Help with preparing for my son's glider contest!

[Nejiri]

Hi everyone. Apologies for the long post but I figured I would explain thing in as much detail as possible. I'm a Canadian living in Korea and I am hoping someone might have some ideas to help my son for his glider contest. He is eleven and recently participated in a school foam glider contest. He put something together using a simple plan available here in Korea and after spending time searching the internet together. Most of the kids who participated had a very similar design since there seems to be very little available here in Korea- they just did a variation of the few planes available in stores. My son got first place which he was really happy about but now he has to represent his school at a bigger city wide contest next month. I wonder if someone might be able to suggest a specific plan he could try and where we might shop for parts that will ship to Korea (the foam isn't a problem but other size motors etc don't seem to be available). He's hoping for something more complex than he made before but still something he can make within 3 hours. I have attached the simple plane (with small motor) he made and some of the contest details below. Any suggestions would be much appreciated.

Some contest details:
1. The gliders have to be made of foam and can be launched by hand, with a rubber band (no twisting of the band to turn a propeller- just pull back and launch) or using a small motor (they call it a "condenser" here- not sure if that's what it is called outside Korea). The gliders can't be remote controlled.
2. The contest "mission" will only be announced on the contest day. Scoring will involve 40% for the "mission" which might include the longest distance flight, the longest length of time in the air or having the glider turn as many times as possible within a certain radius. 60% is for the design itself.
3. Actual printed plans can't be brought with the glider materials to the contest (which seems ridiculous to me ...). It is possible that might not be the case at the bigger contest. He can, however, write out notes about dimensions for each piece and I guess the basic shapes in note form.

 

[ageorge]

That is pretty cool,I would love to study In a school like that.as far for tips maybe raise the elevators slightly so it flies upward and climbs and tilt one elevator higher than the other so it flies circles.You guys probably already knew this but that's the only thing I know to make it fly for longer.. good luck guys also it's not clear from the pic but maybe add under cambered airfoils if not present this way it will gain lift.as for shopping try banggood and search mini brushless motors.as for glider flite test have some free downloadable plans such as the simple soarer and mini sparrow.theese may need scaling down as or else they will require bigger motors.

 

[Craftydan]

Nejiri, welcome to the forum!

I don't have a better source for motors . . . If he's planning on keeping the weight/size in the same range, bigger won't be better. From his "win" I'd guess the plane design works well with that motor, so going bigger just adds weight and drains the cap faster.

If the rules allow it, I'd recommend eliminating the coin (if he can) and going with a bigger capacitor mounted where the coin is. Don't just go physically bigger, look for one with a higher uF rating with a lower voltage rating (10v to 16v should be fine, but don't go much higher). This turns his ballast into a larger fuel tank. Ideally, the new cap would weigh about the same as the coin, but with a MUCH larger capacity. That should keep his motor spinning at higher speeds for longer. If you have an electronic parts store around, that's a good place to look, since the weight of caps is seldom rated. Bring a scale with you.

Switching to a T-tail is not a bad idea - gets the h-stab aligned with the motor when it's running, and out of the wing's wake when it's not.

Otherwise . . . Build, build, build. If he has to build one at the contest within 3hrs, the more he builds them to plan, the less he'll need the plans, and the faster they'll go together (more time left to trim for the goal). Ideally, by the last few builds, he should be off the plans and using his measurement sheet. He may not win the higher level contest (they get progressively harder to win) but I assure you, the higher level winners will not win by luck or better parts. They'll win by disciplined practice. They may need better parts to beat out other disciplined competitors, but better parts cannot make up for practice.

 

[Nejiri]

That is pretty cool,I would love to study In a school like that.as far for tips maybe raise the elevators slightly so it flies upward and climbs and tilt one elevator higher than the other so it flies circles.You guys probably already knew this but that's the only thing I know to make it fly for longer.. good luck guys also it's not clear from the pic but maybe add under cambered airfoils if not present this way it will gain lift.as for shopping try banggood and search mini brushless motors.as for glider flite test have some free downloadable plans such as the simple soarer and mini sparrow.theese may need scaling down as or else they will require bigger motors.

Thanks! As we are both completely new to this, the tips on the elevator positions and trying an under cambered airfoil are useful.

 

[Nejiri]

Nejiri, welcome to the forum!

I don't have a better source for motors . . . If he's planning on keeping the weight/size in the same range, bigger won't be better. From his "win" I'd guess the plane design works well with that motor, so going bigger just adds weight and drains the cap faster.

If the rules allow it, I'd recommend eliminating the coin (if he can) and going with a bigger capacitor mounted where the coin is. Don't just go physically bigger, look for one with a higher uF rating with a lower voltage rating (10v to 16v should be fine, but don't go much higher). This turns his ballast into a larger fuel tank. Ideally, the new cap would weigh about the same as the coin, but with a MUCH larger capacity. That should keep his motor spinning at higher speeds for longer. If you have an electronic parts store around, that's a good place to look, since the weight of caps is seldom rated. Bring a scale with you.

Switching to a T-tail is not a bad idea - gets the h-stab aligned with the motor when it's running, and out of the wing's wake when it's not.

Otherwise . . . Build, build, build. If he has to build one at the contest within 3hrs, the more he builds them to plan, the less he'll need the plans, and the faster they'll go together (more time left to trim for the goal). Ideally, by the last few builds, he should be off the plans and using his measurement sheet. He may not win the higher level contest (they get progressively harder to win) but I assure you, the higher level winners will not win by luck or better parts. They'll win by disciplined practice. They may need better parts to beat out other disciplined competitors, but better parts cannot make up for practice.

Thanks Craftydan. Those are some great tips. The coin isn't required- we just stuck it on because the glider wasn't going anywhere. The capacitor he has is marked 2.7V and 3.3F. I don't know anything about capacitors- had to look up what the F rating was . So I would be looking for a higher F without the voltage getting too high? Thanks for the T-tail tip.

 

[Craftydan]

Nejiri,

I figured the coin was there for balance. it's a common solution for ballast, but some contests have weird rules about what must/must not go on the airframe. If they don't specify what you must use for ballast, then all the more reason to change out the ballast for something that works for you.

From the size, that cap is probably rated for 3.3uF -- 3.3 MicroFarads. Capacitors span over a wide range so they use SI unit abbreviation to show this -- It's easy to find them down into the nano- and pico-Farad ranges, which are 1,000 and 1,000,000 times less than microFarads. A 4.7nF cap may look like it holds more than a 3.3uF cap from the numbers, but looking at the unit, it's almost 1000 times smaller. On the positive side, capacitance and weight are related to each other -- getting a higher capacity cap with a about the same voltage level will almost always be heavier . . . which is your goal in the first place

The voltage rating is a specified property of the cap -- you can get 3.3uf caps in 2.7v or 16v or 120v or . . . you get the idea. The higher the voltage tolerance, the bigger the cap will be for the same Farad rating. If you can find them around 2.7v, so much the better, but in my experience, the higher voltage caps (10-16v) are easier to find. Just don't go below 2.7v or much more than 16v -- you're picking up weight from the extra voltage tolerance for no benefit to you. Replacing that coin with a larger cap, I'd expect it won't be hard to find something with 10 to 100 times that capacity.

One last warning -- when it comes to soldering the new cap in, these capacitors are polarized -- take care to keep the marked leads going to the same wires. reverse them and the cap will go off like a small firecracker. In practice, it's easiest to swap the connections one wire at a time to ensure same goes to same.

Keep playing with this, and you'll both start to see the little things that make it fly better . . . and worse . . .