Enlarging the flap pushrod hole by Bob Collins

When it's time to mate the wings for the initial fitting to the fuselage, it's also time to make (enlarge) the hole in the bottom and side of the fuselage for the flap pushrod to connect from the interior assembly to the flap. On the RV-7A (and I suspect on some of the other models) there are pilot holes in the side skin and and a small hole in the bottom skin to indicate where this operation is to take place. But, for the most part, that's where the instructions end and while there are a few sites that show the finished product, I couldn't really find anything that had a logical progression of steps to result in a hole that was just big enough to do the job, and no larger. As a result, we all tend to go forth and figure it out on our own.

If I could figure out a way to make an online template you could use, I would. Just place it over the holes, trace, mark, cut...done! But I can't so the best I can do is a series of photographs that show what I did.

The first step, of course, is to actually have the wing on the fuselage and the aileron attached to the wing, and held using the bellcrank jig (and in my case, a piece of angle that bisects the tooling holes of the outboard rib) in the neutral position. I connected and tuned both the pushrod to the aileron and the pushrod from the bellcrank to the control yoke, and set the stick to 90 degrees. It has no effect on the flap hole here, it's just that it seemed like a good time to do it.

I reviewed Dan Checkoway's page on the subject to get a good idea of what the hole should look like when completed, and then drilled two pilot holes where indicated and used a step drill to enlarge to 1/4."

I used a Sharpie to indicate the size of the rod end and also mark a relative meeting point between the two holes.

It so happens that when I was back in New England last week, I started the process of straightening up my dad's workshop in preparation for organizing and then selling his considerable tool collection. I found a really nice Dremel set and brought it back to Minnesota with me. Using a small aluminum cutter, I slowly joined the hole on the bottom with the hole on the side.

Basically what I had now is a hole to fit the pushrod through. So I put the pushrod through the hole and looked at the interior assembly to get a better visualization of what had to happen next.

As you can see you have a pushrod going straight up or down -- pretty useless when you look at the interior assembly. It actually slants forward.

This is the same shot (above) from topside, looking down as I fit the pushrod (sans rod end bearings, of course). So, the mission is clear: start enlarging the forward end of the hole with the goal to get put the top rod end bearing on and fit it to the clevis.

And you can see (below) that with a little more Dremel action, I'm getting there:

Then I started getting nervous because it's clear I need to enlarge the hole forward more. But look at the bottom shot (looking up from flat on my back)

It seemed clear to me that with more enlarging forward (to the right in this photo) necessary, that rivet was going to be among the victims. Reviewing Dan Checkoway's picture again, it looked like that was the case with his effort too. But I wasn't sure so I stopped here and posted a message about this on the RV Builders' Group on Yahoogroups. Dan Baier, one of the moderators replied:

Exactly my experience - at least it was so on one side, but strangely, not the other. Go figure. But yes, there'll be at least the two of us with this result, and I also thought that's what Dan's photo showed. (When I was done, I didn't feel the need to do any replacement rivets.)

Armed with that, I attacked the task again. And let the record show that the point at which -- with full down position -- the rod did not interfere with the bottom skin, the hole was right in the middle of that rivet.

Keep in mind, I haven't pulled the battery out of the car here to try various positions (I'll certainly be enlarging more), nor have I shaped any of the holes to accept the rod end bearing when the flaps are fully retracted. That's coming.

As I did this, I thought the rod would travel farther forward as the flaps were retracted. But I was wrong.They rod -- where it enters the fuselage -- appeared to travel farther aft, which is good because I thought I'd originally enlarged the hole too far aft.

Anyway, I ran some wires to my car and retracted the flaps slightly and checked how everything looked.

I retracted them more until the rod end end bearing struck something. Then I took the Sharpie and marked the location where it was interfering, lowered the flaps and removed more skin material.

By the way to help you reference what you're looking at, this is a shot from underneath the fuselage looking outboard between the overlapping flap skin (bottom) and the fuselage bottom skin.

At this point, I began to turn my attention back to the hole on the side, because once you have sufficient fore/aft clearance on the bottom hole, the side hole is what determines how high your flaps can be retracted and the goal here is to have them be fully retracted and lined up with the aileron trailing edge. And, yes, it's true that the height of the pushrod controls that but not if there isn't sufficient clearance in the side hole to allow the pushrod bearing to retracted into the fuselage interior.

So what you want to do here is to take off -- slowly -- more off the top of that hole until you're sure the flaps can't go any higher. This picture below is a difficult one that I took to help me determine whether there was any interference. It's shot straight down from the top of the fuselage.

The top is the inboard side, the bottom is the fuselage side skin.

All seems OK, so now I concentrated on getting everything fine-tuned. That is, raising the height of the side hole to allow full clearance of the rod-end bearing so that the flap would be properly lined up with the aileron when retracted, and removing material around the holes and shaping it to eliminate any possible interference that might hang things up.

And so what I was left with was something like this.

As you can see, my original line that I drew on the side hole turned out to be pretty much correct.

I hooked up the pushrod and adjusted the length to provide proper deployment, and got a nice even line between the aileron and flap.

Now here's where I think I may part ways with some other builders whose sites I've looked at. Here's the flap fully retracted. Again, this is looking straight down into the fuselage.

And here's the flap fully extended.

The pushrod seems to travel just a bit inboard as the flaps are deployed. And it makes sense why. The fuselage outboard skin at this point is curving outward so while the rod is traveling in the same plane, the distance between the edge as it moves fore and aft is going to widen as you move forward. While I like symmetry, I could think of no reason to produce a symmetrical hole here.

One thing: the bolt callout (I think it's a 4-10A) is too short here (at least it was for me)., I also couldn't get a second washer around the bearing. I asked Van's if it's OK to use a thinner washer, and Bruce Reynolds (who really is terrific at providing support, replied, "It is perfectly acceptable to alter the hardware to fit the assembly. We try to get close, but sometimes manufacturing tolerances cause a change." .

With the flaps retracted, according to my SmartLevel, I have a 9 degree deflection. With the left flap fully deployed, it's at 54 degrees, or 45 degrees of travel; that's about 5 degrees more than Van's specs. I notice Dan Checkoway had the same numbers, so I'll have to figure out how to install some sort of stop mechanism at 49 degrees.

I love building my plane.

For further information:

RV-7A ZK-VII Web site (Carl Morgan)
Mike Hoover's RV-9A
Garret Smith's Golf Sierra
Dan Checkoway's rvproject.com