building a glider

[quorneng]

Hello183
You are quite correct. Lighter weight for a given wing size will reduce the sink rate and also the flying speed. For an uncontrolled glider its flying speed is not too critical. If launched to any height it is almost certain to end up at a point down wind unless flown in a flat calm.
Once control is included the ability to be able to fly faster and not to sink too quickly can determine if you can get the plane back to its starting point.

 

[danskis]

quorneng brings up a good point. For ideal conditions, dead air, I mentioned thermals but he also brought in wind as a consideration. To stay aloft in a slight breeze its best to head straight into the wind. This requires some type of control. You might get longer flight times if you add rudder control to this glider even though it add weight. We'll see

As I mentioned before, wing loading is important. What you're doing is trying to minimize wing loading by reducing weight.

 

[hello183]

@danskis I don't have any radio equipment, but I think it would be a cool idea if I could find some other way to be able to guide the thing in the air. But if the wind hits it, doesn't the airplane have a natural tendency to turn towards the wind since it will pivot on the cg because there is more surface area on the tail than the nose?

 

[quorneng]

hello183
A plane in the air has no idea of wind direction. As far as it is concerned the air is stationary, it is simply flying through it. All the wind is doing is moving the air, and plane flying in it, in a down wind direction.
A gust, a short term change in wind direction, can effect a plane but it only lasts whilst the air speed is changing. In general gusts and turbulence are limited to a low level. Once above the highest local tall object (tree or building) the wind speed is pretty constant.
If you want to keep flying in a particular direction of your choice you will need some form of control.

 

[danskis]

Good question - as quorneng pointed out, the plane has no idea of wind direction. Thats a tough one to wrap your head around. But he also says "in a downwind direction". My experience says the plane sinks faster going downwind, with the nose pointed downwind. It believe it does stay up longer with the nose pointed into the wind, which requires a rudder.

You asked which way the nose will point, upwind or downwind if there is no rudder control. Well I'm not sure but I'll find out in a week when our local field opens up again and I'll let you know.

 

[hello183]

The top spar for the center section was just glued on. Maybe i will try to control the rudder of the airplane somehow. Don't control line airplanes get guided by strings like kites? Is there a way I could do something like that? Thanks for the information.

 

[Tench745]

The top spar for the center section was just glued on. Maybe i will try to control the rudder of the airplane somehow. Don't control line airplanes get guided by strings like kites? Is there a way I could do something like that? Thanks for the information.

Control-line planes have a pair of wires that run in at the wingtip, to a bellcrank in the fuselage, and then back to the elevator. These planes fly in a circle around the pilot. Both of the control lines need to be kept in tension to work. I'm not entirely sure how you would implement something like this for a glider, or if it would be particularly fun to fly if you did, but I'm curious to see what you figure out if you do decide to try it.

 

[Piotrsko]

Traditionally for free flight thermal hand launch, you build in a bit of left turn for north hemisphere, but that is for right handed throwers. It circles in a big turn, tightens up in a thermal but still ends up downwind

 

[danskis]

You can do that with a string but then it would be a kite - like the Wright brothers.

 

[hello183]

I don't really want it to be like a kite. Maybe I will try what @Piotrsko said. I can do that by adding trim tabs to the rudder, right, or bending the wings slightly?

I was thinking about another idea to strengthen the wing. I figured that placing trusses between the spars could also help resist the bending, but be lighter than shear webs. Those aren't glued on yet. Any suggestions about this?

 

[quorneng]

A truss like that is ultimately only as strong as the limited glue. A full shear web between the spars and ribs can be pretty thin sheet (grain vertical). It also has a rather bigger glue area, particularly if the web is glued to the face of the spars.

 

[hello183]

@quorneng Aren't most glues stronger than balsa? I believe I heard that someplace. I am using carpenters' glue and I think that glue is pretty strong. If the glue joint is stronger than the balsa, then does strengthening it anymore from there really matter? I haven't glued them in yet but they are all cut now and the wing feels very strong, at least for my application.

 

[hello183]

Wing panels almost done.

The glue joints are ugly, and some have slight gaps and things like that. I have heard that baking soda and superglue can fill that type of thing quite well, and I tried it and it seems to work. Does anybody know any better methods for filling this sort of thing? Also, is there any blade that is sharper than a standard x-acto blade that fits on one of those aluminum handles because I think mine is dull and I'd like to buy more.

 

[Tench745]

Wing panels almost done.
View attachment 228958
View attachment 228959
View attachment 228960
The glue joints are ugly, and some have slight gaps and things like that. I have heard that baking soda and superglue can fill that type of thing quite well, and I tried it and it seems to work. Does anybody know any better methods for filling this sort of thing? Also, is there any blade that is sharper than a standard x-acto blade that fits on one of those aluminum handles because I think mine is dull and I'd like to buy more.

I like standard straight razor blades; they're very thin and quite sharp but they don't fit in an x-acto handle.
So far as I know all x-acto blades are the same thickness. You can buy #11 x-acto style blades a number of places if you need replacements.

 

[hello183]

The wing is nearly done. It weighs about 21 grams. It looks like I was paying more attention to how I wanted the airplane to fly rather than how I wanted it to look. I'll learn for next time. I still have to build a new horizontal stabilizer, then it's just sanding.

 

[hello183]

I went to Walmart and the lightest tissue that I could find was not light enough. I think it is about 40 grams per square meter. The piece I got is about 457 cm long, 43.5 cm wide, and weighs 80 grams. It would be good for plan paper, but Japanese tissue weighs less than 10 g per square meter. We have saran wrap though. I might try to practice adhering that to some random structure and if it looks ok, maybe I will try it for this airplane.

 

[danskis]

@hello183 - is there an RC club in your area? If so, someone might have some leftover monocote iron on type covering they'd be willing to part with.

 

[CthulhuJon]

try here for tissue, they have a selection of light and well priced in-house tissue, 50c a sheet. plus the nice Japanese stuff (but more expensive) https://www.wind-it-up.com/pages/tissue
You could also try an art store rather than Walmart for tissue... something like Michaels or Blick.

btw did you know that you can re-sharpen your exacto blades. Most people throw them out, but you can get a little diamond / whetstone for ~$10 and re-sharpen then many times. You can even do it with fine sand-paper ( glue it to a hard flat surface). But replacement blades are also cheap if you just want to buy them.

 

[hello183]

Thanks for sending that website @CthulhuJon. I think I will buy from there. Also, @danskis, I don't have any flying club.

 

[hello183]

I used the 1/8 scraps from the fuselage to build the horizontal stabilizer today.