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CNG alternative? Dual-fueled Husky to be at AirVenture

S

srv

Active Member
http://www.aviataircraft.com/cng/

Kinda surprised by this, but can't tell if the 7 hour claim is CNG only or CNG + LL tanks from the story:

Q: How long can you fly the Husky CNG on full fuel tanks?
A: The demonstration aircraft can be flown approximately seven hours at a 65 percent power setting.

Q: What does GGE mean and how does that relate to AVGAS?
A: GGE stands for ?gas gallon equivalent,? that is the amount of compressed natural gas it takes to equal approximately one gallon of gasoline in terms of energy. One GGE of natural gas is 123 cubic feet and weighs approximately 5.66 lbs. vs. 6.01 lbs. for 100LL AVGAS.
 
So the fuel is close in weight, not surprising considering they both come out of the same hole in the ground.

What comes immediately to my mind is;

What is the tank weight????

If it is hard to find Mogas at an airport, what do you think it is going to be like to find a CNG pump??
 
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I saw these guys yesterday. I was going to stop and ask the same question about the tank. I'm also curious how they maintain a consistent pressure. I'm going back on Thursday, I'll ask when I go by.
 
Neat

All the way at the bottom of the page...

Q: What is the additional weight of a typical CNG system in a GA aircraft?
A: Of course that depends on the aircraft, and the CNG system being installed. The tank is definitely the largest factor. For example the all-composite “Type 4” tank we installed for this demonstration aircraft has a GGE of 9.2 gallons (35 liters) and weights 95 lbs. empty. In this rapidly advancing field, tanks keep getting lighter and are available in a variety of capacities with even greater weight efficiencies. The balance of the non-structural materials is perhaps 10 lbs.
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Given the tank capacity of 9.2 gallons I suspect their 7 hour claim is burning avgas. Still. Neat stuff. I've driven natural gas vehicles and you can't tell the difference in any way.
 
After reading the linked info.........

So, the full tank weighs just under 150 pounds, and it seems that you would usually have to take it somewhere to fill it.

Then, put it back in the plane------oh my aching back:rolleyes:

Here is an interesting quote lifted from the link, " We have noted several performance advantages using CNG over aviation gasoline. One is increased power output given that octane rating of natural gas is typically 138 vs. aviation gasoline?s 100."

Am I the only one who has a bit of trouble with this statement???
 
If it is hard to find Mogas at an airport, what do you think it is going to be like to find a CNG pump??
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Don't you just steal the bottles off your grill and throw them in the back seat?
 
Mike S said:
Here is an interesting quote lifted from the link, " We have noted several performance advantages using CNG over aviation gasoline. One is increased power output given that octane rating of natural gas is typically 138 vs. aviation gasoline’s 100."

Am I the only one who has a bit of trouble with this statement???
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Actually, that's about right. It varies from around 125 to 140 depending on the exact mix, but the common "pipeline" gas running into peoples homes and compressed for CNG is typically going to yield 135 octane, plus or minus a couple points.

The increased power output is a bit of a stretch - cube for cube and all other things being equal, CNG engines normally deliver about 80% of the horsepower that an equivalent gasoline engine will at the same RPM and manifold pressure.
 
Correct, but higher octane fuels have higher detonation margins can be run leaner and with more advanced timing, which directly leads to more power.
 
tmbg said:
Correct, but higher octane fuels have higher detonation margins can be run leaner and with more advanced timing, which directly leads to more power.
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"Can be" is the gotcha here, the quote from the link only says the higher octane gives more power. Nothing was mentioned about changing (in flight no less) the parameters of the engine such as compression ratio, ignition timing etc when changing the fuel.

With a higher octane fuel you can do a few things to boost power that a lower octane fuel will not support without detonation. But changing the fuel alone will not make a difference if the engine is tuned for the lower octane fuel.

It is all about inter cylinger pressure. Supercharging, higher compression ratio, advancing timing, intake runner tuning, exhaust tuning------all can lead to higher ICP, and that is what will give more oomph------and will likely require higher octane to keep the engine from self disassemble. But the octane is not the cause of the power increase in any significant percentage.

Read what the quote from the link says, not what you extrapolate from the statement.

Mike S said:
" We have noted several performance advantages using CNG over aviation gasoline. One is increased power output given that octane rating of natural gas is typically 138 vs. aviation gasoline’s 100."
Click to expand...

As I said before, I have trouble with their statement.
 
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This exercise is more a PR stunt than a realistic alternative to avgas. I can see limited applications, but the availability/infrastructure problem will make it impractical for a long time. All of the buses and trash trucks in my town are CNG powered, but that is easy, they all return to the same spot every evening. Because of that, they do not require dual-fuel ability and can be built to get the maximum performance on CNG by running very high compression, they are converted diesels, to take advantage of the octane available.

John Clark ATP, CFI
FAAST Team Representative
EAA Flight Advisor
RV8 N18U "Sunshine"
KSBA
 
Mike S said:
At 40 or so pounds full, not an issue.

Also, the BBQ runs on propane, not CNG.
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Having shopped numerous times for a cruising sailboat (but never pulled the trigger.....yet) I can tell you that CNG is significantly less available than LPG. That is true in the US and much more true out of the US. Doesn't seem like a good choice of fuel to me.

Now, when they fly a Husky on used fryer oil from Maccas....
 
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