Tuesday, October 23, 2018

Semroc Snake Jumper Build, Part 3, Replaceable Kevlar Ties

Some Kevlar is stiff, other Kevlar is soft and can start to unravel.
TIPS: I'll usually tie off the end with an overhand knot to prevent unraveling.
Run a bead of wood glue (never use CA glue on Kevlar or any string) and rub it into the Kevlar. After it dries you can cut the Kevlar (wire cutters are easiest for this) and the line won't fray.


Here's how the replaceable Kevlar is tied on.
On the left is the low end of the engine mount. A tight loop is tied around the back end, over the hook on the other side. Feed the Kevlar line through the tube and out the top. Don't glue the Kevlar loop to the centering ring!

On the right is the upper side of the engine mount. A loop is tied in the end of the Kevlar for attachment of the shock cord.

After a few flights you can slip the loop off the back of the engine tube, slide it through the tube and see if it needs replacement.



A forward fillet was applied using a Q-tip taped to a dowel. Put a drop of glue on the Q-tip and spread it around the ring / tube joint. It'll take a few applications of glue drops to get all the way around the outside of the ring edge.

A Run-in at the N.E.F.A.R. Monthly

On October 13 I had an interesting interaction with a another flyer.
While waiting for the next rack, a flyer talked up his 3D printed model. He was pleased with his work. Larger than a BT-60 diameter, it looked thick and heavy. I asked which engine he was going to use. He said: "A D12-7.
I asked to see it to feel the weight. It felt like it weighed a pound.

I suggested: "That seems like a long delay. You might want to go with a D12-3. With a seven second delay it could be on the ground before the ejection charge goes off."
He followed: "I'm not worried about that, I'm just checking stability." Laughing he added: " My last model came in and stuck itself into the ground."
I saw that previous flight after hearing a "Heads Up!" It came in nose first and hit hard near the parked cars.
I said: "I don't want to argue, just check with the RSO.
He raised his voice and said angrily: "I don't want to argue with you either!" He stormed off.
I never raised my voice or insulted him. I just didn't want anybody (or a car) to be hit by a heavy rocket from an inexperienced flyer.

(The rocket pictured above was not the rocket described. It's just a picture I found online.)

Monday, October 22, 2018

Semroc Snake Jumper Build, Part 2, Engine Mount Upgrades

This build will incorporate the new Odd'l Rockets heavy wall BT-20H, an extended length engine hook and replaceable Kevlar.

The BT-20H diameter is a bit wider than a standard BT-20. To make it fit the centering rings sand the inside hole edge with 220 grit sandpaper. Roll the sandpaper around your index finger and rotate around the inside hole. Sand a bit, check the fit and repeat until the tube slides in. It's easier than you think.



To prep the rings for the replaceable Kevlar mount -
Punch a small hole directly opposite the engine hook slot on both rings. A plastic tube from Dollar Store Q-tips will slide through both hole
To use the new eXtended Length Engine Hook (3" long) the BT-20H tube is cut to 3" long.

A notch is cut for the upper bend of the hook. Make the notch 1/4" from the top of the tube.

On the far right is a dry fit of the hook, tube and centering rings. Black electrical tape will wrap around the tube, over the hook and tube, centered between the centering rings.


Slide the engine block in from the bottom, no glue yet.
Use an standard engine casing to push the block forward until it ends up under the top bend of the hook.

A glue fillet is applied around the top of the engine block. You can leave the engine casing in place until the glue dries.

Using the XLEH (eXtended Length Engine Hook) places the engine block under the top bend of the hook preventing movement and tearing of the engine mount tube. The fit of the engine top is also better, not resting at a slight angle in the tube.

Sunday, October 21, 2018

Semroc Snake Jumper Build, Part 1, Parts


The instructions, decals and fin stock were picked up when Semroc discontinued the kit. The rest of the parts are from my Odd'l Little Green Man kit. It uses the same nose cone, body tube and engine mount.



The face card says "Laser Cut Balsa Fins". I don't know if the first prototypes had balsa fins, the other Semroc Groonie kits had balsa fins.
The fin material may have been changed to card stock like the Centuri kit.








I will be using the Odd'l Rockets thick wall BT-20H and XLEH Extended Length Engine Hook for the engine mount. Replaceable Kevlar will be added.

Estes Mini Mars Lander Build #0881, Finished











This was a fun one, even with the flaky decals.
I'm curious how it will recover with the streamer.

Saturday, October 20, 2018

Semroc Snake Jumper Build, Background

The Semroc Snake Jumper was a Goony based on the old Centuri Evel Knievel Sky Cycle rocket.
The instructions are interesting - CLICK HERE 
Check out the rear "positioning disk" and shock cord mount that attached to the engine mount.
The model also had die-cut card stock fins, cut from the same material as the centering rings.

The Centuri kit was available from 1975-78. It probably would have had better sales if the Snake River jump was successful.

The Centuri kit was 1.3" diameter, the Semroc Groonie is 1.8". Semroc called them a Groonie as they were grown up Goonys. Centuri used 13mm engines, the Semroc version uses 18mm.



Carl McLawhorn at Semroc based his designs on the original Estes Goony drawings that were changed into flying brooms and rabbits before production. The original Goony drawings remind you of the old CarToons magazine art.

The Semroc Snake Jumper is 1" shorter and stubbier compared to the Centuri Sky Cycle. The decals reflect the original kit except the face of the "pilot" decal is angrier.

Upcoming Estes Releases -

On TRF, Turbofireball posted this:

My local hobby shop showed me this info today regarding new Estes kits:
EST-0865 Mini Mean Machine Model Rocket Kit (Skill Level 1) $14.99 
EST-1250 Interceptor Model Rocket Kit (Skill Level 2) (Re-Issue) $29.99 
EST-1329 Multi-Roc Model Rocket Kit (Skill Level 3) $22.99 
EST-1969 Saturn V Model Rocket Kit w/Bonus (Skill Level 4) $89.99 
EST-7255 Little Joe I Model Rocket Kit (Skill Level 3) $32.99 
EST-7276 Checkmate 2-Stage Model Rocket Kit (Skill Level 1) $12.99 
EST-7277 Galaxy Glow Model Rocket Kit (Skill Level E2X) $14.99 

"They did not have info yet on what months they would be released, although they expected to receive Little Joe 1's shortly, since Estes now shows them available. The info also confirms Dean Fox's #1969 for the Saturn V. The big surprise was the Interceptor, as that kit didn't make it to the 2018 catalog."



All of these were shown in the 2018 print catalog, but some not  available yet.
The big news is the re-release of the Interceptor!
Here's a link to the blog build: CLICK HERE