RE: Re: Coconut mass launch?

From: <dweigt47_at_gmail.com>
Date: 30 Jul 2016 09:26:35 -0700

I realize flight stability is a complicated subject. I've had some misadventures. I scratch built a lot of models of my own design when a teenager. Many sported low amounts of dihedral. One of my early rudder only planes that flew well developed spiral instability when I moved the CG forward and increased the decalage. It suddenly developed the tendency to go from level flight into tightening spirals in either direction. I didn't understand that until years later. Moving the CG forward increased the effectiveness of the vertical tail, keeping the nose pointed closer to the relative wind, reducing the dihedral effect....

Some years later, I had the privilege of hearing Carl Goldberg speak at my RC club a long time ago. Carl showed us a simple balsa glider. With no vertical tail, it flew fine. With a bit of weight added on one wing, it crabbed, but still flew fine. Carl added a bit of vertical stabilizer, and it spiraled in toward the heavier wing. What amazed me about the demonstration was that it flew straight with the unbalanced wing, as long as there was very little vertical area behind the CG.

Hinge the rudder to let it align with the airflow and reduce the effective vertical tail area is something I wouldn't have thought to try on a model. I know some full size planes have minimal yaw stability if their rudders aren't controlled: their vertical stabilizer area is marginal. Until recently, Quad Cities Challengers were like that. Newer ones have larger vertical tails, and probably aren't.

Don Weigt
Received on Sat Jul 30 2016 - 09:26:35 CEST