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  #1  
Old 10-09-2018, 08:53 AM
bkmerrill bkmerrill is offline
 
Join Date: Mar 2013
Location: Houston, TX
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Default VS Cat Whisker Question

Doing some research/planning and starting to fab doubler for AV-520/CI-159C to be mounted on VS-1006 (not intended to be a debate on archer wingtip antenna). Couple questions/considerations (would like your input):
1) FAA AC 43.13-1B Section 4 calls for 1.5x thickness for reinforcement/repairs for cracks (see Figures 4-21&22, for example). Assume would use similar for antenna doublers? In this case, V-1006 is .025", so .040" should be adequate? Or should I go to .063? Want adequate structural support, but minimal weight or impact to potential flutter characteristics.
2) AC 43.13-2B 309(b)(2) and (b)(4) on antenna installation state: (2) structural backing plate highly recommended (duh) and if they do not attach to load carrying structure, do not provide structural load support. (4) Sandwich the aircraft skin between the antenna base plate and the internally mounted backing plate. With this in mind, I see three potential configurations:
a) Doubler & antenna sandwich VS-1006 (per 2B(309)(b)(4) above).
b) Doubler and antenna atop VS-1006.
c) Doubler and antenna atop VS-1006 with doubler tied into front spar.
For this application, have not seen anyone bend up and tie into flanges as shown in Figure 4-21. Have seen it only on fuse & wing skin antenna doublers.

Here are some examples of each configuration:
a)
b)
c)
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  #2  
Old 10-09-2018, 09:16 AM
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flion flion is offline
 
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Location: Flagstaff, AZ
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Your first picture is the way to go, to provide adequate clearance for the puck and screw heads (if not flush) to clear the rudder counterweight. My opinion is not structurally tested or analyzed but I don't think you will see any flex there. I like the drilled head screws in the second picture. I don't expect a screw to work loose from the nut-plates but if they did they could interfere with the rudder. As for the thickness, I think .040 should do. Once you get the VS built you will see that it's pretty rock solid as it is; there's not a lot of moment arm on any of the parts for flexing and the skin is thicker than, say, the rudder skins just for that purpose. Again, this is without any formal testing or analysis but is what I am doing on my project based on experience with similar structures in my RV-6A.
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  #3  
Old 10-09-2018, 09:35 AM
bkmerrill bkmerrill is offline
 
Join Date: Mar 2013
Location: Houston, TX
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Thanks for your comments. I do plan to use drilled head screws & safety wire similar to 2 above (only 2 mounting holes on my antenna). I am also looking, like you said, at the total thickness in whatever configuration to ensure top of screw/bolt heads are flush or below top edge of VS-1006 flange/VS skin. I believe it’s doable either way. Here are some dimensions:
-Top face of web to top of flange = .615”
-Top face of web to rivet line (preferred whip location)? = .295”
-Antenna = .44” (whip centers at .22”)
-Doubler = .040” or .063”

In other words, I have .615-.44 = .175” space for doubler (if use option 2 or 3), screw heads, washers, etc.

What are the head thicknesses on the drilled head AN3 bolts?
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Last edited by bkmerrill : 10-09-2018 at 09:56 AM.
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  #4  
Old 10-11-2018, 10:50 PM
bkmerrill bkmerrill is offline
 
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Anyone else have thoughts on antenna doubler thickness and/or configuration?
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