Here's a glider design that I'm trying to morph into a pop-pod BG. The glider should fly as shown, with the CG at about 25%. The ballast weight is about 1/8th ounce, or one good ball-shaped fishing sinker. I'm going to build a couple of these to see if I can trim it for a good glide, then I'll work on the pod.

Notice on the 2D views the working margin value of 8769.28... RockSim says it's overstable.

Wingspan: 13.5"
Length: 12"
Weight: 0.472 oz

Enjoy!

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Freewind BG.rkt (34.7 KB, 99 views)

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Craig McGraw

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SAM 0044
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I really like the look of this one, Craig.

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John Thro, NAR #84553 SR
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Thanks!

I wish I knew more about BGs than I do. There's both an art and a science to them, unfortunately I'm neither an artist nor a scientist...

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Craig McGraw

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SAM 0044
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Yeah, you and me both. And I don't generally have either the time or the inclination to spend much time trying to refine things until they work right.

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John Thro, NAR #84553 SR
I was too old when I started! Now I'll *never* become a BAR!

The one rule of thumb that I've always used is to have some stability inducing part of the glider be on both sides of the motor thrust line. I've done this by having the vertical stab under the fuse and the wingtips above the thrust line via dihedral. That said, I do like the looks of the glider.

Kevin,

Behold... The Freewind BG Mk II...

Is this something of what you had in mind? I know the wing tips are not quite where you're describing, but I may have another idea for that...

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More dihedral, man. More dihedral.

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OK, I'm listening about the dihedral issue.

The new Mk IB goes back to the original Mk I plan, but increases the wingspan to 14", and the dihedral to 15 degrees. The wingtip chord is shortened to 1.75", but the wing root remains the same.

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SAM 0044
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And here's the Mk IIIB, with the polyhedral tips. Same wingspan, but the first dihedral is now 15 degrees, and the tips have been adjusted to match the original 90 degrees (relative to each other).

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Craig McGraw

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SAM 0044
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Mark IB looks good - but you still might want to flip the tail upside down - from my reading on the subject, that will increase the stability of the boost (right now it's like having three fins on one side of the rocket and none on the other).

Mark IIIB looks sharp, but you might have too much dihedral in it. The sources I've studied on boost gliders (I don't claim to be an expert) have all said a total of 15 degrees is what you want - For example, if you have a three section wing (flat plane in the center and two dihedralled tips), you want each section to have a dihedral of 7.5 degrees. So, with your four section wing, you'd want each section to be 5 degrees from the next. The more sections of dihedral you have, the closer you are approaching elliptical dihedral (where the whole wing is just a smooth curve) Just for clarification, this is an example of elliptical dihedral:

http://www.ehobbies.com/pkz4700.html

If you haven't been there yet, you might want to check out the Rocket Boost Gliders Yahoo group:

http://groups.yahoo.com/group/rocketboostgliders/

A lot of the boost glider (from small gliders to RCRG) gurus hang out there and throw around a lot of good info there. I am just an unworthy novice compared to them!

Greg