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budyerly(at)msn.com
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 Posted: Mon Feb 06, 2017 8:16 pm Post subject: Ruedi Vogal engine failure! |
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I was reading the Europa Flyer on Ruedi Vogal's engine failure in HB-YJF. Excellent airmanship making a safe forced landing.
By the sounds of the failure, I must bring up a recurring problem with the 912S with XS firewall forward and its exhaust problem.
I highly suspect an exhaust leak may be another culprit to consider, as with red Aeroquip or Parker fire sleeve, fuel vaporization is rare in the XS cowl with the boost pump on for takeoff. I have had two recent experiences with engine roughness due to exhaust leaks and left to continue the engine would have failed at full power. Exhaust leaks don't show up during initial ground runs. When the engine is cowled up, shortly after takeoff, if the exhaust leak is on either aft cylinder or its downpipe, the exhaust will jet out of the leak onto the float bowl and boil the fuel out of the carb in a very short time. This causes roughness then failure normally not a pure just dead silent engine.
The post flight analysis usually is seen as small amounts of soot on the carb body or bowl, upon disassembly, the carb may have a sticky lacquer type feel due to the baked fuel residue. It is really frustrating as during any engine roughness emergency we normally do the following:
Aux Boost Pump - On
Fuel selector - switch to unused full tank.
Reduce power-As required to obtain smooth operations.
Land as soon as possible.
This throttle reduction action refills the float bowl at reduced power (as the jet of exhaust is now diminished) and there is no evidence of a boiling incident. Drat.
I did a poor job of explaining in my Troubleshooting guide on how to look for and solve an exhaust leak. Look for the tan soot trail out of the junction of the pipe to cylinder head joint or the ball socket at the muffler for sure, but one should also make a heat shield to protect the carb from the possible future exhaust leaks. I am not a fan of the 914 drip tray on the older models we all suffered with, but take the idea from the new tray design for the 914. A simple bent piece of aluminum attached to the foot well will work also. I personally have my clients fab a tray, bolted to an Adel clamp on the engine frame and to the 5mm threaded hole in the cylinder head and shaped to deflect any exhaust leak from the carb and wiring. Crude but effective.
I apologize for not including this in my miscellaneous ramblings from one night.
Best Regards,
Bud Yerly
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riddon(at)sent.com
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| Posted: Tue Feb 07, 2017 12:15 am Post subject: Ruedi Vogal engine failure! |
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Eureka!!
Thanks Bud. I think you may have solved a long standing problem I have had with my 912S. After a prolonged climb at full power I often notice some engine roughness and the odd ‘stutter’ as I level out and pull back the power. It soon smooths out and begins to run nicely again. I have tried a number of things to identify this but I have noticed some sootiness on one of my carb bowls so this may well be the answer. I will try sealing the joint and making a shield.
Richard Iddon
G-RIXS
| Quote: | On 7 Feb 2017, at 04:15, Bud Yerly <budyerly(at)msn.com> wrote:
I was reading the Europa Flyer on Ruedi Vogal's engine failure in HB-YJF. Excellent airmanship making a safe forced landing.
By the sounds of the failure, I must bring up a recurring problem with the 912S with XS firewall forward and its exhaust problem.
I highly suspect an exhaust leak may be another culprit to consider, as with red Aeroquip or Parker fire sleeve, fuel vaporization is rare in the XS cowl with the boost pump on for takeoff. I have had two recent experiences with engine roughness due to exhaust leaks and left to continue the engine would have failed at full power. Exhaust leaks don't show up during initial ground runs. When the engine is cowled up, shortly after takeoff, if the exhaust leak is on either aft cylinder or its downpipe, the exhaust will jet out of the leak onto the float bowl and boil the fuel out of the carb in a very short time. This causes roughness then failure normally not a pure just dead silent engine.
The post flight analysis usually is seen as small amounts of soot on the carb body or bowl, upon disassembly, the carb may have a sticky lacquer type feel due to the baked fuel residue. It is really frustrating as during any engine roughness emergency we normally do the following:
Aux Boost Pump - On
Fuel selector - switch to unused full tank.
Reduce power-As required to obtain smooth operations.
Land as soon as possible.
This throttle reduction action refills the float bowl at reduced power (as the jet of exhaust is now diminished) and there is no evidence of a boiling incident. Drat.
I did a poor job of explaining in my Troubleshooting guide on how to look for and solve an exhaust leak. Look for the tan soot trail out of the junction of the pipe to cylinder head joint or the ball socket at the muffler for sure, but one should also make a heat shield to protect the carb from the possible future exhaust leaks. I am not a fan of the 914 drip tray on the older models we all suffered with, but take the idea from the new tray design for the 914. A simple bent piece of aluminum attached to the foot well will work also. I personally have my clients fab a tray, bolted to an Adel clamp on the engine frame and to the 5mm threaded hole in the cylinder head and shaped to deflect any exhaust leak from the carb and wiring. Crude but effective.
I apologize for not including this in my miscellaneous ramblings from one night.
Best Regards,
Bud Yerly
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| | - The Matronics Europa-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
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rampil
Joined: 04 May 2007
Posts: 870
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| Posted: Tue Feb 07, 2017 2:42 pm Post subject: Re: Ruedi Vogal engine failure! |
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Richard,
Make a tray or other effective shield. Do not bother with
trying to seal an exhaust joint. Nothing will withstand the 1500°F
temperatures at full throttle pressure.
I was an early victim of this problem in 2004 during my initial
test flights. It was Phil Lockwood himself who finally figured this
one out and gave us the diagnostic test of soot on the float bowl.
| | - The Matronics Europa-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Europa-List |
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