by Timothy Day (tday@softronics.com)
While perusing the
China Lake Weapons Digest a few months ago, I
happened across this photo of an extremely cool looking bomb, the Mk81 "Snakeye". It is a glide retarded bomb
designed for low-level, high-precision attack while avoiding bomb-fragment damage to delivery aircraft. Having
discoverd model rocketry about 6 months previous, it became a necessity to construct a scale version. | Below are images from my completed prototype at the request of posters in the Rocketry Online "Recovery" forum. I plan on entering this design in the r.m.r. Design Contest once I finish up some construction notes, and get some higher quality images. |
Mk81 Snakeye (prototype)
Finished Length: 14"
Finished weight: 4.2oz (no motor installed)
Main Airframe: BT60
Motor Mount: 18mm
Reccommended engines: B6-2, C6-3
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Completed rocket, ready for flight. |
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View of "open" rocket. The hinges on the airbrakes themselves are epoxied to a length of basswood, which in turn is epoxied to the BT60 tubing for strength. Note the red overspray on the motor mount tube, and the high tech (Diet Coke can) rocket stand. :-) |
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This image shows the "lip" that the rear airbrakes slide into. The rocket
works on a piston system, so when the ejection charge goes off, the rear section is forced backwards, and the airbrakes
are free to open. Note the slots in the fins (kind of hard to see here) that allow the airbrakes to slide forward "inside" the forward airframe. |
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Closeup of the "inside". The hinges that hold the rear portion of the
airbrakes to the motor mount are nylon R/C aircraft hinges. They are generously epoxied to the motor mount, and wrapped
with electrical tape "just to be safe". Yes, thats a green Estes centering ring for the "forward" hinges. |
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Blurry image of the rear end, sans motor |
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Another shot of the rear end. Here you can see how the fins are attached. The next
version of this rocket will have the "split" fins like the real one. Note the high tech "test stand" and the Boba Fett coffee mug for scale. |
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Here's an image of the nose removed, and the piston pushed all the way forward.
The centering rings are plywood (homemade epoxied basswood layers) |
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Here are the vent holes which release the ejection charge gas. there are eight 3/16" holes in the motor mount tube which was CA strengthened. |
Flight Report:
The Mk81 prototype has been flown four times so far, with some damage occuring on each flight. All flights to date have been on Estes B6-2's.
Flight 1: Complete separation due to inadequate ejection charge venting. This flight proved the stability of the rocket, but the piston shot itself completely out of the forward airframe.
Flight 2: Good boost, but again inadequate venting. While not a separation, the ejection charge destroyed the piston centering rings. Replaced the centering rings with basswood.
Flight 3: First successful deployment!! The rocket entered a fast but stable spin on deployment, but soon became unstable. One of the rear R/C hinges broke free on descent. Added electrical tape around the hinges.
Flight 4: Straight boost, perfect deployment. Again, the rocket spun in fast and landed on fairly soft ground. Broke a forward hinge on landing.