Matt's RV-7 Project

My friend Paul recently received his DAR designation, and I had the honor of receiving his first unsupervised airworthiness inspection for an amateur-built aircraft.

I had all my paperwork ready, after triple checking it was all in order – even punctuation matters for this part:

I had the airplane all opened up so he could give it a thorough going-over, basically equivalent to an annual inspection minus a compression check:

After all that, nothing was found to be incorrect, missing, or out of place, so the airworthiness certificate was issued and the traditional photo was taken:

So now after all these years, the airplane project has become an airplane, in the eyes of the law anyway. But I still have a few things to take care of before I'll have the opportunity to see if it will really do airplane things.

I leveled the airplane and used plumb bobs to mark the location of the wing leading edges and the center points of all the three wheels. From these marks I was able to measure the arm figures for each wheel, to be used later when calculating the CG. The measured locations of the main wheels ended up being within 1/10" of each other, so I just split the difference and recorded them both as the same value.

Purpose-designed aircraft scales are super expensive, but these days you can buy pretty accurate digital scales for not much money. I bought three of these 660 lb scales from Amazon and satisfied myself, by standing on each one in turn, that they were probably accurate:

I made some ramps to help me roll the airplane up onto the scales, by gluing together some thin plywood in a stair-step manner:

I cut these to size and rounded the corners of each step – they actually work pretty well, and were cheap to make:

I installed all the removable pieces of the airplane – cowl, covers, panels, interior, and seats – and rolled the plane onto the scales for an initial weight check. This didn't give me accurate weights for each wheel, but I wanted to double-check the total weight before getting too far along:

Then I leveled the airplane and weighed it again, which gave me a proper weight figure from each wheel. Using the measured positions of each wheel, I made a little spreadsheet to calculate the empty weight and CG position.

The airplane is heavier than I'd hoped, which is not a surprise, but it didn't turn out as heavy as it could have been. In the future I might look at a lightweight lithium battery as an easy way to save ten pounds, and perhaps a future panel makeover – or even a composite propeller – will make it lighter as well. Still, for now I have enough useful load to carry myself, my wife, full fuel, and some luggage, which is really the main goal.

As for the CG position, it ended up pretty far forward, which is a good thing for the RV-7. I calculated various loading scenarios, and the only time the aft CG limit is a concern is if I have two big guys, empty tanks, and a whole lot of baggage – not a common scenario, thankfully.

I have to pull everything apart again for the final inspection, but first I had to take a picture of the airplane in the highest state of put-togetherness that it's ever been so far:

I obtained a pair of vinyl N-number decals from Aerographics, and a properly-marked data plate from Aircraft Engravers. I riveted the data plate under the horizontal stabilizer, and stuck the decals on the aft fuselage. For the N-number I used my (and Mary's) initials instead of the traditional "RV" suffix, since it seems like half the CTAF traffic around here is "something something Romeo Victor".

Also from Aerographics, I picked up a set of warning labels to hopefully help people remember not to stand on the flaps:

I still have a few things left to take care of, but for the most part the only things preventing a first flight are paperwork-related:

Sorry I haven't posted any updates lately… I haven't been able to work much on the airplane, because I was spending all my free time earning my CFI in helicopters:

I decided to investigate the use of Sikaflex for sealing the windscreen fairing to the fuselage and canopy, to make it air- and water-tight. The techniques for using this stuff have become well-known in the amateur-built aircraft world since I started my project. If I were to start over again today I'd seriously consider doing an all-glued canopy, but since I already had the fastener holes drilled, I decided I'd more or less follow the plans for the actual windscreen attachment and use the glue only for sealing purposes.

I ordered a half-pint each of 205 Aktivator and 209D Primer, and two tubes of 295UV sealant. Since I didn't want my first experience with this stuff to be on my practically irreplaceable canopy, I decided to do a quick test using a scrap of aluminum and a piece of plexiglass from the local building materials store:

I masked a bond line on the plexiglass and a matching one on the aluminum, and used an acid brush to apply the activator, followed ten minutes later by the primer. I also applied activator and primer to a second area on the aluminum that I didn't plan to glue, just to see how the coverage would turn out. Then after waiting 30 more minutes I applied the sealant to the bond line, cleaned up the squeeze-out, and clamped the pieces together. The last thing I did was to put down a few random dabs of sealant in areas where I hadn't applied primer, so I could see how hard it would be to remove sealant if I got some in a place where I didn't want it.

24 hours later, it looks pretty much the same. The sealant has cured to the consistency of hard rubber, and the primer-only areas are glossy black with some faint brush marks visible.

As I was lead to expect, trying to break the sealant bond just resulted in bent aluminum and broken plexiglass. This stuff really is amazingly strong.

It was quite easy to remove cured sealant from un-primed areas (compare this photo to the one above). However, what's not possible is removing the primer once it's applied, or removing cured sealant that is stuck to the primer. So in fact applying the primer will probably be the most fiddly step, since it seems to stick forever to anything it touches. I'll also have to do a better job of masking the glue lines than I did with this test – note the ragged edge where I was lazy sticking down the tape.

The glued joint looks fairly nice when viewed through the other side of the plexiglass. I was worried I'd have to go to the trouble of masking and painting the reverse side of the glass to avoid having to look through the windscreen at the back of an ugly glue joint, but I don't think that will be necessary.

I wasn't totally satisfied with the amount of primer-bleeding I was getting with garden-variety blue masking tape, so I took a trip to the local automotive paint supplier looking for 3M #218 tape, which is supposed to be better for Sika masking. They didn't have any of that, but they did have some very purple 3M poly tape which I decided to test. I masked off a strip and applied activator and primer, then pulled the tape on one side immediately:

I pulled the other piece of tape the next day. Both methods seem to provide adequate results, although obviously it's better to pull the tape with the surface still wet to get a good clean line. For now I'll plan to use the purple stuff for the final glue-up.

Despite the fact that I put down paper and tried not to spill anything, I still managed to get a few drops of primer on my workbench, which seem to be resistant to my entire arsenal of solvents. Further warning that I'll have to be extremely careful with the primer.