Turbine Grounded

[Cletus]

Well, the turbine is grounded.

Below is a graphical representation of the downloaded data from yesterday's three flights. I had two instances where the RPM suddenly sagged and recovered. Clunk and pickup line, UAT, Fuel feed line, filter, all clean and no visible issues, no visible air bubbles.
This is happening intermittently and seemingly mostly during the period when I am hovering and can get pretty damned scary as it sounds like a flame-out then it aggressively recovers the RPM.
It did this last weekend also and a couple times in flight. After an email exchange with Lou, I checked the “Last Chance” filter and I cleaned-out some debris hoping that that would have solved it. No such luck! ....the first flight yesterday went well and uneventful, then the other two flights the problem showed up again.

Have you gurus seen anything like this? Any ideas?

I'm pulling my hair out on this one. I am considering shelling-out the $150.00 for a new pump but willing to explore other possibilities first.
I have decided to not fly it till I can have a resolution.


Yesterday's three flights:




Last weekend's flight:
Very pronounced when the RPM suddenly plunged deeply (I thought it flamed-out) then the engine shot back up and settled-down again. The graph below shows this at around data point 468 the RPM plunged to 74000 and then shot right back up along with some temp overshoot as could be expected with such an aggressive RPM recovery.

[cbdane]

I would back-flush both the pump and the kero solenoid valve.

[Cletus]

Good idea Brent .........will give that a try tonight.

[lperagallo]

If you have fuel magnets or any type of filter in the tanks, I'd take them out and just use clunks.

Lou

[Cletus]

No filters in the tanks just clunks. Tanks > UAT > pump > solenoid valve > filter > engine.

[lperagallo]

I know you won't like the next suggestion.......but have you cleaned the UAT bag? If you had junk in the fuel filter, you could have plugged the bag. It is a very fine mesh. You can get new bags from BVM or Hanson.

Lou

[FlyFast]

I am no expert perse but, I have investigated the FADEC quite a bit. I am wondering if you are possibly seeing an TX/RX glitch where the FADEC detects a loss of signal longer then 0.5 second (?) which DOES cause the FADEC to spool the engine to idle. Once the signal is re-established the FADEC aborts the spool-down and ramps it back up. Which is what you are seeing.

If that loss of signal occured again within 1.5 seconds the FADEC would intiate a shutdown, which it doesn't.

Possibly check for signal loss on the TX or RX or interference from other sources suggets the intermittent nature of your issue.

[lperagallo]

Originally Posted by FlyFast

I am no expert perse but, I have investigated the FADEC quite a bit. I am wondering if you are possibly seeing an TX/RX glitch where the FADEC detects a loss of signal longer then 0.5 second (?) which DOES cause the FADEC to spool the engine to idle. Once the signal is re-established the FADEC aborts the spool-down and ramps it back up. Which is what you are seeing.

If that loss of signal occured again within 1.5 seconds the FADEC would intiate a shutdown, which it doesn't.

Possibly check for signal loss on the TX or RX or interference from other sources suggets the intermittent nature of your issue.

Flyfast,

You are correct that if the RX didn't get a signal for a time it would attempt a shut down. How it does that depends on the version of the Fadec software running. If that condition existed there is an error code posted in the data stream. I did not see that condition apply in this case based on the data. I actually have an excel program that analyzes the data and reports all fadec states.

Lou

[Cletus]

Ok based on email conversations between Ron, Lou and myself, I've found the thermocouple probe to be about 1/4" inserted and I backed it out to 1/8".
Ron advises to set the FADEC a max temp to 848*C instead of 800*C ....did that!. UAT bag is clean and good flow from Tank and UAT to the pump inlet, no bubbles.
Will go to the field around 2:00pm and attempt to hover an if ok, fly a couple of circuits and report.

[Cletus]

Ok, temperature readings are significantly lower. I guess pulling the probe back 1/8" did that.
But, quite a few RPM drops while spooling up, at flight idle and at takeoff speed.

i can find no air ingress (bubbles) in the fuel lines to the pump or engine.

I was only able to get the bird light on the skids and aborted takeoff for fear of one of those power dips putting me in the ground.

Maybe after a couple of beers, I'll be able to figure it out!

[cbergen]

Easiest thing to change is the fuel pump. I don't believe it to be electrical, or your throttle line would be up and down in time with the RPM's..

[Cletus]

Originally Posted by cbergen

Easiest thing to change is the fuel pump. I don't believe it to be electrical, or your throttle line would be up and down in time with the RPM's..

Yup, that's my next step

[lperagallo]

OK,

Next test. Power the pump with a 4.8 volt pack and let it recirculate fuel from a container and watch to see if you have any moments when you visually see the fuel flow drop. We need to know if the fuel pump has some sort of issue. Run that for a good time and see what happens. If I remember correctly 4.8 volts will make that pump move a lot of fuel.

Chris,

Chime in if you think that is too much voltage for the test.

Lou

[cbergen]

Yea, I think I would try it at 1.5 or at most 3 volts...

If the pump is stuttering, it'll be more likely to do it at the lower voltage.

[Cletus]

Will rig it up tonight and see what gives ....thanks guys!

[Cletus]

OK some progress!
Hooked the pump up to my lab power supply and set the pump up to recirculate fuel. At 1.5v it caught it's ass to startup, then it ran quite feebly . Cranked the volts up to 3v and it was pumping better (I could definitely p faster than this thing), but was hunting from the sound of it, although the flow looked deceptively steady. Cranked-up to 4.5v and the flow came up quite a bit, but the sound of the pump was definitely hunting, it was not a steady buzz and the current draw was fluctuating. Left it hunting at 4.5v, got my screwdriver and whacked the pump a good one! ....the flow shot up immediately and the pump began to run very steadily, no more hunting, but a steady and happy buzz. Shut down and tried to restart the pump and it started up easily at 1v and runs with a steady buzz, steady current draw and even flow now, at all voltages up to 7.1v.
Looks like I will give myself a new pump for my upcoming Birthday this week!
I do intend to fart around with this one though. I suspect the brushes may be the problem.

[lperagallo]

Cletus,

Great News! I checked my stock and I have three 100-C motors and no 200-C pumps. You will need to get one from Flightworks or a Hausel from Wren.

Lou

[Laurens]

Thats good news. I think flying around with a pump like that is kind of risky, good call on getting a new one.

[Cletus]

The pump has now completely failed. It takes 2V at 3A to even start and at 4.5V it draws 4A and runs very hot.
Well, a new pump is on the way from Wren USA and Flightworks has shed some light on the failure:
"Sorry about the issues you are having with your pump …….Typically we recommend the pump be checked and have the seals replaced at the 25 hour mark. That is typically also when turbine manufactures recommend the first check on the turbine itself .…………We have upgraded our pumps to the “-D”. This has a new seal design and material which work much better over the long term."

[Cletus]

Just received a Hausl Series 280 pump from Wren USA (thanks Ron!). Installed it and spooled-up on the lawn. Spool-up, and transition through ground-idle, flight-idle and hover was absolutely smooth! No signs of surging and power-dipping at all. Can't wait for weekend to let her loose in flight and see how she really performs.