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Old Aug 10, 2014, 02:16 PM
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United Kingdom, Birmingham
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Originally Posted by invertmast View Post
Looks awesome man! Count me in if youd like to sell one
cool.... that's made my day
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Old Aug 10, 2014, 03:30 PM
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United States, FL, North Port
Joined Mar 2004
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Originally Posted by meerkat13 View Post
cool.... that's made my day

I like hunters! Id love to have one or Mick reeves' kits, but the exhange rate and shipping almost makes it cheaper for me to scratch build my own composite version of that size.
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Old Aug 16, 2014, 03:57 PM
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Ducting Moulds

Ducting Moulds

I thought I would try something new this week and designed duct moulds to create foam plugs. The idea being that I could them easily cast plugs to try different layups, rather than print and hand finish the HIPS plugs each time I wanted to try a different layup. Im really keen on the ducts having no seams, which is why Im going down the loss foam / HIPS route.

The exhaust mould was easy enough to design, but the inlet mould was a bit more complicated because of the parting lines and it size. I ended up printing the inlet moulds in 4 sections which worked well and good experience for when I come to the wings and fuselage moulds.

It took a couple of attempts to understand that back pressure is everything when casting with urethane foams. I did get some minor chips along the seam when removing the flashing which were easily filled and sanded.

I changed the layup from the last test I did as follows
  • Cut 1 strips of 25g Fibreglass
  • Laid them as slightly overlapping bands.
  • 2 layers no carbon fibre
  • 1 strip of peal ply wound tightly around.

As you can see from the photos it turned into a bit of a train wreck.
  • When I removed the peal ply I could see the layup was dry in areas.
  • The layers had shifted and wrinkled with the inlet layup.
  • As the foam doesnt dissolve in acetone I had to remove the foam mechanically.
  • The foam was very dense and strong due to the amount of backpressure in used.
  • The cured fibre glass felt like tissue, very thin and easy to tear.
  • I managed to remove the foam from the exhaust but it was very weak and the internal surface wasnt great.

I had some old plaster paris so cast a hollow version of the inlet. The thinking been that its would be a lot easier to break and remove then the dense foam. The plaster went off really quick but was good enough for a proof of concept. When I get a chance Ill lay it up.

Im going to revert back to the previous method for the next layups and then take it from there.
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Old Aug 18, 2014, 08:12 AM
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United Kingdom, Birmingham
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Exhaust Duct Loss HIPS method

This is easily my best layup to date and Im starting to get a much better feel for composite work.

The process was as follows -
  1. Exhaust duct printed in HIPS at 0.1mm layer height, 2 shells.
  2. Sanded down to 2000 grit wet and dry.
  3. 2 coats of Ease Release sprayed.
  4. Primed grey acrylic (wont do this again)
  5. 2 x 25g glass fibre (West 205 system)
  6. Left to go off tacky
  7. 30K carbon toe rings added in 5 places
  8. 1 x 25g glass fibre
  9. Left overnight to cure.
  10. Ends trimmed and submerged in Orange turpentine to dissolve the HIPS.
  11. Agitated and scraped of soft HIPS every 20 minutes.
  12. 2 hour later and the part is finished the Orange Turpentine also dissolved the grey acrylic.

Weighs 2.3g and plenty strong enough.

I have done a ABS version which I will layup and then use Acetone to dissolve the ABS. I just want to compare methods to see which is easier.
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Old Aug 18, 2014, 01:59 PM
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Greenwood Indiana
Joined Jun 2004
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Your build is coming along very well. I like how you are willing to try different "recipes" to come up with a part that works well. I might have to try that technique on my F-4 when I can find the time, work and family have consumed every last minute.
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Old Aug 19, 2014, 03:46 AM
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Originally Posted by danj31 View Post
Your build is coming along very well. I like how you are willing to try different "recipes" to come up with a part that works well. I might have to try that technique on my F-4 when I can find the time, work and family have consumed every last minute.
Good hearing from you Dan.

I think that one of the best things about working at this scale is that you really need to consider everything to get the best balance between weight, strength and finish. Going off on tangents is all part of the fun and adventure.

Looking forward to see you back on your builds when time permits. I've been pretty lucky of last but sure do hear you with the work, family, hobby balance.

Be sure to give me a shout if you need your ducts printed etc.
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Old Aug 20, 2014, 06:18 AM
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United Kingdom, Birmingham
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Exhaust Duct - Loss ABS Method

The loss ABS method worked even better then the loss HIPS method previously.
  • ABS was easier to print and finish - could use Acetone Vapor Bath for a supper smooth surface as a final step.
  • Took about half an hour to remove the ABS with the acetone.

I also reduced the carbon toe to two bands around where the duct is glued to a former in the fuz.

The weight is right down a 1.7 grams. The best usable ABS printed duct I've done to date came in at 3 grams and is no where near as strong as this last composite version.
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Old Aug 24, 2014, 04:59 AM
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First duct set complete

I completed the ducting last night. I'm constantly refining the process and for the right hand inlet, managed to get the ABS plastic out with out using acetone. Took about 15 minutes and no mess .

The ABS shroud is printed and finished. I've had some ideas on how I can reduce the amount of printed plastic (weight) so will redesign for the flying model. I'll use this version in the test rig to tie down a EDF system.
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Old Aug 24, 2014, 07:45 AM
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Awesome work!
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Old Aug 24, 2014, 10:46 AM
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upland CA
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Man that's some cool stuff....
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Old Aug 24, 2014, 11:36 AM
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Cheers guys,

Just set it up in the test rig and all looks good
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Old Aug 24, 2014, 12:18 PM
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United States, OR, Portland
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Originally Posted by meerkat13 View Post
I completed the ducting last night. I'm constantly refining the process and for the right hand inlet, managed to get the ABS plastic out with out using acetone. Took about 15 minutes and no mess .
I'd love to hear more about this.

I've been ramping up to do some fiberglass wing layups for a micro hotliner using a lot of 3D printed tools (molds, foam cutting airfoil templates, jigs, etc). I'm really interested in avoiding the "lost ABS" technique. Are able to preserve your 3D printed pattern part with your latest technique?
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Old Aug 24, 2014, 03:23 PM
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Cheers guys,

Just set it up in the test rig and all looks good
Looks GREAT !!
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Old Aug 25, 2014, 05:45 AM
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Originally Posted by elbowdonkey View Post
I'd love to hear more about this.

I've been ramping up to do some fiberglass wing layups for a micro hotliner using a lot of 3D printed tools (molds, foam cutting airfoil templates, jigs, etc). I'm really interested in avoiding the "lost ABS" technique. Are able to preserve your 3D printed pattern part with your latest technique?
Sounds like fun .

I expect with some clever design it may be possible with the wings. The thin walled ABS flexes which is good when removing the former. The glassfibre releases from the ABS really well, just make sure you have a bit of draft on your former.

If add about 0.5 degrees on the exhaust I could reuse the former. The former for the reducer from the EDF to exhaust came out in one piece.
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