Hi all,
I was being asked this question about MOGAS and AVGAS but I was unable to find out why the difference for motor and piston engine aircraft
fuel. I researched on pprune and the net already and what I come to know of is as follows:
I know that:
1. AVGAS is highly refined with very specific Octane ratings
characterizing its resistance to detonation; MOGAS is less refined than AVGAS; it has different octane ratings as well.
2. AVGAS is carefully controlled through supply chain.
3. AVGAS sits longer before going "stale".
3. MOGAS has a higher volatility, lower ignition temperature and
flashpoint, making it more dangerous to handle. Also more prone to vapour lock in the fuel lines as compared to AVGAS.
4. MOGAS has a high lead content. (not sure, what about premium low lead MOGAS??)
I've always known you can't put petrol (MOGAS) into AVGAS engines, but why?? Why we came to choose to use AVGAS as piston engine aircraft fuel; MOGAS as motor car fuel? If MOGAS has similiar octane ratings and actually produces more power (as in horsepower), why don't we use it as piston engine aircraft's fuel? I've read that in choosing a fuel type
(
http://www.ausetute.com.au/fuelsdef.html), we consider factors such as energy value, ingnition temperature, volatility, flashpoint, ease of liquifaction and products of combustion. Are higher volatility, lower ignition temperture and lower flashpoint of MOGAS the reasons why we use AVGAS instead of MOGAS?
I've come to learn from here and from other sources that many aircraft engines such as the Lycoming O-320 have been designed for use of the old 80/87 fuel (Similar to gasoline for car). Therefore, the use of MOGAS for the aircraft engines is acceptable. So, again, why some people so strongly advocate NO MOGAS in AVGAS engines? Why create AVGAS to differentiate from MOGAS in the first place?
Moreover, I was very puzzled with the idea put forth:
Cessna C152 has an engine horsepower of 110hp; whereas motor
car/trucks can have horsepower much higher than that of an aircraft like the C152. Why is that so?
After doing some research, I start to figure out it might be due to these reasons.
1. Many of the training aircrafts are even lighter than some cars/trucks. They really don't need as much power (e.g. for speed) as some motors do for what they are designed for - teaching people to fly an aeroplane.
2. Piston-engine aircrafts have different criteria in power generation when compared to cars. Aircrafts need thrust instead of horsepower. As long as the thrust provided is sufficient for the aircraft operations for its design and different flight phases, it's good enough. On the other hand, race cars require high top speed, therefore, more hp to achieve that. Trucks require high torque factor in order to move the high loads on start, therefore, higher hp as well.
Please correct me if I am mistaken in any areas. Thank you very much and a happy flying 2008!
