 |
Matronics Email Lists
Web Forum Interface to the Matronics Email Lists
|
| View previous topic :: View next topic |
| Author |
Message |
dsavarese0812(at)bellsout
Guest
|
 Posted: Thu Jun 25, 2015 11:40 am Post subject: Engine roughness, as in stops. starts. stops. starts. |
 |
|
Why not confirm the blade angles are correct firstsince the blade angle
has a direct impact on engine RPM. If they are properly set, then move
on to other things.
A. Dennis Savarese
334-546-8182 (mobile)
www.yak-52.com
Skype - Yakguy1
On 6/25/2015 11:01 AM, Rob Rowe wrote:
| Quote: |
I’m a little late to this discussion about magneto erratic failure when hot, but here’s my 5 pence input for what it’s worth.
A few years back I assisted in the commissioning of a magneto tester and in so doing ended up researching the nearly 100 year old information on this topic and discovered just how nuanced it is. Essentially this technology reached its peak interest post (Great) war, with research paper references going back to the 1860s!
For someone who reads a lot of technology papers it’s a humble reminder that latter day technical research is not the only source of learning or innovation.
I’ve provided links to the research papers below, but first I’ll summarise some thoughts that MAY be a scenario for our YAK mag failure experiences;
1 – To create a reliable spark (at least across an air gap on a magneto tester) a ‘teaser’ electrode is needed to create an ion rich area to help allow the spark to form. If this is not present then a spark may form irregularly depending on ion availability.
Point #1 - an ion rich environment is conducive to flash-over
2 – With increasing height air density reduces, as does its electrical insulation properties.
Point #2 – as height increases the voltage required for a flash-over inside the magneto reduces
3 – A leaner cylinder mixture increases the voltage required for a spark-plug to fire
Point #3 – leaning the aircraft in cruise increases the magneto voltage required for spark-plug operation
4 – Magneto impedance (as we’re referring to its AC properties) is related more to inductance than resistance with rising frequency (increasing engine RPM).
Point #4 – in the cruise with reduced RPM then magneto resistive heating may be more apparent, aggravated by #3 where the cruise also requires a higher magneto energy level to be generated
>From the above we might infer that when in the cruise at height the magnetos are at their mostly likely to heat up and are more vulnerable to air insulation break-down.
Now put this in conjunction with Jan Mevis’s observation, that the variable construction quality of the winding insulation (with heat) can lead to any trapped moisture vaporising and breaking down the insulation across weak points.
Then such a break-down would create an ion rich environment around the windings that could trigger premature & successive flash overs to other weak points impacting engine operation - in much the same way as lightning storm ions from an initial strike may often lead to the triggering of multiple events. In this case each event progressively weakens the secondary insulation, making it more likely to fail subsequently when subjected to similar conditions.
Now this is all subject to a LOT of contributory variables, hence why such a perfect (ion) storm failure mode might be a highly unpredictable initial occurrence & subject to small environmental changes that might push a marginally functioning magneto finally over the edge.
Anyway so much for my conjecture, here are the research paper links … enjoy!
Characteristics of High Tension Magnetos (1920) – NACA #58
http://naca.central.cranfield.ac.uk/reports/1920/naca-report-58.pdf
Simplified Theory of the Magneto (1923) – NACA #123
http://naca.central.cranfield.ac.uk/reports/1923/naca-report-123.pdf
The Sparking Voltage of Spark Plugs (1925) – NACA #202
http://naca.central.cranfield.ac.uk/reports/1925/naca-report-202.pdf
Brgds, Rob
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=444037#444037
|
| | - The Matronics Yak-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?Yak-List |
|
|
|
| Back to top |
|
 |
dsavarese0812(at)bellsout
Guest
|
| Posted: Thu Jun 25, 2015 11:49 am Post subject: Engine roughness, as in stops. starts. stops. starts. |
|
|
Oops, wrong thread. Sorry everyone.
Dennis
A. Dennis Savarese
334-546-8182 (mobile)
www.yak-52.com
Skype - Yakguy1
On 6/25/2015 2:37 PM, A. Dennis Savarese wrote:
| Quote: |
<dsavarese0812(at)bellsouth.net>
Why not confirm the blade angles are correct firstsince the blade
angle has a direct impact on engine RPM. If they are properly set,
then move on to other things.
A. Dennis Savarese
334-546-8182 (mobile)
www.yak-52.com
Skype - Yakguy1
On 6/25/2015 11:01 AM, Rob Rowe wrote:
>
>
> I’m a little late to this discussion about magneto erratic failure
> when hot, but here’s my 5 pence input for what it’s worth.
>
> A few years back I assisted in the commissioning of a magneto tester
> and in so doing ended up researching the nearly 100 year old
> information on this topic and discovered just how nuanced it is.
> Essentially this technology reached its peak interest post (Great)
> war, with research paper references going back to the 1860s!
>
> For someone who reads a lot of technology papers it’s a humble
> reminder that latter day technical research is not the only source of
> learning or innovation.
>
> I’ve provided links to the research papers below, but first I’ll
> summarise some thoughts that MAY be a scenario for our YAK mag
> failure experiences;
>
> 1 – To create a reliable spark (at least across an air gap on a
> magneto tester) a ‘teaser’ electrode is needed to create an ion
> rich area to help allow the spark to form. If this is not present
> then a spark may form irregularly depending on ion availability.
> Point #1 - an ion rich environment is conducive to flash-over
>
> 2 – With increasing height air density reduces, as does its
> electrical insulation properties.
> Point #2 – as height increases the voltage required for a
> flash-over inside the magneto reduces
>
> 3 – A leaner cylinder mixture increases the voltage required for a
> spark-plug to fire
> Point #3 – leaning the aircraft in cruise increases the magneto
> voltage required for spark-plug operation
>
> 4 – Magneto impedance (as we’re referring to its AC properties)
> is related more to inductance than resistance with rising frequency
> (increasing engine RPM).
> Point #4 – in the cruise with reduced RPM then magneto resistive
> heating may be more apparent, aggravated by #3 where the cruise also
> requires a higher magneto energy level to be generated
>
> >From the above we might infer that when in the cruise at height the
> magnetos are at their mostly likely to heat up and are more
> vulnerable to air insulation break-down.
>
> Now put this in conjunction with Jan Mevis’s observation, that the
> variable construction quality of the winding insulation (with heat)
> can lead to any trapped moisture vaporising and breaking down the
> insulation across weak points.
>
> Then such a break-down would create an ion rich environment around
> the windings that could trigger premature & successive flash overs to
> other weak points impacting engine operation - in much the same way
> as lightning storm ions from an initial strike may often lead to the
> triggering of multiple events. In this case each event progressively
> weakens the secondary insulation, making it more likely to fail
> subsequently when subjected to similar conditions.
>
> Now this is all subject to a LOT of contributory variables, hence why
> such a perfect (ion) storm failure mode might be a highly
> unpredictable initial occurrence & subject to small environmental
> changes that might push a marginally functioning magneto finally over
> the edge.
>
> Anyway so much for my conjecture, here are the research paper links
> … enjoy!
>
> Characteristics of High Tension Magnetos (1920) – NACA #58
> http://naca.central.cranfield.ac.uk/reports/1920/naca-report-58.pdf
>
> Simplified Theory of the Magneto (1923) – NACA #123
> http://naca.central.cranfield.ac.uk/reports/1923/naca-report-123.pdf
>
> The Sparking Voltage of Spark Plugs (1925) – NACA #202
> http://naca.central.cranfield.ac.uk/reports/1925/naca-report-202.pdf
> Brgds, Rob
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=444037#444037
>
|
| | - The Matronics Yak-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?Yak-List |
|
|
|
| Back to top |
|
|
|
|
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum
|
Powered by phpBB © 2001, 2005 phpBB Group
|
Get Email Distribution Too!
FAQ
Search
Memberlist
Usergroups
Register
Profile
Log in to check your private messages
Log in
