Designs

[jander14indoor]

Since we have a dedicated board for WS now, I thought it might help to organize by kicking off topics around the typical WS questions. Content of string to be driven by subject line (I hope).

[blue cobra]

What are the pros and cons of a single dihedral point, two dihedral points, and tip plates?

[jander14indoor]

From a theoretical point of view, the effectiveness of dihedral is more the further towards the tip you are, leverage and all. So for most effect with least dihedral a eliptical dihedral is ideal. But darned hard to make for the added benefit.

Single break comes furthest from the ideal, but is certainly easy to make.

Double break is only slightly harder and approximates the eliptical form. I also find it easier to make because I have the flat center section to reference when I'm adding wing posts, adjusting wash or checking wing settings.

Tip plates are an extreme form of double break. They're also trying to minimize something called tip vortices. You can see tip vortices in photos of large jets taking off and landing through a cloud of steam or dust, but they are there all the time, and a major contributor to the drag caused by a wing. Many modern jets have tips jutting at odd angles just to control this. I'm not convinced they have much effect on tip vortices in our designs, but they are easy to make, and fly well. One caution though, you have to make sure you are dead accurate in building the tips to make sure you don't get a snow-plow effect greatly adding to the drag instead of improving it.

Jeff Anderson
Livonia, MI

[blue cobra]

Does anyone have this year's rules yet?

[danyalukin]

Technically, yes, a draft of the rules is available online, and its very close to the final one, im sure.

[danyalukin]

Back to the design discussion, what are pros and cons of an elliptical wing and stab, considering the 2010 rules where neither the stab (28cm span) nor the wing have a max chord? Would it be a good idea to have a big chord and an eliptical design on both, like in pennyplanes?

[gyourkoshaven]

I guess I'd put it in this thread. For a team with an average plane, would it be worth trying for a bonus?

[jander14indoor]

Elliptical wings.
Pros, theoretically more efficient (less drag and weight).

Cons, MUCH more difficult to build

Wing/tail chord.
MAX it! Wing area is good, more is better. There is a limit of course because as the aspect ratio goes down, drag goes up (thus elliptical wings become interesting), but its somewhere beyond 15 cm chord.

For all regional contests as there is no bonus, fly a big wing to win. Don't spend much time on a narrow wing until you know you are going to advance. But fly the big wing at the regional.
Last years bonus definitely wasn't worth it. I only saw one bonus plane come close to placing at state, and none at nationals. This years is slightly more generous, but only experimentation will tell if you can beat a really big wing with it.

Jeff Anderson
Livonia, MI

[carneyf1d]

Since im graduated and long gone, can you guys give me an update on the new 2010 rules for WS?

[blue cobra]

Technically, yes, a draft of the rules is available online, and its very close to the final one, im sure.

Where? I couldn't find them through google.

[gyourkoshaven]

The official rules are already out...

Changes: The plane can be constructed of carbon fiber and tape, along with the materials from last year (Wood, glue, etc.). New maximum horizontally projected stabilizer span is 28 cm. No maximum chord measurement for stabilizers. Only one propellor and one motor can be used per flight.

[blue cobra]

The official rules are already out...

Changes: The plane can be constructed of carbon fiber and tape, along with the materials from last year (Wood, glue, etc.). New maximum horizontally projected stabilizer span is 28 cm. No maximum chord measurement for stabilizers. Only one propellor and one motor can be used per flight.

Thanks!
Only one propeller and one motor? I didn't realize that was a problem last year, though that does sound like an interesting build...

[smartkid222]

carbon fiber? what would you use that for?

[jander14indoor]

carbon fiber? what would you use that for?

Stiffness. Can be useful, but not necessary. Example, a thin layer on top and bottom of a floppy motor stick will stiffen it up greatly. Adds weight, but can be compensated for.

Jeff Anderson
Livonia, MI

[smartkid222]

like the boron for f1ds?