Horizontal stab - rear spar cut out

Just a quick question... the plans mention cutting out a portion of the rear spar so the elevator control horn can rotate with the proper clearance. At what point should this be done? Also, I don't see any measurements or anything for how much to remove from the rear spar.

I'm just getting ready to prime these parts, then rivet. Should this be done now or later on when fitting to the fuse?

Thanks!

When you mount it to the fuse, and adjust the elevator deflection, you'll have this opportunity. The fuse is leveled, and the horns are attached to the pushrod at this point. I would not attempt it before then.

You'll remove enough to get the proper control deflection, as specified in the manual.

Joe

Flange removal

I trimmed the bottom flange before assembly. The drawing shows a blockout width of 1" on each spar for a total width of 2" (at least that is the way I read it). I trimmed to a depth just shy of the aft face of the reinforcing bar. I trimmed before assembly so I wouldn't have to worry about nicking the reinforcing bar. I couldn't attest to whether these dimensions ultimately work, as I have not hung the elevators.

aviationgeek84 said:

Just a quick question... the plans mention cutting out a portion of the rear spar so the elevator control horn can rotate with the proper clearance. At what point should this be done? Also, I don't see any measurements or anything for how much to remove from the rear spar.

I'm just getting ready to prime these parts, then rivet. Should this be done now or later on when fitting to the fuse?

Thanks!

Click to expand...

I got kind of stuck on this too when I was working on it, so here is what I did.

First, I checked VAF and found out just where on the plans the cutout on the Rear Spar (HS-603PP) is mentioned. If I recall, it is shown in the upper, left-hand corner of DWG 3 (but check for yourself before making any actual cuts).

Second, although the instructions specify making the cut after the stiffener is installed, instead what I did was to:
cleco everything up,
mark the area to be cut,
remove the clecos,
then make the cut, but make the cut just a tad less than indicated.

I expected that it would be much easier to make the cut before installing the stiffener as opposed to after installing the stiffener.

Third, after installing the stiffener, then I went back and filed out the cut just enough for the horn to function properly.

In retrospect, I think that making the cut before riveting the Rear Spar Reinforcement Bars was the best course.

I hope this helps!

Thanks for the replies, everyone. I may just do it now so that it is done. Might be easier that way. I'll check DWG 3 more carefully, too. I do see the notation where it says to make the cut out, but not any dimensions or anything.

I agree with Joe. You should not make this cut until you see how much, if any, is needed. In many cases the cut is not needed at all.
In any case the cut should not go beyond the reinforcing bars.

Dimension

aviationgeek84 said:

Thanks for the replies, everyone. I may just do it now so that it is done. Might be easier that way. I'll check DWG 3 more carefully, too. I do see the notation where it says to make the cut out, but not any dimensions or anything.

Click to expand...

Look closely at dwg. 3 on the Iso. There is a 1" dimension from the centerline of the stab to the edge of the blockout. Right or wrong, thats what I used.

Fundamental Rule of RV Building:

NEVER cut a piece, drill a hole, or drive a rivet until you have no choice but to do it in order to move on....you will frequently be enlightened about how something needs to be done by some subsequent step - right AFTER you have made the cut or drilled the hole - or driven the rivet. And ....in best John Houseman voice... "you will discover that you did it wrong!"

I'd say wait, unless it is stopping you from proceeding.

Paul

Good point, Paul. As long as it won't be hard to get to/do down the road, it may be best to wait and see what it needs before doing it.

Ah, the wisdom on this board...

Pictures for ref

I had the luxury of having my QB fuselage in the garage at the time, so I cleloed on the parts an marked and cut before riveting things together, my log post for this is here: http://www.mykitlog.com/users/display_log.php?user=rvg8tor&project=403&category=2924&log=47774&row=49

The photo should give you an idea of how much is cut away. I actually cut more than was needed, I just really needed to clear the elevator stop. I cut it to match the opeing in the aft deck which was more than really needed.

This could easily be done later, though you have to be careful to not nick the reinforcing bar, you just want to trim it enough to clear the elevator stop that is there. Oddly enough the elevator stop which came installed on my QB gives me a degree or so more elevator deflection than the plans call for, builder support told me I should be OK but that I could add some material to the elevator horn to limit the elevator travel more. I chose to leave it for now, not flying yet.

Cheers

Thanks, guys. As long as it is easy enough to make this cut with the reinforcement bars riveted on the spar(s), then I see no reason to not wait and make the cut in context.