DIY flight

David Rose's RP-4. Image credit: Jake Stangel
Date:27 October 2011 Tags:, , , , , ,

It’s good to be an amateur aircraft designer in the United States. Engineering software is sold on the shelves, American airspace is the most permissive in the world, and hordes of fellow tinkerers are on hand to help build. There’s no greater thrill than constructing your own plane – except flying it safely.

It was a warm, clear morning in West Texas, a ne day for flying as Mark Stull cruised low over rocky, cactus-filled rangeland. With a popping sound, the control stick suddenly jerked and the plane’s nose tipped down. Stull instinctively hauled back on the stick and the nose came up, but he could tell something was terribly wrong by the plane’s lack of responsiveness. He had to hold the stick almost all the way back just to maintain level flight. Even though he knew the craft’s every wire and strut – he had built the aeroplane from scratch, after all – Stull didn’t know what the problem could be. “I couldn’t think of anything that would suddenly slack the ‘up’ elevator cable like that without letting go completely,” he recalls.

Nerves on edge, Stull nursed the stricken craft 13 kilometres back to the air field, landed and jumped out to examine his aeroplane. A clamp holding the pulleys that fed a cable to the plane’s tail had broken and was barely hanging on, like a f ngernail on a cliff. “If I’d hit the slightest bit of turbulence, it would have popped off ,” Stull says. “I would have lost control, and I’d be dead.”

That was the first time Stull escaped a potentially fatal accident in one of his homebuilt planes. But it wasn’t the last. There was the time an engine mount failed in flight. And there was the time his muffer fell off and hit the spinning propeller. But as far as Stull is concerned, a few mishaps are all part of the game.

The 59-year-old former motor mechanic belongs to a tiny subculture that takes up the ultimate engineering challenge: designing an aeroplane, building it from parts and wagering lives on its airworthiness by flying the creation. “It’s a borderline obsession for some people,” says Jake Crause, administrator of homebuiltaeroplanes.com, the community’s online nexus.

No other country has produced a more storied tradition of aeronautical innovation than the United States, and the vibrancy of the homebuilder community is an extreme testament to this legacy.

This kind of creative aeronautics has never been safer or easier to pursue. Inexpensive computer-aided design (CAD) programs can con-figure airframes, and off-the-shelf flight simulations can verify the blueprints before a designer cuts metal. These programs have helped usher in safe, successful aircraft that can outperform professional models, win races and catch the attention of admirers at air shows.

Still, Stull prefers the intimacy of old-fashioned ways, using pencil and paper to sketch plans that please his eye. Even load calculations can be a matter of intuition. "I have a knack for visualising loads on structural parts," Stull says. "I calculate when necessary. So you just build it robust. But not too robust."

Homebuilt-aeroplane makers are actually a subculture within a subculture. Of the 23 000 amateur-built aircraft in the US, all but a minority were built from professional designs or assembled from kits. Only a handful of builders finish and fly the planes they design – and with good reason. An aeroplane is a complex piece of engineering. A design that is 99,9 per cent perfect could still harbour a fatal flaw. “All it takes is one little thing,” says Martin Hollmann, an aeronautical engineer who conducts seminars on aircraft design. “All you need is the bolt to break on the elevator and you can kiss your ass goodbye.”

According to the US National Transportation Safety Board, homebuilt aircraft are three times as likely to wind up in a fatal accident as industrially manufactured light aircraft. The agency doesn’t keep separate records for planes designed by hobbyists, but the accident rate for those is likely even worse. One of the ways that pilots get into trouble is by improvising tweaks or substitutions to established plans. John Denver, for instance, died in 1997 while flying a kit plane its builder had modified with a relocated fuel valve that Denver apparently had trouble reaching after one of his tanks ran dry. With amateur-designed homebuilts, the problem is even worse: the planes are improvised from tip to tail.

1. Name: David Rose
Location: San Diego
Plane: RP-4

David Rose obviously built the overpowered RP-4 for speed. The experimental counter-rotating propellers, inspired by a Nasa project, run at an impressive 4 800 r/min. Rose can connect both propellers directly to their engines without heavy reduction gearing. The props can change pitch for maximum efficiency at any speed. “It’s a drag-racer frame with skin on it to keep the wind out,” says Jerry Baer, a former pilot who helped Rose build RP-4.

And that challenge is the real joy of building a plane from scratch rather than assembling a kit plane from a vendor. “I started with a piece of paper, and now I have an aeroplane,” says air-race team crew chief Andy Chiavetta, who recently flew his self-designed plane after eight years of construction. “That’s extremely thrilling.”

An amateur aircraft designer can tailor a plane to this or her precise requirements, no matter how outlandish. Take David Rose. Inside his hangar at Montgomery Field in San Diego, this former airline pilot is building a machine that he hopes will earn him aeronautical immortality. If all goes according to plan, a thunderously overpowered racing machine called RP-4 will reach a straight and level speed in excess of 850 km/h and become the world’s fastest piston-driven plane. The 22-year-old record is held by a modified World War II–era Grumman F8F Bearcat.

Rose has been obsessed with speed all his life. In his teens, he built drag racers and started a weekly race meet in Petersburg, Virginia, near his home town. Then he joined the Air Force, where, impatient to break the sound barrier (1 224 km/h at sea level), he took an F-86 to 9 000 metres and then dived straight down on full afterburner. In civilian life, he flew (more responsibly) passenger jets for American Airlines.

In 1990, Rose found inspiration at the National Championship Air Races in Reno, Nevada, where souped-up planes tear around a closed circuit 15 metres off the ground at speeds exceeding 800 km/h. He bought a used Pitts Special biplane and won a trophy with it in 1992 – and then decided he could do better. Using off -the-shelf engineering software, he designed his own biplane.

No big deal, Rose says: “You just crack the books and buy some computer programs.” With the help of former airline pilot Jerry Baer and local mechanic Eric Hereth, Rose built the plane in his hangar in 10 months. Powered by a 170 kW engine, it clocked 360 km/h around the Reno circuit in 2002 and won Rose the Biplane Gold category four times.

His RP-4 project is another beast entirely. Inside the cowling sit two engines, both 4 340 kW Dart V8 “Big M” aftermarket drag-racing blocks, 9,8 litres each, one mounted in front of the other. The massive engines suck 110-octane racing fuel at 450 litres per hour. The exhaust stack produces 1 330 newtons of thrust – enough, Rose says, that “we could fly the plane on the exhaust alone”.

Instead of linking directly to a single prop, the driveshafts turn a gearbox connected to a pair of counter-rotating propellers, 60-cm-long carbon-fibre blades. The experimental design, which offers greater efficiency than conventional props, was developed by Nasa engineers for the rigours of high-Mach flight. At full throttle, the propeller’s tips break the speed of sound.

Rose and Hereth are obsessed with their high-speed project and expect other people to feel the same; the odder the construction, the more the builders want to show it off.

Outside the open hangar doors, a sunset is turning the underbelly of the quilted cumulus Barbie-pink, and the breeze carries the sweet tang of eucalyptus. Rose runs an appreciative hand along the boxy skeleton of 4130 moly-chrome tubing – another of the craft’s unusual features.

Most modern planes have monocoque construction, with the metal or composite skin providing much of the structural strength. RP-4 is built more like a skyscraper, with an internal truss bearing all the major stresses.

This structure is designed to survive an impact of nearly 500 km/h, Rose says. “If the angle is less than 10 degrees,” Hereth adds.

2. Name: Cory Bird
Location: Mojave, California
Plane: Symmetry

In 1989, Cory Bird was a workshop fabricator at Scaled Composites, famed aviation designer Burt Rutan’s company, when he decided to use his knowledge of composite construction to build aeronautical art. “I wanted to show what I could do,” he says. Over the next 14 years he conceived and created a two-seat aeroplane he called Symmetry. The sleek aircraft can reach 456 km/h at 3 000 r/min. The labour of love proved so exquisite that it won a Grand Champion prize at the Experimental Aircraft Association’s big air show in Oshkosh, Wisconsin. Today, the 53-year-old Bird, now a project manager at Scaled, is hard at work on another design for a plane that will carry two and land on shorter airstrips than Symmetry.

3. Name: Mark Stull
Location: Christoval, Texas
Plane: Lucky Stars

Homebuilt aeroplane pilots are motivated by more than aerodynamics. Mark Stull built Lucky Stars with a 1,4-metre ring tail. It took some clever engineering – and some hair-raising test flights – to make it work. Stull added a hydraulic damper to ensure that the tail didn’t swing too far to the side, and balanced the tail by adding weights to the ring. He then moved the seat forward to maintain the craft’s centre of gravity.

Mark Stull sits on a folding chair under the wing of his ring-tailed yellow ultralight, Lucky Stars. Similarly fanciful flying machines are lined up in rows on either side of him, and behind his back a plastic mesh fence marks the edge of a grass runway upon which a dazzlingly eclectic procession of aircraft have been taking off: powered parachutes, flying boats and even a miniature P-51 Mustang.

Wiry and compact, with close-cropped hair, Stull has an angular face that seems as if it were designed for minimum wind resistance in an open-frame flying machine. He has travelled halfway across the country to attend one of the premier events on the homebuilder’s calendar, a Florida fly-in called Sun ’n Fun. One week every spring, aerobatic flight teams, owners of antique military aircraft and all manner of merchandise dealers converge amid throngs of aviation enthusiasts.

There are not many people who build their own planes, but they command outsize respect in the aviation community. They may not all have technical backgrounds, but they like to work with their hands and are confident of their skills. Above all, they are maniacally determined and persistent. “I don’t think they could keep themselves from doing it even if they tried,” HomeBuiltAeroplanes’ Crause says.

Their unique levels of self-motivation mean that builders like Rose and Stull tend to be solitary, beavering away on their creations alone or with a small number of friends. But when they need help, there’s a large, very supportive network of builders spread across the country. "It's a team effort," Hollmann says. "We try to stick together and help each other."

An event like Sun 'n Fun is one of the few occasions when the tribe gets to connect face to face, and the sense of communion can be electrifying: For once, these men are surrounded by human beings who not only understand what they're talking about, but actually care. A reporter from a kit-building magazine stops by and sits next to Stull. "What was the first flight like?" he asks.

"I almost crashed four times," Stull replies. He explains that he had built the control stick so that it hinged at the top instead of the bottom. "It was indescribable how confusing it was," he says. "I did a hop and almost crashed, and I tried again."

In the end, Stull wound up rebuilding the control system along more conventional lines. He is forever tinkering, reconfiguring and trying new ideas. "I can build a plane in three months," he says, "but it takes me up to a month to adjust it."

The importance of strong construction skills became apparent at Sun 'n Fun: the day before, a tornado trashed half the planes in this section of the airfield. Some were crumpled into balls of fabric and mangled spars. Lucky Stars made it through almost intact – the main boom holding its tail in place snapped, grounding it.

Later that afternoon, Stull wanders over to chat with ultralight pioneer and fellow homebuilder John Moody, who is reclining on a lawn chair next to a biplane without a tail or fuselage.

Stull wonders aloud if the ultralight innovator might be asleep, but Moody jumps up, and he and Stull fall into a conversation about the pros and cons of Lucky Stars’ ring-shaped tail. “It’s cool,” Moody says. “I don’t know of any advantages, aerodynamically.”

“It’s mainly for fun,” Stull says. He points out that it has the same aeronautics no matter how the plane is oriented on its longitudinal axis. That leads him to ruminate about his next possible project. “I’ve got some wild ideas,” Stull says. “Since the ring tail worked, why not ring wings? You could fly the plane on edge, sideways!”

Stull laughs, slapping his knee. His outlandish ideas have a history of actually taking flight. In fact, he says, he’s already begun pencilling sketches.

4. Name: Chris Christiansen
Location: Tempe, Arizona
Plane: Savor

Self-taught 31-year-old amateur builder Chris Christiansen designed and flew his third homebuilt aeroplane, the highwing Savor, in just 15 months. That’s especially impressive considering that Christiansen designs with pencil and paper. Yet the Savor, which is intended as a cross-country flying machine, looks very much like a professionally built aeroplane – a good deal, in fact, like Cessna’s new entry in the light-sport aircraft market, the Skycatcher. Except that Savor can go nearly 320 km/h, 100 km/h faster than Cessna’s plane.

Aviation ambition: Build it yourself

Want to take to the skies in a plane that you’ve designed and built yourself? You’ve got a long climb ahead of you, but some inexpensive tools and a supportive community of like-minded pilots will help you on your way.

1. Build virtually first
To test how well your ideas will work in practice, buy a copy of X-Plane, a program that lets you design a plane and then fly it over realistic landscapes. Homebuilt designer David Rose uses the program in conjunction with the CAD program AeroplanePDQ. Total cost, $198 (SA equivalent about R1 400). “With those two programs,” he says, “I can do everything a $30 000 design suite can do.”

2. Design the structure
To configure actual parts and solicit advice on how to put them together, crack open Martin Hollmann’s book Modern Aircraft Design. Hollmann also offers design classes at fly-ins, and structural consulting for intrepid aeroplane homebuilders (aircraftdesigns.com).

3. Get support
The Experimental Aircraft Association, an organisation of aviation enthusiasts, has branches all over the world. Local members can offer encouragement, advise you on technical issues and even help do the work. “A lot of people are willing to volunteer their time just to be involved in a project,” Rose says.

4. Get to work
People who build planes of their own design tend to be retired folk with a lot of energy. “It’s going to take at least two years of full-time work, including weekends,” Hollmann says. “And that’s if you do everything right.”

Planes made to order: Some assembly required

Not totally committed to building an aeroplane from scratch? Consider buying a kit plane instead. Many manufacturers produce partially assembled airframes. Some companies even allow you to come to their factory and assemble the kit with the help of employees, potentially cutting the build time from months to weeks.

1. Shop around
Before you jump in, make sure the plane you’re going to build is the right one for you. Read up on the various available models. The more successful designs have active online forums where builders can share their expertise. “Don’t just base your decision on what a plane looks like,” says Andy Chiavetta, a crew chief for Reno air-races pilot Darryl Greenamyer. “Talk to people who’ve ­ own them.”

2. Dabble
There are three main construction materials used in homebuilt planes: wood, metal and composite. Each has its own advantages and requires different aptitudes. Try them out to determine which suits you best. Every year the massive EAA AirVenture convention in Oshkosh, Wisconsin, holds hands-on workshops where would-be homebuilders can try different techniques.

3. Start small
Manufacturers such as Van’s Aircraft sell partial kits. Buy the tail, and if building it is too hard or unsatisfying, you can rethink your options without wasting months of work and thousands of rand.

4. Be realistic
Even if you’re involved in a builder-assist programme, constructing a functioning aircraft requires a serious time commitment. “There are an awful lot of kit planes out there that get started and are never . nished,” Chiavetta says.

Related videos:
* Mark Stull's Lucky Stars ultralight aircraft
* Meet Savor – Chris Christiansen third homebuilt aeroplane