Scratch Now That's What I Call a Funnel Original Design / Scratch Built

Scratch - Now That's What I Call a Funnel {Scratch}

Contributed by Sascha Grant

Overall Rating: starstarstarstarstar
Manufacturer: Scratch

(Scratch) Now That's What I Call A FunnelBrief:
Huge plastic funnel. 29mm motor mount. Tumble recovery.

Construction:
Parts include:

  • 11.25" x 14.5" Big red plastic funnel
  • 9" x 29mm motor mount tube
  • 2 x 3mm ply centering rings (one about 4.5" and the other about 2.5")
  • .25" launch lug

I saw this huge funnel in a local 'rubber & plastic' retail store a couple of weeks ago and 'rocket' was the first thing that came to mind. The label did say 'Multi Purpose', so I guess they meant rocket, too!

I started by selecting a length of motor mount tube and was pleased to find that it wedged quite well about 2" from the top of the spout. I then cut two centering rings with a hole saw. I selected the smaller ring to sit as close to the top 'ring' on the outside of the funnel (the rings on the outside only show as a slight dimple on the inside) and the bigger centering ring to sit by the larger, lower ring.

I fit the two centering rings to the motor mount tube and pushed everything into place--letting the rings slide down the motor mount tube as they hit up against the inside of the cone.

Once I was happy with the dry fit, I used 12 minute epoxy to glue the centering rings into place (on the motor mount tube).

After the epoxy dried, I estimated the point where the launch lug was to exit at the side of the cone. Holes were drilled into the centering rings and another dry fit showed that the launch lug was correctly positioned (with the exit point coming just below the upper external 'ring').

Using a torch to shine light through the lug, the exit point was marked on the outside of the funnel. I drilled out the exit hole and shaped it to fix exactly with a scalpel blade and finished it off with a small file.

I used Liquid Nails to glue the motor mount assembly into place. Liquid Nails will stick to virtually anything and, once dry, is slightly flexible. I was worried that if I used epoxy the bond would be weak and subject to cracking, leading to failure after flights. The Liquid Nails should flex just a fraction when the cone lands (and now after two test flights, the motor mount is stuck fast where it should be.)

Flight and Recovery:
Because the motor sits quite high up in the base of the funnel, motor prep is done before loading into the rocket. No special retention is used and recovery is by tumble/drag.

This rocket was flown on a G79 KNO3 + Sorbitol experimental motor. Any AeroTech RMS/Single use motor with a similar thrust profile would work. I wouldn't suggest going any lower due to weight.

Both flights were as straight as could be expected with the wind--slight weathercocking but not so much to be a worry. This is a good flier for a day when other rockets would end up stuck in trees.

I would estimate the altitude at perhaps a couple of hundred feet, recovery was faster than I would have liked. When I fly this (at a club meet) I will give a "heads up" prior to launch.

Summary:
My kids were there for the launch, and they said, "that'll never fly." However, both were impressed.

This is a good solid rocket that I think will prove to be a crowd pleaser. The only issue may be the tip of the funnel cracking over time. After the second flight, there was a small chip on the tip where it appears that the plastic is thinner (due to molding issues during manufacture).

The cone cost me $4.50. (It was in a half-price sale!) The ply came to me in a box of rockets as packaging and the motor mount tube was rescued from the recycling. So apart from a little time (an hour or so), it cost me next to nothing!

Overall Rating: out of 5 out of 5

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