Australis (G_T) - RC Groups
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Sep 07, 2017, 02:43 AM
Everything's A Compromise
Larrikin's Avatar
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Australis (G_T)


About a year ago I got all excited about making moulds for a dual purpose F3J(TD)/F5J model.
I currently fly a Vixen so when I saw the SynerJ wing by Gerald (G_T) I knew that I'd be using that wing.

Mean while, models like the Ultima and the Vinco were setting the standard for F5J models and I decided that the design was going to focus on F5J.
As it happens now, more people are entering local F5J events than TD events. The writing is on the wall.

The plan is to mill plugs from MDF and hand finish, then create composite moulds as we did in the SNIPER thread.
Originally, I wanted to make a 2 piece wing. For me, fewer moulds equals less effort and therefore less of a psychological barrier to building. ie, waxing 4 moulds instead of 6, painting 4 moulds instead of 6 ... etc etc

But, logic prevailed and I've opted for a 3 piece wing. The logic is that F5J is relatively new and design criteria can vary going forward.
So, I thought I'd have a short centre panel so that if, in future, spans settled around the 2.5 - 3m area I could still use the tip panel moulds as a wing.

To respect the amount of time that Gerald has put into the SynerJ wing design, I have kept it relatively "pure".
I have added a small section of span traversing the fuselage seat to negate any negative draft angles on the fuselage seat area (thanks Geoff), and I added a small amount of span to the tips for shaping, and what d'ya know? .... 4 meters

It's no coincidence that the centre panel is approximately the same length as a sheet of balsa. I'd planned to hollow mould the wing because there's something not right about spending an inordinate amount of time designing profiles only for the skin to have "cellulitis" from a solid core... IMO!

I have recruited a couple of buddies with special skills to help. One has CAD skills and the other has a mill.
They are welcome to chime in at any stage.

This will be a relatively slow process. I'm hoping that things don't get too heavy and that the project doesn't grind to a halt.

David
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Sep 07, 2017, 02:44 AM
Everything's A Compromise
Larrikin's Avatar
Reserved
Sep 07, 2017, 10:39 PM
Registered User
Luis Moya's Avatar

Options


Thinking outloud about options that might expand the appeal.

-2 Piece fuse?

- X tail?

Good luck with your project.

All the best,

Luis
Sep 08, 2017, 12:04 AM
Everything's A Compromise
Larrikin's Avatar
G'day Luis,
Thanks for your feedback.

Quote:
Originally Posted by Luis Moya
Thinking outloud about options that might expand the appeal.

-2 Piece fuse?
A 2 piece fuselage implies a transport convenience.
The Australis is intended as a personal model (with a few extras for friends and interested people.)
If not traveling internationally, my logic is that local transport doesn't present an issue.
A 2 piece fuselage, however, presents increased complexity and additional weight. (unnecessary in this case)

Quote:
Originally Posted by Luis Moya
- X tail?
I have my reasons for choosing a V-tail. I could present them here but I suspect the thread would degrade into a slinging match. Let's just say, if you read the phrase above my avatar, I designed the tail to how I believe the compromise is skewed towards what I believe to be an important part of the design criteria.
And no, it's not absolute minimum weight.
IMO, the Plus layout is the definitive solution for minimum weight. Brilliant in fact, if that's important to the individual.

Quote:
Originally Posted by Luis Moya

All the best,
All the best to you, too

David
Sep 08, 2017, 11:19 PM
One Idiot is plenty...
Dbox's Avatar
David .
Beautiful plane !
LOVE planform ,proportions and dihedral smooth separation.
Simply perfect to my eye.
Subscribed to Your build.
Thank You for sharing.
Yuri
Sep 09, 2017, 03:14 AM
Everything's A Compromise
Larrikin's Avatar
Quote:
Originally Posted by Dbox
David .
Beautiful plane !
LOVE planform ,proportions and dihedral smooth separation.
Simply perfect to my eye.
Subscribed to Your build.
Thank You for sharing.
Yuri
Hi Yuri,
Thank you for following along.
But please don't think you can only watch.
Feel free to offer your experience too.
"It takes a village to raise a child"
Sep 25, 2017, 08:39 AM
Red Merle ALES VI
Curtis Suter's Avatar
Very nice David! I'm subscribed for sure.
Curtis
Montana
Sep 25, 2017, 04:21 PM
Registered User
Nice design David. Liked your video, well done. Looking forward to your spar system details. It looks like you are well up to speed with wing making techniques. The only thing I haven't seen on these big wings is the armored LE like GT and Phil Barnes do on there F3K models. If you are going to be wetting out a lot of carbon tow I recommend building a simple wetting machine like this one.
https://www.rcgroups.com/forums/show...etting-machine
Good luck with your build.
Rod
Sep 28, 2017, 07:21 AM
Everything's A Compromise
Larrikin's Avatar
Jeeeez ... I just typed up a huge reply/post and just as I was saving the text in the images, the site froze.
Some other time.
Thanks for your reply, Rod. I'd responded to you too.
Bed time.
D.
Sep 28, 2017, 02:51 PM
Registered User
Never mind Dave, I hate it when that happens. I'm very interested in the spar layup schedule you come up with. I haven't seen an analysis of the spar requirements for F5J using these thin airfoils. I too am keen on the classic spar system rather than stressed skin. My feeling is that I can keep the profiles more accurate with just one layer of carboweave on CNC cut cores.
Rod
Sep 28, 2017, 04:15 PM
Everything's A Compromise
Larrikin's Avatar
Quote:
Originally Posted by Wetafly
I too am keen on the classic spar system rather than stressed skin.
Rod
I've heard a rumour that the profile is only there to streamline the spar
I have no spar analysis to guide me because I'm no engineer but I'm relying heavily on my building experience.
I do however, have Gerald's bending moment graph to guide me though.
I've traditionally built DS spars too light. I hope I don't do the same here.

D.
Sep 28, 2017, 05:33 PM
Everything's A Compromise
Larrikin's Avatar

Bars N tubes


Ok, I'll try again.

Rod, I won't be wetting a lot of carbon tow, not enough to warrant a machine anyway.

Like Colin and Kevin of PROGLIDE fame, I'll be using as much off-the-shelf construction as possible. I've had elbow and shoulder surgery on my right side and it's not recovering as fast or as well as would be expected.
Perfect timing for a build (not a buy and install ) because it's a good distraction and chicken soup for the soul.

Speaking of off-the-shelf, I decided to use arrow shafts as the tip joining method. A 65/80 Carbon shaft (tube) for the joiner bar and suitable, tolerance fit, aluminium shaft for the receptacle.

I was almost sure that the 65/80 shaft would be strong enough, but I was only "almost".
So I found a suitable, tolerance fit, carbon tube to sleeve the inside of the 65/80 joiner bar.
For the peace of mind ... I'll carry the extra 4.3 grams.
Having said that, I'll trial the un-sleeved bars for the purpose of having a "weak-link". Should the model flip in a gust, the joiner snaps instead of damaging the wing.

The end-grain balsa caps are made from 70kg/m3, 9.5 mm (3/8") sheet.

For ease of construction, the spar web will be 9.5 mm, cut from the same sheet as the joiner receptacle caps.
The 9.5 mm will carry out passed the mid-panel servo bay then reduce to 6.?mm (1/4") passed the tip panel servo bay then 3.2 mm (1/8") to the tip.

I can hear the weight weenies gasping ... but think about it. If you look above my avatar, "Everything's a compromise" IMO.
The foam I'm using is ~ 37kg/m3. I'm cutting out a small section and replacing that SMALL section with 70kg/m3 vertical grain balsa.
Cap that balsa with a few carbon tows and SHAZAM ... stress free descents under full flap.

Anyhow, we're underway.

David
Last edited by Larrikin; Sep 28, 2017 at 05:39 PM.
Sep 29, 2017, 12:11 AM
Registered User
****
Sep 30, 2017, 07:57 PM
DLG Bug Bit Me
Tim Harbour's Avatar
Thank you for documenting this for us. I read all your threads with interest. I find the way you explain and video things easy to follow and learn from.
Keep it up.


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