Light Aircraft Association

Hi

I come from a background of Jabiru's and Rotax's so please excuse my ignorance.

I am thinking of buying an RV with a Lycoming ( not decided which yet) but fly from a strip and would like to be able to run on mogas. Is this possible with all lycomings, some of them, or none and what mods will I need to be able to do so?

thanks
john

Look up the list of US STCs for mogas. From memory low compression O-320s are fine, high compression are not and O-360s are generally not approved - but I think there are one or two exceptions.

The 'mods' are paperwork only. UK Mogas approvals of other types may be possible that becomes much more demanding - potentially bringing in testing etc.

You have a pm.

My RV6 came with the mogas mod already done. It has a return feed back to (one of) the tanks. I think it's to avoid vapour lock problems. I believe such mods are required to run the engine (a 160hp O-320) on mogas (assuming the mogas doesn't contain excessive alcohol etc).

There are various threads on using mogas with RVs on the Vans Air Force forums. I recommend having a look there.
For example, one bod sensibly decided to have one tank as a mogas one and the other as an avgas one. He has found days when it's been sufficiently warm that the engine refuses to run properly on mogas so he quickly reverts back to Avgas. Admittedly ambient temperatures get higher in parts of the US than here, and I think he noticed the problem at higher altitudes / elevations, but it is food for thought all the same.

One point I would make is RV's are pretty fast and have quite large tanks (e.g. RV-6 : 36 US gallons). Could you make an arrangement with a nearby airfield with Avgas to fill up there and waive the landing fee? You wouldn't lose much range by filling up elsewhere and quickly nipping back to your home airfield again.

Comprehensive list from US here:

http://autofuelstc.com/autofuelstc/pa/A ... gines.html

This is what engines can run on technically of course not what is currently approved by CAA or LAA. Totally different issue. As you can see from the list most Lycomings will be fine. I read there may be problems with some turbo Lycomings when 100LL goes away.

The mogas/avgas in separate tanks idea may be worth sounding out with Francis. Take off and land on Avgas in warm weather, cruise on mogas. Seems a pretty safe bet to me. You know about the hoses and seals issue of course.

Be careful with the listing referenced.

There octane ratings used by Petersen are MON ratings. (hence 80/87 octane) for Avgas etc.

The ratings quoted on the Mogas pumps are RON - which typically is a higher number. Shell Optimax is the highest octance rated fuel generally available in the UK with a RON of 98. This translates - depending on your source to a MON of 87 or 88. In the US there are higher octanes brands available and hence the possibility of using Mogas in the higher compression ratio engines aero engines.

I've not seen any definitive guidance from the LAA on what is and is not likely to be approved but one of my friends has finally got approval for his O-320 low compression engine after a great deal of correspondance with the LAA. (The issue revolved around his O-320 being a high compression model (hence not approved for ordinary Mogas) - which when he got it rebuilt in the US he deliberately chose low compression pistons...)

thanks for the replies. If one needs to fit a return line does one need to remove the tank and clean it to fit a pipe into it for that line. I take it that there are no issues with the valve seats etc.


cheers
john

johnM wrote:If one needs to fit a return line does one need to remove the tank and clean it to fit a pipe into it for that line.

The return line in mine goes into the tank on the fuel gauge and main outlet plate. It does look like the tank has to be removed from the wing, or the wing from the fuselage, to get the plate off but the mod itself is to this plate and not to the main structure of the tank itself, which is somewhat less stressful. Don't fancy drilling holes in otherwise sound tanks

The mod also requires the routing of the necessary pipe from the tank, through the fuselage and onto the engine side of the firewall. More drilling!