Dear scale heli pilots, Last week I was testing a new B212 build and got PHT2...

Adding data evidence

This one is a puzzler! It is unclear whether an air bubble caused the issue but I always run a header tank. I will gather more information and post on this again.

This data would cause me to examine the fuel pump. I would not think that an air bubble would cause the pump to drop voltage before increasing it. Rather, an air bubble, if anything, would reduce the RPM, which would spike the pump (if the ECU catches it fast enough). According to your logs, whatever happened caused the RPM to drop 20,000 AND caused the voltage to drop at the same time. To me, that's the pump not functioning correctly. I would expect the 104,000 RPM to be correlated with the spike, which doesn't happen until the ECU sees 90,000.

1. Run the engine with no blades on the ground and observe your fuel line if possible. See if there are bubbles.

2. Adding a header tank should really eliminate air as an issue (not 100% but close enough that the engine should be able to recover)

3. Consider trying a new fuel pump. Is your pump mounted vertically? Do you have the shortest possible lines from pump to solenoids?

4. On your next flight, hover close to the ground in case it flames out and review the logs.

Overall, it's debugging procedure that will uncover the culprit. Having a new pump is never bad anyway.

Thanks a lot Mike for detailled feedback.

Now done 3 flights with UAT BVM and no issue, so far.. Still not 100% confident however. Its the brand new Jetcat BL pump, here mounted horizontally.
I have now removed a filter between the pump and the solenoids as was hard to blow when comparing with a new one (I make sure to filter the fuel prior and while refueling).

Talking with jet guys of my club they said that UAT is a must have whatever tank type, lines and felt.

Something particular here is that this tank has a cone at the bottom with a vertical line and felt clunk inside - its not thw usual line moving across to go where the fuel is.. Strange setup but as provided by the manufacturer of the fuselage. I know that some removed this cone and replaced with
a free Tygon line.

Here is our theory of what happened
but only speculation:

1. Pump physically accelerated within 0.2s as no fuel in transit suddenly
2. ECU immediatly reduced the voltage to contain pump overspeed from 1.5 to 0.9 volts
3. Sligthly clogged filter + low pump caused sudden low fuel pressure vs high RPM = turbine flameout
4. Pump immediatly recovered with 2 volts spike, seeing RPM decrease, but too late
5. Low RPM detection dictating shutdown (white smoke).

The newly added BVM

The setup

The cone!

Hope sharing this experience will help other pilots. Will fly more and see how it goes. Thanks again.

I like the changes except the horizontal pump. Most manufacturers recommend vertical mounting. Also, I have zero filters in the system. I filter fuel before it goes into the tank. As you have discovered, filters are a fail point. Good luck!

Couple flights yesterday and zero issue. Will order a new pump and review its orientation for being on the safe side (mine was shipped with the very first V2 builds). Thanks for the advice!

Have you now found the error (the cause)?

Hi Uwe,

Action 1: Fuel Line
Installed BVM. Definitively a must have to prevent bubbles entering in the small combustion chamber having to sustain the flame ..
Also useful to keep an eye on fuel line health: more air than usual in the BVM is suspect.

There was no header tank in first place as there is a cone below the tank with felt clunk inside, so supposed to do the job. I've been told that this design isn't 100% safe, especially when low fuel tilting, and some pilots have even suppressed this cone in conjunction with long tubing inside.

Action 2: BL Pump
My BL pump was an early version shipped with the first V2 turbines.
Jetcat Factory was super helpful and they noticed that its voltage was abnormally high in flight, around 1.8~ volts average. A new pump was then installed and the voltage drop down to 1.4~ volts, with exactly the same configuration. Running perfectly since and such difference is suggesting that the old pump had some issue.

Lessons learned
Pump voltage can differ as every setup is different but these BL pumps are expected to run and regulate within expected range, as demonstrated here: too high is suspicious.
Configuring some alarm and observing regurarly the logs does pro-actively help detecting abnormal trends, e.g. clogged filter = more pump demand.

Note: my early BL pump didn't had the warning on its yellow sticker advising to be careful when connecting the bus cables on it: now for me a way to recognize that's an early version.

I've also had problems with turbine stops in the past. For me it was the hose connection directly to the pump on the vacuum line.

In my opinion, it is now very important to carry out all hose connections very carefully. Above all, do not use Festo quick connectors in the vacuum line.

Take a look at my report:

https://scalehelipilot.com/discussions/264432c7-e357-4dbb-97a4-fadb...

Interesting!

To prevent the issue with the Emcotec fueling valve, I implemented dual fill configuration:

1. Refueling
From Emcotec going directly to tank (extra input in it), not impacting fuel pressure on BVM side in case of air leak.

2. Service
From two chained stop valves going to BVM, to remove excessive air eventually accumulated on the top of the UAT.

Requires regular BVM air check and reinforce fuel line health monitoring, amongst other routine verifications.

I wouldn't use cable ties either.

Fully agree, like in this picture (the small tie is to prevent the big one moving around)

It looks like this is the suction line to the pump?

Well spotted, it's an old picture, fixed since with wiring. See above the UAT missing the second fuel valve as old picture.

Status update after one year+ of experience since my last post:

Header tank is a MUST, even if your setup is presumably dealing well with bubbles, thanks to felt clunk, flexible movements of clunck, cone below the tank (look the picture, there is a black cone below the fuselage), etc. Bubbles do happen in some situations and this is possibly more difficult to handle for small turbines.

. I have installed BVM with no issue, great product and size fits perfectly for my 1:7 scale
. Header tank allows to easily detect the presence of bubbles as they are captured in it
. Check the status during routine maintenance and purge any captured air, if needed
. I replaced the Jetcat BL pump - just in case - as the original was shipped with the very early V2.
Maybe was fine but we wanted to clear out anything related to fuel supply as the experienced voltage drop looked strange as highlighted by Mike, see data evidence above
. Current Jetcat ECU firmware v12.85 works really great, this is a very mature version

Just a quick recommandation to those who want to build a model with turbine engine.