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Monday, July 11, 2016

MPC Red Giant Build, Part 2, Engine Mount

I had to make a decision whether to go with the 18mm or upgrade to a 24mm engine. The rocket is 29" tall and close to a BT-55 tube size. If it were a BT-60 and this tall I might have gone with the larger engine.

The mount is unusual, the engine sits between four internal plastic centering ribs. No motor mount tube or engine block, the top of the ribs overhang the top of the engine.
I'll install an ST-7 tube to insulate a hot engine from the plastic ribs.

By itself, the engine easily slides in between the ribs and butts up against the overhang tops.
The ST-7 tube has a wider outside diameter. The ribs were shaved back by scraping them down with the top (not the sharp blade) of my break-off blade knife. The top of the knife blade is used like a cabinet scraper taking off a little plastic with each pass.
When the fit was close the rough sides were smoothed with some 100 grit wrapped around a painting wand casing.

Even without an engine in place the retaining ring would not twist and lock into the fin can. The locking tabs were a hair too long.

I had to shave off small bits to get the tabs to fit and lock. Cut off a little, check then cut a little more. After three tries the turn-to-lock retaining ring did fit and locked the engine casing in place.
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8 comments:

  1. AnonymousJuly 11, 2016 at 10:31 AM

    What is the tube diameter?

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    Replies
    1. Chris MichielssenJuly 11, 2016 at 12:58 PM

      Hi Anonymous,

      The ST-7 engine mount tube I installed is .759" outside diameter.
      The low, wider tube on the Red Giant is 1.58" o.d., the upper tube is around 1.15" o.d.

      Delete
    2. AnonymousJuly 12, 2016 at 2:55 PM

      Thanks. I wanted to see if the fin can was compatible with any standard body tube sizes.

      Delete
    3. Chris MichielssenJuly 13, 2016 at 1:29 AM

      I see why you asked now. The MPC kits are on clearance, cheap enough that you might justify buying one just for the fin can. No, these Chinese tubes aren't standard Estes sizes.

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    4. John AndersonJuly 13, 2016 at 4:31 PM

      Yep, that was why I asked.

      Delete
  2. Naoto KimuraJuly 11, 2016 at 2:32 PM

    Hrm... the engine mount looks similar to what's found in the Estes Shuttle Xpress kit. The main difference is the centering ribs on the Shuttle Xpress are at the front only (they don't extend all the way to the back), and the tailcone engine lock part serves an additional duty of centering the engine at the rear.

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    Replies
    1. Chris MichielssenJuly 12, 2016 at 7:38 PM

      Hi Naoto,
      I never had a Shuttle Xpress kit, I looked up the Estes instructions. The Red Giant fin can is one piece, the Shuttle Xpress is two halves. On the Red Giant the retaining ring also centers the engine at the rear.
      As a side note, there always seems to be one of the Shuttle Xpress models at a club launch. One glider sort-of glides, the other always spirals in.

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    2. Naoto KimuraJuly 13, 2016 at 5:54 PM

      Yep, trimming the gliders ends up getting a bit tricky since the elevators tend to spring back. I end up using strips of cellotape (basically using it to apply tension to pull the elevators up). Not terribly pleased that there isn't anything to keep the gliders from flopping around. (shrug) I mainly got the kit because it happened to be on sale and the nosecone would be useful if I wanted to clone something like the Interceptor II and Greyhawk.

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