Testing a fuel for presence of vodka.

Inquiring Mind

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I'm using ethanol-free auto-gas in my gyro, and that's how it could be quick checked if it is really ethanol-free or what percentage of the ethanol is in tested gas:

1. Fill tall glass with small amount of water (5ml is enough):
1589857216551.jpeg

2. Mark the the glass at the level of water with sharpie, if you use non-marked glass. Fill the glass with the gasoline (about 10 times of water volume for easy estimation of percentage of ethanol in the gas. I added 45ml), then shake it well and let it settle. Here you can see the initial 5 ml of water absorbed 3 ml of ethanol from the gas, so the tested gas contained at least 6.6% of ethanol (3ml/45ml*100):
1589857496483.jpeg
If tested fuel contained no alcohol, the water level after shaking the mix would stay at 5 ml.
 
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WaspAir

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I have a Hodges Fuel Volatility Tester that I picked up years ago when I bought an auto gas STC from Petersen for an O-360, but they never approved the airframe, so it sits in its original box.
 
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Inquiring Mind

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I have a Hodges Fuel Volatility Tester
What is the use of it? To test if the fuel mix is "winter" or "summer" grades by measuring vapor pressure? Is there gas volatility limit set for Rotax engines? Thanks.
 
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DavePA11

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Vodka on the other hand is a simple mixture of ethanol and water, a classic vodka composition is usually 40% alcohol(ethanol) by volume.
 

Inquiring Mind

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Vodka on the other hand is a simple mixture of ethanol and water, a classic vodka composition is usually 40% alcohol(ethanol) by volume.
Not all of vodkas are 40% ethanol - water mix. Check out 50% Smirnoff vodka:

BTW, any fuel tank with E10 gas in it always have "vodka" of various strenght at the bottom of the tank, as ethanol pulls the water out of the air and ethanol-water mixture separates from the gas and settles on the bottom of the tank, exactly as it did in the test I posted.
 
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DavePA11

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Why are there so many Vodka brands if it’s just ethanol and water? Have you ever found ethanol in ethanol-free fuel?
 

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Why are there so many Vodka brands if it’s just ethanol and water? Have you ever found ethanol in ethanol-free fuel?
I don't know much about vodkas, as I don't like them.
So far I've not found ethanol in the gas sold as ethanol-free.
On the pics above - 93 octane gas from Sunoco with 6.6% of ethanol in it.
 

WaspAir

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What is the use of it? To test if the fuel mix is "winter" or "summer" grades by measuring vapor pressure? Is there gas volatility limit set for Rotax engines? Thanks.
No. One of the biggest potential problems from auto gas use in aircraft is vapor lock in the fuel system.

This is from https://www.avweb.com/ownership/avgas-vs-autogas/ :
"While unleaded autogas provides sufficient octane to substitute for 80/87 avgas in low-compression engines, there are other differences that can cause problems when using autogas in some engine installations. The two most significant are lower vapor pressure — which can lead to vapor lock — and incompatibility between some of the additives in autogas and some components (particularly seals) in some aircraft fuel systems.In order to qualify for an STC, a particular airframe/engine combination has to be rigorously tested, to include either a 150 hour engine endurance test or 500 hour flight test, under controlled conditions. The tests also include checking operation at high ambient temperatures, which can create vapor lock. Some aircraft don’t pass — the Piper Apache and Comanche-250, and Cessna Skyhawk with Avcon’s 180HP conversion all failed testing, and cannot legally run autogas "

"Vapor lock is a real issue when using autogas in aircraft engines, particularly at high altitudes on hot days — after all, it’s made for use at sea level, or at most lower altitudes. Cars don’t get up into the flight levels! One way to combat this is to make sure that the autogas you use is fresh (don’t fill the airplane up and then leave it in the hangar for a month). Another is to use a Hodges Volatility Tester to assure that the fuel in question won’t cause vapor lock at the current ambient temperature.


Rotax doesn't know a thing about your fuel system; they just build the engine on one end of it.
 

WaspAir

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Why are there so many Vodka brands if it’s just ethanol and water? Have you ever found ethanol in ethanol-free fuel?
There are hundreds of brands of bottled water, with no ethanol at all. Consumers and marketers make strange choices.
 

Vance

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Having had five engine outs from vapor lock in three different 914 powered Cavalons I can attest to the reality that vapor lock using auto fuel without alcohol can be problematic. Four were over 5,000 feet density altitude; one was at less than 1,000 feet density altitude.

Once 100LL was introduced the problem evaporated.
 

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Having had five engine outs from vapor lock in three different 914 powered Cavalons
I think vapor lock is more of the problem with carburated engines, which I have no plans to own or fly ever.
 
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Inquiring Mind

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In the hangar next to my gyro sits experimental amphibious trike with 914. Owner told me he's being using Sunoco 94 AKI auto-gas on that trike for years without any problems.
 

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It's the SYSTEM, (not just the engine) from tank to combustion chamber, that determines if/where you will produce a problem. I doubt very seriously that your gyro will have identical, tank, plumbing, heat distribution, insulation, sun exposure, etc.
If yours works, great, but don't expect identical results unless you have identical systems.
 

Vance

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Vance - How do you know it was from vapor lock? Were you able to restart the engines in flight?
I don't know it was vapor lock, it is my best guess.
I could not find any problems with any of the three engines so based on my experience and my friends experienced we felt it was vapor lock.
That they all ran fine on 100LL reinforced that opinion.
I was not able to restart the engine in flight or on the ground.
Once it had cooled for an hour each time it started and ran fine again reinforcing my opinion that it was vapor lock.
Discussions with a Rotax vendor at Sun N Fun reinforced my opinion that it was vapor lock. He was not unfamiliar with the problem and did not offer a solution for it.
 

Vance

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I think vapor lock is more of the problem with carburated engines, which I have no plans to own or fly ever.
My fuel injected Lycoming IO-320 sometimes has a hot start problem even on 100 LL that gets worse on unleaded automotive fuel.

It is common enough that there is a hot start procedure for fuel injected Lycoming engines.
Full throttle with lean cut off, when she tries to start you quickly center the mixture and reduce the throttle as she sputters and blows black smoke.
 

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Having had five engine outs from vapor lock in three different 914 powered Cavalons I can attest to the reality that vapor lock using auto fuel without alcohol can be problematic. Four were over 5,000 feet density altitude; one was at less than 1,000 feet density altitude.

Once 100LL was introduced the problem evaporated.
Five engine outs in flight running the same Rotax 914 engines on three of the same type of aircraft in just a few short years is not a fuel type problem.

To wit, I am unable to find a single instance of a running Yamaha engine quitting due to vapor lock, whether on one of the countless thousands of sleds or some 200 aircraft, since they were introduced 17 years ago. These engines have been run for all of these years under all kinds of extremes and conditions at altitudes up to 10,000 ft MSL, in the air and on the ground.

Vapor lock shutting down a running engine is a serious design flaw - be that the of engine or the guy who routed the fuel lines, or a combination of both.

Seems to me someone needs to work this problem out before they kill themselves, and maybe a passenger.

Simply running 100LL is no acceptable solution for so-called vapor lock.
 
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