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Audax F3A - new project for 2013

Old 04-04-2013, 08:55 AM
  #26  
Alex Voicu
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Default RE: Audax F3A - new project for 2013

In the end the mold plug was sprayed with a layer of white gelcoat. Please note that the nose of the model is much longer than needed so we can cut it later either straight for the contra drive, or angled for conventional single propeller setups that require right thrust.
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Old 04-05-2013, 08:26 PM
  #27  
Ryan Smith
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Default RE: Audax F3A - new project for 2013

Incredible, Alex. Very impressive processes utilized to design and manufacture a top-quality F3A machine. I love seeing top quality design and manufacturing to make a top-quality model. You should be very proud. I hope you find it flies extremely well.
Old 04-05-2013, 10:38 PM
  #28  
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Default RE: Audax F3A - new project for 2013

I am not able to see the attached images is there any problem?
Old 04-06-2013, 08:36 AM
  #29  
Alex Voicu
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Default RE: Audax F3A - new project for 2013

Thanks Ryan, i hope you will enjoy the next updates as well. There's still a long way ahead of us, so for now we'll keep working on it and i'm sure we'll have reasons to be proud when the model is up in the air

Highfly3D, for me the pictures above show up without problems, but i experienced some problems viewing pictures in other threads. Maybe it's a temporary issue with the forum server.
Old 04-15-2013, 07:15 AM
  #30  
Alex Voicu
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Default RE: Audax F3A - new project for 2013

Looks like the image upload is finally working, so i'll continue with the updates.

The white gelcoat was sanded smooth, but we weren't fully satisfied with the surface of the mold plug so we sprayed a second layer of grey gelcoat. This was carefully sanded with 1500 grit and water; the white gelcoat underneath shows up here and there but the surface had a very smooth, mirror-like appearance.

I attached a few pictures of the mold plug with and without the canopy. The canopy fitting was not done yet at the time these pictures was taken, so there's a visible gap between the canopy and fuselage.
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Old 04-15-2013, 07:16 AM
  #31  
Alex Voicu
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Default RE: Audax F3A - new project for 2013

When the fuselage mold plug was finished, it was time to add the parting boards. These were laser-cut from MDF and they fit perfectly, confirming the accuracy of the mold plug shape.
Next we waxed the surfaces, sprayed the mold gelcoat (green) and added the fiberglass layers to build the first half of the fuselage mold.
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Old 04-18-2013, 07:24 AM
  #32  
Alex Voicu
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Default RE: Audax F3A - new project for 2013

First half of the mold done, parting boards removed:
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Old 04-18-2013, 07:26 AM
  #33  
Alex Voicu
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Default RE: Audax F3A - new project for 2013

I attached a few pictures showing the completed fuselage mold.
We took the pictures immediately after opening it, so the surfaces are still dirty with wax. The next step will be polishing the molds and cutting the opening in the canopy area.
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Old 04-18-2013, 07:54 AM
  #34  
Alex Voicu
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Default RE: Audax F3A - new project for 2013

For Facebook users, you can see the pictures in higher resolution in my photo album at the following link (you will need to go in fullscreen mode):
[link=https://www.facebook.com/media/set/?set=a.432293993521272.1073741825.100002220265252&type=1]Audax F3A photo album[/link]
Old 04-22-2013, 07:05 AM
  #35  
Alex Voicu
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Default RE: Audax F3A - new project for 2013

A few images of the polished fuselage molds with trimmed canopy flange:
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Old 04-22-2013, 08:53 AM
  #36  
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Default RE: Audax F3A - new project for 2013

Superb...
Old 04-26-2013, 08:00 AM
  #37  
Alex Voicu
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Default RE: Audax F3A - new project for 2013

A few details about the fuselage construction:

We decided to use Airex C55 as the core material, because it's lighter, stiffer, and easier to work with than balsa.

First the molds were waxed and sprayed with white gelcoat. We used 80g (2.9oz) fiberglass cloth for the first layer, then added the yellow airex and the 160g (5.7oz) carbon cloth. The carbon was reinforced with an additional layer of 80g fiberglass, and the final layer was 25g (0.9oz) FG cloth covering the whole surface. In the end we vacuum bagged everything and put it in the oven until the epoxy resin was fully cured.

Pictures show the gelcoat sprayed in the mold and the fuselage lay-up after vacuum bagging.
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Old 04-26-2013, 08:01 AM
  #38  
Alex Voicu
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Default RE: Audax F3A - new project for 2013

The first fuselage came out at 690g, which is not bad for the first attempt, especially considering that we don't need a chin cowl that adds up to the final weight. The nose needs to be cut shorter to fit the 82mm spinner and the canopy flange needs to be trimmed, so this will save quite a few grams.

Todd Schmidt was very kind to help us with a lot of useful advice and we also have a few ideas where we can save some weight, so i'm sure the next fuselages will be lighter.

Pictures of the first fuselage, fresh from the mold:
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Old 04-27-2013, 08:02 AM
  #39  
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Default RE: Audax F3A - new project for 2013

Gorgeous job!!!

And very good weight!!!

Good luck,

Isaac Najary
Old 04-28-2013, 10:26 PM
  #40  
Alex Voicu
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Default RE: Audax F3A - new project for 2013

Thanks Isaac and Highfly3D, i'm glad you like it. I hope the wings will be light as well.
Old 07-29-2014, 09:00 AM
  #41  
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With so many pattern contests for me last year and a lot of work on a full size glider for my friend, it wasn't possible to finish the model in 2013, but we made some progress since then so it's time to update this thread.

Having completed the fuselage, we moved on to the tail surfaces. The mold plugs for the stabs were machined from MDF, here you can see a few images i took during the milling process:

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Old 07-29-2014, 09:02 AM
  #42  
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We didn't took pictures during the stab mold construction, but the process is not different from the fuselage molds.

Pictures of the finished stab molds:

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Old 07-31-2014, 07:52 AM
  #43  
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The stab layup consists of a sheet of 1.2mm Airex as core material, sandwiched between 2 layers of 25g/m2 fiberglass. The internal structure looks like this:



It's maybe a little stronger than needed, so it will be simplified in the future to make it lighter.
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Old 08-04-2014, 09:56 AM
  #44  
Alex Voicu
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CNC Machining the wing mold plugs:

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Old 08-05-2014, 01:57 PM
  #45  
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Wonderful work Alex!

Keep the pictures coming, it's a joy to see good work and craftsmanship. Beautiful lines on your design, I guess the airflow will be very straight (you know what I mean by "straight") on the fuselage.

Best regards

Alejandro

Last edited by apereira; 08-05-2014 at 02:05 PM.
Old 08-06-2014, 05:47 AM
  #46  
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Thanks Alejandro, i hope you're right I'm on holiday right now, but i will post more pictures next week when i'm back home.
Old 08-11-2014, 11:26 AM
  #47  
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Finished wing mold:

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Old 08-17-2014, 11:34 PM
  #48  
Alex Voicu
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We built a few composite fuselages in the past but composite wings are a new experience for us. We only found very limited online material about this subject, so the only way to get it right was to build a pair of wings, see what comes out and adjust the manufacturing process accordingly.

The composite skins are made of 2mm Airex sandwiched between 2 layers of 50g/m2 fiberglass, with a strip of peel ply for the hinge line. Everything was vacuum bagged and put in the oven for curing at 60 deg C.

All the parts for the internal structure were laser cut; we used 3mm liteply for the ribs supporting the wingtube and 6mm balsa for the main spar. These parts were considered critical so they were carbon laminated, which added quite a bit of weight. We also added a few strips of unidirectional carbon between the main spar and the wing skins. All the other parts were made of 2.5mm balsa.

The internal structure alone was 140g, which made it clear from the start that this pair of wings were going to be heavy, but we decided to build them anyway and use them for testing.

A few images of the wing internal structure:

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Old 08-18-2014, 05:55 PM
  #49  
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Looks very nice Alex. Great workmanship!

Is peel ply the normal material for composite wing hinges?

Cheers,
Jason.
Old 08-18-2014, 10:28 PM
  #50  
Alex Voicu
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Thanks Jason. There are many composite models using peel-ply, for example the ZN Line Integral and also the Spark if i remember correctly. Kevlar is also used but it's a lot more expensive and some say it may crack along the hinge line.

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