Fossil fuels are coming under increasing scrutiny, and while we await the better batteries and fuel cells of the future, the search for improved performance and economy cannot wait. Lets look at whats available now.
Diesels are popping up all over Light Airplane Land, possibly because of their reputed reliability and demonstrated fuel economy. For those unable to afford a new DeltaHawk or certified Continental, auto conversions hold sway. One person getting attention for his Governor, a plus-size Jodel derivation, is Charles Kenny in New Zealand.
He initially wanted a D-18, a smaller, lower-powered, two-seat Jodel, which, Kenny notes, was the answer to the oil crisis of the 70s. The little Jodel was too small for Kiwis, though, who, like their American friends, are larger overall than Europeans.
Having spent long hours studying all of the Jodel and Robin aircraft from the single-seat D9 to the latest DR500 President, Kenny said, They all had something that stood out. All I had to do was work out what and change the scale to fit one aircraft.
Kenny scaled the D-18 up 10%, along with other changes. The resulting airplane is like a flying version of Dr. Whos Tardis, small on the outside but amazingly large inside. It has 8 inches of headroom for a 6-foot pilot, and is 44 inches across at the shoulders, giving occupants C-172-like roominess in a compact airplane.
Kenny and friends respond to bovine critic. Note width and depth of spar. Air intakes on starboard wing leading edge provide Mosquito-like cooling for the buried radiator.
Solo flight can be made in any seat, or on the centerline like a big single. The back section of the turtledeck can be lifted off for maintenance, if required. The luggage bay is in two sections, with a lower locker in the front of the main locker for valuables.
The enlarged scale gives a wheel track of 8 feet, 6 inches on 6.00×6 wheels with Cleveland brakes, handy for maneuvering around Hobbit holes and sheep tracks on Kennys 1200-foot field.
In an article he wrote for a New Zealand publication, Kenny explained, Jean Delemontez [co-creator of the Jodel line of aircraft] summed up some of his own creations, arguing that everything had flown before, just not on the same aircraft. This is the case with CCD.
Kenny continued, When I was well through the airframe I discovered the French were onto the same concept, putting a Peugeot diesel into a modified DR300 aircraft (Jodel Delvion). It worked. After tests the French engineers felt the diesel was safe for 10,850 hours (!) at 10 liters of fuel per hour, Diesel or Jet A with 1% oil for added lubrication.
Anyone who builds an airplane knows that if you change something, you may end up changing almost everything. Because this airplane had not yet been built, Kenny felt he couldn’t make any mistakes. Now it has all come together, and only the propeller drive has to be finalized.
At first he tried to copy French PSRU and propeller assemblies, but he couldn’t find out how they mounted the drive to the engine, so he used a modern
Centaflex coupling to help with any torsional problems. However, the Centaflex did not like it when bolted on the prop, so more exploring was required.
Torsional vibration is the price we pay for having compression, Kenny said, and heavy props only add to the problem. In France, Serge Pennecs propellers weigh 7.7 pounds (3.5 kilograms), but Kennys Henry weighs 11 pounds (5 kg), and a Warp Drive 33 pounds (15 kg).
The diesel guys in France approach the torsional problem differently from each other, but now have reliable engines with over 1200 hours of flight time per engine, Kenny said. And Jodel Delvion now has a belt reduction with no torsional coupling, while Serge Pennec has several new Gazaile aircraft flying with the coupling. Pennec also flies his RANS with a Peugeot 1.4 diesel on less than 1.58 gallons (6 liters) per hour.
Thanks to ideas from these folks, belt reduction is being worked into Kennys redrive. A 1:66 reduction will have the engine turning a bit slower than theirs, he said. Meanwhile the last 1000 jobs means its nearly ready to roll-echoing the age-old understanding of a late-stage airplane builder.
Paul Lucas and Bernard Stevinous Greenelis at the 2011 Paris Air Show. Note the interesting DUC propeller and the monowheel retractable landing gear.
Other Diesels, Other Places
Most diesel-powered small aircraft seem to fly with either a VW TDI or Peugeot-Citroen engine, with the Mercedes Smart Car engine having been tried and found wanting so far. Several groups attempted its use, but it seems to be on the sidelines for now. Even Paul Lucas, who with Serge Pennec had been so successful with Dieselis, had to drop out of the Green Flight Challenge with his Greenelis. Reports suggest that the engine/reduction combination suffered from harmonics issues, but the potential is still there. Lucass partner on Greenelis, a lecturer at the Institut Universitaire de Technologie (IUT) of Brest (France), Bernard Stervinou, is reportedly working on smoothing out the rough edges in the engines problems.
The 800cc SmartCar engine (above) with belt-drive PSRU, radiator and plumbing neatly tucked into the cowling.
According to Francois Besse, editor of Piloter magazine, the three-cylinder develops 42 horsepower and will run on biofuel. Expected consumption is 0.8 gallons (3 liters) per hour or, at the cruising speed of 100 miles (160 kilometers) per hour, about 117.6 mpg (2 liters per 100 km). Besse notes this fuel use would be four to five times better than an equivalent two-stroke Rotax. Had it competed in the Green Flight Challenge, Greenelis would have had to fly the 200-mile course at a minimum of 100 mph on about 1 gallon (3.8 liters) of fuel per passenger just to qualify.
Finnish builder Jarmo Hakalas PIK 25s 1.9-liter VW TDI-JH1 sips diesel at 155 grams per horsepower hour, frugal compared to an equivalent gasoline engines 240. Using less than two-thirds the fuel encourages longer travels, as with Hakalas across-Finland-and-back, 1242-mile trip without refueling, similar to Jean-Jacques Ballots trans-France flight in his Gazaile. He does have 63-gallon capacity in his wing tanks, and the TDI uses only 3.7 gph at 100 mph. The airplane and its accomplishments helped Hakala win the Henri Mignet Diploma from the Fdration Aronautique International (FAI) in 2009.
Another Finn, Pekka Hmlinen, uses the same base engine in a Cessna 172. He pulls a claimed 180 hp, so it will be worth watching the longevity of this effort. So far, the installation and early flights look good. He has a variety of videos that display the pulling power of his conversion, a photo gallery and a so-far unexplained rebuild following an apparent to-do with the nosegear. All is beautifully reconstructed and repainted, and we look forward to hearing and seeing more.
A YouTube video shows a Swiss BX-2 Cherry, a small two-seater powered by a VW Lupo TDI, a three-cylinder unit. Collecting more information on this and other efforts is difficult, even in this Internet age, but the message is that others are seeing the plausible benefits of even a heavy diesel engine for its fuel efficiency and are leading the way in true Experimental aviation.
Petrol Can Be Efficient
As people like Michel Colomban in France have shown, thoroughly practical light airplanes can be fashioned around something as humble as a Briggs & Stratton engine. Colombans MC-30 flies well on such an engine with a typical Frenchman onboard, but is somewhat limited for beefier Americans. Besides, he wont sell plans or components in America, having run afoul of our litigious society.
Spiffy and trim with its closed cockpit, Solo can be configured for both tricycle and conventional gear. The wing can be dropped out from under the fuselage for trailering.
All is not lost, however. Three years ago at Tehachapi, California, Rienk Ayers showed me drawings of a small, composite single-seater that would fly an estimated 100 mph on a B&S, burning about 1.5 gph. Its attractive lines, with a vertical tail reminiscent of a baby Lancair, tricycle or conventional-gear options and a projected production price of $25,000, made it seem like a reasonable investment for the weekend flier. A two- or three-person flying club could share the minimal expenses and low operating costs for flying that wouldn’t break the family budget. Ayers estimated that even a complete engine overhaul would cost only about $500.
Ayers announced that following a few lean years, he now has funding for his little airplane. We are still using the V-twin for our base model version, he said. Open cockpit, direct drive should retail for around $25,000 (ready to fly). Fully enclosed with redrive and larger prop, etc., should retail for around $29,000. We also have the high-performance engine package which will use a 75-hp inline twin. The latter will be flown at less-than-maximum continuous power to comply with LSA regulations. Ayers added, For those who want to go Experimental, we will have a turbo-normalized version of the engine that puts out 120 hp and should have a cruise rate at FL10 of over 200 mph (maybe knots). This version of the Solo with the TC engine (and a really nice panel and including the full build-center time) should still be under $39,000 ready to fly.
Open- and closed-cockpit versions of Rienk Ayerss Solo light plane, expected to fly this year with a Briggs & Stratton engine.
The fuel burn on the base engine is less than 1.7 gph (about 70 mpg), Ayers said, and a hot-rod version will burn 5 gph (about 45-50 mpg at turbocharged altitudes) He said hes signed a deal with an engine shop to build firewall-forward packages.
He also plans on either single- or two-piece detachable wings to allow trailer storage and transport. Cleverly, he positioned either tricycle or conventional-gear legs to allow dropping a single-piece wing (a 23-foot span) with its front spar behind the conventional gear or rear spar ahead of the tricycle maingear. Although the fuselage will fit in a 20-foot shipping container, the wing may need some removable tips or a two-piece format to enable easy stowage.
If Ayers can come to market with his vision and it performs as projected, the Solo could be the perpetually looked-for shot in the arm needed to rejuvenate general aviation.
Ayerss single-seater could introduce economy flight to the masses, as Greg Coles GosHawk could be the entre to sport motorgliding. The long, thin wing bespeaks its DuckHawk origins, and its wide spars allow it to haul two into the realm of self-launching, real soaring.
Designed to take part in the Green Flight Challenge, but not ready in time for the competition, GosHawk is now under final construction in Bend, Oregon. Powered by a 60-hp HKS 700E/T engine, with a turbocharged 80-hp version available, GosHawks 570 pounds can carry 480 pounds, for a 1050 pound gross weight.
Because of the added width of the side-by-side cabin, the DuckHawk wings spread to 50.8 feet. Their 83.6 square foot area allows a glide ratio of 38:1 at 52 knots (59.8 mph) and a best sink rate of 130 fpm at 46 knots (52.9 mph).
Such efficiency drops fuel use to a mere two-thirds of a gallon per hour at 100 mph, giving about 150 mpg or 300 passenger miles per gallon. At 150 mph, GosHawk will still show 100 mpg. Maybe Toyota could market it as the Prius G. Because it uses the DuckHawks wings, it will also be a real sailplane, capable of cross-country flights without the engine turning. With one up and at 700 pounds, GosHawk climbs at 1200 fpm and stalls at 42 knots (48.3 mph), practical, real-world numbers.
Opening the Outlook
For years, builders have been constrained by available powerplant and fuel choices. Inspired designers, using a new selection of engines and every type of building material, have opened up the outlook for new creations. As these new craft show their ability to save fuel and lower flying costs, they could also show the way to a brighter future for general aviation.
Dean Sigler has been a technical writer for30 years, with a liberal arts background and a Master’s degree in education. He writes the CAFE Foundation blog andhas spoken at the last two Electric Aircraft Symposia and at two Experimental Soaring Association workshops. Part of the Perlan Project, he is a private pilot, and hopes to get a sailplane rating soon.