AVGAS observations

[Kenlsa]

Our operation runs 4 Jabs (3x170, Gen4-- 1x230 Gen2) as well as a Roko.

 

In the last few months the Jabs (Roko under major repair--tin work) have needed to have their heads removed due to low compression, 6 from memory.  Initially it was only the Gen4s and on inspection there was a large amount of lead in the chamber/ex valve seat. Far more than we would normally see. The engines are mid life. We have been running Gen4 since they first came out as part of a Beta test, and have never had a problem like this before.

We run flat out, with a 25 hourly every 2 weeks per aircraft, with a new motor every 2 years.

 

Typically the lead comes off just by touching it with a finger nail and some of the pieces are the size of a corn flake and break off to bare metal underneath. The remaining deposits only need a light scrape and it instantly powders like corn flour. No real need for a wire brush, though it does clean it up like new, almost instantly.  Previously, lead needed quite some work to remove. Not these last few months. The gen 4 also showed signs of gummy/hard deposits in the ring grooves.

 

Oil was filthy after 25 hours, far more than usual. To keep the rings clean we have reverted (under advisement) to Straight 100 for 25 hours and that fixed the dirty oil problem OK and colour/deposits are now back to normal.

 

What was going on? At least the 230 is OK, so maybe there is something with the Gen4 we said........Until yesterday.

 

As well as another 170 with dud compression on 1 pot, the 230 now has comps in the high 40s. This aircraft is on its second motor (first replaced due to prop strike) and mid life. It has always been high 70s/80. What you would call a keeper of an engine. It was very hard to start when we warmed it up for its 50 hourly. Cold pull thru was low as well. This is our touring plane and isn't used as much.

 

Cyl 2,3 and 6 were lucky to get to 48/80. the rest were at 75/80.  Heads off and inspection revealed the same problem as the Gen4. Finger nail touch method removed a lot of the lead, in large chunks and the rest was easily removed with a gentle scrape. After clean up we found some old lead deposits on top of the valve, that you just could not get off easily (just like old times!).

As stated these are training aircraft and flown every day. We have NEVER had a problem like this, so many in only a few months.

 

So, the committee has decided to run a trial period of MOGAS asap, with a view to completely converting the whole fleet over if it proves beneficial.

I run MOGAS in my Jab with no problems as a private owner and can't see a problem with any fleet use.

 

I know that many of you run MOGAS in your private planes, but I am interested if any schools are running it in their fleet? 

Has there been a bad batch of fuel?

Anybody else note the same in the last 3 months?   

 

I will keep you posted.

Ken

[facthunter]

Dark oil is usually rich mixture. Some deposits may  contain dust.  Do you check blowby indications as distinct from just comp figures?  Any loose carbon deposit may incandesce and cause pre ignition. Nev

[Kenlsa]

All low comps are from ex valve, with evidence of lead hammered into the face. OK after a quick grind and back to flying.

Re the dark oil - induction system is ok with clean filters. No induction changes have occurred. This is not on just one plane, but occurred on 3 at similar times. Just hope it isn't one pilot taking a new plane each time and flying with he carb heat on, looking for dust storms!

Ken

 

[RFguy]

I know a school nearby that runs MOGAS in their  2 x Gen3 Jab engines. (2200) without trouble.

Cowra school runs on MOGAS. (Rotax).

[Boongala]

5 hours ago, Kenlsa said:

All low comps are from ex valve, with evidence of lead hammered into the face. OK after a quick grind and back to flying.

Re the dark oil - induction system is ok with clean filters. No induction changes have occurred. This is not on just one plane, but occurred on 3 at similar times. Just hope it isn't one pilot taking a new plane each time and flying with he carb heat on, looking for dust storms!

Ken

 

All air inducted in to a Jabiru engine (in a Jabiru airframe) is filtered, I’m surprised in view of your above posts you didn’t know that

[Kenlsa]

Kidding,... and I'm surprised you didn't get it 🙂  I have been working on Jabs in our club for almost 4 years, no offence taken.

[Thruster88]

Are the other avgas burners at Gawler, such as the tugs having any problems? I assume there is only one avgas bowser.  

[Kenlsa]

T88, we have 2 tugs but all their maintenance is done at Parafield by LAMEs. But seems like every service they are in need of a heart lung transplant according to the shop!

This( potential) leading problem has only come about in the last few months and picked up at the 50/100 hr service. Zorst valve each time.

Easy to fix but time consuming, and I am glad I have had my Lead Inoculation, so I am quite safe!

The Committee decided last night to go full bore on the MOGAS for the Jabs and ROKO with the Tugs remaining on the AVGAS, though they have an STC for MOGAS and so has my Colt.  I think the tuggies are nervous of a 46 deg day towing a ballasted twin seater to 3000 ft.  They feel safer with Avgas. 

Ken 

[Roscoe]

23 minutes ago, Kenlsa said:

T88, we have 2 tugs but all their maintenance is done at Parafield by LAMEs. But seems like every service they are in need of a heart lung transplant according to the shop!

This( potential) leading problem has only come about in the last few months and picked up at the 50/100 hr service. Zorst valve each time.

Easy to fix but time consuming, and I am glad I have had my Lead Inoculation, so I am quite safe!

The Committee decided last night to go full bore on the MOGAS for the Jabs and ROKO with the Tugs remaining on the AVGAS, though they have an STC for MOGAS and so has my Colt.  I think the tuggies are nervous of a 46 deg day towing a ballasted twin seater to 3000 ft.  They feel safer with Avgas. 

Ken 

Ken what are your thoughts about Jabirus recommendation for Avgas over Mogas due to QC and traceability issues?

[Yenn]

Mogas is good if you can get a consistent quality. I ran my RV4 on mogas for a short while and there was no difference in performance. I went back to Avgas because of the mogas affecting the proseal used in the fuel tank, Only ever used it in one tank and only had problems with that tank. Mogas can vary greatly in quality from different servos, which I think is a bit of a  gamble.

[Kenlsa]

For a starter, I think we are going to drums and pump, supplied direct from the supplier.  That should be interesting as I feel that many younger students wouldn't have ever seen one!

There is a move to go to a bowser later, and we are prepared for it. We will not be dependent on servo fuel. The rate we clock up the hours, stale fuel won't be an issue.

This should keep the risk profile to a minimum. 

I haven't met any Jab pilots using MOGAS who have complained about it, tho I am open to correction on this.

Ken

[Downunder]

Never tried DECALIN with the avgas?

 

[skippydiesel]

4 hours ago, Yenn said:

Mogas is good if you can get a consistent quality. I ran my RV4 on mogas for a short while and there was no difference in performance. I went back to Avgas because of the mogas affecting the proseal used in the fuel tank, Only ever used it in one tank and only had problems with that tank. Mogas can vary greatly in quality from different servos, which I think is a bit of a  gamble.

 

In about 600 hrs of Rotax 912 ULS flying  - NSW & into Qld - never had so much as a hiccup with ULP.  At "home" all 98 RON - "away "both 98 & 95 RON.. On two occasions, circumstance  had me try out a "shandy" of ULP/AvGas. No discernible performance differences.  Always tried for servo's that were likely to have a high turn over of fuel and if possible one of the main brands, but in the end fuelled up with whatever was available.

 

Hardly scientific observation but real experience.

[kgwilson]

I have used Mogas in my Gen 3 3300A engine since new without any problems. Initially I used BP 95 after consultation with others (a number via this site) but switched to 98 after the local BP stopped supply & went to 94 which includes ethanol. Quality control and Jabirus recommendation (done because of possible litigation if they do not issue warnings in their manuals) is the only benefit of using Avgas. There is one dubious benefit of possible vapour locks with Mogas but I've yet to find anyone who has had any with their Jab engine. The bad thing about Avgas is the lead and deposits which can lead to preignition & is poisonous.

 

My leakdowns are all close to 80/80, the pistons & heads look clean when checking via the borescope & the oil is still relatively clean after 25 hours. The ceramic plug insulation stays almost white, the engine starts after about 1-4 revolutions of the prop from cold and instantly when hot. No 5 shows a slight colour & No 6 definitely a bit rich. I've tried to sort it out & have failed but as the engine runs so well I have just given up & accepted it.

 

I've only used Avgas when that is all I could get when away from home so was a shandy. Performance didn't change. I am a private owner & 50-60 hours a year in about 70 - 100 flights. I get my local fuel now from a busy servo 250 metres from the aerodrome & always filter it through a Mr Funnel & have never had any contaminants show up.

 

The cons of Mogas 98 are the aromatics (Toluene, Xylene Benzene) that evaporate off over a few weeks but that is easily controlled by putting fresh fuel in on top if the engine has not run for a couple of weeks. Also 98 stinks & the aromatics permeate through my Vinylester fuselage mounted tank & the cockpit reeks when the canopy is first opened.

 

Most of the GA pistons can now run on Mogas as well so I would think that there is a declining market for Avgas. I'll only use Avgas when I can't get Mogas.

[Old Koreelah]

9 hours ago, kgwilson said:

... Also 98 stinks & the aromatics permeate through my Vinylester fuselage mounted tank & the cockpit reeks when the canopy is first opened...

Kev I too have vinyl ester tanks so that’s interesting. Does 95 have the same problem?
 

This recent AvGas issue got my attention; the buildup of crap inside my combustion chambers had me concerned enough to give my engine a dose of the Subaru cleaner.

Looks like I’ve been waiting in vain for lead-free AvGas. I’ve stuck with proper aeroplane fuel because we were told of Jab engines being damaged by low-quality car fuel, so it’s good to hear that you and others have had years of trouble-free experience with it.
 

I’m very tempted to fill one wing tank with MoGas before a long trip, so I can start, takeoff and climb with AvGas and then switch over to MoGas for cruising. 
 

One problem then is that I’d be using so little AvGas that my drum would only need refilling every second year- and our supplier is a stickler for the rules.

[kgwilson]

The aromatics are lighter with smaller molecules that are able to permeate vinylester. 95 has fewer of them so the pong is not as bad. It goes away once you get fresh air through the cockpit.

 

The following explanation in italics is from a chemical engineer and pilot.

 

What is the Difference between mogas and avgas? 

 

The main difference is avgas is based on completely different chemistry, paraffin (the flammable component of candle wax) and mogas is based on aeromatic hydrocarbons (like benzine). (Forget about alcohol - mogas MUST be alcohol free)

 

The paraffin base makes avgas much more stable (so it can be stored a long time) and it has a much lower Reid Vapor Pressure (a much higher boiling point, to avoid boiling, or vapor lock, at altitude.)

Avgas's paraffin chemistry makes it more dependent on tetraethyl lead to achieve its octane rating, which is much higher than mogas in the first place, whereas mogas's naturally more detonation resistant chemistry, lesser vapour pressure requirements and lower octane requirements allowed for lead to be eliminated in the 70s using other means to achieve its octane rating.

 

The main practical differences in general aviation are mainly that it's not a good idea to store an aircraft with mogas in the tanks for long periods because it will go bad sooner and you will get vapour lock more readily with mogas so you can't fly as high, and heat exposure to the fuel system has to be controlled (such as by using air-blast shrouds on fuel pumps). Vapour lock is less of a problem on gravity fed systems because there is positive pressure all the way through the system. Pump-uphill fuel systems have suction in the fuel lines which is like climbing to a higher altitude.

 

Pilots generally only use mogas in carbureted engines meant for 80-87 avgas but you can use 94 octane mogas in a 100 octane non-turbocharged engine without problems (in Canada, commercial bush operators can use mogas by STC/STA in supercharged engines like R-985s, so the octane rating isn't that big a deal on engines with 8:1 compression).

 

I use mogas in my own airplane, who's low compression 80-87 engine is much happier on it than 100LL (not having to clean lead fouled plugs regularly). The most noticeable differences is it makes a lot more black soot in the exhaust for some reason, with the same leaning practices. I add the occasional tank of avgas periodically because the lead has a beneficial lubricant effect on valve seats.

 

Another minor issue is leaded aviation fuel doesn't like synthetic oil. Synthetic oil's chemistry can't keep the lead is suspension so it forms "lead paint" inside the engine. This was a problem when Mobil AV1 aviation oil was introduced (there was a big class action lawsuit). On mogas, synthetic oil is not a problem (I use Aeroshell 15W50 semi-synthetic in my plane).

 

My engine is gravity fed and there is an electric auxilliary pump directly under the tank outlet so I won't ever have problems with vapour lock.

[skippydiesel]

"

Point of clarification -  ULP... it has a much lower Reid Vapor Pressure (a much higher boiling point, to avoid boiling, or vapor lock, at altitude."

 

The altitude matter may be more of a concern for IFR pilots and pilots operating VFR in countries that allow operations above 10,000f.

 

In the Au summer, temperatures vapour lock is a real potential, to the engines disadvantage - I have found that it is a manageable issue by avoiding take offs when temperatures exceed 30C. On those occasions where I must take off in 30+C conditions I am very careful to do a long run up to clear any "gas", use as much runway as available,  and have an "abort" plan in the event of low engine power.

[Kenlsa]

I note that TEL is only made by 4 refineries, 1 in the US and  3 in China. 

Since this has only happened in the last few months, the conspiracy theorist in me is working overtime........

Ken

[Thruster88]

Piston helicopter operators in northern Australia have been reporting more than usual valve failures in lycoming engines over the past few years. Some believe it is caused by the avgas.

https://www.casa.gov.au/aircraft/airworthiness/information-operators-r22-and-r44-helicopters

[Flying Binghi]

On 25/09/2020 at 2:52 PM, Thruster88 said:

Piston helicopter operators in northern Australia have been reporting more than usual valve failures in lycoming engines over the past few years. Some believe it is caused by the avgas.

https://www.casa.gov.au/aircraft/airworthiness/information-operators-r22-and-r44-helicopters

 

The engine rebuild shops have proof positive it is the crappy so-called avgas available now. 

 

Take a quick sniff of the avgas next time you fuel up - it smells a lot like car fuel now. To reduce the lead levels they have added a lot more aromatics etc.

 

 

 

 

.

[Flying Binghi]

“...Examining the history of avgas supply to aviation operators in the northern parts of Australia, it was evident that over recent years, manufacturers had reduced the absolute levels of tetraethyl lead (TEL) in the avgas product, from historical levels of around 0.75 gPb/l in 2012, to around 0.38 gPb/l in 2018. To maintain the fuel’s Motor Octane Number for defence against damaging detonative combustion, other fuel chemistry variations would be expected – typically an increase in the level of aromatic hydrocarbon components. Data to support explicit conclusions in this area was not available to this investigation, with the manufacturer citing commercial sensitivity concerns...”

 

 

https://austhia.com/PDfs/AHIA-piston-engine-durability-report.pdf

 

 

 

 

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