Wrencat

[Peter Wales]

The modified Wren with Jetcat electronics is now fitted into a Cuatro and testing has started. The first spool up was a 3 second ramp up time, which seemed to be a default setting in the Jetcat ECU, and caused an instant flameout. Resetting it to 15 seconds produced consistent starts and spool up to a preset 1350 rpm. It locked in at that rpm and stayed there through a 7 minute hover.

While trying to set the cyclic trims in flight, the heli lightly bounced on the ground and the turbine shut down. The reason, according to the ECU was low rpm. I wonder if the Jetcat sensors are not picking up the Wren magnets perfectly. More investigation required in that department, or dont bang it on the ground I suppose:)

Anyway, it starts, runs and flies and at this stage I am happy. The chances of the Jetcat software being an exact match for the Wren is very remote so I will have adjustments to make and there will undoubtedly be flame outs, autos and crashes in the future, but it's all good fun.

Here's some pictures of the installation

http://scalehelicopters.org/c1.jpg

http://scalehelicopters.org/c2.jpg

http://scalehelicopters.org/c3.jpg

http://scalehelicopters.org/c4.jpg

The only problem in fitting the Wren into the Cuatro using David Owens conversion kit, was in the X frame over the tunnel. It had to be machined a little to clear the fan. As there is no fan on the Wren turbine there was plenty of metal there and fitting a fan fouled it. A couple of minutes on the mill soon had it sorted.

[Sara]

I'm pleased to hear that it flies!
We don't usually have magnet problems - they either work or they don't - but I don't know if the JetCat ones are the same as ours.
With a Wren ECU "Low rpm" means "the rpm went below the minimum needed for idle, so the engine stopped" and it can have a number of causes, including throttling down too fast (that is, faster than the engine can comfortably manage), in which case, lengthening the deceleration delay helps. However, that doesn't seem applicable in this case, and it might mean something completely different on a JetCat anyway.

I'm watching this experiment with interest.

Sara Parish
Wren Turbines

[WillJames]

Thanks for posting Peter. I LOVE the fact that you fly the coolest stuff and that you are not afraid to PLANT the hell out of one. Sure is fun to watch you fly and look at your cool helis that all actually fly and are not just for looks.