Postal Rocket

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High Impulse
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Re: Postal Rocket

Postby High Impulse » Tue Dec 15, 2015 7:28 pm

I imagine the RRC3 would have really enjoyed the ride ;)

I cut the fins out today and the centering rings and they do feel pretty solid, just need to prevent them from fraying on the edges so i may still glass them or smooth epoxy over the leading and trailing edges.

Centering rings are a little loose inside the body tube but a perfect fit around the motor mount so with a bit of epoxy i think it should come up okay. They are maybe 1-2mm offset in one point for each ring but i think if I orientate them the correct way they will cancel each other out.

Fins are also a bit off with about +/- 2-3 mm between 3 out of the three, so i will have to clean them up a bit with some files and sandpaper.

fins and centring rings.jpg



Also will have to take a bit of the base chord too as i left some extra wiggle room on the fin tabs for when i add fiberglass to the body.

I think slow sounds like a good idea lister, in the current heat ill just have to be careful with it and mix it up in batches.

The arrhenius equation i presume kryten? that thing models everything from chem reactions to nucleation rates for solid-solid transforms.
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Re: Postal Rocket

Postby Lister » Tue Dec 15, 2015 8:04 pm

Re the RRC3 I contacted missile works and they said if the pcb was intact they can fix it which is bloody good customer service.. its been posted over and am wairing to hear back so hopefully it will be back by start of vic season, if not have an atlus metrum easymini and a couple of eggtimer quarks on the way so I can still launch. Im just glad i got the Darkstar nose back :)

What type of ply is that? If your worried about edges there is no need to glass it.. just paint some epoxy on the bits your worried about..

a tip if your centering rings are a bit loose.. laminate X layers of paper around until you get the diameter you want.. it wont be quite as strong as it would if it was the right size but with 4 centering rings it will make two parts of stuff all difference.

When it comes to getting all the fins to the size I want I always cut them out a little larger than needed, put all the fins of that shape together face to face and tape them on each side.. then I use my "bench sander" sand them back to the actual size I want.. once you do a side re-tape it and move on.. you could also clamp them all together and use a file or a sander. That way every fin is EXACTLY the same size and weight.. very handy when doing 6-8 fin rockets.

Sounds like a smart move with the resin.. if using an ice cream container it would be a good idea to sit it an some cold water (if you add salt and ice to water it will drop the temp even more than just ice alone as the salt lowers the waters freezing point.. or something like that?) Like OTT suggested.. if I had of thought of it I would have been doing it this summer, I will be from now on ;)

Did you laser cut the CR's?

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Re: Postal Rocket

Postby OverTheTop » Tue Dec 15, 2015 8:42 pm

Slow hardener is your friend :!:

You can always speed it up a little with the heat gun if needed. It goes a bit runnier when you do that though.
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Re: Postal Rocket

Postby High Impulse » Tue Dec 15, 2015 8:48 pm

Wow that is really great service from missile works. I wish all companies were as good as them.

It's 4mm marine ply from bunnings. I might just paint epoxy in the end, although glassing in it would be good practice too so I will see how eager I'm feeling.

I was thinking a similar thing with the laminating just hadn't thought of what to do it with. The prinary bond will be the epoxy fillets against to he frot and bak of the rings too so I guess that will help with the bind strength.

I'll probably clamp them tomorrow arvo and file them or maybe invert dad's electric sander and use it.

And no I didn't laser cut the fins ;). The 54mm hole saw wa so blunt it burnt the whole way through...
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Re: Postal Rocket

Postby Lister » Tue Dec 15, 2015 9:17 pm

If its marine ply you will need to glass the bevelled edges.. its a soft core and doesnt hold up well (ive tried :) )

I have used Reflex 80gsm printer paper.. worked really well on fins.. can also just wrap masking tape around them to build it up and just use them like normal but you would want a decent fillet.

lmao nice, I have done that.. gives them that professional laser cut look ;)
You can sharpen hole saws with a small file.

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Happy Heyoka
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Re: Postal Rocket

Postby Happy Heyoka » Wed Dec 16, 2015 10:13 pm

Can I suggest you try your local hobby shop for "Bob Smith Industries 20min Finish Cure" for the wooden bits (and, apparently, for the glassing). It looks really nice on ply fins and polishes to a really smooth finish with some patience.
It also seems fairly tough - survived some bitumen landings last time out.

I'm just about to glass wrap some postal tubes (first time) and was going to try a number of different resins including the BSI one which my hobby shop guy says he uses all the time for glassing wings (and is recommended for such by BSI).

Next trick - convincing Australia Post or Officeworks to produce 29/38 or 54 mm ID tubes :D
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Re: Postal Rocket

Postby kopius » Thu Dec 17, 2015 12:12 am

Happy Heyoka wrote:Can I suggest you try your local hobby shop for "Bob Smith Industries 20min Finish Cure" for the wooden bits (and, apparently, for the glassing)


Or you can buy it from Australian Rocketry: http://ausrocketry.com.au/accessories-t ... grams.html



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Happy Heyoka
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Re: Postal Rocket

Postby Happy Heyoka » Thu Dec 17, 2015 12:18 am

kopius wrote:
Happy Heyoka wrote:Can I suggest you try your local hobby shop for "Bob Smith Industries 20min Finish Cure" for the wooden bits (and, apparently, for the glassing)


Or you can buy it from Australian Rocketry


mea culpa :wink:

cheaper than my local guy too!
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Re: Postal Rocket

Postby Lister » Thu Dec 17, 2015 6:48 am

As much as I love fast cure stuff I have found the finishing resins are a fair bit weaker than a wests 105/206 when it comes to laminating.. while thats with the RAG bench testing, I found it was a bit brittle.. put both tubes on the bench (it was actually with nuplex R180 which again is slightly weaker than wests) and pushed down with an open palm and a fair bit of force.. the finishing resin had about 1000 stress fractures appear instantly. The R180 took a sledge hammer to do something similar.

This "test" was not done with blakes epoxy, It was Z poxy finishing resin.

From now on I will be using wests and nuplex R 180 depending on the situation and the rocket.

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Re: Postal Rocket

Postby High Impulse » Thu Dec 24, 2015 7:35 pm

Happy heyoka, I ended up grabbing some nuplex resin to use for both laminating and structural fillets. Hopefully should get around to glassing the tube next week after chrissy has blown over.

Does anyone know approximately how much extra thickness about 2-3 wraps of 185gsm glass will add to a body tube? I could measure it with my verniers but I imagine when i add the resin it will expand it a bit. If it doesnt add too much in thickness i may be able to use one of my test pieces as a 38mm coupler.

So far progress has been slow on the build because of work and other ancillary wastes of time :(.

I have increased the OD of the centring rings by laminating with paper so they are all now a nice fit in the body tube. I have also marked out the location of the rings so all i have to do now is glue them in place.

With regards to this i will be using my own home made motor retainer (essentially one bolt and a nut/washer through the rear centering ring which when tightened up holds the motor in) and I was wondering should i leave an extra 10mm in case my motor retention system doesnt work so hot and i can grind it off and replace with a HAMR retainer? If i do do this though the issue is i have about 5mm between my top centering ring and the end of my motor mount and i am slightly concerned that this is not enough for the adhesion of the glue. (i hope this sort of makes sense).

Also, with regards to the placement and attachment of rail buttons. I will be putting the lower rail button through my rear centring ring (approximately 10mm from the rocket end) and i am under the assumption that the top rail button should go at approximately the CG. However as my rocket has a wooden nosecone the CG is quite far forward, thus i do not have anything to drill into when installing my centering ring. Is this something to be concerned about/how should i ensure that it wont get ripped off or conversely rip something inside my air frame should the screw extend into the interior?

I could place the botton in my top centring ring which is 8 inches from the lower rail button but i am a little concerned that this would not be enough distance between the two to ensure that the rocket doesnt wiggle too much on the rail.

Thanks heaps and I hope everyone has a merry chirstmas.
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Re: Postal Rocket

Postby Lister » Thu Dec 24, 2015 8:27 pm

What is the total length of your rocket? If its not too long and heavy you may be ok with 8" between your buttons.. you can always mount a 1/2" thick cr at the CG of your rocket for the button to screw into or even epoxy a nut into a hole in the cardboard (make sure you plug the thread with wax or grease or anything you can later remove that will protect the thread) and then FG over the hole and put some fg over the back of the bolt onto the inside of the airframe and then do your two layers of FG over the whole tube.. then you drill a hole and take the plug/ melt/scoop the wax/grease out and you have a solid button mount.
Also I found something the other day that might work.. it was a nut that had two wings either side that sat flush with a surface amd had a small lip that sat into the surface.. you put the bolt through from the other side and screw it in. Had a small and a large but I didnt get any as I was in a rush i'll get some next week and see if they would work.

as for the thickness 3 layers would add about .7mm from memory you wont need more than 2... for an exact measurement get your dunny roll and lay up 1, 2, 3, 4, 5, 6 layers and have it so each layer is 10-15mm shorter than the previous layer.. then when its cured you have a layer thickness guide ;)

That retention system should work.. I would leave the mmt overhanging the aft centering ring by 10mm.. like you said you can cut off the rod and install a hamr retainer if you aren't happy with it... I dont get what you mean by the 5mm gap and the glue issue?

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Re: Postal Rocket

Postby High Impulse » Fri Dec 25, 2015 7:19 pm

Total length at the moment is looking to be between 860-900mm depending on how much of the body tube i lose when doing the fiberglassing (it has a couple of staples in one end which I think have compromised the structural integrity of the tube at one end).

I was thinking of putting a backing board behind it of some sort its just the cg is about 200mm from the end of the rocket and my hands dont fit inside so it would be a challenge to try and attach something inside :/.
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Re: Postal Rocket

Postby High Impulse » Fri Dec 25, 2015 7:22 pm

The rocket also has a name now :D

After much pondering it is to be christened "Hyperion" partly after the TV series Skyland and partly because its spacey themed...
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Re: Postal Rocket

Postby Lister » Fri Dec 25, 2015 8:48 pm

Yeah it may be a bit long to have both buttons so close together... If you drill a small hole where you want the rail button, you can poke a nail through and put the nut on the end of a chopstick with some blutack.. apply epoxy around the hole and put your nut down the tube and onto the nail or whatever is poking through the hole.. while keeping it in place with the nail push it against thie wall with your chop stick.. put a drop of CA on the but and let it cure.. the backing plate would need to be a 1/4" thick and you will need to do it much the same way as i suggested with the nut... or just wait until I get the nuts with the backing plate and do it that way?

if you glassing the tube a couple of staple hole a wont make any difference to the strength of the airframe once glassed.

I like the name change.. for some reason it sounds familiar :)

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Re: Postal Rocket

Postby kopius » Sat Dec 26, 2015 5:55 pm

I would happily stick the buttons that close together on a rocket that big. I have seen a 5.5metre x 8" rocket that weighed about 50kg with the bottom button through the bottom CR and the top button only 30cm above it. I was sceptical of it but it worked flawlessly and the buttons remained in tact.

Check the web for Hyperion rockets. The hyperions were a hybrid system good for about 100,000'. I have a photo with one at CTI somewhere and will have to find it. Kewl name either way ;-)


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