Why are experimental / permit twins so uncommon?
The only ones I can think of are the Rutan Defiant and the Cri-Cri. A google also shows up the Velocity V-twin. The fact that such designs have been approved, even registered in the UK, implies that there are no fundamental legislative reasons against them.
I’m aware of the safety-concerns, but would have thought there would still be interest from people who like a bit of complexity or who want to build twin-time. Or who live in Ireland or on Orkney. And price-wise if you wanted a 100 horsepower aircraft it would be much cheaper to get it by buying two Volkswagen engines than one Lycoming, Continental, or even Rotax.
So why so few homebuilt twins?
What has approval got to do with it?
Anyway, no demand is the only reason I can see. Nobody wants to build a twin.
Well, if they couldn’t be approved in the US or the UK then that would explain it.
If you see the low completion rate even for less complex homebuilding, there is no surprise.
I think few people would have the courage to start a twin as their first project – and people who do not finish their first project are unlikely to start their second…
There have been a few, though, in France; I remember a Rutan-style canard with an extra engine up front, and a very beautiful twin pusher canard called the Guépard but that is a couple of years ago, I haven’t seen it recently.
There is the French Mosquito replica too. More of a one-off than a serious attempt at a reproducible homebuilt design.
In the UK I do not believe the LAA have any multi engine types approved. In fact I don’t know if the are even allowed to do so, their authority is delegated from the CAA, with limits.
You could of course forget the LAA and just do it with the CAA directly. Good luck with that.
The Cri-Cri is on the LAA list. Alas I don’t have the skills/time to design and build a twin but it still surprises me given that some people are keen to squeeze all the complexity they can into a homebuilt aircraft. And also given that many designs come from the era when piston twins were still popular.
but it still surprises me given that some people are keen to squeeze all the complexity they can into a homebuilt aircraft. And also given that many designs come from the era when piston twins were still popular.
You have to look at the history of homebuilt aircraft. They were simple and light wood and fabric designs using whatever engine was available. Flybaby and Turbulent and similar. No kits were available, everything had to be built from scratch using drawings and sketches. It’s only during the last 25 years that kits has become popular, and the advanced prepunched skin kits have only been here the last 10 years.
The Cri Cri is hardly a twin in the right sense of the word.