BoB Spitfire 100 Octane fuel

[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

[BRIGGBOY]

Good thread Talisman its about time we got the mk ia fixed. I do appreciate that the 109 is under powered when it comes to top speed as i do like to fly them now and again but a hurricane faster than a spit is just not on.

[klem]

Originally Posted by 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

You're just trying to confuse me aren't you

[335th_GRAthos]

I admit defeat!

[raaaid]

well i understood this in my classes but most of the time i was daydreaming so maybe im mixing things

[Skoshi Tiger]

Good point Raaid.

There is nothing in the 100 Octane fuel that produces extra Horse Power, but it does allows the engine to run in the conditions where the motor can produce more HP. (if that makes sense????)

For example, my valiant with it's 10:1 compression needs 98 octane petrol to run smoothly in all conditions. if I run it on standard unleaded (91 octane) it will ping and knock at even low RPM and is unpleasant to drive at any speed. Using 95 octane I can drive at regular city road conditions, but will get pinging only when I try to flog it!

For true motoring bliss I need the 98 octane fuel to use the entire range of RPM and power in my engine.

AFAICMO, the modifications performed to the Merlin to realise the benefits of 100 octane fuel were in the delivery system to allow the engine to run at the higher boost. The changes to the actual engine were minimal and more for reliability rather than increased power.

Cheers!

[WTE_Galway]

The advantages of the massive stockpile of 100 Octane the British built up before and through the war should not be underestimated.

As an example, the DB605 in Luftwaffe service produced 1450 hp with B4 (87 Octane) and needed Mw50 to achieve more power. The same DB605 running 100 Octane with the Swedish air force produced 1700 hp without needing MW50.

Of course with 100 Octane MW50 would not have have had near as much effect as it is basically an anti-knock agent.