My little Chinese BALLS 2012 Project

Discussions for scratch builders. For the enthusiast that builds from the ground up. Tell us what you've built and what projects you working on in the space race.

Moderator: Moderators

Will this project meet its stated goals? [See slide 2]

Yes
0
No votes
Not a snowballs chance in hell
0
No votes
Maybe
0
No votes
 
Total votes: 0

Passaretti
Mars...........................✓ N5800.........................✓ Next Mission ... ###,###
Mars...........................✓ N5800.........................✓ Next Mission ... ###,###
Posts: 602
Joined: Mon Apr 04, 2011 10:31 am
Location: New York, USA

Re: My BALLS 2012 Project

Postby Passaretti » Tue Apr 24, 2012 10:28 am

air.command wrote:This looks like a seriously cool project Mike! Definitely will be following your build progress on this one. :D

Passaretti wrote: Worst case, I can heat fit it and then cut it off after the flight.


What if you split the fin can along the root edge of one of the fins. Weld one fin along one edge of the split perhaps with a right angle bracket as well and then weld a right angle bracket along the other edge of the split. Then you can easily slip the fincan on the motor and tighten up a bunch of bolts along the right angle through the fin. If you tap holes in the fin (and perhaps the right angle on the other side) and use counter sunk screws you shouldn't incur a drag penalty. If you use enough bolts you should be able to tighten it so it can't come off and then you can take it off again when needed. Whether structurally it will take the load at Mach 3 is another question.

- George


Thanks George and nice diagram!

I'm with ya' on your concept for attaching the fins and keeping the fin-can removable. My original approach was a three-piece can. See attached example. The trouble I kept running into with these concepts was the mechanical complexity and overhead of attachment methods. The drag hit could be quite high as well. I started to veer away from mechanical attachment methods: right angle, fasteners, multi-piece can's etc. and towards bonding the aluminum fins to the aluminum can using some kind of adhesive technique. A bunch of ideas were passed around for employing epoxy rivets, cf or e-glass reinforced joints etc. At the end of the day - I said F it ... I'm going to take the easy way out and have someone weld the damn things on. So here I am ... The trade is that I still need to figure out how to get the fin-can on the rocket - and possibly back off.

I have hope that there is a way slip fit and then bond the can onto the casing; using some solvent to break down the bond after the flight ...

Thanks for the comments - keep em' comin'!

Mike
Attachments
fincan3_.png
Photo Credit - ?
fincan3_.png (223.21 KiB) Viewed 1453 times
Mike Passaretti, TRA 5369

Stewart
Rocket Crew
Rocket Crew
Posts: 250
Joined: Sat Jul 31, 2010 10:15 pm
Location: OAKEY,Qld

Re: My BALLS 2012 Project

Postby Stewart » Tue Apr 24, 2012 12:07 pm

Mike,
Looking at the 98mm caseing drawings , its got a 1/16" high 1/2" wide raised lip at the rear , this should prevent a neatly fitted (firm push fit) fincan from slideing off the rear. All thats then needed is a ring/band thats heat shrunk at the front to hold it all in place - this can be sacrificial. doing it this way makes the fitting/removeal easy and saves the risk of destroying the fincan or motor caseing on removal
Attachments
pro98 case.jpg
pro98 case.jpg (110.06 KiB) Viewed 1444 times
QRS#85
TRA#13049 L2

Passaretti
Mars...........................✓ N5800.........................✓ Next Mission ... ###,###
Mars...........................✓ N5800.........................✓ Next Mission ... ###,###
Posts: 602
Joined: Mon Apr 04, 2011 10:31 am
Location: New York, USA

Re: My BALLS 2012 Project

Postby Passaretti » Wed Apr 25, 2012 10:34 am

Stewart wrote:All thats then needed is a ring/band thats heat shrunk at the front to hold it all in place - this can be sacrificial. doing it this way makes the fitting/removeal easy and saves the risk of destroying the fincan or motor caseing on removal


That's not a bad idea - I'll have to give that some thought ... Thanks Stewart!

Mike
Mike Passaretti, TRA 5369

Space Mark
Juicy Fruit
Juicy Fruit
Posts: 400
Joined: Mon Apr 18, 2011 11:57 am
Location: Perth, WA
Contact:

Re: My BALLS 2012 Project

Postby Space Mark » Wed Apr 25, 2012 11:46 am

Whats wrong with using the UNC thread in the front closure to secure it?
TRA 13845 - Level 3

Passaretti
Mars...........................✓ N5800.........................✓ Next Mission ... ###,###
Mars...........................✓ N5800.........................✓ Next Mission ... ###,###
Posts: 602
Joined: Mon Apr 04, 2011 10:31 am
Location: New York, USA

Re: My BALLS 2012 Project

Postby Passaretti » Sat Apr 28, 2012 6:42 am

Space Mark wrote:Whats wrong with using the UNC thread in the front closure to secure it?


In the case you're under the impression we are talking about motor retention - We are actually talking about how to retain the fin-can to the rocket. There is no airframe over the motor casing - the motor casing is the airframe. The UNC thread on the forward closure will be used to attach the motor to the upper/recovery section of the rocket (see diagram in the slides).

The "fin-can" consists of a tube (aka can) with fins welded to it. The tube or can has an ID that matches (fit - TBD) to the OD of the motor casing. The fin-can will slide over the motor casing and needs to be secured in-place. The thrust ring built into the motor will prevent the fin-can from sliding off the back of the rocket/motor. Radially though, there needs to be something to constrain the can to prevent it from spinning (and sliding up the motor -axially).

Mike
Mike Passaretti, TRA 5369

PK
...
...
Posts: 1710
Joined: Sun Jun 01, 2008 5:07 pm
Location: Perth
Contact:

Re: My BALLS 2012 Project

Postby PK » Sat Apr 28, 2012 9:41 am

partially attached split clamp.
Grub screw through a welded on launch lug.
Glue or silicone caulk.
Thread the od of the thrust ring and the ID of the fincan.
Tabs in the aft of the fincan that engage slots in the od of the thrust ring and then fold over (ie hit 'em with a hammer) to lock in place.
Weld can to thrust ring.

etc...

etc...

etc...

Passaretti
Mars...........................✓ N5800.........................✓ Next Mission ... ###,###
Mars...........................✓ N5800.........................✓ Next Mission ... ###,###
Posts: 602
Joined: Mon Apr 04, 2011 10:31 am
Location: New York, USA

Re: My BALLS 2012 Project

Postby Passaretti » Sat Apr 28, 2012 9:59 am

PK wrote:partially attached split clamp.


Going to explore this option ...

PK wrote:Grub screw through a welded on launch lug.


Hmmm...

PK wrote:Glue or silicone caulk.


All else fails ......

PK wrote:Thread the od of the thrust ring and the ID of the fincan.


Now that's just crazy talk. See below.

PK wrote:Tabs in the aft of the fincan that engage slots in the od of the thrust ring and then fold over (ie hit 'em with a hammer) to lock in place.


See below.

PK wrote:Weld can to thrust ring.



These won't work with the 98 CTI case's because the thrust ring is part of the casing (step/shoulder feature in the machining). The aft closure threads into and completely inside the casing. No portion of the aft closure sticks out (like Aerotech/Rousetech casings). Ie, it's just an aft closure not a closure + a thrust ring feature.

Many thanks for your idears Sir. PK!!

A little birdy told me you weren't coming to Nevada ... I call bullsh*t! Come on out - I'll save you a spot in Tommy's bunk...
Mike Passaretti, TRA 5369

PK
...
...
Posts: 1710
Joined: Sun Jun 01, 2008 5:07 pm
Location: Perth
Contact:

Re: My BALLS 2012 Project

Postby PK » Sat Apr 28, 2012 5:07 pm

Make a case for the reload that does have a closure..
Seriously though. The fincan to case interface has a lot of surface area. Something like Fullers Gap Filler (the greatest nozzle insulating material ever devised) would provide a LOT of holding force...
Loctite 621 is rates at 12PSI in shear.
A little birdy told me you weren't coming to Nevada ... I call bullsh*t! Come on out - I'll save you a spot in Tommy's bunk...

Not going if I can't fly. I have a payload but we aren't gonna have the propulsion sorted in time.
PK

Passaretti
Mars...........................✓ N5800.........................✓ Next Mission ... ###,###
Mars...........................✓ N5800.........................✓ Next Mission ... ###,###
Posts: 602
Joined: Mon Apr 04, 2011 10:31 am
Location: New York, USA

Re: My BALLS 2012 Project

Postby Passaretti » Sun Apr 29, 2012 9:36 am

PK wrote:Make a case for the reload that does have a closure..


Tempting ...

PK wrote:Seriously though. The fincan to case interface has a lot of surface area. Something like Fullers Gap Filler (the greatest nozzle insulating material ever devised) would provide a LOT of holding force...
Loctite 621 is rates at 12PSI in shear.


Will have to find the equiv. gap filler up here - I'm sure we have something comparable. Never used Loctite 621 - will have to check it out too.

PK wrote:Not going if I can't fly. I have a payload but we aren't gonna have the propulsion sorted in time.
PK


What's your payload?
Mike Passaretti, TRA 5369

Passaretti
Mars...........................✓ N5800.........................✓ Next Mission ... ###,###
Mars...........................✓ N5800.........................✓ Next Mission ... ###,###
Posts: 602
Joined: Mon Apr 04, 2011 10:31 am
Location: New York, USA

Re: My BALLS 2012 Project

Postby Passaretti » Sun Apr 29, 2012 9:58 am

Cut the fins out of the 4" x 0.1875"T plate stock today. Cleaned with the orbital sander and tacked (using CA) them to the can. I'm tweaking the mechanical drawing of the fin-can assembly now so I can shop around the weld job to some local welders.

My plan is to get some input from potential welders ASAP. Prior to dropping off for welding, I intend on adding an fin-alignment feature to the fin & can. I'm going to mill three shallow longitudinal slots in the surface of the can (120 deg apart). The root edge of the fin will also chamfered. This will create a feature that allows the fins to be aligned (longitudinally) with relative ease. I'm not so concerned about radial alignment.

Here is my rough approach, let me know what you guys think:

Fin-can Assembly Key Steps:

#1 - Cut out fins, clean up can.
#2 - Consult with welder.
#3 - Add features to fin root-edge / tube to allow for alignment. Add any other features desired by welder.
#4 - Prep. assembly for welding. Build jig?
#5 - Weld fins to can.
#6 - Hone ID of can to OD of motor casing.

Mike
Mike
Attachments
fincan_schem.jpg
Work in progress ...
2012-04-28 17.03.47_.jpg
Shown with a piece of 98mm phenolic coupler tube sitting on top.
2012-04-28 17.03.47_.jpg (221.96 KiB) Viewed 1350 times
2012-04-28 17.00.06_.jpg
2012-04-28 17.00.06_.jpg (204.03 KiB) Viewed 1350 times
2012-04-28 16.59.56_.jpg
2012-04-28 16.59.56_.jpg (209.45 KiB) Viewed 1350 times
2012-04-28 16.59.16_.jpg
My first metal fin-can ... almost.
2012-04-28 16.59.16_.jpg (224.22 KiB) Viewed 1350 times
2012-04-28 16.20.05_.jpg
Made the second and final cut using a sawzall and some water.
2012-04-28 16.20.05_.jpg (144.93 KiB) Viewed 1350 times
2012-04-28 15.39.11_.jpg
Other than trying to find extra blades for my dad's ancient jig-saw, cutting the fins out went relatively smoothly.
2012-04-28 15.39.11_.jpg (133.97 KiB) Viewed 1350 times
2012-04-28 15.29.50_.jpg
Jig saw + a fence ...
2012-04-28 15.29.50_.jpg (143.62 KiB) Viewed 1350 times
2012-04-28 12.19.19_.jpg
Now how the hell do I cut these ...
2012-04-28 12.19.19_.jpg (139.8 KiB) Viewed 1350 times
2012-04-27 21.42.13_.jpg
You get the idea ...
Mike Passaretti, TRA 5369

PK
...
...
Posts: 1710
Joined: Sun Jun 01, 2008 5:07 pm
Location: Perth
Contact:

Re: My BALLS 2012 Project

Postby PK » Sun Apr 29, 2012 10:03 am

You know you're gonna have to machine the ID of that can after you weld the fins on right?
PK

Passaretti
Mars...........................✓ N5800.........................✓ Next Mission ... ###,###
Mars...........................✓ N5800.........................✓ Next Mission ... ###,###
Posts: 602
Joined: Mon Apr 04, 2011 10:31 am
Location: New York, USA

Re: My BALLS 2012 Project

Postby Passaretti » Sun Apr 29, 2012 10:22 am

Yes, this is the current approach.

The wall thickness is ~0.1385" right now, the ID is approx. 3.7415". To fit over the motor the ID needs to be 98mm or 3.8583". My thinking is that it will be better for the welder to weld to a thicker wall than it will be the post-machined thinner wall. The fins are 0.1875" plate which is closer to the pre-machined wall thickness.

The trade is that - yes, the ID needs to come down after the fins are on. However, I've heard positive thing thus for for honing the required 0.054" off the radius. I've been operating under the assumption that the hone will do the trick, as opposed to gun-drilling or using a boring bar to open the ID up ... (the more complicated approach).

This is one of those areas that is OUTSIDE of my expertise - so do chime in, particularly those with experience welding aluminum.

Thank yoU!

Mike
Mike Passaretti, TRA 5369

PK
...
...
Posts: 1710
Joined: Sun Jun 01, 2008 5:07 pm
Location: Perth
Contact:

Re: My BALLS 2012 Project

Postby PK » Sun Apr 29, 2012 10:31 am

Passaretti wrote:Yes, this is the current approach.

The problem with honing is that there will be a variable amount of metal (of varying hardness) to remove. The welds will shrink the metal for a half inch or so on either side of the fin, depending on how quickly the metal cools the same metal will be harder or softer. It might be a bit more than a hone can handle ie, it would eventually get it round, but you might need to take off a lot of metal to get to that point..

I'd suggest giving it to a machine shop and having them bore it which is a very easy thing for them to do.
If you must do it using the Wall Mart approach, try and get your hands on a ridge reamer.. (The clamp type not the rolling body)
PK

Passaretti
Mars...........................✓ N5800.........................✓ Next Mission ... ###,###
Mars...........................✓ N5800.........................✓ Next Mission ... ###,###
Posts: 602
Joined: Mon Apr 04, 2011 10:31 am
Location: New York, USA

Re: My BALLS 2012 Project

Postby Passaretti » Sun Apr 29, 2012 10:41 am

Point well taken. I had thought about the welded areas, how they would behave vs. the unwelded metal during machining/honing. Guess I'll find out ... That is unless a welder tells me he can weld to half the wall thickness with confidence.

And, you spelled Walmart wrong...
Mike Passaretti, TRA 5369

ogivemeahome
Rocket Crew
Rocket Crew
Posts: 439
Joined: Tue Jul 20, 2010 8:06 pm
Location: Brisbane

Re: My BALLS 2012 Project

Postby ogivemeahome » Sun Apr 29, 2012 10:19 pm

Passaretti wrote:... welding aluminum.

It may need 'normalising' (heat & cool very slowly) after welding? This is done with steel fabrication, not sure about al. The nicely machined, round fincan may not stay round due to the stresses introduced by welding.

1.5 mm (per side x length) is a lot of material to remove by honing. Boring would be a better option (IMO) - more likely to be concentric, round and straight. Honing too much takes the soft bits first and the hole wanders all over the place. Chat with a engine re-conditioner to have some boring done? Hope this helps.
A smooth sea never made a skilled mariner. (English Proverb)


Return to “Scratch Built”

Who is online

Users browsing this forum: Google [Bot] and 1 guest