Is CNG a realistic fuel option for GA?

Is your home, or hangar, hot water tank gas fired? If so, you might have a plentiful, and affordable, supply of fuel for your airplane. At least that’s what Aviat Aircraft owner Stu Horn is trying to see come to fruition.

At this year’s AirVenture Oshkosh, Horn along with Greg Herrick, president of the Aviation Foundation of America debuted a dual-fuel, 100LL and Compressed Natural Gas (CNG) Aviat A-1C Husky.

Aside from the large CNG belly tank, the Husky parked in front of the Innovations Pavilion at AirVenture was indistinguishable from any other from the Aviat production line.

Horn (left) and Herrick

Horn (left) and Herrick

Herrick began researching the viability of CNG as a fuel source for aircraft last year. The owner of two Huskys, Herrick reached out to Horn to discuss the idea of creating a proof-of-concept airplane. Once Horn learned more about CNG, he called on six Aviat engineers to make it happen.

This particular Husky, N15NG, was flown to Oshkosh from Afton, Wyoming by Horn. “It has 10 hours on the airframe,” noted Horn at a press conference. “Nine getting to OSH.”

Inside the cockpit, there is a fuel source selector, which can be switched in flight, much like switching from one tank to another.

Internal to the engine, the Lycoming’s IO-360-A1 D6 received new pistons to increase the compression ratio from 8.5:1 to 10:1.

Horn and Herrick noted a number of benefits to using CNG as a fuel source:

  • One GGE (gas gallon equivalent) weighs 5.66 pounds versus 6.01 pounds for 100LL
  • CNG is 138 octane, resulting in more energy per unit of fuel
  • CNG contains no lead, and has 90% fewer smog particulates compared to 100LL
  • CO2 emissions are reduced by 30% compared to 100LL
  • Burning CNG lowers CO (carbon monoxide) by more than 90%
  • Horn expects engine oil to last three- to four-times longer given CNG does not contaminate and dilute crankcase oil

But the kicker to the whole experiment is the potential impact this could have on the cost of flight training. Using the $0.85 as the cost of one GGE of CNG, a training flight might see an 80+% reduction in fuel costs. Depending on the aircraft, that could be $40-$60 per hour according to Herrick.

I touched base with Horn after AirVenture. He admitted he did the CNG project “to do it — prove the concept.”

Since AirVenture he’s been working on the economic model and “identifying strategic partners to work with Aviat on the project moving forward.”aviat_cng_side_left_lo

Asked about feedback during the show, Horn said, “Overwhelming. Surprisingly, different and diverse groups were both enthusiastic and excited.” During and since the show, Horn has been contacted by a utility company president and CNG hardware makers offering to assist. He’s also heard from lobbyists, assuming there must be some government program, thus money, to make this happen. The U.S. Air Force also reached out to Horn, as did members of Congress.

“What’s funny though,” Horn continued, “is they all want you to tell them everything before they decide if they’ll share anything in return.”

Since AirVenture, Aviat has been officially testing the Husky to validate the metrics: consumption, efficiency, performance so they can compare it to the known data using 100LL. And? “The numbers, so far, are holding up quite good.”

What’s next? Horn will pursue an STC (Supplemental Type Certificate) so “we can offer it to the world.” Thanksgiving 2013 was mentioned as a timeframe, but was immediately followed by, “you never know with the FAA.”

When asked about CNG as one part of a dual fuel system as opposed to a single fuel system, Horn doesn’t hesitate. “CNG will work best as a single fuel source.” Useful load is always an issue, and carrying the redundancy of a to fuel system is too much.

As relates to the aftermarket, Horn believes a $12,000 retrofit to an existing airframe and engine is possible. Given the low cost of CNG, as relates to 100LL, an owner who flies 100 hours per year might see a return on investment (ROI) in three years. Given that CNG per GGE is significantly cheaper than 100LL, a pilot might actually fly more hours per year and reduce the ROI further.

For more information:


  1. Terry says

    Wondering about the size and weight of the tank per hours of flight. As far as the bomb thing if it leaks or splits the gas goes up. It doesn’t cover the ground and soak your clothes so you can run through it and star on someone’s Utube. No mater how cheap it is as soon as it gets used for transportation CARB will regulate and certify the components at a huge price just like cars and trucks and the Feds with be right behind.

  2. Jeff says

    Reading about this reminded me of my brothers GMC Jimmy that had a Propane tank in it years ago. He still had the tank, I asked him for it, I might just have a experimental flying with it in a couple of years. Pressure tanks are heavy even if the fuel is lighter than avgas and it has to be removed to refill it with liquid propane or CNG. Now I have to find a carb for it.

  3. says

    This could benefit a flight school type operation that is refueling at their own base every time. I would not expect the infrastructure to be installed at airports across the nation. To add CNG systems is asking a lot when getting a mogas tank is so difficult and it is still a liquid fuel needing no different handling than avgas. CNG has been used before, for a long time, it just does not go mainstream, likely do to the energy density, I remember an experimental biplane (skybolt?) that was at Oshkosh in the early eighties running on CNG.

  4. Richard Baker says

    Natural gas sounds great but the sheer volume needed to be carried aboard in these huge tanks is the problem. The entire mania against “fossil” fuels is loony. Petroleum products have more BTUs per unit volume than any other option. And please don’t go on about electric power.

  5. Jscott says

    If you really want to see whether this is going to fly or not, offer the parts to the Experimental world and forget about wasting tons of $$ getting FAA Approvals in the form of STCs. If it is successful with the Experimentals, then go the STC route. If even the Experimentals won’t fly it, then there’s not much point in spending the $$ for an STC.

    • says

      True about the octane rating, perhaps they mean “efficiency” of the engine, that would be benefited by the higher compression. This is advertising after-all and so the more dramatic the better from that view point.

  6. says

    What is the weight per gallon equivalent? Say you need to fly 3 hours and you plane burns 9 gph on AVgas what size LGN tank do you need, how much will the Gas and tank weigh? I guess you would not take out the other tanks and just go with LNG?

Leave a Reply

Your email address will not be published. Required fields are marked *