Can You Put Automobile Gas in Your Aircraft?

“Automobile gas is not accredited for airplanes.”

Every single student pilot hears this dire warning about using auto gas in an plane engine that was not certified for it. These warnings are typically accompanied by a tale about engine failure and an unscheduled off-airport landing, which normally occurs shortly after takeoff.

“If you are flying without an STC and the feds see you have car gas in an plane not accredited for it, it is a violation.”

Richard Scarbrough, airframe and powerplant mechanic and plane routine maintenance columnist for Traveling

Even though it is correct that the use of vehicle gasoline in an plane can be a difficult organization, it is unlikely that motor failure will transpire so immediately, says Richard Scarbrough, an airframe and powerplant mechanic and aircraft routine maintenance columnist for Flying

“That’s not to say that the use of automobile gas couldn’t develop problems down the highway for the aircraft,” he suggests, outlining, “100LL materials the engine with lubrication as a result of the guide, which vehicle gasoline does not.” 

But with the substantial cost of avgas, is it truly worth the chance? If it is, how would you do it?

Why Would You Want To?

Auto gas is commonly significantly less high priced than aviation fuel. But, mainly because it ordinarily comes in at a reduced octane, (80 vs . 87), the consequence will be decrease compression, as engines intended with bigger compression ratios generally require greater octane gasoline to avoid detonation. To mitigate these challenges, numerous pilots operate a mixture of 100LL and automobile gasoline in their plane.

Scarbrough notes that in order to legally use auto gasoline in an aircraft, the aircraft ought to have a supplemental sort certificate (STC), which is a kind of form certificate issued by the FAA that presents the applicant acceptance to modify an aeronautical product from its unique structure.

“If you are flying devoid of an STC and the feds see you have auto fuel in an plane not certified for it, it is a violation,” he claims.  

These types of violations depend on who catches you—it could be as minimal as “education” on the location or a warning see or letter of correction, which suggests the corrective action a pilot should get inside of a specified timeframe.

The STC is attained from a provider—a company that specializes in the STC—usually for a several hundred pounds.

“Most aircraft homeowners are happy to pay that for the gas STC mainly because they will make up the price of the STC with one or two fill-ups,” Scarbrough points out.

Aircraft house owners who wish to acquire advantage of the STC will have to file a Kind 337 (main maintenance or alteration) with the FAA and in addition, placard the aircraft properly.

Who Has Accomplished This?

Acquiring an STC can be both time-consuming and costly, but for some aircraft operators, the have to have to modify the aircraft comes out of a perception of necessity. This kind of was the scenario for Petersen Aviation in Minden, Nebraska.

Considering that 1983, Petersen Aviation has been providing an vehicle gasoline STC for 48 engine varieties. In accordance to Todd Petersen, ahead of 1983, the family company sprayed crops using AgCats, and the significant expense of 100LL and trouble obtaining a trustworthy source influenced them to appear into the notion of jogging the plane on auto gasoline. They recognized they were not the only pilots dealing with this predicament, and the STC small business was born.

According to Petersen, the STC approach essential them to reveal to the FAA that auto gas would not adversely affect possibly the aircraft or the motor itself. It is a time-consuming procedure, he notes, incorporating that the FAA sees lots of purposes for STCs every yr that aren’t done for the total of exploration and testing and paperwork the applicant has to do.

“To get a supplemental form certificate to operate an plane on auto fuel, you truly need two supplemental style certificates—one for the airplane, the other for the motor,” Petersen claims.

The testing for the fuel STC entails working the unique engine on automobile gasoline and determining if there are any adverse reactions, these types of as detonation or vapor lock. Sometimes, the plane requires alterations to the gas process, these kinds of as various seals or a various gas pump, to make the STC practical.

When an aircraft owner obtains the STC, the airplane receives the 337 sort and any elements that are important to make it function, together with placards stating that the aircraft is functioning on automobile gasoline. 

“These are placards that go on the engine and on the wings [by the fuel cap], and an IA [airframe and powerplant technician with inspection authority] has to put in them,” Petersen claims. In addition, documentation of the STC is built in the aircraft’s logbooks by an IA.

As soon as the STC is in location, the plane can use car gasoline, but you ought to be mindful about the kind you pick, Petersen warns. Car fuel that incorporates ethanol—a type of liquor usually additional to automobile gasoline to cut down carbon emissions—can have a harmful influence on the aircraft except if the motor contains ethanol-tolerant pieces.

“If the plane is stuffed with vehicle gas that contains ethanol and the plane just sits, you are environment by yourself up for motor failure,” Petersen explains. “The seals and gaskets can be ruined when the aircraft sits earlier 10 days. Also, ethanol attracts dampness out of the air and pulls it into the gasoline, so you have to be watchful in a humid atmosphere. The motor could not want to run.”

Petersen implies that plane house owners who want to run vehicle gas search for a filling station that doesn’t include ethanol to the item, noting that marinas are frequently a excellent alternative due to the fact most boats will not get ethanol improved gasoline both.

Lycoming Engines Just take on Vehicle Gas

A single of the widespread problems when utilizing automobile gas in an plane engine is that accomplishing so may void the manufacturer’s warranty. Lycoming Engines provides advice on this. 

According to Brandon Dildine, subject services specialized representative for Lycoming, automotive fuels may be utilized in some Lycoming engines provided they fulfill the prerequisites shown in Assistance Instruction SI1070AB. 

“Use of fuels that do not satisfy the specifications mentioned in this publication may possibly result in motor destruction or failure and will void the engine guarantee,” Dildine states. He provides that unapproved fuels containing additives, this sort of as ethanol or oxygenates:

  • may possibly be additional most likely to vaporize in gas lines producing a loss of electric power
  • may perhaps lead to detonation in the course of regular procedure
  • are a lot less secure and can degrade above brief intervals of time, ensuing in gas that does not meet its previous technical specs usually resulting in a varnish buildup in the gas system
  • can gather humidity from the air much more very easily
  • can lead to corrosion of airframe/motor gas process components 
  • and can cause degradation of seals, hoses, diaphragms, sealants, bladders employed in the airframe/gas technique that are not compatible.

Dildine advises men and women to consult the airframe manufacturer ahead of employing automobile gasoline to validate that the gas accepted for the motor is also suitable with all airframe parts.

Dildine even more warns, “All automotive fuels utilised really should be analyzed to validate that alcoholic beverages is not present, and a gas data sheet should really be received from the distributor for the distinct batch to confirm that all specifications have been fulfilled. 

“Due to federal laws and modifications in seasonal gas blends, the formula could adjust from batch to batch or could become contaminated during distribution when transferred in tanks or pipes that had blended gas in them.”

Katherine T. Burrows

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