What I notice when using normal gasoline in Africa instead of AVGAS is that the engine used more oil. I try to buy barrels of AVGAS where possible but on islands like Sao Tome, that is not easy to arrange, so I run over to the local fuel station with jerrycans and fill them up. Once AVGAS is available again, I will switch over to AVGAS again as soon as possible.
Peter,
Mixing fuels and calculating octane
As with cars, our old aero engines only require the specified high octane fuel when abused (hot, low RPM, high MAP) and per chapter 4 of the Busch book, our engines have nothing to fear from mild detonation.
So hypothetically, of course, if we were going to ignore the manual and use lower octane fuel we would keep the revs up while climbing, set our engine monitor CHT alarm to 400 F (or 420 for Lycoming) – and try not to go to sleep.
What to do if the alarm wakes us? A FADEC automatically retards ignition if it detects critical detonation so the answer is “nothing” for a modern engine. We don’t have FADEC or knock sensors but we can effectively retard ignition manually by grounding one magneto. We may also increase RPM, and, as Busch recommends, reduce MAP.
Zero issues if the aircraft engine was initially a car engine that was designed to run on petrol…
“we can effectively retard ignition manually by grounding one magneto”
How does that work? which mag goes off? (assuming you have dual mags)
If both ignition systems are correctly set to the same timing BTDC, it doesn’t matter which one we ground. The flame front has further to travel from a single spark plug, so combustion takes longer (= greater crankshaft angle at any given RPM) which is why we see a drop in RPM when we do our pre-flight mag check – and also why little or no RPM drop one mag is a clue that that magneto may be too far advanced.
I think most of our “legacy” aero engines have two magnetos (or a dual mag) and two spark plugs per cylinder.
We can use mogas in the C90 in the Vagabond.
It apparently needs to be ethanol free, and we test any we use with a little kit branded as Bluebottle. You pipette a bit into a test vial which has some purple solid in it, and as long as it doesn’t dissolve then you’re good to go.
The premium fuel from our nearest garage has always passed the test for me, and I’ve never noticed any difference in the way the engine runs – although I’ve not used it extensively.
Advantages in this situation:
40p a litre cheaper.
Allows me to return and still refuel late in the evening, after the avgas pump has been switched off.
Small tank (45 litres) means the average bimble can be refuelled from one jerry can, and any flight from two.
So, is “mogas” really car petrol, from a petrol station?
I know many people use the term in exactly that way.
But I thought that there is, or used to be, an aviation product called “mogas” which is car petrol but without the ethanol or other rubbish, and with some better quality control.
I have seen 100LL pumps, 91UL pumps (very rare) but have never seen a “mogas” pump. OK; I don’t do the “farm strip” scene, but filling up 10-20 20-litre jerrycans at a petrol station is a pretty hard job.
I was very satisfied using for 5 years Unleaded 100 from a known petrol station for my C172P. Allways passed the water and alcohol testing.CHTs were lower even in climb.Oil consumption was Nil.Removed my stress to try to land for Avgas refueling when I didnt want to.It also extended the destinations and distances I wished to go.I used WW2 cannisters,a micro funnel,a 12V fuel pump,GOOD GROUNDING and kept fire extinguishers around.The price was half too !
BTW,the possibility of high alcohol is almost nil in southern hot countries.Alcohol is more pronounced in cooler countries for the winter batches.Water is more suspected instead for reasons of neglect or mafia frauds.Happened to me twice in Bulgaria and south Italy.
Ethanol content is the only difference between Mogas and gasoline. Ethanol and rubber parts (engine pump?) do not go well together. However, if you fly to places in Africa where there is a normal gas station but nothing else you can test for ethanol, but if you find it or not in the fuel, you have a choice to fly away from the place with the fuel they have or you can stay there and leave the aircraft on the apron. Talking to ferry and bush pilots there, many of them fill up regularly with normal gasoline to fall back to AVGAS again once available. So, I never found any significant (or mostly not at all) ethanol in the fuel in Africa.
Buying jerrycans at the market in Aden, Yemen
At the local fuel station. No idea what the sign says, but it smelled like gasoline and not like diesel.
Transport of our fuel back to the Aden airport.
Back at the aircraft with the fuel.
Using a fuel filter to filter out sand/dirt and water. The picture was taken at Juba Airport, South Sudan.
If there is ethanol, it might damage rubber parts over time. That is not nice and you never know how long it takes for it to become a problem, but I would always ask the maintenance shop after a ferry flight to have an extra look, but they never found any issues.
As mentioned before, I do see a significant difference in oil consumption, which is very low when flying on AVGAS and much higher when flying on normal gasoline. I am not sure why. Is there anyone here on the forum that would know the reason for the significant increase?
Peter wrote:
So, is “mogas” really car petrol, from a petrol station?I know many people use the term in exactly that way.
But I thought that there is, or used to be, an aviation product called “mogas” which is car petrol but without the ethanol or other rubbish, and with some better quality control.
I have seen 100LL pumps, 91UL pumps (very rare) but have never seen a “mogas” pump. OK; I don’t do the “farm strip” scene, but filling up 10-20 20-litre jerrycans at a petrol station is a pretty hard job.
I was similarly confused as to what it actually is, and probably still am.
As it was explained to me by a fellow Vagabond pilot, the premium fuel from the filling station is certified ethanol-free – or at least some brands are, not all. We cannot use the ordinary fuel because it will contain ethanol. Luckily my closest filling station is the correct brand. Even with the premium, we test each time we fill.
It is not an everyday solution for aeroplanes with tanks running into hundreds of litres, because ordinary jerry cans hold 20 litres and it would be a huge amount of messing around as you say.
However, for a Vagabond with a 45 litre tank it is workable. I just have one jerry can and try to keep it full – if it is empty it gets slung in the back of my car and filled when I next happen to pass the filling station. When full it goes in my garage at home (someone will tell me this is illegal, but neither I nor any enforcement authority care) and then whenever I drive to the airfield I put it in the back of my car in case I need it.
For nearly all flights I refuel afterwards with avgas because it is less faffing around to just use the pump and the saving on such a small quantity is not much. But if I return late when the pump has been turned off (as I often do, I like flying in the evenings) it is very useful to have it, because it means I don’t have to come back another day to refuel the aeroplane (the group policy is refuel when finished).
AeroPlus wrote:
As mentioned before, I do see a significant difference in oil consumption, which is very low when flying on AVGAS and much higher when flying on normal gasoline. I am not sure why. Is there anyone here on the forum that would know the reason for the significant increase?
Could it be the lead in avgas? Perhaps the lead goes some way to gumming up the clearance between valves and their guides, preventing oil getting into the combustion chamber that way?
