Designs

[jander14indoor]

I had to come up eventually. It does every year. Kits.
bluecobra, you are where we want everyone to get, BUT, it is NOT cheating in any way to use a kit. And its a very HARD place to start.

StampingKid and andrewski gave some of the very good reasons why some people use kits. If you are just getting started, or have real problems getting materials, it is a good way to get everything you need in one box.

Now, you might ask why kits are allowed, well, because the point of the event has little to do with designing or building a plane (though you won't succeed unless you can build one). And the rules are written to require a fairly high level of assembly competitence.

The point of Wright Stuff is test, evaluation, and optimization of a complex, non-linear system.
- Thus the logs.
- Design and build skills alone won't win Wright Stuff. I see lots of very good planes at tournaments that don't do well at all. Their logs are always poor.
- Without lots of practice and data, and a clear understanding of what the data is telling you, you can't succeed at this event!

Planes just happen to be such a system that is easily judged and within the doability of students.
- They teach good manual skills.
- They teach good planning (try to hit 7.0 gm exactly by chance).
- Allow some room for design (but frankly, 100+ years of competition with indoor rubber powered planes doesn't leave a lot of room for unknowns).
- Besides, planes are FUN!

Jeff Anderson
Livonia, MI

[eta150]

People use kits because everything is in the box. Everybody doesnot have a hobby store nearby much less a store with ultralight balsa, props and rubber. Buying balsa one place online and props at another and getting rubber elsewhere you can spend more in shipping than anything else. And just because it is a kit doesnot mean it will fly any less or better. You still have to test and adjust to maximize its potential. And there's more to building a kit plane than adding glue. Building a good kit will also teach you more than just how to join part a to part b.

Thank you
I've been at this for 4 years, and I almost always build my own designs
I occasionally use kits as a starting point, but only for the materials, the plans are always my own, and my final result is always individual.

[StampingKid]

Don't know whether this should be here or on airfoils but here it is:
I was googling around and came upon a patent application which proposed partial fences on the wingtips as increasing lift while reducing drag on gliders(vs. both no fence and closed fence). Of course, we are not dealing with gliders here but it seems to me to be an interesting question. I have not used fences in the past but with the big wings I had thought about it. Any thoughts?

[jander14indoor]

That concept is why some of the popular designs have tip fences. For full size planes it takes VERY difficult and detailed calculations to develop tip winglets to show much efficiency. For Wright Stuff, try it and see. One warning. It is disastrous if your tip plates are oriented anything other than parallel. Think of skies snowplowing. Tremendous unneeded drag.

Jeff Anderson
Livonia, MI

[smartkid222]

what is no fence vs. partial fence vs. closed fence?

[calgoddard]

I presume the reference to "fence" is an alternate term for - - tip plate - -. This is a surface that extends vertically from the tips of the main wing as a substitute for dihedral wing tip sections or some other form of dihedral configuration of the main wing such as a full V-dihedral or polyhedral. Your plane needs at least one of these, otherwise it will spiral into the ground. Some people describe tip plates as an extreme form of dihedral.

Normally tip plates extend along the full chord of the main wing and have varying degrees of height and taper. I think Jeff Anderson discussed tip plates this year on one of the Wright Stuff threads.

Some people also use tip plates on the ends of the horizontal stabilizer as a substitute for a conventional vertical stabilizer positioned centrally relative to the horizontal stabilizer, i.e. along the axis of the tail boom.

[StampingKid]

I received an email fro A2Z aka Peck Polymers for a snow sale (it snowed in Denver this week) with a note that you could download for free the Leading Edge plans. The link is

http://www.a2zcorp.us/freedownload/Lead ... nePlan.pdf

You may note on the plans the caveat about the tip plates consistent with Jander's warning to me--the plates must be glued on at exactly 90 degrees.

[jander14indoor]

Cool, and that's a BIG wing, I like it. I still don't think the bonus on the small wings at state or nationals will beat such a big wing, but its close enough that I'm not sure like last year. And that's what makes it a horse race.

Note, this plan uses a laser cut rib, DON'T let that stop you from building it. You can replicate this wing and stab with sliced ribs with only a little effort.

The 90 degrees in the drawing wasn't actually the one I was concerned about. I meant the angle between the tip plate and the spars must be 90 degrees so the tip plates themselves are parallel in the direction of flight. Not that the other angle isn't important too.

Jeff Anderson
Livonia, MI

[blue cobra]

Is a big wing always much better than a smaller wing? Smaller wings have less drag so they could be made more efficient.

[jander14indoor]

No simple answer. Has to do with lift vs drag ratio which has to do with angle of attack. A big wing has more area, can fly at a lower angle of attack for same 7.0 gm lift, so lower drag ratio. It can also fly slower, which lowers drag more. Balance can be calculated but that's beyond my expertise. AND assumes a lot of experimental data that may not exist for planes flying at our very low Reynold's numbers.

Drag also changes with aspect ratio. Fat short wings are draggier than long skinny wings. Again, where is the balance point. If area is equal, long skinny wing wins. If span limited like SO, you have to get real fat before the drag beats the added lift.

In general, large wings in this range will fly longer than small wings. What makes it interesting is the state and national bonus, can they make up for the loss in area.

Jeff Anderson
Livonia, MI