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Old Jun 17, 2004, 06:28 PM
Nathan Chronister
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Willi, that all-white bird must be really pretty in the air. And that's a really clever idea you had. I've messed around with tethered balloons a little. You really will need completely windless conditions if you want the balloons to rise vertically. It happens once in a while though and I'm looking forward to those photos! (Drop it from two different heights so we can factor out the initial freefall stage before it levels off into a glide.) One time I tried to use a couple of party balloons to raise a hook up to my treed Park Hawk to try to get it down. The balloons never got anywhere near the Park Hawk, and a slingshot (despite being illegal in New York) turned out to be a more effective technique. After six months sixty feet up in a tree, that old Park Hawk is still an active member of my flock.
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Old Jun 17, 2004, 08:08 PM
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Old Jun 18, 2004, 08:36 AM
Nathan Chronister
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How did you reduce the flapping amplitude of the Cybird? That's really cool because when I made my own wings for the Cybird gearbox the flapping rate was too low. It climbed great but was drawing too much current. (This is because my spars were much stiffer than the original telescoping/tapered Cybird spars.) Instead of changing the amplitude I had to make the wings smaller.

My experience with foam wings suggests they can take away the lateral stability of the ornithopter. You may need a vertical fin in order to make it stable. (Just about every foam wing flapper I've seen fly has had a vertical fin, and my foam Park Hawk wing was not very stable without one.)
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Old Jun 18, 2004, 10:38 AM
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Old Jun 18, 2004, 02:22 PM
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I have the same experience, Willi. My bird with normal-tail fly stable and is better controllable. Karel
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Old Jun 18, 2004, 11:12 PM
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Old Jun 19, 2004, 07:25 PM
Nathan Chronister
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I did some glide tests with the Slow Hawk yesterday. I hope to do the same for Cybird but I couldn't get mine to glide properly from hand launch so it will have to wait. The Slow Hawk was difficult at first. I had to learn the correct launch technique and adjust the tail position before it would even stay aloft on the steep hill I was gliding it down. The best tail position turned out to be in a straight line with the top of the body. At this setting, the tail contributes lift so the directional control is reversed. I finally got some good glides. These flights were made with little or no wind. If anything, wind was upslope and very light. I tried to launch the Slow Hawk in such a way that it would go into a consistent glide without gaining or loosing too much from the energy of hand launch. Therefore while launch speed is certain to influence these glides, I think you would get similar results if it were controlled for better. By taking only the best glides the results if anything overestimate the actual glide performance. Based on the best four flights (out of >20 attempts) here are my results:

Height: 27 feet
Distance (horizontal, avg of four flights): 99 feet
Time, (avg of four flights): 6.8 seconds
Glide ratio (avg of four flights): 3.7
Descent rate (avg of four flights): 4.0 feet per second

This is a much better descent rate than those reported earlier, presumably because of the tail adjustment. I'm in the habit of pulling back on the stick during glide, but the benefit is illusory. Pulling back on the stick causes a momentary flattening of the glide but hurts in the long run. A descent rate of 4.0 feet per second is just a little worse than my paraglider (3 ft/sec) and should be adequate for soaring in moderate thermals.

For ridge soaring, the glide ratio is more important than the descent rate. Since the horizontal speed was about 10 mph (14.6 feet per second) that will be the maximum wind speed for ridge soaring. Any higher and the Slow Hawk will get blown back behind the ridge. You'll need to find at least a 4 ft/sec updraft in less than a 10 mph wind (actual wind speed is a little more because I'm only giving the horizontal component). In other words, the angle at which the air comes up the slope must be steeper than the angle at which the ornithopter descends. If the wind is half the maximum speed (5 mph in this case) then the air must come up at twice the glide ratio (5 mph horizontal and 8 ft/sec vertical). You'll need really ideal conditions and a pretty steep ridge to ridge soar this thing.

The wings were locked in the recorded glides and it did not glide as well with the wings not locked. The Slow Hawk was flown with standard equipment (8 cell nimh, no nose weight) and was the old design (before planform and spar changes). The new design has a stiffer wing which is probably less draggy so it might have a better glide ratio and certainly should penetrate better.

Nathan Chronister
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Old Jun 21, 2004, 01:36 AM
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Here is an altitude chart from my flight today with the ParkHawk. The spikes are due to the ZLOG unit being exposed and sensitive to sun light.

Kasra
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Old Jun 21, 2004, 01:39 AM
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The max altitude reached was around 350 Feet. I have taken the locking mechanism off of the PH. For majority of the descent, I had the throttle at minimum flapping rate.

Kasra
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Old Jun 21, 2004, 07:15 AM
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Old Jun 21, 2004, 01:55 PM
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Hi Willie,

This is the stock smaller Parkhawk(36" span?) I am running a Razor 300 w/ 2-cell I-Rate 1100 Li-Poly from www.lightflightrc.com . Please note that I was not attempting max climb rate and you can clearly see the climb rate getting reduced. I will weigh the PH and let you know.

Thanks,

Kasra
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Old Jun 22, 2004, 12:55 AM
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I checked the weight. The PH weighs 10 Ounces and the battery pack is 1.8 Oz making the AUW 11.8 Ounces.

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Old Jun 22, 2004, 06:03 AM
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Old Jun 22, 2004, 03:10 PM
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Willie,

Lookup the ZLOG unit also. http://www.hexpertsystems.com/zlog/

I have one. It works great.

Kasra
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Old Jun 23, 2004, 07:39 AM
Nathan Chronister
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Based on the weight and wingspan, it sounds like that's actually a Sunbird/Shrike rather than a Park Hawk. The Sunbird should glide a lot better than the Park Hawk once you get the lock put back on.
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