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rjsampson
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Thought experiment: How well would an airliner REALLY run on AvGas?

Fri Nov 10, 2017 12:25 am

An A320 is fuel critical and lands at the only airport range, a GA airport with only AvGas. Tankering in Jet-A isn't an option, and the aircraft must depart with a tank of AvGas.

By most accounts, this is highly feasible.

But how would the engine react? Performance? FADEC? What sorts of changes/anomalies could you conjecture would show up on the EICAS? Potential damage?
"..your eyes will be forever turned skyward, for there.." yeah we know the DaVinci quote. But GA is so dang expensive these days! :(
 
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Starlionblue
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Re: Thought experiment: How well would an airliner REALLY run on AvGas?

Fri Nov 10, 2017 1:35 am

I have a feeling that modern turbofans are so super-optimised this would be hard. If nothing else AvGas is much easier to ignite, so you'd have big issues with temperatures, ignition timing and such.

Not a turbofan but still a turbine, (some?) King Airs can run on AvGas for a limited time.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
GalaxyFlyer
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Re: Thought experiment: How well would an airliner REALLY run on AvGas?

Fri Nov 10, 2017 2:21 am

Most AFMs have an alternative fuel specification—types of fuel authorized, time limits, flight restrictions, etc. Most engines will accept AvGas with limits on altitudes, fuel temp and OAT limits and total time operated. Not a big issue.

GF
 
fr8mech
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Re: Thought experiment: How well would an airliner REALLY run on AvGas?

Fri Nov 10, 2017 2:30 am

As I recall, from training (mx), the JT9 equipped B747 could operate with gasoline for a max of 50 hours. The instructor said that the combustors would be unsalvageable after being used that way.

I want to say there was an adjustment on the fuel control.

Never did it. Never saw it done. Never heard that it was done.

What kind of indications would you see? Probably higher EGT's for a given power setting.

My guess is that any airline faced with that dilemma, especially with the cost of engines and overhaul, would truck in the appropriate amount of fuel before fueling with gasoline.
When seconds count...the police are minutes away.
 
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Florianopolis
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Re: Thought experiment: How well would an airliner REALLY run on AvGas?

Fri Nov 10, 2017 4:12 am

See this B-36?

Image

Six props and four jets, all burning AvGas. I think the lead in the avgas caused problems in the turbines after a while, and I don't think it burns as hot.

I believe P&W says it's okay in a PT6, but your overhaul time is drastically reduced because of the lead deposits, and they recommend adding a little oil to the AvGas in order to keep its lubricating properties in the pumps, in addition to a max altitude limit because AvGas will vaporize and cavitate fuel pumps at higher pressures. In general, I think most turbine owners will run filtered arctic diesel before they'd run AvGas.

Don't forget that jet fuel isn't always the same. This Boeing chart shows how density and energy content vary slightly. It can cause problems, sometimes, because airplanes are buying and filling a volume unit, displaying a weight, and burning BTUs.

Image

Final, random fact: Turbines run diesel fine, as the army knows (your range and power go down, though). But diesel engines will run jet fuel, too. For the last thirty years, US army deployments have been fueled by jet fuel. Tanks, helicopters, humvees, self-propelled howitzers, all running jet fuel. The only problem you'll usually see is in the fuel-lubricated diesel fuel pumps, which wear out more quickly because jet fuel is less viscous than diesel and doesn't lubricate as well.
 
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77west
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Re: Thought experiment: How well would an airliner REALLY run on AvGas?

Fri Nov 10, 2017 4:37 am

Many airports run their ground service vehicles on Jet fuel, with some lubricant added as noted by Florianopolis above. This discussion came up at work today actually about running engines on different fuels.
77West - AW109S - BE90 - JS31 - B1900 - Q300 - ATR72 - DC9-30 - MD80 - B733 - A320 - B738 - A300-B4 - B773 - B77W
 
strfyr51
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Re: Thought experiment: How well would an airliner REALLY run on AvGas?

Fri Nov 10, 2017 8:18 am

fr8mech wrote:
As I recall, from training (mx), the JT9 equipped B747 could operate with gasoline for a max of 50 hours. The instructor said that the combustors would be unsalvageable after being used that way.

I want to say there was an adjustment on the fuel control.

Never did it. Never saw it done. Never heard that it was done.

What kind of indications would you see? Probably higher EGT's for a given power setting.

My guess is that any airline faced with that dilemma, especially with the cost of engines and overhaul, would truck in the appropriate amount of fuel before fueling with gasoline.

If it came to an emergency Older airplanes would requie 1 qt of engine oil per tamk to add the req'd lubrication to the fuel pumps.
But this is pre-FADEC. post fadec you can run AV-GAS for a limited amount of time before the engines need to be boroscoped looking for damage to the burner cans and Nozzles.
 
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rjsampson
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Re: Thought experiment: How well would an airliner REALLY run on AvGas?

Fri Nov 10, 2017 4:53 pm

Starlionblue wrote:
I have a feeling that modern turbofans are so super-optimised this would be hard. If nothing else AvGas is much easier to ignite, so you'd have big issues with temperatures, ignition timing and such.


:checkmark: Yes, this. This was the "thought experiment" I was trying to propose.

A lot of us are aware of specifications from back in the day, for more rugged engines. So if a modern, FADEC and automated aircraft like an A320 were to be fueled with AvGas, what do you guys think could happen when the "start" switch is selected? Would a bunch of faults be thrown up? Would the systems allow the engine to start at all?
"..your eyes will be forever turned skyward, for there.." yeah we know the DaVinci quote. But GA is so dang expensive these days! :(
 
GalaxyFlyer
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Re: Thought experiment: How well would an airliner REALLY run on AvGas?

Fri Nov 10, 2017 5:07 pm

I think it would start just fine. Remember, the AvGas wouldn’t flow to the FADEC for some time.

GF
 
26point2
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Re: Thought experiment: How well would an airliner REALLY run on AvGas?

Sat Nov 11, 2017 4:24 am

I’m not familiar with avgas trucks. Do they have single point fueling capability? Otherwise, overwing fueling would take ages.
 
fr8mech
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Re: Thought experiment: How well would an airliner REALLY run on AvGas?

Sat Nov 11, 2017 5:10 am

rjsampson wrote:
So if a modern, FADEC and automated aircraft like an A320 were to be fueled with AvGas, what do you guys think could happen when the "start" switch is selected? Would a bunch of faults be thrown up? Would the systems allow the engine to start at all?


Personally, I think it would start just fine and run OK. Just hotter for any given power setting. Maybe, at full power, you'll be EGT limited, not sure. Really depends on the margin built into the engine.

I'm not sure how the A320 captures engine faults, but the EEC may squawk some pressures, especially burner pressure, it's not used to seeing at a given setting and try to make adjustments for them.
When seconds count...the police are minutes away.
 
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zeke
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Re: Thought experiment: How well would an airliner REALLY run on AvGas?

Sat Nov 11, 2017 11:45 am

GalaxyFlyer wrote:
I think it would start just fine. Remember, the AvGas wouldn’t flow to the FADEC for some time.

GF


The D in FADEC is Digital, not hydromechanical/electronic or hydromechanical.
Last edited by zeke on Sat Nov 11, 2017 11:56 am, edited 1 time in total.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
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zeke
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Re: Thought experiment: How well would an airliner REALLY run on AvGas?

Sat Nov 11, 2017 11:54 am

rjsampson wrote:
An A320 is fuel critical and lands at the only airport range, a GA airport with only AvGas. Tankering in Jet-A isn't an option, and the aircraft must depart with a tank of AvGas.

By most accounts, this is highly feasible.

But how would the engine react? Performance? FADEC? What sorts of changes/anomalies could you conjecture would show up on the EICAS? Potential damage?


Running a turbine on AVGAS is prohibited, except for some military aircraft in an emergency. That being said the A320 V2500/CFM56 in general is approved for wide cut fuel (Jet B/JP4 which is essentially 50/50 gasoline/kerosene). The NEO as far as I am aware is not approved for wide cut fuel.

If you had to do it in a pinch, the solution would be to mix the same volume of AVGAS into the tank as you had existing turbine fuel, a home made wide cut fuel, and some static dissipater additives.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
GalaxyFlyer
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Re: Thought experiment: How well would an airliner REALLY run on AvGas?

Sat Nov 11, 2017 8:39 pm

Zeke,

I well aware of what FADEC means, but the fuel in the fuel lines, pumps and controller would be JET A as the tanks would contain a mix of the existing turbine and newly added AvGas. Start would on JET A until the supply system started flowing the mix. If there were enough time, the AvGas having a lower S.G would rise to the top of the tanks. The BR710 in the Global has a long list of alternate fuels, IIRC it included AvGas for limited times. It was authorized in the C-5 (military, of course) with a 50 hour restriction.

Ops on JET A is likely prohibited for many types and operations. In any case, it’s so hard to find AvGas anyway, it’s hard to believe this case would ever happen. Academic.

Russian TC fuel had a very specific restriction as to fuel temp and max altitude of F310 until bulk fuel was below +13C, IIRC. Pretty hard to cool the fuel unless it was already below that temp on fueling. It is, of course, wide cut kerosene.
 
GalaxyFlyer
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Re: Thought experiment: How well would an airliner REALLY run on AvGas?

Sat Nov 11, 2017 9:59 pm

I checked the TCDS, I stand corrected, no AvGas on the Global or either Challengers. Yes, on the C-5

GF

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