Avgas

Hi I am looking for a bit of help, does anyone know where I can get a regular supply of avgas, unfortunatley my local aerodrome have become a little tetchy about putting avgas in anything other than aircraft, a little pedantic I feel but "rules is rules,"(his words not mine). Dont mind a bit of travelling to collect.

Regards,
Mike.

Hi Mike,
I get mine from Wickenby airfield in Lincolnshire, they have a history of supplying to racers as they are not far from Cadwell, so they are well used to it! I have not had any problems so far, but it could be a long way from you though!
Try a few more local airfields and see what they say.
Good luck
Alan

I think you can still buy it at Silverstone, if that's nearer. Best to ask on the VMCC ( Historic ) racing forum - someone near you will know.

I have been looking at the avgas situation again and came across an old post on an aviation site in which the poster said that avgas was a slower burning fuel. With this in mind, he explained that due to this property that on higher reving engines that the fuel can still be burning as the exhaust port opens. I think that at some point within this site a post explained that ignition timing can be advanced ? whilst running on avgas. Is this to help stop this at higher revs? Sadly, the poster did not give any rpm numbers so im wodering if anyone has this info. Would have quite an impact on performance, with this in mind, id have thought.  

The sale of 100LL Avgas for general public use is prohibited in the UK because of the toxic nature of lead emissions and the possible evasion of certain enforceable duties.

Nigel,
There is too much cool cylinder wall available to quench any lingering combustion flame long before the exhaust port opens, be it Avgas as fuel or not. Even more surface area on a big bore/stroke 175, so you can scotch that old myth, and an 8:1 cr will have a pretty inefficient burning phase in the first place!
What is really needed is a nice, fast, complete combustion period. That way timing could be much later and heat energy losses to head, piston and cylinder could be greatly reduced, all helping with power. There is of course a vast difference between desire and having!

Octane numbers are an indication of the difficulty of the fuel to combust, high octanes with lead are harder to combust and have slow speed. Specifically, how much pressure the fuel mix can be placed under before detonation(knock)onset. So it follows that a higher compression ratio will provide for more energy to be released from the fuel but brings the engine closer the thermal threshold that is not to be crossed. Comparison of octane rates are made against a standard where Iso-octane(C8H18) is 100, and N-heptane is zero. Avgas is a slow burning fuel and is not formulated to be otherwise, and is intended to be utterly dependable for low revving four stroke engined,light plane use. Quality unleaded is a faster burning fuel and is much friendlier to our environment.

For a fixed time period, at constant rpm and a fixed ignition point, the timing advance would have to be sufficient to achieve complete combustion, so the situation here is not can advance, but have to, and that brings dangers! To speed up combustion and be able to reduce advance, the available options include higher cr, correct stoichiometric fuel ratio, perhaps even a touch weaker, and better cooling helps with both of these. One absolute pre-requisite is the correct grade of plug, NGK10 minimum and the top spec. fine wire Iridium electrode job may even give a few more revs, such is their discharge efficiency. They are pricey but a lot cheaper than an engine blow!
Top of the list is turbulence, excitation of the combustion mix speeds flame development enormously. Squish action, combustion chamber profile with optimum plug location, surface area to volume ratio all are significant variables that affect turbulence. A compact chamber, a big spark initiating vigorous motion throwing the flame sheet around, exposing available unburned fuel, will all aid rapid flame speed
The situation for the Bantam is made somewhat inequitable, in that one class can play around with ignition settings and advance curves to achieve reliability with power over a wide range, the other cannot!

The now obsolete F1 engines of last year had a bore size of 98mm for a capacity of 300cc. Using this and a laminar flame speed of 1500mm/sec and allowing a favourable 270* of crank rotation to totally enflame the bore, peak rpm comes out at 1,400rpm! Bearing in mind that these engines are capable of some 20,000rpm, some credible perspective can be given to the critical nature of turbulence in the combustion chamber.

Incidentally, these engines have the same stroke as the old 50cc two stroke GP engines, 39.5mm? The best of these, the little Kreidler, would never be able to make 20k revs; imagine what the blowdown period real time would work out at.

Trevor.

I seem to have had my 1st reply deleted or scrubbed or something -- that first message vanished, maybe this will ....?

Before `Premium´ petrol came in we upped the octane by mixing pure Benzene in with our best petrol of the time. We were assured there was no TEL (Tetra-Ethyl-Lead...) but that was not positive...  We always ran a little bit rich as a precaution but holed pistons proved we ought to have been a little bit less-advanced and a little bit more rich. There´s a holed, 250cc piston on my computer showing just how close the 250 ABS was to success or failure by the short bit of high speed practice it exhibitted before seizure. Snetterton -- of course!
That would be 1973-4....

 I am quite sure the unmentionable fuel was not permitted during my Bantam racing time (´68 - 74)  but we did buy `special´petrol that was said to be 98 Octane... We found out later there was nothing really special about it as compared with the best garage pump petrol which was in excess of 95octane at the time. Typically, for a 100% performance,  the difference of 93octane fuel to say 95octane means a timing difference  of  from 11° to 23° BTDC (advance) which is just as an idea of what is involved.***
 My 500cc JAP, `short-four´ engine (grass tracker) was  on 16.5 compression-ratio using a special(again) racing fuel. This was a Track-Fuel consisting of methanol with 1 to 2 percent Puridin(`Dope´trade name for TEL) enabled me to run with an 850 main-jet where others were using 1100 to 1300 . In fact a rival grass-tracker at Mallory (grass track before your time...Whoops!) blew his similar JAP motor with his carb fitted with 1100 main jet. His ignition timing was the same as mine.

As Trevor said , that´s not all the story -- if I remember aright I had a spark advance at 40°BTDC with this Puridin doped fuel and  it must be appreciated that the JAP engine of then revved to only 5000rpm ...

Not much of that,  above,  is of any use to a Bantam racer and what I say here is probably the same but I must tell that which I did with diesel engine development in Canada. By modifying injection pumps & injectors (Whole injection systems really including injection pipes) I achieved a lower longer-lasting combustion pressure which meant a larger Work-Done envelope per cycle than a system where the peak pressure was almost twice as high.
Unfortunately we got dumped by our parent company in Germany before this work was completed...

Which brings me back to that old argument I have about using Direct fuel injection into the combustion chamber. This was done before the war on the famous Crécy (aircraft) engine and during  the war  the German Messerschmidt had direction injection also.  I think it ought to be tried even if the Banatm formula never allows it just to see how much further the development of a Bantam could go.

The Crécy was also a sleeve-valved 2-stroke engine....!!!???

I wonder if the Avgas available at a `better´ price is always the genuine artcle??

Cheers!  

*** values not to be taken literally,  they are from a single-cylinder research engine nothing at all like a Bantam.!

cheers John, again, i thought you posted reply, i deleted my thanks as i thought id been dreaming  Thanks Trevor, had this vision of flames pouring out the exhaust port when coming down the gears to help braking and melting everything  

I must add that what I was referring to was the fuel-injection system in the days of  a plunger pump, high pressure pipe & injector  with everything controlled mechanically -- AND most importantly the engine speed (diesel)  was low relative petrol engine ratings and compared with modern Bantams extremely low. It is then understandable that a long  period of injection and  combustion was better accomodated.

What was achieved was a shaped Injection-Rate curve such that a short, `early´ squirt (for the want of a better word) got the fire going and then the rate of injection was so tailored that a rapid increase of injection brought a corresponding combustion-pressure increase -- just at TDC and after TDC... With the electronic  equipment we had   we could see and measure Heat-Release over the combustion period. With the facility of changing  several mechanical features of the pump, pipe and injector  the injection-rate could be tailored so that a lower, combustion  peak-pressure lasted longer than the earlier uncontrolled pressure rise. It is obvious that the rapid rise of combustion pressure -- occurring before top dead centre, wastes energy by the fact that it is a force against rotation. The ideal situation is to have the peak pressure coming after  TDC and having it  extend to where the conrod angle is more advantageous to use of the combustion energy.

 In effect doped methanol fuels do that.

But getting back to the Crécy engine -- long before WW2 --  by sir Harry Ricardo where plunger pumps and the Ricardo Comet´ combustion chambers  made  it possible to run at 20:1 weak (normal chemically-correct 12.7:1 lbs of air to fuel) mixture  has me thinking someone ought to try something similar with a Bantam engine just for the heck of it.  Running engines on high-octane fuels with a rich mixture -- necessary for reliability -- is  rather crude. I´d really like to hear &  see that someone was trying Direct Fuel injection in a Bantam.

OK -- OK! So I´ll creep away -- shut up -- and hide. You Bantam Racers have enough money consuming absorbers already!

Cheers!

HI all would just like to say that Me and Michael run Avgas on both are 175cc Bantams. We have no problem getting it the airport just needed a letter to say what we are doing with it.
The thing about avgas is it dose not change not like pump fuel with all the crap in it  additives some summer cooling and winter cold starting. As Tom Miller keeps telling you cant have plane fall out the sky. So wen you look at race entries prices its better to finish and that's with the help of Avgas. and as for 175cc bantams not going very well Avgas   I am very surprised that people think that the bikes will not go well. for people that were at Anglesey just ask them   Michael was on a well sorted 175cc Bantam He had four out of the five fastest laps of the weekend and two wins on Avgas. would love to try 50 50 but want to come home two working engines
hope to see you all at a meeting soon this Year
Robbie Ps John on big flywheels too  

Robbie, you are right about the avgas. i have only ever managed to get 5litres off a friend of mine some time back and used it only the once. I think is was at a practice, when my throttle cable came out the carb, then the carb rubber manifold split and finally the gear lever fell off, but it didnt sieze  I have asked my mate if he could get me some more but he said he got it from Gloucester, 100mile round trip.   I have looked at additives but the consensus is there all crap.Its a pity that some form of leaded race fuel (c12 )could be used as thats easier to buy although £84 for 19 litres... Like you say no point in using pump fuel if it wrecks the engine  

Should the availability of Avgas be a problem then there is a very simple solution to the dilemma, ban all fuel with the exception of cheap, universally available, unleaded pump gas.
Mark established the Llyden lap record using pump gas and fixed ignition, so there is no pre-requisite for Avgas to achieve success. We changed, post 2007, to Avgas and found no discernible advantage but it is more expensive, and tricky to get hold of. With every one on the same fuel we have equality, and we remove toxic emissions, at the end of racing the surplus fuel can go into the family car, what`s not to like!

Trevor

I can believe it Trevor...!

I think Mark probably rides (sorry! -- i mean `races´...) that old fashioned way of `FTO´ (throttle fully open) or sometimes shut. I cannot imagine comparing my riding with his but on grass (and Speedway practice)  I had a  quick opening throttle -- the twist--grip had a massive (home-made) drum whereby there was about 20° of movement from idle to flat-out*** the Brit grass-tracks were unlike German Long Tracks in being very short like Speedway tracks with a kidney-shaped-kink, most times,  which meant one would mostly accelerate to max revs and then shut-off...
... for that the timing is fixed and the fuel suited to CR and only max speed  -- nothing in between.

And bigger flywheels to you too Robbie. I am glad someone else thinks about big flywheels the way I do. Fascinating weekend for Michael he seems to have the bit between the teeth...

Congratulations Michael!  -- do it again but watch out for the `Force of G´  -- its a real sneaky SOB....

All the best to all...

CheerS!

***accounts for the problems at Brands Hatch on practice days with Cafe Cowboys -- on Dommies and big BSAs --  having shocks at being passed by a 3-speed Bantam screaming at 8,400 a lot of the time with purposely slipping clutch. One of them wanted to have me banned -- uh oh! I´ve already told that story....

Trevor avgas wasn't permitted when I was riding but it didn't stop some people using it !

Dead right Ned!.....Back in the day I caught one of our champions of the past furtively pouring blue fuel into his tank. When challenged he went the colour of a post box and stuttered it was the oil that that made the colour, but when I asked of him why the same oil didn`t change the colour of our fuel he plonked his helmet on(for protection?) and strode off . Mark thrashed him in all the races on the day so I felt some sort of justice had been meted out. Mind you, at subsequent meetings the enquiry was, politely, made of him and within earshot of others as to whether he was legal this time? Steve was enraged and tempted to get some t-shirts printed with the logo, " OURS IS LEGAL, IS YOURS?" but remained content that, of the miscreant,.... He knows that we know!

But no, there have always have been and always will be, cheaters, and its difficult to legislate against them. But success through cheating is a hollow one and there is always the threat there of being exposed, and instant, and public expulsion should be the penalty.

There is as well the story of another past champion being found to be changing gear one more time, at the same spot at Cadwell, than any other rider was, the implication being pretty plain. Terry Beckett planned a revolt but was eventually mollified and paddock harmony was restored. The offending rider was reduced to 3 gears thereafter. Back then it would have needed factory type investment to achieve that level of engineering input?

Trevor

To think my mentor & engine-prep man thought we´d be cheating by entering a 125 Bantam race with a 150....!!

I wonder how cheats really feel about their winning....

Cheers!

Morning.
Is there anyone out there who has tried mixing avgas with unleaded? Is there an optimum mix percentage.
The small carb im running at present does have a power jet, so im assuming that the addition of extra fuel at higher revs should help protect from getting way too hot...  

I wouldn´t do that Nigel.

Avgas 100LL is allowed in both 175 & 125 BSA Bantam Formulae and it is the best fuel for the job ... No point in scrimping over the price -- the cost of piston & bore come to more ....

I spoke of mixing PETROL With BENZINE at the time (1950) when garage pump petrol was between 78 and 83octane and the buyer, as well as the seller,  did not know what level of octane it was anyway.

Avgas is regulated to be 100octane or over (only slightly over) so if you buy it from an airfield you can be `SURE´ it is OK.  

I don´t know much about Avgas except what´s been said on here before*** and an experience in Africa when a welder tried welding an "Empty" Avgas tanker without following the recognized procedure°°° -- he sort of lost-his-head over it....

As, has been said on here before, it is an unhealthy fuel for humans but good for Bantams...

*** Avgas as aircraft fuel is well-regulated but like most well-regulated sales items it is open to piracy and faking so it is wise to always buy  from a recognised supplier.  

°°° The procedure is to ensure petrol tankers have been empty for a set period of time and filled with nítrogen gas before attempting a weld. When I saw it -- a few hours after the explosion -- the front and back half of the tanker were 60  metres apart. The welder did really lose his head as well as his helper dying of burns!

Nicking it is not a good idea either -- syphoning thieves have been known to die of stomach complications....

Cheers!

Iso-octane. toluene, xylene, benzene, cyclo-hexane, tetraethyl lead, n-hexane, propylene oxide, naphthalene, anti- oxidant additives, anti- icing additives, anti- static inhibitors and much, much more....Avgas! A number of those chemicals are highly carcinogenic and can be absorbed through the skin, with combustion products being toxic...... nice stuff.

Iso-octane is commonly blended with toluene to produce octane numbers , but, toluene is difficult to vaporize and needs a higher temperature to do so. Years ago with the first round of turbo F1 engines , Honda had to pre-heat their exotic toluene based fuel to 70*c to even begin the process, they achieved that by routing the fuel line close to the exhaust pipe?

Lead is the ingredient that protects the Bantam engine far more than a raw octane number. Oxidation of lead during the burn cycle inhibits the formation of destructive free radicals and that suppresses detonation. So why would you want to dilute the lead level by 50% by diluting it with unleaded pump gas and reduce that protection. Unless of course your engine doesn`t need Avgas in the first place.

Trevor

We didn´t know any better, Trevor -- it was a time of 6:1 being a normal compression ratio on 4-stroke engines....

The Walsh Bantam was on 16:1 at a time when 8.5:1 CR (for 4-strokes)  was considered `competitive´ and the Walsh Bantam had a megaphone exhaust ....

The smell of Castrol-R, unburnt Puridin-Methanol in the exhaust ... and the noise of the open pipes --  Ahh...Ahhh...!!

Sickly nostalgia has struck again --- ahh! --- ahhh!

Hi Folks
I hope I don't offend anyone but I feel that this is getting out of hand.
Not long ago there was a post on 'raising the profile of BSA Bantam racing'.
By using avgas, in my opinion is taking bantam racing away from us, and making it more difficult to become involved in racing, by using / sourcing / storing a specialist fuel.
Building a Bantam race bike is not the easy, sourcing parts and getting it built and prepared, but to have the added issue of having to use specialist aviation fuel to be competitive, my view that is not the way forward.
I'm sure that if the only fuel available was what you buy at the garage then this would help, in a way. As the first impression to the layman (me) is that this is getting far too in-depth and specialist, thus excluding the man in the street from racing.
Just my thoughts, not a dig at anyone or the rules, but I feel it needs clarification to keep Bantams racing.
Pete

Surprised no mention of the effect ethanol has on fibreglass fuel tanks in this topic.

Shell Optimax, containing I believe 5% ethanol, caused me no end of grief with the Bantams. The 175’s tank required frequent surgery to plug leaks. 002’s original tank was declared un-repairable by a fibreglass expert. Filters clogged up and float needle operation became a nightmare. Tank lining concoctions, high capacity taps, large transparent filters and different carbs were all tried, but the problem was only overcome on switching to Avgas.

I was never aware of any performance enhancement afforded by the use of Avgas.

The ethanol subject has been well aired in the VMCC magazine over the last few years.

Regards

Chris

Well there you go Chris, if the "modernisers" hadn`t messed with the original formula we could still have steel tanks and there would be no problem with ethanol dissolving all resins known to man! What goes round comes around!
The only way to get Avgas to respond advantageously is to rack the comp. ratio up and get some energy from combustion, 15:1 on a 175 could be quite interesting, for a few minutes at least!

Trevor

a miscalculation led to me using 16.5 :1 ,done a lap and a half! the power-band was very forceful !

back to petes comments , it not hard to get avgas there are airfields every where,you'd have to get in your car and drive to petrol garage to get fuel so go a little further and go to the air field, its constant and cheap compared to race fuels, dosen't rot tanks and rubber or plastic carb parts (lectron float bowls).

road fuels are just that ... road fuel. an engine pushed way beyond there design needs all the help they can be given.

also i'm sure pete that if you were to start racing and you had trouble getting fuel someone would offer to get it for you and you pay at the track.

Well, its unleaded ish ( 0,5mg/ltr)shell v max and castrol r for me   ... got low enough comp, hopefully, ignition 2mm btdc    May find out tomorrow if weathers ok... Ive only asked twice locally for avgas, got "the sorry mate"