Question regarding 100LL in the Rotax 912

[Richard T. Russ]

Hello fellow flyers,

I recently joined your group in preparation for buying a Sport Cruiser of Piper Sport. One of the concerns I have is the Rotax recommendation for not using 100LL. We do not have Mo-Gas at our airport and really don't like the idea of having to fill 5 gallon gans with gass all the time.

Do any of use just 100LL in ypour plane and has this posed a problem. Piper says it is no problem but they also want to sell me a plane.

I would appreciate hearing your comments on the use of 100LL in the Rotax.

Thanking you in advance,

Dick FRuss

[Ben Fitzgerald-O'Connor]

Hi Dick,

You can run on 100LL, but your maintenance intervals and engine life will be shorter. Unleaded is becoming more and more popular over time at airports, and will continue to do so over the coming years - Avgas in the long run is on the way out - environmentally, it has 7 times as much lead as old automotive leaded fuel - evil stuff.

The reason it is not great for the Rotax is that, in the Rotax, as a modern engine, it has water cooled cylinder heads to keep temperatures in control & hence long life & reduced risk of shock cooling - also, the oil lubricates the gearbox, and this can centrifuge the lead out...

Here's a question - how much does AvGas cost Vs Mogas? Here in the UK, fuel is about USD 3 per litre for Avgas, but only USD 1.77 for Mogas - hence it is worh the effort to fill some Jerry Cans! I know your fuel is a fair bit less in the US, but I'm pretty sure that MoGas is still less.Fill up on the way to the airport - it is very little hassle in reality. If you get an air powered (USD 50?) pump, you don't have to balance the cans over the wings, and with 6 hours fuel in the plane you don't need to do this very often.

Oh, and ask your airport when they are planning to convert one of their Avgas pumps to Unleaded - the first time you ask this they may look at you in a strange way, but be sure that this is the way things are going, and a lot of inductry pressure is coming for this for all the right reasons (unless you happen to own an AvGas refinery).

Typically here, we fill up with Unleaded as often as we can (best for our wallet, the environment, and the engine), but fill up with Avgas when away as we need to.

Hope you had a good weekend..

Regards
Ben

PS - Which of our colleagues at Piper gave you this advice? Piper is a big firm, and there is some more education to be done as to the PiperSport which is still a very new product for the organisation. If you can let us know we'll ensure they are briefed accordingly.

[Richard T. Russ]

Hello Ben, Thank you for your response to my questions. Actually piper didn.t personally give me that information. I was at a local fly-in and talking with a couple of Sport Cruiser owners who said that at Siebring Piper had made the statement (that was passed on to me) that you could burn either without a problem.. I guess I will have to change my way of thinking. I have a Piper Lance and it has always been convenient to just fill it up where ever we visit.
Ben, I was visiting with the Sport Cruiser distributor in Florida and they said the same as you. They did suggest that if I do use 100LL that I add Alcor TCP fuel treatment. In Reading the internet about TCP it says that 1 oz of TCP per 10 gallons of 100LL will eliminate the lead problem. Have you any experience with this product? If it would work it sounds to me that this would be a good thing. The cost of the TCP is under $1.00 per ounce.

Our 90 octane Mogas is about $2.79 per gallon. !00LL runs from $3.50 to $4.50 per gallon on average. At our airport PWA, we as a group own our own fuel tank and we pay $3.25 per gallon.
Since I burn 17 GPH now in the Lance, the fuel savings will be significant when I get the Piper Sport.
I look forward to hearing from you.
Best regards,
Dick

[Ben Fitzgerald-O'Connor]

With Mogas, the Rotax recommend 95 Octain or better from my memory - we generally fill with 97/98 here where we get the option as the higher quality fuel. In the UK BP's premium fuel is free from ethanol, but that will vary.

I'll check with people more expert than I in the Rotax, but whilst the TCP might help reduce lead build up at the cyclinder heads, it will likely not help mutch in the gearbox (transferred via the oil)... however, most important with Avgas is to ensure you change the oil regularly - every 25 hours if running on Avgas is best. Oil is cheap, and the Rotax takes about 3 Litres to do a full change, so not going to break the bank, but as I'm always reminded, oil is the blood of the engine, so worth looking after.

NB; You'll notice probably also that the oil burn in the Rotax is a small proportion of that in the Lance - very different engines and aircraft of course, but if you're used to putting in a quart every other flight, then you'll be in for a nice surprise - we burn about a litre every 20 hours or so (new engines may burn more, and they can vary a little)...

Regards
Ben

PS - Fuel is evidently still about half the price in the USA compared to Europe, so you'll be able to enjoy flying for peanuts once you've got your new Pipersport. Are you one of the lucky ones picking up their keys at Sun'n'Fun?

[Richard T. Russ]

Hi Ben,
Thanks for the reply.
No I am not a lucky one picking up a Piper Sport at Sun-N-Fun. Unfortunately there won't be a new plane until I sell my Lance. I'll let you know when I place the order.

Best regards,
Dick

[Ben Fitzgerald-O'Connor]

Dick & All,

I raised this question with Conair here in the UK, who are the Rotax maintanance gurus (and authorised service agents etc.) The answer we have, which we would hence trust is:

'Rotax has gathered from the field experience on using two types of lead scavenging additive. Neither have been tested by Rotax but the experience shows no detrimental effect from the use. We do not have any information on the legality of using this product in the UK & do not know if the CAA accept it as an additive (we believe the CAA have not approved it for use in UK aircraft).
Alcor TCP FAA is apparently approved for certified A/C in the USA.
Decalin only for experimental A/C.
Alcor TCP cannot be carried aboard commercial aircraft.
I understand Decalin is safe for air cargo as it has different carrier solvents.'

- So to summarise, Rotax are saying that the additives are not known to do any harm to the engine, but they do not either recommend their use - I guess this is up to you!

Maybe best to talk to someone with high hours on their engine with these additives and Avgas, to see how their experience has been , this will be your best guide - It would be interesting to compare with another engine not using the additive on same hours.

Regards
Ben

[Wayne Ferson]

My understanding is that Rotax (in the their maintenance classes) no longer recommends TCP but now prefers Decalin as a lead scavenger when you run 100LL. I have also heard talk of flight schools whose Rotax 912s have made TBO with no additive at all on 100 LL. If you run 100 LL its is important not to use a fully synthetic oil, as these oils do not suspend lead as well as a semi-synthetic or dino oil does. Also, the oil change interval on 100LL is half as long. Rotax just changed it to 50 hours from the previous 25. I still change at 25, and I run 100LL only when I am on the road, when I add decalin. The plugs won't last as long on 100LL, and the reduction gear box needs to be inspected and probably overhauled more often. The rotax maintentenance manual now has recommendations on these items. An advantage of 100LL is that it has a longer shelf life than auto gas. Auto gas has its own problems - ethanol. Rotax still says 5% alcohol or less but many run with 10%, and in other countries even higher. If i lived in the corn belt and could only buy high ethanol auto gas, I would mix it with 100LL. - WF