MOGAS and UL98 in Rotax 912 - Real experiences?

[PommyRick]

I'm curious to know how who uses MOGAS or UL98 in their Rotax aircraft? How do you get it the airfield? Is it a headache carrying jerry cans and trying not to spill fuel? Do you experience issues? Do many airfields sell MOGAS? Can you use it interchangeable with avgas? Do many people not use MOGAS at all in their Rotax engines? 

 

[turboplanner]

7 minutes ago, PommyRick said:

I'm curious to know how who uses MOGAS or UL98 in their Rotax aircraft? How do you get it the airfield? Is it a headache carrying jerry cans and trying not to spill fuel? Do you experience issues? Do many airfields sell MOGAS? Can you use it interchangeable with avgas? Do many people not use MOGAS at all in their Rotax engines? 

 

MOGAS is a US term and dangerous to use in Australia because our suppliers are importing all sorts of different blends.

There is a good thread on here about current Australian fuels and the problems when using some of the brands and grades.

[onetrack]

Here are recent threads, there are numerous older threads. Fuel type to use in RA aircraft, and access to fuel supplies for refuelling light aircraft, brings out the biggest variation of opinions and experiences, as you'll find anywhere.

 

https://www.recreationalflying.com/topic/30521-mogas-or-avgas-remote-area-refueling-options/

 

https://www.recreationalflying.com/topic/27017-airfields-with-mogas/

 

https://www.recreationalflying.com/topic/37894-what-is-the-best-fuel-mogas-for-your-engine/

[PommyRick]

Thanks for the links, much appreciated. 

[walrus]

Rotax has a current Service instruction - SI-912 i-001 that details what is required. Anything else, including web posts is hearsay and possibly out of date or just plain wrong - and that comes from a certified Rotax engineer.

 

Rotax requires a minimum RON of 95. up to 10% ethanol is permissible. The SI list various complying national specifications.

 

Avgas reduces your maintenance periods and  possibly increases fuel consumption (mogas has about 3% more energy).

 

Vapor lock is a known issue that is a matter for the airframe manufacturer, not Rotax.

 

I use brand name UL95 fuel from a busy service station.

 

Ends.

 

 

 

 

[turboplanner]

7 hours ago, walrus said:

1. Anything else, including web posts is hearsay and possibly out of date or just plain wrong

2. I use brand name UL95 fuel from a busy service station.

 

Having said this, you then say that.

 

I don't have a problem with an operator using the fuel an engine manufacturer recommends, because that has usually been decided by engineers after extensive testing for reliability.

However, you don't fly an engine, you fly an aircraft, and in RA chances are that the aircraft has been built in a carport by an accountant, and since fuel supply, is right up there with making sure the aircraft has two wings, if you want to survive you have to meet what the engine manufacturer requires PLUS what the aircraft requires as we've pointed out in previous threads.

Unleaded 95 Octane petrol, is unleaded and should meet a 95 Octane test, however:

Australia no longer refines all its domestic petrol where there were a few refiners who worked to a common Australian standard, so in the past your sweeping statement might have carried some weight.

Today "brand name" can mean anything; retailers import refined petrol and diesel from the world market, often on the basis of lowest price. Some shandy petrol down with other, cheaper chemicals.

While one brand name Unleaded 95 Octane might meet the Rotax specification, another might not, and both could be chewing into your tank and fuel lines and blocking your filter.

 

Anyone wanting to check the safety of the fuel they use, or should use, should start with the fuel brand's data sheets. Here's a link to the Shell brand sheets.  https://www.shell.com.au/motorists/shell-fuels/sds-tds.html

 

 

[Old Koreelah]

8 hours ago, walrus said:

Avgas reduces your maintenance periods and  possibly increases fuel consumption (mogas has about 3% more energy)...

I suspected as much: my fuel burn is noticeably lower since switching to 98.

1 hour ago, turboplanner said:

Today "brand name" can mean anything; retailers import refined petrol and diesel from the world market, often on the basis of lowest price. Some shandy petrol down with other, cheaper chemicals…

Our little town is fortunate to have a fuel outlet owned for generations by a local family and managed by a bloke we all know and trust. His brother is a pilot, which is one reason he stocks aviation oils. He has assured me of the quality of their 98.

[walrus]

Turbo, yes, you are right. our fuels are bought on the spot market, I understand mainly from SIngapore. Individual oil companies MIGHT sometimes add their own "secret sauce" of additives, but anyway that doesn't guarantee you anything either because oil companies operate a "borrow and loan" slate throughout Australia so what comes out of a BP pump in Melbourne may well be exactly the same as the Shell product.  We have no way of knowing.

 

Your safety net is that through the tank farms and terminals and the borrow and loan slate, you get a fair amount of blending. I am also aware of Rotax experience in the Third world and the fuels supplied there have been horrendously poor quality with no ill effects. My understanding is that the engine is reasonably tolerant about what it is being fed in the way of fuel.

 

As for vapor lock, that's an airframe issue. Its the airframe manufacturers job to get reasonably cool fuel to the mechanical pump (or the EFI pumps in a 912 iS).

 

I've had exactly one fuel contamination/substitution event in fifty years of driving, and that was a dodgy operator at Peak Hill on the Newall Highway.

 

If the engine was not reasonably tolerant of its diet, it wouldn't have the reliability record it already has.

 

As for oils - thats the reverse. Stick strictly to Aeroshell Sport Plus 4

[turboplanner]

32 minutes ago, walrus said:

As for vapor lock, that's an airframe issue. Its the airframe manufacturers job to get reasonably cool fuel to the mechanical pump (or the EFI pumps in a 912 iS).

 

I've had exactly one fuel contamination/substitution event in fifty years of driving, and that was a dodgy operator at Peak Hill on the Newall Highway.

 

Neither of these has anything to do with the fuel blend and the problems which can occur with some blends.

[skippydiesel]

9 hours ago, walrus said:

Rotax has a current Service instruction - SI-912 i-001 that details what is required. Anything else, including web posts is hearsay and possibly out of date or just plain wrong - and that comes from a certified Rotax engineer.

 

Rotax requires a minimum RON of 95. up to 10% ethanol is permissible. The SI list various complying national specifications.

 

Avgas reduces your maintenance periods and  possibly increases fuel consumption (mogas has about 3% more energy).

 

Vapor lock is a known issue that is a matter for the airframe manufacturer, not Rotax.

 

I use brand name UL95 fuel from a busy service station.

 

Ends.

 

 

 

 

Picky I know BUT ;

 

"............up to 10% ethanol is permissible." Is true as far as the engine itself goes but does not necessarily cover on board fuel tank & delivery systems - check with your aircraft maker  and or use common sense - all components must be ethanol compatible/tolerant to use E10 or any other ethanol blend.

 

"Vapor lock is a known issue that is a matter for the airframe manufacturer, not Rotax" - Again correct however as far as I know no airframe manufacturer has been able to overcome the inherent design of Rotax 9 series (carburettor) engines in that all fuel to carburettors must pass over the engine and is therefore potentially subject to heating and subsequent  "vapour lock" particularly after engine shut down and/or extended holding/taxi time.

 

 

 

Edited January 14, 2022 by skippydiesel

[skippydiesel]

I have been using 98RON in my Rotax 912ULS for the past 10 years/500 hrs or so .

Have , in desperation used AvGas on one or two occasions (no discernible benefit).

On one occasion, again in desperation, resorted to 95RON from a no name brand -  definite reduction in performance.

Have used 95RON from brand suppliers without ill effect or noticeable change in performance.

 

My reasons for using 98RON are;

• Given the widespread belief that ULP can be subject to adulteration during transport/storage, I figure that 98 will give me somewhere between 95 & 98 RON in my tank. This is preferable (to me) for the potential that  95 to be lower than the Rotax specified minimum RON (see above comment)
• In general 98RON is more widely available than 95RON

If possible purchase from an established brand supplier, with a high fuel turn over (for freshness)

[IBob]

1 hour ago, skippydiesel said:

Picky I know BUT ;

 

"............up to 10% ethanol is permissible." Is true as far as the engine itself goes but does not necessarily cover on board fuel tank & delivery systems - check with your aircraft maker  and or use common sense - all components must be ethanol compatible/tolerant to use E10 or any other ethanol blend.

 

 

 

 

 

Not picky at all:

Some months ago I met someone who was waiting for a replacement set of wings for their Jab.
They had been unwittingly using fuel with ethanol, causing the wings to start delaminating.

[Kyle Communications]

I only use 98 and from Caltex or BP ..One of the guys in our club worked for the refinery here before they closed it and he only uses them. So I do that on his advice seeing he was on the cracker for more than 25 years. Never use anything with ethanol as stated above the reasons why. If I had to use 95 then obviously thats all you can get but I would be trying to get it from a good servo not a "cheapie" brand

 

Mark

[Ian]

There are simple tests which detect ethanol in fuel. Food colouring can be used.

Supplying fuel in Australia which doesn't meet standards is an offence. https://www.legislation.gov.au/Details/C2021C00266

Stating that mogas supplied in Australia doesn't meet standards is nonsense. It is just as likely as avgas not meeting standards. The same companies are involved using similar processes.

 

[skippydiesel]

Forgot to address;  There will be lots of differing opinions on these two topic (fuel cans & pumps previously extensively addressed)

 

"How do you get it the airfield? Is it a headache carrying jerry cans and trying not to spill fuel?

I started by using pre loved metal 20 litre oil drums - Pros; no cost, as already had them. Cons; awkward, dont seal well/ fumes and spilt fuel, get rusty bottoms (potential contamination).

I then moved to the plastic replacements to above - Pros; no cost as already had them, no rust/water contamination worries  and they seal well (no spills or fuel degradation). Cons; they are quite delicate and dont take even slightly rough handling or sun warmed fuel pressure (split).

Next - Bunnings Aero Space $18 plastic fuel containers - Pros; Cost effective compared with flashier 4x4 types and traditional metal jerries. Seal well. being jerry shaped easy to strap down for transport. Cons; non really except for the commentary from the (metal jerry) traditionalists and an undersized filler/pour point.

 

" trying not to spill fuel?"

Don't know if I have coved this in the above or if you re refiring to transferring fuel to aircraft tank.

 

Transferring fuel from transport container to aircraft tank ,is a pain no matter high/low wing - As a maturing person, I found lifting 20 L containers into position and then trying to achieve a no spill pour to be quite taxing and sometimes unpleasant due to spilling fuel on myself.

I resolved to purchase an efficient 12V petrol transfer pump. It turns out there are a legion of diesel/kero transfer pumps out there but very few petrol rated ones. What there is tend to be bulky and very expensive. Solution build my own- One Chinese copy ($70) of a high volume/flow Holly positive displacement vain pump, a length of good quality automotive  twin (-/+) cable, length of single auto cable (plus alligator clip) for ground, 2 small Anderson plugs, some black polly fittings and a suitable length of automotive fuel hose I have a pump which will deliver 20 litres in about 3 minutes. Uses the aircraft battery (through an Anderson plug) Comes apart for storing in the aircraft and has so far been perfectly reliable. I use a home made filter funnel for all fuel entering the aircraft tanks.

 

Note: manual petrol compatible fuel transfer pumps are also bulky, expensive and difficult to work on your own (need a slave)

[aro]

4 hours ago, turboplanner said:

Today "brand name" can mean anything; retailers import refined petrol and diesel from the world market, often on the basis of lowest price. Some shandy petrol down with other, cheaper chemicals.

While one brand name Unleaded 95 Octane might meet the Rotax specification, another might not, and both could be chewing into your tank and fuel lines and blocking your filter.

There is a standard for unleaded petrol in Australia, it is reasonable to assume that petrol sold meets that standard.

 

While there are always rumours that petrol is adulterated, it seems unlikely. You would need thousands of litres - literally tanker loads - to make it worthwhile at one servo. Millions of litres at a distributor. It just seems impractical.

 

Most people run their Rotax engines on mogas, if there was a problem we should hear about it.

[Kyle Communications]

My boss at work  has a modified street car with 650hp engine...he does not fill up at his local servo because every single time he does his car is hard to start and runs like a hairy goat...it is a Puma. He fills up about 10km further towards the city at the BP...same fuel grade and it runs perfectly. He is no fool..he programmed the ECU by himself every single parameter and knows a lot about engines in systems. His car is fuel injected as well...so if there is no difference in standards then why does this happen????

 

[aro]

I'm not saying they're all the same - just that they should meet the standard as a minimum. E.g. I don't think there is a separate standard for 98 octane, but 98 octane should meet the 95 octane standard.

 

I tried BP/Shell 98 octane in my Rotax, but it runs much better (smoother) on 95 octane. I asked Bert Floods about it, they said if it runs better on 95 just use it - it meets the requirements.

 

I suspect it is borderline too rich, and the higher density of the 98 octane fuels exacerbates that.

[Kyle Communications]

ARO...that is a whole other minefield I can tell you. A couple of us have been using O2 sensors in the exhaust to check the level to see what the tuning is like.. This also changes dramatically with different muffler systems. We have found the engines we have measured on the ground and inflight the engines are running a fair bit lean in cruise. The jets need to be upsized and actually quite a bit. Both my new Savannah and the RANS S-21 yet to be built...but both engines are built for them. Both engines are big bore kits and I fully expext that I will have to upsize the jets quite a long way to get the engine to run at the right mixture in cruise.

Danny's 912ULS is a stock one and it has a ICP muffler on it..which is a terrible muffler that chokes one side of the engine and gives no back pressure at all on the other side. To get the mixture correct Danny has gone up 2 sizes in jets and now its far better and the EGT's reflect this. So it makes a lot of sense what you are saying but it does rely on length of exhaust header pipes and what type of muffler you have

 

[rgmwa]

I use 95 from a high turnover BP in preference to the 95 available from the recently installed 5,000l fuel facility at our field. I used to use BP98 but got concerned that not flying as regularly as I should meant it stayed longer in the tank than was good for the engine, so I changed to 95.  I'd prefer to use 98 on a long trip if it was available. 

[facthunter]

The days of leaded fuel are numbered but there are still issues of a replacement . There's currently articles on Avweb including a two Octane Possibility (94 and 100). Nev

[Kyle Communications]

I always use a fuel stabilizer in my fuel. It solves the problem of how long you can leave fuel in the tanks. Obviously not for 12 months but for 4 to 12 weeks is ok

 

[kgwilson]

The debate on what fuel to use in aero engines has been going on for years and an numerous threads on this forum and it seems to come down to 

 

a) The devil you know and don't know.

b) What you can get easily

c) What you've been told to use

d What you should use based on manufacturer recommendations.

 

There are 3 advantages to Avgas.

 

1. It has a higher level of quality control than automotive petrol

2. It has a longer shelf life that automotive petrol.

3 It is less likely to suffer from vapour lock at high altitude.

 

There are a lot more disadvantages. It includes the toxin tetraethyl lead, fouls plugs, leaves deposits on the pistons, heads valves etc, costs more, increases maintenance, contaminates lubricating oil, not available everywhere, lower energy content than automotive petrol, the list goes on.

 

Older engines like early lycoming, continental and many others must use Avgas as the materials they are made from, compression ratios etc  cannot cope with unleaded aromatic automotive petrol.

 

Why then do so many owners of modern engines that are perfectly capable of running on automotive petrol still use Avgas with an almost anal fervour. For some I suspect it is what they've been told to do, others because that is what comes out of the bowser at the airfield. Most I suspect have never carried out any research into what is correct, what is historical and what is opinion. Issues regarding quality control are very rare today but the Avgas advocate will always quote a problem that happened somewhere years ago.. Where humans are involved mistakes are made and they can just as easily be made no matter what the product is.

 

What then are the advantages of Automotive Petrol

 

1. It is easy to get anywhere (except at aerodromes)

2. It has greater energy content than Avgas

3. It burns cleaner and does not leave engine deposits & does not include highly toxic lead.

4. It reduces maintenance requirements

5. It reduces engine wear

6. It is cheaper than Avgas

 

The disadvantages include that because it is based on aromatic hydrocarbons it stinks, has a shorter shelf life as the lighter aromatics evaporate off quickly and is more susceptible to vapour lock at high altitude, all, of which are easily overcome by having a well sealed fuel system, mixing some fresh with old fuel in a tank (& you do not need much) & ensuring you have the ability to push cold fuel to the engine.

 

I have said this before on other threads in this forum.

 

I have used 95 & 98 Automotive petrol in my Jab 3300A engine since new. I have never had an issue. The oil stays quite clean through to the next change. I do not need to top up between changes. The pistons, heads & valves stay clean. My fuel consumption is 18-19 LPH at low level at around 2800 rpm and 20-22 LPH at high level at 2850-2900 RPM. Jabiru quote 24-26 LPH using Avgas. My leakdowns are still 75/80 on the worst cylinder.

[facthunter]

You are really not entitled to ASSUME everyone who uses avgas is ignorant. We are all entitled to make our decisions based on what WE KNOW and DECIDE for ourselves. It might be clear cut for you but IF Mogas was the answer for everyone, the US wouldn't be bothered to try to make lead free aviation fuels would they?  Nev

[kgwilson]

I never said everyone was ignorant. Many does not mean all. As I said there are plenty of old engines around that won't run on Automotive petrol. A lot of owners of modern Lycoming & Continentals that will run on unleaded fuel in the US do so. Leaded Paraffin based Avgas is definitely on the wane. OIR, Skyfuel and Word Fuel have all approached us in the last year wanting to provide Avgas on our aerodrome supplying and installing a self bunded portable facility at no cost to us. Our volume estimates are not that great but they are still keen. That's a pretty good indicator of a sliding market  in my opinion.