Sunward quad tilted 18mm to BT70 mounting kit

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Well-Known Member
Jan 18, 2009
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Just purchased a Sunward quad tilted 18mm to BT70 mounting kit.
i have a few BT70 tubes and a nice cose cone, so i thouight i'd try something new in the motor mount department.
The mount kit comes in a plastic bag, with the parts and instructions, and as a bonus, a marking guide for a BT70.

4 mount parts.JPG
The instructions were straight forward although at step 2A you are asked to make a mark on each tube at 51mm - which you never use, but later it asks you to add a wrap at the mark you made at 44mm - i assumed that this is a typo
First thing is to put the engine thrust rings in each of the tubes and then add and glue the motor hooks. at this stage i added the 51mm mark on the tubes that is needed later.
I did not add the wrapps as i don't see why thay are needed. in a normal mount they are there to inhibit over movement on the engine hook, but in this kit the bottom centering ring does that, and if you do add the wraps thay will show on the outside of the tubes which sit outside the BT70.
The next stage is the difficult part and is where i made a mod to make things easier for myself.
getting all four tubes to sit in the two centering rings was problematic, the instructions suggest an extra pair of hands -which i did not have.
so i drill 5 holes through the two centering rings which were placed on top of each other.

4 mount 2.JPG
Next using 5 thin rods i aligned the two rings up. This kept the rings in place and true and square for the next stage - adding the tubes.

4 mount rods 2.JPG
the four tubes are then added, with the inside top centre of each tube flush with the top centering ring.
i added an elastic band to help keep the tubes inplace whilst gluing.
i tacked each tube into place with CA glue.
waited for that to dry, removed the stick and elastic bands and then glued everything.

4 mount tube rod.JPG

4 mount tube rod 2.JPG
After the rods are removed i filled each hole with a blob of glue, with the exception of one hole which is where i will use Kevlar cord as a shock cord anchor.
One of the motor tubes is just slightly out - a mm lower then the others -entirely my fault.

4 mount complete.JPG

4 mount complete bottom.JPG

4 mount complete top.JPG
started to think about the scratch build that is going to use the mount. which i'll write about in the scratch section, but as the mount needs a tube, i thought i'd better post about the body tube, as that needs cutting for the mount.
you get supplied with a wrap to mark out the tube. you cut out the slots where the motor mounts poke through.
i used a marker to colour in the bits of the tube that need cutting out

marking tube 1.JPG

marking tube 2.JPG
Next you cut out the pieces of BT.
i reckon you don't need to be too careful here as you will need to add a fair bit of filler etc to give a good finish.

tube cut.JPG
the motor mount fits neatly into place, there are plenty of gaps, but i'll be filling these.

tube and mount.JPG
finally got round to filling the gaps - came across a realy good filler that is easp to apply and sand.
that's the end to this thread.
will contine with the build of the rocket in the scratch section - when i get around to it.

sf tube mount filled.JPG

sf tube mount filled 2.JPG
the mount was bought as part as a scratch build, and in my rocket it will be below the centre of gravity as the fins will not be that large (still planning so that might change) and i'm putting mass in the nose to go for a tad more stablity.
The sunward kit that uses this mount is called Eruption, the fins are quite large, so the CP will be back further, so it hight be designed to go through the CG for that rocket - but to be honest, i don't know!
finally flew this mount today, only 3 of the four motors lit, and she still flew great, so i guess the canting thing works.