World Record for first human powered ornithopter sustained flight

On Thu, 23 Sep 2010 16:35:52 -0700, Bob wrote:

I am not expert on this and was not involved in construction... the
pylon is merely for wing support at rest, the flapping is achieved by
drawing down on a cable to the underside of the wing, generated lift
makes the wing rise up, and the process repeats.

Thanks for the link to http://hpo.ornithopter.net - its just a shame that
nobody thought to supply it earlier because its a good site and contains
a lot of information.

Now I understand the need for such a high pylon - without it the geometry
would make the cable driven wing flapping a non-starter. As it is, the
angle is still a bit flat for real efficiency: more of the pilot's effort
must go into trying to compress the spar than into bending it down but
fitting an even higher pylon must be pretty much a non-starter.

No, of course not, just that I don't recall other MPA attempts claiming
records until the Cramer Prize had been collected.


This is for a flapping flight.

Certainly, but its still man-powered. The only difference is the way that
grunting and sweat gets converted into forward motion. And, of course,
flapping wings aren't as efficient as a prop.

That, combined with the unavoidable geometric inefficiencies of the
flapping mechanism, explains the 620 watts needed for sustained flight.

By comparison, Daedalus 88, which holds the MPA distance record of 74
miles, flown in a touch less than 4 hours, only needed 200 watts for
sustained flight and flew at about the same speed as Snowbird.

To put these in perspective, a typical human can generate 350-450 watts
continuously for several minutes, which explains quite nicely why
Snowbird ran out of steam after 20 seconds with a reasonably fit pilot
while Daedalus, with a fully fit racing cyclist flying it, was able to
fly for four hours.

Don't get me wrong: now that I've seen some numbers I think the Snowbird
team did an excellent job.

Subsidiary question which others have asked in other places: what is
the glide performance without flapping? The aircraft looks as it it
should be a fairly efficient glider, so I'm curious about its sinking
speed and glide ratio.

The team could likely tell you, see: hpo.ornithopter.net

Glide ratio 20.9:1 - that's pretty good for an aircraft flying at 25.6
kph (16 mph, 14 kts).

At a rough guess its operating at a Reynolds number (RN) of around
300,000 and, from what I can see from the photos, the wing section looks
like one a modern F1C (a free flight engine-launched competition model)
would use. That is an entirely sensible choice for an aircraft operating
at that sort of RN. These sections are optimised for lift generation
rather than low drag, so that makes the achieved glide ratio pretty damn
good since its the whole-aircraft L/D figure, not just the wing section.

As a glider pilot I would describe the sink rate as considerable, lots
of drag, not a floater to my eye.

You might be surprised. From the flying speed and quoted L/D ratio I get
a sinking speed of 0.34 m/sec.

There are very few gliders that manage less that 0.5 m/s. Of course the
glide *angle* looked steep to you because the airspeed is so low.


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