New Design -- Freewind BG

[CPMcGraw]

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. :D

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

Enjoy!

[JRThro]

I really like the look of this one, Craig.

[CPMcGraw]

I really like the look of this one, Craig.

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... :p

[JRThro]

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... :p
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.

[kevinj]

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.

[CPMcGraw]

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... :D

[CPMcGraw]

Here's the Mk III version, with polyhedral tips. The span is now 17".

[gpoehlein]

I can't really tell much difference between 1 & 2, but they both look pretty good. I think what Kevin was really talking about was turning the tail upside down so the vertical control surfaces (rudder) are opposite the boost pod. Also, how many degrees of dihedral do you have there. Rule of thumb is that a dihedral of 15 degrees works about the best, and the dihedral should be wrapped around the boost pod (like you've done). Personally, I like simple dihedral such as you have in versions 1 and 2, and I find complex dihedral as in 3 a bit tedious. Again, the total dihedral should be about 15 degrees.

Greg

[CPMcGraw]

I can't really tell much difference between 1 & 2, but they both look pretty good. I think what Kevin was really talking about was turning the tail upside down so the vertical control surfaces (rudder) are opposite the boost pod. Also, how many degrees of dihedral do you have there. Rule of thumb is that a dihedral of 15 degrees works about the best, and the dihedral should be wrapped around the boost pod (like you've done). Personally, I like simple dihedral such as you have in versions 1 and 2, and I find complex dihedral as in 3 a bit tedious. Again, the total dihedral should be about 15 degrees.

Greg

For the Mk III version, the main wing panels are set for 10 degrees total (+ & - 85 degrees), and the polyhedral tips are at 90 degrees to each other. The stabilizer is set at 30 degrees (+ and - 75 degrees), and the rudders are at true 0 degrees.

The only difference between I and II was the location of the stabilizer attachment, and the shaping of the boom. The wing remained the same. There was no difference in the dihedral between any of the three.

As soon as I get some "housework" done (reconstruction of a wall in my computer room) I'm going to build one of each to see how they fly. I'm starting to get itchy fingers for this project... :D

[GuyNoir]

More dihedral, man. More dihedral.

[CPMcGraw]

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.

[CPMcGraw]

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).

[gpoehlein]

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

[CPMcGraw]

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

Thanks for the additional info, Greg. I'll put the Mk IV and Mk IIIC up shortly, with these improvements. ADDENDUM: They now have their own Mk numbers -- IV and V...

Actually, I already listen in to the Yahoo BG group. I need to look back through the message queue to see if I can find something.

[CPMcGraw]

Following Greg's suggestions, here is the Freewind BG Mk IV.

The vertical fins are now below the stabilizer line, with some trim fins above. The stabilizer mounts to the top of the fuselage, and the wings remain at 15 degrees.

[CPMcGraw]

And now, the Mk V, with both polyhedral wings and inverted vertical tailfins. The main wings are set at 83 degrees, and the tips are at 75, for a total of 15 degrees back from 90. (The total wing dihedral is 30, from tip to tip.) The horizontal stabilizer is attached to the bottom of the fuselage.

[CPMcGraw]

Same design as the Mk V, but with the dihedral at a total of 15 degrees (each panel joint at 5 degrees).

[gpoehlein]

Time to start building, Craig! :p

Greg

[CPMcGraw]

Time to start building, Craig! :p

Greg

Yeah, I know... :o