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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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:
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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.
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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.

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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.

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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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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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Re: Derek's Level 2 Build

Postby Aquaman33 » Mon Mar 02, 2020 11:08 am

I am starting think about a parachute for this rocket.

The weight including the burnt motor will be about 2.7kg.

I have looked at various parachute calculators online and they are suggesting anything from a 5 foot chute to a 7 foot chute.

7 foot seems huge to me.

Does anyone have a reliable calculator or any advice about chute sizing?

The tail cone and motor mount will stick out the back and the fins are swept forward, so it doesn't need to come down super slow. But its for my level 2 so I don't want to risk damage.

Any advice would be great.

Thanks.

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Re: Derek's Level 2 Build

Postby air.command » Mon Mar 02, 2020 11:14 am

Hi Derek,

I've always used this formula for getting a rough estimate of descent rate.

http://web.archive.org/web/20111018045919/http:/my.execpc.com/~culp/rockets/descent.html

It's no longer on-line but available through the web archive. I think OpenRocket can also predict the descent rate based on parachute size, but I am not sure how accurate that is.
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Re: Derek's Level 2 Build

Postby Aquaman33 » Tue Mar 03, 2020 4:46 pm

air.command wrote:Hi Derek,

I've always used this formula for getting a rough estimate of descent rate.

http://web.archive.org/web/20111018045919/http:/my.execpc.com/~culp/rockets/descent.html

It's no longer on-line but available through the web archive. I think OpenRocket can also predict the descent rate based on parachute size, but I am not sure how accurate that is.


Thanks George. I will get my school calculator out.

Open Rocket is saying a 6 foot chute with a Drag Coefficient of 0.75 will bring it down at 4.5m/s. I guess that is reasonable.

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Re: Derek's Level 2 Build

Postby SpaceManMat » Tue Mar 03, 2020 9:06 pm

I’ve just used OR, need to make sure you enter all the parameters correctly but don’t play with the CD unless you are tweaking it based on measured decent rates.
QRS: 124
AMRS: 32 L2 RSO
Highest Altitude: 13,647 feet
Fastest Flight: Mach 1.55
Largest Motor: CTI 1115J530 IM
Current Project: X Wing

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Re: Derek's Level 2 Build

Postby Aquaman33 » Fri Mar 06, 2020 10:38 pm

My 3d printer has been working overtime.

The 2 transitions that go from 100mm body tube to 60mm body tube. The smallest hole in the middle fits the motor mount tube, so they also act as centering rings. These were both 15 hour prints.
Image

For extra strength I printed with 4mm thick walls and 35% infill, which meant they were a little heavier than expected.
Image

Tail cone. The ridge near the top is where I paused the print overnight and then restarted it again. It can easily be sanded out, or left as a feature. 16 hour print.
Image

Only 3mm walls and 25% infill so quite a bit lighter than the transitions relative to its volume.
Image

I designed this centering ring that will be epoxied and screwed to a forward plywood centering ring. The holes around the sides will take metal threaded inserts, which will allow me to securely screw on the forward body tube. I wanted this tube to be removable so I can add different front ends. The small holes in the top allow it to be screwed to the plywood centering ring and the 2 big holes are where u-bolt nuts will sit. These will be filled with epoxy to permanently secure the u-bolt.
Image

Image

A very chunky forward centering ring. This will be the anchor point for the shock cord, but will not be directly secured to the body tube, so I made it chunky for extra security.
Image

The back end. Through the wall fin tabs will fit between the plywood centering rings.
Image

The font end.
Image

The whole thing.
Image

For context its the bit in the red circle.
Image

A little heavier than planned, but not too heavy for a J motor!
Image

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Re: Derek's Level 2 Build

Postby Aquaman33 » Sun Mar 15, 2020 5:58 pm

I started work on the fins.

My process is:
1. Print a template from OpenRocket and glue it to a piece of MDF.
2. Cut the MDF to shape using a circular saw.
3. Draw around the template to transfer the design to 4mm aircraft grade plywood.
4. Rough cut the plywood fins on a band saw.
5. Use double sided mounting tape to stick the MDF template onto the rough cut fin.
6. Use a pattern bit on the router table to make exact copies of the template.
7. Sand.

It sounds long and painful but its actually quite quick and gives you almost perfect copies. Its the closest I can get to laser cutting....without a laser cutter.

Left: Rough cut fins. Middle: MDF template. Right: Fins after trimming with router.
Image

Sanded fins.
Image

Next I will laminate with carbon.

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Re: Derek's Level 2 Build

Postby Aquaman33 » Sun Mar 15, 2020 6:07 pm

I made some progress filling and cutting the tubes last week.

So was able to do my first dry fit.

Image

I said I wanted something a bit different!

Still lots of work to do, but I feel like I might get it all done in time for our April launch.

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Re: Derek's Level 2 Build

Postby Aquaman33 » Thu Mar 19, 2020 9:43 am

Not the most exciting post, but I finished some more 3d printed components.

Contoured rail guide retainers with a nut epoxied in:

Image

Image

An 808 camera sled with a contoured based:

Image

Image

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Re: Derek's Level 2 Build

Postby SpaceManMat » Fri Mar 20, 2020 8:18 pm

Camera shroud is a good idea. I’ve thought about creating a replacement case or at least bottom that fits directly to the rocket to minimise size / drag, but that’s beyond my cad skills. Yours is pretty close, hows it for strength?
QRS: 124
AMRS: 32 L2 RSO
Highest Altitude: 13,647 feet
Fastest Flight: Mach 1.55
Largest Motor: CTI 1115J530 IM
Current Project: X Wing

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Re: Derek's Level 2 Build

Postby Aquaman33 » Sat Mar 21, 2020 1:22 pm

SpaceManMat wrote:Camera shroud is a good idea. I’ve thought about creating a replacement case or at least bottom that fits directly to the rocket to minimise size / drag, but that’s beyond my cad skills. Yours is pretty close, hows it for strength?


Replacement case would be great, but also beyond my CAD skills.

I think this will be strong enough. I printed in PLA+ and orientated it at a weird angle to avoid Z axis weakness.

There is a bolt that goes through the camera to secure it to the rocket, so even if the bracket fails I won't lose the camera.

I am working on version 2 which has the contoured base plate and sled combined in a single item.

Image

Image


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