Wright Stuff 2019 - Designs

[DarthBuilder]

Any idea where I can buy some?

I know that Zeigler at Freedom Flight Models sells them for 5 dollars a roll.

how does mylar compare to cling wrap or a plastic bag? do the advantages lie in the weight, durability, etc?

I think weight but I am not positive on that. Someone will have a better answer

[bjt4888]

Kathryn,

Freedom Flight and Indoor Model Specialties (and other suppliers) sell Ultrafilm. This covering material is technically not Mylar (I believe that this is a DuPont trademark) but is the same material, polyester plastic film. It weighs 142 mg per 100 sq in.

If you want to compare, weigh a small piece of what you are using now.

Brian T

[bjt4888]

Kathryn,

If you are new to the event, you will advance your knowledge considerably if you take the time to read the 2015 Wright Stuff wiki threads. There is a considerable amount of very specific info supplied in the 2015 threads from experienced coaches and students (including some thoughts on covering material and methods).

Brian T
AMA Member since 1968; SO & Physics Olympiad Coach since 2009

[bjt4888]

Kathryn,

A little more info on covering materials. It took a little time for me to find my notes on veggie bag plastic. Very light veggie bags (Kroger bags used to be the lightest; not sure about current bags; you’ll have to test them) weigh about .35 grams per 100 square inches.

There are several benefits of using lightweight covering material (remember that we’re only talking about saving .2 grams covering with ultra film vs. best veggie bags): allows more weight to be put into the structure vs. covering, potentially removes weight from the extremities resulting in anicer flying airplane (recovers from bad air or ceiling hits slightly better), if weight is not put into the structure allows for more ballast which can be moved around to experiment with CG location. Ultrafiltration is plenty strong enough and resists picture fine for SO airplanes. This covering, although the lightest that SO airplanes need to consider, is the heaviest true indoor airplane covering. True international class indoor airplanes us a plastic film that weighs only .05 grams per 100 square inches (fragile and not recommended for SO).

My teams airplanes have been constructing to about 6.8 grams, allowing 1.2 grams of ballast that is moved around to test CG and decalage variations.

Good luck with your airplane.

Brian T

[bjt4888]

Ultrafilm not “ultrafiltration”. Bad spell correct by the wiki.

[calgoddard]

Ikara props are relatively expensive. In my experience, their plastic film blades often detach from their injection molded plastic spars. The blades on the same Ikara prop are often unequally pitched. The P/D ratio of an Ikara prop is too low for optimum indoor performance. It is very difficult to accurately re-pitch an Ikara prop. Most Ikara props are dynamically imbalanced, i.e. one blade and spar combination weighs more than the other. In addition, the thickness of the plastic film blades of an Ikara prop may not be uniform so the blades do not flare equally under high torque when all the blade area behind the spars is cut away. Further complicating matters, the area of the blades of an Ikara prop may not be equal. Finally, an Ikara prop weighs substantially more than a homemade balsa wood prop of similar size yet the additional weight of the Ikara prop provides no significant increase in durability. See my first post in this topic for the basics of how to make a cheaper and better Wright Stuff prop.

[jander14indoor]

I'm going to take a contrary position on covering for Wright Stuff Planes.
Yes, you can save a couple of tenths of a gram using ultrafilm over the lightest available grocery bag coverings, but availability may be an issue for some teams. On an 8 gm airplane budget, I don't think that's critical if you have any issues getting indoor coverings, and not something for teams to obsess over. You can make a perfectly competitive plane with available bags. Besides produce bags, look into dry cleaner bags, frankly I find Home Depot bags to be acceptable weights.

I'd also argue that 1.6 gm of ballast is more than needed to adjust balance. With the difficulty of getting stiff motor sticks, I suggest more of that go to structure. I tend to coach teams to aim more towards 0.5 gm ballast.

My preferences anyway.

Jeff Anderson
Livonia, MI