Skydat DX2 engine RPM problems

[Tribal Croc]

I have a little bit of a concern here
My Skydat DX2 engine RPM is jumping around.
When taking off it jumps from 3600 to 4200 to 5400 all over the show.
At circuit height it settles down after a few minutes and gives me a 5300 -5400
Even on the ground if I want to do a full power test is jumps around 3600, 4000,4800,5200,3600 etc.
Any ideas

[wiskeyfoxtrot]

Hey TC,
Have just spoken to Serge at Amptronics, as i have the same issues as you and mabey more !.
He says that you need to clean the connectors ( orange one - that gets screwed into the sender box ) with some kind of electrical cleaner to get rid of any oxide that may be on the connector pins. Will also try this weekend and report back.
Am also moving my sender box to the front of the trike. It is at present bolted to the engine support and the vibration from the engine is quite bad.

Hope you come right

Later

[V]

Hi Tribal Croc,

is it a new installation or has it been working ok until now? If it's just broke, then check the connections as wiskeyfoxtrot suggests, especially the ground. If it's a new installation, then you might need a ballast resistor between the rpm input (grey wire in the engine loom) and the ground. MGL recommends 220 Ohm for their devices. You need to check with Amptronics what they recommend.

Whiskey, I don't think it's a good idea to move the sender box. While I don't have any hands-on experience with Skydat installations, generally the sender box's purpose is to encode the signals, so that there are fewer cables to run to the instruments, less possibility for interference or other signal distortion. Especially your CHT and EGT readings may suffer if you move the box to the front. Keep it as close to the engine as possible.

If vibration is a concern, then try to mount it on the airframe somewhere nearby, ie. bottom of the pylon, but still, keep it as close to the engine as possible.

Hope this helps.

Cheers,

V.

[Tribal Croc]

Thanks guys
WF – I think they call it electrical silicone spray – I have tried it but same story
V – It’s an old installation it actually started before I sent my trike for the crank replacement and is still doing the same
Thinking maybe it’s a problem with the Skydat unit
I don’t like to fiddle with things I don’t understand so
Now next question is it safe to use as is Keep in mind that it only happens on take-off and settles down in flight and as far as the engine - all sounds good definitely no drops in RPM

[V]

Hmm, I'm not sure how safe it is to operate the engine. There might be problem with your charging or ignition coils. If either of them fail, then you have a serious problem at hand. I would definitely try to get to the bottom of it with two simple tests for the start:

1. Using a multimeter, measure the resistance of the coils as per Rotax manual. Also keep an eye on the voltage - the DX2 tells you what your current voltage is. Too high is just as bad as too low.

During the crank replacement your charging and ignition system would have been checked, but perhaps coils got damaged somehow during the assembly or the problem wasn't apparent yet.

2. I would try to borrow a rev counter and see what it shows. Easiest is to get a handheld laser tachometer from ebay (mine was about R150 incl. shipping) and point it at the prop while running the engine on the ground at different throttle settings. You can either calculate the engine rpm based from the gearbox ratio, but really, you're just interested whether there is any fluctuation and whether it corresponds to the jumps on the DX2 or not.

I would definitely suggest chatting to the folks from Amptronics, they might give you more ideas.

Cheers,

V.