Bf 109 F series

Shortround6 said:

If they all laughed then you asked the wrong question.

IF you run an engine on 87 octane fuel and set it up correctly and then switch to 100 octane and do NOTHING to the engine you will get a ZERO PERCENT increase in power. ALL these men are quite correct.

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Good one.

I used to have a Subaru WRX (great car) and the engine control computer would adjust the power depending on the fuel. Rated for 98 octane you could (in an emergency) run it on 95 octane. Plus here in Australia there are some significant variations between the different 98 octane suppliers, one in particular was renowned for being a bit dodgy while BP's was excellent. And yes you could feel the difference between them.
The best I found was actually one of the cheapest with 10% ethanol, trouble was your fuel consumption suffered, very noticeable if you pushed it hard. Once ran through nearly a third of a tank on a (very) fast run up Mount Buffalo.

One advantage, not often mentioned, was how easy it was for RR to alter the carburettor to provide higher fuel flows for the higher boost. A much harder task on the mechanical fuel injection systems that the Germans used.

The other thing that has to be remembered is that all the planes of that era aged very quickly and their performance deteriorated quite quickly.
Dings in the leading edges (or even just cracked or badly applied paint), engine aging, etc.

I can easily see someone in a well used Mustang with a lot of hours under its belt and close to a major service having a real hard time against a brand new late model 109G or a K.

Mike Williams has some stuff on the Crossbow (anti V1) efforts, where they were trying to get as much speed out of their fighters as possible. AFDU would get a stock service plane, clean it up and add anything like 10-20mph to it.

Just like a bug splat would destroy a 'laminar' wing's airflow, even little dents, bad paint, panels on the wing or fuselage not quite matching (after being opened and closed many times), replaced rivets or screws poking out a bit ... all could take a lot of speed off a plane. Then there was the engine aging.

Plus you could just get a bad brand new one, the British suffered more from this than did the Germans (at the beginning of the war, towards the end their quality was shocking, starving slave labourers are not exactly motivated to produce good quality stuff) or the Americans given their overall poorer quality control (the endemic British issue).

Even RR had issues and it was good (at least as good as anyone else, certainly better than most, reasonably arguably amongst the best), again there is some figures on Mike's site about variances in FTH between different engines (of the same type of course).

The British standard was +- 3% in performance. That means of you had a (say) Spit LF IX, book speed of 404mph, and it was a bad one your max was only 392mph (and 416 on a good one, smart senior pilots made sure they got the good ones ... and looked after their service crews) and then it would age quite rapidly getting steadily slower as time went on in a sort of downward 'saw tooth' way (decline until service, then a rise, then a decline again, with each peak being slightly less than the previous one).

Modern warbirds are lovingly looked after and kept right up to spec so their performance is probably closer to ideal than anything that was operational during the war. (thanks to a lot of great people like GregP here)

Poorer quality control? At least our Merlins has interchangeable part! The British Merlins surely didn't.

Go work on one. I have. Custom-fit parts for EACH engine. Weird but it works when all the parts fit.

This is why I am always sceptical when people chime in with the "the figures are not relative as the plane was in bad shape" argument, I would argue that was the condition of a front line aircraft, not a factory fresh one!

GregP said:

Poorer quality control? At least our Merlins has interchangeable part! The British Merlins surely didn't.

Go work on one. I have. Custom-fit parts for EACH engine. Weird but it works when all the parts fit.

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Well the British ones were supposed to a well, and the rebuilding organisations (often forgotten) broke down Merlins and rebuilt them from scavenged parts all the time.

Depends on the era I suppose, Ford UK made a tremendous contribution by having all the plans re-drawn to higher tolerances to make sure of interchangability (as Stanley Hooker notes in his book). The early ones I suppose were were more 'hand built' than the later mass production ones (when Packard, Ford, Glasgow, etc got up to speed.)

Overall US quality control was vastly better than the UK at that time, only later did the US decline (relatively at first, then absolutely as the accountants took over) in that regard. Germany started off as the best, but all that forced and slave labour does not a happy workforce make, so they went down the tubes as time went on. Bit like modern Volkswagons, get an older German made one and it is superb, get one (and we have this issue here in Australia right now) from one of their 'other plants elsewhere' and they are rubbish.

OldSkeptic said:

Good one.

I used to have a Subaru WRX (great car) and the engine control computer would adjust the power depending on the fuel. Rated for 98 octane you could (in an emergency) run it on 95 octane. Plus here in Australia there are some significant variations between the different 98 octane suppliers, one in particular was renowned for being a bit dodgy while BP's was excellent. And yes you could feel the difference between them.
The best I found was actually one of the cheapest with 10% ethanol, trouble was your fuel consumption suffered, very noticeable if you pushed it hard. Once ran through nearly a third of a tank on a (very) fast run up Mount Buffalo.

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Not sure if you are agreeing or not.
A modern "engine control computer" does do something to the engine, it changes the ignition timing at the very least, it may or may not alter fuel flow. Put in poor fuel and the engine control computer detects the engine "knock" and retards the timing until it goes away. Power is reduced. Old aircraft engines used fixed timing (for the most part). If the engine was set for 20 degrees BTDC then that is what you had had idle or at max RPM.
Allisons used for training in the US and run on 91 0ctane fuel had their timing retarded and the boost control modified to limit total boost. A few of these engines would up in Europe without being reset and there was quite a flap (investigation) when these engines failed to give proper performance with 100/130 fuel.

DonL said:

You will be confronted with his research and his site every time the issue is the Bf 109, simply there is no other site at the web, which provide more german primary sources and documents about this a/c.
This is simply a fact.
To discredit him, because of his behaviour (to your opinion) and also try to discredit his site, research and provided primary sources will not function!
You will be also chanllenged in the future with his provided primary sources about the Bf 109, if you deny this sources or discredit his site, you automaticly discredit primary german sources.

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I have no problem with using primary German sources, which is why I have in my library books by the likes of Prien Rodeike, Pethrick, Smith and Creek etc - credible aviation historians with a record of solid research; I do not need to refer to kuffie's selective "research", nor do I ever bother. As for Kuffie's lamentable, mendacious behaviour - that is not my opinion, it is on the internet for all to see...

jim said:

I asked greek air forces mechanics

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When was the last time any of them worked on a recip using 100 octane? An in-line recip?

FLYBOYJ said:

When was the last time any of them worked on a recip using 100 octane? An in-line recip?

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Mr Flyboy J

For the history, Hellenic Air force used 3 C-47s until a few years ago
But the mechanics i asked were veterans of HAF and members of my aero clumb. They had experience on Harvands, Noratlas, Alpatros, Canadairs( both with the original engines and with the turboprop engines) etc.
Moreover all of them had off duty experience with general aviation small aircrafts. Plus extensive theoritical internal combustion engine education.

Shortround6 said:

If they all laughed then you asked the wrong question.

IF you run an engine on 87 octane fuel and set it up correctly and then switch to 100 octane and do NOTHING to the engine you will get a ZERO PERCENT increase in power. ALL these men are quite correct.

HOWEVER, 100 octane fuel allows you to change either the compression ratio or, on a supercharged engine, the amount of boost used. Or some combination of both.

But that is NOT SIMPLY providing higher octane fuel. To change compression ratio usually requires new pistons. To change boost requires a new supercharger or new supercharger gears or at the least changing the supercharger boost controls.

The best ( or easiest) example is the Merlin. The Merlin III was good for 1030hp at 16,250ft at 6lbs boost with 87 octane fuel. 100 octane fuel is good for a potential 30% increase over 87 octane ( argue with Sam Heron, not me). When the British ran them on 100 octane ( actually 115-120 performance number) There was absolutely NO CHANGE in power ABOVE 16,250ft. The supercharger was maxed out and could supply no extra air above that altitude. Below that altitude the supercharger could supply extra air and the higher octane fuel allowed higher pressure without detonation. Max power was 1310hp at 9,000ft at 12 lbs boost. The increase from 6lbs boost to 12lbs boost is about a 28.5% increase in manifold pressure. A few other things are going on like different intake temperatures and pumping losses than can affect things by a few %.
Please note that further increases in power required new superchargers (Merlin XX and 45) different supercharger gears and finally the two stage supercharger. Also note that the British fuel changed twice AFTER the first 100 octane as used in the BoB.
G0 back and ask the professionals what happens when you increase the manifold pressure by 25-30%. It should increase the amount of fuel and air going though the engine in any given time period by 25-30%.

The performance number scale is much more linear than the octane rating scale. 87 octane is 68.5 on the Performance number scale. 100 octane is 100PN. Going from 100PN to 130PN should give another 30% ( if the supercharger can supply 30% more air the engine doesn't break/bend). Going from 130 to 150 should give about another 15%

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Mr Shortround6
I dont understand.... Where do we disagree??
I agree that better fuel leads to better output. But it requires major engine changes
When i up tuned my FZS 1000Fazer , i turned to 100 octane gasoline. But in order to take advantage from that fuel
1)Changed the pistons and the gaskets
2) Rejetted the carburators( not that simple procedure)
3)Used a new exaust system
4) The engine had by its mother company large strength reserves
5)) New bigger cooling radiator ( and that for an naturally breathing engine. A supercharged one would require even more cooling)
6) I improved the internal engine surfaces for better flows
7) Modified the engine ignition
8) Used improved lubricant parts
Plus a number of small detail improvements(plugs etc). With all these i got 17% more power( okay it was a conservative choise)
Plus many hours to fine tune the improved engine. And now the engine can run only on 100 octane fuel ( a bad idea during economic crisis)
How they got 30% more power from merlin III without major component improvements? How they used additional supercharging without cooling the air? I dont accept the claim that they simply put in the majic new fuel( asterix majic filter?) and they got 1300hp. And thats i have read on that site

to answer your final question , if you increase the in flow mixture by 30% (HOW???) and the engine is not prepared to take the machanical load , you destroy the engine. As simple as that

Going to 100oct allowed a higher boost to be used, nothing more and as pointed out above that only worked under 17k ft alt as the supercharger could not provide enough air at higher alt's.

This was limited to 5 mins at a time to keep temps under control.

no need to replace internal components in this case.

Aozora said:

No Mr jin this is just adding to your crap. The reason why no-one finds fault with Mr Kurfurst, and why Mr Williams hasn't bothered to answer is because Mr Kurfurst's response to anyone trying to debate his facts and figures is usually so unpleasant/nasty/full of distortions and half truths that ANY "discussion" isn't worth the trouble. You are indeed a "worthless amateur" that you can take Mr Kurfurst so seriously.

As it is you don't even have the decency to call Mr Williams a liar to his face, using your real name, via PM, so your opinion isn't worth a whole lot.

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Mr Aozora
1)I dont call him liar because i try to follow the forum rules. Plus ,as Lw fan, i must be extra cautious
2) My name is known to the moderators, but what s the point?
3)Did you have the decency to read Mr Kurfust respond article? FULL of evidences
4)So, you and your author, dont answer Mr Kurfust arguments because he "isnt worth the trouble" . Excellent ,democratic habits.... for 8 years old children. What about answering his arguments and let each reader reach his own conclusion? Or ,simply, your author can not answer Mr Kurfust s arguments
5) I would like to remind you that a worthless amateur (according to the scientists of its era) discovered America

i am skepitcal of most reported data. its not that cut and dry. manufacturers were in competition so they put their best foot forward...the best stats they could provide. i accept more info that puts the findings in a range that will give you a good average. there are so many variables it can be difficult to nail down exact figures. temp, air density, humidty, are never consistant but all will affect flight characteristics. the same plane flown on 3 different days could give you 3 very different readings. most tests are subjective or looking for a specific issue. sometimes mechanics will give the plane some help..lessening weight....tuning it up...etc. i am a fan of all the ww2 ac...so as to which one was best....depended on the day and the pilot and...and..and.

jim said:

Mr Shortround6
I dont understand.... Where do we disagree??
I agree that better fuel leads to better output. But it requires major engine changes
When i up tuned my FZS 1000Fazer , i turned to 100 octane gasoline. But in order to take advantage from that fuel
1)Changed the pistons and the gaskets
2) Rejetted the carburators( not that simple procedure)
3)Used a new exaust system
4) The engine had by its mother company large strength reserves
5)) New bigger cooling radiator ( and that for an naturally breathing engine. A supercharged one would require even more cooling)
6) I improved the internal engine surfaces for better flows
7) Modified the engine ignition
8) Used improved lubricant parts
Plus a number of small detail improvements(plugs etc). With all these i got 17% more power( okay it was a conservative choise)
Plus many hours to fine tune the improved engine. And now the engine can run only on 100 octane fuel ( a bad idea during economic crisis)

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WHich shows that you cannot just pour the new fuel in the tank.

jim said:

How they got 30% more power from merlin III without major component improvements? How they used additional supercharging without cooling the air?

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That is a difference between aircraft engines and ground (car, motorcycle, boat) engines. ALL major (over 500hp or so) aircraft engines used superchargers and just about every ONE was set up for a full throttle (throttle plate all the way open) from 1500 to 4000 meters above sea level. If they opened the throttle fully at sea level they could destroy the engine. They had extra supercharger capacity they couldn't use at low altitude with the lower grade fuels. The ability to flow more air at low altitudes is already there. Wither the engine is strong enough to withstand the power is another question. However 'a' Merlin had been run at 1600hp for 15 hours on a test stand when preparing the "speed Spitfire" and even high power settings for short periods of time. The strength was there. In 1939 Rolls was claiming an max time between overhauls of 240 hours for fighters and 300 hours for bombers. That does not mean the engine was guaranteed to last that long but if the engine made it that far it should be pulled for overhaul. This engine "life" was around twice what some other engines were offering so you could trade higher output for shorter engine life and that is what was done. EVERY use of over boost had to be noted in log books and engineering officers decided when to pull engines for over haul. Also please note that that at altitude the air is usually cooler than at sea level.

jim said:

I dont accept the claim that they simply put in the majic new fuel( asterix majic filter?) and they got 1300hp. And thats i have read on that site

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You are free to believe as you wish but since those figures and modifications are listed in several books put out by Rolls-Royce and have nothing to do with Mr. Williams site I am not sure how you figure that Mr. Williams is lying or making things up unless Rolls-Royce is also lying/ making things up and doing so in books published 35 years after the war ended. They adjusted the boost limiting device and changed to a different spark plug and that was it.

jim said:

to answer your final question , if you increase the in flow mixture by 30% (HOW???) and the engine is not prepared to take the machanical load , you destroy the engine. As simple as that

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In order for the supercharger to deliver 6-6 1/4 lbs of boost at 16,250ft it had to compress the outside air at over a 2:1 ratio, perhaps 2.3:1. When you drop down to 9,000ft from 16,250 ft and compress the air 2.3 times you get 30% more air flow in pounds per minute than at 16,250 ft. with that particular supercharger.

bobbysocks said:

i am skepitcal of most reported data. its not that cut and dry. manufacturers were in competition so they put their best foot forward...the best stats they could provide. i accept more info that puts the findings in a range that will give you a good average. there are so many variables it can be difficult to nail down exact figures. temp, air density, humidty, are never consistant but all will affect flight characteristics. the same plane flown on 3 different days could give you 3 very different readings. most tests are subjective or looking for a specific issue. sometimes mechanics will give the plane some help..lessening weight....tuning it up...etc. i am a fan of all the ww2 ac...so as to which one was best....depended on the day and the pilot and...and..and.

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A lot depends on how the contracts are written. Most US contracts had an allowable tolerance on weight and performance of around 3%. EVERY production aircraft was weighed and EVERY plane was test flown before acceptance. Manufacturers were penalized (not paid the full contract price) if the planes were overweight ( and some times penalized per pound once the agreed tolerance was exceeded) and inspectors could either reject low performing planes to be reworked at company expense or invoke performance penalties in the contract.
It took a mighty brave company to oversell a plane and then sign a contract guaranteeing that level of performance. Curtiss lost over 14,000 dollars on the second prototype XP-46 because it wouldn't hit promised performance levels.
Screw up the estimates/promises on a production batch of 500 aircraft and the company could go bankrupt.

Any more insults and you all will be banned. Thread closed.

jim and aozora, don't even sneeze.

The Usual Suspects...