BD-5A/B factory engines

I have a long technical fascination with the BD-5 homebuilt aircraft. The engines were one of the main reasons for its demise, but I found the history of the engines in the factory prototypes confusing and difficult to understand. The four profile drawings that I had seen, but did not understand, triggered an in-depth study. Slowly, the history surfaced, that it included some small surprises.
1/72 BD-5J under construction	1/72 BD-5J N3038V finished	BD-5J census	BD-5A/B factory engines

Engines used in the Bede factory prototypes

Five different engines were used in the four factory prototypes that were flown during the BD-5A/B development:

N500BD:
- initially fitted with the Polaris engine, during the time it had a V-tail
- on display with this engine at Oshkosh, 1-7 August 1971
- first flight over the runway, in ground effect: 13 September 1971
- redesign with a swept horizontal stabilizer and elevators, and a conventional vertical tail
- during the rebuild, a Kiekhaefer Aeromarine 440 was installed. I think it was installed in the upright position, with the inlet side on the right. An air inlet scoop was required because of the large air filter. A Kiekhaefer Aeromarine logo was applied to the air scoop
- high-speed taxi tests in January 1971 (? probably 1972) revealed that the new configuration gave too large pitch trim changes with speed. No further development
- repainted in the then-standard Bede scheme of white with a red stripe, late 1972
- used in a publicity photo together with N501BD and N502BD. The latter was brand-new, therefore the photo was early 1973
- on display in the EEA museum in the second color scheme
N501BD:
- swept horizontal stabilizers and elevators (fighter style), placed higher on the fuselage, better suited to the propeller flow
- eventually this tail was replaced by the definitive one-piece all-flying horizontal tail
- first flight over the runway: 31 May 1972. Out of ground effect according to Bede
- first real flight, away from the runway: 11 July 1972
- on display at Oshkosh, 30 June - 5 August 1972, with the definitive horizontal tail and Kiekhaefer engine
- demonstrated at Bede Open House at Newton, Kansas, 19 and 20 August 1972
- reportedly shown at the 1973 Paris Air Show
- initially had the Kiekhaefer Aeromarine 440 engine like N500BD, but it was installed differently. It was rotated on its side, with the inlet side up. N501BD was not flown with this engine, it was replaced before the first real flight
- Kiekhaefer Aeromarine (or Kiekhaefer Aeromarine Motors, Inc) was a then-new company founded in 1970. The 'old' Kiekhaefer-Mercury later became Mercury Marine. Kiekhaefer Aeromarine engaged Alexander Lippisch (of Komet fame) in an advisory role, then pulled out of the project, and threatened with legal action to stop BD-5 advertising the Kiekhaefer name (see 'BD-5S - at last a BD-5 with no engine problems' in Air Progress, June 1975 issue). Jim Bede's version, as reported in his book, was that Kiekhaefer would produce the order for 3,000 engines at the end of a production run of 15,000 to 20,000 for Bolin snowmobiles. When that order was cancelled, legal problems called for leaving the production line as it was, preventing the Bede order to be produced
- had a Hirth 650 cc installed after Kiekhaefer Aeromarine pulled out. The article 'The mighty Hirth - out of the snow and into the blue' in Flying magazine, September 1973, reports that the engine was installed on its side initially, because the carburetor projected way out of the block. This is supported by a photo, that also shows dual ignition. Most of the test flying was done with this configuration
- last flight: 8 October 1972. Crash-landed on a country road after an engine failure (mixture cable broke). It the 33rd flight, and the fourth flight with the 'A' short wing
- not repaired since N502BD would be available soon. Instead reused as the 'Truck-a-Plane' simulator. Just before Oshkosh 1975, 38 customers flew the simulator and the actual aircraft (N502BD or N503BD)
N502BD:
- first flight: 26 March 1973
- present at Oshkosh, 1973
- present at Oshkosh, 1975
- possibly still exists, owned by Frank Verbeke (owner of Alturair company), La Mesa, CA. On display at Oshkosh in 1989
- had one engine: the Hirth 650 cc. If I read the article 'The mighty Hirth - out of the snow and into the blue' from Flying magazine (September 1973 issue) correctly, the engine was installed upright in this aircraft, simplifying installation. I have yet to find a external difference - maybe some slits on the right fuselage side, near the carburator position for the Hirth
N503BD:
- first flight: probably around February 1974
- initially flew with a Hirth 650 cc
- was also flown with the Hirth 720 cc, but derated to ~52 hp for a longer engine life
- present at Oshkosh, 1974
- updated at one point with airscoops on both sides of the fuselage, for engine cooling. Left side scoop was larger the right side scoop
- Hirth went into voluntary liquidation in 1974
- in February 1975, the Japanese Xenoah G72C-C was installed. This was a prototype, not a series production engine. Sometimes the name Xenoah Chaparell is used. Chaparell was a snowmobile manufacturer, that used Xenoah engines among others. Maybe they also did distribution for Xenoah?
- present at Oshkosh, 1975, fitted with Xenoah engine
- last flight: 23 November 1976, Newton, Kansas. Stalled during climb after take-off, crashed, pilot killed. Pilot was new to BD-5.
N504BD sailplane:
- first flight: probably January or February 1975
- was seen at a Bede open house in the summer of 1975
N5BD jet:
- first flight: 20 July 1973
- Demonstrated at Oskosh 1973, but damaged on 1 August 1973. It hit the landing lights when the thrust attennuator closed
- was seen at a Bede open house in the summer of 1975
- last flight: 7 August 1975, Edwards AFB. Stalled during landing approach, crash landing, USAF pilot survived with severe injuries

Engine data

The following engines were either flown or projected during the BD-5A/B development:

Manufacturer	Model	Capacity	Power	Cilinders	Type	Ignition	Carburetor(s)	Weight	Comments
Polaris			32 hp (Bede) 36 hp (Bede)	2	2 stroke		two		a 1970 Polaris brochure lists 292, 335, 398, 436, 488, 744 and 792 cc engines
Kiekhaefer Aeromarine	440Aero	433 cc	40 hp (Bede folder) 40 hp (Kiekhaefer folder)	2	2 stroke	single	one	72 lbs (Bede folder) 72 lbs (Kiekhaefer folder)
	525Aero	523 cc	55 hp (Bede folder) 50 hp (Kiekhaefer folder)	2	2 stroke	single	one	74 lbs (Bede folder) 72 lbs (Kiekhaefer folder)
	575Aero	573 cc	70 hp (Bede folder) 60 hp (Kiekhaefer folder)	2	2 stroke	single	one	76 lbs (Bede folder) 72 lbs (Kiekhaefer folder)
Hirth	?	440 cc	40 hp (Bede folder)	2	2 stroke	double ?
	F20	650 cc	55 hp (Bede folder) 52.5 hp (Jane’s 74-75) 45 hp (BD-5B/D/G POH)	2	2 stroke	double	two	87 lbs dry (Jane’s 74-75)	full model designation is F20BA1. F20 designation was never mentioned in period articles, only '650cc'. However, the designation is mentioned in the 'BD-5B/D/G Pilot's Handbook'. Jane's 1974-1975, in the engine sectiom, also uses the F20 designation.
	F21	720 cc	70 hp (Bede folder) 60 hp (Jane’s 74-75)	2	2 stroke	double			Jane’s 74-75 says 718 cc. Electric starter. F21 designation was never mentioned in period articles, only '720cc'. However, Jane's 1974-1975 does use the F21 designation.
Xenoah	G72C-C	726 cc	65 hp (BD-5B/D/G POH) 60 hp 70 hp	3	2 stroke	double	three	157 lbs	'BD-5B/D/G Pilot's Handbook' says: "Model designation of the engine is G72C." 65 hp is at 6250 rpm at SL.

Notes:

It is rather unclear whether electric starters were installed on the engines, or a pull-starter was employed.
BD-5 jet team pilots Fornoff and Bishop both stated later: "I would not fly the Hirth engine"
Keith Hinshaw, in 'Bede-Micro Update' in Sport Aviation, May 1982, states that the Hirth 440cc was worn out after just 130 hours, too worn for a rebuild, and he wouldn't use it.
Xenoah is also spelled as Zenoah, but the engine data plate says Xenoah. Apparently the company switched to the 'Zenoah' name later.
Keith Hinshaw, in 'Bede-Micro Update' in Sport Aviation, May 1982, states that only three certified Zenoah engines were built - Zenoah elected not to produce the engine. It was very costly at 5,500 $ in 1982.

Engine photos

Shown below is my best understanding of the engines, but nothing is set in stone! Note that the engines with and without cooling shrouds look vastly different. An effort is underway to credit all the photo sources.

Polaris
	caption suggests Kiekhaefer

Kiekhaefer Aeromarine
upright
flat	caption says Hirth		Oshkosh 8 August 1972

Hirth 440 cc	none found so far

Hirth F20 on its side			photo upside down?

Hirth F20 upright

		different:	different:	probably:

Hirth F21	none found so far

Xenoah G72C-C					with accessories:
		later models?:

Engines in profile drawings

1. Polaris most likely. Butterfly tail. Exhaust is not correct, it came out of the side on N500BD. Note fuel tank behind pilot. Source: Ebay. Can also be found in the October 1971 issue of 'Science and Mechanics'.
2. Most likely the initial Hirth installation (on its side), on its inlet side. The cooling air exits from the bottom. Exhaust routing unclear - are the two 'wing profile' shapes the exhaust ports in the side of the fuselage? N502BD had one such exhaust port. Source: Ebay
3. Hirth most likely, upright installation. Two exhaust ports, correct cooling air exit. Source: Ebay
4. TRS-18. With bell-mouth inlet, best suited to a plenum chamber-type air inlet.

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