Could you you elaborate please? How did you solve the problem?

Jan

Andy and Andre',

Today I decided to take some measurements between my three identical engine and bypass installations. Decided to do this before I run any tests; first because I don't have a usable fireX now and second, because I might pick up the reason for my problem on this particular install.

What do you know; a glaring difference between the three installations became very obvious.

After measuring my problem setup I found that the turbine exhaust nozzle was 15mm and 25mm closer to the thrust pipe than compared to my other two installations (both of which I have absolutely no problem with).

Maybe I am too close and therefor choking the turbine during spool up to full power, which in turn is then not allowing for a proper venturi effect to form around the turbine???

What do you think guys - I'm quite keen to move my turbine further forward (away from the thrust pipe) by at least 15mm.....

Again, thanks for your help.

Jan

Found that on very hot days it was worse so came to the conclusion that it was not getting enough air in the front and battled to get the RPM up on start up, pump over fueled and caused flaming.

Took the top off the bypass and left it off. Doesn't flame on start-up anymore.

Hi all,

Eventually after many test and changes the mystery has been solved. My turbine now starts, runs and go to maximum rpm as it should, without starting a kero fire after starting. During the past few weeks many of the industry experts assisted and I wish to thank each and everyone who made constructive suggestions.

In short and without going into the scientific why's and wherefores I will explain the conclusions and outcomes we've arrived at. I will not bore you with the calculations that helped prove my problem.

Basically, the reason I was getting fire after start, when running up the turbine to full power - was because the venturi effect from the exhaust flow into the thrust pipe was so strong, that air was being drawn around the turbine (inside the bypass) and starving the turbine from air on the intake side (in front) of the turbine. Why then is this not the case with my other two identical installations? The only difference between my three jets is the volume of available air in front of the turbine. The problem jet has the smallest intakes and between 30 and 50% less air in front of the turbine.

So how to overcome the problem? First, by opting for (what I thought) a generous gap around the turbine, I actually made it worse. If I cut the gap from 12mm to 6mm then the venturi effect is less and less air is 'robbed' from the front of the turbine. Second, and this is what I've done (as confirmed by my friend with his Hawk) I provided more air at the rear of the turbine which could be drawn by the venturi effect, without having to draw air from the front of the turbine - I now have a 25 x 100mm cutout in the top cover of the hatch and have also opened up all the scale intakes in the fuselage. It is actuall amazing to feel how much air is being pulled into the fuselage through all these new openings, when the turbine is running.

So no more stalling turbine (the technical name for what was happening in my situation).

Hope my experience will help anyone having similar problems in future, when using a bypass.

Cheers,

Jan

Good update and very interesting Jan! glad to hear you are back in action :)

Super post Yan. This type of real world troubleshooting and lessons learned is invaluable.

Did you notice an EGT change at full power with the new openings you cut into the bypass?

Could you please post a pic of your install. I am having the same issue with my 180 powered hawk

Hi guys,

As indicated in my initial post, I have deliberately not named any products in this thread (only way I believe to avoid the brand bashes here on RCU from dragging us all down to their level) but I will respond to specifics if anyone who is genuine, needs to know - please send me a PM.

For the record; EGT changes have been minimal, heat inside the fuselage is now higher and I would continue to minimise my ground manuovering time. I might add that both the turbine and jet kit manufacturers were part of the solution in my case. I have no doubt that they will both share this information and use it in future to the benefit of their customers as they are proactive and most professional in all their developments thus far.

Thank you again for all the constructive help you guys have provided - we can always learn more, no matter how long we've been doing this.

Cheers,

Jan

Why would you not post the pics? Its not a specific manufacturing problem, just a funny combination of factors that added up to a problem.. A responsible manufacturer would want the info public so they could incorporate in their knowledge base on the ac.. What if the next guy isn't a handy with his fire extinguisher and his post is my brand x turbine burned up my brand y plane...

Bly jy het dit opgelos.
Andre

Great info! You cut a hole in the top of your bypass and opened up your scale vents in your jet! Thanks for sharing!

Since you said you had manufacture help, we know it wasn't an FEJ jet. :p

But I'm sure we can find someway to bash anyone here! LOL!