VansAirForceForums  
Home > VansAirForceForums

- POSTING RULES
- Donate yearly (please).
- Advertise in here!

- Today's Posts | Insert Pics


Go Back   VAF Forums > Model Specific > RV-14
Register FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 01-06-2019, 08:32 PM
iamtheari iamtheari is offline
 
Join Date: Nov 2017
Location: ND
Posts: 220
Default Engine mount grounding

The hardware bag for the engine mount was backordered in my finishing kit so I can’t actually put it on my plane yet. But I did prepare it for installation and came up with a question. The plans say to file four of the bolt holes down to bare metal to electrically bond the engine mount to the fuselage. That will electrically bond the engine mount to the bolt, but not necessarily to the fuselage. I primed the longeron assemblies. Should I sand off primer beneath the engine mount nuts, or does the bolt through the hole in the firewall do a good enough job?
Reply With Quote
  #2  
Old 01-06-2019, 10:25 PM
mturnerb mturnerb is offline
 
Join Date: Apr 2015
Location: Ponte Vedra, FL
Posts: 834
Default

There's a grounding strap engine to mount. Section 43, pages 05 and 08.
__________________
Turner Billingsley
RV-14A In Progress
N14VB Reserved
https://turnerb14a.blogspot.com/
Reply With Quote
  #3  
Old 01-06-2019, 11:22 PM
iamtheari iamtheari is offline
 
Join Date: Nov 2017
Location: ND
Posts: 220
Default

Quote:
Originally Posted by mturnerb View Post
There's a grounding strap engine to mount. Section 43, pages 05 and 08.
Thanks. That sets my mind a bit at ease about the results of the step Iím questioning. I am still curious about the step itself, though, which call for filing off powder coat specifically to ensure an electrical bond between the engine mount and fuselage. The ground strap seems like the better solution to that problem and itís already part of the plan, so why the focus on filing off the powder coat here?
Reply With Quote
  #4  
Old 01-07-2019, 12:33 AM
gasman gasman is offline
 
Join Date: Mar 2007
Location: Sonoma County
Posts: 3,485
Default

Quote:
Originally Posted by iamtheari View Post
The hardware bag for the engine mount was backordered in my finishing kit so I canít actually put it on my plane yet. But I did prepare it for installation and came up with a question. The plans say to file four of the bolt holes down to bare metal to electrically bond the engine mount to the fuselage. That will electrically bond the engine mount to the bolt, but not necessarily to the fuselage. I primed the longeron assemblies. Should I sand off primer beneath the engine mount nuts, or does the bolt through the hole in the firewall do a good enough job?
I don't see the need to ground the engine mount to the firewall when the Lord mounts will isolate the motor case from the mount.

I would ground from your firewall battery ground bolt, to the motor case with a very good cable. I used welding cable with crimped and soldered eyes. And a second one from another firewall location. If your motor ground fails, the starter ground path will be through your engine control cables.....

The cable ends did have proper soldering techniques and heat shrink to avoid flex failure.
__________________
VAF #897
2019 =VAF= Dues PAID
Reply With Quote
  #5  
Old 01-07-2019, 12:41 AM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 7,957
Default

Quote:
Originally Posted by iamtheari View Post
The plans say to file four of the bolt holes down to bare metal to electrically bond the engine mount to the fuselage. That will electrically bond the engine mount to the bolt, but not necessarily to the fuselage.
I think that is a misprint.
The actual reason is because powder coat is not very hard.
The small contact area on edge of the tube will quickly compress the powder coating and reduce the loading on the bolt.
__________________
Any opinions expressed in this message are my own and not necessarily those of my employer.

Scott McDaniels
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
Reply With Quote
  #6  
Old 01-07-2019, 02:12 PM
iamtheari iamtheari is offline
 
Join Date: Nov 2017
Location: ND
Posts: 220
Default

Quote:
Originally Posted by rvbuilder2002 View Post
I think that is a misprint.
The actual reason is because powder coat is not very hard.
The small contact area on edge of the tube will quickly compress the powder coating and reduce the loading on the bolt.
That makes more sense to me. Thanks. I just looked in section 40A and the tri-gear instructions don't say anything about this. Page 40B-02 step 3 says of the filing, "This will ensure that the engine mount is electrically bonded to the fuselage." Obviously I filed it off no matter the reason, but now I can comfortably build on without sanding primer off the longeron end pieces...once I get the bolts, that is.
Reply With Quote
  #7  
Old 01-07-2019, 02:49 PM
Mike S's Avatar
Mike S Mike S is offline
Senior Curmudgeon
 
Join Date: Sep 2005
Location: Dayton Airpark, NV A34
Posts: 14,482
Default

Quote:
Originally Posted by gasman View Post
I would ground from your firewall battery ground bolt, to the motor case with a very good cable.
Yep, this...
__________________
Mike Starkey
VAF 909

Rv-10, N210LM.

Flying as of 12/4/2010

Phase 1 done, 2/4/2011

Sold after 240+ wonderful hours of flight.

"Flying the airplane is more important than radioing your plight to a person on the ground incapable of understanding or doing anything about it."
Reply With Quote
  #8  
Old 01-07-2019, 03:28 PM
Avoca1us Avoca1us is offline
 
Join Date: Jun 2015
Location: Reynoldsburg, OH
Posts: 6
Default

Quote:
Originally Posted by iamtheari View Post
That makes more sense to me. Thanks. I just looked in section 40A and the tri-gear instructions don't say anything about this. Page 40B-02 step 3 says of the filing, "This will ensure that the engine mount is electrically bonded to the fuselage." Obviously I filed it off no matter the reason, but now I can comfortably build on without sanding primer off the longeron end pieces...once I get the bolts, that is.
This omission in the tri gear instructions is a serious one. The battery is grounded to the firewall, and the engine is grounded to the engine mount. The engine mount must be electrically connected to the firewall for the engine ground to reach the battery.
Reply With Quote
  #9  
Old 01-07-2019, 03:44 PM
DanH's Avatar
DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 8,078
Default

Forget grounding to the mount. Run one of these...

http://www.bandc.aero/braidedbondingstrap.aspx

...from the engine case ground point (on the right rear) directly to a firewall mounted forest of grounds (link to 48 tab example)...

http://www.bandc.aero/groundblock48-tab.aspx

...and ground everything there.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
Reply With Quote
  #10  
Old 01-07-2019, 04:20 PM
rv7charlie rv7charlie is offline
 
Join Date: May 2006
Location: Pocahontas MS
Posts: 3,343
Default

Quote:
Originally Posted by Avoca1us View Post
This omission in the tri gear instructions is a serious one. The battery is grounded to the firewall, and the engine is grounded to the engine mount. The engine mount must be electrically connected to the firewall for the engine ground to reach the battery.
Not the best plan for a number of reasons.
Potential to magnetize the mount. (Fun with whiskey compass swinging)
More failure points, with corrosion prone materials, between engine and ground.
Potential for somewhat higher resistance path than needed when starting (steel instead of copper).

Probably more, but I'm lazy at the moment.

What Dan said, or just pick up some welding cable, as someone else mentioned. Almost as flexible as the braid, and comes standard with a non-abrasive coating. :-)

Charlie
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 07:15 AM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.