all in all i think you have a fuel issue

the ecu is self learning , i think there has been or there is something changing in your fuel system
the ecu uses the resistance of the pump to measure the pump voltage.
now if you pump has to work hard to get to idle the ecu sets the voltage higher to get to this.
now if in your flight something changes or has less resistance the ecu needs time also to learn the new curve.(stability delay)
and you have a higher idle.
now since you almost never fly idle in flight ,but just on landing this is when you notice the idle has gone up.
please check your fuel system i think you are using eather to long lines , to many tanks , thin plumbing or something else.
and dont worry we had similair problems with the bigger turbines , we use the same ecu.
and always we could trace it back to the fuel system.

Hello,

Just some comments on setting up the 44s:

The main problem on tunning this engine is that a high voltage battery is used to allow the starter to have enough rpms to reliably start the engine. The pump is very powerful and only need a couple of volts to run the engine at full power, so the 80% of the regulation margin of the electronics is wasted reducing the battery voltage.

At idle the pump run very slowly, so it is very unstable in its RPM (pump rotor rpm I mean). Usually a 1/1000 of voltage change on the pump cause a significant rpm change in idle RPM of the engine, making very difficult a reliable regulation. Also, the drag and performance of different pumps is very noticeable at these low pump speeds. I mean that at, say, 3V all pumps pump approximately the same 200ml/m (+/-25ml) and differences are very small, but at idle (0,2V) at bit more sticky pump can flow half of fuel of another, making a big difference in engine RPM.

Some tips and clarifications:

-Acceleration: The MW44, if overfueled in acceleration, usually flames-out. Bigger engines raise the EGT well before suffering flameout or combustion instability, so the ecu can "see" that it is pushing too much the engine and take the appropriate actions. On the 44 usually the ecu don't see anything until too late.
So, if the engine flames out in acceleration, increase the "accel delay" until the acceleration is stable. Values of 40 and higher are usual.

-Deceleration: Here the 44 behaves different too. A too fast deceleration cause the combustion chamber too cool down and the RPM undershoot the idle settings. This undershoot can cause a flame out, but usually what happens is that the ecu reacts raising the power of the pump at idle (calibrated at startup). This higher value cause the once the engine stabilize internally and the combustion chamber heat-up, burning better the fuel, a increase in idle RPM.

-Stability: Lower number, less stable is the engine in rpm. Use a value of 100 or higher.

It is very difficult to keep a stable idle on this engine, and a change in 55k to 58k don't have any influence on flight. The thrust change is of 0,3N (0,065lb).

About the engine landing on a high idle, can be different causes, for example a incorrect mix on the transmitter that modify the idle value, but specifically on the 44 I would think in 2 main possibilities, either easily identifiable after the flight. One is the problem of engine undershooting in deceleration, as previously commented. The second is related to fuel installation that cause that the pump should work harder to pump fuel when tank full than in empty (tanks in series, etc).
To diagnose, the best is to download the data from the ecu, but if you don't have the cable, you can do it "manually"

First you should annotate the values of power of the pump (value under the temperature reading) at idle after starting the engine and the throttle percentage (value at the left of the "pulse=xx" reading. After the flight, when the engine show the 90Krpm, and before shutting down, check again these 2 values.
If equal or less, then the problem is related to fuel system (pump, tanks, etc) that modify its delivery from full to empty (or the pump is too draggy at cold).
If the Pw of the pump is higher and the throttle percentage is the same, then the engine had its rpm under the minimum in any part of the flight. Usually a too fast deceleration.
If both values are higher, then the problem is in your TX.

DO NOT install a restrictor in the fuel line, this will overload the pump and the electronics, the amperage of the pump will raise a lot at full power, increasing the wear on the pump and using a lot more battery. What we need is to have the pump running faster at idle to have more stability, and a restrictor put the load at full power, not at idle. What is a very good solution to derate the pump at idle is to install a adjustable bypass. This is simply a "T" fitting in the line from the pump to the engine, with the 3th output going to the fuel tank (or to the pump input via a second "T"). The return line have a adjustable valve in series, so that part of the pumped fuel can be returned to the tank. This allow the pump to run a higher speed at idle but with same back pressure, and at full power the pressure at the pump output is the same as without this bypass, so no extra load is placed anywhere. If any of you want to try it, I can explain how to adjust the bypass valve, but now I'm a bit in a hurry.

Regards,

Gaspar

Hi Gaspar,

That's a great explanation ! I'm especially interested in your comment about the restrictor . I was running my original MW 44 without a restrictor with good success . I then purchased a 44 Gold and it uses a restrictor . I found that it only raised the idle and full PW's by approx 10 percent . I would love to find out more about the bypass idea. My original 44 converted to autostart needs 100 on the Accel delay to run properly .

Marc

Could someone go over what these parameters actually do. It will help our understanding. I can guess at accel , and deaccel , but what are we dealing with in stability delay? Maybe ECU designers can chime in. Doug

Gaspar

Thanks a lot for the great explanation! I am going to print this thread and include it with my instructions to the engine. The guys at Wren might want to add it their manual also. It would be very helpful.

I would be interested in how you set up a bypass also when you have time.

Hal

H.Dale
Could you share what Gaspar said?

Thanks

booker-RCU,

READ post #127...Oops make it #27........

Tailwinds,

John

Can't find post 127 but 27 seems to be it.
Thanks

I'm haveing the same basic problem with my Simjet 700 except it flames out when I give a fairley rapid movement of the throttle.

Galen

Thanks, everyone! It's good to know that we can rely on knowledgeable friends like Gaspar and Sandor to help people.
Anyone whose problems haven't been solved by the above, please email me at Wren - I will be back at my desk tomorrow.

Sara Parish
Wren Turbines

Hello,

Regarding the bypass to derate the pump:

-Install a "T" fitting in the line between the pump and engine.
-On the 3th exit of the "T" fitting install a regulable needle valve.
-The exit of the valve can be routed directly to the fuel tank or, trough another "T" fitting, to the input of the pump. The idea is to have some of the fuel pumped going back to the pump input.

Once installed, fully close the needle and start the engine.

Set the engine at full power and slowly open the bypass. The engine rpm will drop and the fadec will increase the pump power to recover. The goal is that at full power the indicated pump power (value under the temperature) be between 600 and 800 units at full power.

Once this adjusted, return to idle slowly. Surely the engine will stop if set too fast, as the fadec should recalibrate itself with the new behaviour of the pump. If the engine stop, that's OK, no problem, on next start the fadec will recalibrate.

As the pump now will be less efficient, it is posible that on next start the ramp of the pump must be increased to have a fast start, this should be experimented after adjusting the bypass. Acceleration time could need some tweaking too.

It is important to adjust the bypass ONLY at full power, and once adjusted, fix it and don't touch anymore.

PLEASE NOTE THAT THIS IS NOT AN APPROVED PROCEDURE BY WREN NOR SIMJET. USE ONLY AT YOUR OWN RISK.

Regards,

Gaspar

I realize this is an MW44 thread but I thought I'd let you folks know that I put the fuel bypass on my SJ700 . It seems to of solved the problem. Throttle movement will not cause it to flame out and RPM at Idle is steady (+ - 1000) The acel. delay is set at 40 and the PW at full thrust is 745. We'll see how it does in the air. I'm very optomistic at this point.

Galen

Just a note... the instructions for my old JDE Wren 54 highly recomend a bypass.

Galen,

What was your previous Acceleration delay before the bypass and what did you use as a regulator ?

Marc

Marc,
I had the acel. delay as high as 120 but it would still flame out with rapid throttle movement. I am using an OS 40 needle valve replacement but one side is threaded and the fuel line will not seal off. I have ordered a GMS remote needle valve from Tower.
http://www2.towerhobbies.com/cgi-bin/WTI0001P?&I=LXEHJ5
http://www2.towerhobbies.com/cgi-bin/WTI0001P?&I=LXEHD3
This should work fine.

Galen

Galen.

I'm running 120 on the AD for my original MW44 . Let me be clear that this is not the Gold that I have . The Gold is running beautifully with an AD of 10 . My other 44 is one of the originals that was modified by the original owner for autostart and then further developed by myself . I'm going to give the bypass a shot . Sounds like it worked wonders for you !

BTW , did youn return to the tank or the pump inlet ?

Marc

I just went from one side if the fuel pump to the other. Added a total of 6 in. of fuel line.
I didn't have time to try a lower AD setting, 40 was just a starting point. I will try lower settings when I get the new needle valve.
Galen

Well I guess its time to send everything back to Wren, I have had nothing but problems with this Wren MW-44 gold. I tried to fly my Savex L-39 yesterday after going through the whole fuel system ,I replaced all the fuel tubing ,checked all the connections. found nothing abnormal.I am using the 2 plax bottles in series like everyone else . My problems from day one have been unsteady idle,and high idle after a flight. I also noticed when I move the throttle stick just one or two clicks the engine accellerates to 80 or 90 k rpms after that the the throttle is fairly linear. It checked the transmitter and there is no mixing affecting the throttle channel, and I have tried to relearn the stick calibration 4 times. Last week I flew, and on the first flight ,on the first full throttle pass the engine made a loud sound and shot a 5 foot flame out the tailpipe, It sounded exactly like the sound you get on a wet start. I quickly shut it down, and landed it deadstick. I restarted it and it ran ok, and then I got three flights on it ,but the performance (speed) at full throttle is at least 30 -40 mph slower than it was when maidened it, it still accells to 195,000 rpms, but it definetely lacks the high speed performance it had on the first flights. Each time I landed the idle speed was getting higher,62 k, 68k and the last flight it was 91k at idle. Now back to yesterdays flight, after replumbing the whole fuel system during the week. I started it up and it idled 55k , throttle was still very sensitive for the first 2-3 clicks, I took off and flew 1/2 throttle around the field, then I acclerated to full throttle and after about 4 seconds at full throttle it made the loud noise and shot a 5-6 foot flame out the tailpipe , it was still running but blowing flames. I shut it down , and made another dead stick landing off the field,(bent my new Yann oleos slightly). I then refueled and tried it again, on the ground I ran it up and the rpms went to 207,000 rpms!!! ???? at full throttle. Also my egt from day one seems low, It idles at 420 degrees and at full throttle its only 480-490. I tried another flight and Got the same result, loud noise like a wet start, and 5 foot flame out the back, shut it down in the air and landed dead stick, made it back this time luckily.I think I have a fuel pump problem (sticky pump), or maybe an ECU problem. I can't figure it out and I am very fustrated, especially after waiting 3 months to get the engine, due to availability and shipping problems. I will e-mail Sara at Wren Tommorow and see what needs to be done to rectify this. I am also concerned at the performance loss, it just doesn't have the top speed it had on the first couple flights. I only have about 11 flights on it and the total ecu time is around 100 minutes. Maybe someone else has experienced this?? Very fustrating!!! Jack.

I was witness to Jack's flights yesterday. In both cases after being airborne about 3 minutes the plane went into flamethrower mode. This has really got us as it happens on full power. The sound is exactly like a pulsejet [German buzzbomb] with flame extending out the rear 4-5 feet. Somehow to much fuel is entering the combustion chamber and the unburned portion is entering the pipe and igniting there. Jack said the ECU was allowing the engine to run above 195,000. That combined with his low temp. readings could be a big problem. Jack , double check your temp. probe and make sure it is inserted far enough into the gas stream. Also at this point a new jet pipe might be in order once you get things worked out. I've got problems of my own as you know. Good luck Doug

Have you tried downloading the data from your last few flights to see what is going on. You may have a pump problem. Where the pump is sticky and then lets go after a while, sending too much fuel into the engine.

Well I thought I had my problem solved but it's back to square one for me too. I set my AD to 40 and ran my engine twice with no problems. Yesterday the local Hobbytown had a grand opening and I was asked to demonstrate my turbine. I tried to run it for the crowd. It started okay but when I tried to run it up it would sputter and flame out at around 120,000. The only difference I can tell was it was a much hotter day than the day I had the successful runs.

Where do I go from here?

Hal

Hotter days + larger AD times....

I have experienced the same problem with 54s and 66s in Alabama.
(Generic no name 54s and 66s)
It’s all about efficiency of the compressor this time of year.
With the tail cone remove do a test run.
If it runs then the weather has exceeded efficiency curve of the compressor.
I have seen this occur most on turbines that are tweaked for max power.

Johnny

John , do you mean run the engine without the jet-pipe or the exhaust cone thats part of the engine? I might put mine back on the test stand , so there would be no pipe. Doug

With it sputtering and starving for fuel I'd check the fuel filter screen for a clog. The screen is very fine so a visual check may not show anything and U might need magnification or just back flush it in a cup of kero. You didn't say what type of oil your burning some of the total loss oils used may be clogging the screen. Try some 2 cycle premix variety if your still having no luck with everything else.

Charley , thats one thing i haven't tried. Will back flush and try again.If this was the problem I'm gonna kill myself!!. It's just obvious enough to overlook. Thanks Doug