Scratch Standard AGM-78 Original Design / Scratch Built

Scratch - Standard AGM-78 {Scratch}

Contributed by Marlin Meyer

Published: 2010-06-14
Manufacturer: Scratch
(Contributed - by Marlin Meyer - 06/14/10) Scratch Standard AGM-78

Brief:
I saw this missile at the Air Force Museum in Dayton, OH and decided I had to build it. A single stage, mid-power (24mm) missile that retrieves on a large 24 inch parachute. This is based on the Launch Pad rocket kit.

Construction:
Parts from Apogee Components:

  • 20080 nose cone
  • (2) 10198 (BT-80) body tubes
  • 13045 tube coupler
  • 15028 centering ring for parachute shelf
  • 12012 engine mount kit
  • (2) 13057 launch lug
  • 4 fins made of 1/8" Balsa

Easy assembly. I built mine with Titebond II wood glue throughout. The fins were papered to add more rigidity. The long strakes were cut in one piece and sealed with Fill 'n Finish, and sanded before attaching to the body. The parachute shelf is a great idea that anyone who has built a Launch Pad kit before knows about. It is simply a centering ring glued into the body tube that keeps the chute from moving down the tube and effecting the CG. I attached 100lb Kevlar® for my shock cord to this centering ring. The motor mount is recessed and like the LP kits I added material behind it for strength. Instead of a coupler, I took a piece of scrap BT-80 and made my own. I also covered that with heat resistant tape. The recessed motor mounts have a tendency to char the tube. This prevents it.

Finishing:
Rustoleum sandable primer, sanding, some repairs, three coats of Valspar white. I printed the decals from a file that was shared with me.

Flight:
I would recommend any of the following:

F24W-4, D15T-4, E9-4, E6-4, E18W-4) Because this is a relatively heavy rocket, I wouldn't use longer delay motors

My first flight I launched F-24. This was a low altitude flight (just over 100 ft) The missile flew straight, chute deployed after apogee and landed about 90 feet from the launch pad.

Second flight was D15-4. Very similar, but better altitude. This time it went about 350 ft.

Recovery:
The shock cord is 150 lb. Kevlar® attached at the parachute shelf. I usually put a wrap of masking tape where the cord meets the top of the body tube to help prevent zippering. I flew on a very calm day and used a Top Flight 24" parachute which worked very well.

Summary:
PRO's: Great looking, fun to build

CON's: Rather heavy for a 24mm motor. If you want altitude, this isn't it.

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