I have never entered a posting on RCSE, but I find that I can no longer remain silent
on this thread. Using a little bit of physics,
I calculated the height gain obtained from converting the excess energy of a launch
into potential energy of height. Using the
initial velocity mentioned (54 mph) and a final velocity of 20 mph with no losses due
to drag, 82 feet of height gain could be
realized. This result is independent of weight. Velocity at the time of release is, of
course, dependent upon the throwers abilities
and that is where the weight comes in. The result is quite sensitive to the release
velocity since it is squared.
Now, Dick Barker's figure of 84.6 mph could theoretically produce a height gain of 221
feet. Now that would be impressive! Come to
think of it, I have seen Joe Wurts throw and that is impressive. But, I have never
seen him produce a 220 foot throw, though.
Throwing some other numbers into the frey, if your toss nets you 221 feet of altitude
and your sink rate is the magic 1 foot per
second produced by the latest simulation results, under dead air conditions (no
thermals) you should not hit the ground for 3
minutes and 41 seconds. How come it always arrives at the ground in something like 30
to 45 seconds? There seem to be some slight
discrepancies between the numbers bandied about. Which, if any, are the more correct?
Even a 90 foot toss should net a minute and a
half with a 1 ft./sec. sink rate. As Rush Limbaugh says, "run the numbers" and you can
usually spot the bogus claims.
I suggest that on a calm evening, someone go out to the field with a 8 foot or higher
step-ladder and a buddy. Give it the old
heave, and set up for minimum sink. Have the buddy stand tall on the ladder and time
the flight from his head height to the ground.
Divide height by time and you have a pretty good estimate to use for min. sink rate.
Now do your best throw, measure the hang time,
and calculate the throw height using your sink rate. I know that I'd be interested in
a real answer. Or alternatively use an
observer and some trigonometry.
Keep em flying
Al Scidmore
Dick Barker wrote:
> 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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