L2 build

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camacd
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L2 build

Postby camacd » Wed Apr 13, 2016 9:10 pm

I've made my decision and done a first pass design for my L2 cert rocket. Hopefully it will be ready for the May Launch.

I want it to be versatile and handle a range of motors, and so I've designed it to hold a CTI Pro54 6 grain case. That will give me I,J,K capability.

In order to make the most of that power, I want to keep the diameter down, but I decided (after much consideration) to steer away from minimum diameter at this stage.

SO I'm using 65mm phenolic airframe. That will be pretty easy to work and relatively forgiving. I have a mate who is a painter, so I'll be consulting him before I make a mess like I did on my L1 build.

The materials were ordered today, so hopefully in a few days I can confirm weights of a few components and finalise the design.

I will re-use the AV sled from the L1 rocket. everything on that seemed to run pretty well.

Perhaps some guidance on fin thickness. If I max the motor out it will be getting up to almost mach 2. How do I determine the ideal fin thickness? They will be relatively small with a root chord 150 long and about 75 high. I will be putting generous fillets.

Overall length will be 1500mm, max weight with largest motor about 3440g.

Performance with the biggest K motor is expected to be Mach 1.96, and apogee 3600m using a K1440.

Should be fun.

Further reports as progress happens.

Cam
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Re: L2 build

Postby ROCKet STAR » Wed Apr 13, 2016 9:33 pm

Sounds like a fun project. Not sure if you are planning this, but it would probably be a good idea to glass the phenolic tube. It would probably hold up to Mach 1, but I think it may struggle close to Mach 2 without strengthening.


As for fin thickness, it depends a lot on the material you are planning on using. I wouldn't push fins of that size made of 3.2mm plywood to that speed, but 3.2mm G10 would likely be ok. I have flown fins made from 3.5mm balsa to those sorts of speeds with a carbon fibre tip-to-tip.
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OverTheTop
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Re: L2 build

Postby OverTheTop » Thu Apr 14, 2016 7:24 am

I successfully flew a 54mm rocket with similar sized fins to Mach 1.8. Fins were 3.2mm G10 fiberglass. Airframe was fiberglass as well. The airframe was slotted and the fins carefully fitted and glued into the slots (not just stuck on the surface and relying on "peel" strength.

As for phenolic, I have no experience.
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camacd
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Re: L2 build

Postby camacd » Thu Apr 14, 2016 7:50 pm

[quote="ROCKet STAR"]Sounds like a fun project. Not sure if you are planning this, but it would probably be a good idea to glass the phenolic tube. It would probably hold up to Mach 1, but I think it may struggle close to Mach 2 without strengthening.


Thats probably a good suggestion. I've never done much with fibreglass before, so there's a good chance of a VBM. (Very Big Mess). I do have a mate who is pretty good though. Perhaps if I drop around to his house with a bottle of Jack Daniels. .......
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camacd
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Re: L2 build

Postby camacd » Wed May 04, 2016 7:48 pm

So a slight problem has emerged.

Even with the smallest motor required to get my Level 2 cert, I'm going to exceed the allowable ceiling at the launch. Its a good problem, I suppose, but it means a rethink of my plans.

So it looks like a chance to relaunch my L1 rocket at the May launch, and it get to put a little more time into the build of the L2. That's probably good, because I haven't actually started building L2 yet.

So Westmar it is.... and I can put a nice big motor in it and really get it up there. Hopefully the BRB i've ordered gets here in time and I'll be able to find it.
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Re: L2 build

Postby martymonsta » Wed May 04, 2016 9:56 pm

Hey Cam.

For your 1st flight of the rocket and especially if you have never flown a BRB, I would put it up on something a little smaller for its maiden flight. You will want it to go high enough that you can check all your electronics and tracking, but not so high that you can't visually track it. That way if you struggle with the tracker you can still recover. It will be a struggle to track visually at 13k'

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Re: L2 build

Postby OverTheTop » Thu May 05, 2016 7:52 am

I'm going to exceed the allowable ceiling at the launch.


A bit (lot!) of nose weight? Maybe an additional bit of airframe and coupler that you can slot in to the airframe.

What about a blunt (flat!) nosecone?

Early deployment of drogue?

You could have some fun with this :D
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camacd
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Re: L2 build

Postby camacd » Sat May 07, 2016 1:01 pm

Thanks for the feedback everyone. After some discussion about whether I might get interference between my altimeter and GPS, it seems that whilst interference is possible, I can probably get it to work with them both in the same bay. I will need to test this on the ground but as the BRB has not arrived yet I have opted to take the chance and make the AV sled to carry both devices. If the ground testing indicates a problem, I will cut the nosecone open and stuff the GPS in there.

I have also decided to fibreglass the phenolic airframe. I'm not a very experienced fibreglasser, so I do this with some trepidation, but I figure this is a skill I will need to develop if I want to progress with the sport. I have done one practice on some leftover tube from my previous build. I learned some things that I need to change, but overall not bad for a first try. I'll do one or 2 more practices before I do it for real.
Attachments
AV Sled completed 1.jpg
The sled fabricated and drilled. It even matches the drawing.
"He who says it can't be done is liable to be interrupted by somebody doing it". - My Mum

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OverTheTop
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Re: L2 build

Postby OverTheTop » Sat May 07, 2016 1:06 pm

If you are getting into fiberglassing, check out these rotary cutters. They work fantastic, compared to scissors, in my opinion.
viewtopic.php?f=52&t=5383
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Re: L2 build

Postby Lister » Sat May 07, 2016 2:49 pm

OverTheTop wrote:If you are getting into fiberglassing, check out these rotary cutters. They work fantastic, compared to scissors, in my opinion.
viewtopic.php?f=52&t=5383

I swear you own shares in the rotary cutter companies :P

What cloth are you using on your tubes?

camacd
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Re: L2 build

Postby camacd » Sat May 07, 2016 3:01 pm

Good question Lister. I just bought some from Bunnings. It is a pretty coarse weave, and left a pronounced weave finish which I was wondering what to do with as far as filling.

If you have any recommendations....
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Re: L2 build

Postby Lister » Sat May 07, 2016 3:49 pm

From memory the bunnings stuff is 175gsm plain weave.. and very bloody expensive. But it will do the job. As for filling holes, bumps, imperfections you will need a lightweigh body filler, or if they arent huge imperfections use a high build spray putty. As OTT has said before you can spray it in a cup and paint it on for small areas.

Would help if you had a photo of the tube so we can see what you're dealing with.

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OverTheTop
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Re: L2 build

Postby OverTheTop » Sat May 07, 2016 3:57 pm

Epoxy and Q-cell microballoons is what I would use. Large portion of Q-cell. Personal choice.
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Re: L2 build

Postby Lister » Sat May 07, 2016 4:06 pm

I was going to suggest that too OTT but thought he had some weird micro balloons?

camacd
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Re: L2 build

Postby camacd » Sat May 07, 2016 7:38 pm

I know nothing about these microbubbles or nanofarts or whatever. This sounds a bit more sophisticated that just slopping a bit of Taubmans on.
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