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Nov 19, 2019, 10:51 AM
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Discussion

Designing a simple, affordable F3res glider (openRES)


I was getting excited about F3res, when, unfortunately, I lost my old 2m spirit. searching for some free plans to this category couldn't find anything recent. given that I have some free time, but little money, I decided to make my one version.

I have tried to scratch build some smaller planes before, and I have a basic understanding of aerodynamics, but I don't have much experience so I hope to make this plane open source. Meaning all help is welcome, and at the end all plans and laser cut files would be posted here. Also any future improvements of this design should be share here.
I am designing using the resources posted in the F3RES resources threat, plus some old books on model design, but the general idea is to make a simple version using what is already successful. I am not aiming for a high performance glider, but something in between and old timer 2m glider and a modern F3RES.

Some design considerations
  • Budget of less than 100 dollars (including covering film and electronics) fingers cross.
  • Use standard accessible parts (should be possible to buy most component on banggod or similar)
  • Balsa is cheap where I live so I am going to favor balsa over carbon.
  • Portability is important so it should be a 3-piece wing. ideally with removable tail.
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Nov 19, 2019, 10:56 AM
Registered User
Thread OP
So far Iím thinking to go with AG35 in all balsa wing with d-box construction.
also aiming for a weight of 500g.
Nov 19, 2019, 01:10 PM
the kitty litter of rcgroups
rdwoebke's Avatar
I would start with the Allegro Lite plans as a starting point.

Ryan
Latest blog entry: Supergee wing mount pylons
Nov 19, 2019, 03:30 PM
Sagitta Fanboy
Yeah, pretty much build an Allegro lite with a balsa box fuselage and all-wood spar.

That's what an X-RES really is, and also the RaySER I'm building now.
Nov 19, 2019, 03:38 PM
the kitty litter of rcgroups
rdwoebke's Avatar
A person might be able to go with a cheaper arrow shaft boom too and do pod and boom. The Allegro boom is great and it is awesome at what it does but at ~$25 that is 1/4 of his budget. I wonder if there is some other less expensive option that might work OK given that the design parameters are not full pedal winch launching.


Ryan
Latest blog entry: Supergee wing mount pylons
Nov 19, 2019, 03:41 PM
Sagitta Fanboy
Quote:
Originally Posted by rdwoebke
A person might be able to go with a cheaper arrow shaft boom too and do pod and boom. The Allegro boom is great and it is awesome at what it does but at ~$25 that is 1/4 of his budget. I wonder if there is some other less expensive option that might work OK given that the design parameters are not full pedal winch launching.


Ryan
I think that a cheap boom is doable, but the balsa box fuselage will win on cost, as it's only a few dollars of balsa. Given the $100 limit the balsa box leaves more headroom for other stuff.
Nov 19, 2019, 04:42 PM
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Thread OP
I didnít mention the allegro lite because of the materials restrictions, but mostly because I am intimidated by drelaīs designs, they are so masterfully build that seems too far out of my capabilities as a builder.

Just looking at the allegro lite tiny nose, I know I will end up having to add another 30cm or so to balance the plane.

but yes I will have it as a main reference, thanks .
Nov 19, 2019, 05:56 PM
Registered User
The X-RES is all wood structure, both wing and fuselage. It is stiff and strong, and just happens to be the lightest of all the F3RES designs we have built here. The only serious carbon part is a all-flying tail mount, which could be dispensed with. In Europe, it remains a serious contender. Two of my teammates flew them at the recent F3RES International in Albuquerque.

There is a new crop of designs emerging in Europe this winter. Carbon tubes are finally being supplanted with built-up spare and steered, D-tube wings. Some serious lightness coming our way, gang.

Go for it, Leader!

Greg
Nov 19, 2019, 06:01 PM
the kitty litter of rcgroups
rdwoebke's Avatar
Iím m a complete hack and I built an Allegro. It has been one of my favorite planes since 2005. Anyone can do it.

Ryan
Latest blog entry: Supergee wing mount pylons
Nov 19, 2019, 10:24 PM
B for Bruce
BMatthews's Avatar
Quote:
Originally Posted by rdwoebke
A person might be able to go with a cheaper arrow shaft boom too and do pod and boom. The Allegro boom is great and it is awesome at what it does but at ~$25 that is 1/4 of his budget. I wonder if there is some other less expensive option that might work OK given that the design parameters are not full pedal winch launching.


Ryan
Having fallen prey to the idea of an arrow shaft and having it bite me I'm going to suggest a different option.

On a design I did some years ago I opted for an arrow shaft. But at high speeds the arrow shaft flexed and the model went into a tuck. The full flying stabilator didn't have enough control to pull out. I was lucky and had thermaled up very high when I opted to try a "speed run" with the new model. So I had enough time and altitude to push in full down to inverted and nose up a little with enough speed and rudder rolled back to upright. And I was by then flying slowly enough that the boom wasn't flexing downwards any more. I gingerly flew around at lower speeds until I landed and packed up for the day. I managed to modify it to work but that's another story.....

Now one thing that arrow shafts have going for them is that they are amazingly durable and relatively cheap. But what I'd suggest in order to avoid my near pitching disaster is to opt for two shafts bonded together into a figure "8" and fill in the center grooves with some lightweight filler or cover them with a balsa cover. Or simply buy some 1/2 or 5/8" diameter thin wall tube for the boom in the first place. Straight diameter thin wall tubing isn't all that expensive.

A set of Allegro Lite wings would not be a bad idea. Although you COULD get away with using the same wings but with a 10% reduction in the wing chord all along the span to aid with saving a bit of weight. And that sort of slight reduction would put you in the proper wing area compared to a lot of the other designs. But run the numbers on such a plan and see for yourself.

Keep in mind though that the secret of the airfoils on the Allegro Lite wings is the use of the extended upper side sheeting. You need to copy that for the airfoils to work as promised.
Nov 19, 2019, 11:01 PM
a.k.a. Bob Parks
bbbp's Avatar
Back in the days of the Lighthawk DLG they used a strand of carbon tow glued with epoxy along both sides of the tube from the end of the fuse to the tail. It really stiffened the carbon shaft.

BP
Nov 20, 2019, 01:55 AM
Registered User
mhodgson's Avatar
Quote "Keep in mind though that the secret of the airfoils on the Allegro Lite wings is the use of the extended upper side sheeting. You need to copy that for the airfoils to work as promised."

And yet many of the F3RES models use (successfully) AG 36-38 sections without sheeting or considerations of the facets on the top surface.

For the fuselage I would go for a balsa box type. You could even consider a triangular cross section boom- much to recomend for stiffness to weight .Simple, light and I would say stiffer than a carbon arrow shaft.
Nov 20, 2019, 05:15 AM
Registered User
Samba F3-RES V1 plans are available as JPEG, but pretty well done at 1:1 scale, so getting a vector drawing from that file would be easy.
Nov 20, 2019, 11:50 AM
Registered User
Thread OP
so far Iím planning on a very similar wing to the allegro lite, I just made minor simplifications on the geometry. Almost the same construction method, (thanks for the tip on the extended upper side sheeting, I was already thinking on shortening it).

For the fuselage I was thinking wood, but looking for arrow shafts I found some interesting tubes used in kites, by a brand called skyshark they sell nice quality tubes in different stiffness, even tapered ones for around 12 dollars. Luckily, unlike rc gliders, there is a community of kite builder in my country and I may be able to find one this tubes.
I am still thinking first an all wood fuselage would be a better option, but I may try both methods for comparison.
Nov 20, 2019, 12:55 PM
Registered User
It is tough to beat carbon tubes for light for the back 1/2 of a fuselage. Here is where I get mine: https://www.kitesandfunthings.com/De...bon-tubes.aspx

JDK


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