Scissortail

The Scissortail Flycatcher is the State bird of Oklahoma. It seemed like a fitting name for this rocket.

I was thinking about a method of recovery that was more-or-less passive. One that didn't require any preparation, and would be fairly fool-proof and easy to use. What came to mind was some way of changing the configuration from one of low drag (flight) to one of high drag (recovery). Several gliders do this, as do helicopter-recovery rockets. I was looking for something a bit more novel. This is what I came up with.

It's a six inch BT20 with a stock Estes plastic nosecone glued on. I made two spars from basswood that carry the fins. The fins are from a Baby Bertha kit I bought and turned into a Baby Fat Boy before Estes came out with one. The spars pivot on a wood dowel just under the nosecone (I think I probably used a bamboo skewer). There are arms on each spar below the pivot point, that attach to elastic thread. The tension provided by the thread swing the spars out into the recovery position. The other end of the elastic is retained by a ring (made from a scrap piece of body tube) glued on the aft end of the rocket. A conventional style engine block ring (with cardboard disk plug) holds the engine in place during flight. Prior to flight, the spars are swung into flight position and an engine is inserted. Short arms at the aft end of the spars are held against the engine by the tension of the elastic threads, and the engine prevents their movement. At ejection, the engine is kicked out of the body tube, allowing the spars to swing up into recovery position. The rocket uses tumble recovery.

Very cool idea!

Yes, nice!!!

Do you have some plans you would be willing to share, thats a neat design and would go well with my Gyroc.

rharshberger said:

Do you have some plans you would be willing to share, thats a neat design and would go well with my Gyroc.

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Ditto!!!

Make sure you run a simulation in Rocksim or other program, or do a spin test with it. A fairly short rocket with those huge fins is almost certain to be unstable unless you add a bunch of nose weight.

gldknght said:

Make sure you run a simulation in Rocksim or other program, or do a spin test with it. A fairly short rocket with those huge fins is almost certain to be unstable unless you add a bunch of nose weight.

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Not. The big, long swept fins create a bunch of base drag increasing stability.

Mindsim Says! Its most likely stable as is due to the long fins extending behind the aft end of the rocket, its basically a Baby Bertha with a few mods and scaled down.

Glad you folks like the design. The design is fairly simple, I made it without any plans. The spar is 1/2" x 1/8" basswood 6" long. The nosecone was one that came with an Estes BT20 pack (don't know part number). The pivot was made by first gluing squares of 1/8" plywood on either side of the body tube. I think I drilled holes in everything first. The spars went on next, then another square of 1/8" ply on each side to hold everything in place. The arms at the top of the spars are more 1/8" basswood, the pieces on the aft end of the spars are 1/8" ply. One thing I would do differently would be to increase the angle of the arms so that they have more tension (make them point more toward the nose). The ring that holds the elastic at the aft end (I think) was from fax paper roll or something. It's a close fit on the outside. You could use a short piece (1/2") of BT20 tubing, split so it would fit over the body tube. The elastic is run through small holes on the arms, knotted, and secured with glue. Run the elastic through the ring at the aft end, pull tension, put on some glue, and use a spring clamp to hold it until the glue dries. The only thing not shown is the launch lug. It's about an inch long, centered on the body, and on a balsa standoff so that the launch rod will clear the arms at the aft end.

Sorry I don't have more/better pictures. My camera broke (battery door), and I'm looking for a new one. If anyone wants pictures, I can try taking some with my phone, but I don't know how good they will be.

Cool. I am thinking the fins when deployed are going to counter each other, so gonna cause a lot of drag (good) but shouldn’t rotate?

Neat design! I like the little details like hinge mechanism, the elastic, and how you've offset the holder clips on the bottom one so that they don't interfere with each other when the engine ejects. Hope the 1/8" ply and bamboo skewer are strong enough to handle the torque of those long arms.

Perhaps make the elastic replaceable as well? Hook or thread loops for elastic/rubber bands?
Round off the square holder plates on top?

While it ought to be stable, I agree about doing a swing test just in case. Lots of 3/32" (1/8"?) Bertha fins and engine weight may make it marginal.

Very cool and different!!!

(Psst... make it glide like a real flycatcher on the next round? )