Sunday, September 22, 2013

The Big Fix, MMX Red Max to 13mm Engine Conversion

I have two BT-5 models that don't perform that well with MicroMaxx engines. They just don't get an altitude to justify using an engine.
These were carded models built a few years back. This Red Max has a body skin print wrapped around a BT-5 tube.

I thought I'd try to remove the MMX mounts to use some 13mm engines I found on sale.

The inside of the hand rolled MMT tube was scored with a hobby knife to raise an edge I could grab.

Long pliers were used to hold the raised cardstock tab.
The pliers were turned and the mount removed in a spiral.
It was easy to remove.

The model already had a 13mm engine block in place.
One side of the block was lifted with an awl.
A new Kevlar line was knotted and slipped through the hole.
There is no room for even a streamer. Nose-blow recovery should be  fine for recovery.
This one should fly better with a 1/2A3-4t engine.


  1. Chris, I have both a Red Max and a Goblin cardstock model, and both fly very well on the 1/2 A3-4T. Just for fun, try a full A sometime, it will really get impressive altitude. I have a cardstock Der Big Red Max in minimum diameter MMX, very similar to your skywriter downscale. It flies very well and I recommend this route for an MMX Max fix. Any plans to draw any more cardstock models? I really enjoy your goonies/astro-1/big bertha models!

  2. Thanks, I'm glad you like the models.
    I'm working on four new carded down scales to pass the days while stuck here in Mexico. A Estes Marauder, Rogue, Centuri Bandito and a Black Brant VB.
    I've got to get home, build and fly them before releasing the PDFs. Give me a couple weeks and I'll announce them on this blog.
    It still amazes me how high a BT-5 model can get on a 13mm A engine.

  3. Will you need to add weight to the nose?

  4. I don't think so. The standard Red Max (BT-60 based size) is very stable.
    A 13mm engine probably weighs about the same as the MMX in it's centering rings and built up engine mount. The first time I fly it I'll know for sure!

  5. Or you can send the dimensions to me anytime and ill get you a CP for rocksim.

  6. Thanks Jeff!
    I finally got Open Rocket to open up, I may try it there first.
    I'm still here in Mexico, the model isn't handy.
    If I can't get it right, I'll send the dimensions your way.

  7. Chris I've build your Black Brant VB (love it) and have the fin plans for the Centuri Bandito (but, I'm not sure if the fin plans were yours...?) Did you ever get to post the carded models of the Estes Marauder and Rogue? I've hit the carded and MMX models up a bit hard as my parks are a bit limited. The Sacramento model rocket club remains grounded and Moffet here in CA is a bit far.

    1. Hi Scott,
      I haven't posted the Marauder and Rogue yet, I still have to build them and test fly before they are released. I'm sure they are stable but I have to be sure.
      The Bandito fins were scaled down from plans I found online, at
      If you haven't found it yet:
      Wayne Hill has posted plenty of carded models.
      Sorry to hear about the Sacramento club. I drove past Moffett field on my trip in November. Landings on concrete must do a lot of damage.

  8. Chris,

    You said, "Red Max has a body skin print wrapped around a BT-5 tube", but I can't find the Red Max body skin pdf on or anywhere else. Do you know if that skin is available for download anywhere?

    1. Hi Scott,
      It took a search or two. It's in the Rocketry Forum, drawn up by Greg Poehlein. The Red Max is at post #47 here:
      The single PDF page to print is here:

      Greg has done some great down scales, check the rest of the TRF thread to check them out.