Ok, so if you were running a spitfire with 100 oct would you have to change the plugs drain the tanks, clean out the fuel pipes etc before putting 87 in it?

What I'd like to know is, once the engine was converted was that it.. Did it stay as a 100 oct only engine? Earlier in the thread there were comments to the effect that they used both fuel types in the same machines. I find this hard to believe.

It's an important point because if it's a big job to change fuels then surely it makes no operational sense to switch, that also would mean that if a spit landed at an airfield other than it's own( a common occurrence during BoB) and they didn't have 100 octane then that's one machine out of action.

Logically this makes no sense. You'd only convert if you were confident that it wouldn't impact on operations. This is speculation on my part, just a thought bubble really.

Sure I did and it is true.

I don't know the plugs authorized for 87 Octane fuel. Do you?

Since 87 Octane is more volatile than 100 Octane, the hotter plugs will work fine but that is a guess.

Most importantly, a set of plugs is much cheaper than Avgas especially in a WWII Fighter; they are even cheaper than a tank of oil. The RAF would save a considerable amount of money if they ran units on rest and refit status on 87 Octane as noted in the January 1942 Operating Notes.

That is exactly why they note other units not on operational status, 87 Octane!!


I know you’re trying to be sarcastic but maybe you can see things from a more grounded perspective.

This idea that a squadrons will run one fuel for a test flight in say the morning and then go through all the changes in the afternoon for an operational mission then reverse the whole thing for an engine test is simply not a goer. The effort and potential for a mistake and or conamination is just too great

When you look at the OOB some squadrons are down as operational and others as non operational. I am confident that operational squadrons would have used 100 octane and non operational squadrons 87 octane

When a squadron was rotated North they didn't become non operational, they could still be called on for missions but the chances of combat were much reduced. Some squadrons that had very heavy losses sometimes were deemed non operational but that wasn't the norm.

Bases normally held some 87 octane for aircraft passing through, station hacks, squadron communication aircraft and the like but the aircraft that could be used on ops would have been well looked after and besides at the height of the battle you couldn't take the chance of being caught on the ground changing fuel.

I don't know the plugs authorized for 87 Octane so I can't tell you. It is a possibility. I can tell you if you could do it, it would noted in the operating instructions or the maintenance manuals.

I can also say, you could not use +12lbs boost if you contaminated the system with significant amounts of 87 Octane.

I think you are beginning to see the maintenance nightmare airplanes can be even with something as simple as putting new gas into them!!

:grin:

If I wanted to convert and it was not possible to convert the entire force, the first thing I would do is get as much 100 Octane gas to the airfields as I could before anyone converted. Then my conversion pool has a supply of gas.

In theory, the operating limits of the engines were not raised no matter which avgas you put in it. As long as you did not use +12lbs with 87 octane gas, you sould be ok with an engine modified for 100 Octane.

There is a thing called a ferry certificate that covers things like this in aviation. Depending on the technical issue, it can be complicated or very simple to get one. I am sure in the RAF, something like this was a phone call to the Maintenance officer who did the paperwork and approved it in order to ferry a plane back under special conditions.

Typically you can always go higher in octane but never lower in piston engines but airplanes are not typical. In airplanes each installation even of the same engine type is different. You generally can't tell much about the Merlin in a Hurricane by looking at the Spitfire's instructions for example. That is why the Air Ministry tested both types.

Your 87 Octane engines in theory could run without incidence on 100 Octane. It would be specified in the Pilots Notes and the fuel tank placarded for all fuel types authorized for the aircraft.

As far as I'm concerned, Crumpp is American, which means his PPL was easy and cheap. He wouldn't be able to afford it or understand it in England. He can't even drive a car with a manual gearbox.

On the other hand, you are a snoodler with nothing above your cerebellum. If I were to weigh your head, it would be much lighter than average, you don't come out very well.

All very well and good - how about finding some documentation confirming your speculation about the RAF using 100 Octane for nothing more than operational trials?

Was there enough 100 octane fuel available to allow all operational frontline units to fly all defensive sorties flown throughout the battle - yes or no? If no why not - with documentation.

Why would you do that Glider? I don't think anyone is saying that.

What would be worth it to do is change the fuel type when the units rotated out for rest and refit. They are not doing any operational flying under that status and unless they had an additional mission to gather data on the fuels use, there is no reason to continue to use 100 Octane. I am sure maintenance trend data over as many hours of flight time was required before the entire force converted but you don't need it from every squadron.

Crumpps steps to conversion.....

If I wanted to convert and it was not possible to convert the entire force, the first thing I would do is get as much 100 Octane gas to the airfields as I could before anyone converted. Then my conversion pool has a supply of gas.

The next thing I would do is convert as many squadrons as possible to be able to use 100 Octane. That timeline is going to be based on how fast the parts required can enter the system and reach the point of use. I would convert as many aircraft as possible without violating the required logistical ratio so my airplanes can continue to fly and I am not without airplanes due to maintenance awaiting parts. Now I have pool of capable aircraft.

As much as possible all of my operational squadrons using 100 Octane would be down in 11 Group in the thick of the action.

If logistics said I only had enough fuel for 16 squadrons by September then you can bet when a squadron rotated out for rest and refit, they would go back to 87 Octane and their replacement would come from that pool of converted units.

As logistics increased my usable fuel supply, I would add operational squadrons to other areas until the entire force was converted.

How about some documentation supporting your claims?

The fact the RAF did not complete conversion to 100 Octane until around January 1940 is evident in the Operating Notes.

The documentation is posted and been posted several times.

What I said is what I see in all the documentation posted in this thread.


It is a fact the RAF did not complete conversion to 100 Octane until around January 1940. That is evident in the Operating Notes.