My second build.

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Lister
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Re: My second build.

Postby Lister » Thu Mar 31, 2016 7:40 pm

Well done mate. Looks fantastic so far. Glad to see your sim was so accurate :)

Is it the other rocket your using the 12" nylon chute on?

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Digit
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Re: My second build.

Postby Digit » Thu Mar 31, 2016 9:06 pm

No mate that came with a much larger nylon one. I put the 12" in my first rocket actually. Would it suit this one? I just threw a crappy plastic 18" that I had in it for now. I'd like a quick swap system so I can have one good chute and deployment bag and just share it around.
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Lister
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Re: My second build.

Postby Lister » Thu Mar 31, 2016 9:17 pm

Go into your sim and change the chute size to 12" and see what the descent rate is.. if its between 15-25fps it should be fine.

With the swivels we were talking about you can get small clips with them that you can use to easily swap the chute out.. just make sure you have a loop on your shock cord to attach the clip to and tape over any bits that could snag.

For larger rockets I (and most people) use quick links which you can get from bunnings or miami stainless up your way have a very good range, try to get stainless steel ones, the galvanised ones generally arent as strong. You can get them in a range of sizes but im not sure if they have ones small enough.. could be a bit heavy for this rocket.

also with that Nomex deployment bag that should take any chute smaller than the 12" and upto a 16-18" ripstop nylon chute depending on the design and weight of material.

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Digit
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Re: My second build.

Postby Digit » Fri Apr 01, 2016 11:05 pm

Lister wrote:Go into your sim and change the chute size to 12" and see what the descent rate is.. if its between 15-25fps it should be fine.


OR shows a ground impact velocity of 20.8 ft/s with a 12" as opposed to 12.5 ft/s with the 18" so I should be right to use it yea?

Also today I got all my filleting done and will be ready to start sanding and painting tomorrow after an overnight cure.
For anyone interested here is a view into the MMT's from rear of rocket:

Image

I have however developed two issues with my fins that I'm rather disappointed in myself with :(
I have one set of fins slightly out of alignment between the sustainer and booster even tho I tried to use a clothes peg jig and had them all aligned whilst gluing them, and another set of fins with a tapered separation ending in about 3mm at the fin tip between sustainer and booster.

Image
The misaligned fins.

Image
The ugly gap.

As this is my first scratch build I would appreciate any advice so as to make sure I don't make these sorts of mistakes again.

Cheers.
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Re: My second build.

Postby OverTheTop » Sat Apr 02, 2016 9:39 am

OR shows a ground impact velocity of 20.8 ft/s with a 12" as opposed to 12.5 ft/s with the 18" so I should be right to use it yea?

Chute choice is the responsibility of the flyer. It depends on manyl factors, including rocket mass, build strength, size of field, altitude, crosswinds, hardness of landing zone, personal choice and a few more.

20fps is the ballpark for "normal". You can land a rocket at 50fps or higher if the rocket is of suitable design and strong enough and the LZ is soft.

Looking at your rocket with the fins protruding past the airframe I personally would be looking for slower landing to avoid damage.

Think and choose :D
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Digit
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Re: My second build.

Postby Digit » Sat Apr 02, 2016 11:58 am

Thanks for that, I'm just not too sure of ideal recovery speeds yet. I think I will stay with the original 18" for this one to give my design the best chance of a smooth landing. :)
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SpaceManMat
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Re: My second build.

Postby SpaceManMat » Sat Apr 02, 2016 12:22 pm

Is the bent fin caused by warping? Might want to wet it, reclamp the fins again and place in the sun for a day (with no weight on the fins). Once it's straight then prep for painting straight away, preferably on a dry day.
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Re: My second build.

Postby Digit » Sat Apr 02, 2016 2:03 pm

The roots look perfectly aligned to my eye so as you suggest I believe the fin is warped somehow from when I laminated them. Perhaps the glue took longer to dry on one side than the other? As it's less than a fin's width out It really easily moves back into position with my finger which I think is why it looked good and aligned in the peg.

I've taken your advice to try straighten it but this time I've gone to Bunnings to get a few little plastic F clamps.

Should I have had a flat weight on my laminated fins as they dried?

As for the fins with the gap all I can put that down to is workmanship (how I had them jigged for glueing, letting glue dry with airframe nose side down etc.) as they mated well on the cutting mat and during a dry fit of all my parts.
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Re: My second build.

Postby Digit » Sun Apr 03, 2016 6:12 pm

So early this morning I removed the clamping and was happy to find the fin had straightened. So I moved straight onto the priming and painting:

Image
Undercoating.

Image
Matte white applied.

Image
A bit of masking and some matte black applied.

Image
Home made water-slide decals applied.

Image
Semi gloss clear coat applied and she is ready for a maiden flight next weekend :)
('walking the catwalk' on an SCR launch pad)

Image
Home made CoP water-slide decals for both liftoff and sustainer configurations.

My learning outcomes from this build:
-I suddenly respect scratch builders a lot more lol.
-balsa wood, there are different 'grades' available (although not from my regular hobby shop, I would have to source from online next time).
-I can't just cut balsa fins out willy-nilly like plywood, or fabric etc. trying to conserve material, I need to run grain parallel to the fins leading edge for maximum strength.
-My technique for paper laminating fins appears to have warped one of them during curing, even though I laminated both sides of each fin in succession to try prevent this I think next time I will place a flat weight on top whilst the PVA dried.
-I should have made the cut in airframe for my sustainer booster separation AFTER having marked all my straight edges for fin slots and launch lugs. Having made this my first cut I then had to work with a witness mark to keep these aligned for the rest of the build, which added unnecessary difficulty.
-Whilst I tried to design my fins to mate nicely between stages I wasn't thinking of the recovery phase of my sustainer and I now have 3 small delicate points that may sustain damage on impact. I've gone to a relatively large parachute with no spill hole to hopefully prevent this.
-I've learned a lot more about what affects stability having had to design my build in OR before purchasing the parts. (the first few iterations were a bit scary).
-I believe I've learned a way to direct stage black powder motors and still be able to use a motor retention hook.
-I've had a chance to try masking off for a multiple colour paint job.
-I have made water slide decals (from laser jet stock) for the first time, my smaller decals applied beautifully, but I tried to apply the rocket's name all in one hit. This was very difficult and in hindsight I should have done this in at least two parts.
-As I have already used a kevlar cord before I decided to try 6mm elastic strap this time and I have learned a new way to attach a shock cord (inside triple folded heavy paper stuck to inside of airframe wall). Just from a building standpoint I already prefer the kevlar.

Well that's all I can think of for now. Let's see how she flies!

Cheers 8)
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SpaceManMat
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Re: My second build.

Postby SpaceManMat » Sun Apr 03, 2016 8:12 pm

That's a pretty nice look rocket, think you've done pretty darn good.
QRS: 124
AMRS: 32 L2 RSO
Highest Altitude: 10,849 feet
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Lister
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Re: My second build.

Postby Lister » Sun Apr 03, 2016 8:21 pm

Awesome job mate.. cant wait to see your next build :)

When laminating or making fin panels its a good idea to use two flat surfaces.. tiles, very smooth ply wood, metal plate and use one as the base and one as the top.. you need to use something to stop it sticking, I use Glad bake (dont use cheaper brands as things sometimes stick to the cheap ones) or mylar fory fin panels.. mylar gives a glossy finish. Once you have your fin panel laminated put some spacers around the laminated panel so your top doesnt squash the panel and the put the top flat plate on and add a bit of ply to the top of that, then you can add weight to the top or clamp the two plates together.. im building a flow press style panel press for laminating and making FG/CF panels.

someone else probably has another way to do it :)

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Re: My second build.

Postby Viking » Mon Apr 04, 2016 12:38 am

Very nice!
Your laser decals look a nice solid black too.
The laser printer I use at work doesn't print decent blacks. Look ok, but on a white background and near any black paint they end up looking dark grey. I have to print two and stack them, it's fun trying to get 1.5mm letters to line up!!
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Digit
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Re: My second build.

Postby Digit » Mon Apr 04, 2016 9:53 am

Thanks for the kind words and thanks Lister for the advice.
Viking I seem to have fluked my decals the first time but I did change some settings in my printer first which may have helped. First I changed the print resolution from 600dpi to 1200dpi (essentially getting twice as much ink in the one spot) then I changed media type from regular paper to heavy paper, which made a visibly slower printing speed on my machine. And lastly I used my manual feed tray (where you'd put an envelope for example) to minimise the amount of rollers the sheet would have to snake through inside printer.

After letting sheet dry for a minute in document tray I took it outside and weighed down four corners and gave it a light coat of Testors decal setting spray, let this dry for five minutes and then gave it a second generous coat. After another five minutes it went straight onto the rocket.

Hope that helps (you might already be doing all this)
Cheers
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Re: My second build.

Postby Viking » Mon Apr 04, 2016 1:09 pm

Cheers mate, yeah I've tried playing with settings but still not getting nice blacks.
It's one of those huge A3 office machines on wheels, pretty sure they're built for speed and quantity, not quality. Might have to fork-out for a decent home laser.

Good idea doing the decal spray on the whole sheet, that was my first mistake with diy decals, I was cutting them from the sheet and then clearcoating(Microscale liquid decal film) which ended up gluing the edges to the backing sheet in some places which ofcourse ended up in tears(and tears!)
The next sheet was done like you, cleared the sheet before cutting, no drama's now! :D
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Re: My second build.

Postby october sky » Tue Apr 05, 2016 5:45 pm

That looks awesome and I'm sure it flies as well as it looks ! 8)
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