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nuckolls.bob(at)aeroelect
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 Posted: Tue Feb 04, 2014 8:09 am Post subject: Teaching vs. Propagandizing |
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At 08:23 PM 2/3/2014, you wrote:
| Quote: | Bob, You also have to take into account that unlike the LyCo's, the
Rotax has a five piece crank that is pressed together with nothing
but the pressure of the fit to keep it together and aligned. <snip>
Rotax engines are just a different animal.
|
Understand. This isn't a study in design
philosophies. It's a sifting of the simple
ideas in work -> heat -> loss of finish ->
more heat -> destruction over time.
Temperature rise in mass is a time dependent
phenomenon. The parts at risk of failure
need to take on energy that begins with a
very low value (new, slick surfaces) and builds
as the level of destruction advances.
Most engines run minutes producing a high
percentage of rated power with no more oil
on moving parts than that which was used to
assemble it. Then there's the notion that
destruction of cylinder walls (of significant
mass with water on the other side) had
anything to do with rod failure that went
from start to completion in 10 seconds.
I've spend a lot of my career sifting
through narratives for the purpose of
assembling data bits into a coherent picture
of cause and effect. "No piston
lube resulted in breaking a rod and
pushing the end through the crankcase
at 1000 rpm" does not paint a coherent
picture.
There is MUCH that is not said/known
and as such is a poor tool for educating
the listener with any better understanding
than they get from watching a Hollywood
portrayal of fantastic physics. Memorable
perhaps but it's akin to telling our
kids they'd better behave or the "boggy
man is going to get you." We've conducted
similar exercises here on the List with
close examination of narratives in the
flying rags that I've dubbed "dark-
n-stormy-night" stories. In this case:
"Better not have your EFIS system rebooting
right after start up lest the engine put
a rod through the crankcase."
The difference between teacher and propagandist
is the ability to bring all the simple-ideas
in a narrative together for that coherent
picture. The puzzle may be ten pieces or
1000 pieces but until they've been
fitted into place, the integrity of the
narrative is suspect.
Remember that math teacher who insisted
you write down all the steps for solving
a problem? The goal WAS NOT to get to the
right answer on one problem . . . the goal
WAS to understand HOW to get to the right
answer on all problems.
Bob . . .
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rickofudall
Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA
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| Posted: Tue Feb 04, 2014 1:45 pm Post subject: Teaching vs. Propagandizing |
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Bob et al, It's been seven years since I saw that engine at Lockwoods. At the time I didn't think to take pictures, however I have a request in to Dean Vogel, there, to see if I can get one or two pictures of it. I've had the misfortune to blow up an engine or two over the last 50 years. The first was an Alfa Romeo four cylinder that blew a head gasket. I had just had the engine rebuilt after I over revved it and spun a rod bearing. The book said to re-torque the head every 1300 miles. I had a date and thought I could get it the next morning. Sure enough, white steam began pouring out of the exhaust a block from her house. The trip odometer said the engine had 1317 miles on it. The fellow I sold the car to did the same thing. Dave, as I recall, got a little over that but did not reach 1400 miles. Alfa was quite serious about the 1300 mile re-torquing. I was 19 and it made an impression on me that the manufacturer generally knows his product.
Back to the Rotax. First, your assumption that it would idle at 1000 rpm. It's a geared engine that idles at 1800 to 2200. Kinetic energy increases at the square of the speed, does it not? So we have around 4 times the energy from the idle speed you used as an example.
Rotax piston fits. As I said, somewhere back, the allowable piston to cylinder fit for a 912 is .0000 to .0009". It is perfectly acceptable to have a size on size fit up. Even at .0009" it does not take much to seize a piston.
When I examined the damage, one of the things that impressed me was the absence of metal discoloration or burned oil on the parts, in this case break in lube. This is why my recreation of events concentrated on the failure of the built up crank. I just didn't see the damage signature that I've seen in a typical rod failure event. What there was, was a lot of impact damage.
If I'm lucky enough to get a picture or two, I'll pass them along.
Rick
On Tue, Feb 4, 2014 at 10:08 AM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
| Quote: | --> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>
At 08:23 PM 2/3/2014, you wrote:
| Quote: | Bob, You also have to take into account that unlike the LyCo's, the Rotax has a five piece crank that is pressed together with nothing but the pressure of the fit to keep it together and aligned. <snip> Rotax engines are just a different animal.
|
Understand. This isn't a study in design
philosophies. It's a sifting of the simple
ideas in work -> heat -> loss of finish ->
more heat -> destruction over time.
Temperature rise in mass is a time dependent
phenomenon. The parts at risk of failure
need to take on energy that begins with a
very low value (new, slick surfaces) and builds
as the level of destruction advances.
Most engines run minutes producing a high
percentage of rated power with no more oil
on moving parts than that which was used to
assemble it. Then there's the notion that
destruction of cylinder walls (of significant
mass with water on the other side) had
anything to do with rod failure that went
from start to completion in 10 seconds.
I've spend a lot of my career sifting
through narratives for the purpose of
assembling data bits into a coherent picture
of cause and effect. "No piston
lube resulted in breaking a rod and
pushing the end through the crankcase
at 1000 rpm" does not paint a coherent
picture.
There is MUCH that is not said/known
and as such is a poor tool for educating
the listener with any better understanding
than they get from watching a Hollywood
portrayal of fantastic physics. Memorable
perhaps but it's akin to telling our
kids they'd better behave or the "boggy
man is going to get you." We've conducted
similar exercises here on the List with
close examination of narratives in the
flying rags that I've dubbed "dark-
n-stormy-night" stories. In this case:
"Better not have your EFIS system rebooting
right after start up lest the engine put
a rod through the crankcase."
The difference between teacher and propagandist
is the ability to bring all the simple-ideas
in a narrative together for that coherent
picture. The puzzle may be ten pieces or
1000 pieces but until they've been
fitted into place, the integrity of the
narrative is suspect.
Remember that math teacher who insisted
you write down all the steps for solving
a problem? The goal WAS NOT to get to the
right answer on one problem . . . the goal
WAS to understand HOW to get to the right
answer on all problems.
Bob . . .
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Mk IIIC
Thanks, Homer GBYM
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nuckolls.bob(at)aeroelect
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| Posted: Tue Feb 04, 2014 2:15 pm Post subject: Teaching vs. Propagandizing |
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At 03:40 PM 2/4/2014, you wrote:
| Quote: | Bob et al, It's been seven years since I saw that engine at
Lockwoods. At the time I didn't think to take pictures, however I
have a request in to Dean Vogel, there, to see if I can get one or
two pictures of it.
|
<snip>
| Quote: | If I'm lucky enough to get a picture or two, I'll pass them along.
|
Great. If he could also expand the narrative to
explain the sequence of events along with photos
of the participating features . . .
Bob . . .
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rlborger(at)mac.com
Guest
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| Posted: Tue Feb 04, 2014 3:02 pm Post subject: Teaching vs. Propagandizing |
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Gents,
This thread should probably be on the Rotax list, but sometimes we take what we can get where we can get it.
I too have attended Lockwood’s 91X class and have seen the engine and heard the story from Dean. There was also a second story related which involved loss of oil due to vibrational damage to an extended fitting to mount the oil pressure sensor. A fitting was inserted between the oil pressure sender and the engine case. The fitting was put in place to add a pressure switch to illuminate a light should the oil pressure drop below the switch pressure set point. Now you have a classic mass on a spring with the sender hanging out on that extension. I don’t remember how long that arrangement held up but I don’t believe it was very long before the extension piece broke, the gentleman’s low oil pressure lamp illuminated and the contents of the oil sump were dumped overboard. Again, the report was that the engine probably didn’t run longer than 10-20 second before it seized once the oil was gone. I can’t speak to the accuracy of the 10-20 seconds without oil before seizure not having been there in either case. But the takeaway point was that the Rotax 91X engine requires continuous lubrication and that any interruption in that lubrication would be detrimental to your engine.
BTW, I have moved my oil pressure sender off the engine and onto the firewall using a length of SS braided pressure line. Saves vibrational stresses on the sender and the fitting to the engine.
One of the many things I like about my Grand Rapids EIS 4000 is that it stays up during engine start and the default page shows oil pressure so I know immediately upon engine start if there’s oil pressure.
Just my 2¢ and worth at least half that.
Blue skies & tailwinds,
Bob Borger
Europa XS Tri, Rotax 914, Airmaster C/S Prop (50 hrs).
Little Toot Sport Biplane, Lycoming Thunderbolt AEIO-320 EXP
3705 Lynchburg Dr.
Corinth, TX 76208-5331
Cel: 817-992-1117
rlborger(at)mac.com
On Feb 4, 2014, at 3:40 PM, Richard Girard <aslsa.rng(at)gmail.com> wrote:
Bob et al, It's been seven years since I saw that engine at Lockwoods. At the time I didn't think to take pictures, however I have a request in to Dean Vogel, there, to see if I can get one or two pictures of it.
I've had the misfortune to blow up an engine or two over the last 50 years. The first was an Alfa Romeo four cylinder that blew a head gasket. I had just had the engine rebuilt after I over revved it and spun a rod bearing. The book said to re-torque the head every 1300 miles. I had a date and thought I could get it the next morning. Sure enough, white steam began pouring out of the exhaust a block from her house. The trip odometer said the engine had 1317 miles on it. The fellow I sold the car to did the same thing. Dave, as I recall, got a little over that but did not reach 1400 miles. Alfa was quite serious about the 1300 mile re-torquing. I was 19 and it made an impression on me that the manufacturer generally knows his product.
Back to the Rotax. First, your assumption that it would idle at 1000 rpm. It's a geared engine that idles at 1800 to 2200. Kinetic energy increases at the square of the speed, does it not? So we have around 4 times the energy from the idle speed you used as an example.
Rotax piston fits. As I said, somewhere back, the allowable piston to cylinder fit for a 912 is .0000 to .0009". It is perfectly acceptable to have a size on size fit up. Even at .0009" it does not take much to seize a piston.
When I examined the damage, one of the things that impressed me was the absence of metal discoloration or burned oil on the parts, in this case break in lube. This is why my recreation of events concentrated on the failure of the built up crank. I just didn't see the damage signature that I've seen in a typical rod failure event. What there was, was a lot of impact damage.
If I'm lucky enough to get a picture or two, I'll pass them along.
Rick
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nuckolls.bob(at)aeroelect
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| Posted: Wed Feb 05, 2014 9:46 am Post subject: Teaching vs. Propagandizing |
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At 05:01 PM 2/4/2014, you wrote:
--> AeroElectric-List message posted by: Robert Borger <rlborger(at)mac.com>
Gents,
This thread should probably be on the Rotax list, but sometimes we take what we can get where we can get it.
I will suggest this is an appropriate discussion
for the purpose of honing our critical analysis
tools. Most of the 'tiger teams' on which I served
at Beech were not wrestling with electrons . . .
but they were grounded in the same physics that drives
everything made up of matter and driven by energy.
I too have attended Lockwood’s 91X class and have seen the engine and heard the story from Dean. There was also a second story related which involved loss of oil due to vibrational damage to an extended fitting to mount the oil pressure sensor. A fitting was inserted between the oil pressure sender and the engine case. The fitting was put in place to add a pressure switch to illuminate a light should the oil pressure drop below the switch pressure set point. Now you have a classic mass on a spring with the sender hanging out on that extension. I don’t remember how long that arrangement held up but I don’t believe it was very long before the extension piece broke, the gentleman’s low oil pressure lamp illuminated and the contents of the oil sump were dumped overboard. Again, the report was that the engine probably didn’t run longer than 10-20 second before it seized once the oil was gone. I can’t speak to the accuracy of the 10-20 seconds without oil before seizure not having been there in either case. But the takeaway point was that the Rotax 91X engine requires continuous lubrication and that any interruption in that lubrication would be detrimental to your engine.
Great example!
BTW, I have moved my oil pressure sender off the engine and onto the firewall using a length of SS braided pressure line. Saves vibrational stresses on the sender and the fitting to the engine.
There you go . . . this is a demonstrable example
of fitting all the puzzle pieces together. I'm
betting that the fittings which broke were brass . . .
a non-ferrous material of which all such materials
have a service life.
There's a feature in the study of strengths of
materials called the S/N to Failure. Stress
levels/Number of cycles to failure curve for
steel becomes flat at some value of S/N
below N of 10M. The rule of thumb for testing
steel parts is, "If you can't break it in
10,000,000 cycles, you aren't going to break it."
On the other hand, non-steel parts have a service
life at ANY stress level. It's just parts like
wings, struts and tail feathers are so lightly
stressed that their service lives far exceed the
expected life of an airplane. But poor attention
to details of design, operation and maintenance
have proven spectacularly catastrophic.
It's that sneaky old s/n ratio thingy that makes
us attentive to adding wire support immediately
adjacent to a crimped or soldered bundle of wire
strands.
Having a rudimentary understanding of s/n ratio
is useful for stringing wires, installing rivets,
building support brackets . . . and yes . . .
evaluating cause-effect for connecting rods coming
through the crankcase. It'a all the same physics.
One of the many things I like about my Grand Rapids EIS 4000 is that it stays up during engine start and the default page shows oil pressure so I know immediately upon engine start if there’s oil pressure.
Just my 2¢ and worth at least half that.
Undoubtedly . . .
Blue skies & tailwinds,
Bob Borger
Bob . . . [quote][b]
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rlborger(at)mac.com
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| Posted: Wed Feb 05, 2014 10:25 am Post subject: Teaching vs. Propagandizing |
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On Feb 5, 2014, at 11:46 AM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com> wrote:
At 05:01 PM 2/4/2014, you wrote:
Gents,
There you go . . . this is a demonstrable example
of fitting all the puzzle pieces together. I'm
betting that the fittings which broke were brass . . .
a non-ferrous material of which all such materials
have a service life.
Robert, If I remember correctly, the fitting was brass. Broke off just about flush with the oil pump housing. Which is right where the maximum vibrational stress would have been applied.
Blue skies & tailwinds,
Bob Borger
Europa XS Tri, Rotax 914, Airmaster C/S Prop (50 hrs).
Little Toot Sport Biplane, Lycoming Thunderbolt AEIO-320 EXP
3705 Lynchburg Dr.
Corinth, TX 76208-5331
Cel: 817-992-1117
rlborger(at)mac.com
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nuckolls.bob(at)aeroelect
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| Posted: Wed Feb 05, 2014 12:27 pm Post subject: Teaching vs. Propagandizing |
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| Quote: | Robert, If I remember correctly, the fitting was brass. Broke off
just about flush with the oil pump housing. Which is right where
the maximum vibrational stress would have been applied.
|
Bingo . . .
Bob . . .
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tim2542(at)sbcglobal.net
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| Posted: Wed Feb 05, 2014 1:04 pm Post subject: Teaching vs. Propagandizing |
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Most of us probably know this, but cantilever mounted engine pressure senders is bad practice, steel or brass. I have personally seen steel ones break.
Tim
| Quote: | On Feb 5, 2014, at 12:25 PM, "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com> wrote:
> Robert, If I remember correctly, the fitting was brass. Broke off just about flush with the oil pump housing. Which is right where the maximum vibrational stress would have been applied.
Bingo . . .
Bob . . .
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nuckolls.bob(at)aeroelect
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| Posted: Wed Feb 05, 2014 4:30 pm Post subject: Teaching vs. Propagandizing |
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At 03:04 PM 2/5/2014, you wrote:
| Quote: |
Most of us probably know this, but cantilever mounted engine
pressure senders is bad practice, steel or brass. I have personally
seen steel ones break.
Tim
|
Yeah, those threads do offer a powerful stress
riser. Coming off a crankcase with a low mass,
soft overhang is probably never wrong.
Bob . . .
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