We finally got approval from the LAA to proceed with our build – the RV-14 designs are still going through the final stages of sign-off, but they have allowed us and one other UK-based builder to commence with the project whilst the final issues are ironed out. Rather scarily, that means we have no excuse not to go for it – so here we go!
Our LAA inspector visited the workshop at the beginning of last week and spent some time talking us through the project stages, common issues and mistakes, which was very helpful. We also agreed the points at which he’ll need to come and inspect/approve the work as we progress. We’re very lucky to have found someone who lives close by, so we can ask his opinion relatively easily and he doesn’t have to come far to inspect.
Today we kicked off with construction of the vertical stabilizer. J had already done some preparatory work cutting parts down to size during the week, but for the bulk of it we knew we would be able to work much faster with two people, so we’d set aside what looked set to be a rainy Sunday for building.
The part of the kit we are completing first is the empennage – this consists of the plane’s tail (including rudder, horizontal stabilizer, elevator and vertical stabilizer – helpful image showing these bits here) and the back part of the fuselage.
The kit instructions (basically like a giant, scary ikea book!) start with the vertical stabilizer, which is generally acknowledged to be one of the most straightforward parts with which to begin the build.
The first thing we needed to do was cleco the various bits of metal together and shape them to ensure they all fit properly. This is easier said than done, especially as there’s a metal skin that needs bending around the inner assembly – definitely a job for two people if possible!
I’d never heard of clecos before discovering the world of kit aircraft, but they are incredibly useful little gadgets that we will be using throughout the build. Clecos are used for assembling the structure so you can check everything fits, and align and shape the parts and drill any holes needed. Doing it this way gives you confidence that you’re amending the parts in a way that ensures they will fit when you come to put everything together at the end – that’s the theory, at least!
There are two main sizes we’re using for this stage – the copper-coloured ones correspond to holes drilled with a #30 drill (for a 1/8″ or AD4 rivet) and the silver to #40 drills (for a 3/32″ or AD3 rivet). The sizing is weird, I am still getting used to it!
Clecos have a central piece of metal and two more flexible pieces either side, and a moveable ‘button’ on top. When the button is compressed with special cleco pliers, the two side pieces are pulled in. This makes the cleco small enough to go through the drilled hole. Once the cleco is in and you let go of the pliers, the side pieces expand again and they hold it securely in place. They can be removed again using the cleco pliers. Another incredibly useful invention is the cleco clamp, that can be used to hold together skins of metal that perhaps don’t have holes in them so you can’t use normal clecos.
We’ve quickly discovered that with two people working on the build, it’s essential to have two sets of cleco pliers – otherwise you won’t get the time benefit of having two people working in parallel, and you’ll find yourselves squabbling/losing them all the time. I suspect there will be other tools where we find that’s the case!
The great thing about using clecos is that you feel like you’ve achieved something, when in reality you haven’t done any work! You can quickly pull the parts together into something that looks like it could one day be part of an aeroplane, but your sense of accomplishment is fairly short-lived as you have to take it apart and actually work on all of the bits so they’re ready for actual assembly…shaping, drilling, de-burring, scuffing, dimpling and priming (see steps below).
Here are all the vertical stabilizer pieces held together with clecos – we think it looks a bit like a hedgehog!
Shaping the ribs
Once the structure is held together with clecos, it’s relatively easy to see what re-shaping needs to take place to make sure it fits properly. The vertical stabilizer, like other elements of the plane where a metal skin forms the outer part, has a series of metal ‘ribs’ inside it for strength. In the RV-14 kit, these ribs are already approximately the right shape, but the edges (called ‘flanges’) need to be bent so that they fit exactly flush with the skin when everything is assembled. The edges of the ribs also come slightly bowed in the kit, so they need to be ‘fluted’ (have a small bend put in) to pull them flush with the outer metal skin.
It’s a case of trial and error – look at the structure, take it apart, estimate the amount you need to adjust it by, then make the adjustment and align it again to see if it’s enough. Lesson 1: Always better to bend them too little and keep going, than to bend them too far and have to go back. The latter will eventually weaken the metal and could mean you have to re-order the part and do it all again (not recommended). Thankfully our practice kits already revealed this lesson, so we hopefully managed to avoid screwing anything up too drastically this time.
Assembling the structure with clecos also allows you to plan, mark and accurately drill any remaining holes, so we worked our way around these as well. Luckily for us, much of the RV-14 kit has pilot holes already drilled, so there were only a few that we had to measure and drill from scratch. The rest just require to be drilled to size (the hole enlarged using a slightly bigger drill bit), which goes quite quickly once you’ve set it up properly.
Clecoing the structure together also allows match drilling when drilling holes to size – with it assembled, you drill through all the bits of metal that will ultimately be riveted together at the same time and at exactly the same angle, so your holes should match up well when you come to rivet.
Our inspector already warned us that for every minute of drilling or riveting, there would be about 20mins of setting up first – that was definitely the case today!
Finally, some tools I recognise: files and sandpaper* – thank you, year 9 D&T!
*Actually we’re using emery cloth as it’s metalwork, but still 🙂
When drilling holes in the aluminium parts, small shards of metal can be deposited around the sides – these need to be removed and smoothed down so they don’t scratch other parts and also to avoid them becoming a point of uneven stress when the plane is flown.
The metal kit parts have been partially pre-cut in the RV-14 kit, but whenever metal snips are used to cut them, you get a small bump (or ‘burr’) along the edge every time the snips are reopened. Like the burrs on drilled holes, these can cause damage to other elements or create concentrated areas of stress, so they need to be smoothed out so that the edge is straight and free of sharp and uneven bits of metal.
We have a small electronic scotchbrite wheel for polishing and de-burring in the workshop, which works well with larger pieces as you can run along the edge quite quickly. However, most of the work will be done by hand using different grades of file and finishing off with emery cloth.
It’s hard work but it’s quite satisfying as you can see the difference you’re making. We also found it very motivating that there are such important safety reasons why de-burring needs to happen.
Once we’d got rid of the sharp edges and imperfections on the metal, we scuffed all of the surfaces to get them ready for priming. The primer will adhere much better to the surface if it’s been a little rubbed up beforehand, so we used scotchbrite pads to do this. J found it quite upsetting to ruin a beautiful new shiny surface, but as it will be covered in primer anyway, I guess it doesn’t really matter.
The main market for this make and model of aircraft is in the US, where many builders choose not to prime their parts (or only to do so minimally). That’s fine in a dry climate far from the sea, but I’m afraid that in the lovely damp UK we are forced towards the other end of the scale! The outer skin of the aircraft will be primed and painted right at the end, but any internal surfaces need to be primed as we go along to protect them from corrosion.
We’ve seen a lot of back and forth on the various kit-build forums about which order to do the scuffing, de-burring, priming and dimpling, but given how many different viewpoints exist, we just decided to do what made sense for us today, and as we go along we will probably develop our own philosophy on what works best.
Dimpling & countersinking
Finally (for today, at least), each of the holes that will receive a flush rivet (flat ones) needs to be prepared so that the head of the rivet will sit flush with the metal skin – i.e. so it won’t poke out and interfere with other parts/ruin the aerodynamics.
Universal rivets (with a rounded head) are also used a fair bit on the aircraft, but flush rivets are mainly what’s visible on the outside. On universal rivets, the rounded head sits above the surface, so you don’t need to dimple or countersink. For flush rivets, you need to make space for the head so that it doesn’t protrude above the skin.
In thicker bits of metal, you do this by countersinking – drilling the main hole and then drilling part of the way down with a larger drill bit (specially-designed ones are called countersink tools) to make space for the head of the rivet. In thinner bits of metal, such as the skin, you can use dimpling, which involves making a dish-like impression in the metal into which the rivet head can fit.
For dimpling, you use a dimple die based on the size of the hole you’re trying to dimple. The dies are called ‘male’ and ‘female’ (for obvious reasons I think, see below…) and you set them up so that the dimple in the metal is in the right direction to receive the rivet (in theory at least…we have done it wrong more than once, but thankfully it’s something that’s relatively easy to correct!).
We had to dimple most of the outer skin for the vertical stabiliser, and also along the edges of all the ribs that will sit inside. Most of the dimples were done on a c-frame dimpler, which is the easiest method, but when they’re harder to reach, you have to use a ‘hand squeezer’, or in extreme cases you have to re-purpose the rivet gun to get at the particularly tricky ones. Thankfully we only resorted to the gun for 4 holes, did about 100 with the hand squeezer and all the rest with the c-frame, which saves your arms.
Again, we found dimpling to be a two-person task, especially with the large outer skin – one person needs to hold, but it’s almost impossible for the same person to see the holes that are being dimpled, and even less possible for them to somehow stretch around the metal and do the dimpling themselves. I’m sure this is a task for which solo builders have to ‘borrow a neighbour’.
The next task will be to wash the parts we’ve prepared with a special detergent (to remove marks and residue – including all the fingerprints we’ve created by touching it!) and then paint them with primer, before we move onto the rudder. I expect future posts on the build will be shorter as I won’t need to explain all of the techniques, so well done if you’ve got this far, and stay tuned for more progress!
Hours on build so far: 16*
* As we are working together on the project, we’ll be quoting the time taken in terms of ‘man hours’ – so if we both spend 5hrs working on the project together, we add 10hrs to the total, just as if we each spent 5hrs working independently.