BoB Spitfire 100 Octane fuel

[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

[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.

[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

[NZtyphoon]

From Price The Spitfire Story (Haynes, 2010, p. 106) - Spitfire I N3171 with the CSP was tested in March 1940, and wasn't fitted with armour plating, and IFF; the CSP was heavier than the two-pitch, by about 115 lb, so this and the other added weight would have pulled back climb performance, as described by ATAG_Dutch

The main benefits of the CSP were a greatly improved take-off distance (Two pitch: T/O 320yds, 490 yds to clear 50 ft screen versus 225 yds, and 370 yds respectively). It also meant the pilot didn't have to remember to change the pitch settings, and there was less strain on the engine.