LIFE OF MOGAS

[Flooi]

Anyone have any idea how long mogas (95) will last in an aircraft (912S) before octane become too low for safe flying?

[Flooi]

Is julle nou vasgevra? Horace- any comment?

[KFA]

From wikipedia

Quality gasoline should be stable almost indefinitely if stored properly. Such storage should be in an airtight container (to prevent oxidation or water vapors mixing), and which can withstand the vapor pressure of the gasoline without venting ( to prevent the loss of the more volatile fractions), and at a stable cool temperature (to reduce the excess pressure from liquid expansion, and to reduce the rate of any decomposition reactions). When gasoline is not stored correctly, gums and solids may be created, which can corrode system components and accumulate on wetted surfaces, resulting in a condition called "stale fuel". Gasoline containing ethanol is especially subject to absorbing atmospheric moisture, then forming gums, solids, or two phases (a hydrocarbon phase floating on top of a water-alcohol phase).
The presence of these degradation products in fuel tank, lines, carburetor or fuel injection components makes it harder to start the engine, or causes reduced engine performance. On resumption of regular engine use, the buildup is often eventually cleaned out by the flow of fresh gasoline. The addition of a fuel stabilizer to gasoline can extend the life of fuel that is not or cannot be stored properly. Some typical fuel stabilizers are proprietary mixtures containing mineral spirits, isopropyl alcohol, 1,2,4-trimethylbenzene,or other additives. Fuel stabilizer is commonly used for small engines, such as lawnmower and tractor engines, especially when their use is seasonal (low to no use for one or more seasons of the year). Users have been advised to keep gasoline containers more than half full and properly capped to reduce air exposure, to avoid storage at high temperatures, to run an engine for ten minutes to circulate the stabilizer through all components prior to storage, and to run the engine at intervals to purge stale fuel from the carburetor.

[Flooi]

I found this. Dankie Stefan.

http://www.bp.com/retail/liveassets/bp_ ... anksv4.pdf

[John Boucher]

I don't think my good mate Horace is on this forum but I will ask him for his knowledge... I am popping around to his house tomorrow so will do so then!

[John Boucher]

If the fuel is bought from a filling station with a high turnover... and you then indeed get 95 then the following...

The fuel will roughly lose 1 octane point per month. Also to note is the AKI. Thumb suck AKI of fresh 95UL is 90 and this also loses a point per month.

The 912UL 's AKI requirement is 87 and thus you should not leave fuel for longer than 3 months I would imagine (but I wouldn't any way!)

The 912s and 914 requirement is 91 but do we get that?

My personal rule is that I leave the minimum possible and always try and fly with fresh fuel

http://www.rotaxservice.com/rotax_tips/rotax_feed4.htm

The site refers to "avoid fuel older than 3 weeks"

[Flooi]

If the fuel is bought from a filling station with a high turnover... and you then indeed get 95 then the following...

The fuel will roughly lose 1 octane point per month. Also to note is the AKI. Thumb suck AKI of fresh 95UL is 90 and this also loses a point per month.

The 912UL 's AKI requirement is 87 and thus you should not leave fuel for longer than 3 months I would imagine (but I wouldn't any way!)

The 912s and 914 requirement is 91 but do we get that?

My personal rule is that I leave the minimum possible and always try and fly with fresh fuel

http://www.rotaxservice.com/rotax_tips/rotax_feed4.htm

The site refers to "avoid fuel older than 3 weeks"

Thank you sir. Very very informative! Consider then that the 912/s/4 flyers need to refresh fuel after lengthy summer
rains where weather is unfit for flying- -- sometimes for long periods. And then there is the airspace closures that come
up now and then. So drain it from your tank for your car and buy fresh fuel!

[KFA]

http://www.rotaxservice.com/rotax_tips/rotax_feed4.htm

Thanks, that was the one I was looking for

[Bundy]

Now my Microland buddies would say..... "If you worried about this...you're not flying enough!"

Interesting debate....kinda like "What oil should we be using?" Ask 5 different AP's.... you get 5 different answers.

A lot of guys I fly with also put in fresh fuel before they fly. Is there not an additional risk of condensation in the tank if left "half" or even "quarter" full?

For Stef and myself, we fill up the tank after flying for two reasons:

1: It's a partnership and we are each responsible for our own fuel cost so just courteous to leave your flying pal with a full tank of juice...
2: Reduces the risk of condensation in the tank by having it full?

It is rare that our plane is not flown by either Stef or myself in a 3 week period so to be honest I'm not too concerned? I agree though that if the aerie stands for a prolonged period...rather drain the tank and replenish with fresh "go go" juice.

[John Boucher]

I always "drain" prior adding fresh fuel....

Do the WCM tanks have drain points for the purpose of fuel inspection?

[Bundy]

I always "drain" prior adding fresh fuel....

Do the WCM tanks have drain points for the purpose of fuel inspection?

Affirm....right at the bottom...strategically placed so you can moer your head on the exhaust or prop while you bend down to check...

Staying on the subject of water contamination...(and I believe this applies to any aircraft)...

My initial Instructor taught me that the first thing you check when you get to your plane is for water in the fuel. This must be done before you even move the aircraft for any reason. It's the first thing I check after I've taken the hanger cover off...chocks and "wing tip ties" still on...IE the trike has not moved since it was last parked.
This ensures that any water present will be at the bottom of the tank and will/should immediately reveal itself in the tester tube.

I see many people topping up their tanks and only then checking for water (which will then still be in solution) as part of their pre flights...which to me is completely useless?
Even just pushing the plane out of the hanger to do a preflight will swirl the fuel and any minute traces of water around....which may not be picked up in a subsequent check?

That is another reason why I/we keep our tank full....afterall, how do you know your jerrycan did not have a bit of water in it?

Just my opinion.

[John Boucher]

My initial Instructor taught me that the first thing you check when you get to your plane is for water in the fuel.

Wise instructor...

My containers get fresh fuel which I empty on re-filling aircraft - nothing is left standing over for next time!
I don't do jerry cans because I want to see what is inside the container!!
I do not leave any residue in the container - klaar!
I do not use anyone else's container - I trust my own!

Each to their own

[mulderpm]

Always try to fly with as fresh a fuel as possible. If you do not intend to fly for a long time or return to fly after a long time of no flying, put your aeries fuel in your car or lawn mower and fill up with fresh fuel.

The way I understand it is, the main reason to use higher octane fuel is to prevent pinging or pre-ignition or knocking. This is caused by the lower ignition temperature of lower octane fuel, causing the fuel to ignite too early (Before Top Dead Centre), before the spark ignites it fully. The higher the compression ratio of the engine the earlier a specific octane fuel will ignite. Therefore, the higher the compression ratio the higher the octane required. A petrol 4 stroke engine has about a 10:1 compression ratio requiring 95 octane at the coast and 93 octane inland and a diesel engine has about a 22:1 compression ratio. On some high performance petrol cars you get up to 13:1 compression ratios. These engines have knock sensors and electronic control units to allow them to run on 95 octane.

Now, a two stroke Rotax engine has an effective compression ratio of 6:1. 93 Octane is therefore quite sufficient at any altitude. I have never heard about a two stroke engine that pre-ignites nor one with knock sensors. I use 93 octane unleaded (metal free) and have never had a fuel octane related problem. I have also never had condensation water in my fuel when doing the pre-flight fuel drain test. I do this first thing after removing the hangar cover. Then nothing moves, including sedimented dirt. Maybe at the coast and with high rates of temperature change this could be a problem.

When I fly cross country I sometimes fill up with 95 octane, as I have heard that, it is a better quality fuel. I do not notice any difference between the two.
For a 582, Rotax specifies a minimum of MON 83, RON 91, AKI 87 and leaded or unleaded or AVGAS 100LL or Ethanol 10. So, only Diesel is excluded.

I do not use my jerry cans because they rust and you cant see inside. Jerry cans are for my cars diesel when going into the bundus.
My siphoning pipe also has an in line fuel filter.

[Bundy]

Thanks Paul...interesting stuff.

So if you lose roughly 1 octane per month....can we deduce that if you only fly once a month or so, in terms of the "longevity of fuel" it would be better to fly on 95 octane?

[mulderpm]

Hi Al,

Any octane between 90 & 100 should be ok. The higher the better because it gives room for "impropper storage " as is the case in your aeries fuel tank. In a plastic fuel can, made for that purpose, and with all the vents air tight, the fuel should not age. My rule is, if I can smell the fuel it is not properly stored.