Originally Posted by
Len Todd
IMHO, conflating a Rxer's failsafe and a ECU's failsafe above does NOT get you off the hook for confusing the OP's original question. KISS
To the above specific points, … The ECU failsafe has nothing to do with the Rxer's Failsafe. The ECU does not care if there is a Rxer failsafe. The ECU failsafe functions at a total loss of Throttle Signal, Hi/Low Turbine exhaust temp, etc. (e.g. like total loss of power to the RXer or the throttle harness disconnected from the ECU.) Even if the throttle is brought back to idle by a failsafe on an RXer, a throttle signal is still there. Even if the throttle channel was reversed and the RXer's failsafe was not reset, the throttle signal would still be there. Once RC learned, both of these signals would be above low trim, so even a normal shutdown would not be initiated, let alone a throttle based ECU failsafe!
First time turbine jet setups need to be face-to-face with someone who has experience with the particular radio and turbine and set them up on the bench together! Otherwise too many things get missed (e.g. flight modes, reasonable control throws & flap settings, CGs and wire routing, etc.) This type of collaboration is much more effective than trying to ferret out the useful information from a bunch of off-topic forum B.S. - KISS.
You are right about verifying that both failsafes work correctly though. Shut off the transmitter, and see what happens. A failsafe takes 2 seconds. A normal shutdown cycle will be immediate at low trim. Again, these are two different functions triggered by two or more different initiating conditions.
As far as knowing when a ECU failsafe has occurred, with the thousands of flights I have either done myself or observed on the flightline here, I can't recall anyone experiencing a failsafe. I personally don't think it is worth confusing a normal setup to maybe see a turbine message relating to an event that most-likely will never happen! Again - KISS. All you need to know is in the book!
There is nothing for me to get "off the hook" for as I answered his original question completely accurately. While I provided more information than he needed, because it wasn't clear what he did and didn't know, everything I said was 100% correct, had been tested and I knew for a fact worked with the system in question. If someone chooses not to believe the truth because they couldn't verify it in the manual or it didn't appear to work for them for some unknown reason, it doesn't make it any less true.
As for your comment that The ECU Fail safe that shuts down the turbine on loss of signal has nothing to do with the Receiver fail safe, that is completely wrong as your receiver fail safe behavior is the only way for the ECU to know that your system no longer has contact with the airplane. This information is clearly spelled out in JetCats manual, at least the older ones and even page 64 of the Kingtech G2 manual says the same in a bit more round about way when they state the meaning of the warning message "RC SIGNAL LOST/INCORRECT: The signal received from the RX is wrong (outside calibration margin) or absent". That behavior is exactly what I described and makes the ECU totally dependent on the fail safe behavior of you receiver. While the turbine can shut down for all sorts of reasons, several of which you described, this is the one and only way the ECU knows that you have lost control of the model and it needs to shut down the turbine, which is what was being discussed here.
While is true that the old 72Mhz system would generally stop sending a servo pulse if signal was lost, the vast majority of modern systems (all of them?) have a fail safe behavior that is either set automatically during binding or needs to be configured in order to work. I don't believe Spektrum even has the ability to stop sending a servo pulse on the throttle channel and as long as there is power to the receiver it will output a valid servo pulse on the throttle channel, The only way the ECU can tell there is no RC control is if this servo pulse changes to a value outside the range learned during teach RC or stops being sent completely. I don't know of any modern systems that stop sending servo pulses on fail safe by default, which some such as Jeti can be configured to do this. If you bind a Spektrum receiver with a throttle setting that will be used to shutdown the turbine, it will stop on loss of control, if you bind with throttle set to the idle position it will go to idle on loss of control and not stop, if you reverse the throttle channel after binding it will go to full throttle on loss of control. I've seen this happen first hand.
As for never having seen a loss of signal at an event, I've seen it first hand. The airplanes fail safe wasn't set correctly, turbine went to full throttle I've also seen people have what they thought were flame outs because they were had a hold just long enough to send them into fail safe which immediately stopped the turbine due to their fail safe setting. They were baffled because ECU logs indicated normal shut down and were chasing electrostatic discharges, blocked fuel filters, replacing UATs, etc.The signal loss was brief and due to having a Cortex Pro installed, the hold condition wasn't even noticed other than the turbine stopping in flight. Until I looked at their transmitter and pointed out they were having multiple holds on every flight it never occured to them it was a radio issue that was causing the flame outs. They moved their remote receivers around, the holds went away and no more in flight shut downs.
I completely agree that it's best to get face to face help for these types of things and I have nothing against keeping things simple or ignoring the shut down cause as long as you have verified that your fail safe settings are correct and your turbine shutdown on loss of RC signal. However saying you don't need to do anything or is has noting to do with your fail safe setting is completely wrong and if believed to point of not verifying fail safe works, potentially dangerous.
Having seen these issues first hand is why I simply couldn't ignore a statement saying that you don't need to worry about your fail safe because it has nothing to do with anything and your turbine will simply shut down on it's own if you lose signal.