French-manufactured aircraft have a tradition of being based on wooden airframes. There’s Avions-Mudry’s CAP 10B, and the Jodel, for example. It’s not something one really thinks about, though; in most people’s minds aircraft are based on metal or composite airframes, maybe with the exception of classic tube-and-fabric taildraggers.
Wandering the halls at Aero Friedrichshafen (Europe’s leading show for general aviation) earlier this year, I come across a Robin, a French manufactured aircraft. I know them well, having flown in several when I lived in France. One could say I have a soft spot for them.
I quickly corner a person wearing a Robin jacket. It’s Steven Bailey, an authorized sales partner for Robin. I ask him if this is really a wooden turbine aircraft parked in front of me.
“Yes,” he laughs. He explains why wood is an ideal material for airframes: “Wood is strong, but at the same time very light. There’s not a lot of vibration in flight, so it’s comparatively quiet inside the aircraft. Because wood flexes in turbulence, passengers will notice less of it than in composite aircraft. Wood doesn’t fatigue and the glue we’re using works better the hotter it gets. Wood is also easy to repair; if there’s damage to the wing, the wing can be fixed, whereas a composite aircraft would probably require a new wing.” Bailey also noted a safety benefit. "I wouldn’t recommend that you try this at home, but in the event that you had to ditch in the ocean, the wood makes the airplane float. It’ll go down eventually, but not as fast as a composite aircraft.”
The wood used to make the wings and the airframe (yes, the whole aircraft is made of wood, with the exception of the cowling and the fairings) differs depending on the workload. Areas likely to experience stress are made of a wood as strong as mahogany, but from a sustainable source; most other areas are made of spruce, because of its flexibility.
Bailey adds that the wooden airframe by itself weighs less than 220 kilograms (485 pounds). A fully equipped aircraft would probably weigh 630 kilograms (1,389 pounds), which makes for a useful load of 399 kilograms (879 pounds).
I slide my finger over the shiny, pearly paint on the wing. I can feel the wooden spars. Smooth. “The wood is covered with a really thin light-weight fabric (Diatex). This smoothes the wood, creates an even surface and makes for a better finish when the aircraft is painted,” Bailey explains.
The Robin’s turbine engine is a French-made Turbotech. The aircraft can run on “anything, probably even Scottish whiskey,” jokes Bailey. But seriously, the Robin can burn Jet A, automotive diesel, avgas, UL91, and—with a little tweak to the injection system—also hydrogen.
It seats four people and in- and egress is possible from both sides by sliding the big canopy forward. Surprisingly, the gear is not retractable. “At the speed the aircraft is going, the drag caused by the gear is minimal.” Bailey explains: “Daniel Triques [Robin’s chief engineer from 1972 and still active in the company] has always maintained that retractable [gear] is not worthwhile for an aircraft cruising at less than 150 knots. Adding it would add to the weight, reduce the useful load and add to the price of the airplane.”
Talking about price: The airframe of this light-turbo aircraft is based on Robin’s DR401, except for the engine cowling. That’s where pricing starts at around $350,000, though the price has not been set, yet, and will need to increase to allow for the engine.
If there’s one big downside, it’s that a wooden turboprop will require patience: Certification isn’t going to happen for a while because of the European rules and regulations, and the installation of a turbine engine in a light aircraft. Bailey also mentioned that working with wood requires a very special skill set, a highly trained workforce, and therefore a longer production time.
Watch this space.