Aviat, Aviation Foundation unveil concept CNG-fueled single-engine aircraft
31 July 2013
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| Aviat Husky CNG. Click to enlarge. |
Airplane manufacturer Aviat Aircraft, Inc. and Minneapolis-based Aviation Foundation of America, Inc. unveiled the first dual-fuel, piston-powered aircraft to operate on both compressed natural gas (CNG) and aviation gasoline. The Aviat Husky CNG is on display outside the Innovations Pavilion throughout AirVenture 2013 in Oshkosh, Wis. (29 July through 4 August).
The proof-of-concept Aviat Husky CNG, which flew more than 1,000 miles from Aviat’s headquarters in Afton, Wy., to be at AirVenture, can be powered by CNG or 100LL aviation gasoline with the flip of a switch. It is a mostly standard Aviat Husky A1-C that has been fitted with a 3600 psi (248 bar) CNG fuel tank in addition to its standard aviation gasoline tanks. The only modification made to the engine, a Lycoming IO-360-A1 D6, was the installation of new pistons to increase the compression ratio from 8.50:1 to 10:1.
The 200 hp Lycoming four-cylinder engine power the aircraft with a cruise speed of 143 mph. Flight endurance at 65% power setting is approximately seven hours.
The Husky’s gasoline capacity is 52 gallons of 100LL, 50 of which is useable. In this demonstration aircraft both the CNG and 100LL tanks may be filled to capacity and still carry a 220 lb. pilot and 70 lbs. of gear.
The all-composite Type 4 tank has a GGE equivalent capacity of 9.2 gallons (35 liters) and weights 95 lbs. empty. The tank is removable and can be refilled using a CNG refilling system, either personal or at a commercial location. If the tank were to be non-removable it would be filled from a nearby CNG refueling system.
Greg Herrick, president of the Aviation Foundation of America approached Aviat’s president in early 2013 with the idea of building an aircraft to demonstrate the advantages natural gas can offer general aviation aircraft. The advantages, Herrick noted, include fuel cost savings, cleaner burning fuel and no lead emissions.
Compressed natural gas power is up to 80% less expensive than the national average of $6-per-gallon aviation gasoline. There is no lead in compressed natural gas, the presence of which is currently a significant issue with aviation gasoline. It is also a much cleaner burning fuel, reducing smog pollutants by 90% and reducing CO2 emissions by 30%.
Engine oil remains significantly cleaner therefore improving engine life, while aircraft performance is enhanced as CNG typically burns 138 octane versus the current 100 octane of aviation gasoline.
In terms of performance, Aviat said that exhaust gas and cylinder head temperatures run approximately 20 °F cooler with CNG, allowing the pilot to maintain more advantageous engine operating temperatures. This is particularly advantageous during climb. The company also suggests that engine performance at higher altitudes will prove to be better because of the higher octane rating of CNG. Engine starts are also instantaneous with no hot start issues and there is no risk of vapor lock.
In a production environment, the company estimates the dual fuel CNG option may add between $12,000 and $15,000 to the base price of a gasoline powered aircraft.
Aviat Aircraft of Afton, Wy., manufactures the Husky, Pitts Special and complete kits for the Eagle biplane. The Husky, “America’s favorite taildragger,” has become the most versatile aircraft in its class. It is designed for off-airport landings, for recreational flying as well as observation and cargo hauling operations. It can be flown at any time of the year and needs little more than a clearing to be able to land.
A useful load of just 290 pounds with full tanks isn't much. Cutting fuel to half tanks would add about 150 lb to that.
A Dewar for LNG would probably be lighter and carry much more fuel than the CNG tank. That might be a more productive route.
Posted by: Engineer-Poet | 31 July 2013 at 08:41 PM
Good point, E-P.
To carry the equivalent of 52 gallons of LL gasoline, the airplane will have to carry 500 lbs of empty CNG fuel tank weight, excluding the weight of the fuel, which would weigh over 200 lbs more. So, cross-country flying with CNG is out of the question. However, for flight school and local flying, the plane will need to carry just over one hour's worth of fuel, thus reducing combined fuel and tank weights to just 150 lbs.
Reducing cross-country flight duration from 7 hours to 3.5 hours will add nearly 400 lbs to the payload capacity while using low-cost CNG. This type of aircraft can land on almost every pasture, thus it can land on a farm equipped with CNG filler, and be on its way for another 3 hours of flight. A much longer flight is not so good for the bladder!
Posted by: Roger Pham | 31 July 2013 at 11:28 PM
You need fuel reserves of 45 minutes to an hour for safety's sake, so the useful duration isn't as great as that.
On the other hand, being able to swap CNG tanks between students could make the aircraft much cheaper to operate as a trainer.
Posted by: Engineer-Poet | 01 August 2013 at 07:15 AM
$1.50/gal vs $6/gallon av fuel costs will find some interest.
Posted by: kelly | 01 August 2013 at 08:14 AM