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Skipping the Endurance Bus

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art(at)zemon.name
Guest

Posted: Sun Aug 07, 2016 6:37 am Post subject: Skipping the Endurance Bus

Folks,



Please double-check my logic. I am designing the electrical system for my BD-4C, which is a largely mechanical airplane. Totaling up the typical current draw for everything except pitot heat, I am at 21 amps. Max draw is 28 amps. Since a B&C backup alternator can supply 30 amps at cruise RPM, it seems that I don't need an endurance bus at all. Instead, I would have the following emergency procedure:

 	  Quote: 	
		  In Case of Alternator Failure

Primary alternator OFF
Backup alternator ON
Pitot heat OFF (unless required for flight)

	


I do still need to add a couple of items to my equipment list but neither draws much current: electronic ignition and a second com radio.

Does this make sense? Am I missing something?

    -- Art Z.

-- 

http://CheerfulCurmudgeon.com/"If I am not for myself, who is for me? And if I am only for myself, what am I? And if not now, when?" Hillel

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donjohnston

Joined: 13 Dec 2009
Posts: 231

Posted: Sun Aug 07, 2016 2:51 pm Post subject: Re: Skipping the Endurance Bus

That's the logic I used.



Primary alternator, secondary alternator (20a), battery. 



My final backup is my iPad with Foreflight connected to a Stratus II that should be able to run for at least five hours. 



If I have failures on all of those then someone up there really doesn't like me.

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ceengland7(at)gmail.com
Guest

Posted: Sun Aug 07, 2016 4:51 pm Post subject: Skipping the Endurance Bus

On 8/7/2016 9:36 AM, Art Zemon wrote:

     

      	  Quote: 	
		         Folks,         

         

         Please double-check my logic. I am designing the electrical           system for my BD-4C, which is a largely mechanical airplane.           Totaling up the typical current draw for everything except           pitot heat, I am at 21 amps. Max draw is 28 amps. Since a           B&C backup alternator can supply 30 amps at cruise RPM, it           seems that I don't need an endurance bus at all. Instead, I           would have the following emergency procedure:

         

         

                     	  Quote: 	
		               In Case of Alternator Failure

                                                        Primary alternator OFF                 
Backup alternator ON                 
Pitot heat OFF (unless required for flight)                            

           	
         

                    I do still need to add a couple of items to my equipment             list but neither draws much current: electronic ignition and             a second com radio.

           

           

           Does this make sense? Am I missing something?

           

           

               -- Art Z.

           

           

           -- 

                        http://CheerfulCurmudgeon.com/                              "If                 I am not for myself, who is for me? And if I am only for                 myself, what am I? And if not now, when?" Hillel

             

           

         

       

     	
     The only question would be whether you intend to fly IFR, &     actually need pitot heat. Plan B might be in order, because that     alone would probably take almost half your backup alt's capacity.

     

     On a tangent to that...

     

     A friend who's a retired Pratt engineer built an RV-6A a number of     years ago. His choice of engine monitor had the option of adding air     data, so his regular ASI was hooked to the standard pitot, and the     ASI input on the monitor was hooked to a 'pitot port' installed in     the pressurized section of the cowl above the engine. Airspeed     indications of the two indicators agreed with each other within a     couple of knots, over the speed range of the plane. 

     

     Charlie

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art(at)zemon.name
Guest

Posted: Sun Aug 07, 2016 7:12 pm Post subject: Skipping the Endurance Bus

Charlie,



Good catch. Yes, this will be an IFR airplane. To the electrical load analysis that I have already done, I still need to add the second comm radio and the second EFIS screen, but those are minor loads compared to the pitot heat.

Cheers,

    -- Art Z.



On Sun, Aug 7, 2016 at 7:54 PM, Charlie England <ceengland7(at)gmail.com (ceengland7(at)gmail.com)> wrote:

 	  Quote: 	
		                     The only question would be whether you intend to fly IFR, &     actually need pitot heat. Plan B might be in order, because that     alone would probably take almost half your backup alt's capacity.

     

	




-- 

http://CheerfulCurmudgeon.com/"If I am not for myself, who is for me? And if I am only for myself, what am I? And if not now, when?" Hillel

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nuckolls.bob(at)aeroelect
Guest

Posted: Mon Aug 08, 2016 12:53 pm Post subject: Skipping the Endurance Bus

At 07:54 PM 8/7/2016, you wrote:

  	  Quote: 	
		  On 8/7/2016 9:36 AM, Art Zemon wrote:

  	  Quote: 	
		  Folks, 



 Please double-check my logic. I am designing the electrical system for my BD-4C, which is a largely mechanical airplane. Totaling up the typical current draw for everything except pitot heat, I am at 21 amps. Max draw is 28 amps. Since a B&C backup alternator can supply 30 amps at cruise RPM, it seems that I don't need an endurance bus at all. Instead, I would have the following emergency procedure:



   In Case of Alternator Failure



 Primary alternator OFF  Backup alternator ON  Pitot heat OFF (unless required for flight) 

  I do still need to add a couple of items to my equipment list but neither draws much current: electronic ignition and a second com radio.



 Does this make sense? Am I missing something? 	
	


   

   Do you have a battery contactor?

   The e-bus structure eliminates the load

   of a battery contactor during endurance

   ops.



 



 

   Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Mon Aug 08, 2016 12:56 pm Post subject: Skipping the Endurance Bus

At 10:10 PM 8/7/2016, you wrote:

  	  Quote: 	
		  Charlie,



 Good catch. Yes, this will be an IFR airplane. To the electrical load analysis that I have already done, I still need to add the second comm radio and the second EFIS screen, but those are minor loads compared to the pitot heat. 	


   Have you ever shared a proposed disribution

   diagram? It would be MUCH easier to for

   electron-herders to convert words into

   copper-reality when offering advise.



 

 

   Bob . . .

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art(at)zemon.name
Guest

Posted: Mon Aug 08, 2016 2:46 pm Post subject: Skipping the Endurance Bus

Bob,



Thank you for mentioning the contactor. Yes, I will need one. No, I had not gotten far enough through my design to remember it. And no, I had not realized that the contactor uses significant power to stay closed. I'll add it to the list.

I found White-Rodgers contactors at Aircraft Spruce and the data sheet lists continuous power of 9 or 10 W which I figure to be approximately 0.75 A at 13.8 V. http://www.aircraftspruce.com/catalog/pdf/11-03161.pdf 

Does that sound right for planning purposes?

    -- Art Z.



On Mon, Aug 8, 2016 at 3:52 PM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

 	  Quote: 	
		    At 07:54 PM 8/7/2016, you wrote:

  	  Quote: 	
		  On 8/7/2016 9:36 AM, Art Zemon wrote:

  	  Quote: 	
		  Folks, 



 Please double-check my logic. I am designing the electrical system for my BD-4C, which is a largely mechanical airplane. Totaling up the typical current draw for everything except pitot heat, I am at 21 amps. Max draw is 28 amps. Since a B&C backup alternator can supply 30 amps at cruise RPM, it seems that I don't need an endurance bus at all. Instead, I would have the following emergency procedure:



 	
	
  In Case of Alternator Failure



 Primary alternator OFF  Backup alternator ON  Pitot heat OFF (unless required for flight) 

  I do still need to add a couple of items to my equipment list but neither draws much current: electronic ignition and a second com radio.



 Does this make sense? Am I missing something?

   

   Do you have a battery contactor?

   The e-bus structure eliminates the load

   of a battery contactor during endurance

   ops.



 



 

   Bob . . .  

	




-- 

http://CheerfulCurmudgeon.com/"If I am not for myself, who is for me? And if I am only for myself, what am I? And if not now, when?" Hillel

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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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art(at)zemon.name
Guest

Posted: Mon Aug 08, 2016 3:07 pm Post subject: Skipping the Endurance Bus

Bob,



Here are the diagrams that I have so far: 

https://drive.google.com/open?id=0BzOP2gb9_3RQUHpIMjNfa0NnQW8

The overview is basically my table-of-contents and it has the list of devices with power requirements.

Cheers,

    -- Art Z.





On Mon, Aug 8, 2016 at 3:55 PM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

 	  Quote: 	
		    At 10:10 PM 8/7/2016, you wrote:

  	  Quote: 	
		  Charlie,



 Good catch. Yes, this will be an IFR airplane. To the electrical load analysis that I have already done, I still need to add the second comm radio and the second EFIS screen, but those are minor loads compared to the pitot heat. 	


   Have you ever shared a proposed disribution

   diagram? It would be MUCH easier to for

   electron-herders to convert words into

   copper-reality when offering advise.



 

 

   Bob . . .  

	




-- 

http://CheerfulCurmudgeon.com/"If I am not for myself, who is for me? And if I am only for myself, what am I? And if not now, when?" Hillel

- The Matronics AeroElectric-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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