Derek's Level 2 Build

Discussions on mid/high powered model rockets using F powered motors and above.

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OverTheTop
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Re: Derek's Level 2 Build

Postby OverTheTop » Mon Nov 18, 2019 7:22 pm

Sounding reasonable to me :)
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Aquaman33
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Re: Derek's Level 2 Build

Postby Aquaman33 » Mon Dec 02, 2019 1:04 pm

After a few delays for various reasons I have finally started work on the body tubes.

As mentioned previously I wanted to strengthen the cardboard tubes with fiberglass sleeves:
Image

I wrapped 2 couplers in Teflon tape and inserted them in either end of the body tubes. The couplers served 2 purposes:
1. They extend the length of the tube so that the fiberglass lays nice and flat at the ends.
2. They strengthen the tube so that you can tighten the ends of the sleeve without crushing the tube.

This is the first tube on a cheap Bunnings rotisserie ready for epoxy:
Image
The sleeve is secured tightly at either end with electrical tape and zip ties.

I applied a generous amount of epoxy with a foam roller and used my hands (gloved) to squeeze it through the sleeve. Then I wrapped it in peel ply and left if overnight.
Image

Unfortunately the folds in the sleeve wouldn't lay flat on the tube so epoxy pooled under the folds. The folds are there because the manufacturers store the sleeve rolled up. The fold is the dark line that you can see at 1 o'clock under the peel ply. It's clearly visible and feels slightly raised.

After speaking to the sleeve manufacturers I made some changes for my second attempt:
1. I turned the sleeve inside out
2. I secured it a lot tighter at either end
3. I left the whole thing on the tube for a week and placed it out in the sun to try to heat and soften the sleeve.

This seemed to work much better as the fold is hardly noticeable on the second tube.

But jury is still out on whether the finish of the coloured fiberglass is good enough.

I had a lot of issues getting the resin to flow evenly into all the gaps as you can see in this close up.

Image

Perhaps I need to thin the resin or switch to a thinner finishing resin.

The fiberglass is fibers are saturated, but there are gaps between the fibers.

But the good news is the tube seems really strong. So worst case scenario is I fill it and paint it.

For the larger diameter body tube I will use a section of 150mm PVC pipe as a mandrel. The sleeve only just stretches over this, so will need reinforcing with some regular fiberglass cloth. The finished diameter will be about 160mm.

Image

And finally here is a rather bad mock up of what it might look like.

Image

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Re: Derek's Level 2 Build

Postby air.command » Mon Dec 02, 2019 1:23 pm

Great update Derek! The fluro colours really stand out. I didn't realize that you had such problems with the fold in the sleeve. The carbon fiber sleeves we use have a similar fold, but we've never had an issue with it once it was wetted out and put on the mandrel. I'll have to keep your workaround in mind when we use the fiberglass sleeves.
I was surprised about the surface finish, especially with the peel ply. Did you wet out the peel ply after you put it on? We normally put the peel ply on, and then use the roller to fully wet out the peel ply so that you don't see any white air pockets under it. Just like when you wet out fiberglass.
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Aquaman33
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Re: Derek's Level 2 Build

Postby Aquaman33 » Mon Dec 02, 2019 3:28 pm

air.command wrote:Great update Derek! The fluro colours really stand out. I didn't realize that you had such problems with the fold in the sleeve. The carbon fiber sleeves we use have a similar fold, but we've never had an issue with it once it was wetted out and put on the mandrel. I'll have to keep your workaround in mind when we use the fiberglass sleeves.
I was surprised about the surface finish, especially with the peel ply. Did you wet out the peel ply after you put it on? We normally put the peel ply on, and then use the roller to fully wet out the peel ply so that you don't see any white air pockets under it. Just like when you wet out fiberglass.


I did wet out the peel ply, but possibly not enough. I may go over it again with more epoxy and another layer of wet peel ply.

I think the carbon fiber sleeves are softer so are easier to flatten when they are wet. The fiberglass sleeves are more like a plastic type material and the material seems to have a lot of memory.

I don't believe I will have any issues with the large orange tube because the sleeve is stretched so big, but this means there will be bigger holes between the fibers.

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Re: Derek's Level 2 Build

Postby Aquaman33 » Sat Feb 15, 2020 9:01 pm

Once again this project went dormant as I became the king of procrastination.

I have managed to make some 100mm body tubes that are strong and quite light. But the finish isn't good enough to have the coloured fiber glass showing. But that's okay, with a little filler and paint they will be fine.

But I have decided that the larger 150mm body tubes have beaten me.....or at least they have beaten me within the time frame that I have available. I made a sample tube, but its not good enough to meet my standards. So I will shelve that idea for now as I want to get this project finished in time for our club's high power launch in April.

So the 3rd incarnation of this rocket will look like this:

Image

As I have mentioned before I really didn't want a conventional design, so I really like the idea of the transitions to the smaller middle section. This is something a bit unusual, but achievable in the time I have.

100mm body tube fore and aft. 60mm body tube in the middle. Length is approx 1.5m and it will weight about 2.25kg without the motor.

Stability is coming out at about 2.5x the larger body tubes.

The transitions and the tail cone will be 3D printed from by Fusion360 designs.

The motor mount tube will run from the tail cone forward through both transitions. This will provide a strong spine, so I am not just relying on the transitions for strength. It also acts like a stuffer tube to get the motor ejection charge up to the front of the rocket (should I decide to use motor ejection).

The forward body tube will be bolted on, so I have the option to add a longer front end and AV bay at a later date.

Because this design is thinner and lighter than my previous design it will fly a bit higher. Sims suggest about 3,000 feet on most J motors.

I have started work on centering rings.

For the 100mm rings I used an Apogee plywood ring as a template (left) and cut some rough copies on my band saw (middle) and then used a flush cut router bit in my router table to make exact copies of the template (right).
Image

I used 6mm aircraft grade plywood, which is incredible strong and light.

The mid section is the weakest part of the rocket, so I wanted some really thick centering rings to add lots of strength. They would have been hard to make out of plywood so I designed these and 3d printed them.

Image
Image

I will probably have 3 in the mid section, one at either end and one in the middle.

Now on to the transitions.


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