-14 Rudder

[climberrn]

Any cracks found on -14 rudders? Specifically at the rivets of the forward and rear ends of the ribs?
Ordered a -14 rudder for my -7A and am considering making .020 skins for it during the build. The standard -7 rudder is not holding up well at those rivets with the new 390. Don't mind building a new one but would rather it be my last one on that plane. Am aware of people using the -8 rudder on the -7, but I'm going with the -14 one for a couple of reasons.

 

[bjdecker]

I ran into this on my -7 with IO-360-A1B6 (200HP). When you roll the rudder front edges together, the skin deforms a bit and flexes into the stiffeners just behind the spar. Deburr and rounding the forward edges of the stiffeners will eliminate the potential for cracking due to this. I also applied a little neutral cure RTV (wad of bubblegum) to the areas between the rudder spar and each stiffener.

Mad props to DanH -- I can't draw worth a darn. Here's the idea tho -- side view from the top of the rudder assembly; skin (green), spar (blue), stiffeners (orange)...

Clear as mud?

 

[climberrn]

I ran into this on my -7 with IO-360-A1B6 (200HP). When you roll the rudder front edges together, the skin deforms a bit and flexes into the stiffeners just behind the spar. Deburr and rounding the forward edges of the stiffeners will eliminate the potential for cracking due to this. I also applied a little neutral cure RTV (wad of bubblegum) to the areas between the rudder spar and each stiffener.

Mad props to DanH -- I can't draw worth a darn. Here's the idea tho -- side view from the top of the rudder assembly; skin (green), spar (blue), stiffeners (orange)...

Clear as mud?

View attachment 69841

Got it. Vans also suggested a light coat of pro seal under the forward and rear stiffener rivets. The cracks formed from the rivets. Fine for 700 hours with a 200+ HP high compression parallel valve engine. After the new engine I’m finding small cracks after every long trip. The -14 stiffeners tie into the forward spar so that should help. Also found a couple cracks forming at the aft rivets to the stiffeners.

 

[roadrunner20]

I'm about to begin building an 8 rudder for my 7. Since it's been about 21 years since I built one, seems to me, best practice was to run a bead the entire length of the aft folded trailing edge. I know Vans has recommended placing a daub on the stiffener aft.
Am I misremembering this?

 

[climberrn]

I'm about to begin building an 8 rudder for my 7. Since it's been about 21 years since I built one, seems to me, best practice was to run a bead the entire length of the aft folded trailing edge. I know Vans has recommended placing a daub on the stiffener aft.
Am I misremembering this?

Vans told me to put a dab on the forward and aft edge of the stiffeners. I did a very light coat of Locktite Epoxy Adhesive, E-90FL under the entire stiffeners, and Locktite Epoxy Adhesive, E120-HP under the trailing edge seam (which you don’t have). The E-90FL is very easy to work with in the combo tubes and is actually a structural adhesive, unlike pro seal. Would definitely recommend that over the pro seal for strength and ease of application.

Excess easily cleaned up with denatured alcohol.

 

[roadrunner20]

Vans told me to put a dab on the forward and aft edge of the stiffeners. I did a very light coat of Locktite Epoxy Adhesive, E-90FL under the entire stiffeners, and Locktite Epoxy Adhesive, E120-HP under the trailing edge seam (which you don’t have). The E-90FL is very easy to work with in the combo tubes and is actually a structural adhesive, unlike pro seal. Would definitely recommend that over the pro seal for strength and ease of application.

Excess easily cleaned up with denatured alcohol.

Thanks. I'll look into your suggestions. I'll also take a look back at my builder log to see if I called out what I had done at the time. I have zero cracks with my > 1300 hours of flight.