Posted by: Bernardo Malfitano a.k.a. AirShowFan | Apr 22, 2014

An introduction to homebuilt kitplanes

The Glasair 2 being built by the Boeing ONE BCnF project will be certified by the FAA as “Experimental, Amateur Built”. What does this mean? Apparently, some airplanes out there are built by amateurs. How many? Are they safe?

I currently co-own and regularly fly an RV-6A, an airplane that is very similar to the BCnF team’s Glasair. It, too, has an airworthiness certificate that says “Experimental, Amateur Built”. I firmly believe that this kind of airplane embodies a unique combination of safety, performance, innovation, customizability, and service history. These are terrific and seriously under-appreciated airplanes.

This blog post is an introduction to the world of “home-built” airplanes, something that few people – even in the aviation industry – ever think about. By the end, I hope that you will realize why so many pilots love these airplanes and would not want to fly anything else.


 

Entrance door to 787-8 prototype at Farnborough
[Photo by MilborneOne, licensed under Creative Commons]

“EXPERIMENTAL”

You may have noticed that, during flight tests of new Boeing airplane models (such as the 787, 747-8, now the 787-9, and soon the KC-46), the word EXPERIMENTAL can be seen over the entrance doors and in other locations.

What does this mean? To make a long story short, it means that the FAA has given the airplane a “special” airworthiness certificate: Enough analysis has been done of the airplane’s structures and aerodynamics, enough testing has been done on its systems and materials, and enough of its components’ design mimic those of successful airplanes from the past, that the FAA says that it’s safe enough to go flying. However, the airplane has not yet met all the criteria required by an FAA-certified commercial airliner, such as demonstrating the capabilities of its brakes, wing structure, the Vmu, its behavior in icing conditions or while flown over-weight or over-sped, etc. In short, everything about its design says that it should be a fine airplane. It just hasn’t demonstrated yet how it behaves in all kinds of tricky situations – and these demonstrations are something that must be done before a paying passenger can get in.

But demonstrating all these capabilities is very expensive. The tests done to certify the 787 added up to many many millions of dollars, and this is a non-negligible fraction of the price of each airplane once the model starts being delivered. For airplanes meant to be sold in smaller numbers, the cost of certification becomes an even bigger fraction of the acquisition price.

Airplanes that will only ever be flown recreationally or for research purposes, i.e. that were never intended to transport paying passengers, often remain “EXPERIMENTAL” for their entire lives. Their “special” airworthiness certificates are not temporary.

“Experimental” certification brings us many of the most fun aspects of the aviation world. If you go to an airshow and enjoy watching ex-military airplanes flying around (whether it’s a piston-powered B-29 or Spitfire from World War II, or jet-powered MiGs or AeroVodochodys from the 1950s-1970s), many of them are certified as Experimental and carry special airworthiness certificates. Many research aircraft used to test new concepts or to break records, such as Burt Rutan’s amazingly fuel-efficient airplanes (Voyager, Catbird, Boomerang… not to mention, SpaceShipOne) are certified as Experimental.

In fact, the freedom to fly an airplane that is Experimental – that does not need to be tested as rigorously as an airliner – is what has allowed for much of the aeronautical innovation over the past few decades. Roadable airplanes (a.k.a. “flying cars“), parachutes that are large enough to gently lower the entire airplane to the ground in case of catastrophic failure, even the use of composite construction… all were pioneered by small groups of people whose budgets were orders of magnitude smaller than Boeing’s, and who could only afford to develop airplanes that were certified Experimental.


 

Zenith Zodiac kit
Zenith promotional image of Zodiac 650 kit. Some assembly required!

HOMEBUILTS

Throughout the history of aviation, it often happened that a person or small group had the creativity and resources to develop and build an airplane, but did not see enough market demand to create an airplane factory to mass-produce it. These people would then sell their airplane drawings: It would be up to the customer to build the airplane. This started with Santos Dumont’s Demoiselle in 1908, and still goes on today. That was the birth of the homebuilt airplane.

Homebuilt airplanes’ engines are nearly always supplied by a relatively large manufacturer, typically the same engines used by factory-built airplanes. Some of the harder-to-make components might also be supplied by professional shops, which may or may not be affiliated with the group that originally developed the airplane. There exist many independent third-party companies that offer products and services to help people build their airplanes.

Starting around 1970, when some of these airplanes started selling in large numbers, some companies started supplying nearly-complete airplane kits, including almost all components for the airplane. Many modern airplane kits are said to include “everything that does not come in a jug” (i.e. paint, oil, fuel, etc.). In other words, most builders nowadays do not have to fabricate any components at all, just assemble them. These are essentially “Ikea airplanes”.

Old-fashioned plans-built airplanes take thousands of person-hours to build: wood has to be cut, sheet metal has to be bent, steel tubes have to be welded, fiberglass has to be laid up, and so on. Kits with pre-formed, pre-welded, pre-molded, and/or pre-machined parts then brought the build time down to the range of approximately a thousand hours. These are the most popular today, and include the Glasair 2 being built by the ONE BCnF team. The most modern (and most expensive) “quick build” kits, however, come with pre-drilled holes and other features that make it possible to assemble the airplane in just a few hundred person-hours. The creators of these kits sometimes even allow customers to visit the factory to build their airplanes under professional supervision. (Thanks to Lean manufacturing principles, Glasair has managed to get their build process of their latest kitplanes down to two weeks of full-time work. To the many thousands of people who have spent years putting together a homebuilt airplane, two weeks is nearly unbelievable. Of course, if you have a sufficiently large group of people, with the required skills and centralized management, it’s possible to turn a kit into an airplane in one week).

Because they are not built by professional mechanics/machinists, these kit-based (or made from scratch, based on plans) home-built airplanes are certified by the FAA as “Experimental, Amateur-Built”, or EAB.

There are currently about 32,000 homebuilt airplanes registered with the FAA.

The largest manufacturer of airplane kits is Van’s Aircraft, creators of the RV series. There are over seven thousand RVs flying out there, over a third of which are RV-6s like mine, the most popular EAB out there. Next on the list is Glasair, who has delivered over three thousand kits. The Glasair 2 is the most popular, with over 1,200 flying. Many other kitplane companies each have several hundred airplanes flying, built in garages and basements and small airplane hangars around the US (and in a few other countries).

Some kitplanes are designed for extreme performance, restricting them to niche markets. For example, the latest Lancairs are designed for long-distance travel, so they are pressurized and fast and fuel-efficient. However, their slow-flight characteristics are tricky, so they must be landed at high speeds, making them impractical for use at small airports with short runways. On the other extreme, the Highlander SuperSTOL is designed to be an uncompromising bushplane, sacrificing speed for the ability to take of and land nearly anywhere.

As a structures engineer in a company proud to make the first carbon-fiber airliner, I feel it’s especially worthwhile to point out that EABs were significant in the history of composite airplane structure. In 1979, two important airplanes made their first flight. One was the original Glasair. Its beefy structure, relatively small wings, and powerful engine allowed for high speeds and exciting aerobatics. The other was Burt Rutan’s LongEZ, whose large efficient wings and weight-conscious construction gave it better fuel efficiency than any other two-seater out there. Both were made 100% out of composite materials. A few years later, Lancair – also with an all-composite airplane – tried to bring together the best of both worlds, and started creating a series of airplanes that are fast and fun to fly, but also exceptionally lightweight and aerodynamically efficient. The success of these airplanes over the 1980s was one of the factors that encouraged the “mainstream” manufacturers, and the FAA, to start trusting composites in primary airplane structure.

The EAB world is amazingly diverse. It includes everything from bushplanes to racer airplanes to replica fighters and bombers, from fabric-covered biplanes to jets, from tiny one-seaters to fast twin-engine five-seaters to surprisingly large turboprops that can carry ten skydivers, and they’re made of everything from wood to aluminum and fiberglass and carbon-fiber. It is especially interesting to look at photos from EAB conventions and read about the record-breaking attempts that go on there and elsewhere. The homebuilt kitplane word is a microcosm of the general aviation universe, and indeed one of the fastest-growing segments of the industry.


 

Graph - Statistics on causes of light airplane accidents

EAB SAFETY

Many people, when they first learn about amateur-built airplanes, immediately ask:

Are they safe?

The short answer is:

Yes. Homebuilt kitplanes themselves are not significantly less safe than factory-built airplanes.

This can be broken down into five points:

(1) The pilot-training requirements for flying an EAB are the same as for a factory-built airplane. You need a current pilot’s license to fly a homebuilt kitplane. If the engine produces more than 200 horsepower, then you’ll need a High Performance endorsement from a Certified Flight Instructor. If it is an old-fashioned tail-dragger, then you’ll need a Tailwheel endorsement. If it has flaps and retractable gear and a variable-pitch/constant-speed prop… Complex endorsement. If it has more than one engine… Multi-Engine rating. If it weighs more than 12,500 pounds… Type rating. If it can land on water… etc. Just because you built it, that doesn’t automatically mean that you can legally fly it!

(2) The vast majority of accidents in EABs are cause by pilot error, not by mechanical failure. Nearly all accidents in EABs – and this is also true of factory-built single-engine airplanes – are caused by three factors: Flying into bad weather (such as icing or low visibility), mis-managing fuel (which typically means running out, but not always), or stalling the airplane shortly after takeoff or shortly before landing (due to getting too slow to fly, or turning too tight at slow speeds). You see these same causes at the top of many, many, many, many, many, many articles and discussions about light airplane accidents. These are all things that pilot training aims to eliminate, and that new pilots are tested on before the FAA grants them a license to fly. When you look at General Aviation accidents, the airplanes themselves are almost never at fault. Besides, accident rates for EABs are less than 1% higher than those for factory-built light airplanes. (Also, insurance rates are about the same, all other things being equal. This indicates a comparable level of risk between EABs and factory-built single-engine airplanes).

(3) Many homebuilt kits have been in production for decades, are thoroughly understood, and unlikely to cause unpleasant surprises. The Glasair 2, the EZ, most RVs, etc., are extremely polished and reliable products and have had practically all of their bugs ironed out. As with the 737, the most recent versions benefit from a long list of improvements over the first models. As for those early models: They have been flying for so long, and in such great numbers, that pilots know the potential issues that they must keep an eye out for. Service Bulletins over the years have recommended a variety of modifications to prevent these issues. This might not be true for newly developed kitplanes or for those flying in very small numbers, but it is true of the popular ones like the Glasair 2.

(4) The airplane is carefully inspected by the FAA before an airworthiness certificate (even a “special” one) is issued. All steps of assembly, plus any parts fabrication done by the builder, the installation of systems, etc., must be meticulously documented. (This is why so many homebuilders create blogs and post pictures every time they install a bracket, rivet a skin, sand a fairing, lay up a fillet, plug in a radio, etc.: You have to document when and how everything was done, and the easiest way is to just photograph everything and post it online as you go). The FAA DAR goes over all these records, and thoroughly inspects the airplane itself, before signing it off. After that, the first 25 to 40 hours must be flown over non-populated areas, close to the home airport, and with no passengers on board. These hours must include everything that the pilot may wish to ever do with the airplane: flying fast and slow, high and low, various weights and CG positions, various engine settings, aerobatics, etc. This ensures that all components behave as expected, in all conditions. While not as thorough as Boeing’s flight tests, this requirement does a good job at preventing EABs from causing any surprises later on while taken on long trips and/or while carrying passengers.

(5) It is possible to design and manufacture an airplane kit that takes into account the fact that it will be built by amateurs. For example, structural margins are very high, so that if a large number of rivets are mis-installed and pop out, the remaining ones can still carry the necessary loads. Relatively few kinds of fasteners are used, to reduce the chance that a wrong fastener is used in any given location. (The same is true of Ikea furniture). The checks done before every flight, and once a year during the airplane’s annual inspection, focus on the things that might not work well if they were not installed properly.

In fact, as a Boeing employee who sometimes deals with errors made in our factories, one thing is very clear to me: Our machinists also make mistakes. This should not be surprising: They’re only human and they have tough jobs. Sometimes they drill a hole slightly off from where it was supposed to go, or mis-install a fastener, or don’t properly connect an air duct, or scratch the structure because they used the wrong tool to remove sealant. When we develop Boeing jets, we take all this into account, and we design a lot of redundancy and fail-safety into our airplanes. Our maintenance inspections and Quality Assurance practices look for the most likely or dangerous mistakes, and our manuals have fixes for nearly every “whoops” that has happened. It’s part of doing business when your products are so complex and made largely by hand. People make mistakes, we have ways to catch them and fix those mistakes, and we try to develop designs such that (in case a mistake is not caught) no single mistake by itself would cause a fatal problem. The same is true for EABs.

In short, the difference between an airplane built by an amateur who might make mistakes, and an airplane built by professionals who might make mistakes, is smaller than most people think.

I remember having a conversation with a friend once, when I tried to explain to him how Boeing thinks about structures durability. At one point he says “So, assume that a perfect airplane comes out of the factory…” and I stopped him and said “No, assume that people make mistakes, that there are flaws in the structure from day zero, and go from there. If you ever assume that everything was and will be done perfectly, you’ll be unpleasantly surprised someday”. Most Boeing engineers share this mindset. The same is true for the people who develop and sell airplane kits.


 

Minimal instrument panel vs high-tech panel
The two extremes in instrument panels. [Photos by Ahunt and Spartan7W, licensed under Creative Commons]

WHY CHOOSE AN EAB?

Of course, the ONE BCnF program chose to work on an EAB so that participants would gain experience in building an airplane.

Similarly, most people who choose to build a kitplane do so because it is a challenging and educational project, one that gives the pilot an unparalleled level of knowledge about their airplane.

But even pilots who do not wish to spend time building an airplane – pilots such as myself – often prefer to fly a homebuilt kitplane rather than a factory-built airplane, and will buy an airplane that someone else built.

Why is that?

One reason is speed. Most factory-built airplanes that can fly at 200mph are either twin-engine airplanes or fast single-engine four-seaters. They are very expensive, and burn a lot of fuel. Most factory-built two-seaters have difficulty exceeding 100 knots. If you don’t need your airplane to carry more than two people but you want to get places fast, then what you want is a Glasair, RV, EZ, etc.

Another reason is aerobatics. Factory-built aerobatic airplanes are either relatively slow and sluggish (Aerobat, Citabria, Musketeer…) or are completely impractical airshow stunt-planes that require great skill to fly and that have limited range (Pitts, Extra). If you want something in between – snappy enough to be fun, but easy to fly, and still capable of easily going on a long trip – then only a kitplane will meet your needs.

Unfortunately, the market for fast two-seaters and for aerobatic traveling airplanes is very small. One attempt at a factory-built airplane like this led to bankruptcy within a year. That is why the EAB world is the only way to get a fast, efficient, easy to fly, aerobatic airplane.

Finally, and perhaps most importantly, EABs are also inherently attractive because of how easily they can be modified and customized.

In a factory-built airplane, any proposed modification must be approved by the FAA (at least by an AR). This is true in single-engine airplanes just as it is for airliners. Analysis (and often testing) must be performed to demonstrate that any modification will work reliably and will not lead to an accident. Modifications as simple as re-shaping a control surface, adding an instrument to the panel, replacing the exhaust pipe with a different one, or adding an autopilot actuator to the control system, cannot be done without exhaustive (and expensive) tests and analysis.

On an EAB, on the other hand, the owner is free to do whatever they wish. Major modifications must still be first flown by a pilot experienced with flight-testing, but this is a minor restriction. (“Major” and “experienced” are loosely defined). If you can think of a way to make a wingtip or an engine cowling that is more aerodynamic, to squeeze a bigger engine into the nose (and stretch the tail boom for balance), to make the landing gear retractable, etc., there is nothing to stop you from making your vision a reality. The owner of an EAB does not have to “put up with” the decision of their airplane’s designers. Any desired modification is just a matter of time, money, and fabrication skills… and is flown “at your own risk”.

In practice, most homebuilt airplanes are fairly “stock”, and only incorporate some minor modifications that have been done successfully many times in the past: “This EZ has the Roncz canard”, “That Zenith has the BRS parachute”, “Here’s an RV with the Anti-Splat nose gear”. Typically, only aeronautical engineers and experienced mechanics cook up their own modifications.

The instrument panel, however, is another story. There are many suppliers of cockpit instruments, ranging from old-school round dials to 787-like digital displays. The bare minimum panel contains only a magnetic compass, plus one tiny screen or a handful of watch-sized “steam gauges” that just show you the most essential information: airspeed, altitude, engine RPM, and fuel and oil levels. On the other extreme, some pilots install GPSs, angle-of-attack sensors, G meters, manifold pressure and exhaust temperature sensors, attitude indicators, autopilots, radio instruments that can pick up all kinds of navigational beacons, electric flaps and electric trim – and maybe some lights to indicate the angles of the flaps and trim tabs… enough instruments to fly through the mountains in zero-visibility weather. Most homebuilders end up somewhere between these extremes, flying an airplane that is a little better-equipped than a World War I biplane but a little less decked-out than a stealth fighter.

The instrument panel is a large part of the “pilot experience” in any airplane; It is comparable to the operating system on a computer or smartphone. It’s what you’re looking at the whole time, and it largely determines what you can do with your machine. So, it better be intuitive. EABs are attractive because they allow you to customize your panel to your heart’s content, put everything in “the right place”, get rid of clutter, and add whatever gadgets you personally find to be most helpful. No two people’s computer desktops or iPhone home screens are identical… Similarly, no two homebuilders’ instrument panels are the same. In a factory-built airplane, you have to get used to the instrument panel that comes with the airplane, no matter how counter-intuitive or awkwardly-placed some gauges or knobs are. In an EAB airplane, you can make it “just right”.


 

Bernardo Malfitano flew RV-6A N611RV all the way to Sonoma
Yours truly.

IN CONCLUSION

I was recently filling out a survey for people who are involved with EABs. It ended with an interesting and very general question: How does the fact that you fly an EAB affect your life in general?

The best answer that I could come up with: Most people, even most people who are in aviation (such as engineers and pilots), think that EABs are far less safe than they actually are. This misconception sometimes negatively impacts how other people view me: When they find out that I fly a homebuilt, they imagine that my airplane is rickety and unreliable, that its structures and systems and controls must be continuously on the verge of failure, that it must handle awkwardly or be uncomfortable for long trips.

None of these things could be further from the truth. Structurally, most high-performance EABs are massively overbuilt (typically 6G limit / 9G ultimate, compared to Boeing’s 2.5G/3.75G structure), allowing me to regularly perform maneuvers that would rip the wings right off of any Boeing commercial jet. Just the small size of the airplane allows for the control system to be a simple and reliable collection of thick cables and stiff rods, rather than the complicated hydraulics or computerized fly-by-wire actuators found on jets. The engines and systems on most EABs are either identical to those on factory-built light airplanes, or have decades of incident-free service history despite not having been FAA certificated. Long trips are perfectly doable.

As for the finer points of polish and handling: While it is true that some EABs sacrifice polish (e.g. interiors) for weight, and sacrifice forgiving and/or precise handling characteristics for higher speed and lower drag, this is not true of the most successful EABs such as RVs and Glasairs. When it comes to popular EABs, control surfaces are well-balanced, handling is stable, and force gradients are positive. (For example: The more you want the airplane’s nose to come up, the harder you pull on the stick, and vice versa). In fact, these popular EABs fly more “like a video game” than do most factory-built airplanes. While flying in a Glasair, almost anyone could simply hold the stick and easily command the airplane to do exactly what they want: The handling is just that intuitive and easy. These airplanes are designed from the start to be recreational, to make for the most enjoyable pilot experience. Easy and intuitive handling are big selling points.

I hope that you have enjoyed this glimpse into the world of EAB homebuilt kitplanes. If you would like to learn more, there are many great resources out there, such as web forums and your local EAA chapter. And if you did enjoy this blog post, let me and the ONE BCnF team know, and I could come to guest-blog again. Thanks!


Responses

  1. Thanks for posting, Bernardo!
    Russ Gelfan

  2. Well stated. I don’t think I would change a thing.

  3. Great article. As an RV-8 builder and pilot, I’m certainly a fan of E-AB. I think as more folks learn about the virtues, they’ll get onboard too. Although there are a few factory-built airplanes on my bucket list, none of them offer what I wanted when I built my RV-8…for any price.

  4. […] homemade airplanes. BCnF makers produce everything from racers to fabric-covered biplanes. This post is a good introduction to the fascinating world of BCnF, and is a great place to start if […]

  5. Did I miss it, where you tell us what kind of airplane is behind “Yours Truly”?

    Because I wasn’t reading for 100% retention… and could have missed it even if I was. Not just what mddel name and number, but what kinds of capacities etc. would be interesting to know.

    • Shucks, there it is in the very top of the story!

  6. Very nice article. Always I say: airplane was project to fly as a bird. The Pilot shut down this bird allmost the times.


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