AdamFrisch wrote:
They do fly one one engine, I’ve heard from a user.
Historically they have been fitted with a variety of engines: some do, some don’t.
I’m not sure whether a 4 stroke would be possible. 2 strokes typically have a higher power to weight ratio and the original engine was very light.
Within the UK, the LAA has this to say:
The aircraft has only been accepted with the JPX PUL 212 engines fitted as shown on
the drawings. The accepted propellers are Aerostructure MC/692/200. The JPX engines
are no longer available. Various other engines such as Hirth F33 are under
consideration.
That means that within the UK it would likely be difficult to get a Cri Cri to fly again if one of its engines is ever damaged beyond repair. Even in a more liberal regime, I think it would be reasonable to consider whether installing a heavier engine with more power output and perhaps different resonances, would be a good idea without further calculation and perhaps modification.
gallois wrote:
Nowadays, builders are using engines Valmet, JPX, Limbach, 3W, Rotax, Zenoah, Hirth, and I am glad to see, that are recommended also Czech ZDZ Model”
Hmm, I wonder what kind of Rotax engine can be used on the Cri-Cri 
Weight is obviously an issue, and so is frontal area (drag). With two engines out in the wind, this creates lots of drag. Then there is also the tuned pipe for a two stroke that takes lots of room and some drag. Propeller is another thing. What’s needed is a light engine with low frontal area and it has to be direct drive for the propeller to be reasonably sized.
There are lots of paramotor engines. They tend to be purpose designed with redrive that is intrinsically designed with the engine and so on. It seems to me that lots of work is needed to make this work, if even possible due to bearings. These engines are at least designed for the right “mission profile” (high continuous power). A large model aircraft engine would fit right in I guess. Then you get small size, light weight, power, but high consumption and they are not designed for the mission profile at all (a TBO of 10 hours? ) Drone engines would probably be perfect, but with a “mil stamp” the price is a factor 10 higher.
gallois wrote:
you can make the same case for the bumble bee cannot possibly fly. The physics are all wrong.
I wonder where exactly this comes from. No physicist or aerodynamic engineer has ever said such a thing. What has been said is that airfoil theory/physics cannot explain how most insects fly.
Anyway, I’m simply wondering what kind of engine would fit since JPX is long gone. I initially would think there is a gazillion 2 strokes around with 20-ish HP, like engines for paramotors in particular. Plenty of manufacturers of high quality stuff. It’s just that converting such an engine to direct drive and low frontal area looks like a substantial task since thee paramotor engines are very purposely designed for paramotors exclusively. I’m sure it can be done, but not by the average kit builder. Not unless someone makes a mod kit.
Quite a few engines would be suitable, all from the RC world…
Names like DA, O.S., DLA, ZG, Roto, Mintor, etc. Available in all HP and displacement…
What about a couple of MOKI 5 or 7 cylinder 400cc radials, that would sound pretty cool, no? 
What do you mean a mod kit. Each Cri Cri is individual based on Michel Colombans plans.
The engines are on mounts, very close to the fuselage of the aircraft and forward of the pilot’s seat. Each exhaust runs along the exterior either side of the cockpit, venting towards the rear. The exhaust does provide some heat to the cabin interior by its closeness to the fuselage.
Many different engines have been tried and work perfectly well. A friend here has just done it the expensive way and got 2 of the type used to drive a STIHL garden tool. I’m not sure if he was talking strimmer, chain saw or hedge cutter.
As far as I know 2 types of jet engine have and are being tried. These are of the mini variety possibly used in drones or model aircraft.
AFAIK only one, at present, is flying with 2 electric motors. Its performance is only 10kph slower than the jet engine versions.
The Airbus electric test Cri Cri has 4 electric motors 2 each side. The test pilot loved it, but it will never go into production of course. Its an experiment.
So as you can see it is quite flexible in terms of engine usage and is open to the builder to experiment.
I rather like the idea of some of the lightweight rotary engines that are being developed. If they ever really come to fruition. Mistral, Wilksch, Wankel and Mazda all had a programme for these at one time or another.
We don’t have an LAA here. We have an RSA which is a bit like the EAA and we have OSAC, part of the DGAC which checks out experimental aircraft and can deliver a CDNR.
gallois wrote:
. A friend here has just done it the expensive way and got 2 of the type used to drive a STIHL garden tool. I’m not sure if he was talking strimmer, chain saw or hedge cutter.
This reminds me of something.
It’s german but watch it to the end anyway. And no, it is not a fake, it’s real.
Ha great they could be just perfect for the Cri Cri.
If i decide to build one I’ll bear them in mind :)
gallois wrote:
Ha great they could be just perfect for the Cri Cri.
That guy really tops it… highly innovative of totally useless but fun objects. He has space, time and nobody to stop him is the line of those commercials. The only commercial ever I downloaded all of them. (Ok, there was the Pepsi one with We will Rock You but well…. )
gallois wrote:
What do you mean a mod kit. Each Cri Cri is individual based on Michel Colombans plans.
Anything can be done, but that doesn’t mean it should be done, or that it can be done by the average person. IMO the best choice of engine would be a paramotor engine. Lots of them around, high quality, light, high power to weight, the ability to produce high power continuously over longer periods of time, low weight, right HP range. By the face of it just perfect. But looking a bit closer, you cannot simply grab one and put it on a Cri-Cri. You have to modify it for direct drive of the prop, which most certainly requires a hub + most possibly an extra bearing. You have to make the (tuned) exhaust from scratch for it to be streamlined. You probably also need a to rework the fuel system. There is a whole lot of things that has to be done, and they are definitely not easy tasks for an average builder. For a guy with skills and tools, this is no problem however. Lots of work and trial and error, but nothing that isn’t doable. For the average amateur aircraft builder, forget it. Even if the guy with skills and tools offers a kit for others to purchase, this is no easy task.
A model aircraft engine would fit right in, no problems whatsoever of any kind. But what do you get? You get high power, low weight, but low TBO, high fuel consumption. It’s not really fit for the mission profile at all when looking a bit closer.
A drone engine would also be perfect. Then you also get durability and some sort of TBO, but what? 30h instead of 10h ?. The problem is they cost 10x that of model aircraft engines. A 20 HP model aircraft engine isn’t cheap to start with, €2-3k ?
Then there are tons of garden variety powered tools. Compared with all of the above, you get some durability in some cases, but low power to weight.
The original JPX was perfect by the looks of it, and this is what made the Cri-Cri popular in it’s time. Building an aircraft (even from scratch from drawings) is easy compared to re-working engines from scratch (and get a reliable result). It’s just the way it is.
If I were to build a Cri-Cri, I would probably first ask some of the paramotor engine makers if they could modify a couple of engines for me. The certainly could, it’s more a question of price. It will not be cheap I guess, maybe around €5-10k or more per engine. A unmodified paramotor engine cost about €4-6k (and up). Then again, I could end up with a model aircraft engine instead. They are simple and easy to work with, easy to get spare parts and so on. It could be a better choice, even if it results in fiddling with the engines every 2-3 flight hours. It would work, but it’s not a long tern viable solution IMO.
An aircraft without an obvious choice of a running and reliable engine, is dead in the water. A thing for the extreme enthusiast. I’m not saying no such engine exists for the Cri-Cri, but so far in this thread I have not seen any. Going electric is probably the best choice? Then you get reliability, TBO and also weight (if you can sacrifice endurance). + lots and lots of coolness
