The use of 100 Octane Fuel in the RAF pt 2

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The one question that often knocks them off balance is, if C3 was so popular, effective and plentiful why was the DB605 designed for lower octane fuel.
 
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.
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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.
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I should have emphasised that some publications have cited 100 octane as being critical without mentioning the use of constant speed props.

The story of the props is interesting because, as most of us know, the original de Haviiland unit fitted to Hurricanes, Spitfires and Defiants was a two speed unit. In June 1940 de Havilland manufactured conversion kits which turned the two speed propeller into a constant speed unit; these kits were fitted to all frontline de H props by de H specialists in a "crash" conversion programme which lasted about a month (McKinstry Spitfire: Portrait of a Legend 2007 page 172.) Some Hurricanes were already fitted with Rotol CS propellers and there were two squadrons (19 and 54 Sqns) of Spitfires using these units in May. The Rotol units were also fitted to Spitfire IIs and the small number of Hurricane II's which started operations in September.
 

Thanks for sharing the full scans (mine was from a library book), yes no doubt there're similar tales out there - I remember my Father telling me he had 100 octane in his cigarette lighter - and he was based in Gosport.
Going back to Tim Vigors - I loved the piece about sanity towels and the Brewster Buffalo - did I laugh at that!!
 
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The addition of these technical factors to the aircraft can make a nonsense of informaiton from any reference book regarding max speed of the Spitfire Hurricane - becasuse it depends, when and with what added! So you need:
A, 1939 Spitfire Hurricane - max speed?
B, 1940 ........ ditto ....... ... ditto ... - with CS prop,
C, 1940 ......... ditto ..... ..... ditto ... .... ditto .. 100 Oct ?
 

Mike Williams has provided two graphs comparing the performances of Spitfires and Hurricanes using +6.25 lbs and +12 lbs boost #171.

Alfred Price The Spitfire Story shows the following:

Spitfire I K9793 (de H two speed propeller, no armour, no IFF)

Service ceiling: 34,400 feet
Take-off run (0 wind): 320 yards: clear 50 feet: 490 yards

Height/Max Speed/Climb

18,600: 367 mph: 1,700 ft/min
20,000: 366 mph: 1,305 ft/min

Spitfire I N3171 (Rotol C/S propeller, no armour, no IFF)

Service ceiling: 34,700 ft
Take-off run: 225 yards: clear 50 feet: 370 yards

Height/Max Speed/Climb

10,000 feet: 320 mph: 2,895 ft/min
15,000 feet: 339 mph: 2,430 ft/min
20,000 feet: 353 mph: 1,840 ft/min

The major improvements in T/O distance and climb rates can be seen; the de H C/S speed conversion kit would likely have given similar figures: It would be interesting to know how much heavier the C/S de H prop unit was after conversion. More details Spitfire Mk I N.3171 Trials Report
 
On Spitfire props
The original fixed pitch 2-bladed wooden, installed at factory to first 77 production Spits. 83lb/38kg.
de Havilland two speed propeller 350lb/159kg
Rotol C/S propeller 500lb/227kg.

Source:Alfred Price Spitfire MarkI/II Aces

One main impact of CSU was that it made fighting clearly easier, Pilot didn't need to worry on pitch when moved from horizontal flight to climb/dive and back to horizontal etc. And especially CSU didn't have time or height limits as the higher boost allowed by 100oct fuel.

And German fighters also had CSU, IIRC from 39 onwards at latest. British fighters got them by crash operation during Summer 1940. Before that Blenheims had had priority for CSUs

Juha
 
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Actually the max speeds at rated altitude were very similar.

See the tests refered to in the above posts.

It was the take of and climb that showed tremendous advantages.

Think of the propellor as the gearing in a car. The fixed pitch prop would be locked in high gear. A two position prop would be a 2 speed car and the VP or constant speed propeller would be a car with many speeds in it's transmission but with the same top gear ratio.

Fighters had a good enough power to weight ratio to get by starting in "top" gear which is why the available V-P propellors went into bombers in 1939. Try starting a loaded truck in high gear
 
NZTyphoon said:
I should have emphasised that some publications have cited 100 octane as being critical without mentioning the use of constant speed props.
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Hi NZTyphoon

I take your point that 100 octane fuel by itself may not have made the critical difference, however, in as much as my interest in this instance is in the performance of the aircraft that fought in the Battle of Britain, its doesn't make much sense to me to separate out the various modifications/improvements such as fuel and propellers since the performance obtained was a function of both in this case.

As the following 1944 excerpt from Flight demonstrates, folks have been arguing this point before the war was even over.

 
Hi Juha:


I concur with your assessment as to the merits of the CSU. Regarding the crash program, you may find the following of interest:

F/O Paul Richey, 1 Squadron, 15 May 1940, France:
Paul Richey DFC, Fighter Pilot (Redwood Press, Wiltshire 1990) p 93.


F/Lt I. R. Gleed, 87 Squadron, 19 May 1940, France:
W/C Ian Gleed D.F.C., Arise to Conquer, (Random House, New York 1942) pp. 62-63.










242 Squadron, June 1940
Hugh Halliday, No. 242 Squadron, The Canadian Years, (Canada's Wings, Ontario, 1981). p.78.


242 Squadron Hurricane in France with Rotol constant speed propeller.


32 Squadron Hurricane with Rotol constant speed propeller at Hawkinge, 29 July 1940.


501 Squadron Hurricane with Rotol constant speed propeller at Anglure, France during May 1940.


Conversion of Hurricane Two Pitch Airscrews to Constant Speed











 
Hello Mike
and thanks again for those ORB pages!
Very much appreciated.

Yes, it would have been more accurate to write that also the older fighters in front-line units also got their CS props during the Summer 40, installed by teams sent by manufactures.

Juha
 
IIRC the teams went to each airfield and there was a four stage process.
1) The team would show the ground staff how to convert the first aircraft
2) Get the ground crew to help with the second aircraft
3) Watch the ground crew do the third aircraft.
4) Then comment on the ground crews performance and leave them to do the rest while they moved on to the next airfield.

In this manner all the aircraft were quickly converted as each team only spent one day at each airfield.
 
Hello Glider
Yes, when I checked the system from Morgan's and Shacklady's Spitfire bible, according to them it went like that, and all teams were from de Havilland.

Juha
 
Interesting information Mike: the letter alone confirms that the British knew that 100 octane fuel was in general use in RAF fighters in 1940. I'll see if I can find that "Pitch Panic" article.
Here 'tis:
http://www.flightglobal.com/pdfarchive/view/1943/1943 - 2888.html

I note the variety of MUs mentioned as holding the Rotol Spitfires for 54 Sqn; 6 MU, 9 MU and 24 MU with the majority coming from 6 MU. 611 Sqn experimented with a Spitfire fitted with a "Cottonised" PR canopy with perspex blisters and mirrors. All sorts of interesting details.
 
I don't think the name 100 octane was in very common use amongst the troops initially
I believe it was just refered to by colour which was green
 
Hello NZTyphoon
very interesting article, and that clearly have been the source of Morgan and Shacklady, wording is so similar. But in the article there are mistakes, for ex Mike's photos on ORBs clearly show that already on 1st Nov 39 19 Sqn got a Spit with CS propeller for testing and some sqns got Hurricanes with CS propellers while in France.

Juha
 

Hi Juha,
Yes, the article doesn't mention the Rotol props for some reason, yet Flight was describing Rotol C/S units in 1937:
http://www.flightglobal.com/pdfarchive/view/1937/1937 - 1732.html
and 1939
http://www.flightglobal.com/pdfarchive/view/1939/1939 - 0834.html

Mind you, we are getting off topic. In this article there is mention of Merlin engines using 100 octane fuel and de H constant speed propellers in December 1938.

walter sagitta | de havilland | 1938 | 3453 | Flight Archive
 
Glider said:
Very good piece NZ, it shows what can be dne when people knuckle down and get on with things.
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Hi Glider,
I started exploring the Flight archives a few months ago; there is some really good information available that, in some cases, I have not seen in print elsewhere.
 

Exactly! Thanks Juha! Thanks for posting that article NZTyphoon. Just as Juha noted, that seems to be the source for other recounting of that story, including Morgan Shacklady. Clearly the article was written from the De Haviland point of view. A huge omission in the article is the contributions of Rotol. 65 Squadron, which S/L Cooke led, was based at Hornchurch along with 54 and 74 Squadrons (quite a few other squadrons having rotated through during the Dunkirk evacuation). All 54 Squadron Spitfires had been equipped with the Rotol constant speed propeller since December 1939 so Cooke must have known all about its advantages. Documentation in post 186 clearly shows new Hurricanes were equipped with Rotol constant speed units and delivered to Squadrons by at least by April 1940. This is not meant to diminish de Haviland's retrofit program but there is another side of the story not often told.
 
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