Here are a few more videos from today’s flying session. We had a great time with a bunch of kids. I think we will have a larger group of kids for our next outing! I’ve offered to help the kids with repairs and any building so will be looking forward to that.
(2009-07-30)
It looks like Eduardo has made great progress. As I went through the pictures, I was going to suggest he find a bigger place to fly, and he did.
Paulownia is another wood that is light, almost as light as balsa. It is widely available in the Orient. A tree of wider distribution is cottonwood. The roots are soft and light, similar to balsa, but very porous. Unfortunately also somewhat brittle.
His first prop was not spinning very freely. Prop bearings can be made of metal tube or coiled wire. Ball point pens are a good source of metal and plastic tube. Metal washers can be used, or glass beads, or solid plastic from food cartons. Cardboard saturated with varnish or similar material will hold its shape better.
The prop shaft must make a slight angle to the wing, 3 to 5 degrees. I set the wing position by glide testing with the motor on, doubled over if possible, but no turns, and moving the wing until it makes a slow, steady descent. Usually that works, but the Squirrel zoomed and the wing had to be moved backwards.
My Squirrel weighed 5.9 grams and I estimated it would fly with a 20″ loop of 1/16″ rubber. I must have given the 20″ motor to one of the kids and not replaced it. I flew it with 1,600 turns on a 14″ motor and it did 1:02 in the Gym, after zooming and hitting the floor a couple times and having the wing moved back. It will do better after some tuning.
Gary Hinze
I would like to introduce my new friend Eduardo who lives in Brazil. He discovered the Squirrel through the internet and has taken interest in making one.
He downloaded the free instructions and went through the video instructions but the materials required were not available locally.
He’s quite resourceful and started to experiment with what he had.
Pictured at the left are some fruit trees which are in his neighborhood.
He used twigs from this tree in order to perform a few experiments.
Here are a few shots of his first experiments using the twigs, tissue paper and a propeller from a toy.
As you can see in the videos it is already looking promising. He also experimented with some foam and other materials. Based on the videos I sent him some suggestions. I figured that the wing needed to be moved back to get the balance right. You will notice that the plane noses up and drops at the end of the test. Also, there the propeller causes drag so needs to be wound up a bit for test flying.
He made a “Mini Squirrel” that was even smaller (pictured below).
I didn’t get any video of the Mini Squirrel but he sent me more of his experiments which included printed paper gliders and a commercial snap together toy.
I believe he used the material in from the snap together toy to make a Squirrel.After a lot of experimentation Eduardo found better materials and got his first great flights. I was pretty thrilled to recieve the email after he got some good flights!
“Thank you! You do not know how happy I was when I made it fly. All the neighbors out to see the Squirrel.”
Eduardo has figured it out and has a Squirrel that is flying well as you can see from the pictures and video collage below.
Brazil is an amazing place that I’d love to visit someday.
I’ve created an alternate design for the winglets that make it easy to carry your Squirrel with you in a small box. I call it the “Briefcase Squirrel”.
Here are a few details on how to make it and how it works. The winglets are attached by a small elastic band such as the ones women use for their hair (often found in dollar stores). It allows the winglet to spring up and down.
If you can’t easily find small elastics here is a way of making them:
Here are some shots of the prototype.
Here’s a neat plane Gary sent me:
“This is an AMA Cub reduced in proportion to a 100 mm propeller and made of foam. It is too heavy to fly in the living room, which was the design goal. Neither Lou nor Michael have been able to get theirs flying. I know why. It is way too heavy. Mine is a couple grams lighter than theirs and it barely fits when everything is just right, but circles downward. More power spirals in faster. Left aileron roll levels the wings and climbs, but hits the wall. It is also hair’s breadth sensitive on the controls.
It has been a bit windy for outdoor flights. I want to get the tailplane incidence sorted out. I have some ideas on that and outdoor testing might work if the air is calm. Usually you can’t tell the results of an adjustment outdoors because what it does might have been a result of uneven air, not the adjustment.”
I asked:
Why is it so heavy? What does it weigh? What about cutting circles in the wings and cover the holes with tissue? What about scraping the propeller? What about a smaller stick?
He replies:
Darcy: So if the Ikara Butterfly weighs less than 3g, and your Moth flies well at 2.595 grams, then assuming you have similar wing area on your Tiny Thom, I guess you need to loose like a gram.
Does that make sense?
How thick is that wing material? What if you cut triangles into it and covered with tissue triangles?
I wonder if there’s a way of getting a couple of 10ths off that motor stick.
Gary: Yes, losing a gram would help.
The wing is Depron foam that is 1.36 mm thick and weighs 6.97 gm/100 sqin. The foam in the Ikara Kolibri is 0.33 mm thick and weighs 3.65 gm/100 sqin. The tail is Durobatics foam that is 0.77 mm thick and weighs 2.35 gm/100 sqin, but is too flimsy for the wing. It is fuzzy on one side and soft, so it is hard to reliably measure its thickness. It is marginal on the tail. It works OK in the Moth because the moth has 8.3% camber that stiffens it. Kolibri foam would help, but would be used on the tail as well. There is another foam that is a little thicker that might be better in stiffness for this wing. The economies of the diecut process require that all surfaces be cut from the same sheet.
The intent of this design is that it be a quick clip together that a 10 year old can make in 5 minutes and then it will fly reliably in the house.
The motor stick could be thinner. The other guys are using 1/8″ square. (They call their plane “Wee Thomas”.) But that requires a nose block so the stick can fit in the prop bearing and there isn’t room for the tailplane taper.
I will be going over all the weights again tonight to see whether I can save enough to justify building another plane. I am thinking of a Moth with a 1/16″ x 1/8″ stick.
I just remembered, I can’t get the prop assembly any lighter. Or not by much, anyway. All the parts are off the shelf. I could scrape the prop a little, but that isn’t going to help much and we can’t expect kids to scrape a prop with a razor blade. That limits how much weight we can take off everything else. The wing is already jammed up against the prop hanger. Taking more weight off everything else will move the CG forward into dive location. It might be possible to take weight off the wing, add weight to the tail and have the whole thing lighter without moving the CG. That is a more complex calculation, might be worth doing. Then there is the problem that the production version is intended to use a heavy plastic wing clip, 1.1 gram itself, instead of the balsa stick and two dental rubber bands.
I think we have painted ourselves into a corner. I think we must start over.
