Cracking Up... - Jun 2007

Interesting point that made me think... Perhaps a different sort of stress could be a sort-of shock cooling; ie (even after running 2 mins at low RPM) shutting down in cold air may ??? particularly stress the metal.

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Date:         Mon, 18 Jun 2007 21:35:52 +1000
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G'day Xoggers,

John A wrote:

"Gets pretty hot here in summer so I am careful to idle the motor for a minute or two before turning off the engine. So I am still uncertain as to what causes the cracks. "
Interesting point that made me think... Perhaps a different sort of stress could be a sort-of shock cooling; ie (even after running 2 mins at low RPM) shutting down in cold air may ??? particularly stress the metal. So, what would be the wind chill factor after shutting down and and gaining altitude in a big thermal on a hot day ... Perhaps more cumulative metallurgical stress than just landing and shutting down?

I have never had a problem with overheating, moreso keeping it warm in cold air.
I have thought that a cowl flap of sorts on the intake would be helpful esp upon restarting a cold-soaked engine. to bypass that yellow-fibreglass-sleeve-thingy on top of the 912A.

I asked my partner who is pretty good on engines & he says that it is vibration more than anything that will cause the cracks. Many GA engines have beefier pipes and a "rosejoint"  arrangement futher down the pipe to absorb stress esp if the pipes has been fitted out alignment.

                                             ******************
Roland wrote:

"I am looking for gray matter during preflight "

I have been missing Grey Matter all my life but not much I can do about it...

Yours Soaringly,
Sandra Shemango.
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Date:         Mon, 18 Jun 2007 08:40:46 -0400
Reply-To:     "Ximango Owners Group (XOG)" <XIMANGO@HOME.EASE.LSOFT.COM>
Sender:       "Ximango Owners Group (XOG)" <XIMANGO@HOME.EASE.LSOFT.COM>
From:         Bruce Schimmel <bruce@SCHIMMEL.COM>
Subject:      Re: cracking up...
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Dear Sandra and Fellow Xoggers,

Sandra. thank you for your witty description. I, too, have been 
looking for grey matter for years. I think there's been some 
operating in this discussion.

I've heard from mechanics and engineers that a "heat pocket" forms 
just below the reinforced turn. The new design, I believe, is 
entirely smooth. I'll let you know when I get mine, which are on 
order at Ximango. Meanwhile, I'm grounded.

Another explanation for the break that I've heard is that the pipes, 
in addition to heat spots, are stressed by holding up the  weight of 
the entire piece of plumbing.

And finally, there's water. A couple years ago, you might read in the 
archives, there was some discussion of coating the pipes with a 
ceramic to cut down on rusting, and to act as a kind of heat shield.

So the pipe are cracking because:

1. heat build up at joints
2. stress for carrying too much weight
3. the effects of water

Have I got this right?

Speaking of grey matter. I wish I spoke Portuguese, so I could 
translate some of these insights for the fine folks at Aeromot.

yrs, Bruce



On Jun 18, 2007, at 7:35 AM, shemango wrote:

> G'day Xoggers,
>
> John A wrote:
>
> "Gets pretty hot here in summer so I am careful to idle the motor 
> for a minute or two before turning off the engine. So I am still 
> uncertain as to what causes the cracks. "
> Interesting point that made me think... Perhaps a different sort of 
> stress could be a sort-of shock cooling; ie (even after running 2 
> mins at low RPM) shutting down in cold air may ??? particularly 
> stress the metal. So, what would be the wind chill factor after 
> shutting down and and gaining altitude in a big thermal on a hot 
> day ... Perhaps more cumulative metallurgical stress than just 
> landing and shutting down?
>
> I have never had a problem with overheating, moreso keeping it warm 
> in cold air.
> I have thought that a cowl flap of sorts on the intake would be 
> helpful esp upon restarting a cold-soaked engine. to bypass that 
> yellow-fibreglass-sleeve-thingy on top of the 912A.
>
> I asked my partner who is pretty good on engines & he says that it 
> is vibration more than anything that will cause the cracks. Many GA 
> engines have beefier pipes and a "rosejoint"  arrangement futher 
> down the pipe to absorb stress esp if the pipes has been fitted out 
> alignment.
>
>                                              ******************
> Roland wrote:
>
> "I am looking for gray matter during preflight "
>
> I have been missing Grey Matter all my life but not much I can do 
> about it...
>
> Yours Soaringly,
> Sandra Shemango.
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Date:         Mon, 18 Jun 2007 11:53:33 EDT
Reply-To:     "Ximango Owners Group (XOG)" <XIMANGO@HOME.EASE.LSOFT.COM>
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From:         John Lawton <Thrmlseekr@AOL.COM>
Subject:      Re: Cracking up
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Hey Bruce,
 
Have I got this right?
 
FWIW, most Europa's flying, about 500 or so now, use the 912S/914  as the
engine of choice. Cracks similar to what have been described here  have been
reported by Europa owners, too. Most of what I've heard about is with  914's,
though. One theory is that mogas, or an additive in mogas, speeds up  the
corrosion of the pipes and leads to cracking. The weird part is some using  mogas
develop cracks and others using mogas don't. So, vibration must  play a fairly
sizable roll as part of the cause of the cracks.
 
A quick way to find leaks in exhaust systems is to use a shop vacuum that 
has a blower option. Hook the vac up to blow and duct tape the hose to the 
exhaust pipe. Using soapy water in a spray bottle you can quickly  check any
suspect areas and even a hidden crack will show up as bubbles.  Even with exhaust
or intake valves open there should be enough pressure with a  typical shop vac
to make the soapy water bubble, but if not, rotate the prop  forwards through
a couple of revolutions while monitoring the soaped areas  for bubbles. Just
don't rotate the prop backwards unless you want to replace  your slipper clutch
and gear box!
 
9,100' cloudbase here yesterday in the Sequatchie Valley with 7-9 knot  lift.
Susan and I did a 210 nm triangle. Gotta love a good drought!
 
Regards,
 
John Lawton
Whitwell, TN (TN89)
Ximango #135
 





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Date:         Thu, 21 Jun 2007 12:32:54 EDT
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From:         Chuck Cheeseman <XimangoUSA@AOL.COM>
Subject:      Re: Cracking up
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John,
 
Welcome, and keep up communicating the technical info from your  experience!
 
Chuck - Ximango USA



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Date:         Thu, 21 Jun 2007 12:35:41 EDT
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From:         Chuck Cheeseman <XimangoUSA@AOL.COM>
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In a message dated 6/18/2007 8:41:04 AM Eastern Daylight Time, 
bruce@SCHIMMEL.COM writes:

Speaking  of grey matter. I wish I spoke Portuguese, so I could 
translate some  of these insights for the fine folks at Aeromot.



Bruce,
 
The people at Aeromot are on the XOG mailing list and get everything  you
folks send!
 
Chuck
Ximango USA



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Date:         Thu, 21 Jun 2007 12:43:14 EDT
Reply-To:     "Ximango Owners Group (XOG)" <XIMANGO@HOME.EASE.LSOFT.COM>
Sender:       "Ximango Owners Group (XOG)" <XIMANGO@HOME.EASE.LSOFT.COM>
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In a message dated 6/18/2007 11:54:09 AM Eastern Daylight Time, 
Thrmlseekr@aol.com writes:

vibration must  play a fairly
sizable roll as part of the  cause of the cracks.



Getting the propeller balanced has been reported some years ago by an owner 
as making the exhaust crack problem go away.
 
Chuck
Ximango USA