MW44 Flameout Problems
 

I must be the only person on the internet that cannot get a MW44 running. I have an autostart MW44. It will start and idle okay but once I throttle it up it flames out usually somewhere around 85 - 120K. I have replaced the fuel tank, the lines, fuel and I have run it with and without a UAT. No luck!

I emailed Sara several days ago but for some reason she has problems receiving my emails and I'm not sure she got it. I was wondering if anyone has any suggestions? Will the acceleration and deceleration delay have any effect on running?

Thanks.

Hal

RE: MW44 Flameout Problems
 

yes it will!
however i am not sure you can set them try to set the acceleration delay up by 10 points and see if it goes away.
if it is gone try slowly to go back.
what is strange is that Wren always test their 44,s on each ECU.
so it could be you have a diferent problem.
i am sure Wren will read this and will help you out..

RE: MW44 Flameout Problems
 

You can try to bump up your accelleration delay. That should help. Also you can put a restrictor in the fuel line. The PW will go up, but you will get a steadier running engine.

RE: MW44 Flameout Problems
 

Sarah and Roger are on holiday till next week, thus the slow email response.

Increase your acceleration delay by 2-3 clicks at a time and this should help eliminate the flames. This simple adjustment slows the delivery rate of fuel to the motor. In simple terms, your motor is running "rich" on acceleration.

Hope this helps.

I will forward this thread to Wren and you will get a response next week.

Cheers

RE: MW44 Flameout Problems
 

We are currently having an issue with a 44 also.

It runs fine on the ground. But when I head down the runway and gun it, it flamesout.

Once flying around its good, but once I lined up for a full throttle pass and it flamed out, destroyed an airframe because of it.

RE: MW44 Flameout Problems
 

Thanks for the help.

What about the Deceleration delay? How should I set it?

Hal

RE: MW44 Flameout Problems
 

Shok...
The most common cause of flame out on acceleration down the runway is air in the fuel lines. Are you using a UAT??


Set the deceleration delay the same way...decrease a tick at a time . Be careful not to get the setting to low or the motor will quit if you decelerate to fast.

I have my TP with restrictor set at 9 for deceleration.

RE: MW44 Flameout Problems
 

yes using a UAT, this started after about the 30th flight

RE: MW44 Flameout Problems
 

As I understand it, the problem may be with blocked fuel needle(s). Increasing the accel delay only masks the real problem AND destroys the superb throttle response. The needles are very small.

Sara is on Holiday and will be back on Monday the 19th.

Dave Rigotti

RE: MW44 Flameout Problems
 

To all,

I will call Sarah early Monday morning and direct her and Roger to this thread.

RE: MW44 Flameout Problems
 

Try running it again and see what the hand unit says at the exact second it cuts, look at the rpm and see if it drops a split second before the it stops. If it does then its the rpm sensor. Another way to test it is to plug the hand unit in and spin the engine over and watch the rpm reads right down to 200 if the final reading is much higher, say 800 or so then theres sensor problem . I had the exact same problem on someone elses engine the other day, flamed out at the same rpm as you and the rpm only read down to 900 but once I got a strong magnet and rubbed it round the inlet it sorted it out straight away ( a tip I got from that guy who did the RAM ecu's) , read down to 200 rpm and ran perfect.

try it it might just work!
jason

RE: MW44 Flameout Problems
 

Hi, I have a similar problem with the 54 mk2. My problem occurs at idle more so than at any other setting. My rpm reading on the data terminal reads 2600 without the engine running. It didn't start doing that until I put the engine on a Y/A Stingray and used the green cowl/inlet. Do you suppose I'm having issues with magnetism as well. Also noticed that it only registers a reading when a servo appears to be under load, ie; srevo noise. When the load is taken off the servo, the data terminal indicates 0 rpms. What type magnet are you using to de-magnetize. I'm also running standard noise traps on all long servo leads.
Steve

RE: MW44 Flameout Problems
 

Hi Steve
Your problem could be a result of spooke rpm readings.
I have 3 possible "spooke" generators.
Try to move the fuel and gas solenoids to another position.
My tests shows that the solenoids should be placed as far away from rpm sensor as possible.
Another possible error is bad battery, it will also give you spooke readings on the rpm also, when low voltage.
Also check the fuel pump, and relocate pump as far away from rpm sensor as possible if necessaery.
Hope this will help you.

Regards
Anders Wikman

RE: MW44 Flameout Problems
 

Hal,

I have had the same problem. I have one of the initial batch of 44 autostarts (before they discontinued them and switched to the Gold).

In my Savex L-39, I have probably put twice as much fuel through it on the ground as I have in the air, trying to stop it flaming out on acceleration. As I got it from Wren, the acceleration delay was set at around 15-20. It would flame out at about 120k. Pushing the accel delay up to about 30 initially cured it, but after a couple of flights on the same day the problem returned. Upping the delay to 45 seemded to stop it flaming out. Returning to fly the next day it would again flame out on accel with the same settings that worked the previous day. I eventually had to set the delay to 60, but then started to see some other major problems, such as not being able to reach full power, erratic throttle response and one case of it not dropping below about 90k even with idle set. I spen about 10-15 starts that day trying to troubleshoot it.

Talking to Sarah and the team I sent it all back and they found that some of the fuel nozzles were blocked and that the NGV was cracked (probably the result of a hung start due to a failing battery). $300 of repairs later and with some of the new Gold parts installed and a FOD screen added it should be back in my hands any day now, supposedly putting out more thrust than before. It's now a hybrid configuration, not the full Gold spec. I also have had Wren replace the NiMh battery with a LiPo as after only a couple of hours the 650mAh battery had lost almost half of its capacity and could hardly support 2 starts and a run.

According to Wren the acceleration delay setting is not very sensitive with the bigger numbers, and changes in ambient temperature can significantly effect the required settings.

Good Luck

Paul

RE: MW44 Flameout Problems
 

Thanks Wikman, I'll try some of your solutions.
Steve

RE: MW44 Flameout Problems
 

It might be worth downloading the data from the Fadec and e-mailing it to Sara. They are pretty good at diagnosing problems from this data.

If you have fluctuating RPM readings when the engine is stationary then this can be caused by servo interference. You can get a lead to go in the RPM line that stops it. It is not a problem as the sensor signal when the engine is running is much stronger than the interfering servo. I have it on my L39 due to the close proximity of the elevator servo but it does not cause any problems with engine running.

RE: MW44 Flameout Problems
 

Yep, same. A few of my servos appear to cause rpm fluctuation when the engine's not running but when it is, the fluctuations aren't registered. Hope you get your problem sorted out. As we all know, the guys and gals at wren will do all they can to help you.

RE: MW44 Flameout Problems
 

Thanks for all of your help. It's comforting to know that there are people all over the world offering help. I've learned alot and will continue to learn alot through this venue. Once again, thanks for your help.
Steve

RE: MW44 Flameout Problems
 

I'm having a problem along these lines that showed up on my second test run. Since pulling the engine out of my A-4 and installing in the L-39 the idle stability jumps around. It's showing between 54000 and 58000. It does not want to settle down to a very reliable 55K as when I had it in the A-4. There are two main differences, in the A-4 there were no servos near the engine and the fuel tanks and pump were located very close to the turbine. In the L-39 the elevator servos are on either side of engine center and the fuel pump is all the way up at the nosewheel firewall. I'm sure the long run of small diameter full line from pump to turbine is causing a slow response in the overall control loop. Is there something I can change to test this out. The idea of coming in to land with the power above idle , even a little bit is disconcerting. I want to maiden Saturday, so what do you guys think? Doug

RE: MW44 Flameout Problems
 

I had a similar issue.

Here are a couple of things you might want to try.

Raise the idle slightly. This seems to help and doesn't affect the residual thrust.

Make sure you have the TX setup correct to give enough 'headroom' at the bottom end (i.e. idle should be above 10% from memory).

You could also try changing the stability delay figure.

RE: MW44 Flameout Problems
 

I also have problems. I have a Wren 44 gold ,on board start version in a Savex L-39, I just maidened it about a month ago, and I now have 8 flights on it. From the very begining on a test stand , Brand new, the Engine was unsteady at idle I would accellerate fine but after running it up and returning to idle the rpms were 65K at idle. I e-mailed wren and Sara had me Set the stability delay to 10 and then run the engine up and down several times slowly, then shut it down and set the stability back to the standard 30 setting. This seemed to work and the next run was fine. After installing it in the plane the first flight was good and the idle after landing was 62-63k .I thought it to be a little high, Sara said it thakes the Ecu time to learn the idle. I have just put 4 flights on it on monday night,the first flight it flamed out on the first fast pass, it made a loud swoshing noise, I thought the tailpipe came out. I dead stick landed it fine and, rechecked it, everything was fine. I then refueled and flew it 3 more flights, each flight the rpms at Idle were getting higher and higher, the last flight the rpms were 91,000, This is way too high . I need to try and get this fixed or send the complete engine back to Wren, I only have flown it 8 total flights, I am hoping this can be rectified without sending it back, Thanks Jack George.

RE: MW44 Flameout Problems
 

Man, wish I could remember the guy’s name that told me about this problem.
Johnny klinner

RE: MW44 Flameout Problems
 

Doug, your L-39 came out great , nice scheme. Looking foward to flying them together. Hopefully we can get this engine problem resolved. Jack.

RE: MW44 Flameout Problems
 

Looks like the acceleration delay may have been my problem. I set the acceleration delay to 40 and it started and ran okay. I will try and come down one click at a time. My idle is a little unstable though. The stability delay is currently at 50. Should I go down on it?

My deceleration delay is currently at 20. Should I come down on it also?

Hal

RE: MW44 Flameout Problems
 

do yourself afavour first:

first start the engine let it settle to idle.
then go from idle to full throttle slowly within 10 seconds not faster not slower.
on full throttle hold it for 10 seconds.
then go down to idle again in the same matter.
the learning curve should be ok now.
let it run to idle for a minute or so.
shut down.

>> My idle is a little unstable though. The stability delay is currently at 50. Should I go down on it?

leave that it will not help you with this ..


>>My deceleration delay is currently at 20. Should I come down on it also?

if it does not flame out on throttle back dont change it


a well knows issue is for you guys who have flame outs on the runway:

most of the time when you start the engine, some fuel could get trapped in the back lower end of the turbine.
now as you nose up with the plane , or accelerate the fuel could get sucked thru the turbine wheel causing it to flame out.
so when you started the engine it would maybe a good thing to go for full thottle first tilt the nose a bit up to let the resident fuel out.

RE: MW44 Flameout Problems
 

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.

RE: MW44 Flameout Problems
 

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

RE: MW44 Flameout Problems
 

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

RE: MW44 Flameout Problems
 

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

RE: MW44 Flameout Problems
 

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

RE: MW44 Flameout Problems
 

H.Dale
Could you share what Gaspar said?

Thanks

RE: MW44 Flameout Problems
 

booker-RCU,

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

Tailwinds,

John

RE: MW44 Flameout Problems
 

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

RE: MW44 Flameout Problems
 

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

RE: MW44 Flameout Problems
 

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

RE: MW44 Flameout Problems
 

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

RE: MW44 Flameout Problems
 

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

RE: MW44 Flameout Problems
 

Galen,

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

Marc

RE: MW44 Flameout Problems
 

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

RE: MW44 Flameout Problems
 

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