Frequently Asked Questions
Airworthy AutoGas is a patent pending, ethanol-free, 93 octane, premium unleaded automotive gasoline that includes octane improving and vapor pressure stabilizing components, in such proportions that the final blend meets the requirements of ASTM D4814 and Lycoming Engine’s Service Instruction 1070 “S”. Airworthy AutoGas, unlike traditional automotive gasoline, is designed for use in powering spark-ignition internal combustion engines used in aircraft applications.
Although it is similar in composition to Aviation Gasoline formulations, Airworthy AutoGas, which meets the requirements of ASTM D4814, is technically referred to as an automotive gasoline. However, Airworthy AutoGas, unlike automotive gasoline, has been formulated in such a manner, and is handled and distributed in such a manner, making it more compatible for use in aircraft.
An AutoGas Supplemental Type Certification (STC), is documentation provided in the United States by two parties, the Experimental Aircraft Association (EAA) and Peterson Aviation, through which a particular airframe and powerplant are granted certification, approved by FAA, for the use of automotive gasoline in that airframe and powerplant. For more information on this subject, click on the “AutoGas STC” tab at the top of the page, and visit the Peterson Aviation website.
ASTM D4814 is a motor fuel specification, which outlines numerous requirements that automotive gasoline must meet, in order to certify its quality and suitability for use in motor vehicles. Each requirement set forth within the ASTM D4814 specification must be tested, and met, by means of a specified test method. Every gallon of Airworthy AutoGas is tested, and certified as meeting the requirements of ASTM D4814.
Lycoming Engine ”Service Instructions” (SI) describe and provide guidance for voluntary, or required, modifications made to specified Lycoming Engines. The subject of Service Instruction 1070 S is “Specified Fuels for Spark Ignited Gasoline Aircraft Engine Models”, which includes a lengthy list of those Lycoming Engines that are approved for use of automotive gasoline that meets the requirements of ASTM D4814, that has a minimum 93 octane, and that has a maximum vapor pressure of 9.0 psi. Airworthy AutoGas meets or exceeds all of these requirements, and then some.
Airworthy AutoGas is UNLEADED:
From an environmental perspective, the use of Airworthy AutoGas contributes directly towards reducing the emission of lead into the atmosphere, which, in turn, promotes a cleaner environment and reduced health risk to citizens.
Reduced Maintenance Costs:
Many pilots report that the lead contained within 100LL AVGAS actually contributes to a host of problems, including fouled spark plugs and sticking valves. Therefore, the use of UNLEADED Airworthy AutoGas may very well result in reduced maintenance costs for aircraft owners.
Unlike traditional automotive gasoline, Airworthy AutoGas has been formulated in such a way as to provide a consistent, year-round, low vapor pressure, which contributes to reduced potential of vapor lock and other hot fuel issues.
Airworthy AutoGas contains no ethanol, no other alcohols, or additional oxygenates, as required by existing EAA and Peterson Aviation STC’s and Lycoming Engine’s SI 1070 “S”.
Due to the multitude of variables involved in the pricing of fuels, and the fact that Airworthy AutoGas LLC is a producer and wholesale distributor of Airworthy AutoGas, it would be inappropriate, and imprudent, to state “the price per gallon of Airworthy AutoGas”; the fact of the matter is that, at this point in time, we just don’t know. However, that said, we can claim that Airworthy AutoGas will be sufficiently cost-effective, in relation to the cost of 100LL AVGAS. Just how cost-effective Airworthy AutoGas will be, will be a function of the marketplace.
Vapor Lock, and hot fuel issues such as hard starting or no starting after a hot soak, and poor throttle response, occur when excessive gasoline vapor accumulates in the fuel pump, fuel line, carburetor, or fuel injector, resulting in the reduction or interruption of fuel supply to the engine; these things should always be of concern! However, Airworthy AutoGas is formulated with great attention given to its ”volatility characteristics”. Specifically, unlike traditional automotive gasoline, which may have a high, erratic, or unknown vapor pressure, AirworthyAutoGas is formulated in such a way as to reduce vapor pressure which reduces the potential for vapor lock. Regardless, as with any gasoline, the potential for vapor lock can not be eliminated, and should always be of concern.
All gasoline, including Airworthy AutoGas, is composed in part of volatile components, which have a tendency to evaporate. To reduce the effects of this evaporative tendency, and to ensure the integrity of the gasoline within your aircraft fuel tanks, two common sense measures should always be kept in mind: 1) keep fresh fuel in your tanks, and 2) keep your tanks full. Time, heat, moisture and evaporation are enemies of fuel quality. So, fly more, fuel more, and keep your tanks full.
Volatility, simply put, is a term used to describe a gasoline formulation’s tendency to vaporize. Volatility, or the tendency to vaporize, is important because liquids, such as Airworthy AutoGas, do not burn; rather, their vapors burn, as within the combustion chamber of an aircraft engine.
Consequently, gasoline may be formulated in such a way as to vaporize easily, which allows a cold engine to start quickly and to warm up smoothly. Or, gasoline may be formulated in such a way as to vaporize less easily which may reduce the potential for engine vapor lock and other hot fuel handling issues.
It is important to note that while there is no single best volatility for gasoline, in aircraft applications, consistency of the volatility characteristics of a given fuel is of paramount importance.
There are three properties used to measure Volatility: Vapor Pressure, Distillation Profile, and Vapor-Liquid Ratio.
Vapor pressure is defined as the pressure exerted by the vapor when it is in equilibrium with the liquid upon which it rests, as with gasoline. The vapor pressure of gasoline is measured at 100 degrees F, and at a pressure of one atmosphere, expressed in pounds per square inch (psi).
Vapor pressure is the single most important property for cold-start and warm-up of engines. And, in aircraft applications, lower values are better, towards reducing the potential for vapor lock and other hot fuel handling issues.
Gasoline is composed of hundreds of different hydrocarbon species, with differing boiling points. Therefore, unlike boiling water for instance, which is a single molecule (H2O) that boils at one temperature (212 degrees F), gasoline boils, or distills, over a range of temperatures.
A distillation profile, or distillation curve, is established by taking a sample of gasoline and increasing its temperature gradually, and noting, at specific points ( 5%, 10%, 20%, 30%, and so on), the temperature at which that percentage of sample has evaporated.
The distillation profile of a given gasoline formulation may be broken into three segments: Front-end, Mid-range, and Tail-end. Each of these segments may be formulated so as to provide the formulation with certain desired characteristics. For example: Front-end volatility may be adjusted to provide easy cold starting, easy hot starting, and reduced potential for vapor lock or other hot fuel handling issues. Mid-range volatility may be adjusted to provide rapid warm -up, smooth running, fuel economy, and power. And, Tail-end volatility may be adjusted to provide reduced engine deposits and reduced fuel dilution of oil.
The vapor locking tendency of a gasoline is actually influenced both by Front-end distillation profile and vapor pressure. However, the property that correlates best regarding vapor lock, and other hot fuel handling issues, is the temperature at which a gasoline forms a vapor-liquid ratio of 20 (V/L=20). This is the temperature at which a gasoline exists as 20 volumes of vapor in equilibrium with one volume of liquid at atmospheric pressure. Gasoline formulations with higher V/L=20 values provide greater protection against vapor lock and other hot fuel handling issues.
First, knocking or pinging is the sound of abnormal combustion. During normal combustion, the spark plug initiates the combustion, and the burning flame front fans out rapidly across the combustion chamber until most of the fuel is consumed. During abnormal combustion, the unburned fuel located ahead of the flame front ignites spontaneously, and also burns very rapidly resulting in a rise in cylinder pressure, which is what creates the knocking or pinging sound. Knocking is a result of too low of an antiknock rating of the fuel for a given engine, and heavy or prolonged knocking can be very harmful to an engine.
Octane number is a measure of a gasoline’s antiknock performance, or its ability to resist engine knocking, as it burns within the combustion chamber. There are two laboratory test methods to measure octane number; ASTM D 2699 and D2700. The D2699 method yields the Research Octane Number (RON), which correlates best with low speed, mild-knocking conditions, whereas the D2700 method yields the Motor Octane Number (MON), which correlates best with high speed and high temperature knocking conditions.
As RON and MON are measured by means of a single-cylinder laboratory engine, they do not completely predict the antiknock performance of multi-cylinder engines. While there is a procedure for measuring antiknock performance in automobiles, resulting in what is called Road Octane Number (RdON), it is complex, which led to attempts to more easily predict RdON from RON and MON. The resultant equation, which approximates RdON, is R+M/2, or RON + MON/2, and is referred to as the Antiknock Index (AKI). The AKI value is what is commonly seen in the United States at retail gas stations (87, 89 and 91).
Airworthy AutoGas contains no ethanol, no other alcohols, and no additional oxygenates.
BOB is an acronym used within the petroleum industry to describe a Blendstock for Oxygenate Blending. Essentially, BOB is the “base gasoline” to which an “oxygenate” (oxygen bearing compound such as ethanol), will be added at a motor fuel terminal.
Generally speaking, BOB is received by a terminal via a petroleum products pipeline and then segregated as “regular” and “premium” within terminal storage. The “oxygenate”, typically ethanol at 10% by volume, is added to the BOB, along with various additives, such as intake valve deposit or combustion control deposit additives, as a tanker truck is loaded “at the terminal rack”, prior to delivery to a retail gas station.
Depending upon geographical location and retail market factors, and again generally speaking, the AKI values for regular and premium BOB may be 84.0 and 88.5, respectively. The addition of the “oxygenate”, again typically ethanol at 10% by volume, adds approximately 3.0 AKI points to the BOB, bringing the final blend AKI value to those posted at your local gas station (87, 89, and 91).
The use of a BOB in aircraft should be avoided.
There are many reasons to avoid the use of a BOB as fuel in your aircraft, but perhaps the primary reason, with specific regards to those aircraft with an AutoGas STC, centers on the fact that automotive gasoline used for this purpose must meet the requirements of ASTM D4814. BOB delivered from a refinery is typically certified as meeting the requirements of ASTM D4814 with ethanol added; meaning, the BOB itself is not certified as meeting the requirements of ASTM D4814. And, certain critical fuel characteristics vary dramatically before vs. after the addition of an oxygenate (ethanol).
Airworthy AutoGas is Airworthy by Design not by Chance.
Airworthy AutoGas, LLC is the producer and the wholesale supplier of Airworthy AutoGas, and is in the process of identifying Flight Schools, Fixed Base Operators (FBO), and other Aviation Gasoline Suppliers that may be interested in purchasing wholesale volumes of Airworthy AutoGas. If you are a pilot desirous for Airworthy AutoGas to be made available at your local FBO, we encourage you to have your FBO, or current supplier of aviation gasoline, contact us directly.
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