Hi Manuel,
This is interesting since most free flight gliders are going for duration, but you are going for max L/D. I agree with John about going larger, heavier, and flying faster. I've been running simulations on lots of wings of various size gliders on XFLR lately, ranging in span from 12 inch to 100 inch, but always looking for max duration. The L/D numbers are in there as well, so I will look through the wings I have modeled and see what it shows for L/D.
You mention your goal of 25 to 1 glide ratio. This assumes you launch from 20 feet high and cover 250 long distance with only 10 feet loss in altitude. Just curious if you are taking into account the height of your body and outstreched arm while standing on the atrium. Are you really launching from 20 feet high or is it more like 25-26 feet? I'm curious because it makes a huge difference in the glide ratio you need to hit the opposite wall at 10 feet high.
Also would love to know the wing dimensions of your stretched zwiebox as well as the weight, better yet a photo I could put in my cad program to calculate it's wing area and such. I see this as a great chance to get some real world data on L/D of a known design to help validate the accuracy of xfoil and XFLR at these Reynold numbers.
As a quick check, for what it's worth I just ran some XFLR simulations on 24 inch CLG wing with 3.5 inch root chord. I ran the plane at three weights. At 27 grams, max LD is 10.8, at 42 grams max LD is 12, and at 60 grams max L/D is 13. So according to this, as the RE climbs with the faster flight associated with more weight, you benefit from more efficient operation of the foil. Then very roughly I increased the span to 30 inches (no planform optimization) and this boosted max LD up to 14.5 at 80 grams. If in fact you are launching from about 26 feet you only need and L/D of 15.6 to achieve your goal, so that's not far off.It might be interesting to see what happens if you add some weight to your existing zwiebox.
I'm tempted to build some 30 inch wings simulations for you in XLFR to see what combination of weight, planform and foil gets you the best L/D. If I have time to do this I will share what I find.
Paul
--- In Indoor_Construction_at_yahoogroups.com, Manuel Cisneros <macs8953@...> wrote:
>
> Over the last couple of years I have built a couple of specialized
> gliders for a friend of mine who's company has a yearly contest that
> involves tossing a glider off a 20' platform inside a large atrium and
> awarding a prize to the glider that goes the longest distance. The
> atrium is ~250' X 80' and about 40' tall. No, the atrium is not open to
> the public and is only usable for the glider contest as it involves
> flying a straight line across the length of the atrium, anything that
> circles doesn't do too well, I've tried.
>
>
>
> The gliders I've built are based on Oldenkamp's Zweibox, I think the
> lines (curves?) of this glider are aesthetically superior to most other
> HLG/CLG/DLG designs I've seen. I stretch the wing to 22" but otherwise
> the planform is per the original plan from MAN. The wing is 1/8" sheet
> with molded in undercamber and polyhedral, the tail feathers are 1/32"
> thinned at the tip to near translucency, and the fues is medium 3/32".
> This results in a glider that flies the length of the atrium and
> consistently hits the opposite wall at about 5'-6'.
>
>
>
> The first year one of these gliders was flown at the contest the 2nd
> place glider flew about halfway across the atrium, as I mentioned above,
> my glider hit the opposite wall. The next year someone entered a glider
> that made it almost all the way across the atrium, landing about 5'
> short of the wall. Last year another glider hit the wall about 3' below
> my most recent glider, I took this as a slap in the face and am about to
> start building a new glider for this year's contest.
>
>
>
> What I am shooting for is building a glider that will hit the opposite
> wall at around 10' (25:1 glide ratio). I'm not sure if this is
> possible, but I'm going to try.
>
>
>
> I think an indoor style, built-up design is the way to go. Does anyone
> have any pointers at indoor towline designs I can take a look at? Since
> these gliders are suppose to be tossed rather than launched (the spirit
> of the contest is such that the glider never goes above launch height)
> the model only has to be sturdy enough to survive gliding, not launching.
>
>
>
> Any ideas?
>
>
>
> Manuel.
>
Received on Sat Aug 28 2010 - 08:46:03 CEST
This archive was generated by Yannick on Sat Dec 14 2019 - 19:13:46 CET