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Homemade RC Glider

Old 05-11-2019, 08:51 AM
  #1  
aaindthu
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Default Homemade RC Glider

Hello,

I wanted to do slope soaring so badly and I have finally found a place in Chennai to do slope soaring, but the hill was too rugged and covered with thick vegetation. I had a motorless Flying wing glider and I was afraid I would lose the model somewhere among these bushes and I Never did slope soaring before. So I am going to build a motor glider. This time with some good quality materials and extra functions like spoilers etc. So I thought I'll start a build log (again), if that's okay.
Here's the basic sketch of the glider
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I have decided to start with wings. It's going to be 2 meter long and made of foam, supported by 4mm thick plywood spars.
I have done the frame work on the wings.
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The in-between spaces will be glued with High density foam and the space at the centre of the frame is for the fuselage.
The two short square-beams at the centre will be glued to the fuselage permanently and wings should slide in and out for easy transport. No rubber-bands this time.
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The frame weighs 240 grams without the square beams. Seems light enough to me, for a 2 meter wing. Or, should I be concerned?
Please tell me what you think.
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Old 05-11-2019, 09:21 PM
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quorneng
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aaindthu
The nearest 2m solid foam wing powered glider I have is an ST330.
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The wings including a pair of aileron servos and an aluminium joining tube weigh 340 g.
At 240 g for your basic structure I think your complete wing is likely to end up a bit heavier.
Extra weight for a slope soarer is not too much of a problem except more weight means it will fly that bit faster and will need more wind up the slope to keep aloft.
For faster flying your wing section does look to be on the thick side.
To give an example the wing of the ST 330 is 220 mm front to back and is 24 mm thick.

I will follow your blog with interest.
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Old 05-12-2019, 03:16 AM
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Quorneng,
That was valuable information, some number for reference-exactly what I wanted. Thank you very much.
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Old 05-13-2019, 03:27 AM
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The wings ended up being too heavy. I am going to replace the wooden beams with aluminium wire from cloth hanger and cut off half the length of the frame on each side of the wing.
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Old 05-13-2019, 08:39 AM
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Check plans available at, Aerofred.com and outerzone.com
You can download the PDF's for free for many, many model aircraft, including gliders with proven designs
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Old 05-13-2019, 01:49 PM
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Wildflyer,

Thanks for the links.
But, in a way, I think my design is also a proven design. Because, it is simple, conventional and
there are many similar gliders out there.
It's the same fuselage, wing and V-tail (also very conventional).
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Old 05-19-2019, 02:57 AM
  #7  
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The wings ended up weighing 400grams. But I got another idea to make it even lighter.
so I am going to build the wings for the third time.
This time without the plywood.
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Old 05-20-2019, 01:24 AM
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I have done a LOT of slope soaring. Weight is often not a big issue for slope gliders. All depends on the height of the hill and how strong the wind might be. I have seen slope gliders made out of solid maple wood.

I have taped a 16" spike onto my ZAGI foam slope wing for ballast.

EPP foam is popular for slope gliders as it is almost indestructible.

So, tell us about your hill, the height of the hill and typical wind speed.
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Old 05-20-2019, 06:22 AM
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AEAJR,
Hi,

The wind at my place is not strong at all. It's moderate breeze at maximum and at times it drops to zero wind for 5 seconds or so. The thick vegetation obstructs the wind speed further.

I don't know how to measure the height of the hill. But you can have a look at it in google maps 3d view. here's the link https://www.google.co.in/maps/place/12%C2%B057'19.4%22N+80%C2%B004'25.1%22E/@12.9630339,80.070029,203a,35y,142.87h,79.02t/data=!3m1!1e3!4m9!1m3!11m2!2sVaUz2PnZz8Utim3t-5qpy7FvTod16A!3e1!3m4!1s0x0:0x0!8m2!3d12.95538!4d8 0.073626?hl=en

Because the wind speed is gentle to moderate, I am trying to keep the weight as low as possible.
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Old 05-20-2019, 12:18 PM
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aaindthu
With that sort of location I think you are quite correct to keep the weight, and thus the flying speed, as low as you can, particularly as that type of "mound".hill will not produce the strongest lift for any given wind speed.
What is required for slope soaring is that when your glider is flying a bit faster than the wind speed going up the slope it is gliding at an angle a bit less than the angle of the slope.
To do this needs a suitable combination of flying speed and aerodynamic efficiency. The slower the wind speed and the more gentle the slope the harder it gets to find a workable combination.
Without previous experience simply do the best you can and have a go.

Just a point but have you ever seen anyone else flying gliders at that location?
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Old 05-20-2019, 04:21 PM
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Build it light but make a provision for adding ballast for those days when the wind is stronger and the lift is strong.
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Old 05-21-2019, 01:26 AM
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aaindthu
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Originally Posted by quorneng View Post
Just a point but have you ever seen anyone else flying gliders at that location?
No, I've never seen anyone else doing anything
At all at that location. Thank you very much.
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Old 05-21-2019, 03:16 PM
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Wings are almost done.
Servos are not yet installed. And then I will put some tape on it for strength.
As of now, the wing weighs only 212 grams. including the aluminium wires from cloth hanger.
I am expecting the total weight to come around 300 grams. Will post pics soon.
​​​​​
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Old 05-21-2019, 05:39 PM
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I look forward to some pictures.
If you really do achieve 300 g for a 2 m span wing it will indeed be pretty light.
I hope it proves strong enough to survive more than one flight! .
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Old 05-22-2019, 03:15 AM
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Originally Posted by AEAJR View Post
Build it light but make a provision for adding ballast for those days when the wind is stronger and the lift is strong.
Great idea. Also, I might add FPV stuff on to this glider. So I already thought about making room for a second battery which could also be used for ballast. Two birds with one stone??

​​​​​
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Old 05-22-2019, 05:30 AM
  #16  
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Now, mate, for your next design, use a better airfoil. That one in your pic is a very high-cambered very thick airfoil, which might be okay on very light wind days, but it won't have the wide speed range that's needed on the slope. You should build LIGHT but make provision to add plenty of ballast for penetration in better lift days. SD7084 is one of my favourites.
Go fer it!
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Old 05-22-2019, 06:05 AM
  #17  
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Here are the pictures of my almost complete wings.
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The aluminium wires fit perfectly into the Gel Pen refills / inners that I have glued
on top of the wings.
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Now I know this looks like a poor design and may fold easily. But I have another trick.
Here is a rough sketch of what I'm going to do to the fuselage where the wing will attach.
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I am going to glue some extra piece of foam to either sides of the fuselage where the wing root will touch the fuselage.
This extra piece of foam will have a large hole, in the exact shape of the wing cross section cut into it.
The wings will be made to go through this extra piece of foam before touching the fuselage.
This extra piece of foam should be able to restrict unwanted movement of the wings.

I know this setup is not on the better side of aerodynamics. I have read about "uniform cross sectional area rule".
The place of joining the wing and the fuselage should be preferably narrow to reduce drag.
But, it's a compromise that I'm making, between strength and better aerodynamic properties.
But, will it work as intended??
Please tell me what you think..

Last edited by aaindthu; 05-22-2019 at 07:38 AM.
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Old 05-22-2019, 06:13 AM
  #18  
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Originally Posted by Jools View Post
Now, mate, for your next design, use a better airfoil. That one in your pic is a very high-cambered very thick airfoil, which might be okay on very light wind days, but it won't have the wide speed range that's needed on the slope. You should build LIGHT but make provision to add plenty of ballast for penetration in better lift days. SD7084 is one of my favourites.
Go fer it!
Yes sir!! I did change my flat bottom airfoil to a semi symmetrical one. But it is just a hand drawn airfoil. I don't have a name for it.
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Old 05-22-2019, 10:41 AM
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Hi..... another home design - you have really got hooked into this !!

OK ... Slope Soaring - one of my favourite modes - but sadly where I live is not possible. We have some cliffs along the beachline - but the rise is near vertical and sharp 90 at top - making the lift envelope very narrow and deadly if misjudged.

Looking at your 'hill' - the first that strikes me - is the circular mound profile. This may seem to give you 360 coverage for any wind direction - but in fact may prove less than ideal. In light winds - the air flow is able to divide and most flow round the mound, with only a small part going up and over. As the wind increases - the 'up and over' increases but becomes more fanned out and can lead to side downdrafts.
The lift area of such topo is usually very narrow and limited.

Now we add in your description of the 'ground state' - too rugged and covered with thick vegetation. - The Rugged is not a problem for lift - but given your description of light winds - the vegetation may create low level turbulence.

I have attached a number of pages scanned out of a very good book on Soaring ... apologies to Author ... but it has relevance.

Note Fig 7 ... the round hill.

Motorised is going to be the answer here .... but beware of those dead areas ...
Attached Files
File Type: pdf
Slope hills.pdf (2.87 MB, 13 views)
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Old 05-22-2019, 11:44 AM
  #20  
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solentlife,

Thank you so much for the PDF.
They're really informative.
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Old 05-22-2019, 02:11 PM
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Here's a table to help ..

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Old 05-26-2019, 07:47 AM
  #22  
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The wings ended up being too heavy....
No. Just kidding. The wings weigh merely 292 grams !!
Here are some pics of the wings attached to the fuselage that is in its raw shape.
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fuselage looks short to me, so I am going to elongate the tail by glueing some extra foam and sand the whole thing into a perfect shape.

Last edited by aaindthu; 05-26-2019 at 10:25 AM.
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Old 06-05-2019, 02:38 PM
  #23  
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This is what the glider looks like now...

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Old 06-05-2019, 04:10 PM
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Those proportions certainly look reasonable.
T tails are popular in full size gliders (keeps the tail plane clear of long grass/crops when landing in a field) but can be a bit delicate in models as in a ground loop landing (a wing tip touches first) the rapid rotation it causes can damage the tail fin as well, particularly if the elevator servo is mounted at the top of the fin as well.
Will the motor. ESC and battery in the nose does it get the CofG something like right without having to add significant nose weight?
With no wing dihedral and almost full length ailerons it could be quite 'sensitive' in roll and could initiate a serious spiral dive if full aileron is applied when flying close to the stall speed.

Just a crude test but with every thing, including the battery, in place does the wing feel strong enough to allow it to be lifted just by its wing tips? If it can the wing should be adequately strong enough to do a loop without breaking.
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Old 06-06-2019, 12:02 AM
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Well, I know where the wing is going to break if / when it does.
(Plenty of aerodynamic elements we could discuss, but this is just a tip on the structure).
The wing will be dead rigid ending right at the end of those spars, then it'll be flexible (unless there's an internal spar we can't see).
What it means is structurally the greatest strain in a loop or rough landing will be concentrated right at the end of those spars because they're the same length. Not so good.
My tip with the next design: Use 3 spars, one long one near the 33% chord position at the thickest part of the wing, going maybe 1/5th to 1/4 the wing span. Another, shortish one towards the LE, then another towards the TE, splitting the difference in length. What it means is the forces won't be all concentrated at one point along the span, but staggered, spread along a longer section of the span.
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