Aeroplanes with less than the Wrights' 12 horsepower?
 

The Wright Brothers' 1903 Flyer flew on the 12hp generated by Charlie Taylor's engine. I wondered what other self-launching, man-carrying aircraft have flown since on the same or less horsepower? To narrow it down, lets exclude man-powered aircraft. So far all I can think of are the English Electric Wren (404cc ABC 7.5hp) and the Abbot Baynes Scud 3 or Carden-Baynes Auxiliary (250cc JAP 9hp).

What others are there?

Smallest I could think of was the Rutan Quickie but that was designed for a 18hp Onan engine.

Slightly cheating, because it had two of them, but the Lazair was powered by the 9.5 hp Rotax 185.

Are we talking Brake hp, SAE hp or RAC hp?
Obviously recent engines can be run on a dyno to measure the hp, but how was the hp actually measured on these earlier engines?
Don't forget the 'norm' in earlier times was simply to calculate it using the RAC method (really for taxation) which bore little resemblance to the actual output with (for instance) an Austin 'Big' 7 of 900cc rated at 7.99 RAC hp but actually giving 25 bhp when measured on a dyno.

The DH53 Hummingbird was designed for the same Lympne Light Aircraft Trials in 1923 as the EE Wren. I think the prototype had a 750cc Douglas engine but can't easily find its power. There is a story that Geoffrey de Havilland was flying it home from an exhibition in Belgium and was humiliated to be overtaken by a goods train. Very low rice pudding coefficient, that!

Surely the Jaguar must come pretty close to qualifying?

:E

PDR

The Gossamer Albatross crossed the English Channel in 1979. One human pilot-power, about 0.4hp...

Was it the Hatfield man-powered aircraft that was fitted with a model aircraft engine to assist in trials?
IIRC the story was that it accidentally flew well beyond the overshoot as there was no installed pilot facility to stop the motor .......

The lowest powered aeroplane I can think of is the English Electric Wren from 1921, powered by a 7.5 hp ABC engine.
One still exists, on Shuttleworth, and it is still flying, but these days accelerated to flying speed by a bungee cord.
I believe that the first Birdman was powered by about the same amount of power, but later they used 15 hp engines.

I don't know about the Hatfield aircraft (Puffin?), although in 'Delta Papa' the late Derek Piggott mentions flying the SUMPAC at Lasham with the assistance of a Madewell 49 model aircraft engine that he bought whilst in the RAF. The Madewell 49 is about 8cc...


https://cimg4.ibsrv.net/gimg/pprune....2ff039a0b4.jpg
Madewell 49 model aircraft engine used on SUMPAC

My Monnet Moni had a comparatively massive 30hp from 292cc! (and cruised at 85mph ias)

I think I'm right in saying that that was when he decided that the perceived wisdom of the time of very low-powered light aircraft was never going to work.
That led to the idea of adapting parts of the plentiful Airdisco V8s into the Cirrus to power the Moth.
That seemed to work...
The motorcycle engine idea, in theory, would probably work better now as 750cc 'bike engines now as opposed to then are very different. Probably lighter and certainly vastly more powerful. However, I'm sure a modern engine screaming at 10,000 plus rpm to develop its 100 plus bhp is entirely unsuitable for an aircraft, not to mention deafening.

Heading off on a tangent a bit, but the ill-fated Bugatti 100P replica used motorcycle engines. The accident report highlighted that it wasn't the engine but the clutch/transmission/gearbox that contributed to the power failure and subsequent crash. If your engine runs up to 10,000 rpm, you're going to need some way to get those revs down to below 2700 for your prop.

To show that low power is still used, here's how an Aeronca C3 powered by JAP goes:
Low RPC flight

The point being missed by people advocating this sort of thing (along with suggestions that many car engines of 200-300bhp would be cheap lightweight alternatives to "expensive, heavy and archaic" aero engines, is that a 200bhp car engine (or a 100bhp bike engine) is designed and stressed to develop this power only for very short periods, and its "max continuous" rating is usually less than half and often barely a third of this. Car and bike engines only use full power for accelerating from a standing start or climbing *very* steep hills - the rest of the time they chug along at 30-50bhp (or 10-20bhp for the bike engine). Aero engines are required to run at a much higher cruise power level so the mechanical and thermal stresses (and things like oil cooling) are very different.

For example the most powerful version of the 3.2litre Porsche Flugmotor was rated at 240bhp, whereas the same basic engine used in sports cars was offered in versions that produced over 380bhp. The geared cams and twin ignition systems needed for aero application weren't responsible for the power deficit.

At another extreme, the 1040ish BHP produced by one of last season's F1 turbo-hybrid engines (1.6litre V6, mandatory 16k rev limit) was indeed a continuous rating, with some circuits having over 60% of the lap at full power (and achieve better than 50% thermal efficiency while doing it, which is frankly mind-blowing). But these engines have a TBO of less than 15 hours, and as with some aero engines, many of them never reach the TBO...

PDR

The last semi-successful car-to-aircraft engine conversion (just my opinion of course) is the Thielert / Continental range of diesel engines, based on Mercedes automotive engines. Although they are nice to fly behind, the engine is a lot more complex than a comparable Avgas-burning four-cylinder and there is hardly anything of the automotive version left in the final product. They also need to use a gearbox, and this component is what you'll be opening up regularly as there are several parts that need to be replaced, and replaced again, before the engine itself reaches its 2100 hour life limit.

But was the Wright Flyer actually "self-launching"?

I recall it was sent down some rails by a rope launch to get to flying speed?

Yes... that was Bryan Allen, an approx10.5 stone racing cyclist and indeed averaged something between 0.25 and 0.4 HP its estimated I believe. He flew a lot further than the 22 miles across the Channel due to cross and headwinds too.
However, today, a lot more is known about cyclists output and think its rumoured 0.7 HP is possible for sprints. Phew !!!

Another fact, Paul McCready's Gossamer Condor which won the £50,000 figure of 8 Kremer Prize was optimised for about 6 ~8 mph I believe whereas Albatross was upped to 10-12 mph to reduce the crossing time by reducing wing area and refining Condor further.
Power to stay airborne is of course I think proportional to speed cubed (equiv to minsink in a glider)
The Hatfield Puffin managed 900+ yards.. but wasn't really able to do a 180, well maybe not a 45 even? Ran out of runway eventually I was told.