> > So, that begs the question, why is 200 gallons of fuel stored in the tanks > of an airplane more save than 20 gallons of fuel stored in approved > containers that are completely sealed? > >
Fuel handling It isn't the storage of fuel so much as the handling. But by not allowing storage of fuels in the hangars, you pretty much eliminate the handling of said fuels. Almost all hangar leases will stipulate no storage of fuels and no refueling in the hangars. As Oscar points out, that's a huge liability should you spark a fire in your hangar and burn down several expensive planes around you. Since I store my fuel in a tank in the back of my truck, I always pull the plane out clear of the hangar for fueling. You will vent quite a bit of fuel vapor while refueling. In a closed hangar, you can accumulate sufficient vapor to create a fire/explosion hazard. Fueling should be done outside where fuel vapors will disperse into the air. Storing large quantities of fuel > 5 gallons requires proper ventilation. Mogas has a significantly higher vapor pressure than 100LL. With temperature variations, the fuel tanks need to breathe. Storing any quantity of fuel in a sealed container is a bad idea, although small quantities like a 5 gallon gas can are designed to withstand the expansion. I use a pressure cap on my storage tank to prevent over-pressurizing the tank due to expansion (and contraction). This unit vents like a radiator cap at 2 1/2 lbs positive pressure, and allows the tank to breathe back in a 1 1/2 oz negative pressure. <http://www.fmbtruckoutfitters.com/pre-vent-fuel-cap-and-coupler-kit-fits-most-liquid-transfer-tanks-1910-5/> I also found that when my tank was still a rusty red color, on average, I was loosing roughly 7 gallons out of 100 over a 3 month period due to venting and evaporation. By repainting my fuel tank white, I was able to reduce my fuel loss to roughly 1 1/2 gallons over the same period. 100LL vs Mogas Those of you that know me know that a number of years ago I was dead set against running Mogas in our airplanes. I've changed my tune over the last few years. Accumulation of lead on the valve stems is one of the chief causes of valve guide and valve stem wear. The lead is in the fuel to raise the octane of the fuel, but using a higher octane than necessary doesn't buy you any increase in HP or performance. With hardened valves and valve seats, lead is no longer needed to keep the exhaust valves and seats from exchanging metal. So, as long as you can find Mogas with a sufficient octane rating to keep you out of detonation, your engine will be better off running the Mogas. However, there are also down sides to using Mogas. As previously mentioned, it stinks. Additionally, it has a higher vapor pressure, so if your engine is prone to vapor lock, it may not be the right fuel for you. This is especially true if you are using one of the thottle body carb replacements. They can run Mogas, but are unable to vent off vapors from boiling fuel like a float type carb. I have seen this happen, even with 100LL while test flying with an Aerocarb on a Sonex. The problem was addressed by adding a cooling shroud and blast tube to the gascolator. We used a thermal probe to measure the temps at the gascolator and found that it had been cooking itself at 185? in the air flow at the engine outlet. Had the pilot have chosen to run Mogas, it likely would have resulted in an in flight engine failure rather than the really rough running engine he had using 100LL. You want to do some careful testing to assure yourself of the heat tolerance of your fuel system before committing to running Mogas. However, if your fuel system is designed to be heat tolerant (it should be regardless) and your engine can run properly on the octane levels of pump gas, then the smell of Mogas becomes the smell of savings while you fly, and savings in long term maintenance on your engine. Over the last 2 years, my records show that I have saved roughly $1800 in fuel costs vs buying my fuel at the pump located right next to my hangar. -Jeff Scott Los Alamos, NM
