Horizontal Mods and Reinforcements

51fixer · **Posted:** Tue Nov 06, 2012 9:45 pm

The Navy seemed to do mods to the Horizontals.
What have you seen?
In 1944 Corpus Christi moded the control surface attach brackets by installing steel bushings. I wonder if a few holes would show wear so they did them all as replacements may have been unavailable?

I've heard of Horizontal spars having reinforcements installed. I haven't seen any except for these. The reinforcement was transferred to a new set of horizontals so it is missing from these photos but you can see what they had done-

Rear side had straps from attach fitting inboard.

Front side shows an angle from spar to skin.

The empty rivet holes down the spar show how far it went.
These are from a SNJ-5.

bdk · **Joined:** Sun May 02, 2004 1:16 am **Posts:** 11281

Harvard 4 has a diagonal stiffener on the bottom skin at the inboard end (at least mine did) that ties into the inboard rib with a small clip, so they aren't really interchangeable from side to side.

51fixer · **Posted:** Mon Nov 12, 2012 6:04 pm

The Horiz I have been working on is an early 77-21001 assy. Later they made the 84-21001 metal and the 88-21001 out of wood.

The Navy had changed the lower stringers based on the lower set was anodized.
Looked closer and actually measured them and found they were beefier.
Original angle is .020 alclad bent 90* 5/8" X 5/8" and these are still on the upper skin assy.
These on the lower skin assy are .032 11/16" X 11/16"
All rivets are 1/8" on the lower skin now vs many 3/32" on the orig. with the exception of the fwd spar/leading edge/skin which are still 3/32" countersunk.

51fixer · **Posted:** Sun Jan 13, 2013 11:39 pm

Latest horizontal I'm working on has the J stringers-
One is cracked-

Caused by lifting the tail by the bottom of the horizontal as far as I can tell-

On both sides the bottom skin shows buckling upward as evidenced by the bent stringers.
If you see it on the skin better check inside real close.

And check to make sure your spot welds are still secure for those with the spot welded construction. I've had to add some conventional rivets to tail feathers where the welds had failed.

51fixer · **Posted:** Fri Mar 15, 2013 6:20 pm

I got another horizontal to fix.
A 84-21001 with the J stringers that are spot welded to the skin.
Upper skin is cracked at the last spot weld of the rear short stringer. It emanates from the spot weld circle and is about 5/8" long.
This is next to the 1st rib.
After removing the upper skin the other short stringer is cracked on the stringer itself at the same end next to the 1st rib
The lower skin has a spot weld popped in the same place.

Mark D · **Posted:** Sun Mar 17, 2013 6:13 pm

bdk wrote:

Harvard 4 has a diagonal stiffener on the bottom skin at the inboard end (at least mine did) that ties into the inboard rib with a small clip, so they aren't really interchangeable from side to side.

BDK - Are these the stiffeners you mean?

Mark D

chippie51 · **Joined:** Fri May 18, 2007 6:28 pm **Posts:** 192

We're half way through the rebuild of one of the horizontals for our T-6D. We've found a degree of corrosion which has been taken care of by way of deoxidine and alocrom. However, we do need a centre main and leading edge rib, the one that the middle hinge attaches to. We could make one and have laid out the tools, but before we cut metal does anyone have an un-drilled original available?

Many thanks

bdk · **Joined:** Sun May 02, 2004 1:16 am **Posts:** 11281

Mark D wrote:

bdk wrote:

Harvard 4 has a diagonal stiffener on the bottom skin at the inboard end (at least mine did) that ties into the inboard rib with a small clip, so they aren't really interchangeable from side to side.

BDK - Are these the stiffeners you mean?

Mark D

Exactly!

51fixer · **Posted:** Sun Jul 28, 2013 7:35 pm

chippie51 wrote:

We're half way through the rebuild of one of the horizontals for our T-6D. We've found a degree of corrosion which has been taken care of by way of deoxidine and alocrom. However, we do need a centre main and leading edge rib, the one that the middle hinge attaches to. We could make one and have laid out the tools, but before we cut metal does anyone have an un-drilled original available?

Many thanks

I have gotten some parts from Lance for the Horizontal..

chippie51 · **Joined:** Fri May 18, 2007 6:28 pm **Posts:** 192

Thanks Rich, the bits we needed are now on their way from Lance. Should be able to complete our horizontal shortly.

If my ailing memory serves me correctly recall hearing about a tailplane bracket which should be modded by cutting it in half. Something to do with avoiding cracks forming. Is this correct or have I been drinking too much?

Thanks

51fixer · **Posted:** Sun Sep 15, 2013 8:39 am

chippie51 wrote:

Thanks Rich, the bits we needed are now on their way from Lance. Should be able to complete our horizontal shortly.

If my ailing memory serves me correctly recall hearing about a tailplane bracket which should be modded by cutting it in half. Something to do with avoiding cracks forming. Is this correct or have I been drinking too much?

Thanks

They can do this if there is a space between the spar, and its build up pieces, and the machined groove in the fitting. The crush will cause a crack on the fiiting like shown in the photo-

From a post in the Bald Eagle thread which shows the cut type as called out in the American AD-

Matt Gunsch wrote:

NOS never installed

chippie51 · **Joined:** Fri May 18, 2007 6:28 pm **Posts:** 192

Thanks Rich, that's great. Perfectly demonstrates why the modification was needed. For the modification are they simply cut down the centre line, or is there a prescribed amount of material which needs to be removed each side of the cut?

Thanks

bdk · **Joined:** Sun May 02, 2004 1:16 am **Posts:** 11281

Cut down the centerline. As long as the two halves don't touch.

chippie51 · **Joined:** Fri May 18, 2007 6:28 pm **Posts:** 192

Many thanks gents, much appreciated.

chippie51 · **Joined:** Fri May 18, 2007 6:28 pm **Posts:** 192

One other question if I may?! The parts catalogue calls for 5B3-7 bolts as rudder stop buffers. Not something I've come across before. Does anyone have one at all, or is there an alternative?

Thanks,

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Horizontal Mods and Reinforcements

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