I have a feeling that there may be a bit of skepticism about the 80 or 90
foot numbers for discus(tm) style launching so lets take a look at launch
speed instead:
Back in February Joe Wurtz said:
>Anybody out there have any data on throwing endspeed vs. weight? It would
>be quite interesting to put this into the analysis. I have been using 80
>ft/sec for the throw velocity, which equates to 54 mph. This ended up being
>quite close to reality based on the radar gun on the field at the AZ contest
>a couple of weeks ago. Quite a few folks got to 50 mph, and the best throws
>were at about 53 mph.
Guess he can view this as a late reply to his question. To get an idea of
launch speed I grabbed one of my UpLink-58 HLGs the way I would hold it for
a discus style launch and balanced the right wing on a 4 drawer file cabinet
so the wings were level when my arm was extended. I then measured from the
center of the wing to my nose while I was facing the same direction as the HLG.
This number was 58 inches or 4.83 feet. Lets assume this is the radius of the
circle the hlg follows during the launch. Now we need to decide how far around
the thing travels when launching and how long it takes to get to the release
point. For these I needed a bit of help. In mid July Gary Whitney posted a URL
for some IHLGF photos that had a sequence of my tossing a 11.5oz UpLink. He
photographed it with a Panasonic digital video and then captured the frames on
his computer. The sequence shows about 460 gegrees of plane rotation from start
to release. The .jpg pics also had a number sequence so I would guess he stored
all of the frames then picked out just enough of them to show how the launch
works. The ones he showed were numbered from 7 to 22 - in other words 15 frames
or 1/2 second at the standard rate of 30 frames per second. I went over to the
park a while ago to try and see if this is correct. It seemed a bit fast but
the launch takes well less than a second. For now I will guess that he had the
frame snatcher set for 24 frames per second. In that case, 15/24 is .625
sec which seems about right. Can you tell us what you did Gary?
Now for a bit of very simplified math as it was a long time age when I went to
school. The plane travels in a circle with a radius of 4.83 feet and covers
460 degrees. The path length would be pi * 2 * R * 460 / 360 or 38.78 feet.
Assuming a uniform acceleration from start to release the hlg would have to
be going twice as fast at release as it would if it just kept circling my
nose at a steady rate of 460 degrees every .625 seconds. Sounds right - how
do we get the number? How 'bout brute force: 38.78 feet divided by .625
seconds = 62.048 feet per second average. Multiply by 2 for 124.1 feet per
second at release. You can't verify this at release with a radar gun as the
right wing tip is going a whole lot faster due to the extra 29 inch radius.
Yah, you gotta build things strong to stand the side forces that lever things
into a straight line. Anyway, this works out to 84.6 mph at release for the
11.5 oz ship the video sequence captured at IHLGF. It whistles pretty loud
on release.
What I need now is for Gary Whitney, Joe Wurtz, John Hazel, Dave R.(Barnyard
Science), or others to confirm that the numbers makes sense and how it would
translate to height on the 11.5 oz plane and on the newer 9oz one. Wing is a 7
percent 6063 looking thing but with a bit more camber. The launch is at zero cl
as my feet are still on the ground when I let go. My launch preset arcs it up
till I turn it off which is normally in the 70 to 80 degree range if I want max
height.
Dick Barker
Seattle, WA
- The Old Fart Glider Flyer -
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