Builds Rockets for NASA
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- Aug 27, 2011
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So what makes this different?
1. I have a problem with bending/bowing of the rotors in launch configuration on these "tubeless" rockets due to the stress from the pull bands. This is especially true when I go down to 1/16" balsa. Here I have added an internal 1/16" strip orthogonal to the rotor. It does help a little bit, and the position internal acts as a "stop" or edge to prevent INTERNAL bowing (bowing of the mid portion of the rotor length from bowing toward the central axis.)
2. I use much smaller Rotor Stops/Band Displacers. These are about 1/2", and seem to work just as well as the 1" ones. Since the are positioned like (and unfortunately and unintendedly) act like Canards, they definitely hurt the stability of the model, and certainly add a bunch of drag, so the smaller I can make these (as long as they work) the better. They are a TriLaminar mixed balsa and basswood ply. What I have found works best so far is to use 1/32 basswood for the two outer layers, the orientation is perpendicular to the the long axis of the rocket.
There are TWO reasons for this orientation.
First, these are slightly wider span-wise compared with the internal/encased 1/16 balsa, so they create a "notch" to hold the band in place. Since the tendency is for this to slip laterally, if the outer plates were PARALLEL it would just snap the edges off (been dere, done dat, didn't even get a T-shirt.) The second is it provides strength in this axis.
The INTERNAL section is 1/16" balsa, with the grain orthogonal to the above basswood strips and parallel to the long axis of the rocket. Again it is slightly (1/8") shorter in span to create a notch.) The Rotor Stops have to exert force in orthogonal directions when the rotor deploys, getting "banged" between the rocket's hub's side (long axis of the rocket) and the attached rotor, which at the point of impact is roughly at right angles to the hub (actually a little less, to allow for a bit of dihedral.) It also adds to the overall strength. The width is just enough to let the stretched rubber band slide into the slot, if I make it any narrower the band gets stuck and becomes ineffective. The total width is 1/32 plus 1/16 plus 1/32, so about 1/8 inch. I debate whether to put a neutral airfoil on this. yes, it would reduce drag, but it also makes it more break-able.
3. I am going back to using "used" Estes Solar Igniters and toothpicks for the distal (tailward) attachment site for the band. Of course, hard to beat the price! What I REAAAALLLY like is that, after doubling it and twining the strands, I can put a VERY acute bend on it. The acuteness of the bend allows this to withstand quite a bit of force without ending, but it is EASY to bend and unbend to attach and release the bands when I need to.
4. Also seen on the above image is a small forward launch lug. I sent one of my rockets to Tim Van Milligan, who tried it out I think at one of the NARAM events. It only had a rear lug. Apparently it binded ("bound"?) on the rod on his first try, and he never tried it again. The forward lug also keeps my lugs from breaking off while on the rod or rail. Since they are attached to BALSA, rather than to a cardboard or fiberglass rocket tube, it tends to shear off with a thin strip of balsa when on the rail for a significant length of time if there is much wind.
BTW, the spelling is chosen to keep this from coming up as a trademark issue or in other searches. I kind of made up the name on the spot (got tired of calling it "just another AirBrake rocket", hopefully less tired than you guys get from viewing them!)