Mogas or Avgas ?

[Tango Oscar]

Hi Everyone

I am the proud new owner of a tri-gear Europa with the Rotax 80hp engine. Having looked at the Rotax website, they recommend Unleaded Mogas as the engine will run 'cleaner' than if Avgas is used. Also the service interval is shortened with Avgas. So, it seemes a simple decision which fuel to use. Is it that simple though ? The storage of Avgas is much more controlled. Refueling at destination airfields could prove a difficult, let alone the cost of the taxi to/from the pertol station.

What do other Rotax owners use ? Maybe a combination of the two ?

Any info greatly apprecieated.

Tango.

[FlyingForFun]

TO,

If you use Mogas, you are restricted to not flying above a certain altitude (6000' I think), and not flying with tank temperatures above 25 degress C. If your Europa is anything like mine, you won't have a tank temperature guage, so you will have to take a conservative estimate of the tank temperature to ensure you stay legal.

For this reason, you will probably find it more practical to run on Avgas in summer, and if flying over mountains or large bodies of water. Otherwise, Mogas is not only the better option, but it's also cheaper.

Bear in mind that if you run on a mixture, no matter how small the amount of Mogas you use, you must treat the fuel as if it were 100% Mogas.

FFF
--------------

[Algirdas]

TO, I now use a 2 stoke Rotax, used to use an HKS 4 stroke. Mogas is apparently better for these engines (inc. 912) (runs cleaner, less deposit buildups), and I use it for preference, but when landing out I use 100LL just because it's less grief to get hold of. Never had a problem with either, and no problems that I have heard of in rotating usage of both. Just for the sake of belt and braces, I always get mogas from high-turnover service stations - I might be wrong, but the constant pump flow probably helps avoid dirty nozzle internals, storage debris and the like.
Fred's unbranded petrol from the back of the donga where he filled up a car last week if he's lucky might not be the best thing to bet your airframe on.

[Tango Oscar]

Thanks for the replies Gents.

It seems a combination is the most practical solution.

I'm intending on selling a couple of shares to help with the fixed costs and recover some capital. Are either of your aircraft group aircraft ? If so, do group members just pay for the fuel regardless of whether it is Avgas or Mogas and claim it back from the flying costs ? Or do you operate with a dry rate, making sure the tanks are always full at the end of the flight.

As before, any info greatly appreciated.:ok:

[Algirdas]

TO,
my current craft is 100% mine. My previous one was syndicate - each member paid a wet hourly rate, and when buying fuel away, submitted fuel bills - the syndicate re-imbursed these at the per-litre rate that the syndicate could buy for at home, rather than the actually paid rate - if that makes sense. Usually a max of 20% difference between the two - i.e. when filling away from home, the trip cost you the wet hourly rate, plus any paid markup on fuel charges.
A

[FlyingForFun]

Mine is a group aircraft, and we pay a dry rate - thus you pay for whichever fuel you put in. (The biggest argument against charging a dry rate - the temptation to over-lean - doesn't apply to our Rotax 914 because it doesn't have a mixture control.)

Algirdas mentions using fuel from a high-turnover station. He suggests that the constant flow may reduce dirt building up in the nozzles, and that is probably true. But the constant flow does not help the filters! We used to use fuel from a fairly quiet garage just outside the airfield, and found we had to change the filters every few hours. Checking the state of the filters was a vital part of the pre-flight, and the first action for a rough-running engine was to turn on the boost pump which bypassed the main filter and used a backup filter instead. We never put two and two together until the garage closed and we were forced to use one further away... and then our fuel filter problems went away.

FFF
-------------

[Volume]

Read Rotax SI-18-1997 (http://www.rotax-aircraft-engines.com/pdf/dokus/d03338.pdf) for more information. It seems the lead from Avgas (contained in the blow by gases) accumulates in the engine oil and leeds to problems with the gears. Additionally the scavengers added to Avgas promote corrosion.
So : If you don´t fly many hours a year, mogas will ´gum´ in your tank and in your carbs, causing problems. Avgas cause corrosion to your engine´s internal parts, if you don´t fly much.
Only sollution : fly more ;)
Anyway it seems to be important to use the right oil with the gas you normally fly, if you fly on Avgas don´t use fully synthetic oil (for corrosion reasons) and use oil with gear additives and change oil more often.