I need to create internal fillets against the fins between the motor Mount and the Air-frame. The gap is very small – ~12 mm. So I’ve purchased some 5 mm diameter tubing with some 50 mm syringes to get the glue down there. I have used some thin doweling with masking tape to help direct the end of the tube to where the glue needs to go. Below are a few pictures:-

 

The process will be:-

1. Suck up 25 cubic cm of Araldite into the gun
2. Clean end
3. Insert gun up to the ‘zero’ mark
4. Push 1 cubic cm of araldite in
5. Withdraw 1 notch

Repeat step  4,5 will tall the way out

I’ve finally purchased glues for the rocket.

I have West Systems 105, 206 and 403 filler for the external fillets.

I have J-B Weld Epoxy for the root fillets.

For the internal fillets, I’ll probably be using West Systems 105/205 (no filler). What I will need to get the epoxy up the rocket into the area of interest is a tube/syringe.

 

Yet to purchase the pipe.

I’ve discovered that the fins are not exactly (or even close) to 120 degrees apart. The distance between two sets of fins is the same, while the other Fin/fin distance is greater than the other two by 5mm. Not terribly good. What this means is that the Jig that I made to hold the Fins in place ONLY has perfect alignment in ONE position. i.e. I cannot rotate the rocket and have the fins line up in the slots of the wood.

This has meant that I need to change my fin install procedure, by allowing me to rotate the WHOLE Jig into position, so that each fin that is being glued is vertical. I’ve done it as follows

 

 

 

We can take the wood stand off and attach it to the Jig, pointing out the other side. This allows us to install the other fin pointing down to the wooden base.

The next step is to profile the fins and to score/sand the roots and tangs. Some important decisions to make are:-

• How to evenly sand the surface of the fins (so it is symmetrical)
• What profile is required – at leading edge and trailing edge.
• How to score the fins

We concentrate on the first two here.

Fin Symmetry

When I examined the fins, the first thing I noted was that the chamfer in them is not symmetrical to begin with. This is unfortunate, but I’m just going to have to work with it.

 

Well, that is something we will need to work with. I had a vision of a semi-circle shaped leading edge, but this is probably not possible now. Will probably make them parabolic, or elliptical in shape.

 

The tools to sand down the fins

The first tool I created to sand down fins was the following:-

 

The problem with this is that the sandpaper lifts off from the surface and interferes with the sanding process. The area of sandpaper available sanding is reduced because it needs to be sandwiched between the pieces of wood. Because the longest section of fin to be sanded is 250mm, this means we can’t sand the edge down (along the whole length) in the same stroke. This is a big disadvantage, and was one of the identified issues we wanted to solve.

Some tests were done to see if we could get a nice job done using wood and it looks like it “should” work. See below:-

 

As you can see, the edges look very well curved. I did this curve by doing sanding at ~30 degrees, ~45 degrees, ~60 degrees. Then I did a ‘curving’ action to try and get it rounded. This makes a ‘semi-circle’ like edge.

I decided to build a simpler sanding plate. I needed:-

• Sandpaper
• Spray Glue
• Plywood
• Clamps

I followed the instructions very carefully. Spraying both the sandpaper and plywood, then letting them sit for 10 minutes. Then I put the two together and I clamped them over night. I decided to put 80-grit sand-paper on one side and 240-grit sand paper on the other side.

Here is the end result.

Notice how there is some bare plywood accessible on the edge of the sanding board. We have drilled some holes into this can can mount this to a large piece of plywood. This allows mounting the sanding board on a solid (non-moving) bench. See below.

 

 

 

 

 

 

One of the steps I’m coming up to is the attachment of the fins to the Air-frame/Motor Mount. For a good join and a good rocket build it is important that we:-

• Sand/score the root of the fins
• Sand the Motor Mount where they are going to be glued
• Sand/score the Tang of the Fins for the fillets later on
• Important that the Fin/rocket do not move for 3 days while it dries
• Very important that the fins are precisely 120 degrees apart and are perpendicular to the air-frame

The the last two bullet points, we have build up a “jig” to hold everything in place. Below are some pictures of it.

 

 

 

 

We want to hold the fins completely still while it is drying. For this, we have used two square pieces of timber and some G-clamps to keep the fins steady. See the photo below.

 

 

 

 

I have checked the steps many times over several days, trying to make very sure I have not mis-understood anything, measured anything incorrectly, missed any steps that might be good to do now.

I then performed several dummy (pretend) attempts at gluing the motor mount into the Airframe, to help me anticipate any potential issues and also have the best procedure to glue this motor mount into the Airframe. I was able to confirm that I could see where the glue was in relation to the lines inside the air-frame.

 

 

I made two batches of araldite actually. Wanted to make sure I had more than enough glue.

I put glue on the stick end and turned in my hand as I put it down in between the two lines. I used the cut-out in air-frame (for the fins) to ensure I got the glue in the right spot. The occasional motion of the air-frame stopped glue from dripping from the edge and allowed me to paste a nice layer of araldite in the air-frame. Then I loaded the motor mount  and twisted in back and forward to ensure the glue was spread about in between the centering ring and the air-frame.

Then I put the whole rocket into the vertical position as shown below:-

The glue requires 24 to 72 hours to completely cure. So we will give it the complete 72 hours (Sunday 09:30 to Wednesday 09:30). We want the BEST possible result

 

We checked that the motor mount was indeed sitting 27mm outside the end of the Air-frame. See the photo below.

I had a look from the top to see how it looked.

 

A lot of work needs to be performed before we can attach (glue) the motor mount inside the Airframe. Below is a list of steps I have done:-

1. Mark out where the Motor Mount needs to be glued in relation the end of the airframe
2. Mark the upper/lower points inside the air-frame where we need to apply the Araldite.
3. Choose the Glue to use for the joint. Will go for 24hr araldite because it is easier to handle (more viscid), doesn’t set as fast, so giving more time to apply and have a stronger bond.
4. Cut off a piece of doweling and mark on the stick where it  is right up to the crucial part of the air-frame requiring glue. I rounded the ‘glue’ end to help in application of glue.
5. Creating of a stand which will sit the rocket on to ensure that the Motor Mount protrudes from the Air-frame the exact distance – 27mm
6. Find and set-up a place where we can erect the rocket to dry for 24hrs.
7. Scuff the Motor mount where the Fins are eventually going to be attached.  Made sure surface is clear or dust and rubbish. Easier to do this BEFORE the Motor Mount is glued in.
8. Make sure no tape left on motor mount
9. Inspect the Top centering ring to be very sure it is glued sufficiently well.
10. Tape down Nichrome wire to the bottom of the motor-mount so that it doesn’t get in the way

As you can see there is a massive amount of preparation before we even start applying any l glue.

Below are some pictures of the pieces worked on in this preparation.

 

 

 

 

 

I purchased an Aeropak Tailcone suitable for 76mm Motor Mount and 3.9″ Air-frame. The weight of all its parts together is 150 grams.

 

Here are some pictures of it.

 

I had to carefully sand down the motor mount external surface, approximately 1″ from the bottom to allow me to fit the threaded Aeropak mount component on. See pictures below.

 

I had to sand, then test, then sand multiple times, to ensure I didn’t over-do the sandpapering.

I have to clean the motor mount, remove the fibreglass dust to test joint and to ensure it is ready for gluing, later on.

 

One of the very important steps I have to do soon is to glue the motor mount (via top Centering Ring) into the main Air-frame tube. I have to be particularly careful here because we want to have the motor mount sticking out just enough to ensure that there is adequate room to install the Aeropack Tailcone. So here I am conducting a trial Dry-run installation.

 

 

 

 

As you can see here, I’ve used wires to allow me to remove the AFT Centering ring, which I’ll need to do at some point during the install.

I’m reasonably confident with it, but going to double check it.

 

I’ve started Step 1 of the Rocket build.

 

I decided to purchase a Syringe pack of 24 hr Alaldite glue. I choose 24hr glue because it offers strengths up to 150kg. I choose to get it in syringe form to help with the delivery of equal amounts of Part A and Part B.

I was very careful to follow the instructions. The instructions said to mix it for a minute and then let it rest for 5 to 10 minutes. So I did this.

Before doing any gluing I marked 7cm down the motor mount, so I would glue it in the right place. I also marked the strap.

I was very particular about the GRIT of sand paper. I wanted to ensure I had low enough grit to ensure I get a good join.

I sand-papered it over a larger area than the strap because the glue will spread out beyond the Motor Mount. Increased surface area, increased strength.

 

Then I cleaned the motor mount of dust.

I wanted to make sure glue did get everywhere I don’t want it, including INSIDE the motor mount. So I’ve taped it well.

 

Following the instructions on the Araldite, I applied glue to both materials.

 

Then I brought the two together and used making tape to keep the two together as it dried. The glue job was complete at 16:00. So by tomorrow morning it will be dry. It won’t be at it’s max strength, but it will be enough to start on the other end of the strap.

I will probably apply more araldite over the cord, below where the centering ring is to be, to get increased bond strength.