Scratch glider build

[Reed Goodwin]

Well, it's not necessarily rocket-boosted (not planned for....... yet) but out of boredom last week I decided to make something. Being in my school apartment, I only had a bunch of popsicle sticks and some wood glue, so my options were pretty limited. Then I remembered a project that we were told about but never assigned for my aircraft controls class: building a balsa glider. Well, I decided to skip the balsa and make one from popsicle sticks.

After some planning I decided to go for a large main wing using a NACA 4412 airfoil and a small horizontal tail in the back using a NACA 4412 but with half the chord of the main wing. I pretty much skipped most of the stability calculations as that's a bit too much work to put into it, so I will be playing with the tail angle before finally fixing it's position. The only calculation I did do was to calculate trim speeds so I could figure out about how much incidence I needed in the main wing.

To save weight, I decided to make the airfoil shape using several popsicle sticks carved to the right shape and then skinned with paper. I cut notches in the bottom of the wooden airfoil ribs to fit a span-wise support. I kept to the general size requirements for the original project, making the wingspan 11" and the tip to tail length a little over a foot long. So this is the build...

Here is the main support running front to back that will hold the wing and tail:

To get the airfoil shapes, I copied the drawing from one of my aerodynamics textbooks and then glued the drawings onto the popsicle sticks:

I then started the tedious process of carving out the general shape and then sanding it down to the precise size. This is one of the airfoils for the main wing, with the two notches cut in it for the span-wise supports:

I repeated this for all 12 main wing airfoils and six tail airfoils (these were a pain) until I had a nice little pile:

I then constructed the span-wise supports for the main wing, bringing my parts pile up to this:

At this point I did a dry-fit to see how it was all gonna look and to be sure everything fit. Not all the joints are a perfect fit, but the popsicle sticks themselves aren't perfect, so it all works out. Here is the main wing:

And here is the tail dry-fitted:

Today I started gluing the airfoils to the supports. Having limited tools, I resorted to using my graph paper to help me square things up:

The large popsicle stick coming off the tail is how the tail will be attached and adjusted to the rest of the glider. It fits between the two popsicle sticks in the main tip-to-tail support and so can be slid and rotated as necessary.

After I glue each airfoil on, I go back and add wood glue fillets to the joint to help strengthen it:

This is where I am currently at, gluing the airfoils on. My next task will be to cut the notches in the main support for the main wing. Then it will be time to skin the wing and tail with paper. Once that is done, I just need to attach the main wing and then to some testing to find the right position for the tail

So far it is looking like this glider will end up weighing in around 30 grams, far less than I originally expected. Based off this weight, it seems that even with a level wing, I would only need about 15 feet per second speed to trim. I'm looking forward to testing this puppy out. My only fear is that I'm gonna need to slap a vertical tail of some sort on it: something I hadn't planned on but can pretty easily add.

Questions and comments are quite welcome.
Reed

 

[Reed Goodwin]

Does anyone have any thoughts on the need or lack thereof for a vertical tail? I'm not gonna have a movable rudder, so I wonder about the effectiveness if I were to add it.

Anyhow, I've been gluing stuff like a madman. I finally have all the ribs glued on the wing so now I need to start thinking about skinning it:

I also skinned the horizontal tail. I began by applying glue to the bottom (flat) surface of the airfoils and then laying it onto a sheet of typing paper to approximately the right size:

Once the glue dried, I applied glue to the top surfaces of the airfoils and then pulled the paper over it. I left about an inch of excess paper so I could apply tension and get the skin tight. Once the glue dried, I cur the excess off:

I then repeated this process for the other half of the tail:

Reed

 

[judo]

Ooh, I love a good masochistic project.

 

[JRThro]

Does anyone have any thoughts on the need or lack thereof for a vertical tail? I'm not gonna have a movable rudder, so I wonder about the effectiveness if I were to add it.

That looks like a cool project, Reed.

If you don't add a vertical tail, how will you get the stability that a vertical tail provides?

 

[Reed Goodwin]

Yeah, that's what I was thinking as well. I guess I was thinking about the rudder contributions to stability as that's what we discussed most in my stability class last semester. Yeah, I should know this kind of stuff now... haha
Reed

 

[Reed Goodwin]

Alright, time to update. I have been avoiding classwork and spending time on this instead. I finally got around to skinning the wing. I used the same method as I used for the tail. Here is half of the wing skinned:

I then skinned the other half of the wing:

My original intention was to mount the wing on the bottom of the fuselage, however after thinking about it, I realized that the wing would get damaged much more if it were on the bottom. I then decided to mount it to the top of the fuselage, protecting it some, and giving a small improvement in roll stability. By moving it to the top, I needed to find a more secure way of mounting it to the fuselage. I started by gluing some tabs in the fuselage where the wing mounts:

I then set about gluing the wing to the fuselage, primarily using the slots cut in the fuselage to begin with. Here you can see how it mounts to the fuselage (the nose is to the right):

Then I cut some more popsicle sticks in the rough shape of the airfoil to put between the tabs and the wing airfoils. I then slathered glue everywhere, filling the gaps:

All I have left for wing strengthening are some fillets on the underside joint. Then it will be time for some preliminary flight testing once everything dries up.

At this point I think it is very likely that I will be adding a vertical tail, but we will see...
Reed

 

[mjennings]

We did 6 foot wingspan gliders for my intro to aero course, your best friend on these is a belt or disc sander, nice work!
The Seniors in Aerodynamics with the same professor had to design their own airfoils by using sources and sinks in the free stream equations.

 

[Reed Goodwin]

Well, I test flew this guy to see roughly how it behaved. In short, it behaved badly, haha. I realized the other night that I goofed up my Cl calculations and had been assuming unit wingspan, even though I was working with an 11" span. So that meant my trim speed went up to about 20fps again. I think that speed might be a little high for a hand-thrown glider.

When I flew it, there was an obvious lack of stability, especially when it slowed down as it would just begin to tumble. I was able to get it to have fairly level flight immediately after coming off my hand, but it was tough to get consistent results. The other problem that I had thought might pop up was the durability of the wings. Even when it landed in grass and not on the asphalt, it dinged the wing up pretty good. The lack of a rigid leading edge and the fragility of the trailing edge ribs, caused some damage.

Anyhow, while it was entertaining to build, I think a little more work would be necessary to get a successful flight. It was fun to build, though. Now it's time to try to learn to fly this RC plane I have...
Reed