BoB Spitfire 100 Octane fuel

[Kwiatek]

Originally Posted by Talisman

BlackSix,

Firstly, thank you very much for all your efforts on behalf of your customers in response to our feedback. This flight sim (please see link below) appears to provide a good example of the Spit 1A with regard to the aircraft flown in the Battle of Britain. Is there any chance that we could have the Spit represented something like this, as it was in the battle with 100 Octane fuel in CloD too? Many flight sim lovers are missing this in CloD at the moment.

http://www.a2asimulations.com/store/solo/spitfire/

For example, the link includes the following statistics for the Spit:

General Information - Supermarine Spitfire Mk IA
The Spitfire Mk IA was the initial production version with some minor modifications. It utilized the Merlin III engine, and with the availability of high-octane fuel, was able to be overboosted to 12 psi of manifold pressure using a boost control cutout. This greatly increased the top speed, but was discouraged in all but the most dire emergencies. In the event, most pilots considered any form of air combat a dire emergency, and the overboosting of the Merlin III became routine. This aircraft also made use of the Rotol constant speed propeller which improved performance substantially as compared to the original, two-bladed wooden props fitted to the Mk IA.
• Empty Weight: 4,999 lbs.
• Wingspan: 36.8 feet
• Wing Area: 242 square feet
• Normal Takeoff Weight: 6,050 lbs.
• Maximum Takeoff Weight: 6,250 lbs.
• Top Speed @ sea level: 289 mph TAS
• Top Speed @ sea level: 340 mph TAS (War Emergency)
• Top Speed: 354 mph TAS @ 20,000 feet MSL
• Top Speed: 410 mph TAS @ 20,000 feet MSL (War Emergency)
• Stalling Speed, clean (6,000 lbs.): 81 mph IAS
• Stalling Speed, landing (6,000 lbs.): 69 mph IAS
• Service Ceiling: 34,700 feet
• Powerplant: Rolls-Royce Merlin III, 1300 HP War Emergency, 1025 HP for takeoff.
• Armament: ( .303 caliber machine guns with 300 rounds per gun.

note the difference in top speed at sea level when boost cut-out is operated. This is the sort of historic experience many of us would like to see when we fly the Spit 1A in CloD; just like when we read the real life combat reports.

Happy landings,

Talisman

Sry Talisman but posted data used by A2Asimulations for Spitfire MK1 are totaly wrong expecially with Emergency Power. Even Spitfire MKIX wasn't such fast

[klem]

Originally Posted by Kwiatek

Sry Talisman but posted data used by A2Asimulations for Spitfire MK1 are totaly wrong expecially with Emergency Power. Even Spitfire MKIX wasn't such fast

As you know Kwiatek, A2A simulations state that their Spitfire MkI is of a particular period March-May 1940 with 2-pitch props, and claim they were light enough to achieve these speeds although they do admit the 410mph in the handbook is a typo, their model doesn't actually achieve that speed. If I can quote them:
"The majority of Spitfire I testing at RAE etc was done pre 12 lb boost.You need to be very careful when analysing tests to match conditions to dates. Most tests done early were only at 6 1/4 and LOW weights, making those aircraft (March 1940) much faster. There was a steady drop off in speed as the marque progressed and the Mk II was slower again. What changed (and what was MUCH more important) was the climb rate.

2 pitch airscrews gave faster speeds than ROTOL (much lighter) but the climb was inferior. Given that climb to altitude was the main problem, the heavier props won out even though they delivered lower speeds. "

As you also know, they do not take the Spitfire MkIX max 335mph max as an indication that their lower powered MkI is incorrect because the MkIX was much heavier and therefore presumably slower.

To me its just more examples of just how complex these issues become without reference to specific configurations and perhaps the A2A configuration and results aren't relevant to what we are trying to get hold of: 100 octane CSP Spitfire Ia's of the BoB period July-October 1940.

I think its best to leave it to the devs to come up with the correct data for the given configuration and loadouts from everything that is available 'out there', or more likely an amalgam of it.

BlackSix has already said that the whole 100 octane/boost matter has been referred to Luthier for consideration.

[Kwiatek]

Originally Posted by klem

As you know Kwiatek, A2A simulations state that their Spitfire MkI is of a particular period March-May 1940 with 2-pitch props, and claim they were light enough to achieve these speeds although they do admit the 410mph in the handbook is a typo, their model doesn't actually achieve that speed. If I can quote them:
"The majority of Spitfire I testing at RAE etc was done pre 12 lb boost.You need to be very careful when analysing tests to match conditions to dates. Most tests done early were only at 6 1/4 and LOW weights, making those aircraft (March 1940) much faster. There was a steady drop off in speed as the marque progressed and the Mk II was slower again. What changed (and what was MUCH more important) was the climb rate.

2 pitch airscrews gave faster speeds than ROTOL (much lighter) but the climb was inferior. Given that climb to altitude was the main problem, the heavier props won out even though they delivered lower speeds. "

As you also know, they do not take the Spitfire MkIX max 335mph max as an indication that their lower powered MkI is incorrect because the MkIX was much heavier and therefore presumably slower.

To me its just more examples of just how complex these issues become without reference to specific configurations and perhaps the A2A configuration and results aren't relevant to what we are trying to get hold of: 100 octane CSP Spitfire Ia's of the BoB period July-October 1940.

I think its best to leave it to the devs to come up with the correct data for the given configuration and loadouts from everything that is available 'out there', or more likely an amalgam of it.

BlackSix has already said that the whole 100 octane/boost matter has been referred to Luthier for consideration.

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.

[klem]

Originally Posted by Kwiatek

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.

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.....

[winny]

Originally Posted by klem

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.....

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!

[klem]

Originally Posted by winny

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!

Just chewing the cud now...

Yes and I actually made a mistake over the K9787 prop - it was a fixed pitch wooden prop, quite light. 5819lbs all up, Merlin II, +6.25lbs, 361mph at 18,000 (360.5 @20k).

K9793 with the MerlinII and the 2-pitch metal prop and weighing only 5935lbs put up 366mph at 20,000 feet.

N.3171 weighed 6050lbs during its tests (231lbs heavier than K9787), Merlin III (same power as II) same boost +6.25, heavier Rotol prop, blown canopy and bulletproof windscreen, 354mph at 20,000. I don't think Alfred Price would argue with that. The ~6mph loss was attributed to the bullet proof screen but I can't help feeling that weight had something to do with it and perhaps the canopy too. Just to keep the Spit/109E comparisons in order, here's that level speed chart again:-
http://www.spitfireperformance.com/spit1vrs109e.html

One final point on N.3171, the speed tests were made at 3,000 rpm but they also reported:
"The results show that the maximum level speed is reached with the airscrew controlling at 2800 engine r.p.m. On increasing the r.p.m. to 3000 the speed was reduced, on the average by 4 m.p.h." So perhaps we could add 4mph to that 354mph result.

And again this shows the danger of just reading off max speeds as gospel. All three aircraft had different weights, different props plus a couple of other bits on N.3171.

[raaaid]

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

[ATAG_Dutch]

Originally Posted by klem

And again this shows the danger of just reading off max speeds as gospel. All three aircraft had different weights, different props plus a couple of other bits on N.3171.

Yep. I've been running some 'time to climb' tests and comparing with Alfred Price's Data, a much better test IMO.

The results with the Ia compared to the IIa are 'illuminating', and they show the CSP Ia performing no better than the DH metal 2-speed prop.

See here if you're interested.

http://theairtacticalassaultgroup.co...=8095#post8095

[Talisman]

Originally Posted by Kwiatek

Sry Talisman but posted data used by A2Asimulations for Spitfire MK1 are totaly wrong expecially with Emergency Power. Even Spitfire MKIX wasn't such fast

Hi Kwiatek,

Thank you for your post. I was not asking for exactly the same as the A2A Spit as I said:

"Is there any chance that we could have the Spit represented 'something like' this, as it was in the battle with 100 Octane fuel in CloD too?"

My point is that CloD appears not to have made any attempt to give us the correct Battle of Brittain Spitfire, or Hurricane for that matter. This is very dissapointing to so many flight sim enthusiasts, as 100 Octane fuel was a long term plan that the British arranged and put into action specially in time for the BoB. As I understand it, along with the Rotal prop and the way radar, air observations and intelligence was used to inform strategy and tactics, 100 Octane fuel was one of the fundamental reasons for RAF success in the air, when so much was against them.

At least on the axis side, CloD appears to have attempted to provide aircraft to the correct specification (if not actuauly achieved flight performance) and does not appear to have missed something so fundamental; of course I stand to be corrected on that as I am no expert and I must say that I have enjoyed being educated by my involvement with this sim and the community. Infact, I have found IL-2 to be a great history lesson for me, particularly on the Eastern front.

Happy landings and 'Salute' all,

Talisman