this aeroplane than with Spitfires fitted with fixed pitch wooden and 2-pitch metal airscrews. "

http://www.spitfireperformance.com/n3171.html


Spitfire MK1 with 2-stage DH prop (without addition armour) reachedmaximum speed - 367 mph ( 590 kph) at 18 600fy

Spitfire MK1 with Rotol ( with aditional armour) reached maximum speed - 354 mph ( 570 kph) at 18 900 ft.

So in level speed it would be only a few mph difference if both would have the same aditional armour.


In CLOD now only biritish fighters have huge performacne error but German ones too - 109 is also too slow plane according to RL data.

Originally Posted by klem (Post 390729)

I'm not sure where we're going with this Kwiatek.

The conclusion says that there is a drop in max speed with the Rotol vs 2-pitch. I think thats what A2A are saying.

In Tests 18th Aug - December 12th 1938 K.9787 MerlinII, DH5-20 returned 361mph at 18,000 feet, boost +6.4.

That report you linked says that Merlin III engined MkI N.1371 with Rotol achieved 353.5 (~354)mph TAS at 20,000 feet/3,000 rpm/Boost dropped off to 5.25. Actually thats the top speed at altitude A2A are claiming for their Ia.

This seems to be what the devs should be looking at:
http://www.spitfireperformance.com/spit1vrs109e.html

Anyway, we could go round and round for ever.....

Originally Posted by winny (Post 390735)

There is a slight problem with k9787 ( 1st production Spitfire ) as a reference for mk 1a's. It was much lighter than a mk 1 in BoB trim. All up weight of k9787 was only 5819 lb, mk 1 in BoB trim 6155 lb ( source Alfred Price Spitfire in combat). It didn't have the bullet proof windscreen, which cost 6 mph, the IFF aerials cost about 2 mph, no armour plate.. Etc.

Top speed according to price of a fully equipped mk 1 in the summer of 1940 was nearer 350 mph. It's a minefield! :)

Originally Posted by raaaid (Post 390801)

well the bigger the better is not true check this wiki on octanes:

Octane" is colloquially used as a short form of "octane rating" (named for the ability of octane's branched-chain isomers, especially isooctane, to reduce engine knock), particularly in the expression "high octane". However, components of gasoline other than isomers of octane can also contribute to a high octane rating, while some isomers of octane can lower it, and n-octane itself has a negative octane rating

edit:

for what i know the antiknokcing charachteristic dpened on what kind of engine

so the fuel is syn with engine, normally revolutions

i just learnt it can even be negative

edit:

imagine i fuel creates a flame tongue in 0.1 seconds
the sync so the fuel doesnt expand while the piston contract and knoks depends on the speed of it

the antiknocking chararacthericstics of fuel that is the octanes determines how much does it take to burn