Manufacturer: | Scratch |
Spyglass 1 is a rocket glider. This is different from a boost glider in that, in a boost glider, parts of the rocket separate to transition from rocket to glider configurations. Most commonly, a pod containing the motor and a small recovery system is jettisoned, and what's left bears a very strong resemblance to a free-flight hand launch glider, the sort that might be flown in a model airplane duration competition.
By contrast, in a rocket glider, everything that's attached to the rocket when at motor ignition must remain attached through boost, coast, transition, glide, and recovery.
As you might imagine, it's a bit more of a challenge to build a rocket glider that flies well; it's common to see configuration changes involving changes in position or angle of flight surfaces. Oddly (at least to me), competition designs seem to gravitate right back to the old standby hand launch glider, with a front motor pod and either the wing or the motor pod sliding under impetus of some kind of elastic after the motor ejection burns a string under tension.
These models are complex to build, harder to trim than a normal boost glider, and due to the extra drag of the external motor pod, tend to glide somewhat less well than the pop-pod designs. Until recently, though, there hasn't been much choice; the Edmonds Ecee is an interesting design, but is to heavy and draggy for competition, and the few other sorts of rocket gliders around are even more complex and harder to trim than the sliding-wing or sliding-pod sort.
Now, though, there's Spyglass 1. As you can see from the accompanying reduced plan sheet, Spyglass 1 doesn't have a pod. Instead, it accomplishes the configuration change using telescoping tubes (from which I took the name), powered by the motor ejection charge alone. In boost configuration, the wing and tail surfaces act as fins. At deployment, the inner tube is forced to the rear against a stop. This moves the CG to the rear, as well as increasing the moment arm of the tail surfaces, allowing them to raise the nose into a stable glide position. In glide configuration, the model is aerodynamically clean, with no external mechanisms, pods, hooks, or other excrescences to produce drag; even the transition from the larger outer/forward tube to the smaller inner "tail boom" tube is smoothed by a conical shroud. A vee tail also reduces drag, with the result that when properly trimmed, Spyglass 1 has a light, floating glide and is capable (without particular care to select top quality wood for the prototype) of durations exceeding 30 seconds on a 1/2A3-2T in dead air -- which is to say, it glides about as well as an Edmonds Aerospace Deltie (which sheds its pod at ejection).
Complete plans are available for download from:
The plans consist of two large monochrome TIFF files (one is 11" x 14", the other is 8.5" x 11"), a text file containing building instructions, and a license agreement, all in a single ZIP file.
I should also mention that although Spyglass 1 bears some resemblance to Yitah Wu's Falcon XTRG, the two were developed independently over about the same time frame. Both models were first test flown in April 1998. Though there are gross similarities, careful examination will show that we solved the same problems in different ways in several instances, and neither of us had announced our design when the other was designing and constructing his model.
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