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  #11  
Old 07-08-2018, 06:16 PM
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Originally Posted by rongawer View Post
Having read the PAFI update, it doesn’t appear to be a “back to the drawing board” statement, but rather a mitigating the differences between the two fuels to create a common standard.

.....
I'm not sure there needs to be a common standard.

You could buy 100NL and 100SW for example and your POH could approve both, but with different W&B and perhaps operating limitations as previously mentioned.

Unless the idea is to get one standard (100-REPLACEMENT) so an FBO can order either fuel each time he fills his tank. That interchangeability sounds very difficult (impossible?) with the energy density and weight/gallon differences mentioned so far.

Perhaps we'll see the Swift fuel "watered down" to the same density as the other stuff.
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  #12  
Old 07-08-2018, 06:25 PM
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Quote:
Originally Posted by az_gila View Post
I'm not sure there needs to be a common standard.

You could buy 100NL and 100SW for example and your POH could approve both, but with different W&B and perhaps operating limitations as previously mentioned.
Most airports I know only have one set of tanks for AVGAS; that being the argument at my local airport as to why they don’t sell MOGAS. That alone would be the economic reason for a single standard.

The main reason for not standardizing on two standards (aside from driving engineers like me nuts with the duality) is that everyone has to account for it requiring extra tooling, knowledge, regulation, compliance, etc...[think SAE and Metric) The FAA could approve two standards, however, I think it is highly unlikely due to the added burden of multiplicity. And from what the PAFI update says, it appears they’re looking for one standard.

There needs to be one standard in order for the fuel to be economical. So yes, you could have two standards (think VHS and Betamax), but eventually one will win out for simplicity sake.

Even more so, note how many times folks have issue with putting Jet A into Avgas tanks or vice versa (it’s actually pretty common - especially if you own a Diamond Twinstar), now multiply that by a huge factor. I think dual 100 octane fuels would turn into a fueling crazy time.
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Last edited by rongawer : 07-08-2018 at 06:33 PM. Reason: grammar
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  #13  
Old 07-08-2018, 08:17 PM
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The only fuel (so far) that is completely fungible with existing avgas and still conforming is G100UL.

I have a feeling it will be to market sooner than the others now that the PAFI project has finally failed. Time will tell.
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  #14  
Old 07-08-2018, 08:29 PM
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Originally Posted by RV10inOz View Post
The only fuel (so far) that is completely fungible with existing avgas and still conforming is G100UL.

I have a feeling it will be to market sooner than the others now that the PAFI project has finally failed. Time will tell.
I disagree that the PAFI project has failed. The FAA states that the completion date has been extended to December 2019, which is to fulfill what was previously discussed.
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  #15  
Old 07-08-2018, 09:08 PM
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Quote:
Originally Posted by rongawer View Post
Most airports I know only have one set of tanks for AVGAS; that being the argument at my local airport as to why they don’t sell MOGAS. That alone would be the economic reason for a single standard.

The main reason for not standardizing on two standards (aside from driving engineers like me nuts with the duality) is that everyone has to account for it requiring extra tooling, knowledge, regulation, compliance, etc...[think SAE and Metric) The FAA could approve two standards, however, I think it is highly unlikely due to the added burden of multiplicity. And from what the PAFI update says, it appears they’re looking for one standard.

There needs to be one standard in order for the fuel to be economical. So yes, you could have two standards (think VHS and Betamax), but eventually one will win out for simplicity sake.

Even more so, note how many times folks have issue with putting Jet A into Avgas tanks or vice versa (it’s actually pretty common - especially if you own a Diamond Twinstar), now multiply that by a huge factor. I think dual 100 octane fuels would turn into a fueling crazy time.
That wasn't really my point.

Think of it more like Shell vs. Mobil.

Your FBO stocks one or the other, as long as they can mix in your tank, it's up to the pilot to account for it.

If I want 10% more range with a little extra weight penalty I would just search for a 100SW FBO using airnav.com when I am on a trip.

I wasn't implying that one airport needs to sell both and have two tanks.
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  #16  
Old 07-09-2018, 05:50 AM
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Quote:
Originally Posted by az_gila View Post
That wasn't really my point.

Think of it more like Shell vs. Mobil.

Your FBO stocks one or the other, as long as they can mix in your tank, it's up to the pilot to account for it.

If I want 10% more range with a little extra weight penalty I would just search for a 100SW FBO using airnav.com when I am on a trip.

I wasn't implying that one airport needs to sell both and have two tanks.
Well, ok, let’s suppose your airport stocks your favorite brand and you’re happy with that and you plan for that specific fuel usage. Unfortunately, it’s not as simple as Mobil vs Shell vs Swift. And you’ve hit on the crux of the matter - it’s fuel compatibility [there’s that standards thing...] When you get car gas, even from Bubba’s Gas N Go, it is formulated to a standard.

You decide to go on a little trip, but there are only two airports on your route of flight and both have the other brand. Can you mix the two fuels? Are they compatible? What happens if they react with each other in your tank and fuel lines? Do you need to drain your remaining fuel first? This is the big issue and the main question PAFI has to resolve. If both fuels can be made compatible, then a standard can be developed and then, well, boo yah, we have a fuel to use.
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Last edited by rongawer : 07-09-2018 at 05:59 AM.
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  #17  
Old 07-09-2018, 07:36 AM
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Quote:
Originally Posted by rongawer View Post
Well, ok, let’s suppose your airport stocks your favorite brand and you’re happy with that and you plan for that specific fuel usage. Unfortunately, it’s not as simple as Mobil vs Shell vs Swift. And you’ve hit on the crux of the matter - it’s fuel compatibility [there’s that standards thing...] When you get car gas, even from Bubba’s Gas N Go, it is formulated to a standard.

You decide to go on a little trip, but there are only two airports on your route of flight and both have the other brand. Can you mix the two fuels? Are they compatible? What happens if they react with each other in your tank and fuel lines? Do you need to drain your remaining fuel first? This is the big issue and the main question PAFI has to resolve. If both fuels can be made compatible, then a standard can be developed and then, well, boo yah, we have a fuel to use.
Nah, I said "as long as they can mix in your tank"

Perhaps it's more like Pure Regular vs. 10% Corn+Regular.

Two completely different standards but it doesn't really matter which one you buy - and yes, one even has less energy density.
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  #18  
Old 07-09-2018, 08:06 AM
Canadian_JOY Canadian_JOY is offline
 
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Two other important considerations haven't been mentioned here. They are perhaps less important to our smaller aircraft, but of some considerable importance to the larger piston aircraft in commercial service.

Two on-board systems are heavily reliant on the Specific Gravity of fuel. Capacitance-type fuel quantity indication systems and many fuel flow systems are only accurate when used with a single type of fuel.

If one were to introduce fuel with a new Specific Gravity and, even worse, to co-mingle it with fuel of another Specific Gravity, one would never be able to know how much fuel has been consumed or how much fuel remains in the tanks. This might seem trivial to us, but when loading a big piston twin, a 10% shortfall in fuel loading could eat drastically into reserves.

To put it into more practical terms, imagine flying your RV with capacitance fuel probes and a flow meter / totalizer. You are used to burning 8GPH of 100LL. You flight plan for that figure. What is your brain going to do when you lean at cruise and see 7.2GPH, or 7.6 GPH for the same power setting? When you look at your fuel gauges and think you've got 10 gallons remaining but you only have 8 in the tanks. What happens if your on-board systems don't interpret the change in fuel density as a direct 10% linear offset?

I know that, theoretically, all of this should be a wash. Heavier fuel by 10% that also yields 10% more range should mean the same number of miles to dry tanks. We, being humans, will undoubtedly find a way to turn this simple conversion into disaster.

My mind keeps going back to the infamous Gimli Glider, an Air Canada B767 that landed deadstick at Gimli, Manitoba, when a combination of issues with the fuel quantity indication system and compounding human errors around pounds/kilos/inches/centimeters/litres/gallons saw the airplane loaded with far less fuel than was needed to reach its destination. This scenario is likely looming large in FAA minds, and I can't blame them for being cautious in insisting on mitigation strategies before turning us loose on this new fuel.
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  #19  
Old 07-10-2018, 07:11 AM
rvsxer rvsxer is offline
 
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Quote:
Originally Posted by Canadian_JOY View Post
Two on-board systems are heavily reliant on the Specific Gravity of fuel. Capacitance-type fuel quantity indication systems and many fuel flow systems are only accurate when used with a single type of fuel.
That's why capacitive systems on heavy aircraft have densitometers. Kerosene-based fuels vary widely in density based on temperature. But it's only a problem if you upload multi-thousand pounds of fuel. If you are worried about the small difference in Avgas densities you are cutting your fuel reserves too fine.
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  #20  
Old 07-10-2018, 07:24 AM
Canadian_JOY Canadian_JOY is offline
 
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Quote:
Originally Posted by rvsxer View Post
That's why capacitive systems on heavy aircraft have densitometers. Kerosene-based fuels vary widely in density based on temperature. But it's only a problem if you upload multi-thousand pounds of fuel. If you are worried about the small difference in Avgas densities you are cutting your fuel reserves too fine.
While I agree with your comments about densiometers in heavies burning heavy fuel, I would assert that a 10% error in fuel quantity sensing is a considerable error in small aircraft. It may equate to the entire VFR reserve amount. This could leave one landing with zero reserves when one felt they had the VFR minimums. Not good, and likely the reason why the FAA is insisting on mitigation strategies.
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