Peso del modello e quote di lancio

[moonwalkerfj]

Per chi si fosse perso questo post del guru Drela datata Agosto 2005:
"
markdrela
Registered User

Join Date: May 2001
Location: Cambridge, MA USA
Posts: 1,635


There is clearly an optimum weight for maximum launch height, and this must depend on the size/strength/weight of the thrower. I'm only 140 lbs, and so I can launch my 8 oz SG2 considerably heigher than my 12+ oz Blaster.

Here's a simple model of what's going on:

Assuming good technique, we can also reasonably assume that the thrower's muscles provide a fixed amount of energy (max muscle force x muscle motion distance), which isn't affected much by glider weight. The energy goes into all moving parts: glider, arm, torso. Assuming everything has the same rotational speed, the energy of any part is proportional to the square of its radius from the center of rotation.

Imagine launching a 30 oz DLG. Almost all the available energy will go into the glider, since its mass*radius^2 number is much bigger than everything else.

Now imagine launching a 15 oz DLG. Its mass*radius^2 still dominates, so it still gets most of the energy. But since it has half the mass of the 30 oz DLG, it will blast off sqrt(2) = 1.4x faster, and go almost twice as high. This is basically what the plot at www.pcm.at shows.

Now launch a 10oz DLG. Launch speed will increase, and the arm and torso will eat up more of the available energy. So the glider doesn't blast off quite as fast as it might be assumed at first (e.g. by the plot at www.pcm.at ). But the mass is less, so this smaller amount of energy will still make the 10oz glider go higher.


As the DLG gets lighter and lighter, most of the energy will eventually end up in the arm and torso, and the launch speed will no longer increase with decreasing glider mass. But air drag will continue to get more and more significant. So clearly there will be an optimum weight in there somewhere. For me it's probably less than 8 oz, since I can still "feel" that the 8 oz mass is significantly limiting my throw speed. For a really big guy, 8 oz might be closer to his optimum. Dunno."

In sostanza dice che il peso ideale del modello dipende dal lanciatore, strutture troppo leggere non pagano solo perchè diventano troppo flessibili e aumenta la resistenza, liu vola a 224g ma sente che per il suo fisico il modello è ancora troppo pesante....... Almeno così mi pare di avere capito.