Nutplates on Firewall

[skelrad]

There are a number of callouts for nutplates to attach adel clamps on the firewall. For nutplates that just attach to new doublers, that's no big deal of course. But I'm not sure about the nutplates that attach to the firewall stiffeners. The plans say to drill out a few existing rivets and upsize for bolts, and then install nutplates. Since the firewall is already mostly riveted in place, do you just drill the nutplate rivet holes and then countersink through the firewall stainless and into the stiffener? Obviously that will mean the rivet just blows through the stainless since it's so thin. I'm not sure how else to go about attaching the nutplate to these existing stiffener locations though. Am I missing an approach that's just staring me in the face?

 

[terrye]

Since the firewall is already mostly riveted in place, do you just drill the nutplate rivet holes and then countersink through the firewall stainless and into the stiffener?

Yes, that's all I did. If you don't countersink too deep, the rivet head will also clamp down the SS firewall.

 

[gkochers]

A good location to use NAS 1097 "oops' rivets to minimize countersink depth.

 

[Norman CYYJ]

Yes, that's all I did. If you don't countersink too deep, the rivet head will also clamp down the SS firewall.

The rivets that are holding down the nut plates are primarily just stopping the nut plate from turning making it so that you don't have to have a wrench on the other side. The object that is being held down also adds some clamping force to hold the stainless steel in place which is primarily a fire barrier between the engine area and the passenger area.

 

[AlphaCharlieBravo]

Brandon
I just installed a screw with a washer and nut. No nut-plates at least through the firewall angles. I also have the two access panels in my top skin installed so no issue for access.
A

 

[skelrad]

Thanks all. I went ahead and countersunk through both layers. It left more meat on the stainless than I expected, so worked fine.

 

[jjb]

A good location to use NAS 1097 "oops' rivets to minimize countersink depth.

Concur. While definitely not required, NAS1097AD-3, aka “nutplate rivets” work especially well.

One quick turn of a deburring tool or microstop countersink bit in the 3/32” hole is adequate countersink for them. That does not enlarge the hole even in the thin firewall stainless steel, and does not even get to any underlying aluminum angle.

 

[Scott Hersha]

If the nutplate rivets don’t interfere with the installed adel clamp, like in the picture above, you can just use button head rivets instead.