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Dave Yost

I'm New Here
This question is for some one who has built an RV-4 and remembers this operation when building the horizontal stab spar. (HS402 (2) and center bracket HS-410)

Drawing 3a calls for the tongues on HS-410 to be 3 ¼ inches. It then calls out to trim the flanges out of the HS-402 spars, so that there are 41/2 X 31/4 tongues on both of the HS-402s that mate up to HS-410. Well, here’s the problem: The HS-402’s are tapered, and if you remove the entire radius as called out in the instructions and drawing 3a, you end up with about 3 and 1/64th” tongues, NOT 31/4”. This now voids all of the holes (½ and 3/16 tear out spacing requirements) on HS-410. In addition, if you leave HS-410 at 3¼, it WILL prevent the skins from mating flush (top and bottom) to HS-402 out side of the 8 degree bend.

Did anybody else out there encounter this?

If So-

Did you trapper HS-410 to match the taper of the spars? Or did you just taper out side of the bend? What about the spacing on the hole schedule on HS410?

The bad news is I scrapped HS-410 (5 hours of labor); the good news is I caught this before match drilling the spars or I would have scrapped them too. It would be one thing if this was + or – a 16th or so, but we are talking almost ¼ of an inch difference between what the drawing calls for and what is possible with the parts that are in the kit.

Thanks Dave
 
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It's been awhile, but . . .

Hi Dave,

I tapered the HS-410 tongues to match up with the HS-402 tongues. I did have a slight overlap (where the HS-410 tongue was slightly larger than the HS-402 tongue) but I tapered it enough so it would not cause a skin fit issue on the skeleton.

I did adjust the hole pattern slightly to maintain the necessary edge clearance requirements.

Just my opinion . . . as long as you don't rivet too close to the edges of the metal (so you don't develop fatigue cracks) and have quality rivets, adjust these parts as necessary to make it work. I have found little inconsistencies like this throughout the project, and have had to tweak things here and there. The plane still flies great!

What did get me on my first attempt with the horizontal stab, were these two things:

(1) Make sure YOUR elevators match up with YOUR horizontal stab! In other words, double check that the space between your bearings matches up with the space between the brackets.

(2) Make sure you have enough space between the two "sides" of your stab so that it will later mate well with your fuselage. In other words, I'd treat the 5 3/16, 4 1/4, and 3 inch gaps shown on the "top down" view of the stab as MINIMUMs. As it turns out, I added a few small shims on some of my fuselage bulkheads to make the upper skin flow real well, so my fuselage was just slightly larger where the stab mates up. I fixed this by shaving about 1/16 inch from the inner portions of the horizontal stab leading edges.

Hope this helps,

Rick
 
Propblem

Hi Dave

The problem is that you have taken the dimensions of the 410 as being the starting point to work from. In fact this is one of those instances when you have to match drill the parts based on what material is left on the HS 402.

I my case I was left with 3 1/16 slighly more than you. You can as suggested taper the 410 to match the 402, or let it overlap the 402. The important point is that you have at least two times the diameter of the rivet as edge clearance.

I will send a photo of mine to your email, sorry but I cant work out how to post it on there.

Beware though there are many instances where dimensions are given but if you use them you will find insufficient edge clearance. Always offer up the parts before drilling holes!!

I have sent the photo but my confuser did not like your emai address can you confirm you got it.

Regards
WAM
 
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Got the pic, thanks Steve.

Yea, your absolutely correct. I am kind of a "By the book" guy. So, when the book said "fabricate HS-410 as shown on drawing 3a" I did! :D:eek:

I can see I have a little over the horizion thinking ahead of me on this project.


Thanks guys, I know how to proceed now!

Dave
 
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