Bede BD-5

The Bede BD-5 Micro is a series of small, single-seat homebuilt aircraft created in the late 1960s by US aircraft designer Jim Bede and introduced to the market primarily in kit form by the now-defunct Bede Aircraft Corporation in the early 1970s.
The BD-5 has a small, streamlined fuselage holding its semi-reclined pilot under a large canopy, with the engine installed in a compartment in the middle of the fuselage immediately to the rear of the cockpit, either a propeller-driving engine – or jet engine in the BD-5J variant. The combination of fighter-like looks and relatively low cost led to the BD-5 selling over 5,000 kits or plans, with approximately 12,000 orders being taken for a proposed factory-built, FAA-certified version. However, few of the kit versions were actually completed due to the company's bankruptcy in the mid-1970s, and none of the factory built "D" models were produced, as a result of the failure to find a reliable engine for the design.
In total, only a few hundred BD-5 kits were completed, although many of these are still airworthy today. The BD-5J version holds the record for the world's smallest jet aircraft, weighing only.

Design and development

The Micro concept

Development of the "Micro" dates back as early as 1967, when Jim Bede was inspired by the Schleicher ASW 15. Along with his chief designer, Paul Griffin, they make preliminary designs of what would become the BD-5. At the time, however, Bede was working on the Bede BD-4.
Serious work on the Micro started in 1970, with construction of the prototype starting in earnest late that year. While the BD-4 was fairly conventional looking, the Micro was a radical design. It is an extremely small one-seat design that looked more like a jet fighter than a typical general aviation aircraft, with the pilot sitting in a semi-reclined position under a large fighter-like plexiglas canopy only inches above the pilot's head. Behind the cockpit was a compartment housing a two-cylinder air-cooled piston engine driving a pusher propeller.
For improved performance the aircraft featured both a V-tail and retractable landing gear in order to reduce drag. Calculated drag was so low that split flaps and spoilers were added to the wing in order to improve deceleration for landing. This was apparently the first application of spoilers on a light aircraft. The low drag implied excellent performance; with the 40 hp engine it was expected to reach "nearly", while the larger engine allowed it to cruise at 200 mph with the "B" wing, and have 1,215 miles range. With the shorter "A" wing,, it would be fully aerobatic and have a slightly higher top speed. Builders could optionally buy both wings, switching them in about 10 minutes.
In addition to being easy to fly, the BD-5 was also intended to be easy to build and own. The fuselage was constructed primarily from fiberglass panels over an aluminum frame, reducing construction time to only a few hundred hours. Although the early designs required some welding in the landing gear area, it was planned that this would be removed in the kit versions, so construction would require no special tooling or skills. Even the cost of operation would be extremely low, offering fuel efficiency of. With the wings removed, the aircraft could be packed into a small custom trailer, allowing it to be towed away by car for storage in a garage, and from there to any suitable flat area for takeoff.
Bede published an information booklet about the BD-5 in November 1970. Several very positive magazine articles appeared at this point. The October 1971 issue of Science & Mechanics had the BD-5 on the cover, listing the price as $1,950. The associated article showed the construction of the original prototype, with numerous claims about how easy it was to construct. The August 1973 issue of Popular Science also covered the aircraft, although it listed the price at $2,965 with the 40 hp engine. The "miniature fighter" generated intense demand. As one author put it, "Even before the plane first left the ground, thoughts of flying the sleek, bullet-shaped aircraft with its pusher prop stimulated the imagination of nearly everyone who had heard of the program."
On February 24, 1971, the first $200 deposit to reserve a "place in line" to receive a kit was accepted, with the target shipping date being May 24, 1972. By August 1971, 800 deposits had been taken, even though the first BD-5 prototype had yet to complete high-speed taxi tests. By the end of the year, the company had taken over 4,300 orders, making it one of the most popular general aircraft projects in modern history.

Flight testing

N500BD

The prototype, N500BD, flew briefly on September 12, 1971, powered by a Polaris Industries snowmobile engine. This was sixteen months after deposits had been taken, which led to some griping in the press.
The stability of the aircraft with the original V-tail was marginal at best and clearly needed a redesign. With the original fibreglass fuselage, this was a time-consuming process, so the decision was made to switch to an all-metal fuselage with the components incorporating compound curves produced using hydroformed aircraft-grade aluminum alloy. These could be modified with relative ease during the testing cycle. It also made economic sense as the orders rolled in, the $30,000 in tooling would be spread over what was now a large order book.
By December 1971, the tooling for the new fuselage was in development. The aircraft now featured a longer, more pointed nose, whereas the N500BD had been patterned on the ASW 15 and had a more rounded, egg-like shaping at the front. While this work was in progress, Bede continued to experiment with modifications to the empennage, eventually abandoning the V-tail for a more conventional rudder and horizontal stabilizer layout with highly swept surfaces. Further testing on N500BD showed flow interference between the horizontal surfaces and the propeller, and the stabilizer was raised six inches to correct it, placing it about midway up the rear fuselage.

N501BD

The first example of the new fuselage arrived in March 1972, and was fitted with a new Kiekhaefer Aeromarine engine Bede had seen at the Oshkosh Airshow in 1971. Finished as N501BD, numerous small delays prevented it from flying until July 11, 1972. These flights demonstrated continued problems with the pitch stability; after briefly considering an all-flying stabilator, it was again redesigned with more area and less sweep, becoming much more conventional in layout.
The program was now far too large for Bede to handle alone. In March 1972, he hired Burt Rutan to head the flight test department, who was soon joined by Les Berven as chief test pilot. They took over development, giving Bede more time to work on business issues. This was proving difficult enough, as Kiekhaefer and Bede could not reach an agreement about deliveries, forcing him to change to a similar 40 hp Hirth Motoren design, then selecting a larger 55 hp Hirth, instead.
Several additional problems turned up during testing. Stick forces were very low, but this was easily addressed by making the servo tabs 50% larger. A more worrying development was that the engines all had problems with mixture due to changes in engine speed or load, which led to rough engine operation. In August, while Bede was demonstrating the BD-5 to the FAA in order to receive permission to fly at Oshkosh, the engine seized. On its deadstick landing, the aircraft overran the runway, buckling the nose gear. Incorrect mixture was identified as the cause of a second wreck of N501BD, in September 1972, when the mixture control broke and Berven had to execute another forced landing. This landing resulted in damage to all the gear and the fuselage as well.
Since N502BD would be ready in two months, they decided not to repair N501BD, and it ended testing after about 30 hours of flight time.

N502BD

N502BD ran into problems of its own. Early models used a variable speed belt drive system to transfer power from the engine to the propeller shaft. This was removed from N502BD and it suddenly began exhibiting a serious vibration problem during taxi tests. Experts were called in, and a freewheel clutch and additional bearings added to correct the problem, but it was not until March 26, 1973, that N502BD flew. From then on the test program seemed to go more smoothly, although this aircraft also suffered two dead stick landings, one from a pinched fuel line occurred while the plane was being observed by the Popular Science author, and another due to metal in a new engine's cylinder.
By the time the test program neared its conclusion, the aircraft had undergone major changes. One victim of the program was the shorter "A" wing, which calculations showed would only improve performance at speeds very close to V_max. Flight testing also showed the stall speed with the smaller wing was decidedly high. Split flaps and spoilers had also disappeared. The canopy and cockpit dimensions had changed, the aircraft had new landing gear systems, and the tail was completely new. Estimated top speed was also reduced 10%.
The biggest change, however, was the engine. The original plans to use a 40 hp model proved to be decidedly underpowered, although they were still offered for a time. It was the need for more power that would fit into the very small engine bay that demanded the use of a high-revving two-stroke engine, and few examples of such a design in the desired power class were available. Additionally, two-stroke engines are very smooth running at high RPM, but have real problems running smoothly at low RPM. Even after months of effort, the Hirth designs showed rough running and high minimum power outputs when idled. Two-strokes also have high fuel consumption, and it was expected that the larger engines would burn between 4.5 and 5.5 gallons per hour.
By this point, it seemed the basic design was complete, and Bede turned his attention to other projects. One was the jet-powered BD-5J, which boosted performance to. There was an attempt to sidestep the engine problem with the BD-5S glider, with lengthened wings and no engine, which prompted Air Progress magazine to sarcastically note, "At last, a BD-5 with no engine problems." This glider version did not fly well and the project was scrapped. Some work on a BD-6 was also carried out, essentially a downsized BD-4 single-seater. There was some criticism that Bede should have attended to the basic BD-5 rather than move on to these other projects. Bede also decided to seek FAA certification of the BD-5D as a production aircraft and sell it complete, and began taking $600 deposits for this model.