Section 11-3 Drilling elevator horns but trailing edges are not lined up!

[bertschb]

I'm getting ready to drill the elevator horns (Section 11-3). I taped the elevator counterbalance arms to the horizontal stabilizer as called out in the plans. I then looked at the trailing edges. The trailing edge of the left elevator is 1/2" higher than the right!

It seems to me it's more important that the trailing edges are lined up with each other rather than the counter balance arms lining up with the horizontal stabilizer. I'm thinking the plans should have us clamp the trailing edges of the elevators before drilling the horns.

What do you guys think?

 

[stigaro]

I believe there was a thread here about this a few days ago. Yes, the trailing edges should be aligned and it's not uncommon that the elevator horns are not lined up.

 

[bertschb]

I remember reading a post about the horns not being lined up and folks just said basically none of them are. Mine are off by about 1/8". I'm not worried about that.

I'm concerned about my trailing edges being off by 1/2". The plans make no mention of even checking the alignment of the trailing edges. It just has you tape the counterbalance arms to the HS then drill the holes in the horns. I'm a new builder and it seems like I'm missing something.

 

[PaulvS]

I remember reading a post about the horns not being lined up and folks just said basically none of them are. Mine are off by about 1/8". I'm not worried about that.

I'm concerned about my trailing edges being off by 1/2". The plans make no mention of even checking the alignment of the trailing edges. It just has you tape the counterbalance arms to the HS then drill the holes in the horns. I'm a new builder and it seems like I'm missing something.

I also believe that it is more important for the trailing edges to be aligned than it is for the counterbalance arm positions to be matched to the HS

The instructions in the plans to align the arms would be fine if the parts were perfect, but if there is any twist in either of the elevators or the HS it's not going to work.

So I would check multiple ways to work out why there is a discrepancy. Use string lines pulled along the trailing edges of the elevators to see where they meet. It could also be done with two long straight edges. A digital level at various stations along each elevator will show up any twist. If there is any, then I would average it out and drill the horns so that the elevators are aerodynamically matched.

 

[bertschb]

So I would check multiple ways to work out why there is a discrepancy. Use string lines pulled along the trailing edges of the elevators to see where they meet.

View attachment 53957

I did as you suggested and attached a string to both outside ends of the elevators. Everything looks surprising straight (the trailing edges of the -14 elevators are straight so no need to see where strings meet). Looking at it from the top, back and ends everything lines up really well. It's actually better than I expected. The only thing I noticed is the trim tab is not quite aligned with the rest of the trailing edge of the left elevator. It's off by about 1/16" maybe?

 

[Richard Connell]

A laser level is a very quick and accurate way to check the alignment of the TE too.
Also very handy for general incidence checking, wheel pant alignment, control surface twist etc.
well worth investing in one.

 

[bertschb]

...well worth investing in one.

So far I've spent $9,990.89 on tools for this build. Might as well shoot for 5 figures....

 

[PaulvS]

I did as you suggested and attached a string to both outside ends of the elevators. Everything looks surprising straight (the trailing edges of the -14 elevators are straight so no need to see where strings meet). Looking at it from the top, back and ends everything lines up really well. It's actually better than I expected. The only thing I noticed is the trim tab is not quite aligned with the rest of the trailing edge of the left elevator. It's off by about 1/16" maybe?

That all sounds good but it's puzzling why the counterweight arms are in different positions? If you were to clamp the left elevator so the arm is flush with the HS and then use the string line along the trailing edge to align the right elevator, by how much is the right side arm out of alignment with the HS?

 

[bertschb]

If you were to clamp the left elevator so the arm is flush with the HS and then use the string line along the trailing edge to align the right elevator, by how much is the right side arm out of alignment with the HS?

I actually did that and it's 1/4".

 

[PaulvS]

I actually did that and it's 1/4". I thought it was more than that initially.

The geometry is possibly such that 1/4" at the counterbalance arm equates to 1/2" at the trailing edge, if that is what you initially measured? If so, then I think it would be better to drill the horns with the trailing edges aligned and the cb arm out by 1/4", rather than have the trailing edges out by 1/2". Anyway, this is one of those situations where it is worth measuring twice or thrice and being sure, before committing!

 

[Brantel]

My trailing edges and counterbalance arms aligned well back in the day but the actual weldments did not. (RV-7)

 

[bertschb]

The geometry is possibly such that 1/4" at the counterbalance arm equates to 1/2" at the trailing edge,...Anyway, this is one of those situations where it is worth measuring twice or thrice and being sure, before committing!

Ohhhhh, yes, that makes perfect sense. Sheesh! Thank you so much for your help. I went back and edited my posts.

And yes, I'll be measuring multiple times and have my wife take a look at what I'm doing as well. It seems like quite a few people get this step wrong and I don't want to be one of them.

 

[bertschb]

A laser level is a very quick and accurate way to check the alignment of the TE too.
Also very handy for general incidence checking, wheel pant alignment, control surface twist etc.
well worth investing in one.

Can you recommend one?

 

[Richard Connell]

Can you recommend one?

Someone else here is probably more qualified to recommend one for you. You likely have a much bigger range to choose from than we will ever have where I am.
I don’t think you need to spend too much to get something that will be adequate for home handyman use.

 

[bertschb]

Someone else here is probably more qualified to recommend one for you. You likely have a much bigger range to choose from than we will ever have where I am.
I don’t think you need to spend too much to get something that will be adequate for home handyman use.

OK, thanks Richard. I've never used one and there are a gazillion of them for sale on Amazon. I watched a couple reviews on Youtube. A laser level would definitely work better than string

I'll keep researching...

 

[abaden]

I bought this one: Huepar 3D Cross Line Self-leveling Laser Level 3 x 360 Green Beam Three-Plane Leveling and Alignment Laser Tool, Li-ion Battery with Type-C Charging Port & Hard Carry Case Included - B03CG Pro https://a.co/d/h8q9VHR

It seems to work pretty well. I used it for making sure my steps were at the right angle and even, and for some painting projects around the house. I did some research and couldn’t justify the $500+ name brand ones.

 

[Halleffect]

OK, thanks Richard. I've never used one and there are a gazillion of them for sale on Amazon. I watched a couple reviews on Youtube. A laser level would definitely work better than string

I'll keep researching...

This is a good one. You'll use the relative angle function on the control sticks and control surfaces. https://www.aircraft-tool.com/Detail?id=ATS360

 

[bertschb]

Does anybody else have counterbalance arms that don't line up with each other with respect to the horizontal stabilizer? I went ahead and drilled the holes in the elevator horns and the trailing edges are lined up with each other perfectly but one counterbalance arm is above the HS and the other is below it by about 3/16" on each side when in the "trail" position. It really bugs me but I don't think there is anything I can do to correct it.