I'm operating one of the smaller turbines and ever since the heat and humidity has arrived the operation has become unreliable. The idle speed is all over the place and it shuts down when approaching full power. My buddy has the exact same setup and his has been going into "buzzbomb" mode , flames and all while flying at full power. There has been talk of compressor stall at high speed. What are we dealing with here and should I just put the plane away till fall??????????????? One frustrated jet jockey.....

Can you be a bit more specific... What engine, What ECU.. few parameter changes can help and depending on brand, I may have some info...
Todd

Todd , it's a Wren 44.Original version, not new "gold." Has Gaspar FADEC. This engine has a full power rpm of 190,000. As I approach this the engine either just cuts out or automatically goes to a lower rpm. The display reads "low speed" ???? Wren says they think the tail pipe is causing it. Doug

Best advice one can give is to send turbine and Ecu out for service and let them go over everything.

I had the same sort of problem a few years ago. after tinkering with it myself, on several atempts, I just packed everything up and shipped it out for service, that was 2 years ago and still running great.

just my 2 cents

Mark

Sounds like blocked fuel needles.....

Dave

I have seen this situation before in high temp high humidity situations. Can be caused by the mixture being off a bit due to the air density. Not sure what menus are available from Wren on the Gaspar Fadec but if you can bump the acceleration delay (accel delay) value up a bit it may go away. Could be a restictive pipe but if it runs fine at lower ambient temps I would venture to guess it's a mixture problem....
I would look to see if this parameter is accessible in your menu, if it is bump the value up 5 points and see if it clears up the combustion. If not accessable, perhaps roger can walk you through the steps to access this setting. Each engine brand using the Fadec has different unlock codes to get to sub menus... worth a shot before having to send it in...
BTW...what does the engine temps look like as you approach this RPM? If you have the data cable, download your run file and send it to me, might be able to see something there as well...
Todd

I have noticed since I started the thread on MW44 flameout problems a lot of people have responded with the same problem. Many of them are in the U.S. I wonder if the hotter tempertures here as opposed to England and Europe could be causing the problems with these small engines. I have not been able to get mine to run especially when the temps are in the 90's.

I have two of the engines so I am going to try the other one. If I can get it to run okay I will send mine back to Wren. I may have blocked needles like Dave says.

Hal

There is a definite link between climate and problems with the MW44s flaming out on acceleration. This is due to surge which is made worse by high ambient temperatures. Mike Murphy says that the remedy is to increase the acceleration delay to slow the rate of acceleration slightly. Without having a climatic test cell (and only Rolls Royce have one of those!) we can't anticipate what settings are going to be needed. We have had engines tested in warmer climates and David Gladwin has had no problems in Australia at 40 degrees C, but all engines are different and the smaller ones are more sensitive, so some will be affected more than others. All engines are tested thoroughly before they leave here and only the ones which perform well are sold, but we cannot tell how an individual engine will react to high ambient temperatures.

We have recently discovered that another cause of flameouts can be the position of the tailpipe. Two years ago we recommended 10mm from the end of the exhaust, but have discovered that with the higher-power 44s a larger gap of 25-30mm is needed.

Sara Parish
Wren Turbines

Let me say first of all that Wren has been outstanding in their commitment to custumer service. The Wren"44" is an engineering marvel. I know it's tough trying to provide a fix to a customer when there are so many variables. Weather and temperature being one and installation details being another. Both of these items have changed considerably when I moved the turbine from my JHH A-4 to the Savex L-39. First I never flew the A-4 in temperatures above 70 degrees. The L-39 has seen nothing but 80-90 degrees plus and higher humidity. Secondly and I think this is important, the turbine in the A-4 sat in a clean unubstructed airflow. I converted it from ducted fan operation. The Savex is anything but clean and unubstructed. I have two shampoo type bottles that I partially heat formed to fit around the starter motor, to help minimize C/G change when burning off fuel.There is about 2" clearance from tanks to front of intake. I'm sure air gets to the compressor but it must be extremely turbulant. I have seen some installs that apeared to have very little airflow to the engine , such as the F-86 , but they still run so it's somewhat confusing. I guess I have to pull the gear and install on my test stand. If the problems go away I'll know it's the installation. Doug

high ambient temperatures + humidity

alabama (Arm pit of the world)
Johnny

Posted on the L39 thread, thought I'd copy across here- just in case someone actually uses the search function!