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Glass for IFR
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rocketbob(at)gmail.com
Guest

Posted: Fri Mar 02, 2007 10:07 am Post subject: Glass for IFR

On 3/2/07, linn Walters <pitts_pilot(at)bellsouth.net (pitts_pilot(at)bellsouth.net)> wrote: 	  Quote: 	
		              Bob J. wrote:

  	  Quote: 	
		  The best approach is to use a wet vacuum pump and a separator.  I know of many wet vaccum pumps that outlived the engines they were installed in. 	


  They're heavier, and the separator isn't that efficient.  That's why the dry pump is standard on most 'newer' engines.

	


So what if they're heavier.  They last forever!  We're talking a pound or two difference.  The reason why dry pumps became fashionable was because someone thought it would be a clever way to  cut costs in certificated aircraft production. 



 	  Quote: 	
		   	  Quote: 	
		     I don't know of a single dry pump that I've ever seen that didn't fail in the shear coupler.  I've never seen on where the vanes wore out. 	
 Well, that's why the pump fails.  The vanes are plasticized carbon, and the centripetal force keeps the vanes in contact with the pumps outer wall, which causes them to wear down slowly.  The vanes are the sacrificial parts.  When the vanes get thin ..... about 1/4" wide or so, they jam in the ports and the shear coupling fails.

	


I don't see how a vane can jam into a port.  I've taken dry pumps apart and the ports are only a 1/4" or so in diameter.  When they fail due to vane wear what will happen is that they will fall out of the stator in the open area ahead of the port, then will jam between the body of the pump and the next vane that comes along. 

I can show you a box of about a half dozen cores we have on our airport of dry pumps, all of them have vanes in excellent shape.  The vanes will outlast the shear coupler.  Ask any A&P that has replaced many of these and I will bet you a beer you will get the same answer.  In every single one I've seen the drive coupling failed.  Why?  To use your analogy of the fuse, imagine a 5A fuse on a 10A circuit.  Now lets analyze the design of a dry pump.  Lets say the shear coupling is more rigid, perhaps 50% stronger.  Now lets say a vane fails, what happens?  The pump will grind itself internally to death, and if it causes a seizure of the pump, then a stronger shear coupler will fail.  As long as the bits an pieces can't get into the engine, or the instruments, there's no problem.  Which normally they can't unless the dry pump is used to inflate deice boots.  In those installations however they have screens to prevent junk from getting in the boots (Piper Aerostar comes to mind.) 



Wet pumps such as the Garwins have a thinned down section of the drive shaft to act as a shear coupler if the pump seized.  In dry pumps the shear couplers are plastic, it doesn't take much torque to make them fail. 



 	  Quote: 	
		   	  Quote: 	
		     If the dry pumps didn't have the silly shear coupler they would be far more reliable. 	
 Can't agree with that!  That's like replacing a fuse with a piece of metal. If the shear coupling didn't fail when the pump jammed ..... some other, weaker, link in the food chain would have to ...... maybe internal to the engine.  Who knows???  I sure wouldn't want to find out!

	


The weak link would then be the carbon stator and the vanes, and if they fail there should not be any cascading effect other than no vacuum pressure.  I believe the shear couplers fail from being subject constant pounding of the engine power pulses. 

 	  Quote: 	
		   FYI ..... I had a dry pump last more than 2000 hours on an O-235 ...... and yes, it failed as I was climbing out through the soup.  Sigh.

 Linn

	


Regards,

Bob Japundza

RV-6 flying F1 under const.

  [quote][b]

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sisson(at)consolidated.ne
Guest

Posted: Fri Mar 02, 2007 11:41 am Post subject: Glass for IFR

Many people are starting to realize the problems associated with the plastic couplings and are replacing it every two years. The guys who are doing this are getting a lot of trouble free time from the dry pumps. The problem seems to be the life of the coupling is getting pushed too far  The vanes are designed to go a long time, and in industrial applications, they do, unless they ingest something like foam from an aged out filter. … Maybe a $11 coupling every couple of years or so, along with a new garter filter, may save a lot of grief and money..  

   

Just an opinion,  

   

Phil  

       [quote][b]

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pitts_pilot(at)bellsouth.
Guest

Posted: Fri Mar 02, 2007 12:06 pm Post subject: Glass for IFR

Bob J. wrote:

  	  Quote: 	
		  On 3/2/07, linn Walters <pitts_pilot(at)bellsouth.net (pitts_pilot(at)bellsouth.net)> wrote:       	  Quote: 	
		       Bob J. wrote:

      	  Quote: 	
		  The best approach is to use a wet vacuum pump and a separator.  I know of many wet vaccum pumps that outlived the engines they were installed in. 	
     

        They're heavier, and the separator isn't that efficient.  That's why the dry pump is standard on most 'newer' engines.

   	
   

 So what if they're heavier.  They last forever!  We're talking a pound or two difference.  The reason why dry pumps became fashionable was because someone thought it would be a clever way to  cut costs in certificated aircraft production.   

   

    	  Quote: 	
		             	  Quote: 	
		    I don't know of a single dry pump that I've ever seen that didn't fail in the shear coupler.  I've never seen on where the vanes wore out. 	
     Well, that's why the pump fails.  The vanes are plasticized carbon, and the centripetal force keeps the vanes in contact with the pumps outer wall, which causes them to wear down slowly.  The vanes are the sacrificial parts.  When the vanes get thin ..... about 1/4" wide or so, they jam in the ports and the shear coupling fails.

   	
   

 I don't see how a vane can jam into a port.  I've taken dry pumps apart and the ports are only a 1/4" or so in diameter.  When they fail due to vane wear what will happen is that they will fall out of the stator in the open area ahead of the port, then will jam between the body of the pump and the next vane that comes along.   

   

 	
 I've not seen that failure mode.  The vanes I've seen (personally, and in my limited experience) all had plenty of 'room' left on the vane.  However, there was wear on the ports and the face (side of the pump) had a little 'tit' worn there that 'could' have caused the failure.  There wasn't any other explanation for the failure.

  	  Quote: 	
		        I can show you a box of about a half dozen cores we have on our airport of dry pumps, all of them have vanes in excellent shape.  The vanes will outlast the shear coupler.  Ask any A&P that has replaced many of these and I will bet you a beer you will get the same answer.  In every single one I've seen the drive coupling failed.  Why?  To use your analogy of the fuse, imagine a 5A fuse on a 10A circuit.  Now lets analyze the design of a dry pump.  Lets say the shear coupling is more rigid, perhaps 50% stronger.  Now lets say a vane fails, what happens?  The pump will grind itself internally to death, and if it causes a seizure of the pump, then a stronger shear coupler will fail.  As long as the bits an pieces can't get into the engine, or the instruments, there's no problem.  Which normally they can't unless the dry pump is used to inflate deice boots.  In those installations however they have screens to prevent junk from getting in the boots (Piper Aerostar comes to mind.)   

   

 	
 The rubber shear coupling degrades over time and heat in the engine compartment, so it's nowhere as structurally sound as when it was born.  The busted couplings broke into chunks when 'tested'.

  	  Quote: 	
		        Wet pumps such as the Garwins have a thinned down section of the drive shaft to act as a shear coupler if the pump seized.  In dry pumps the shear couplers are plastic, it doesn't take much torque to make them fail.   

   

 	
 I've encountered the swame necked-down shaft on dry pumps too.  I thought the couplings were a rubber compound, but they could be a flexible plastic.  In any event, they don't have a long lifespan under good conditions.  Maybe changing the coupling instead of the pump every 500 hours is a better cost idea.  I dunno.

  	  Quote: 	
		         	  Quote: 	
		             	  Quote: 	
		    If the dry pumps didn't have the silly shear coupler they would be far more reliable.     	
     Can't agree with that!  That's like replacing a fuse with a piece of metal. If the shear coupling didn't fail when the pump jammed ..... some other, weaker, link in the food chain would have to ...... maybe internal to the engine.  Who knows???  I sure wouldn't want to find out!

   	
   

 The weak link would then be the carbon stator and the vanes, and if they fail there should not be any cascading effect other than no vacuum pressure.  I believe the shear couplers fail from being subject constant pounding of the engine power pulses.

   

 	
 Could be.

 Linn

 do not archive

 [quote]      

   

   

    	  Quote: 	
		       FYI ..... I had a dry pump last more than 2000 hours on an O-235 ...... and yes, it failed as I was climbing out through the soup.  Sigh.

 Linn

   	
   

   

   

 Regards,

 Bob Japundza

 RV-6 flying F1 under const.

    	  Quote: 	
		  

	
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ronlee(at)pcisys.net
Guest

Posted: Fri Mar 02, 2007 1:33 pm Post subject: Glass for IFR

 	  Quote: 	
		   Many people are starting to realize the problems associated with the 

plastic couplings and are replacing it every two years. 
	




Not a bad idea if it is really the coupling that fails.  In my

case I saw the innards broken.  That likely led to the coupling shearing 

as opposed to the other way.



I will have to examine the Rapco 215cc I get to see if it is easy to 

replace the coupling.  



Ron

Lee



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Tim_Lewis(at)msm.umr.edu
Guest

Posted: Fri Mar 02, 2007 2:59 pm Post subject: Glass for IFR

I lost my vac pump right at 500 hours, in the soup (RV-6A).  I tend to agree with replacing them every 500 hours (or perhaps a bit sooner).    

 

 However, for my RV-10, I've bought the new SigmaTek Aeon vacuum pump (to run the artificial horizon which is my failover source of attitude info if there's a problem with my AF-3500 EFIS).  The Aeon is on sale at AC$ right now.  It uses a dual action piston rather than rotating vanes.  It has a 5 year, 2000 hour warranty.  Seems promising.

 

 Tim

  	  Quote: 	
		  -- 

Tim Lewis -- HEF (Manassas, VA)

RV-6A N47TD -- 850 hrs

RV-10 #40059 under construction 	
 

 

 Jack Lockamy wrote: [quote]                   

Maybe the better way to approach inevitable vacuum pump failures is to have the pump rebuilt/replaced every 500 hrs instead of waiting for it to fail.  I believe this is the same timeframe (500 hrs) that Slick magnetos are also recommended to be rebuilt/replaced.  Would be any easy way to remember when the pump needed replacing (i.e. 500, 1000, 1500, 2000 hrs, etc.)   

    

Certainly would be cheap insurance and if nothing else... peace of mind when flying in the soup as others have mentioned.   

    

Jack   

    

do not archive   

    	  Quote: 	
		  

	
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B25Flyer

Joined: 06 Mar 2006
Posts: 11

Posted: Sun Mar 11, 2007 7:34 pm Post subject: Re: Glass for IFR

I was "just passing thru" and saw this post and could not resist a comment.



I am now on my second Dynon IFR airplane. (RV-4 and F-1 EVO)  I have flown over 500 hours behind Dynons with lots of actual including low approaches.



Here are my thoughts.

A steam gauge Altimeter, Airspeed Indicator & T/Coordinator are cheaper and a more independent source of backup info than standby glass unit.  



An autopilot is very important in an IFR RV.  Both for Dynon failure and for keeping the airplane rightside up when you are looking at charts.



If my Dynon ever fails, the autopilot will come on imeadiately.



If I was unwilling to fly in the clouds without the autopilot engaged, then I wouldn't be flying in the clouds.



I keep an old Lowrance 500 in my "little oh $hit" bag along with a vice grip, screwdriver, some Zip ties, a Mag light, some batteries,  and some other goodies.   (sorry no handheld VHF. I won't have a spare hand to use it anyway) 



A second EFIS might be a viable backup for the first, but I could fly to heck and back with a T&B Alt, Airspeed, and handheld GPS.



My greatest fear in an all electric airplane is a lightning strike that fries  everything that is turned on.   That would be a bad day.  I don't have a good answer for that.   If the T&B and the Dynon both quit, I have a big problem.   But I can name several other scenarios that are more likely to cause just as big a jamb.



My $.02



Tailwinds,

Doug Rozendaal

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mr.gsun+rv-list(at)gmail.
Guest

Posted: Sun Mar 11, 2007 8:42 pm Post subject: Glass for IFR

Good two cents.

 

 I've got a Blue Mountain EFIS and a backup Dynon.  No round gauges at all.  Although I'm a long way from my IFR rating, I hope it will work well enough to get back home if it clouds up at the last minute.  

 

 Greg



On 3/11/07, B25Flyer <dougr(at)petroblend.com (dougr(at)petroblend.com)> wrote:[quote] --> RV-List message posted by: "B25Flyer" <dougr(at)petroblend.com (dougr(at)petroblend.com)>



I was "just passing thru" and saw this post and could not resist a comment.

 

I am now on my second Dynon IFR airplane. (RV-4 and F-1 EVO)  I have flown over 500 hours behind Dynons with lots of actual including low approaches.



Here are my thoughts.

A steam gauge Altimeter, Airspeed Indicator & T/Coordinator are cheaper and a more independent source of backup info than standby glass unit.



An autopilot is very important in an IFR RV.  Both for Dynon failure and for keeping the airplane rightside up when you are looking at charts.



If my Dynon ever fails, the autopilot will come on imeadiately.



If I was unwilling to fly in the clouds without the autopilot engaged, then I wouldn't be flying in the clouds.



I keep an old Lowrance 500 in my "little oh $hit" bag along with a vice grip, screwdriver, some Zip ties, a Mag light, some batteries,  and some other goodies.   (sorry no handheld VHF. I won't have a spare hand to use it anyway)



A second EFIS might be a viable backup for the first, but I could fly to heck and back with a T&B Alt, Airspeed, and handheld GPS.



My greatest fear in an all electric airplane is a lightning strike that fries  everything that is turned on.   That would be a bad day.  I don't have a good answer for that.   If the T&B and the Dynon both quit, I have a big problem.   But I can name several other scenarios that are more likely to cause just as big a jamb.



My $.02



Tailwinds,

Doug Rozendaal





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http://forums.matronics.com/viewtopic.php?p=100030#100030  [quote][b]

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dav1111(at)cox.net
Guest

Posted: Mon Mar 12, 2007 3:36 am Post subject: Glass for IFR

I agree with Doug on the autopilot. While I would not  fly hard IFR without one, I do sometimes fly IFR with the autopilot on and  ready to engage.

  

 As for fear of lighting, after having installed XM Weather  on my GRT moving map overlays, I will no longer fly IFR without XM Weather to  help keep me clear of nasty things that produce lighting and  thunderstorms.

  

 Russ Daves

 N710RV - (RV-10)

 First Flight 7/28/06

 N65RV - RV-6A Sold

    [quote][b]

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