A background of air travel gas

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Aviation gas has actually been constantly boosting for virtually a century, and also it proceeds today with the advancement of unleaded air travel fuel.

Jimmy DoolittleJimmy Doolittle

Jimmy Doolittle established several rate documents while shedding very early variations of Shell avgas. As much back as the 1930s, the benefits of high-octane air travel fuel(avgas)were identified. When he was employed by Shell Oil business in 1930, Jimmy Doolittle left the energetic Army however was still in the Army books. He supervised

of Shell’s air travel division as well as highly promoted creating greater octane air travel gas. Covering had the ability to create 100/130 octane, however as a result of the procedure made use of, it mored than one hundred times extra costly than regular automobile gas. The greater octane gas permitted greater compression proportions with the resultant better horse power, without raising the engine dimension. Doolittle established the globe’s high-speed document for land aircrafts in 1932 making use of Shell avgas. That very same year, he won the Bendix Trophy Race from Burbank, California, to Cleveland, Ohio, in a Laird Biplane as well as he took the Thompson Trophy at Cleveland in a Gee Bee racer with a typical rate of 252 miles per hr.

The good news is for the Allies in World War II, a French designer, Eugene J. Houdry, arrived to the United States in 1931. He created a procedure to fine-tune 100/130 avgas that was much less costly. In France, he had actually been looking into transforming coal right into gas. Dealing With Sun Oil in the United States, he developed a procedure utilizing a regenerated stimulant to transform evaporated oil right into high octane gas. It was referred to as the Houdry Process, and also it happened at the last minute for the Allies in WWII. The initial massive plant came online in 1940, and also the British had the ability to customize their airplane engines to utilize the brand-new greater octane air travel gas for the Battle of Britain. The increased (turbocharged) engine efficiency surprised the Germans. The rate of the Spitfire raised from 340 miles per hr in 1939 to 425 miles per hr in 1944.

The typical avgas made use of by Germany throughout WWII was B-4, with an octane score of 91/100. They additionally had amounts of C-3, which had an octane ranking of 95/120. By 1943 (battle finished in 1945) they were capturing up, creating a restricted quantity of an incredibly C-3 with an octane ranking of 150. Devastation of refining ability by the Allies stopped prevalent use the greater octane avgas. Japan’s air travel fuel came to a head out at 87/91. The initial number is the octane ranking at a lean combination, as well as the 2nd number is the octane ranking at an abundant blend.

The growth of 100/130 avgas was at first a situation of Catch-22. The engine makers required a gas that can hold up against the greater compression proportions and also not detonate too soon. At the exact same time, the gas refiners required a big adequate consumer base to manage to establish the refining ability for high octane avgas. The aeronautics needs in WWII pleased both needs. By the end of after that battle, 17 Allied refineries were creating high octane avgas.

Avgas features

In the very early days of avgas advancement, various other variables besides the octane degree required to be resolved for powering airplane engines at high elevations. The gas needed to have a reduced vapor indicate protect against vapor lock. High elevation = reduced outdoors stress, which needs a reduced vapor factor. A reduced vapor factor indicates you can reach greater elevations (reduced stress) prior to the avgas relies on a vapor. “Sea degree” fuel develops into vapor at mid elevations because of their high vapor factors. Gas pumps do not function well on vapors! The thickness additionally requires to be relatively continuous and also not gel at the reduced temperature levels in the high elevations (the ISO temperature at 25,000 feet = -30 levels F). The later phase WWII piston engine boxers can fly over 30,000 feet.

Lead warningLead warning

Tetraethyl lead enhanced avgas dramatically, however it featured severe downsides. The major initiative, nonetheless, got on increasing the octane degree. Tetraethyl Lead(TEL)was the primary additive utilized to stop early ignition or surge in the cyndrical tube. A fast melt that triggers the gas to increase on a wavefront is the wanted problem. Continual ignition, or knocking, can blow an opening in the piston. TEL was affordable, and also it worked. On the other side, way too much TEL might lead to ignition system fouling without any ignition renovation. While fiercely questioned today, lead was believed to offer some lubricating substance for the piston rings as well as minimized endure the shutoffs as well as shutoff seals.

Formerly there were a number of qualities of air travel gas readily available from the significant oil firms: 80/87, 91/96, 100/130, 108/135, as well as 115/145. With the decrease of avgas manufacturing and also the boost of jet/turbine gas manufacturing, the different qualities were minimized over time to one main quality of 100/130 and also consequently 100/130 LL typically referenced simply as 100LL.

Qualities and also requirements for avgas are released by ATSM International. The spec for 100/130 as well as 100LL is ASTM D910.

EPA activities to obtain the lead out

The removal of lead ingredients began in the 1970s to stop youngsters from obtaining lead poisoning. When they ate woodwork, this largely taken place. Babies frequently ate on their baby crib rails or various other trim job and also consumed lead from the paint. The lead additive in paint had useful homes. Lead offered the paint toughness and also usually lasted longer than water-based paints of the 1980s as well as 1970s. It took roughly 10 years prior to the paint producers created a method to make water-based paint as long lasting as the “old” lead-based paint.

The project proceeded to get rid of lead from a lot of items. Next off, lead was gotten rid of from auto fuel. Once more, the lead additive aided also shedding as opposed to the ignition of the gas in the cyndrical tube. Lead in solder was following. Solder utilized to have a big percent of lead, which aided it thaw at a “reduced temperature level” and afterwards hold strong when cooled down. Lead-free solder does not function also in digital applications: “tin hairs” are an even more considerable trouble with lead-free solder. Aeronautics electronic devices suppliers were formerly able to obtain a waiver to make use of lead-based solder as a result of the essential nature of the avionic computer systems, yet no more.

Each time the guidelines were tightened up to get rid of even more uses lead, it was a number of years prior to “workarounds” were established. We are currently on the cusp of removal of the waver for 100LL avgas. In January 2022 the EPA claimed it will certainly release an Unleaded Fuel Endangerment Finding, which might be the initial step in making 100LL prohibited. Job has actually been recurring for numerous years to establish a practical choice.

Decrease in exhausts


The United States airline company fleet made use of to take in large amounts of leaded avgas. While the removal of 100LL avgas is the existing target of ecological teams and also the EPA, there has actually currently been a considerable decrease in lead exhausts. In the 50s as well as 1940s, we had thousands of Douglas DC-3, -4, -6, -7 airplane as well as the Lockheed Constellations, Boeing Stratocruisers, and also many various other army as well as private piston airplane in solution. A number of the air transportation as well as armed forces transportation airplane had 4 engines with a much greater variation. They took in substantial amounts of leaded avgas. During that time, the avgas had 0.12%TEL. Today 100 LL has an optimum of 0.056% TEL. In 1945 the United States generated 28.4 million lots of leaded air travel fuel. Today it is roughly 0.56 million loads.

Despite the decrease in lead discharges, the extensive removal of 100LL is anticipated quickly. This is not simply as a result of the ecologists yet as a result of the business economics of offering a decreasing market. As revealed formerly, there were 5 qualities of avgas, yet today just one remains in quantity manufacturing. Apart from some custom-made auto racing blends, 100LL is the only fuel item that still has TEL.

. Intensifying the financial circumstance, leaded as well as unleaded gas can not usually be saved or moved in the very same storage tanks because of contamination from the leaded gas right into the unleaded gas. The accessibility of TEL is one more concern. Beyond China, there is just one producer of TEL, which remains in Europe. It mishandles for the refiners to create leaded gas for such a little market that remains to lower. The refineries’ result of kerosene-based Jet/turbine gas has actually much outmatched facility hydrocarbon-based avgas considering that the 1960s.

Advancement to unleaded 100 avgas

A number of business have actually created unleaded avgas. Hjelmco Oil firm presented quality 91/96UL which was authorized by the Swedish Civil Aviation Authority in 1991. In 2006 Hjelmco presented the unleaded quality 100 UL which at the very same time was evaluated as well as reviewed by one more European Civil Aviation Authority. Hjelmco states that the gas fulfills ASTM avgas basic D910 criteria (100 LL criterion) throughout with the exception of power web content (offers 1-2 % capacity greater gas intake).

In the United States, Shell Oil has actually generated little amounts of reduced octane unleaded avgas. Exxon Mobil as well as Philips 66 have actually researched and also growth job. According to Phillips 66 Frequently Asked Question on Unleaded Aviation Gasoline, in 2020, they claimed they are targeting 2025/2026 to “advertise” UL100. Swift Fuels is generating UL94 and also is working with a no-lead 100 octane avgas. General Aviation Modifications Inc (GAMI) has a significant benefit. They are the initial to acquire an STC for use their G100UL ™ unleaded 100 octane avgas, which was revealed at EAA AirVenture Oshkosh 2021. They are additionally proactively increasing the Approved Model List (AML). Since October 2021, they had 611 aircraft/aircraft engines provided on the AML.


GAMI seems in the lead in the meantime, after making a dash at AirVenture 2021. The value of the STC need to not be ignored. GAMI experienced the FAA Issue Paper procedure, which suffices to discourage also seasoned qualification designers. It would certainly take the oil firms significant effort and time in an FAA qualification program. It’s likewise a location in which the large oil business have little experience. Having stated that, the FAA’s Piston Aviation Fuels Initiative Project (PAFI) appears to remain to sputter along.

Hurdles and also benefits

Extra benefits for GAMI are:

  1. Their unleaded avgas (G100UL ™) can be blended with 100LL without any unfavorable communications.
  2. It generates somewhat even more power (BTUs) per gallon and also considers somewhat greater than 100LL at 6.25 vs 6.0 extra pounds per gallon.
  3. Because both gas are authorized for airplane usage, transport centers do not require different tools for 100LL and also G100UL.
  4. No engine alterations are needed.
  5. There is the opportunity of longer TBOs because of cleaner-burning with an absence of lead down payments.
  6. There is additionally the opportunity of using artificial electric motor oils with longer oil modification periods.
  7. Much less regular ignition system modifications.

If the large oil business will certainly be eager to integrate ingredients that they really did not design or create, it is uncertain. Some huge design business have a prejudice that if they really did not develop it, it can not be any type of great. It also has its very own phrase, “NIH”– Not Invented Here.

The business that mix gas will likely be the very early adaptors for G100UL manufacturing. Avfuel, a nationwide gas representative, will certainly take care of all the communication with the oil business or blender or food processors’ manufacturing side. Avfuel will certainly additionally take care of the circulation to the FBOs. GAMI will certainly preserve total quality assurance.

The advancement of avgas proceeds as we relocate right into the period of mogas as well as unleaded 100 avgas. Locating mogas without ethanol might be the following difficulty.

Bob began flying at 17, winding up as a CFI and also avionics designer prior to retiring. With the exception of a brief job in the Army Air Corps, his dad functioned as a study drug store on air travel gas at Shell Oil. He existed from the late 1930s till the very early 1960s. It was an interesting time to have actually been associated with air travel gas growth and also his daddy frequently discussed General Doolittle’s participation.
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