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Jon Howes
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Posted: Tue Mar 18th, 2008 07:56 am |
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A very old model. Flew like a demented hornet, a little unstable, dates from about 1980.
Interestingly (to Kjell if no one else), Kjell would describe the wing motion as "fan-flapping" since the phasing of incidence changes was passive and max amplitude of flap also tended to concide with max amplitude of incidence. Wings were 180 degrees out of phase, early thinking so longest flight was about 8 seconds. If I did it again, the lower wings would lead by 90 degrees to get a bit of spanwise flow going and smooth the motion out. I would also control the incidence phasing mechanically since passive phasing is never optimum.
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 Last edited on Tue Mar 18th, 2008 08:53 am by Jon Howes
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Jon Howes
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Posted: Tue Mar 18th, 2008 08:02 am |
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Moving on, in about 1982 or so I got interested in slab wings. No pictures of these experiments but they consisted of rigid wings moving on a pantograph mechanism to try to reduce ornithoptering to the simplest possible motion.
The reasoning was that if the wing is considered to be a glider on the downstroke then the mass of the rest of the aircraft may also be considered as being pulled up towards the gliding wing. As the wing and body meet, the wing is suddenly unloaded, the body drops a bit and an incidence snatch of the wing allows it to return to the starting position relative to the body.
The first model on these lines was a pair of gliding kites moving against each other coupled by lines which controlled both incidence and di the winching. Worked to a degree but very hard to launch and easily upset by the slightest current of air.
I moved on from this to the rigid wing plus pantograph mentioned above but had no success as I built it much to heavily, also, rubber power meant that a TDC and BDC snatch occurred wasting lots of energy as the mechanism backlash was taken up.
Last edited on Tue Mar 18th, 2008 08:04 am by Jon Howes
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Jon Howes
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Posted: Tue Mar 18th, 2008 08:15 am |
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Real life got in the way of interesting stuff for too long in the 1980s so I did not get back to ornithopters until about 1992. Mostly I was doing theoretical studies based around the gliding downstroke model with a lower loaded upstroke, one useful result was the propulsive efficiency of a glider, something of fundamental importance but seems to have been missed in the past. As I have posted before, this is:
Eta=((L/D)^2)/((L/D)^2+1)
Since, if the upstroke can be made non-damaging by keeping it short and unloaded, this is close to the potential propulsive efficiency of a basic ornithopter (not a nasty, flappy membrane one however) it is a rather important result.
I wanted to smooth out the motion and started to consider articulation of the wing. This also means that elements of the wing need to carry different flap angle and incidence phasing. The options are fairly simple for two-stage articulation (more stages have been considered): The outer panel can lead the inner or vice-versa. If the outer panel leads the upstroke will have reduced span, the tip path will form a loop in the same direction as the tip vortex which is plainly not wanted so the inner panel must lead the outer.
With a leading inner panel the spanwise motion forms part of a travelling wave, travelling away from the body. A very cursory examination showed that this was equivalent to the flow caused by a spanwise vortex street with the flow at the wing location travelling outboard along the span.
Here is a front view of the wing with the inner panel leading the outer and showing the tip path loop:
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 Last edited on Tue Mar 18th, 2008 10:12 am by Jon Howes
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Jon Howes
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Posted: Tue Mar 18th, 2008 08:20 am |
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I had a diagram of the spanwise wave motion somewhere but cannot find it, however, I AM SURE YOU CAN WORK IT OUT FOR YOURSELVES!!!!!!!
What this led to was my articulated model of 1994. This did not simply carry an articulated wing with phasing of the panels, it also had correct incidence phasing using a skew hing at the articulation joint. The inner panel was a floating membrane to blend the outer panel incidence to the wing root incidence. This model was very successful, regularly putting in flights in the 4 to 5 minute duration range with rubber power. When fully sorted it also had a very slow flap rate of about 0.5 hz
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Jon Howes
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Posted: Tue Mar 18th, 2008 08:21 am |
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| And my infamous, barely legible sketch of this monster: Attached Image (viewed 1074 times):
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Jon Howes
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Posted: Tue Mar 18th, 2008 08:24 am |
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| It had been at the back of my mind for a while that there is really nothing particularly magical about flapping flight and flapping is simply partial, rather than full rotation. I contemplated a few concept with 360degree flapping (otherwise called rotation, note that this idea is not original, Alphonse Penaud proposed a model on the same principle in the 1870s) and built one like this: Attached Image (viewed 845 times):
 Last edited on Tue Mar 18th, 2008 08:27 am by Jon Howes
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Jon Howes
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Posted: Tue Mar 18th, 2008 08:26 am |
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| It flew really well! I have been contemplating a full scale runabout based on the same principle, something like this: Attached Image (viewed 691 times):
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Jon Howes
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Posted: Tue Mar 18th, 2008 08:31 am |
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With the spanwise flow benefits of phased articulation and the skew hinge to control incidence phasing it is a small jump toi realise that skew can also be applied in three dimensions to allow the wing panel to move forwards and aft as its incidence changes. This allows the constantly loaded, minimum energy wake to be achieved. With my other work on non-planar wings coupled to all the other tweaks and twist, very high propulsive efficiency plus high span efficiency should be achievable. This led to my full scale project proposal.
This machine is foot launched and landed with a rowing action using a combination of sliding foot rest and pivoted control yoke.
The intention is to take advantage of the very effective foot take off to allow most of the early hydrolytic energy burst to gain height before using the power assisted glide to extend the flight:
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 Last edited on Tue Mar 18th, 2008 08:33 am by Jon Howes
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Jon Howes
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Posted: Tue Mar 18th, 2008 08:37 am |
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So far, I have built a pilot support frame, tested it to destruction (it passed), built another pilot frame and a grossly overweight pilot seat, now to be replaced by a frame with a fabric sling. Designed the wing aerodynamically in fairly fine detail and need to pull my finger out and finish the b*gg*r off. I will take some pictures of where it is at at present and post as soon as it is dry enough outdoors to avoid wrecking my lightweight woodwork.
Commercial break; here is my old Bleriot (1/8 scale, rubber powered, a pig to build, nice wooden pram wheels however!):
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 Last edited on Tue Mar 18th, 2008 08:57 am by Jon Howes
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Jon Howes
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Posted: Tue Mar 18th, 2008 09:11 am |
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| The pre-test pilot frame parts: Attached Image (viewed 840 times):
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Kjell
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Posted: Tue Mar 18th, 2008 09:13 am |
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Jon.
Many thanks for showing this pictures and drawings.
Have you made any project with electric motor+gear drive?
Kjell
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Jon Howes
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Posted: Tue Mar 18th, 2008 09:53 am |
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| Here is the derivation of glide propulsive efficiency: Attached Image (viewed 688 times):
 Last edited on Tue Mar 18th, 2008 10:14 am by Jon Howes
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Jon Howes
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Posted: Tue Mar 18th, 2008 09:54 am |
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Kjell,
I have used electric drive but did not find the result worth the trouble.
Jon.
Last edited on Tue Mar 18th, 2008 10:17 am by Jon Howes
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Jon Howes
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Posted: Tue Mar 18th, 2008 10:03 am |
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| And here is a graph of glide efficiency vs L/D ratio: Attached Image (viewed 680 times):
 Last edited on Tue Mar 18th, 2008 10:15 am by Jon Howes
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Kjell
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Posted: Tue Mar 18th, 2008 10:23 am |
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Jon Howes wrote: Kjell,
I have used electric drive but did not find the result worth the trouble.
Jon.
Jon.
What kind of drive unit do you recommend?
Kjell
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