Fuel is the lifeblood of aircraft and pilots. Most aircraft need it to power their engines; pilots need it, in the form of oxygen and proper nutrition, to power themselves. The November issues of General Aviation News will turn the spotlight on fuels — all kinds — and look at the current state of affairs, as well as what we can expect
As always, we’d love to hear from our readers. Email General Aviation News Editor Janice Wood with your feedback.
A difference in aircraft fuel systems that I never hear mentioned has, I believe, a large effect on operation with MoGas as far as its vapor lock is concerned. High wing aircraft with gravity fuel system always operate with positive fuel pressure. Low wing aircraft with wing fuel tanks have a pump which is drawing fuel up from the tanks. In most cases the engine driven fuel pump is at least two feet above the fuel level. In a climb attitude, the fuel lift is even farther. This suction is causing a lower pressure in the fuel between the pump and tank, which will increase the risk of vapor lock. I know of three cases where this has occurred.
In one case, winter blend Mo Gas was still in the tanks on the first hot day of Spring in South Texas, and the engine tried to quit while climbing through 5000 ft. This aircraft, a Van’s RV-9, had a cooling shroud and cold air duct blowing on the engine driven fuel pump, so pump temperature should not have been contributing to the problem. The other two cases that I know of, were both Piper PA-28’s.
Why has this question about Mogas not been brought up at these regional AOPA “meet the members” get togethers and if it has what was there answer to the question. The so called little planes that use Mogas would be flying more hours in Kalifornia if it was available here. When I head north to Oregon I plan for a fuel stop at S30 for Mogas,now I can plan for Grants Pass.thanks GP airport manager!!!
Mogas is 92 octane auto fuel which is primarily ISO-octane, heptane (for starting) and toluene (for anti-knock). This fuel is good for most low compression aviation engines that operate at lower altitudes < 8,000 ft MSL and lower temperatures, where vapor lock is a potential problem, since toluene and heptane have high vapor pressures. Mogas has a higher potential for vapor lock. AVGAS is pure ISO-octane and does not contain heptane or toluene (using TEL). It stores for long periods (up to 1year and resists vapor lock). The only problem with AVGAS is the hard starting issue, since it does not have heptane. The new aviation fuels, without TEL will use mesitylene and this is a methyl benzene additive and known carcinogen. You don't get something for nothing. I say leave AVGAS alone. Any replacement will cost pilots more and Mogas works fine too.
“Mogas” is a generic term for ALL autoMOtive GASoline. Hence the term. It does not refer to 92 octane alone. Any automotve gasoline may be called Mogas, as opposed to Avgas which similarly, is a contraction for Aviation Gasoline.
Avgas is not pure isoctane. It can and does contain toluene, isobutylene and isopentane in addition to isooctane. 80/87 Avgas never contained aromatics. 100LL always has.
The vapor pressure of Avgas is held back to a maximum of 7.5 psi which reduces the likelihood of vapor lock, as opposed to Mogas which typically had a higher vapor pressure, though not so high today as it was twenty to thirty years ago.. In the 1990’s EPA forced refiners to lower the vapor pressure in order to cut down on evaporative emissions. Hence the fuel became more like Avgas in respect to it’s ability to resist vapor lock.
The purpose of hot fuel flight testing was to discover whether or not an airplane was likely to develop vapor lock under hot conditions on Mogas. Some airplanes failed these tests, others did not. Some needed modifications, others did not. Only those that passed this series of tests were able to receive auto fuel STC’s. These tests were done primarily to 12,500 feet but in the Baron and 210 we flew them to 17,000 feet.
Therefore it is false to assert that Mogas is only suitable for low compression engines below 8000 feet. Many 91/96 engines are STC’d for 91AKI auto gas and indeed, even the I0-520 and I0-470 may use 91AKI if an Anti-Detonation Injection (ADI) system is installed. ADI can make up an octane deficit of around 12 points which is why it can be used to operate a 100 octane engine on 91AKI fuel.
Todd, thanks for the detailed information. I think AVGAS and MOGAS are currently sufficient for the aviation community. The cost of certification on new fuels will result in higher end user costs. The GA fleet uses approximately 200+ million gallons/yr of AVGAS and this is insignificant compared to the 140 billion gallons/yr on automotive fuel use. My only concern is: Is it worth it?
The bad news is that one or two contrails at 30,000 feet do more damage to the environment than all us at 5000 feet. It was proved years ago when some researchers noted an unusual temperature change of around 3 degrees over the United Stated. They had no idea what caused the HUGE anomaly. Then other researches who were looking global satellite photos on that disaster day of Sept 911 and found that over the USA, there was no unusual cloud cover. They backed up and went foward a fews each side of 911 and noted the USA was covered with contrails. THATS WHEN THE SCIENTISTS DISCOVERED THE EFFECT OF A/C AT HIGH ALTITUDES. This is both the USA and Europes dirty little secret. The airlines are big business so who cares how much damage they are doing.
Around 70’s I am not shore of the date I had a new motorcycle. About that time they came out with gasohol. When I started using It several problems started happing with my Bike. I had it looked at by the dealer. He stated that the gasohol caused the problems. The dealer said continued use of this product would void the warrantee or worse ruin the engine. So now ask your self do you want this in your engine at 5500 ft.. Motorcycles are on the ground & well you know the rest.
Yes, the mogas is the answer for the small airplanes that outnumber those that have to have the lead in the fuel. The problem is though that the majority of aviation fuel is purchased by the high compression aircraft engine operators even though there are fewer of those engines than those the little airplanes that can in fact use the mogas without lead. It would seem then that there is such a demand by the high compression engines, a substitute for lead is required in those engines and unless a viable substitute for that lead in those engines is not available then there would never be a viable need to eliminate the lead in the fuel because the mogas that most of the little airplanes use is not enough demand to eliminate the need for the leaded fuel. What about the Bardhal “lead substitute” product and other brands that they sell to put in the old muscle cars? What is in that formula? Will it work in high compression aircraft engines like it can in the high compression auto engines? Or how about having an AD for the high compression engines that would require the operator to simply add the lead on every refueling of mogas if a universal mogas was given a blanket approval? The ethanol is another problem that can be fixed easily because the ethanol is added to the mogas after the fact. All you have to do is not add the ethanol for the shipments to the airports.
Agreed. However, here in Kalifornia where our government is so busy protecting us from ourself ALL gasoline has at least 10 percent alcohol. There is nowhere where we can purchase mogas that is alcohol free. I don’t know how many GA aircraft there our in CA but wish somebody could figure it out .
Jeff – The state of California is NOT a mandatory E10 state. You have ethanol in all of your gasoline because of the cosmic convergence of the Federal RFS mandate in EISA 2007 and the economic greed of the largest gasoline producers who used California’s gargantuan gasoline demand to meet their quotas under EISA 2007 so they could delay upgrading smaller terminals in rural states like WY, MT, the Dakotas and the core of the Midwest.
Sorry, you can’t blame the ethanol in your gasoline on your state legislature. However, for aviation use, you can do something about it. Import mogas from Oregon, Nevada and Arizona and add infrastructure to your airports to pump it. Nothing prohibits that at all.
Ironically, I live in Oregon and we ARE a mandatory E10 state, only one of 5, but I can get E0 for my LSA and homebuilt and we have one airport that pumps E0.
Good topic. The entire future for light aircraft can be summed up in one word – mogas. The US is now the world’s largest producer of refined gasoline and will become the world’s largest producer of crude oil by 2020, maybe sooner given the amazing results of fracking. Jet-A diesels and electrics will have their niche places in the US, but it makes so much common sense to adopt the same fuel found at 100,000 gas stations for our tiny fleet of piston airplanes. They could all run on it today, most with no modifications. We just need to get our airports & FBO to support it, the largest challenge of all. Their inaction on mogas is the reason many are leaving aviation and many airports are on life-support.