Did you guys reinforce your empennage fiberglass tips for rivets?

[Desert Rat]

Looking at drawing 3 & 6 for the RV7 it looks like if you attach the HS and VS tip fairings per print, you just pop rivet them on with CS4-4 rivets right to the fiberglass. There's no callout for any kind of aluminum backing strip.

Are you guys doing it that way and if so, any issues with cracking the fiberglass? I'm all about weight savings back there so if it works hey, it works. But it just seems a little odd that there wouldn't be something a bit more robust that a thin piece of fiberglass for those rivets to pull up against?

 

[PaulvS]

Looking at drawing 3 & 6 for the RV7 it looks like if you attach the HS and VS tip fairings per print, you just pop rivet them on with CS4-4 rivets right to the fiberglass. There's no callout for any kind of aluminum backing strip.

Are you guys doing it that way and if so, any issues with cracking the fiberglass? I'm all about weight savings back there so if it works hey, it works. But it just seems a little odd that there wouldn't be something a bit more robust that a thin piece of fiberglass for those rivets to pull up against?

I reinforced the emp fiberglass tips by gluing on with epoxy a 5/8" aluminum square at each rivet. The weight penalty is next to nothing and it will stop the rivet potentially pulling through and splitting the glass when it is set.

 

[thehagg501]

I used a half inch strip of aluminum the length of the holes and used proseal to attach.

 

[rvbuilder2002]

All of Vans demonstrators are built per the recommendations in the plans.
There has never been any problems.

 

[scsmith]

The loads are super small. Just rivet them in, no backing needed.

 

[PaulvS]

All of Vans demonstrators are built per the recommendations in the plans.
There has never been any problems.

How do you know that none of the fiberglass holes cracked underneath, since they are hidden? Or are you saying there have never been any problems because nothing fell off?

 

[rvbuilder2002]

How do you know that none of the fiberglass holes cracked underneath, since they are hidden? Or are you saying there have never been any problems because nothing fell off?

If they have never fallen off, there is no warping or distortion, and no cracking in the painted surfaces (in general they look the same as they did when the airplane was new), I would call that not having any problems

Particularly since some of the airplanes I am referring to are more than 25 years old.
Additionally, do you have any idea what those airplanes go through when they spend a week on display at OSH

And since you added the extra weight and spent the additional work time to reinforce yours, how do you know they wouldn't have been just fine if you hadn't?

 

[RV6_flyer]

If they have never fallen off, there is no warping or distortion, and no cracking in the painted surfaces (in general they look the same as they did when the airplane was new), I would call that not having any problems

Particularly since some of the airplanes I am referring to are more than 25 years old.
Additionally, do you have any idea what those airplanes go through when they spend a week on display at OSH

And since you added the extra weight and spent the additional work time to reinforce yours, how do you know they wouldn't have been just fine if you hadn't?

I have another RV that is over 26-years old and has over 3,500 flying hours that has no evidence of fiberglass tip cracking when installed according to designer's plans / instructions without reinforcement. It also has landed in 49-states and been north of the Arctic Circle.

The late great aircraft designer John Thorpe once said: "Only make it as strong as necessary and as light as possible."

 

[bjdecker]

I used aluminum backing strips, aluminum squares, and #6 washers most recently.

 

[PaulvS]

If they have never fallen off, there is no warping or distortion, and no cracking in the painted surfaces (in general they look the same as they did when the airplane was new), I would call that not having any problems

Particularly since some of the airplanes I am referring to are more than 25 years old.
Additionally, do you have any idea what those airplanes go through when they spend a week on display at OSH

And since you added the extra weight and spent the additional work time to reinforce yours, how do you know they wouldn't have been just fine if you hadn't?

Oh dang that means I probably wasted some of my life cutting those little squares and drilling holes in 'em an stickin 'em on... and as for the rest of the build... I also primed EVERYTHING!

 

[RV8JD]

The late great aircraft designer John Thorpe once said: "Only make it as strong as necessary and as light as possible."

John Thorp was a great engineer and designer!

Designer Spotlight: John Thorp

Amy Laboda, John Thorp, Richard Eklund, Piper Cherokee, Thorp T-18, Lockheed, Lockeford, all-flying tail, stabilator, NACA 63A-412 airfoil, Eklund Engineering, Derringer, Lodi Field, spark retarder, Model A Ford, Boeing School of Aeronautics, Rudy Paulic, Thorp Aircraft Corporation, XT-3...

www.kitplanes.com

 

[nohoflyer]

I simply used the pop rivets.

 

[uk_figs]

Per plans, 15 years and 850 hours and seem to be fine.
Figs

 

[HFS]

Two sides to this issue, and all builders choose the path they feel most comfortable with.

My (personal) take on it - reinforcing "washers" is a form of insurance. We want it, we just hope we never need to use it ...

So I used NAS1149 washers P/N FN416P. McMaster-Carr P/N 95229A260, and the whole pack (100 ea) weighed less than 1 oz - not a bad insurance premium.

Bonded them in place with an epoxy adhesive - anything will do if it keeps them in place until the Pop rivet is installed.

YMMV - and may depend (sometime) on your choice.

HFS

 

[Stevea]

Sure, per plans will work. But personally, I never liked the crunching sound heard when pulling a blind rivet or squeezing a standard AN solid rivet in a non-backed up fiberglass hole. Sure the assembly holds up.....but the "crunching" sound is the fiberglass/epoxy matrix (or fiberglass/polyester resin matrix) being pulled apart radially, or being crushed in compression as the rivet is set.