MOGAS & AVGAS ??

[wiskeyfoxtrot]

Hey guys, mabey im just thick, but can you tell me the difference between Mogas & Avgas.
Are there different ocatne ratings like we get in our normal fuel etc. does the costal fuel (Avgas ) differ from up here in the highveld?
Had an argument with a mate of mine, and said i would ask the experts about it !

Thanks guys.

Later

[Morph]

Mogas - Typically UNLEADED 95 Octane Petrol

AVGAS - Typically highly Leaded 100 Octane

You can use Avgas in your ROtax motor, but due to the leading you will notice fouling of the plugs a lot quicker

[KFA]

I was bored so I got this complements of wikipedia
100LL
The most commonly used aviation fuel is dyed blue for easy visual identification. 100LL, spoken as "100 low lead", contains a small amount of tetra-ethyl lead (TEL), a lead compound that reduces gasoline's tendency to spontaneously explode (detonation or "knock") under high loads, high temperatures and high pressures. Sustained detonation causes catastrophic engine failure.

TEL, is known as an anti-knock compound. TEL's effect on detonation resistance is known as the "octane rating," derived from comparing performance of the gasoline under test to mixtures of iso-octane and normal heptane in a special test engine. If the product tests like 90% iso-octane and 10% normal heptane, it receives a "90 octane" rating. As higher levels of anti-detonation capability were required, the curve was extended beyond 100% iso-octane and called "performance rating." Example: a 118 octane rated gasoline is more detonation resistant than an 87 octane rated gasoline.

Historically, many post WW2 developed, low powered 4 and 6 cylinder piston aircraft engines were designed to use leaded fuels and a suitable unleaded replacement fuel has not yet been developed and certified for most of these engines -- although some were designed for 91/96 octane AVGAS (long since discontinued) and many Continental and Lycoming light airplane engines designed for 80/87 continued in production. Engines designed for 80/87 can use AVGAS 100 or 100LL with special precautions to prevent lead buildup and lead fouling of the spark plugs.

Some of the lower powered (100hp to 115hp) aviation engines that were developed in the late 1990's are designed to run unleaded fuel, but use 100LL if unleaded fuel is not available. An example being Rotax 912.

Numerous current (2010) certificated reciprocating-engine aircraft require high-octane (leaded) fuels.

As of Jan 2010, 100LL has a TEL content of 1.2 to 2 grams TEL[6] per US gallon, or 0.56 grams/liter and is the most commonly available and used aviation gasoline. 1 gram of TEL contains only 6/10 of a gram of lead.

Many general aviation aircraft engines were designed to run on 80/87 octane,[citation needed] roughly the standard for North American automobiles today. Direct conversions to run on automotive fuel are fairly common and applied via the supplemental type certificate (STC) process. However, the alloys used in aviation engine construction are rather outdated, and engine wear in the valves is a potential problem on automotive gasoline conversions. Fortunately, significant history of mogas-converted engines has shown that very few engine problems are actually caused by automotive gasoline. A larger problem stems from the wider range of allowable vapor pressures found in automotive gasoline; this can pose some risk to aviation users if fuel system design considerations are not taken into account. Automotive gasoline can vaporize in fuel lines causing a vapor lock (a bubble in the line), starving the engine of fuel. This does not constitute an insurmountable obstacle, but merely requires examination of the fuel system, ensuring adequate shielding from high temperatures and maintaining sufficient pressure in the fuel lines. This is the main reason why both the specific engine model as well as the aircraft in which it is installed must be supplementally certified for the conversion. A good example of this is the Piper Cherokee with high-compression 160 hp (120 kW) or 180 hp (130 kW) engines. Only later versions of the airframe with different engine cowling and exhaust arrangements are applicable for the automotive fuel STC, and even then require fuel system modifications.

Vapor lock typically occurs in fuel systems where a mechanically-driven fuel pump mounted on the engine draws fuel from a tank mounted lower than the pump. The reduced pressure in the line can cause the more volatile components in automotive gasoline to flash into vapor, forming bubbles in the fuel line and interrupting fuel flow. If an electric boost pump is mounted in the fuel tank to push fuel toward the engine, as is common practice in fuel-injected automobiles, the fuel pressure in the lines is maintained above ambient pressure, preventing bubble formation. Likewise, if the fuel tank is mounted above the engine and fuel flows primarily due to gravity, as in a Cessna high-wing airplane, vapor lock cannot occur, using either aviation or automotive fuels.

In addition to vapor locking potential, automotive gasoline does not have the same quality tracking as aviation gasoline. To help solve this problem, the specification for an aviation fuel known as 82UL has recently been developed. This fuel would be essentially automotive gasoline that has additional quality tracking and restrictions on permissible additives. This fuel is not currently in production and no refiners have committed to producing it.[8]

The main consumers of avgas at present (mid-2000s) are in North America, Australia, Brazil, and Africa (mainly South Africa). Care must be taken by small airplane pilots to select airports with avgas on flight planning. For example, U.S. and Japanese recreational pilots ship and depot avgas before flying into Siberia. Shrinking availability of avgas drives usage of small airplane engines that can use jet fuel.

In Europe, avgas prices are so high that there have been a number of efforts to convert the industry to diesel instead, which is common, inexpensive and has a number of advantages for aviation use. However, avgas remains the most common fuel in Europe as well.

[wiskeyfoxtrot]

Thanks Morph & KFA
Very interesting read.

So avgas can be used in my Rotax if nothing else was available ?

" Avgas price & availablity " This has been one of the things that has " worried " me about buying a fixed wing aircraft, only to find that you are now stuck with massive fuel costs & non or little availablity. Have looked at some of the posts on Avcom, where they have shown the costs of Avgas around the country at different airports - scary stuff. does not look like it is regulated ?
I do like the Jubi aircraft but with avgas type motors find that it is not what i would want, hunting for fuel ? etc.
Both have pros & cons it seems. You mentioned diesel. Can that be used for aviation engines ( high sulpher content ) ??

Is JET A1 power parafin??, with a couple of secret ingredients??

Thanks again guys,

Later

[Wargames]

So avgas can be used in my Rotax if nothing else was available ?

In short, yes. But not for extended periods of time. Remember, that your engine is made for mogas.

" Avgas price & availablity "

You need to do a bit of flight planning to find out who has avgas, and who not.
On the price issue, its a bit of a rip off. I got avgas at wonderboom in december at 10.50 per litre. Then flew to kimberley, and got avgas at 7.50 per litre. So yes, it is a rip off.

Is JET A1 power parafin??, with a couple of secret ingredients??

Don't know the exact formula, but if no jet fuel available, you can replace it with a mixture of 75% Diesel mixed with 25% parafin. It halves your overhaul time though.

[Morph]

So avgas can be used in my Rotax if nothing else was available ?

In short, yes. But not for extended periods of time. Remember, that your engine is made for mogas.

it won't damage the engine, just require the plugs to be changed more frequently, and in the case of a 4 stroke, the engine oil as well

[wiskeyfoxtrot]

Thanks Morph, KFA & Wargames,

As usual you guys are a wealth of information!. Good to know these things when you are out somewhere and no mogas is available etc,

Think i need to start selling Avgas, looks like you can make a decent living from just that

Thanks.

Later

[HansK]

Spoke to Louis at Springs. He said that most engine failures on Jabbie's he has inspected, was fuel related, mostly detonation.

[wiskeyfoxtrot]

Have done a little more checking up and found that some aircraft that are supposed to use Avgas have been using Mogas. These aircraft have been bought new and have only ever used Mogas with no bad wear or side effects after many hours on the motors ?

also said to me that the octane rating is a big factor......

With the way the prices are going at the moment , and with emmission regs getting stricter im sure that the days of Avgas are numbered.
Do these fuels ( Avgas ) perform better at altitude ?

another can of worms?

Later

[skybound®]

Avgas price & availablity

I would say it is the other way around - Avgas is available at every airfield that sells fuel. There are many certified aircraft where a STC exists allowing the owner to convert to Mogas - the reason why it has not been that popular is that other than perhaps Kitty Hawk - there are no Mogas vendors at airfields.

[JvTonder]

I say stick to what the books tells you. I have a 912 and only fly 95 mogas, if I use avgas the TBO gets cut in half. You can use avgas or 93 in a pinch but don't make it a habit.

[Chunky]

I only use mogas, Shell 95 unleaded in my RV6 with a 0-320.

You can feel a difference between Avgas and Mogas but not much. One thing for sure is the fact that Mogas will perculate. If I stop for 15 min or less and start up again and go, the fuel has perculated every single time without fail.

[wiskeyfoxtrot]

Sorry to sound "doff " but what do you mean by "perculating "?,

[THI]

Sorry to sound "doff " but what do you mean by "perculating "?,

Making coffee after the flight Just joking...

[Rudix]

I say stick to what the books tells you. I have a 912 and only fly 95 mogas, if I use avgas the TBO gets cut in half. You can use avgas or 93 in a pinch but don't make it a habit.

Not the TBO, that stays the same bu the service intervals become 50 hours and not 100 hours but I agree, for a 912 95 is the best option.

The Jabiru engines are fine on 95, according to the Jabiru engine manual RON 91 or above is fine.