First of all, let’s come to a definition of wire. Of course, we all know what wire is…round metal (mostly round) thin threads meant to either constrain cattle or transmit electricity. I think it is the second one we need to deal with, barbed wire notwithstanding for the first one.

Now, some stuff you may never have considered before. What is the most conductive metal? Another way of saying that is, what metal provides the easiest path for electricity to go from one point to another? Ask that around the chapter barbeque and the most predominant answer will be gold. The predominant answer will be wrong. The correct answer is silver, followed by copper, gold, aluminum and then a whole bunch of stuff we don’t have to deal with.

Silver wire, for those of you who are building reasonable aircraft, is not available. After 65 years in this business, I’ve never seen silver wire.

So, copper wire is our metal of choice. Not quite so fast. Have you ever seen those beautiful roofs in the cathedrals of Europe? Mostly all green. The green is what we call verdigris and is a copper amalgam. They started out copper, but the years of exposure to a polluting atmosphere turned them into literally translated (ver [green] gris [made gray with vinegar]), but hardly what we want on our airplane wires. And verdigris forms on copper nearly instantly on exposure to polluted air.

There is a solution, perhaps not an optimum solution, but a practical one. Coat copper wire with a very-very-thin coat of tin (or tin’s son from the marriage of tin and lead: solder), and then you have an excellent conductor with a thin coat of “pretty good” conductor. The best of all possible worlds.

One more refinement and we are ready to go. Those of you familiar with house wiring know that Romex (solid copper house wire) doesn’t take a lot of flexing or vibration to work-harden and break. Since there is a fair amount of vibration in most of our aircraft, especially those of you “privileged” enough to fly behind a Jacobs radial (they don’t call them “Shakey Jakes” for fun), we had best figure out a way to keep solid wire from breaking.

The best way (so far as we can tell) is to use a lot of very small wires in parallel instead of one big solid wire. We call this “stranding” and it is designated on the wire spool like this: AWG #24 Strd7/32. Thus we have a #24 gauge wire made up of 7 strands of #32 wire wound in a spiral, and it is virtually impossible in the real world to flex this wire enough to break it. Yes, there is a mil-spec that dictates how many times a machine could bend this wire at a given bend angle to break it, but for our purposes (not being willing to sit there bending it back and forth a few thousand times to finally break it), it is not prone to flex breakage.

Somehow along the way, we needed to codify our wires so that the early engineers amongst us could specify what wire size we should use for a particular application. Since the electrical systems evolved prior to the United States’ entry into the world order, our predecessors picked systems for each country according to their measurement systems. It was a cacophony until somebody noticed that nearly every country eventually signed onto the United States system and thus was the universal adoption of the AWG (American Wire Gauge). England, of course not being too thrilled with those upstart colonies that beat them fair and square in 1783, adopted an identical system called the Browne & Sharpe Gauge (aka Birmingham Wire Gauge or Stubbs Iron Wire Gauge).

I think that the above copper wire table (downloadable as a true spreadsheet from www.rstengineering.com) might be a valuable addition to your collection of digital electronic tools.

More of Weir’s Weird Wires next month. Until then…Stay tuned.

The post Hi-Yo, Silver! Away! appeared first on KITPLANES.

I am hoping to catch some readers who are just now narrowing down their final choice for a first-time aircraft kit purchase. This is a big decision that will become a major focus of time and money for months to come. You have probably been doing lots of research to select the best kit that fits your needs. If you feel a little apprehensive, that is a good sign that you are taking this venture seriously! Having once been in this situation myself, let me shed some light on some critical issues that you might not have considered. I don’t want you to fall into an uncomfortable trap that might not be obvious at this stage of your building journey.

A common problem occurs when a kit builder finds they have encountered a construction task that is either confusing or appears too challenging to complete. Or worse, there is doubt as to whether the task was completed correctly and safely. The great news here is that popular kit manufacturers have nearly eliminated this issue over time with better documentation, tech support and building techniques geared toward first-time builders. We all have different talents and abilities when it comes to building. Most kit vendors have designed their products to ensure success for most first-time builders.

What Can Go Wrong?

It is easy to overlook that the kit manufacturer you have chosen does not make the engine you need to install. But because an engine is required for flying, they can steer you toward those engines that might be a good fit for your airframe—those having proper weight, power, etc. They might even sell you the engine for a one-stop shopping experience. You may get an economic advantage with this type of purchase, and at least you’ll know you are buying a recommended powerplant for your kit. Nevertheless, there are some things to be aware of.

That great documentation you used while building the airframe probably does not exist for engine installation tasks (also called firewall forward installation). Ask your kit manufacturer and find out if this is true. I cannot think of a more challenging effort than installing, plumbing, wiring and testing an aircraft engine. You need more and better documentation and tech support rather than less. Sadly, it rarely exists. This is a big bump in the road for many first-time builders.

What Tasks Are Involved?

Engine installation is one of the most complex and fascinating areas of the entire project. Once the large, metal block of an engine is physically mounted, you move on to attaching fuel lines, pumps, hoses, throttle cables, air ducts, ignition cables, batteries—the list goes on and on. If you are not familiar with the skills required for this step (and who is the very first time around?), then daunting is a good word to describe the entire task of engine installation.

Why does it have to be this way? The companies that make the airframe kits don’t usually know what engine you will install—and the engine manufacturers don’t know what airframe is being used. This arena becomes even more challenging when you consider that an engine mount is a custom item that needs to match a specific airframe to a specific engine. Who should design and create instructions for the first-time kit builder on how to install these?

If this is not your first airplane kit, then a lot of these issues are less challenging. But for the first-time builder it can easily be a showstopper when it comes to finishing the aircraft. Even if a company packages and sells all the parts needed for an engine installation, I’ll bet the step-by-step, easy-to-follow instructions on how to assemble it all won’t be included!

My advice to any first-time builder researching aircraft kits is to always find out what instructional help will be available when it comes time to install the engine. Even if the engine choice is not made at the time of airframe building, that issue does not go away.

What Are Your Options?

At the top of the list of kits that simplify engine installation is Van’s RV-12/RV-12iS. Step-by-step instructions detail every nut, bolt, wire and hose used in the airframe kit as well as firewall forward. This kit all but guarantees that the first-time builder will succeed! I am not aware of another kit model sold today that can match its all-encompassing documentation.

While this might look like the perfect first-time builder kit, remember that all things in life are a compromise. Examine this kit’s price tag, single engine choice and low-wing design. If these are not an issue, then you have a great option for a kit choice.

Next on the list of aircraft vendors that do a reasonable job of supporting firewall forward installation are those that strongly recommend a specific engine model. As an example, Sonex Aircraft has traditionally urged builders to use the engine they supply (the AeroVee) in their Sonex aircraft kit. If you go this route, you receive good instructions on how to not only assemble that engine (the engine is a kit!) but also very specific instructions for installation. Again, the drawback is that you are limited to using just this engine if you want this very high degree of firewall forward instructions.

The next and largest category of kit manufacturers is those that recommend a limited choice of engines that they will “support” in their airframe kit. What this usually means is that the kit manufacturer has assembled and sells a package of firewall forward components that are needed for a specific engine. With this package you have everything you need to complete your engine installation—and hopefully the package includes some documentation. Ask to preview this documentation before you buy. Is there enough detail for you to complete the installation? I can almost guarantee it will not be in the form of step-by-step details like the airframe instructions may have been. Hopefully, the kit manufacturer will provide support if you need it. By using their engine components, they should be able to help you if you get stuck.

Compare this to purchasing an engine model that has no prepackaged firewall forward components, even if the airframe kit vendor agrees it can work. You are then on your own to find the right parts. This is a common path toward failure for many first-time builders.

Another category of engine installation support comes from custom engine manufacturers that have tried to make it easy for you to install their powerplants. This effort includes firewall forward component packages, documentation the engine manufacturer produces and videos showing typical installations. In some cases, a great engine may not be that great if you struggle to get it installed correctly or don’t understand how to wire and plumb it.

Ask to preview the documentation so you will know in advance what you are getting into. Do not rely solely on promises from the vendor as to how easy it is to get it installed. Also do a bit of research, online and by talking to other builders, to be sure you will get the support you need.

Be nice to yourself by making it easy to succeed as a first-time builder. Choose your engine wisely. Plane and Simple!

The post Where Are the Instructions? appeared first on KITPLANES.

Twenty-four years ago, a very refined version of CircuitMaker/TraxMaker was released and was nicknamed CMTM2K (CircuitMaker TraxMaker 2000). Several particularly noxious bugs were replaced with elegant solutions to the program, and it has been my go-to (for the last 24 years) when I wanted to make a prototype PC board.

In 2001 I came by this relic of an elderly 1958 Cessna 182A that I rescued literally from chickens roosting on the rear seat and the wings in a farmer’s barn rafters. Total disaster. Nothing to do but to rip out all the innards (including the wiring) and start from scratch. It may not qualify as a homebuilt, but not a stitch of fabric or a centimeter of wire remained inside. It was then coated inside and out with zinc chromate and painted with the best automotive paint I could find.

But I digress. It also got completely new wiring along with some new and some upgraded avionics. The documents I got with the paperwork were sketchy as to the old wiring, so this was going to be a project from scratch. The saving grace was that this was a two-year project and by the time I got around to doing the wiring, CMTM2K had been released. Even better, the authors of CMTM2K named me a beta tester and authorized me to distribute it to anybody I thought would help work out the bugs in the program.

I drew the electrical system of the airplane totally with CMTM2K. I tell you right now, each and every wire, each and every connection and each and every pin got a name, a number and a place in the wiring package, and it remains today in my 182 aircraft documentation both in print and digital format. You can have your own full copy of CMTM2K, including all updates and a full manual, at www.rstengineering.com and then to CMTM2K. It’s a 45MB file, so it may take a while.

The problem, of course, is that a PC board layout program has no need for alternators, starters, nav/coms or ADS-Bs, so those devices had to be added to the library. Piece of cake. CMTM2K allows you to make as many new devices as you wish with as many pins as you wish. Takes you 10 minutes to make a relatively complex new “part.”

The rest of this column will explain why these “homemade” parts (done the way the downloaded manual describes) let you draw your homebuilt electrical system to your heart’s content.

What Does It All Mean?

Let’s take a look at the drawing. What a spaghetti diagram! Not really. Let’s start from left to right.

That little symbol in the upper right-hand corner is a 3-amp “keep alive” circuit breaker, which is what the FAA allows directly from the battery without a master Battery On switch. It is generally used for a clock or other device that draws a small amount of current but shouldn’t need to be reset on every flight.

To its immediate right is an 8-pin screw-type terminal strip for connecting wires that may need to be reconnected someday. Pin 1 at the top is a 5-volt incandescent bulb connected by a half-watt 33-ohm resistor to Pin 2.

Pin 2 is connected by a wire to the “Reg” connector of the alternator. Just before it connects to the Reg connector, it has a small dot on another wire to a 75-ohm resistor and another wire headed up to the Regulated terminal of the voltage regulator. That little dot means that those two wires are connected. (Sloppy work, Weir. How am I supposed to know 23 years later that the square box in the upper right-hand corner is the voltage regulator? Deduct 10 points from your score.) As a contrary example, note that the same wire from Pin 2 crosses a wire to the overvoltage relay but without a dot. When two wires cross without a dot the wires are not connected.

Flow is not always from left to right. Note that the alternator output is connected to the aircraft battery through the ammeter and master relay directly to the battery.

There are 10 such sheets in the N73CQ file, one for each instrument or radio in the aircraft. Changing an instrument or a radio? No big deal. Just take the schematic file for that particular device and change it to reflect the electrical change. Of course, there will be a notation in the regular logbook of the weight and balance change, yes? Please?

There are some items that may show as a “wire” on the schematic but may not technically be a physical wire. Both the alternator and the starter show a wire going from the Gnd (ground) terminal to what we affectionately call “ground.” Universally in a metal ship, “ground” is the metal airframe, so these two large items have bolts to the airframe engine (and then through the mount) to the airframe. Likewise, the battery is shown with the (-) minus terminal grounded. There’s also a bolt and terminal to the airframe close to the battery. In fabric and glass ships, this “ground” is not so well defined, and each designer has chosen their own personal way of making sure that each grounded device has an extremely low resistance to all of the other grounded devices.

Why is this so important? With a metal aircraft that is properly riveted together, all of the metal sheets are like very small resistances in parallel, which gives very, very small resistances from the tail feathers to the spinner. Very small resistances give very little heat and concomitantly very little voltage drop and very little heat generated. However, in a fabric/glass ship there needs to be one very large conductor from the battery to the rest of the aircraft. Why? Heat.

Let’s presume a 12-volt battery behind the baggage compartment and the starter on the back of the engine. Let’s also presume the designer isn’t as well up to speed on Ohm’s law as you and I, and he takes a #10 wire from battery to engine—about 1Ω. When the starter kicks in, it draws 100 amps. Now P=I² x R, so that wire is going have to dissipate about 1002 x 1 or 10,000 watts. That’s going to melt a lot of plastic and set a lot of fabric on fire, so we now have to balance putting in a fatter wire (more dead weight) and heat reduction.

Here’s a little teaser to end this month’s column. If any of you can tell me why the 182 was renumbered 73CQ, you’ll receive a hundred bonus points. More later. Until then…Stay tuned…

The post CircuitMaker for Aircraft appeared first on KITPLANES.

The effect that COVID had on the homebuilt industry affected almost everyone. Parts, if you could get them, were often backordered for months—or years—and costs ballooned terribly. Glasair Sportsman and GlaStar builders were especially hit hard. While the shutdown of the company’s exalted Two Weeks to Taxi program garnered the headlines, DIY builders were orphaned indefinitely while the company regrouped for better days.

Sometime mid to late 2023, a thread emerged on the Glasair Owners’ group from builders seeking options for obtaining 521-1501-003 static ports. While most static ports are pretty basic—a flange with a small hole, or in the case of RVs, where a pop rivet (sans mandrel) replaces a bucked rivet—the Glasair design has a beveled segment that bisects the centerline of the port. This adds more than a minor complication to the machining process. According to a post by Arlo Reeves, “The shape was arrived at…after flight testing.” And so it was that this small and relatively unassuming little part was holding up progress for about two dozen builders.

Suggestions popped up for various solutions and one builder, Jan Detlefsen, even had a port 3D printed in aluminum. Eventually, builder Brian Hoffman from Michigan stepped in and offered to machine a batch based on a drawing that was derived from a factory part by another builder, Gus Gustavson.

In between all this, KITPLANES’ web editor, Omar Filipović, asked if I would be interested in looking at the part for a Home Shop Machinist column and (hint, hint) possibly make a few extras. I was happy to tackle the idea of how to make it in the home shop, but I am not set up for production. If it came down to it, I might have been persuaded to make a few for the most urgent in-need owners. But as it turned out, Brian offered to make as many as the community needed. Brian is what I call an “orphan part angel.” As those who got static ports from him know, the price he charged was a fraction of what the lowest-priced job shops wanted. So, basically, he did it for free (at least in terms of labor). If nothing else, it shows the value of having a solid owners group to support whatever kit you decide to build.

The challenge to making the static port was, as mentioned previously, machining the bevel per the dimensions in the Gustavson sketch. When you’re working from a sketch, where no tolerance limits are provided, it leaves no room for error! Machinists prefer to have engineering drawings over sketches. In other words, a drawing with not only the necessary dimensions, but general tolerances (except where noted to be higher or lower than the general tolerances), as well as specifications for edge treatments, surface roughness and finishing. So, when making a part or parts from a basic sketch like this, you need to take a few moments to think, Do I need to make this exactly like the sketch? Are the dimensions nominal (see sidebar below)?  In the case of the Glasair pitot static port, the bevel feature is obviously critical. Why else would it be there?

To get the bevel right, I spent some time making up a fixture block to clamp the part for milling the face. This solved two problems: how to hold a round part in a vise for milling and how to keep everything square.

The post Orphan Part Angel appeared first on KITPLANES.

Many of you may know my real job in life was in technology. For many years I had responsibility for large data centers, including financial services. As you can imagine, there was not a lot of tolerance for downtime. In the connected world in which we live, money is changing hands 24 hours a day. There is no good time to have a failure. I feel the same about aircraft and that has influenced my thinking when building.

One of the lessons I learned early was that backup systems should not be of the same design or manufacturer. The best example in aviation was with the F-22, which had supposedly the most tested aviation software in history. On its first deployment to the Pacific theater, all the systems in the aircraft went belly-up when they crossed the international date line. Luckily, they were escorted back to Hawaii by the tanker.

Sparks and Gauges

I think the two most critical systems in our amateur-built aircraft are the flight instrumentation systems and the ignition systems; I try to lower the risk tolerance as much as possible for each of those systems. As an example, in our RV-10 I have dual Advanced Flight Systems 6600 EFISes and dual ADAHRS. For one backup I have a Garmin G5, which is also wired to the screens in case of a rare failure of both ADAHRS units. On top of that, the Avidyne IFD550 has its own ADAHRS and synthetic vision. The autopilot is a TruTrak Sorcerer, which can fly a full instrument approach whether it is coupled to the EFISes or just to the Avidyne. The EFISes and the G5 also have their own independent backup batteries. I think the chances of a common failure between all of them should be quite low.

For the ignition systems, I have one electronic ignition system and one magneto. I have used this same setup in all my aircraft except for those equipped with the Rotax engine. We are seeing an increasing number of aircraft through the shop that have dual electronic ignitions and I am not yet comfortable with that configuration. I will share my reasoning.

First, I do agree with the extra benefits that come from electronic ignition. From my own experience, the addition of an electronic ignition system seems to help with starting (especially hot starts), the engine seems to idle better and fuel consumption decreases. There’s also enough evidence that most of the benefit, perhaps even 95%, comes with the addition of the first system and not much is gained by adding a second one. So, in my mind, the addition of a second electronic ignition system probably increases the risk factor more than it increases the benefit.

I have used all the different electronic systems currently available and have seen failures from each of them on customers’ airplanes. Some have been teething problems, some have been due to lack of maintenance and others were due to installation problems. It doesn’t make them bad, or even one better than another one. Most recently I had a failure of an electronic ignition system in my helicopter that forced a precautionary landing. It turns out that was due to an untested application problem.

Keep the Mag?

My practice has been to install one electronic ignition and one magneto. Magneto, you say? I can hear the groans! Here’s my logic: If I have smoke in the cockpit, I want to be able to turn off the master switch and sort it while not having to worry about the engine. Yes, I know some ignition systems are supposed to be connected directly to the battery, but what if that is the wire that is burning, or it becomes compromised? Some of the wiring I’ve seen in amateur-built aircraft (and even certified ones) is atrocious. Owners with the self-powered version of the E-MAG systems are muttering that it doesn’t matter if the ship is powered but what if that P-lead wire burns and goes to ground? That will shut down a so-called P-MAG system.

The other advantage of magnetos is that they have millions of hours on them in the field. With proper maintenance, they have a proven high degree of reliability. I think electronic ignitions could achieve the same degree of reliability eventually, but it will be a while before we see enough hours on them across all the varying applications seen in amateur-built aircraft. For the record, I was glad that I did not have two of the same electronic ignition systems on my helicopter when the one failed, as the magneto allowed me to maintain enough power to make an uneventful landing. My experience with this brand of ignition system in the airplane world has been great and I probably would not have thought twice about having two of them if I was inclined to use two electronic ignition systems.

Something for the Non-Builders

There’s another facet that influences risk tolerance in our amateur-built aircraft—the number owned by non-builders is rapidly increasing. We see many on their third or fourth owner. Most of the new owners do not understand the details or inner workings of their aircraft and most of them do not even have a POH (Pilot’s Operating Handbook) or wiring diagrams. In more than one instance, I have seen aircraft equipped with dual electronic ignition systems that require a backup battery and the owner had no idea of how to test it or where it was located. In multiple cases, the backup battery was old, corroded and nonfunctional and an aircraft electrical system failure in flight could have stopped the engine, too.

I’m not here to say my way is the only way, but for me, it is about risk tolerance. All these systems, including magnetos, have specific installation and maintenance requirements. They range from periodic inspections, required parts replacements including spark plug wires, forced-air cooling and even paying attention to service bulletins, especially mandatory ones.

Even in the certified world there are some unknowns as to the potential impact of electronic ignition and high-compression pistons on things such as propeller hubs. In our amateur-built world it seems as though the variations are endless, so no doubt it will take even longer before we have enough data to understand all of the consequences.

For those of you with dual electronic ignition systems, I would encourage you to make sure you understand the installation details in your aircraft and the specific maintenance and testing requirements. As a final test, I would encourage you to periodically shut off the master switch (on the ground of course) and verify the engine remains running. There’s a similar test for E-MAG ignitions to ensure the internal power source is operational; do it. For those with a backup battery for the ignition system, a periodic in-flight load test should be run as well. Make sure you have a voltage reading on that battery.

The post Risk Tolerance appeared first on KITPLANES.

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This month’s home shop project was suggested by Matt Burch. Matt sent a couple of photos of a cool time-saving tool he made to probe the center electrode of aviation spark plugs when measuring their resistance values. Mechanics call this type of tool a “third hand,” which simply means it provides the services of a third hand. In the case of checking plug resistance with an ohm meter, this little guy eliminates all the fumbling and bumbling associated with the job.

The design itself is both supremely clever and ingeniously simple—an insulator with a spring and screw center conductor. The screw is a common 8-32 stainless steel flathead and the spring is a 1-inch-long by 0.160-inch-diameter right-hand-wound compression spring from a ballpoint pen. The spring can be found in many Parker and Paper Mate pens. The spring “threads” onto the end of the screw and once assembled inside the insulator, it’s pretty much on for good (think Chinese finger trap). The flathead screw provides a place for the probe to make contact, or if you have an alligator clip for your ohm meter/multimeter, a place to clamp to.

While the tool itself will be of little interest to owners of engines with automotive plugs (Rotax, Jabiru, et al.), this project is perfect for someone just getting into, or thinking about getting into, machine work. As an introduction to basic lathe techniques, it covers the basics of facing, OD turning, drilling and thread tapping. The material used for the insulator is Delrin, which is a DuPont brand of nylon that is particularly fun to machine. It cuts cleanly and you can take aggressive cuts even with an underpowered benchtop lathe or mill. And, where some plastics are prone to melting and gumming up drill bits and cutters, shavings shear off Delrin like peeling a potato. Even in the worst-case scenario—taking too big a cut at too fast a feed rate—Delrin simply tends to go from peeling to slivers of plastic flying off the cutter as the material fractures away from the surface. Yet even with the most aggressive cuts, the machined surface usually still looks fine. The one caveat is when drilling: It’s best to peck drill to keep the flutes from clogging with plastic.

That’s it for now. It’s time to get back in the shop and make some chips!

The post Assistance for Resistance appeared first on KITPLANES.

In my last column, I described construction details for the fuselage section of the Affordaplane ultralight project. (See the April and May/June issues for Part 1 and 2.) Now let’s look at construction of the empennage and wing assemblies. Remember, this is a plans-only type of build using off-the-shelf materials and tools intended for a novice builder. Keep this objective in mind when reviewing the construction and design details. A complete free video series on YouTube shows each step of this construction.

The components of the empennage (rudder, elevator, vertical and horizontal stabilizers) are all formed from 1-inch 6061-T6 aluminum tubing. These tubes must be bent into their respective shapes, matching template patterns drawn on your workbench. (Use some craft paper for this!) What is the easiest way to form these simple bends? I found that using an electrician’s conduit bender did the job nicely. With a little practice, each tube was formed to the proper shape and then fitted with a gusset to join its ends.

Hinges are needed between the rudder and vertical stabilizer as well as the elevator and horizontal stabilizer. The plans call for a simple, strong design using stainless steel L brackets attached with stainless steel rivets. As can be seen in the photo, the L brackets are positioned so they align for joining with conventional AN clevis pins and cotter pins. My job in demonstrating this construction was to show how to locate these hinges for perfect alignment before drilling in place. While this technique for creating hinges is not unique, it was a good fit for this project where we want easy installation using robust components. The hardware needed to attach the tail feathers to the fuselage is also shown in a photo and illustrates how only off-the-shelf hardware is used to reduce the need for complex components.

In a similar fashion, the wings for the Affordaplane were easy to fabricate from 6061-T6 tubing of various diameters. The spars, ribs and bracing structures are all made from this tubing fastened with AN hardware. Using standard lumber, I made a full-size jig for the wing utilizing the workbench as the platform. The Affordaplane wing design has a leading and trailing edge spar made from this aluminum tubing, and the lip of the workbench edge holds each of these spars in their exact position during the build. This results in wings that can be built precisely without requiring advanced skills or tools.

Wing ribs were shaped from half-inch tubing that was formed around a simple wood jig. This could be done by hand and the wood jig provided consistent bends. The ribs were attached to the front and rear spars with gussets and rivets. To obtain a strong connection to the front spar, the forward ends of the ribs were shaped by trimming with a large-diameter hole saw so that they would match the curve of the spar at the attachment point.

After weighing the wings for future reference, the tail feathers and wings were joined to the fuselage and rigged. The elevator-to-stick connection is implemented with a push-pull tube. The rudder is controlled by cables. The ailerons are managed by a combination of pulleys and cables using all AN hardware components. After rigging was complete, everything was taken apart for covering and painting.

Fabric and Paint

Is it fair to expect a first-time builder to be able to fabric cover their aircraft? Yes! My videos show the step-by-step process for covering this ultralight with the extra-lightweight Poly-Fiber fabric using water-based glue from Stewart Systems. While I am not a fabric covering expert, there is no specific task that is difficult in this process. The water-based glue system means there are no bad fumes or dangerous solvents. Scissors, an electric iron and a paintbrush will get your wings and tail covered and ready for flight. I am not exaggerating that this final step of aircraft building (which often scares first-time builders) is quite easy when you can watch videos showing each step of how to cover specific Affordaplane components.

You can’t leave the fabric uncoated—and I was not going to fall into the trap of using expensive aircraft paint—as the Affordaplane would quickly become not so affordable. I experimented with premium, exterior, high-gloss latex house paint. Just a couple coats and it worked great. I was very happy with the result and the ease of applying it with a foam roller. You can spend as much or as little time as you want with colors and designs, and the paint is available at your local hardware store.

In our final installment next issue, we will entertain the need for an engine and engine mount. Can you guess how a first-time aircraft builder is going to fabricate an engine mount? And remember, no welding! The Affordaplane plans do not require a specific engine for this airframe, so builders are on their own to choose one that fits their needs. Remember, our need is that the aircraft makes the 254-pound ultralight weight limit, so this will guide our decision. Plane and Simple.

The post Building the Affordaplane, Part 3 appeared first on KITPLANES.

Pilot holes are the initial holes drilled in a part to establish the position of a fastener. They are smaller in diameter than the fastener that will occupy the hole. These days, many kit parts include predrilled pilot holes.

Matched holes are corresponding holes in mating parts—for instance, the holes in a fuselage side skin and the longerons to which it attaches. When a manufacturer says their kit has matched holes it means many parts (seldom all) are ready to Cleco together right out of the box.

Match drilling pairs parts that don’t have pilot holes to parts that do. In match drilling, a part with pilot holes is clamped to its mating part and the pilot holes guide the accurate transfer of the pilot holes to the undrilled part so they match.

Step drilling is the process of incrementally enlarging a hole to its final size. Also called up-drilling or final drilling.

My well-used copy of the Standard Aircraft Handbook (5th Edition) addresses step drilling and fastener hole sizes. I recommend you give both Chapter 3, “Drilling and Countersinking,” and Chapter 4, “Riveting,” a look-see. Advisory Circular 43.13-1B, Acceptable Methods, Techniques and Practices—Aircraft Inspection and Repair, seems mute on the topics of pilot holes, step drilling and match drilling.

Drilling Pilot Holes

In the absence of kit-provided pilot holes, a kit’s construction documentation will define the location and, often, size of the pilot holes that need to be drilled in each part. Some parts are intentionally bereft of pilot holes. Those parts will get their holes during match drilling, which we’ll get to shortly. As an important aside, you may see large pilot holes (for instance, 3/16-inch diameter) called for in some parts. Though defined as a pilot hole, for accuracy you’ll step drill to that size rather than drill to that size from the first. More on step drilling in a bit.

Drilling pilot holes begins by getting them properly positioned. Measure carefully, mark accurately with a fine-point marking device (an ultra-fine Sharpie on aluminum or steel, a pencil on wood) and then remeasure after double-checking the plans. There’s no point in placing a perfect hole in the wrong place.

Should you center punch? I’ve seen aluminum parts under 0.062-inch thick distorted and damaged by aggressive center punching. Therefore, I recommend drilling pilot holes in material thinner than 0.062 inch without center punching. It’s not difficult if you use a sharp drill bit, guide the point into position with your thumb and keep the drill perpendicular to the part. If you can’t make that work, center punch thin parts as lightly as possible on a hard surface to minimize distortion.

Drill pilot holes with a sharp drill bit of the proper size. What is the proper size? Like everything, that can be debated ad nauseam. Here are my experienced thoughts. For finished holes and fasteners larger than 3/32-inch diameter, a #40 bit is a good start. For 3/32-inch diameter fasteners, a #41 bit works well. An undamaged silver Cleco will pass through a #41 hole, yet enough material will remain for match drilling.

In general, I drill pilot holes in material up to 1/8-inch thick by hand. For thicker material I use a drill press. You’ll develop your own standard based on your ability to hold a drill perpendicular to the material being drilled. Hand-drilled holes are best done on a wood-topped workbench to keep the part from flexing and minimize the burr that forms as the bit exits.

Match Drilling Holes

Match drilling begins by aligning and clamping mating parts together and double-checking their positions against the construction documentation. Double-checking a part’s position against the plans is worth every moment it takes. Drill through each pilot hole to transfer the hole to its mating part. If you’re working in metal, install Clecos as you go. I strive to have a Cleco or clamp next to each hole I’m drilling, and a Cleco in every other hole as I go…depending.

Another area of debate is what size drill bit should be used to drill the matched hole. I use the same size drill bit as the existing pilot hole, but there are some who favor drilling the match hole to the next size; for example, drilling a #30 match hole through a #40 pilot hole. You’ll come to your own method through experience. Paramount is that each hole is round, properly sized and drilled perpendicular to the surface of the parts.

Step Drilling Holes

Step drilling improves the odds the final holes are round and in perfect register. Pilot holes are incrementally enlarged—step drilled—to their final size with mating parts clamped or Clecoed together. It’s important to note that pilot holes can’t be counted on to guide a drill bit through an existing hole in a thick stack-up of parts (more than 3/16-inch, depending on how careful you are), especially in wood, aluminum and other soft materials; therefore, just as while drilling pilot holes, care must be taken to keep the drill perpendicular to the material and centered on the existing hole. If you get lazy you may have a round entrance hole and an elongated exit hole. A typical progression for step drilling looks like this:

#40 bit (the final size for 3/32-inch rivets)
#31 bit (for 1/8-inch flush rivets as dimpling enlarges the holes)
#30 bit (for 1/8-inch protruding head rivets)
#21 bit (for 5/32-inch rivets)
#11 bit (for AN3 Bolts and 3/16-inch rivets)
1/4-inch bit (6.4mm for 1/4-inch rivets)
5/16-inch bit

If you’re looking for a pattern, each step is 20% to 25% larger than the existing hole.

The final drill sizes I provided are referenced in the Standard Aircraft Handbook and are well-proven for both rivets and bolts. I was surprised to find AC 43.13-1B, Section 7-39, “Bolt Fit,” states: “Generally, it is permissible to use the first lettered drill size larger than the nominal bolt diameter, except when the AN hexagon bolts are used in light-drive fit (reamed) applications and where NAS close-tolerance bolts or AN clevis bolts are used.” Note the inclusion of the qualifier “generally” and the reference to lettered drill bits, not numbered bits.

Finishing Up

After the holes in mating parts are drilled to their final size the parts can be divorced from each other, deburred, cleaned and Clecoed back together. Fasteners are installed when directed by the construction documentation.

My high school drafting teacher opened his self-guided classes with these words: “The only rule in drafting is there are no rules in drafting”—before he disappeared into the wood shop to build furniture for himself. There are rules, of course, but his point, obvious even to a high school freshman, was that when the existing rules don’t work, do what makes sense within the scope of accepted practice. And so it is with aircraft construction. As always, your kit’s manufacturer should be consulted when you have specific building questions. Now, let’s recess for an online Question and Argue session. Wear layers, in case it gets hot.

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My initial thoughts were one of two things: Either something had gotten changed/broken with the cooling systems, such as baffles or the plenum, or perhaps it was a configuration system with the new panel. Examination of the engine compartment revealed nothing was amiss. The new Garmin panel requires proper configuration of the CHT and EGT thermocouples for accurate temperatures, and I verified the configuration was correct for the J-type thermocouples that were installed.

One other thing had occurred since the panel upgrade—we had installed a SureFly electronic ignition system. Occasionally I have seen electronic ignition systems cause higher CHTs, and I had configured this SureFly for variable timing during the installation. We verified the configuration on the SureFly was correct and that both it and the magneto were timed properly for 23° before top dead center. Yes, over time we have found that the six-cylinder Lycoming engines perform better at 23° of ignition timing versus 25°.

So, the next step was to put on my thinking cap and ponder what would cause high CHTs. Since it wasn’t the ignition timing, there was a high probability it could be lean-running cylinders. My next thought was to check the intake gaskets and O-rings. This one had a cold-air induction intake system, so there were O-rings at the bottom of the intake tubes versus the hoses that are usually installed. Sure enough, they looked horrible and I could see some blue stains from the fuel around a couple of them.

Interestingly, the customer stated that the panel upgrade took about 10 months, during which time the aircraft was not flown. Bingo—the seals had all dried out. Boy, they had really dried out. It took quite a bit of scraping and wire brushing to get the gaskets off the cylinder heads, and on top of that, a couple of the O-rings looked like they had not been installed correctly.

The engine start-up after replacing everything was very telling. The engine idled noticeably smoother and all EGTs were evenly matched. The run-up was also very good, and things were looking very promising. Of course, we were anxiously watching the CHTs as full power was applied.

We took pictures at every thousand feet of altitude while climbing to 5500 feet. The results were amazing. The highest temperature on any one cylinder was around 403° F, and all the temperatures started to decrease above 4000 feet. I was really happy with the results and so was the customer.

The bottom line is that we are more often seeing intake gaskets and hoses/O-rings as being the culprit for high CHTs. For some reason, they are often overlooked during normal inspections. I encourage all of you who are doing your own maintenance to routinely check them every 300–400 hours and, of course, after the engine has sat for any length of time.

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