The use of 100 Octane Fuel in the RAF pt 2

[NeilStirling]

I think its worth posting this, it may have been posted before

http://www.wwiiaircraftperformance.org/100-octane/100oct-consumption-bob.jpg

 

[Juha]

OK Kurfürst
A simple question, let's assume that you are right and only ¼ of FC fighters used 100oct, and to make the case a little bit less obvious lets assume, that they were more active than those sqns using 87 oct fuel and used 1/3 of the fuel consumption of FC, so June –Aug FC would have used 10.000tons 100oct and 20.000tons 87 oct, in Sept 14.000 tons 100oct and 28.000 tons 87 oct. and so on. Ups, the real other than 100 oct fuel consumption was clearly less than that presumed FC's 87 oct consumption. So, what you think all those trainers, bombers, Hudsons and 4-engined Sunderlands used? Plus of course those fighters to which there was not enough 87oct?

Juha

 

[NZTyphoon]

The calculations by NZTyphoon only take account the actual combat sorties, but ignore the training flights during which the more seasoned pilots initiated fresh replacements into combat flying, and integrated them into the unit.

This was one of Fighter Command's biggest weaknesses through into 1941; there was little "on the job training" utilised by squadrons, particularly during times of intensive operations. As a consequence many pilots arriving fresh from training were flung straight into combat with little initiation. In brief - there was little Squadron level training and OTUs were not properly organised until 1941. Johhnie Johnson, for example, described how he arrived on an operational squadron in late September 1940 only to find that as a tyro he was ignored by the experienced pilots. He did not receive additional training until he was transferred to 616 Sqn in October.

 

[Mike Williams]

Hi Merlin:

And another (though it may have already have been quote) - from Tim Vigors autobiography - 'Life's too short to cry': - p.137

Driving through London we saw little traffic. Petrol rationing had, by this time, really started to bite. It had not affected us pilots too badly as, quite illegally, we used to top up the tanks of our cars from the petrol bowsers used for refuelling aircraft. As long as this was done reasonably discreetly the authorities kindly turned a blind eye. What effect 100 octane fuel was having on the pistons and cylinders of my Ford 8 remained to be seen. so far EGO (part of the car's no plate) was still going like a bomb. in fact the diet seemed to suit her.

I've read similar stories along those lines. Here's one from Tony Bartley of 92 Squadron followed by a scan of the Vigors reference you mentioned:

Tony Bartley DFC, Smoke Trails in the Sky, (Crecy Publishing Limited, Wilmslow, Cheshire, 1997), p. 35.

Tim Vigors DFC, Life's Too Short to Cry, (Grub Street, London, 2006), p. 137.

I'm fairly certain I've a few more around like these; I just have to dig them out.

 

[NZTyphoon]

Strolling through the Flight Global archives I came across this article from June 1945; the last paragraph of page 612 and the first sentence of 613 are interesting:

The Air Ministry had the foresight to realise the critical importance of high-duty fuels, and this led to the issue of a specification for 100 octane in March, 1937—sufficiently before the war to enable our fighters to use it from the very start, although it did not come into general use throughout the whole of the R.A.F. until August, 1940.

This accords with the August 7 paper presented elsewhere http://www.wwiiaircraftperformance.org/100oct-7aug40-allcommands.jpg; now, assuming that this took some time to come into full force it is noticable that consumption of "Other Grades", (87 octane) of fuel drops off cf 100 octane starting in September:
Sep - 100 octane = 14,000 tons; 87 = 23,000 tons
Oct - 100 octane = 17,000 tons; 87 = 18,000 tons
Nov - 100 octane = 15,000 tons;87 = 13,000 tons
Dec - 100 octane = 16,000 tons;87 = 11,000 tons

By the winter of 1940 the amount of air activity declined - the changes in fuel consumption fits the pattern that more RAF aircraft were starting to use 100 octane while use of 87 declined. By April 41 both 100 octane 87 show 22,000 tons each, coinciding with the time that fighters such as the Beaufighter and Whirlwind and heavy bombers such as the Stirling, Halifax and Manchester were coming into service - training was also being reorganised (I'm not sure when OTUs came into being) . Just another peice in the jigsaw of proper historical research.

 

[parsifal]

One way to control a debate that a person does not agree with is to act so obnoxiously as to get that thread closed. At least then the conclusions being drawn in that thread wont continue to be analysed and the things upsetting to a member are no longer in his face so to speak.

This is really sad, because for most of us the debate is engaging, the information being brought forward detailed and interesting. I would suggest that when someone is deliberately acting to get a thread closed, the best thing that the rest of us can do is simply to pay no attention to the trouble maker. This is not a luxury open to the mods, my comments are for the members, including those causing the trouble and those reacting to it

 

[NZTyphoon]

There are some points worth raising about how the availability of 100 octane fuel affected the performance of RAF fighters: According to Alfred Price:

The higher octane fuel allowed an increase in supercharger boost from +6 lbs to +12 lbs, without risk of detonation that would damage the engine. A pilot could select the additional boost for five minutes by advancing the throttle 'through the gate' to the fully forward position. The emergency power setting increased the maximum speed by 25 mph at sea level and 34 mph at 10,000 feet. It also improved the fighter's climbing performance between sea level and full-throttle altitude. (Spitfire Mark I/II Aces 1939-41 page 19)

According to Alex Harvey-Bailey The Merlin in Perspective - the combat years the Merlin III generated 1,310 hp at 9,000 feet using +12 lbs compared with its normal rating of 1,030 hp using +6 lbs at 16,250 feet. There do not seem to be any + 12 lb figures for the Merlin XII of the Spitfire II or the Merlin XX of the Hurricane II.

Points worth noting:
1: So far I have not seen an analysis of how often +12 lbs boost was used during the battle - ie: how often did pilots resort to going through the gate and in what circumstances?

2: Con: The critical altitudes at which the +12 lbs boost had the most effect were well below the Merlin III's usual full-throttle height of about 16,000 feet - much of the combat during the battle took place at higher altitudes.

Pro: Even so the provision of 100 octane gave pilots an option during attack or evasion - the combat reports show that Luftwaffe aircraft were caught and shot down at lower altitudes after RAF pilots went through the gate; of course it would be impossible to know how many Luftwaffe aircraft were shot down or damaged because RAF fighters were able to use the extra boost, without going through every single combat report from both sides. Similarly it would be interesting to know how many RAF pilots lived to fight another day because they were able to use the extra boost.

3: Con: Pilots were limited to +12 lbs for a maximum of five minutes: if the extra boost was used pilots had to note this in the engine log book because it was considered to be an extra load on the engine. The engine mechanics had to check the engine and replace the wire to the throttle gate.

Below please find documentation related to 100 octane use by the RAF leading up to and during the Battle of Britain:
Emergency +12 lbs./sq. in. Boost Operation: Pilot's Notes, Merlin II, III and IV, 4th Edition, April 1940, page 6.

Mike Williams # 48. Apparently Morgan and Shacklady say that the life of a Merlin engine dropped from c. 100 hours to 10-20 hours - no documentary evidence provided, however.

Pro: Five minutes may not seem a long time, but in air to air combat where encounters usually lasted less than 1 minute it was more than enough.

Overall I would suggest that at times the effect of 100 octane fuel on the Battle of Britain in particular has been overstated. In some publications it has been cited as being critical to the outcome. However, because the performance increases conferred on RAF fighters was below the heights at which most combat took place it would have only been effective in a limited number of situations. Because it provided RAF pilots with options they would have otherwise lacked, the provision of 100 octane fuel was a valuable added tool, but not absolutely critical.

 

[Glider]

There are some points worth raising about how the availability of 100 octane fuel affected the performance of RAF fighters: According to Alfred Price:


According to Alex Harvey-Bailey The Merlin in Perspective - the combat years the Merlin III generated 1,310 hp at 9,000 feet using +12 lbs compared with its normal rating of 1,030 hp using +6 lbs at 16,250 feet. There do not seem to be any + 12 lb figures for the Merlin XII of the Spitfire II or the Merlin XX of the Hurricane II.

Points worth noting:
1: So far I have not seen an analysis of how often +12 lbs boost was used during the battle - ie: how often did pilots resort to going through the gate and in what circumstances?

All we do know is that Downing sent a note to all units reminding them that they should not overuse the extra boost.
As for the circumstances the following link gies some examples. Spitfire Mk I versus Me 109 E

3: Con: Pilots were limited to +12 lbs for a maximum of five minutes: if the extra boost was used pilots had to note this in the engine log book because it was considered to be an extra load on the engine. The engine mechanics had to check the engine and replace the wire to the throttle gate. Mike Williams # 48. Apparently Morgan and Shacklady say that the life of a Merlin engine dropped from c. 100 hours to 10-20 hours - no documentary evidence provided, however.

They were limited to five minutes but this was often exceeded. Also it didn't have to be one five minute burst per flight. If they allowed a cooling off period this could be repeated. I will need to find the quote but I am sure that to pass the RAF tests this flight cycle was repeated by Rolls Royce and the engine lasted about 1.5 hours at 12 lb boost before failing. I should emphasise that this is from memory only and it was over a considerable number of flights.

Overall I would suggest that at times the effect of 100 octane fuel on the Battle of Britain in particular has been overstated. In some publications it has been cited as being critical to the outcome. However, because the performance increases conferred on RAF fighters was below the heights at which most combat took place it would have only been effective in a limited number of situations. Because it provided RAF pilots with options they would have otherwise lacked, the provision of 100 octane fuel was a valuable added tool, but not absolutely critical.

I don't know about Crtical but I would cetainly say very important not just for the reasons you stated but simply because of the better climb performance. Intercepting is about speed but as important is climb, if you cannot get up to the attacking bombers you don't intercept them and you are a sitting duck for the escort.
A thirty percent increase in power plus the extra efficiency of the Constant Speed Prop is something any fighter pilot would give their right arm for. Imagine the impact on the car you drive let alone a fighter plane.

 

[NZTyphoon]

I don't know about Crtical but I would cetainly say very important not just for the reasons you stated but simply because of the better climb performance. Intercepting is about speed but as important is climb, if you cannot get up to the attacking bombers you don't intercept them and you are a sitting duck for the escort.
A thirty percent increase in power plus the extra efficiency of the Constant Speed Prop is something any fighter pilot would give their right arm for. Imagine the impact on the car you drive let alone a fighter plane.

Yup, improved climb and improved take-off performance were both important.

They were limited to five minutes but this was often exceeded. Also it didn't have to be one five minute burst per flight. If they allowed a cooling off period this could be repeated.

Good point; also note that the pilot didn't have to use up the five minutes in one go; he could (for example) use 5 'squirts' of 1 minute each.

I will need to find the quote but I am sure that to pass the RAF tests this flight cycle was repeated by Rolls Royce and the engine lasted about 1.5 hours at 12 lb boost before failing. I should emphasise that this is from memory only and it was over a considerable number of flights.

I have seen this information as well - couldn't say where.

Please note I am not trying to understate the importance of 100 octane and +12 lbs boost - one intangible worth thinking about is the effect on the morale of RAF pilots knowing (for example) that they could call on the extra power when being chased at low level by angry 109s. However, there were limitations to its use that are worth considering, as well as the benefits.

 

[Shortround6]

Combat may have started well above the altitude at which 100 octane provide an advantage but the combats often decended to altitudes were it did, indeed some combats id wind up down at sea level.

The 100 octane advantage could be simply that a British pilot and plane escaped to fight another day or that a German pilot and plane didn't get back across the Channel. Enough of these little differences added up over time could mean quite a difference in the odds after a month and half.

 

[NZTyphoon]

Combat may have started well above the altitude at which 100 octane provide an advantage but the combats often decended to altitudes were it did, indeed some combats id wind up down at sea level.

The 100 octane advantage could be simply that a British pilot and plane escaped to fight another day or that a German pilot and plane didn't get back across the Channel. Enough of these little differences added up over time could mean quite a difference in the odds after a month and half.

One pilot who benefitted was Al Deere: On 12 August he shot down a 110 over the channel only to be attacked by a 109; Deere escaped using +12 boost. Three days later Deere unwittingly chased a 109 across the English Channel only to find himself near Calais/Marck airfield and in the sights of two 109s who decided to chase him. Deere escaped across the channel only to be forced to bale out. Although he doesn't mention using +12 in his book, I presume he did? I will endevour to find out...

 

[Mike Williams]

Hi bigZ:

In "I kept no diary" by Air Commodore F.R Banks. He mentions that he gave a paper in Jan of 37 in which he pleaded for the development of British military engines to take 100 octane fuel. Which despite critical opinion from oil company representatives the Director of Technical Development of the British Air Ministry agreed with his paper.

"So by 1940 the Merlin's power was increased by this fuel from a combat rating of 1,000(plus) bhp to over 1,300 bhp, and 100 octane became available to Fighter Command ready for the BOB..."

"In June 1930, only 3 months before the start of WWII, a company tanker, the Beaconhill, set sail across the Atlantic for the UK. with a full cargo of 100 octane fuel. We began stockpiling this fuel though the decision to use 100 octane for Fighter Command was not made until March 1940 and that for its use by Bomber Command came in 1941."

The author also suggests for more detailed information:-

Milestones in Aviation Fuels by W.G.Dukek, D.P Winans and A.R.Ogston. Paper given at A.I.A.A. Designers and Operators meeting, July 1969, Los Angeles.

Sorry I couldn't scan the extract as I am still unpacking after my relocation to NZ.

Thanks for sharing that information. Here are the scans confirming your post. Other members might find the information of interest.

Air Commodore F. R. Banks, I Kept No Diary , Airlife Publications, Shrewsburg, 1978, Appendix II Fuel pp 234-236

Here also is the relevant portion from the Dukek paper that Banks referred to:

 

[109ROAMING]

Although he doesn't mention using +12 in his book, I presume he did? I will endevour to find out...

Let me know how you go with that , I assume your referring to his autobiography?

I have his biography so let me know if your unsuccessful there and Il take a look and see what I can dig up

If you've got both books then sweet!

 

[mhuxt]

Thanks for posting that Mike. Is the blend for Mosquito Merlins referred to above distinct from 150-octane?

 

[Njaco]

Can I ask a rather stupid, dumb question? What exactly is the importance of 100 octane fuel as compared to others? It seems to me at least, that an increase in power, however small or large, doesn't really warrant this much controversy. Can someone explain this to me?

 

[Mike Williams]

Hi NZTyphoon Glider:

Overall I would suggest that at times the effect of 100 octane fuel on the Battle of Britain in particular has been overstated. In some publications it has been cited as being critical to the outcome. However, because the performance increases conferred on RAF fighters was below the heights at which most combat took place it would have only been effective in a limited number of situations. Because it provided RAF pilots with options they would have otherwise lacked, the provision of 100 octane fuel was a valuable added tool, but not absolutely critical.

I don't know about Critical but I would certainly say very important not just for the reasons you stated but simply because of the better climb performance. Intercepting is about speed but as important is climb, if you cannot get up to the attacking bombers you don't intercept them and you are a sitting duck for the escort.

I would characterize the use of 100 octane fuel during the Battle of Britain as conferring a significant performance increase relative to performance while using 87 octane. I think one could argue that, when taken together, 100 octane fuel, constant speed props and pilot armour incorporated just before the Battle of Britain were indeed critical to the success of the RAF. Take- off, climb, level speed, acceleration and turn would all have improved with the increased boost made possible by 100 octane fuel. Let's just look at level speeds for the moment.

Comparing A.&A.E.E. data of a Spitfire I operating at 6.25 lbs/sq.in. against R.A.E. data of a Spitfire I operating at 12 lbs./sq.in. shows an increase of speed of 31 mph at sea level and 18 mph at 15,000 feet obtained through the use of 100 octane fuel and 12 lbs. boost.

Comparing A. A.E.E. / R.A.E. data of a Hurricane I operating at 6.25 lbs.sq.in. against Hawker data of a Hurricane I operating at 12 lbs./sq.in. shows an increase of speed of 22 mph at 5,000 feet and 26 mph at 10,000 feet which extrapolates to an increase of approx. 20 mph at sea level and 9-10 mph at 15,000 feet obtained through the use of 100 octane fuel and 12 lbs. boost. RAE tests showed a gain of 31 mph at 5,000 feet 29 mph at 10,000 feet with 12 lbs boost.
.

 

[Mike Williams]

Thanks for posting that Mike. Is the blend for Mosquito Merlins referred to above distinct from 150-octane?

Hi Mark:

That piqued my curiosity as well. I don't know the answer to your question but it certainly deserves looking into. The Ministry of Aircraft Production Grade 100/150 specification states that 100/150 grade fuel contained mono-methyl-aniline not exceeding 2½ per cent by volume. Banks notes the Mosquitoes used fuel containing 8 percent mono-methyl-aniline. Gracious…

 

[parsifal]

Can I ask a rather stupid, dumb question? What exactly is the importance of 100 octane fuel as compared to others? It seems to me at least, that an increase in power, however small or large, doesn't really warrant this much controversy. Can someone explain this to me?

Hi NJ

It has a lot to do with revisionist history. The "pro-allied" camp in this debate are saying that 100 Octane was in widespread use in the RAF from an early stage, and that this made a huge difference to the performance arcs of the spits and hurricanes that used it. It is pretty well known that the Luftwaffe only used higher rated fuels on a very limited scale, and that this only chnged relatively slowly as the wasr progressed. The allies on the other hand embraced the widespread use of high octane fuel from an early stage. Whilst german fuels were comparable in their octane ratings, they were never fully adopted on a widespread scale, or at least on not a wide a scale as the allies did.

By arguing that 100 octane rated fuel was not widespread, the pro-german revisionists can argue with even greater conviction the superiority of german technology over the allied tech development, and that the allies only won because of brute strength. A variation to the "we were stabbed in the back" argument that gained so much favour in weimar germany after wwi, and assisted the Nazis in their rise to power.

At least thats how i sees it.....

 

[claidemore]

well said parsifal.

 

[Njaco]

Thanks Parsifal. I was just curious why such a small thing as fuel type would create such a furor.