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Trying to make my first unpowered glider

#1
Making my first two channel glider, need some feedback on my wing. The specs are as follows.

30" wingspan
4.25" chord
7:1 aspect ratio
Airfoil is .5" max thickness @ 1.25" back from leading edge
5" of undercambered wing tip on each side
~15° dihedral

Anybody got any idea on how this wing suited for gliding? I'm planning a 20" long fuselage with a CF tube boom.
 

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mayan

Well-known member
#2
That V shaped type of wing worked well for me when I used to build blasa wood gliders. Here is the build I followed maybe this can work with foam board based parts too. Although I think the angle might have been 45 degrees.

You can also use the FT Tiny Trainer fuselage as a reference because the sports wing of that model looks similar to the shape of your wing and is great as a glider too. Although I would personally recommend a wing more similar to the shape of the FT Simple Soarer because of the dehidril and polydehidril I feel that helps the plane stay straight and evens out faster. Correct me if I am wrong @Hai-Lee, @Arcfyre, @d8veh, and any one else... :)
 
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d8veh

Well-known member
#3
Making my first two channel glider, need some feedback on my wing. The specs are as follows.

30" wingspan
4.25" chord
7:1 aspect ratio
Airfoil is .5" max thickness @ 1.25" back from leading edge
5" of undercambered wing tip on each side
~15° dihedral

Anybody got any idea on how this wing suited for gliding? I'm planning a 20" long fuselage with a CF tube boom.
It'll fly, so go ahead. The only thing that looks a bit dodgy to me is the tips, though it might be just how it looks in the photo. It looks like the leading edge curves up at the tips, where it would be better straight or maybe even curving down a bit

You need about 2 deg incidence on the wing compared with the tail.
 
#4
Thanks for the help @mayan. Funny you mention the Tiny Trainer fuselage. I've been looking at it to get an idea of overall plane dimensions, just scaled down a bit.

It'll fly, so go ahead. The only thing that looks a bit dodgy to me is the tips, though it might be just how it looks in the photo. It looks like the leading edge curves up at the tips, where it would be better straight or maybe even curving down a bit

You need about 2 deg incidence on the wing compared with the tail.
I had the same thought about the wingtips after I made it. I removed the paper from the inside of the top of the wing so it would fold over smoother. The front edge of the tips is flaring up. I'll need to come up with a solution for that.

I've heard some people do -1° on tail and +1°-2° on the wings. Is there an difference between that and doing 0° on tail and +2°-3° on the wing?
 

d8veh

Well-known member
#5
I've heard some people do -1° on tail and +1°-2° on the wings. Is there an difference between that and doing 0° on tail and +2°-3° on the wing?
Yes it depends on the wing profile (the shape of a fore and aft section though it). For your one, 2 deg on the wing and zero on the tail will work.If you were building a competition glider, you'd need to be a bit more precise, but then you'd have to chuck what you've already done. You don't need to get too hung up on rules. They'e only guide-lines. Just about everything can be made to fly one way or another. It's just that different things have different flying characteristics. It's good fun to play with different parameters to see how they affect the flight.
 
#6
Yes it depends on the wing profile (the shape of a fore and aft section though it). For your one, 2 deg on the wing and zero on the tail will work.If you were building a competition glider, you'd need to be a bit more precise, but then you'd have to chuck what you've already done. You don't need to get too hung up on rules. They'e only guide-lines. Just about everything can be made to fly one way or another. It's just that different things have different flying characteristics. It's good fun to play with different parameters to see how they affect the flight.
Thank you for the info. I realize it's probably neurotic to care about 1° here and there when we're talking about an imprecise foam wing. I just love to learn and implement what I can.

I ended up taking a piece of tape and using it to camber the wing tips to the same camber as the main airfoil.
 
#7
I concur with what @d8veh said, it will fly. Your main focus should now be on keeping it light and making sure the longitudinal stability is adequate.

The latter basically involves 2 things:

- making sure hstab is large enough and far enough away from the wing. A rule of thumb for your design would be to make it about 22-25% of wing area and have at least two wing-chords gap between the wing and the hstab.

- getting the CoG right. With adequate hstab (as above) 1/4 of mean chord is a safe starting point, then if the glider seems sluggish to react to elevator you can start moving it backward in small increments. But be wary of it bringing too far back.

The issue with the wingtips is they will stall before the midsection does (tip-stall), that's why it's important to get stability right, otherwise you are likely to be surprised by some pretty nasty stalling behavior egg. if you overcontrol in response to unstable flight (whioch happens if the plane is tail-heavy).
 
#8
I concur with what @d8veh said, it will fly. Your main focus should now be on keeping it light and making sure the longitudinal stability is adequate.

The latter basically involves 2 things:

- making sure hstab is large enough and far enough away from the wing. A rule of thumb for your design would be to make it about 22-25% of wing area and have at least two wing-chords gap between the wing and the hstab.

- getting the CoG right. With adequate hstab (as above) 1/4 of mean chord is a safe starting point, then if the glider seems sluggish to react to elevator you can start moving it backward in small increments. But be wary of it bringing too far back.

The issue with the wingtips is they will stall before the midsection does (tip-stall), that's why it's important to get stability right, otherwise you are likely to be surprised by some pretty nasty stalling behavior egg. if you overcontrol in response to unstable flight (whioch happens if the plane is tail-heavy).
Thank you for the info. I had heard about the 22%-25% of the wing area. My hstab is currently 24% of the wing area. My plan was to start about an inch back from the LE for the first COG test, which comes out to just under 1/4 mean chord. I'm having the wing mounts/tail feather mount printed right now.
 
#13
I’d love to see a video of it flying :)
You and me both! Money is tight right now, trying to save up for me and my fiance to move. So it will be a minute while I save for the electronics.

Thanks! It's my first scratch build; I'm pretty happy with how it turned out.

Nice progress. How about a mk 2 version of the wing supports with the cross-piece set into the wing to reduce drag?
Is MK2 a model that I should use for reference? Or are you saying MK2 as in version 2?
 
#15
Well, I got it squared up today and started messing with the nose weight. With the CG 1/3 of the wing back, it would nosedive, so I tried with the CG 1/2 of the wing back, and it flared up a little bit then nosedived, taking my tail feathers off. Gotta reglue and try again.
 

d8veh

Well-known member
#16
Stick with the G-spot 1/3 of the wing chord. I'd adjust the glide with the tail angle o!r wing incidence, which are basically the same thing. For fine adjustment, you can cut some elevator tabss into the tail.