Wren 44i switchover problem

[DenisFerrari]

Hi all,
I have a T-Rex 700 converted to Wren 44i hely engine and I'm flying since last year with great satisfaction.

52 cycles so far, +10 hours, never had big issues apart of some rare first fail starts, but nothing to worry about.

Today, after 2 nice flights, I've not been able to start the engine anymore, sequence starts normally, flame inside the engine is established, Pre-heat goes but in the exact moment of phase pass to Switchover, Egt goes down , Starter rpm tried to keep 18/19000 Rpm and it seems flames goes away or get so weak, almost nothing. And I toggle cut switch.

I've tried few times, same results.

* Pump power is perfect, even recharged, no changes.
* Main fuel tank, UAT and circuit all perfect.
* Filter before fuel entering the engine 100% clean and perfect
* Pump seems fine, no leakages at all
* Burner seems fine (when engaged I see 0.3V drop on displayed voltage), in fact Ignition and Preheat are executed quite regularly
* Starter motor seems ok, Bendix clutch aswell, nothing different from previous times
* No alarms on the Data Terminal
* Checked the vales operation : perfect.
* Even swapped valves (tubes on their exit) and plugs on the FADEC : same results
* Manually tested the fuel pump (through Data Terminal test, disconnecting fuel inlet in the engine) and doing "Fuel Pump Prime" and "Burner Prime" I see fuel regularly coming out the tube,
* I've never touched too much FADEC parameters, apart of "Pump Start Point" (couple of points last winter) and "Pump Power Ignit. K" (couple of points). Anyway, I've tried to inquired last one to make Ignition and Prehet phases more robust : no improvements. Also, tried to inquired sensibly even "Pump Start Point" to make Switchover start more effective : no improvements.

Staying on DT 2nd monitor page (the one with Ib etc.) I see around 4 to 5 Amp during Ignition and as soon as started motor starts, I see 8 to 9 A on Ib...is that normal and should it be less?

Checked the starter motor (removing the plastic cap) during starting : no sparks, nor smoke, it seems normal too.

I remember that during last part of starting sequence, Ib indicated should drop down to 0.3-0.5Amps...instead - even when during switchover engine is not starting - I see 18/19000 Rpm and current around 7-9A...

Could my problem have something do with high Ib current ?

Also, on the DT, as soon as switchover starts, I see Pw parameters going until 90%..with engine stopping, Egt falling etc...

Could my problem be generated by fuel pump ? Anyway, as told, I had 2 flights just before, where everything was still perfect, in particular pump operations of course...

Any idea or suggestion you may have is very welcome !

Thank you
Kind regards
Denis Ferrari

[KevinChiu123]

Is it possible that one of those 2 valves is out of order?!

One for starting, one for running the engine?!

[DenisFerrari]

Originally Posted by KevinChiu123

Is it possible that one of those 2 valves is out of order?!

One for starting, one for running the engine?!

Hi,
no , valves are ok, I tested then.

I even swapped fuel tubes at their outfeed (swapping of course 2 correspondent plugs on FADEC) : same exact result.

Denis

[HybridCycles]

Could it be the main fuel line is plugged inside the engine?

[DenisFerrari]

Originally Posted by HybridCycles

Could it be the main fuel line is plugged inside the engine?

...could be, but I don't know how to inspect it.

If it was, strange I could fly "normally" 52 times, even couple of flights done yesterday morning just before problem...

Of course, I'm waiting Wren UK email support asap.

Keep sending your ideas os thoughts, are very much appreciated

Denis

[Kiba]

As the fuel pump gets more run time on it you will have to tweak with various startup parameters as the pump wears in.

If the burner/preheat is working fine and the turbine is increasing in temperature normally during preheat but then the sequence is failing at switchover with decreasing EGTs, the first thing I would try is to increase pump start point by 2-4 and try again. You may have to increase this value even more if the sequence fails at switchover. If you see a lot of white smoke or the turbine seems to lazily increase RPM at switchover you can also try increasing the "min flow" parameter by a few points at a time. Don't increase it too far at once or you might have an excessively hot start from excess fuel at switchover.

The original fuel pump on my turbine lasted about 170-something flights and then the turbine began having a lot of failed starts and began to require fiddling with the startup parameters for nearly every start. Seems the pump flow characteristics at the low PWM and pump speeds used at startup had become unpredictable. While I wasn't happy with the relatively short lifespan of the original fuel pump a new fuel pump took care of the issues.

[DenisFerrari]

Originally Posted by Kiba

As the fuel pump gets more run time on it you will have to tweak with various startup parameters as the pump wears in.

If the burner/preheat is working fine and the turbine is increasing in temperature normally during preheat but then the sequence is failing at switchover with decreasing EGTs, the first thing I would try is to increase pump start point by 2-4 and try again. You may have to increase this value even more if the sequence fails at switchover. If you see a lot of white smoke or the turbine seems to lazily increase RPM at switchover you can also try increasing the "min flow" parameter by a few points at a time. Don't increase it too far at once or you might have an excessively hot start from excess fuel at switchover.

The original fuel pump on my turbine lasted about 170-something flights and then the turbine began having a lot of failed starts and began to require fiddling with the startup parameters for nearly every start. Seems the pump flow characteristics at the low PWM and pump speeds used at startup had become unpredictable. While I wasn't happy with the relatively short lifespan of the original fuel pump a new fuel pump took care of the issues.

Hi Kiba

thank you for the suggestions and I know and see that you should have deep experience on Xicoy FADEC linked to Wren 44 Hely engine pump too

Now, in my case, this is what started to happen yesterday :

https://www.dropbox.com/s/rvm47v5e3w...O0324.mp4?dl=0
https://www.dropbox.com/s/a9kp42wkmu...O0326.mp4?dl=0

This started to happen after 52 cycles only.

During these period here ambient temp is 35°c very humig, I didn't expect to have this happenign yesterday that's been one of the hottest day of the year here around

For sure it started to happend step by step, in fact in the last 20/30 starts I started to see transition from PreHeat to Switchover being more and more difficult, but rarely failed start on that point.

In this period I only increased by 2 points "Pump power at Ingnit. K." to make little more robust Ingnition and PreHeat, that's getting slower and slower anyway.

What in the recent period what I started to hear - while passing to Switchover phase - was a consistent dropping in Egt, sometimes hearing internal combustion slightly disappearing and reappearing just few seconds after, then recovering from Egt colder situation, then going slowly through Switchover and reaching FuelRamp until Idle etc.

One additional note I remembered just now:
I remember that yesterday on the last successful start, I saw that engine was struggling little bit more than ever to reach Idle, Rpm indicated were something like 53000-54000, and it took 10-15 long secs to reach Idle and - as soonit reached - it slighlty overrun the 55000 up to 57000-58000 next auto-regulationg and coming back to 55000 +/-

.... could this have been a sign of pump wearing and gettin gcloser and closer to a point whrere I really need to play with some ancillary parameters to keep engine starting-up reliably ???

Probably you're right, pump in this case changed quite a lot, only after 52 cycles.

Said all this, this is a summary what I've tried to do in nearly 20 start attempts I did last weekends :

For sure I've tried to increase (for the 1st time) up to 4 points "Fuel Start Point" that I know it's the regime at which fuel pump runs at beginning of Switchover.

Should I try to increase it even more ? And do you think it can happen between 2 consecutive flights ? Maybe so. I think I will try to increase it even more...for now I had something like 32/33 Iand I reached 37 no big changes, but tried couple of times.

Yes, during Switchover failing, I see some light white smoke coming out, very light, not a lot.

Also, never had a flame out or violent start on that engine.

Maybe it would be worth to increase Pump Min Flow parameter too (I don't not exactly know what is it for), of 2-3 points like per your suggestion could be ?

Finally, I've also increased Pump Power Ignition K to make Ignition + Preheat phase more robust, and in fact it seems to be, but problem is at switchover transition.

I'm still convinced all the rest if fine, I'm sure valves are ok, fuel line in a perfect clean nominal condition, no dirt anywhere, inspected everything around the engine, all is clean and tidy.

I'm starting to be convinced that I've a situation where pump maybe needs to be changed with new one, or fight little bit more with parameters...

Any additional suggestion by you all Wren 44 Hely engine users (and not) is very much appreciated

Thank you
Denis

[Kiba]

Based on the videos and what I see and hear I'd say you need to increase the pump start point. I'd bump it in increments of 2 and try.

When my fuel pump started having issues it went from starting and flying perfectly to not starting in a single flight. After that one flight I had to increase the pump start point by 10 or 12 to get it to start the next time-- the pump problems were dramatic and immediate.

If you still don't see an improvement in switchover after you've increased the pump start point multiple times (say you've increased it 2 at a time to 8 or 10 over your current setting) I would then reduce the pump start point back to where it is now, increase the min flow by 2-3, and then test again. If it still has issues at switchover with the increased min flow then start raising the pump start point again 2 at a time and see if that takes care of the issue.

FYI, fuel pump start point is the commanded fuel pump duty cycle (speed) during switchover and min flow is the commanded main fuel solenoid duty cycle (how fast the solenoid pulses open and closed) during switchover. Both will begin to increase as the turbine gains RPM after switchover, but during switchover the FADEC will drive the fuel pump speed to the fuel pump start point parameter and cycle the main fuel solenoid according to the min flow parameter.

It takes a careful balance of the two, if the fuel pump start point is too low the fuel pump may run unevenly or/or stall and if it's too high it can cause a hot start and flaming from excess fuel. A min flow that is too low can cause uneven combustion (you may hear surging, popping, or see white smoke) and if it's too high it can result in flaming or an excessively hot start.

[DenisFerrari]

Originally Posted by Kiba

Based on the videos and what I see and hear I'd say you need to increase the pump start point. I'd bump it in increments of 2 and try.

When my fuel pump started having issues it went from starting and flying perfectly to not starting in a single flight. After that one flight I had to increase the pump start point by 10 or 12 to get it to start the next time-- the pump problems were dramatic and immediate.

If you still don't see an improvement in switchover after you've increased the pump start point multiple times (say you've increased it 2 at a time to 8 or 10 over your current setting) I would then reduce the pump start point back to where it is now, increase the min flow by 2-3, and then test again. If it still has issues at switchover with the increased min flow then start raising the pump start point again 2 at a time and see if that takes care of the issue.

FYI, fuel pump start point is the commanded fuel pump duty cycle (speed) during switchover and min flow is the commanded main fuel solenoid duty cycle (how fast the solenoid pulses open and closed) during switchover. Both will begin to increase as the turbine gains RPM after switchover, but during switchover the FADEC will drive the fuel pump speed to the fuel pump start point parameter and cycle the main fuel solenoid according to the min flow parameter.

It takes a careful balance of the two, if the fuel pump start point is too low the fuel pump may run unevenly or/or stall and if it's too high it can cause a hot start and flaming from excess fuel. A min flow that is too low can cause uneven combustion (you may hear surging, popping, or see white smoke) and if it's too high it can result in flaming or an excessively hot start.

Kiba,
thank you very much for clear reassuring explanation and suggestions on how to proceed.

At this point I'm quite sure it's happening what you saw it already happen...

Glad to know that to you too this happened in a very abrupt way, that is from one flight to the next start attempt.

I will do some more tests next weekend and I'll report the results

Thank you again
much appreciated

Kind regards
Denis

[DenisFerrari]

Kiba,
I'm just curious.

When this happened to you, after some tubing on two parameters sggedted, did you have a reliable startups for some time, or you needed to chenge them often?

I mean, do you think it's probable to find a quite reliable set of parameters or better to think to change the pump with new one and surely start from better situation ?

Thank you again

Regards
Denis

[Kiba]

I remember having to tweak the startup parameters after the first 40 flights or so and then those settings worked OK for the next 100 flights or so until it started having all kinds of problems. Near the end of the life of that fuel pump I was having to to tweak the startup parameters every couple of flights and one out of every four starts might have been successful, most just failed at switchover with long drawn out sputtering/surging/popping noises and dropping of EGT.

With the new fuel pump, it needed some tweaking after the first 25 flights or so and hasn't needed adjustment since then. For the new fuel pump I ran hoses into a little container of kerosene and powered it off a D battery for about 4 hours to help wear things in before installing it in the heli. The new pump required entirely different startup parameters than the old pump.

[DenisFerrari]

Originally Posted by Kiba

I remember having to tweak the startup parameters after the first 40 flights or so and then those settings worked OK for the next 100 flights or so until it started having all kinds of problems. Near the end of the life of that fuel pump I was having to to tweak the startup parameters every couple of flights and one out of every four starts might have been successful, most just failed at switchover with long drawn out sputtering/surging/popping noises and dropping of EGT.

With the new fuel pump, it needed some tweaking after the first 25 flights or so and hasn't needed adjustment since then. For the new fuel pump I ran hoses into a little container of kerosene and powered it off a D battery for about 4 hours to help wear things in before installing it in the heli. The new pump required entirely different startup parameters than the old pump.

Kiba
interesting, thank you!

Denis

[GLimo]

There is advice on many forums to 'run in' a new fuel pump and I have done so whenever I have replaced one. A small can of fuel/oil mix and two pipes are perfect as a reservoir and a single NiCd as a power supply. Also a good pump should start at about 0.4 or 0.5 volt and this will increase as the pump wears.

The Xicoy (v10) will re-learn (Providing your Pump Start Point is set to Auto + xx) the changing start characteristic of the new pump over the first starts, so this needs to be factored in once it's in the machine and active.

/DG

[DenisFerrari]

Originally Posted by GLimo

There is advice on many forums to 'run in' a new fuel pump and I have done so whenever I have replaced one. A small can of fuel/oil mix and two pipes are perfect as a reservoir and a single NiCd as a power supply. Also a good pump should start at about 0.4 or 0.5 volt and this will increase as the pump wears.

The Xicoy (v10) will re-learn (Providing your Pump Start Point is set to Auto + xx) the changing start characteristic of the new pump over the first starts, so this needs to be factored in once it's in the machine and active.

/DG

Hi
thank you for the suggestion.

Pump Start Point (that I've learnt is the regime at which fuel pump will run at switchover) parameter has a value that - increasing it until necessary - I think it will solve my actual impossibility to start-up (good Ignition, failing switchover) my engine after 52 good cycles.

As told before, start-up cycle by cycle - I was starting to "feel" some difficulty during transition from Ignition to Switchover with consistent Egt falling and combustion slighltly disappearing and then reappearing, then recovering into switchover until start-up cycle completion.

Now, mine one is a Jan 2014 engine, W44i and of course with latest Xicoy, think v10.

How do you set this parameter to "Auto + xx" ??

Thank you

Regards
Denis

[GLimo]

Hi Denis.. The Pump Start Point and all the other settings are detailed in the Xicoy V10 Manual (In the Start Menus page).

http://www.espiell.com/FAD10.pdf

There is as good an explanation as I could give there so I have just posted the link.

/DG

[Kiba]

I thought that the "auto+X" pump start point was only applicable for manually started or auto-gas (propane start) applications so the FADEC can accurately determine lowest possible speed for the fuel pump at switchover (since in a manual or propane start engine the fuel pump doesn't start running until switchover, and a sticky pump with a fixed start value could either caused a failed start or hot start.)

With a kero start turbine the fuel pump is already running and supplying fuel to the burner at switchover (via the "pump power ign-k" parameter) so the "auto+X" pump start option really doesn't apply since the FADEC isn't trying to start the pump spinning. In auto-kero the "pump start point" must be set to a fixed value since the FADEC is only increasing the pump speed from the "pump power ign-k" value at ignition & preheat to the "pump start point" value at switchover in a kero-start application.

Correct me if I'm wrong, but this is what was told to me by Wren when I was having starting problems and diagnosing the faulty fuel pump. I asked about the "auto+X" pump start point setting and was informed this was only used for manual or auto-gas start applications.

[DenisFerrari]

Originally Posted by GLimo

Hi Denis.. The Pump Start Point and all the other settings are detailed in the Xicoy V10 Manual (In the Start Menus page).

http://www.espiell.com/FAD10.pdf

There is as good an explanation as I could give there so I have just posted the link.

/DG

Thank you.

Isn't it this AUTO+X possibility on FUEL START POINT parameter available only for gas start engines ?

Regards
Denis

[GLimo]

Hi Denis,

Something you'll need to test however, consider once the start is over on either gas or Kero, the Ramp process is probably the same.

You have 3 start systems for a turbine - Manual, gas and Kero. The object of them all is to get the turbine up to speed before you set off the fuel to make the turbine run. The only major difference is the manual start doesn't warm the engine before the Run fuel is fired in.

I am thinking the RUN fuel ramp should be similar for the gas or Kero because the Xicoy manual states... "Pump Start point” - Set the start power of the pump. Exactly same as gas start." , although this contradicts the static start value Wren preconfigure.

I don't have a kero device so I can't test this.



My Pump start on the Gas is Auto+1 - I found Auto+2 a bit harsh and 'Flamey'. My fuel Ramp setting is a 006 as per the manual.

Give these a try and see how it goes.

BTW - Its Pump Start Point you are looking for not Fuel Start Point....

/DG

[DenisFerrari]

Hi all,
good news, I could make my Wren 44i Hely engine start-up normally and reliably again!

Here's a quick report of what I did during my last test/flying session :

Parameters used for 1st successful start (and flight) :
* PUMP POWER INGITION K. = 37 (Original value so far was 32) ; this make Ignition + Preheat more “robust”
* PUMP START POINT = 44 (original value so far was 33) ; this made transition from preheat to switchover with almost no Egt dropping and also made switchover phase lasting just few seconds (as I was used to see) and then Fuel Ramp etc. I heard “puff-puff” sounds during all Switchover and fuel ramp, but no flames at all, all seemed normal.
* I’ve noticed that Idle was reached but with consistent overshoot in Rpm (until 67/68K Rpm!) and consequent very very slow return back to Idle, then 2K Rpm under Idle, then up again towards Idle…I then think at the slope parameters, in particular PARAMETER 30 (pump ramp slope from 33K Rpm to Idle)…

Parameters used for 2nd start (and flight) :
* PARAMETER 30 = 3 (original value was 4) (fuel pump ramp slope from 33K Rpm to Idle) ; i did not observed any big overshoot while reaching Idle and Rpm at that stage appeared much more close to 55K Rpm

* At the end of the flight, just 30 secs after landing and after throttle stick to minimum like normal, I still continued to hear the engine not at Idle, but at higher Rpm. I even could connect the DT and I was still monitoring 86/87K Rpm…in very slow descent until 55K Rpm anyway. I also just moved the throttle stick 2 clicks up and down and it seemed the Rpm reduction was much consistent. See also the attached chart (file “SECOND_Cy54_11-07-2015"), where you can easily see this on its final (right most) part.

* Here’s this start-up video : https://www.dropbox.com/s/zs216iod9p...O0329.mp4?dl=0

Parameters used for 3rd start (and flight) :
* PUMP POWER INGITION K. = 36 (previous value was 37) ; this make Ignition + Preheat little bit softer and longer, but still “robust”
* PUMP START POINT = 43 (previous value 44) ; transition from preheat to switchover still with almost no Egt dropping and probably little less “puff-puff” sounds during all Switchover and fuel ramp.
* At the end of the flight, just 30 secs after landing and throttle stick to minimum, I could hear the engine very close to Idle, little bit higher anyway, DT was showing something like 60k Rpm with very slow descent. Much better than 2nd flight end anyway. See also the attached chart (file “THIRD_Cy55_11-07-2015"), where you can easily see this on its final (right most) part.

* Here’s this start-up video :
https://www.dropbox.com/s/nryorb29uz...O0330.mp4?dl=0

Conclusions :
I’m so happy and satisfied, and it seems that with this new set of parameters, engine start-up is reliable enough again and so its performance

Doubts:
why did I need to change so much these couple of parameters to make the engine start again between one flight and the next ? ..well, one possibility could be because maybe - as I told you already - I got used to hear cycle by cycle engine struggling little bit more every time, exactly between preheat and switchover in fact.

What about the engine Rpm remaining little bit high at flight end ? Well, probably was happening little bit even before, but never like on 2nd flight end where I could also hear higher engine regime - as told - still around 86/87K Rpm, descending to Idle so slowly, and after 30/35 secs of throttle stick at minimum.

Any comment or critics you have are - as always - highly appreciated!

Thank you all.

Happy flying

Denis

[DenisFerrari]

Hi Wren pilots
...any comments on results summarized on my previous email ?

Happy flying and all the best
Denis