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timallard
USA
4 Posts |
 Posted - 02/16/2009 : 14:04:33
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After about a month of intense work, here's a novel design of HPA glider for those interested to consider:
http://mallard-design.blogspot.com
Like most people I want something you can really soar and not have the wings fall off.
cheers,
Tom Mallard
Software - Web Apps
Industrial Design |
Edited by - timallard on 02/16/2009 14:08:44 |
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Alan Krause
23 Posts |
Posted - 02/16/2009 : 22:14:12
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so do you think this is something that would work into an article for Human Power?
thanks
Al |
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timallard
USA
4 Posts |
Posted - 02/20/2009 : 10:03:04
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quote:
Originally posted by Alan Krause
so do you think this is something that would work into an article for Human Power?
thanks
Al
Yes, it'll include the work to get an up to date review of HPA's and what can be gleened to use for an human power assisted take-off sailplane.
the pilots I've talked to also think we can build good wings that are portable, FAA certified, and be light enough for a human powered take-off, and, recently ran across a link to a team in Canada with almost identical design goals so I think no one's given up on the concept (haven't gone back to it yet).
The key to me for any chance at a practical machine was when I figured out a way to change chord height. You have to change wing shape, a soaring wing profile can't be too fat, you need speed but it can't get off the ground with the thrust from a person.
Even with that trick my vision of taking off is to interval your way up, climbing hard and backing off, sinking and picking up speed to jam the next climb, repeat until you're in a riser or have enough altitude to leg it to one.
Yeah, good article material.
Tom Mallard
Software - Web Apps
Industrial Design |
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Alan Krause
23 Posts |
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Talos
United Kingdom
32 Posts |
Posted - 07/19/2010 : 02:05:16
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Tom; all gliders experience drag, which would slow your glider by causing a deceleration if it wasn’t for the intervention of gravity. The fact that the glider doesn’t slow is because gravity is countering the deceleration that drag is causing. As your glider descends it loses potential energy (height) and this energy has to go somewhere. It reappears as kinetic energy (speed) in the aircraft thus countering the tendency to slow. In other words, this energy is always exactly the same as the potential energy being lost due to drag. If you use gravity to descend faster you’ll increase the drag and lose more potential energy which is converted to kinetic energy, i.e., its the transfer of potential energy into kinetic energy that makes the glider travel faster.
Now, if the glider is trimmed to rise up it cannot receive any energy from gravity so it must convert some of its new found kinetic energy back into potential energy (height). In other words, it will slow considerably due to (a) converting speed into height, but, (b) it is still experiencing drag.
This means it is impossible for a glider to rise up higher than it was previously unless its speed is reduced to less than it was initially, and this means it will subsequently lose lift (height) yet again. In other words, it cannot gain height by successive descents and ascents (Phugoid oscillations). If you have a head for the ‘abstract’ take a look at this article from The Proceedings of the National Academy of Sciences of the United States of America. Part of it concerns the Phugoid oscillations of a gliding microraptor, but the physics are the same for all gliders. Scroll down to Fig 3 (about half-way down the scroll bar).
Website, www.pnas.org/content/104/5/1576.full
If you want to learn more about potential and kinetic energy take a look at my website. |
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n/a
26 Posts |
Posted - 07/22/2010 : 08:42:07
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Two points:
Biran Alen (apologies if ive spelt his name wrong) sights Phugoid oscillations (thanks talos) as the reason for the failure of the earlier British attempts at HPA. Specifically through inept cyclist with no knowledge of flight. ; as the amplitude of the oscillation increases it will tend to coincided with the baseline. Ie, the ground.
Secondly, with thicker profile foils the air is accelerated over the top surface of the wing. This requires energy input from the system, which is later recovered as lift. This process can never be 100% efficient, so though a thicker chord generates more lift it also generates, proportionately, more drag.
As HP is so low the craft must have minimal drag, so i invite you to find the lowest drag foil section....
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timallard
USA
4 Posts |
Posted - 09/22/2013 : 16:15:46
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Revisiting after many moons, still like this concept, it got published in the first issue after reorganization, still want to try to build a successful one.
Tom Mallard
Software - Web Apps
Industrial Design |
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timallard
USA
4 Posts |
Posted - 09/22/2013 : 16:28:38
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In answer to the concerns about increasing drag with chord height, I found a profile that increased lift-to-drag ratio yet overall drag was about the same as when the chord height was minimum.
Doing this jumps the ability to climb but doesn't reduce the wattage needed, that's why I always ended up thinking that to take off you have to sprint @85-90%, recover on a glide, sprint again, recover again and be able as an athlete to do enough of them to gain a thermal or uplift on a hill.
Having the switch from drag profiles for higher speeds vs takeoff is a problem that I want to solve with battened upper wing surfaces, sails, that gave the flexibility to change, keep it light and somewhat simple on rigging it so it's one lever for the pilot.
It's a big ask but worth a try, still want to build one.
Tom Mallard
Software - Web Apps
Industrial Design |
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Talos
United Kingdom
32 Posts |
Posted - 09/29/2013 : 11:34:26
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Tom, take a look at this talk on Understanding Flight by David F Anderson, and forget about airfoil shapes.
www.youtube.com/watch?v=hQ99JkaOwEk
Talos |
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