kirkj

My Feedback: (61)

just got 2 140RX turbines for a twin build, and in the manual it mentions that the ECU supports 'parallel operation' for twin engine models.
there is nothing more said, and no details. any Jetcat experts know the deets? sounds like a feature i could use.

siddus74

done a couple of p20 projects ... just learned the RC individually then yleaded them .. job done ...

Scott.

siclick33

It's explained in the manual here:

http://www.jetcat.de/downloads/rxengines_manual_eng.pdf

Page 41 in the limits menu, titled 'StartUp mode'.

I don't think there is any more to it than that but am happy to be corrected.

Carsten Groen

Rumor is that a v10 ecu can control up to 4 engines (because of the bus system). Shoot maybe Udo Toepfer from jetcat germany an email, he has always been helpfull (but running each engine on a seperate ecu would add some redundancy one would think ?)

dubd

Pulling up this older thread to see if anyone has details on how this feature works. Can you set up the engine so that one engine goes to idle if the other engine quits?

Carsten Groen

I have sent JetCat Germany an mail about this, will get back when they answer.
Maybe Bob knows something: http://www.rcuniverse.com/forum/fb.asp?m=11364660

Carsten Groen

Got a response back from JetCat (I'm interested in this as I have ordered a Mibo A10 and 2 x P100RX for it)

They have a feature they call "crosscheck", they need the ECU's, engines and LED boards to do the change. You can then set it so that if one engine flames out, the other can shutdown or go to a fixed RPM (and I assume, you can afterwards take control over the other engine)

According to the folks here, the Mibo A10 with "mini engines" will not behave too badly during a single engine flameout, so I will keep the engines standard...

Lance Campbell

I can’t speak to the V10, but I am very familiar with its operation on the V6, with a pair of 120 SE’s. I explored this in great depth in setting up my SR-71.
To utilize it, an extra �pigtail’ needed to be attached to each of the led boards in the plane, so they could be cross connected, and therefore have an awareness of each other. Once the physical is taken care of, there are extra menu options that you can access via the ground control units.

You can modify 3 parameters….

1. When the engines are greater than XXXXX rpm apart from each other, it goes into a �limited’ mode, as indicated by a �L’ on the ground unit. You can set the RPM number that they are apart before it goes into this mode.
2. Next parameter is time, that if it is exceeded, it triggers an action. If it has not exceeded the time, when it’s in �limited mode’, the ECU that has the higher RMP, is trying to lower itself to match the RPM on the lower engine. This is really cool, and you can see it working when watching the 2 ground units at the same time. Practically, it really is only put into this mode for a second or two if you slam the throttle back and forth quickly, unless you’ve had a failure.
3. Last parameter is what the engines do. If step two above has triggered, in that its attempt to equalize the engines have failed, then it will do an action. You can pick a couple different actions. The one I chose was to simply shut down the running engine. I’d say this is only a valid train of thought if you have extremely separated engines, such as a SR-71 like mine, or say a ME-262. Anything like an A-10, or especially a F-4 Phantom, you’d instead pick the option to keep the other running. But for me, I’d rather have a dead stick to deal with, than a spin, and possible fire, because I didn’t react quick enough to get the other engine shut down while it was in a spin.

I worked the parameters for quite a time, and got it working pretty well. The thing is, you need to set the RPM numbers tight enough to be effective, but yet, not to tight that it triggers too easily. It’s not as easy as you’d think… 10,000 RPM difference for a single second is easily possible at the top end of your power, as each engine his peak just different from each other…. But.. Think about landing, and the engines are at idle… say one dies on landing approach, and you don’t realize it, and then decided you want to punch it and do a go around. Perfect setup for a snap/spin… low, and slow, and now you add full power to only one engine. So, that same 10,000 that works for high power, now, is a huge range on the low end. The engine that just died needs to actually spin down for a few seconds, for the range to be big enough. Or, as I found out, the practical answer is, the running engine will spool up a bit, then reach out of range and then shut down, hopefully before the stall/spin.

Whenever you have one engine die (such as me shutting off the fuel valve for example), its ground unit would read the expected: “Low RMP”, as the reason for the shutdown. Then the 2nd engine’s ground unit would read: “2nd Engine Fail”. Great info to see what happened and why.

However…

After doing all the setup and getting it working well, I was faced with a technical glitch that could not be answered. 3 times when I was taxiing around at idle speeds… literally moving the throttle just one click on the transmitter, both engines would die simultaneously. When I would look at the ground units, BOTH of them would say: “2nd Engine Fail”. To me, this felt like going to my 2 sons, and seeing a mess in the floor, and they both pointing at each other saying: “He did it!”.

I spoke with JetCat about it and was not able to get a concrete answer about this behavior, and then decided to disconnect it until I could find out for sure. The 3 times it happened, it was always at near idle and on the ground taxiing about. But without a black and white answer I didn’t feel comfortable continuing to use it in the air.

Upon reflection, I got to wondering if this feature was more geared to drone usage, where twin engines are used, and basically run at full throttle until one dies due to whatever reason (being shot down), and it kills the other engine. The initial parameter for the RPM difference is like 50,000, which would be applicable in a full throttle or off, frame of mind for drone usage, but might not have the fidelity for a much smaller number that I was trying to tune it to. (In the 5,000 to 10,000 range)

Since this setup work in the beginning, I’ve just run them independently, and have learned that a smooth hand on throttle changes helps a bunch in the air, and to date have 30+ flights and all is well so far. I’d love to hear your results on V10 of the ECU. Maybe it’s a different in the software and the issue I’ve seen has been addressed, but it would be nice to hear that clearly from JetCat.

I think the feature is great, and would love to use it, but I need 100% confidence in it, that it would not cause more risk than it solves.

Lance

CraigG

My Feedback: (40)

Wow Lance, great explanation and discussion about "real world" experience with this issue. There is a lot more to operating twin turbines than first meets the eye and this is just another wrinkle. Thanks for posting that info.

Compliments again on your fabulous SR-71! It's one of the coolest and most unique r/c turbines I have ever seen.

Craig

Carsten Groen

Great info Lance!
I would guess that they implemented it the same way on the V10 ECU's, anyway I will not bother with it on the A10.
I'll shoot JetCat and email and ask if the V10 works the same way or not....

rhklenke

My Feedback: (24)

Yep, Lance gave the answer - and has experience with it too. I learned about it from Bob Wilcox and he sent me more info. on it, but I never actually tried it.

I worked on a NASA project that had several twin turbine engine airplanes (think twin- or tri-engine airliners with two engines on the wings) powered by P-70's. We had very few engine problems and actually never had an in-air engine out. We did have one time though where, on a go around, the pilot advanced the throttles and for some reason, that we never tracked down, one of the engines "hung" at around 70,000 RPM and did not spool up faster for a good 10 seconds. The other engine spooled up to max RPM normally, and when it did so, the aircraft yawed 45 degrees so quickly that the pilot couldn't respond quickly enough on the rudder. Luckly, it was the engine farthest from the flight line that hung, and the aircraft yawed out into the open field and flew away OK once the other engine "unhung" and spooled up. It was a quite exciting experience though and would not have been fun if the engine closest to the flight line had hung...

It was during the conversation with Bob about what had happened and how to possibly avoid it in the future that he brought up this "hidden" functionality for twins in the later JetCat ECUs. He didn't seem to have a lot of experience with it or many recommendations on settings, and as I said, we never really tried it either.

To me, an indication on the ground, readily available to the spotter, as to engine status and perhaps RPM, would be much more useful in a twin.

Bob

CraigG

My Feedback: (40)

Agreed Bob. It's even nice to know before and during takeoff that both engines are spooling up normally. You can think both engines are spooling up but its virtually impossible to know for sure by sound alone. Twice I have begun takeoff with my A-10 with one engine not having transferred to tx control (I always start mine individually via the GSU) and therefore remaining at idle. One time I realized it and aborted the takeoff, the other time I mistook it for a crosswind and got airborne before I figured it out. Managed to fly a pattern and land ok but a real time readout of both engine rpm's would have been nice.

Now I always do a partial runup with the GSU's connected to make sure both engines are responding.

Craig

Lance Campbell

Thanks Craig!

I’ll add one other thing I do, just to be on the safe side. And a bit of a pre-apology to those around me in the start-up area….

If you advance the throttle slowly after just starting, on a JetCat, when you hit full throttle, after a moment you’ll see flash by very quickly on the ground unit: “Parameters Stored”. I could be wrong, but it’s been my understanding that it’s calibrating and storing the exact pump voltage needed for max RMP, (and therefore a throttle curve to match), based on the exact temperature, altitude, and pressure on a given day, and weather conditions.

I do this full throttle run up on every start up, to ensure that both engines are totally on the same page, since if they are not, it can have a more pronounced effect given the wide distance between them.

So, like I said, sorry to the ears close by, and I do it as quickly as I can, but I get a nice warm fuzzy feeling seeing both of the ground units flash that they are calibrated and ready for the upcoming flight, and each seeing the same atmospheric conditions together.

On my other planes, I just do this once, when we get to a new location for the weekend, and then don’t worry about it for the rest of the outing.

Lance

rhklenke

My Feedback: (24)

That's correct from what I've been told, but I believe that its just the max. pump voltage that is stored (or maybe that's what you meant). Also, its only the later versions of the ECU/engine electronics that do that. If you have any older V3.X or V4.X ECU's like I do, then they don't have this functionality...

Bob

Justflying1

Comes up with this.

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