Elastic Launched Glider C

himlynx
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Re: Elastic Launched Glider C

Postby himlynx » September 23rd, 2012, 8:51 pm

this year's rules limit the wingspan to 30 cm. There is no fuselage or chord limit. There is a 10g max wt and the nose has to be larger than 13.7 mm. Lots more rules.
My thought is that a multi wing model would not survive the launch. Also it will weigh a lot more and weight is a killer for this event.

Thanks. I can't find the rules at the national or state websites. Could you post the link ?
A limit of 10 g on the weight will preclude very large wings or fuselages.
Biplanes are more rigid than monoplanes. With bracing, they will withstand launch forces better than monoplanes.
What matters for endurance is the wing loading ie weight divided by wing area, not the weight per se.

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Re: Elastic Launched Glider C

Postby chia » September 23rd, 2012, 9:57 pm

Thanks. I can't find the rules at the national or state websites. Could you post the link ?
Only trial rules are ever posted anywhere online - the official rules can't be for copyright reasons. You'll have to buy a copy of the rules manual or ask a coach to see them.

Seems that even though the rules allow for mylar wings, just the balsa edges + ribs won't be enough to withstand the force of launch, unless they're really sturdily built... so far my attempts at solid balsa wings have been less than stellar :T oh well, I need new wood anyways.
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Re: Elastic Launched Glider C

Postby jander14indoor » September 24th, 2012, 11:38 am

I have read the old rules to which a link was given in the Helicopter - Future Aviation Events forum. I gather that the length and wingspan are both limited to 30 cm. Further, in the AMA website there was a reference to the wing chord being limited to 3 inches. Now I have two questions for the rule makers:
1. Are biplanes and triplanes allowed ?
2. Will Science Olympiad have a limit of 3 inches for the chord ?

The usual caveat, NOTHING HERE IS OFFICIAL, opinions (however educated or from whatever source) are only opinions. If you want clarifications to the official rules, submit them to the official site.

AMA rules have come up in the past since the flying events LOOK a lot like AMA competition. THEY AREN'T. The only rules for SO events are in the books or on the NSO website. However much we use our knowledge of AMA rules (that's where a lot of us came from, and is a way to enjoy this sport beyond our SO years) to develop SO rules, NO AMA practice or rule, however common, is binding on SO events.

Example, some long time AMA flyers got indignant about students managing rubber torque in Wright Stuff with something known as torque burners to significantly extend their flight time. Not allowed by the AMA rules they were used to. Well, it wasn't in the SO rules, so it WAS legal, in SO competition. In fact, it was the way to win if you were in a low ceiling site. Out of the box thinking is intentionally allowed/encouraged by SO rule writers.

Another example, AMA gliders do not allow folding wings. Nothing in the SO rules on that. Hmm, could that be intentional?

Biplanes/triplanes. Do the SO rules explicitly state monoplane? Rule out multiple wings? If not, the general rule is "If it aint forbidden (unless unsafe) its allowed."

Note again comment opinion vs official above.
<SNIP>Seems that even though the rules allow for mylar wings, just the balsa edges + ribs won't be enough to withstand the force of launch, unless they're really sturdily built... so far my attempts at solid balsa wings have been less than stellar :T oh well, I need new wood anyways.
Um, again opinion, but where in the rules does it say you need to use balsa for the spars? If you look around on the web, you'll find a 3.2 gm Penny Plane made with carbon fiber spars. It flew very well. I don't KNOW that will work for glider level forces, but Penny Planes have a larger span than these things, so...

OH, and keep in mind a glider that works well for a tall site MAY be very different than one that works at a low site. At least they are in AMA competiton. And while the rules don't apply, physics is physics. You'll learn a LOT from their experience.

Jeff Anderson
Livonia, MI

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Re: Elastic Launched Glider C

Postby chalker7 » September 24th, 2012, 3:24 pm

Everyone should listen to what Jeff says above, he's a smart cookie who knows what he's talking about.
The one thing I'd suggest though is to stick to solid balsa (perhaps with some carbon reinforcements if you're feeling adventurous) wings for the first few iterations of your designs. The covering on built up frames (be it mylar, tissue or otherwise) induces a large amount of drag, especially on launch. This can be overcome (in particular with some of the strategies Jeff hints at) but before you reach that point you'll have quite a few gliders either explode in your hand from the extreme launch forces or only get halfway to the ceiling. In either case, it's probably better to figure out the general aerodynamics of these things before moving on to the more advanced techniques and getting frustrated by skipping steps.
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Re: Elastic Launched Glider C

Postby Rowerguy508 » September 24th, 2012, 6:44 pm

I've found that the wider the circle the longer the flight and the better the score.

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Re: Elastic Launched Glider C

Postby twototwenty » September 25th, 2012, 7:52 am

Hmm, that is actually an interesting point...for that to be true, it would have to mean the glider would drop approximately the same amount in one circle, and thus a larger circle would cause the glider to drop slower. Alternatively, a glider could have a constant drop rate, and the size of the circle would make no difference. Personally, I don't know the answer and would like to. Does anyone who knows a lot about this event (Mr. Anderson?) know for sure?

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Re: Elastic Launched Glider C

Postby fleet130 » September 25th, 2012, 8:58 am

The following simple analysis ignores many factors that could influence the outcome, but I suspect it is generally valid:

An object in motion continues to move in the same direction unless acted upon by some force. Greater variation from a straight path requires a greater force. A glider also requires force (acting against gravity)to to stay aloft. Energy is used to produce these forces. The amount of energy available (transferred from the elastic during launch) to a glider is finite. If more energy is used to produce a tighter circle, there will be less available to keep it aloft, which will result in a shorter flight time.
Information expressed here is solely the opinion of the author. Any similarity to that of the management or any official instrument is purely coincidental! Doing Science Olympiad since 1987!

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Re: Elastic Launched Glider C

Postby fanjiatian » September 25th, 2012, 11:44 am

I believe that I read somewhere that said if the nose moment was too long and not enough mass, the glider wont transition properly. Is that what you are talking about, piisamazing?

I cant find where I read that from.. and I still havent flown a glider in a gym yet nor have i gotten any of my gliders to transition from an upward toss in my living room :(

I dont understand why too long of a nose moment would affect transition, as long as the cg was correct :? >.<
I built a Simple Simon that wouldn't transition but did once I added bit of weight to the nose. I think my CG was too far back.
Unfortunately, the plane broke after crashing into a table :(

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Re: Elastic Launched Glider C

Postby twototwenty » September 25th, 2012, 12:16 pm

The following simple analysis ignores many factors that could influence the outcome, but I suspect it is generally valid:

An object in motion continues to move in the same direction unless acted upon by some force. Greater variation from a straight path requires a greater force. A glider also requires force (acting against gravity)to to stay aloft. Energy is used to produce these forces. The amount of energy available (transferred from the elastic during launch) to a glider is finite. If more energy is used to produce a tighter circle, there will be less available to keep it aloft, which will result in a shorter flight time.
That's an interesting way of looking at it, but it does make sense. Thanks!

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Re: Elastic Launched Glider C

Postby jander14indoor » September 25th, 2012, 12:57 pm

Wow, way to much credit for knowledge pushed my way. I know some things from experience, not everything by far. Possibly due to training and inclination as an engineer I can see lots of alternative things to look at. BUT, I DON'T know the answer to many of the questions or suggestions I pose!!

One of the reason we vary from AMA rules is because for the most part solutions are well known. We throw in oddities to see what comes out! The other rules writers, chalker7 and others, have guesses and debates, but we don't KNOW. What we do know is when you let thousands of bright students compete and try things you get wonderful results. Look at the chinook helicopter results last year!!

Note, chalker7 knows AT LEAST as much as I do about this stuff, he's equally worth listening too.

Of course, that's not to say I don't have an opinion on where to go!

Turn size vs time. Fleet130's explantion is dead on. It takes energy to fly. Gliders DON'T fall, they fly. They are NOT parachutes or rocks. The only energy comes from the potential energy of their height above ground. Its a fixed amount once you launch your glider. It takes energy to turn, tighter turns take MORE energy (larger force component horizontally perpendicular to flight path). That takes away form that limited intial energy, you HAVE to descend faster.

Side comment on energy available. Its actually dependant on two things, formula is E=mgh. m is mass, g is gravity constant, h is height h is limited by the ceiling you are flying under, about the only thing you can do is make sure you transition to flight as close to that ceiling as you can. You'll note that more mass will give more energy (as well as height). Problem is, it also takes more energy to creat the lift to offset that mass. I'll leave it as an exercise to the students (in other words I'm feeling lazy and don't know the answer off the top of my head (though I suspect I know what it is)) whether it is in theory or practice worth it.

Another off topic comment on energy and flight. Fighter pilots talk almost purely about energy when they discuss dogfighting. Everything they do is to manage their energy. He who keeps the most energy generally wins. This lets them talk equally about turning or climbing, or whatever.

Jeff Anderson
Livonia, MI


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