Had an interesting day today, and not in a good way! I went along to Merryfield today, but didn't fly my Raptor as the Gliding Club were using the airfield. After a couple of flights with my edf foamy, I jumped in the car to drive home. There was some strange sounds coming from my Raptor, and on closer inspection I noticed the sequence lights on the Jetcat IO panel were flashing randomly. Rx power was off, but I had connected the ECU battery to check the system. I was surprised to see the ECU doing anything with the Rx power off, as I was under the impression that with Rx power off the Jetcat ECU should be off too. I disconnected the ECU battery and drove home.

When I got home I decided to check over the system. I'm running a Jetcat P120 with an old ECU - looks like a version 4.9 ECU, but has V5.0 marked on it, although the GSU says it's a V4.9 ECU. ECU power is a LiPo battery. It's been faultless for 20+ flights. I switched on the radio gear, and ECU indications were all normal, no unusual flashing going on. I initiated a start sequence, which began normally, so I aborted it, thinking that at least the electronics were working correctly. It was still nagging me that something wasn't quite right though, so I decided to do a full start.

With the GSU still plugged in, I went through a full start sequence. Lights all indicated correctly, engine spooled up normally and gas light up was fine. As the fuel started pumping though, I had 2 foot flames out of the jet pipe. I selected shut off, which took about 3 seconds as it's done using the throttle trim, closed the manual fuel valve in the feed line to the pump, and fired the CO2 extinguisher into the engine bay and, as it's a fully ducted system, also into the intakes and tailpipe. Glad to say the flames went out!

According to the GSU, the shut down was due to Powerfail. Max Temp 792, Max RPM 38000. With the Rx power off, should I be able to get anything out of the ECU? Plugging in the GSU brings up the full menu, but I thought you needed Rx power on to be able to do this?? I've tested the fuel/gas valves and glow plug using the test menu on the GSU, all working fine. While I was making a note of the figures, the ECU lights all came on at once again, with the GSU flickering and telling me the ECU version and not much else. This was cured by removing the battery and then reconnecting it. I'm wondering now if there is an electrical fault in the ECU, allowing it to power up without Rx power.

Any advice will be gratefully received! At this point, I will be removing the ECU, valves and wiring harness from the Raptor to give them a careful inspection, and set up the motor for some ground tests. In terms of damage to the airframe, it was relatively minor but I'll need a new bell mouth as mine got badly burnt, the removable tail section will need work as it's scorched and I'll probably need a new bifurcated jet pipe.

Hi Pat, sorry to hear you are having problems, to the best of my knowledge any JC ecu inc. gsu before V6 should not operate without a signal from the rx.
V6 is a modern exception to that rule but only because it is designed to stay on after rx power off for auto cooldown then shuts itself down automatically.
So logic dictates the ecu should not be able to operate with the rx turned off even with the ecu power available which to my mind indicates an ecu fault, just my thoughts.
Regards,
Gary.

Pat if your turbine is set to idle at loss of RX signal, then it makes sense that the IO lights would be flashing with the ecu powered up doesn't it? Otherwise the turbine would automatically stut down with RX power failure.

Duncan

Hi Duncan

It is set up to go to idle if the Rx goes into failsafe, and this is checked by switching off the transmitter. Not sure what happens if the Rx is switched off though - hence my question. From memory, the ECU has always been off with the Rx off, and when you switch on the Rx you get the beeps as the ECU initialises. The sequencing lights stay off until you advance the trim out of cutoff, then start flashing in order until you open the throttle, and then they indicate in accordance with the start sequence. Just seems odd that the ECU had any power with the Rx off, and very bizarre that all three LED's were on at once.

The newer V6 ECU's have the power on with Rx off facility so you can power off the radio gear while the turbine is still going through the cool down sequence, but this early version has no such clever stuff. I have a V5 ECU that I'll use to test the turbine with. This one ran on NiCds, so I'll need to get it sorted for LiPo power first.

Cheers - Pat

When the ECU battery is plugged in, regardless of the receiver switch position or whether or not the transmitter is on, the ECU will continuously drain the battery, eventually discharging it.
The JetCat manual is very specific about this, suggesting unplugging the battery at the end of each flying session, if you use Lithium batteries to prevent overdischarging. They do not recommend using lithium ion cells. (high impedance)

If the battery had been drained sufficiently, the reason for the powerfail warning is obvious.
I suggest you completely charge your LiPo batttery and give it a go at full charge after conducting a full check and completing the repairs.

Another sugestion for you is to NEVER blow a fire extinguisher up the tailpipe...always discharge it down the inlet, even if the bypass cover is installed.
Reason: You don't need any burning fuel in your (or anyone elses) face!

Pat/Gary,

Can't help you with your issue but I had a very strange occurence a few weeks ago.

After the last flight of the day on my Hunter, powered by a P160SX, I turned the radio off and let the turbine continue the cooldown process. The all completed absolutely normally and I packed up for the day. Now I normally unplug the ECU battery as the ECU will continue to drain the battery a tiny amount but on this occasion I forgot about the battery and instead I left it plugged in. I realised whilst driving home but wasn't too concerned as the turbine won't run without the radio on.

However later that evening I was playing with my TX and I kid you not I heard the starter motor enagage on the turbine for a second of so. To re-iterate the RX was NOT on when it did this! I was completely amazed at this behaviour as it was the first time I have ever seen this. The turbine didn't start thank god, only the started motor engaged as explained.

As a result I am telling everyone that is it vitally important to completely power down the ECU by unplugging the battery. I have no idea whay it behaved likeit did but I believe its related to the relatively new facility where you can turn the radio off and the cooldown continues. Previously, without the radio on, the ecu would stop working immediately.

And before anyone else asks the ecu works fine as I have flown the model 4-5 times since.

Geoff.

Hi Harley

I do disconnect the battery from the ECU before putting my jets to bed for exactly the reasons you mention. The battery was fully charged before the incident, and still shows 89% capacity so no problems there. The shutdown was not normal, and although I had selected a shutdown the starter motor was still engaged and spinning the turbine. Glad I had the manual fuel cutoff valve to stop fuel flow to the motor. In the heat of the moment (pardon the pun) I can't remember the exact order of events, but I did disconnect the battery from the ECU once I'd put the fire out - this may have caused the powerfail indication.

Cheers for the advice about fire extinguishers - I must admit I gave a squirt up the tail pipe just to ensure the flames were fully out. Fortunately they were, and there was no one else around the model to worry about. I'll bear your comments in mind for the future though.

Very interesting Geoff, I always do that anyway, on my new Wren 160 they instruct you to do just that (Projet ecu).

The problem I have is that on one of my jets I use the new Jetcat I/O charging socket and it would mean unscrewing that and unplugging the lipo as my ecu is buried beneath the radio tray, a pain.

Mind you I would not operate any of my models without a fuel tap, at least if the worst did happen no or very little fuel could get to the turbine,

Thanks for the info,
Gary.

I agree Gary, a manual fuel tap is very important. I learnt this many years ago after having a wet start(very spectacular 6 foot flame) when the fuel valve controlled by the ecu stuck open resulting in fuel being pumped into the turbine when I fuelling the model.

Hi Geoff
I bet you were surprised! I can almost understand that behaviour with the new ECU's having the cool down facility - but mine is an older version without such luxuries. Anyone out there still operating the older ECU's, if the Rx is off can you confirm you get no lights or beeps from the ECU? This was what surprised me. With Rx power off, all three LED's were on, and it sounded a little like the fuel/gas solenoid valves were operating in a random fashion.