JSF-TC

My Feedback: (2)

There's been a number of posts here recently concerning high idle problems with both the Wren 44 and SuperSport. I have one of each, and have been beset with high idle problems on the 44 since late last year. Discussions with Wren resulted in replacing the fuel pump but with no improvement. The motor then spent over a month back with the Wren team trying to solve the problem. Nothing specific was found, but it was a good time to get an overhaul and bearing change.

After re-installing it in my L39, the first 2 flights were normal, and then the high idle problem resurfaced. With it set at 55k prior to take off, and the throttle never below about 40% throughout the flight until the landing flare, it would taxy back in with the idle anywhere between 65-80+k rpm.

I replummed the whole fuel system with large diameter tubing to ensure a easy fuel feed and I've just ground run it. On the first run, after a smooth calibration run up and down followed by some throttle transients at part power, the idle was high at 67k. Three runs later I was pulling on the fuel pump leads and prodding the fuel pump, as mentioned in a previous post here and the engine suddenly shutdown. Interesting!!!

I pulled the protective cover off the back of the pump motor, exposing the circuit board. After another start, I started pushing and pulling on the board. Any slight pressure on the circuit board would cause the motor rpm to drop. Holding pressure for a few seconds and then releasing would cause the motor to have a high idle, replicating the in-flight symptoms. Pushing down on the center plastic motor end cap surrounding the rotating motor shaft (without touching the shaft) would also cause an rpm drop, including complete shutdowns. This would also explain two or three motor shutdowns that I have experienced on some slightly heavy landings, with both the old and new fuel pumps.


Following up on the other thread regarding Wren problems with the Hausl fuel pump, I believe that I have identified the cause of at least my high idle problem. I'll contact Sara tomorrow for a new pump to try.

This may be worth checking on the other motors that have experienced idle problems.


Paul

noahb

My Feedback: (67)

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Wayne22

My Feedback: (2)

Perhaps you should clarify what "the runaround" is.......

I've never heard of anyone getting less than excellent service from Wren......

noahb

My Feedback: (67)

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GSR

My Feedback: (145)

How do you "put bearings" in these little Mabuchi can motors?????? Scott

jason

My Feedback: (1)

Hi Paul

How are your tanks set up? Do you have a single tank and a UAT? Or do you have two tanks and a UAT? If you do have two tanks then are they plumbed in series there is a good chance that you will get higher idle rpm once one is empty. If it was me I would check what the PW is at when the engine is it's correct idle and fly it. Then when you land and the RPM is higher at low stick I would check if the PW is the same but you need to be quick checking because the ecu will be trying to correct the high idle so the PW will be dropping slowley. If it is then the ECU is doing its job and either the pump has loosened up during flight so supplying more fuel for a given voltage or the fuel system becomes less restrictive as the tank/s empty.

Jason

TREADSTONE

Cant believe for one second that Wren would not listen.

What made 'Your friend' arrive at the conclusion it was the pump bearings?

Wren Turbines USA

My Feedback: (39)

Paul,

I do have pumps in stock....let me know if I can help you.

WrenTurbines

Paul,

Thanks for phoning me this morning, it was a useful discussion. We're getting a replacement pump out to you asap and I'm glad you are prepared to do some investigation and testing, to help get to the bottom of this problem.

Sara Parish
Wren Turbines

Wren Turbines USA

My Feedback: (39)

Paul,

Your replacement pump is on the way. You will have it by noon tomorrow via USPS. I pm'd you the tracking number.

HarryC

My Feedback: (1)

My question is why the ECU's, which Wren buys in from outside, don't adapt more rapidly? For example, the Supersport in one of my models hadn't flown for about 6 weeks due to poor weather, and at first start up it idled at 65k. Why? I left it alone and watched it, it took 3 to 4 minutes to very gradually step down to the correct idle. In fact it took about a minute before it even started to modify the PW value, so it looked like nothing was happening. I can understand the ECU thinking that if PW=100 was used for idle last time then that is what it will use initially this time, but when it can see that the rpm is so far off target why doesn't it adapt more rapidly and actively manage the PW value in seconds in order to hit the required rpm?
Perhaps the problems that some people are seeing are caused by the ECU being extremely slow to react to changes in conditions, so slow that it seems that the high rpm is stuck and is not adapting?

Gaspar

That's not correct.

The ecu calibrate the idle power every and each time that the engine arrive to idle during startup phase. Just in the moment of that the rotor RPM arrive to idle the ecu store the current pump power as "idle setting" for this particular run.


Gaspar

Vincent

My Feedback: (61)

Gaspar,
The ecu must be set at a specific hi and low (idle) rpm flashed into its memory. Why doesnt the ecu just adapt and deliver the correct voltage to the pump to compensate for the + or - rpms as needed. No other turbine that i can see suffers from this hi idle problem, they all use over flow tanks and miles of fuel tubing with multiple tanks?? I do not own a wren but i have a friend with a ss who has had the same issues.
V..

Jack28

My Feedback: (19)

I had an high idle problem on a Wren 44 gold, and it would idle normally for the first 3 flights , then the idle would gradually go up with each flight thereafter, It turned out to be insufficient battery power to the ecu, the small battery (4.8 v nimh 600 mh) that came with the turbine was not up to the job, I replaced it with a 1100 mh battery and all was well after that. Wren's service is excellent, I am sure they will sort it out.

Gaspar

No, te ecu don't have any specific value flashed in to the memory. It calibrates the value at each start. You can have your engine idling at pump power of 100, you shutdown and tweak the installation or change to a bigger pump, and in next startup you will see your engine running at idle at, perhaps, 50 or 150.

The problem is only of the pump. If the software corrects faster, usually this ends in under rpm, and engine stopped, not good for a safe fly.

Important debugging info if your engine suffer this problem:

1) At startup, leave the engine to start on its own and wait several seconds after it display "running" before increasing the throttle to leave time to stabilize.
2) Once at idle, anotate the value of Pump power ( PW=xx)
3) Do not do a full power run with the header tank connected.
4) If after flight the "high idle" symptom appear, check again the value of Pump power ( PW=xx)

- If higher than before: This means that the engine RPM have dropped below idle during flight, and the ecu reacted incresing the minimum flow to keep the engine alive. Usually symptom of a too fast deceleration.
- If same than at startup: This means that with same pump power the engine is receiving more fuel. Comon causes are a sticky pump or tanks in series that make the suction harder when all full. On a particular costumer the problem was a "automatic" filling valve which failed under suction.

In any case, giving us the values of pump power before and after the problem can give us vital info to debug your problem.


Gaspar

HarryC

My Feedback: (1)

Gaspar, my radio has mechanical trims, and after initiating the start sequence I did not touch the trim or the throttle stick. Idle was 65k rpm, it stayed there for about a minute then the PW value slowly decreased, it took about another 2 or 3 minutes to get down to 45k rpm. So I don't think either of the reasons you have given will explain the high idle or why it took so long for the ecu to reduce the PW value to get it to the correct idle. I then did the 5 seconds throttle up and 5 seconds throttle down to help it learn any new settings it needed. For the rest of the day and the following day the idle was correct at every start.

Harry

Gaspar

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HarryC

My Feedback: (1)

I use Mobil DTE Light oil.
If start was overfuelled, would the pump not be running at too low a value initially to compensate for the surplus fuel?
H

Ray Davis

My Feedback: (1)

Gaspar...doesn't/shouldn't the ECU just continuely re-adjust the pump voltage in order to maintain a stable idle RPM (55K for the 44-Gold)? Certainly if calibrated correctly on start-up....unless, perhaps, there is rapidly and large varying fuel system restrictions, e.g., beyond the ECUs ability to respond that fast. Which I think highly unlikely!

After all, the ECU is 'fast enough'/it quickly varies pump voltage to accommodate desired throttle demand/RPM extremes very nicely when all is well. So, I could understand a 'hunting' idle if there are truly changing fuel system conditions, but why it 'hangs' at a high idle is still a mystery to me. Unless, as you say it is solely a pump problem. And those of us w/ 44-Gold idle and flame-out problems have had them resolved almost solely w/ pump replacements, I believe.

I don't think we should be asked to up voltages w/ bypasses or replace our pumps as you suggest, however. I think Wren needs to resolve this and let us know just as soon as they have a capable, stable, and reliable pump. I've great faith they will!

Ray

Vincent

My Feedback: (61)

Ray,
What pump is wren using for their motors?? isn`t it a Hausl like jetcat uses??
V..

sidgates

My Feedback: (2)

Gaspar,
Where can I buy the XEL80 pump?

Gaspar

Not difficult to understand, the scenary here is that the fuel system is changing its conditions (up and down) while the engine is running. Up cause high idle, not a big issue in these small engines. Low cause a flameout, a issue much more serious. So the ecu is programmed to keep the engine alive, so it never leaves it to run below idle. If this cause a "high idle" situation in the engine, this is a very minor issue compered with a flameout. If the ecu is programmed to drastically decrease the pump if the idle is over the calibrated, on next "cycle" of fuel restriction/pump failure/too fast deceleration... the engine will flame out. Not good form my point of view.




here : http://www.xicoy.com/catalog/product...60&language=en

Gaspar

George

My Feedback: (57)

Well, I just experienced the flame out issue today on my 44 Gold powered Grumania F-100, but fortunately it was after I landed. This is only the third flight on the aircraft and the engine was running when it came by me on landing, but once I stopped to taxi back, nothing; it was stopped. There was no smoke, no infamous flame-out sound, nothing, just a non-running engine. I don't have much running time on this engine, so my Wren experience is is VERY little compared to other manufacturers.

I'm assuming it may be a deceleration issue as Gaspar has mentioned? I never go to full idle during the flight, and after this incident , I'm definitely not going to! My ECU is a digitech, is that also made by Gaspar? What should the deceleration value be?

George

Ray Davis

My Feedback: (1)

Vincent....I don't know which pump I have...whatever Wrren supplied. I'll take a look.

Gaspar, I understand your answer, but again, seems to me we'd have to have fuel conditions that vary by the second for the ECU not to accommodate and correct it to a steady state (e.g. idle at 55K). And, a relatively steady state fuel restriction condition that would require greater pump voltage still ought to shortly settle the idle out to 55K, maybe in a few seconds. This, rather than continuously 'hang' steadily at something higher like the 70-80K as many of us experienced.

Except for one the recent flameout that was quite possibly compressor stall, my 44-Gold has run flawlessly after Wren supplied me w/ a new pump mid-last season. Hadda be the pump...never changed a thig, otherwise.

But, I still don't get why the ECU should seem unresponsive to what seems routinely varying fuel system conditions []. Tx!

Ray

gooseF22

Gaspar
how do you suggest modifying settings or what to do if the motor doesn't accelerate smoothly, such as hesitating or popping/gurgling when you advance the throttle. Is that also a fuel pump problem?

Its not unusual to see 97-98 pump power after the motor warms up. is that ok.

I have alot of outstanding help here but wanted to hear your opinion.

dave