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Author Topic: New F3K DLG Build  (Read 442 times)
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egejce
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« on: August 20, 2020, 08:31:40 AM »

Hi,

I have decided to make my first F3K model. I know that will be hard to achieve the performance of the high end models that are on the market but I enjoy making models from scratch.

This will be the first time that I’m using the software XFRL5 for designing the plane.

The wings will be made out of XPS foam covered with glass fiber cloth, for the airfoil I decided to use Mark Drela AG-27. As spars I would probably use carbon fiber tube from a fishing rod, as well as for the fuselage.

I made some simulation with the XFRL5 and for now looks good.

Now I’m working on preparation for the foam cores cutting.
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Squirrelnet
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« Reply #1 on: August 20, 2020, 09:27:16 AM »

Nice choice Egejce . I shall be watching this one with interest
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piecost
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« Reply #2 on: August 20, 2020, 10:34:18 AM »

Egecce, I too would love to see details of your build.
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OZPAF
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« Reply #3 on: August 20, 2020, 09:46:23 PM »

I'm also interested to see how you build this Egejce.

John
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egejce
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« Reply #4 on: August 21, 2020, 06:37:59 AM »

I have made the preparation for the CNC cut (the equivalent of making the template for the ribs)

Now to find the time to set up the machine end make the cut. The airfoil is thin, I hope there will not be a lot of unsuccessful treys.

Thank you for showing interest in following my build. I must warn you my builds are usually slow (have two little kids that have a priority). Smiley

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Re: New F3K DLG Build
Re: New F3K DLG Build
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egejce
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« Reply #5 on: August 22, 2020, 12:35:17 PM »

Hi,

I was cutting the foam wing cores today. I found out that it's not that easy to cut thin airfoils, and including the groove for the spar it's impossible  Sad

So the idea of using carbon fiber tubes for the spars it's out. I will cut the wings and include vertical spar.

I manage to cut a good core from the third try, so I will go with them.
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Re: New F3K DLG Build
Re: New F3K DLG Build
Re: New F3K DLG Build
Re: New F3K DLG Build
Re: New F3K DLG Build
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piecost
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« Reply #6 on: August 22, 2020, 01:39:05 PM »

Looking good. Is that a CNC hotwire?

What foam are you using; what is its density?
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egejce
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« Reply #7 on: August 22, 2020, 01:49:46 PM »

Yes this a CNC hotwire that I build not long ago. I've made a post about it here https://www.hippocketaeronautics.com/hpa_forum/index.php?topic=25445.0

I used XPS from a local storage. Don't know it's density.
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OZPAF
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« Reply #8 on: August 22, 2020, 07:41:28 PM »

The foam  core looks nice Eg. Are you going to use a balsa TE? I have noticed that taking the foam to a knife edge adds a small amount of unwanted reflex to the airfoil at the TE especially when covering with glass.

As for the spar a shear web capped with carbon flanges will be stronger than a tube, with less weight - if not a little more work.

I'm also curious about the lines behind the airfoil TE on your screen shots. Are these to help the CNC machine to index?

John
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egejce
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« Reply #9 on: August 23, 2020, 04:41:45 AM »

I don't plan to use balsa as TE. When lamenting with fiberglass I plan to use the left foam from the cut as a mold. This way I thing the wing will keep the intended form.
For zeroing the CNC I have 4 micro limit switches that the CNC goes to before cutting.
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egejce
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« Reply #10 on: September 02, 2020, 03:50:09 PM »

Finally I covered the wing cores with some fiberglass and some carbon reinforcement.
I didn't use vacuum bagging, just pressed them in the foam that the cores ware cut off.
They are not strong to withstand loot of abuse, but I thing that for normal flying they will do OK.
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Re: New F3K DLG Build
Re: New F3K DLG Build
Re: New F3K DLG Build
Re: New F3K DLG Build
Re: New F3K DLG Build
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OZPAF
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« Reply #11 on: September 02, 2020, 08:55:41 PM »

Nice work. I have always believed that with low density EPS that pressing produces better results than vacuum, as it gives a uniform displacement under load unlike vacuum which can vary with local hardness.

If you make another set of wings - why not add a shear web between the top and bottom carbon caps. A light layer of cloth at +_ 45 deg will add alot of bending strength with little increase in weight.

John
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egejce
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« Reply #12 on: September 03, 2020, 04:14:11 AM »

Thanks John,

Your remark is OK. I was thinking of cutting the core and inserting a vertical piece of balsa with fiberglass between the top and bottom spar, but tat would take more time to prepare.
I'm trying to build this plane with as little effort as possible, this s my first DLG build and it's all about try to build one end try flying it.
Also I'm using materials that I have, last few planes that I have build ware with classical wings (balsa ribs, carbon spar and little fiberglass).
I plan to order some carbon fiber cloth and a vacuum bagging equipment for my next project. I'm not fully satisfied with this wings, I thing vacuum bagging will give little better results.

Vasil
 
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OZPAF
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« Reply #13 on: September 03, 2020, 05:34:17 AM »

Quote
I was thinking of cutting the core and inserting a vertical piece of balsa with fiberglass between the top and bottom spar, but tat would take mo
Using glass cloth is all that would be needed. q2-3 layers of 35g/m2 cloth on the bias would be sufficient. Apart from being stronger than the balsa - in some ways it is easier. The laid up cloth will not be much thicker than paper and will only need a knife cut in the foam. It does need a little more preparation - sanding in slots for the carbon caps but the end result is much stronger. We used it on winch launched 2m gliders, glass skins and carbon capped spars- although these were using ply webs but glass would have been better.

Quote
I thing vacuum bagging will give little better results.
  I have found that pressed wings using a custom press are much better for light EPS(desnsity 2lbs/ft3 and less) foam cores.

Good luck with your model.

John
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egejce
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« Reply #14 on: September 07, 2020, 02:32:39 AM »

I've manage to build the rudder and elevator this weekend ad did some little work on the fuselage.
I made them from light 3mm balsa, much simpler and nicer than foam core.
Now is time to start putting all together Smiley
I'm thinking of glassing the wing with one more layer of thin fiberglass, but lets weight all together and than I will decide. I want to stay around 300 grams if possible.
 
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Re: New F3K DLG Build
Re: New F3K DLG Build
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OZPAF
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« Reply #15 on: September 07, 2020, 03:56:22 AM »

What are you using for a fuselage? Does the nose cone come off for radio access?

Also what are you using for the hinges on the elevator and rudder? A good quality tape would be enough at this size and weight.

Nice clean work.

Good luck with it and thanks for putting up your CNC hot wire cutter info.

regards
John
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egejce
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« Reply #16 on: September 07, 2020, 07:39:51 AM »

Hi John,

I will make the rear end of the fuselage from a carbon fiber tube from a fishing rod. The wings will be bolted on front and of this tube. The front end I've placed reinforced balsa strip to mount servos, receivers and the battery and I plan to build the canopy around everything afterwards. Probably use balsa wood and fiberglass to reinforce it. I plan just to have an removable top for access to the electronics.
For a hinge I used Kevlar cloth that I have it at home. It's heavy but this is just an first try build, I have never used a Kevlar hinge before.
Now I'm waiting for the servos that I've ordered. I will use futaba s3114. I think they will be ok for this plane.

Regards,
Vasil
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OZPAF
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« Reply #17 on: September 07, 2020, 09:19:55 PM »

Vasil do a trial on some scrap with your kevlar first. Usually only very light kevlar is used and although i don't have any experience with it myself - it is also recommended(Mark Drela) that the threads cross the hinge line at an angle of at least 45 deg - not 90. If the kevlar is too stiff then either a good 25mm wide clear tape or a silcone ( outdoor quality for UV protection) will work. The silicone only needs to be very thin at the actual hinge line.

I have used tape on F3B glider ailerons - it was quite common in the 80's-90's and very reliable. I have also used it on the elevators of a small rc glider similar to yours.

John
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egejce
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« Reply #18 on: September 09, 2020, 02:39:07 AM »

Hi John,

I've catted the elevator and rudder and the Kevlar hinge is actually working wary well. Haven't cut the ailerons on the wing. 
Yesterday I put one more layer of thin fiberglass in the wings. Weighted them this morning, they are  about 45 grams heavier. Now they are about 180 grams but much stiffer.
Now I predict the whole model RTF will weight around 350 to 370 grams. I will try to find a lighter battery solution. I'v planed to use standard battery back size AAA that is 50 grams.
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Re: New F3K DLG Build
Re: New F3K DLG Build
Re: New F3K DLG Build
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OZPAF
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« Reply #19 on: September 09, 2020, 04:36:35 AM »

Quote
I will try to find a lighter battery solution.
. 200-300mah LiPo would be enough.

Have a look at the recommended equipment for this glider from Hyperflight

https://www.hyperflight.co.uk/products.asp?code=LONGSHOT-4&name=longshot-4-dlg-1-5m

John
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egejce
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« Reply #20 on: September 13, 2020, 11:25:37 PM »

Hi,

The plane is almost done. Now it's ready for the electronics, when they arrive.
And in the end to make the canopy. The 50 gram battery pack that I have is OK. If I use a lighter one I will probably need to add weight in the nose as ballast.



 
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Re: New F3K DLG Build
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OZPAF
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« Reply #21 on: September 14, 2020, 05:54:52 AM »

Well done.

John
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