| BD-5 | |
|---|---|
| Guinness Record Holder, The World's Smallest Jet, BD-5J N3038V. | |
| Role | Homebuilt |
| Manufacturer | Bede Aviation |
| Designer | Jim Bede |
| First flight | 1971 |
| Introduction | 1970s |
| Status | ~150 airworthy, ~30 flying |
The 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, and a propeller or jet engine in the BD-5J variant, mounted immediately to the rear of the cockpit. 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.[1] 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 produced, brought on by the failure to deliver a reliable engine for the design.
In total, only a few hundred BD-5 kits were completed, although many of these are still being flown today. The BD-5J version holds the record for the world's lightest jet aircraft, weighing only 358.8 lb (162.7 kg).
Contents |
Development of the "Micro" dates back as early as 1967, when Jim Bede was inspired by the Schleicher ASW 15.[2] At the time, however, Bede was working on the Bede BD-4 design. The BD-4 was a fairly conventional looking high-wing four-seater, but it offered good performance and was fairly inexpensive. Over the lifetime of the company about 600 BD-4s were sold, a success by any measure.
Serious work on the Micro started in 1970, with construction of the prototype starting in earnest late that year.[2] 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 "prop plane," 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 40 hp engine driving a pusher propeller. Two versions were planned, the BD-5A with "short" 14' 3" (4.34 m) wings tuned for high speeds and acrobatics, and the BD-5B with a 21' 6" (6.55 m) wings for longer range and powered glider use. Builders could optionally buy both wings, switching them in about 10 minutes.
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 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.[3] The low drag implied excellent performance; with the short wings it would reach 210 mph (340 km/h) in cruise, while the long-wing BD-5B would be only slightly slower and have an extended range of 1,215 miles.
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.[4] [N 1] Even the cost of operation would be extremely low, offering fuel efficiency of almost 40 mpg. 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.[5][6]
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 and a top speed of 215 MPH. 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.[5] A feeding frenzy followed as the "mini 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."[2]
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.[7] By August 1971, 800 deposits had been taken, even though the first BD-5 prototype had yet to complete high-speed taxi tests.[2] By the end of the year, they had over 4,300 orders, making it one of the most popular general aircraft projects in modern history.
The prototype, N500BD, flew briefly on September 12, 1971, powered by a 36 hp Polaris Industries snowmobile engine. The stability of the aircraft with the original V-tail was marginal at best, and clearly needed a redesign. With the original fiberglass 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, as assembly line production of stamped metal parts is expensive to set up but less expensive in the long run.[2]
By December 1971 the tooling for the new fuselage was in development. The aircraft now featured a longer, more pointed nose, whereas the more ovoid N500BD had been patterned on the ASW 15.[2] While this work was in progress, Bede continued to experiment with modifications to the tail, eventually abandoning the V-tail and changing to a more conventional vertical rudder and horizontal elevator layout with highly swept surfaces. Further testing on N500BD showed flow interference between the horizontal surfaces and the propeller, and the elevator was raised six inches to correct it, placing it about mid-way up the rear fuselage.
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, so the tail was again redesigned with more area and less sweep, becoming much more conventional.[8]
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 followed by Les Berven as chief test pilot.[2] 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 440 cc 40 hp Hirth Motoren design, but then selecting a larger 650 cc 55 hp Hirth engine instead.
Several additional problems turned up during testing. Stick forces were very low, but this was easily addressed by making the servo tabs 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 Bede was demonstrating the BD-5 to the FAA in order to receive permission to fly at Oshkosh, when the engine seized. On its deadstick landing, the aircraft overran the runway, buckling the nose gear. The air-fuel mixture was identified as the cause of the crash of N501BD in September 1972 when the mixture control broke and Berven had to execute a forced landing.[2] Since N502BD would be ready in two months, N501BD was not repaired.
However, N502BD ran into problems of its own. The earlier models used a variable speed belt drive system to transfer power from the engine to the propeller shaft, but this was removed from N502BD and it suddenly began exhibiting a serious vibration problem. Experts were called in,[9] a freewheel clutch and additional bearings corrected the problem,[10] but it was not until March 26, 1973 that N502BD flew. From then on the test program seemed to go more smoothly.[11]
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 Vmax (the highest available speed). Flight testing also showed the landing speed with the smaller wing was decidedly fast. Split flaps and spoilers had also disappeared. The canopy and cockpit dimensions had changed, the aircraft had new landing gear systems and a completely new tail section. More ominous was the fact that the engines had already been changed twice. What remained, however, was the basic concept of the fighter-like pusher aircraft which, if anything, had improved in looks.
By this point it seemed the basic design was complete, and Bede turned his attention to other projects. One was a jet-powered BD-5, the BD-5J, which is detailed below.[1] Another was the Bede BD-6, a single-seat version of the BD-4 based on the same Hirth engine being used in the BD-5. Still another was the "new" Bede BD-7, a two-seat side-by-side version of the BD-5 of which a prototype was built.[12] There was even an attempt to sidestep the engine problem with the BD-5S, a glider (S for Sailplane) version 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. 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.
By the middle of 1973 the basic design was complete and the tooling set up for production. The engines were the only part holding up deliveries, so Bede offered to ship the kit with the engine to follow. This was a fairly attractive option; it meant the builder could "get to work" and hopefully complete the airframe by the time the engine arrived, at that point expected in September 1973.[3] Many builders took the company up on the offer, only to receive incomplete kits and plans.[13]
All three Hirth engines were offered; builders could keep the 40 hp design, or "trade up" to the larger 55 hp or 70 hp engines. The latter, which Bede had developed with Hirth, was now considered the baseline engine for the aircraft as the original 40 hp proved to be of insufficient power. In a late 1973 newsletter to prospective owners, Bede suggested the 70 hp model and discouraged use of the smaller engines.[14] Prices had risen throughout the 30 months since the deposits were first taken. Originally priced at $1,799, the base price was raised to $2,599 with the 55 hp, and owners were offered a "trade up" for the difference in price if they had ordered the aircraft with the original 40 hp engine.
When 1974 came around, the engines were still not being delivered in quantity, although some started to arrive early that year. At that point, unexpectedly, Hirth went bankrupt after about 500 of the engines had shipped. Once again the design lacked a suitable engine, but this time the search for a replacement ended with a Xenoah design from Japan. Development of this engine was lengthy, and in the end it would not be certified for export until 1978, although this was not expected at the time.[15]
In the meantime, Bede came up with another novel solution to the problems of converting pilots to the new aircraft. They took an engine-less example and bolted it to the front of a pickup truck on a trapeze, attaching the pilot's throttle control to the truck's. Pilots could test fly the aircraft without danger - if a problem developed the driver of the truck simply hit the brakes.[16]
After more than 5,100 kits had been delivered to prospective builders, the kits stopped shipping as well. Although the company was effectively bankrupt at this point, work on the BD-5D continued for some time. The bankruptcy became official in 1979, by which point the BD-5 project was long dead. During the bankruptcy proceedings it was learned that the money ostensibly being used to build kits was instead being spent on a variety of projects. As a result, Bede entered a consent decree with the FTC to no longer accept deposits on aircraft for a period of 10 years.[17]
Many owners stored, abandoned, or sold their incomplete kits, but a few hundred diehard builders finished them with a variety of engine solutions designed by third parties and former Bede Aircraft dealers. Having to hunt for an engine was only one problem. The time to build the aircraft was much longer than quoted, as much as 3,000 to 3,500 hours. Some of this was due to the need to fit their selected engine into an airframe designed for the Hirth, which was no longer available. Additionally, the construction techniques had improved somewhat since early Bede designs, but fastening the panels still required drilling, deburring, dimpling, drilling again and deburring again for each rivet. With the original mixed-construction design this would not have been as much of a task, but with the all-metal version this was extremely time consuming.[18] While Bede claimed the aircraft could be put together by anyone in a garage, builders generally agree that doing so without proper construction techniques could result in a potentially dangerous aircraft. One way to overcome that issue is to use a set of properly laid-out jigs to align and drill the pilot holes for the airframe, wings and other components.[19] For all of these reasons, it was some time before completed BD-5s started to appear.[20]
Additionally, some of the kits were shipped with missing parts, adding to the confusion.[19] All of this led to a rash of kits being sold for fire sale prices, although this did allow the builders that were looking to complete their kits to do so at bargain prices.[7]
Over the next few years the aircraft garnered a terrible safety record. Although Bede had suggested using the B wings,[14] the earliest kits shipped only with the short "A" wings. All four examples completed with these wings crashed on their first flight, three on takeoff and one lasted long enough to crash on landing. In three of the four crashes, the pilots were killed. Of the first 25 completed, with both the "A" and "B" wings, 14 crashed with 9 fatalities.[21]
Even when examples with the "B" wings were completed, the safety record did not improve greatly. Several crashes in the -5B models were found to have taken place due to engine failure on takeoff, both due to the mix of "oddball" engines as well as endemic cooling problems.[22] The reason this is such an issue with the BD-5 is twofold – the high line of thrust means an engine failure immediately results in an unexpected (for most pilots) nose-up attitude change. Pilots who fail to fly the aircraft first and then attempt to restart the engine inevitably stall, with the associated consequences. This was aggravated by the fact the original wing had a very sharp stall with little warning and a nasty tendency to "snap roll."[18] To make matters worse, a documented manufacturing error in some wing skins delivered to kit builders exacerbated the problem. A rather small center of gravity range also added to the problems of properly trimming the aircraft.
With the demise of the Bede Aircraft Company, the BD-5 entered a sort of limbo while builders completed their kits. The early safety problems and the challenge of adapting a suitable engine exacerbated delays. Over the next few years, however, solutions to most of these problems arrived in one form or another. Many other changes have also been incorporated to improve the original design. Today the BD-5 is a rewarding, if demanding aircraft.
For instance, the problem of finding a suitable engine with 60 to 70 hp yet still weighing under 100 lbs was a serious problem in the 1970s, but today there are a number of "off the shelf" designs in this class. The widely available Rotax 582 is a 65 hp engine of 80 lbs in standard configuration, almost tailor-made for the BD-5. Other engines successfully used in BD-5s include the Subaru EA-81, Honda EB-1 and EB-2 (with and without turbocharging), Hirth 2706, AMW 225-3 and 2SI 808. A BD-5A fitted with a Rotax 618UL 74 hp two-stroke, two-cylinder[23] water-cooled engine.[24] holds the current FAI C-1a/0 class speed record (less than 300 kg aircraft) with 351 km/h (just over 218 mph). Problems with the abrupt stall were mostly addressed by Harry Riblett, an airfoil designer who documented a procedure to apply a slight reprofile of the wing root airfoil which softened the stall response of the aircraft without any significant performance degradation.[25] The reprofile presents other unique problems associated with the way it is applied to the wing upper surface, essentially gluing foam to the aluminum skin and covering with fiberglass. Similarly, the small center-of-gravity range has since been addressed with 5.5- to 13-inch stretch kits for the fuselage.
Several companies were formed to help builders complete their kits, and many of the aftermarket modifications were worked into these services. Today, BD Micro Technologies of Siletz, Oregon continues to offer kit building support, including new-build kits featuring (optionally) all of these modifications, and even the BD-5T, a turboprop version of the BD-5 using a modified Solar T62 turbine powering a mechanically-controlled variable-pitch propeller. Alturair, Inc. of San Diego, California also offers extensive parts and construction assistance services.
Bede Aircraft Company has since re-formed and has been working on several new designs. Bede has hinted at a two-seat tandem version of the aircraft called the "Super BD-5" using a certified aircraft engine and a number of modifications and improvements, but to date nothing other than a preliminary design drawing has been made available.[26]
While the new Hirth engine was being tested, Bede decided to create an unconventional variant of the BD-5 with a small jet engine. The result was the sleek BD-5J, a 300 mph (480 km/h) aircraft. The design used the Sermel TRS-18-046 turbojet (now Microturbo, a division of Turbomeca), which produced 225 lbs of thrust and was used on a Caproni certified motorglider design. The original engines were produced under license by Ames Industrial in the USA. The wing was modified to an "intermediate" size between the original A and B wings, with a 17 ft span.
Bob Bishop had purchased 20 BD-5J kits as soon as they had appeared, and many of the flying examples started life in this batch of twenty. Versions from the original batch became a popular airshow fixture. Throughout the 1980s and until 1991, Coors flew two of them as the "Silver Bullets." Budweiser also had a BD-5J called the "Bud Light Jet", but that contract has long expired and the aircraft was lost as a result of an engine compartment fire from which Bob Bishop successfully bailed out. The aircraft also appeared in the opening sequence of the James Bond film, Octopussy.[1]
Many of these aircraft have since been involved in crashes. The loss of the Bud Light Jet was caused by an incorrectly specified fuel flow sending unit which burst in mid-flight and caused fuel to be sprayed directly into the engine compartment. The fuel ignited when it came in contact with the hot components of the turbojet engine, forcing the pilot to trade speed for altitude, climb and bail out. The aircraft then went into a flat spin and pancaked into the ground, but was sufficiently intact to allow the cause of the fire to be determined relatively quickly.
On June 16, 2006, while practicing for an air show at Carp Airport in Ottawa, Canada, Scott Manning fatally crashed in his "Stinger Jet," the last BD-5J that remained on the airshow circuit. The Transportation Safety Board of Canada investigated the accident and issued a report assigning the probable cause to the incorrect installation of the right wing, which caused the flap on that wing to suddenly retract in flight and create a "split flap" condition. The aircraft rolled to the right and Manning was unable to recover in time.[27][28][29]
Recently, the BD-5J operates in the national security arena. The aircraft is certified by the United States Department of Defense as a cruise missile surrogate, with Bishop's Aerial Productions offering a version known as the Smart-1 (Small Manned Aerial Radar Target, Model 1).[30] The radar return and general performance characteristics make it a useful aid in training. On June 27, 2006, while flying one of these aircraft, pilot Chuck Lischer, a highly experienced professional air show pilot, impacted trees on final approach to the Ocean City Municipal Airport in Ocean City, Maryland in a fatal accident.
The BD-5J has also held the Guinness record for the World's Smallest Jet for more than 25 years. Bob Bishop originally garnered the record with one of his jets, and in November 2004 the record changed hands to Juan Jiménez,who purchased the aircraft from the original builder[31] whose BD-5J weighed in at 358.8 lb (162.7 kg) empty weight, 80 lb (36 kg) lighter than Bishop's jet and the lightest documented weight for a BD-5.
As of 2010[update], there were an estimated 150 BD-5s in airworthy condition.[7]
Data from {name of first source}
General characteristics
Performance
|
||||||||
|
||||||||||||||
