Page 1 of 1
Rotax 912 mogas/avgas
Posted: Sun Jan 17, 2010 5:56 pm
I know that the use of avgas reduces the time before service from 100hrs to 50hrs. Can anyone tell me what the ratio of mogas to avgas is if using mogas as the primary fuel, but filling up with avgas on trips out, before I have to consider reducing to the 50hrs for a service?
Posted: Sun Jan 17, 2010 9:38 pm
What l do is to make notes in my fuel log and then ratio the times. The service is therefore calculated using a linear scale, 100% MOGAS equals 100hrs, 100% AVGAS is 50hrs, if its 50:50 then the service is done at 50% x 50hrs = 25hrs + 50hrs = 75hrs. 25% AVGAS would give a service at 25% x 50 + 50 = 62.5hrs. Seems to work and be in keeping with the requirements. Clearly if you use AVGAS for 50hrs you will need to do the service straight away. My mathod works on teh basis that MOGAS is the standard use, AVGAS being used only when no other option exists.
Regards John Wighton(Aerodesign)
Posted: Mon Jan 18, 2010 2:00 pm
That question was asked at one of the LAA-organised Rotax maintenance awareness courses, which I attended last summer. The concensus (unofficial) was that if Avgas use was kept at less than one-third of the total, then, in conjunction with using a good lead scavenging oil, the service interval could be kept at the full Mogas-only number of hours.
I guess the idea being is that it allows sufficient time for the Mogas and oil additives would remove any build up of lead deposits.
Please treat this note as hearsay. I am not qualified in any way to pronounce formally on the subject. If you want a qualifire comment, I could contact the maintenance organisation which ran the course.
Europa XS Mono #550
Posted: Mon Jan 18, 2010 4:40 pm
Rotax service instruction SI 912-016 tells you all you need to know.
Chapter 3.3 goes into the use of Avgas.
The quickest way there is by this link.
Posted: Mon Jan 18, 2010 4:43 pm
We tend to avoid Avgas whenever possible, but it is not always possible when touring away from home.
If we manage to keep it below 10% of the fuel total in 100 hours, we simply service the engine on an early-rather-than-late sort of basis.
You only have to have a look at the '912 on Avgas' internal photos to see how bad Avgas is for the oil, this is definitely a real issue!
Posted: Mon Jan 18, 2010 7:03 pm
Thanks for the advice, I'll treat the 100hrs as a percentage and base it on the 30% rule as indicated on the Rotax service bulletin.
Posted: Tue Feb 23, 2010 1:44 pm
John Wighton wrote:The service is therefore calculated using a linear scale, 100% MOGAS equals 100hrs, 100% AVGAS is 50hrs, if its 50:50 then the service is done at 50% x 50hrs = 25hrs + 50hrs = 75hrs. 25% AVGAS would give a service at 25% x 50 + 50 = 62.5hrs.
Hang about on that second calculation!
AVGAS 25% of 50 hours = 12.5 hours.
MOGAS 75% of 100 hours = 75 hours.
That's 87.5 hours interval, not 62.5.
Or am I missing something?
Somebody once called me Mr.Pedantic. I had to point out that should be Mr.Pedant.