Re: Re: Possibly interesting balsa test

From: Bill Gowen <b.gowen_at_earthlink.net>
Date: Fri, 30 Jun 2006 13:42:33 -0400

Dave
Balsa test:
I'm going to plead ignorance on this one. I find it more interesting to whittle on sticks than to re-learn all the math I've thankfully forgotten. The test was pretty easy to set up if you want to pursue it further.

Glider turn question:
Tapio pointed out that a likely reason that tilting the stab works is that you are changing the lift vector of the stab and pointing the lift vector to the outside of the turn. Kurt convinced me awhile back that the best way to turn an indoor glider was with the rudder. The reason that stab tilt doesn't work very well on indoor gliders is that they typically have small stabs that are actually functioning as stabilizers and not as auxiliary wings like on indoor duration models. So if the stab isn't lifting then tilting it is not going to have much effect on the turn.

Your balloon glider is more like an indoor duration model than an indoor glider and your stab is probably sharing part of the lifting. I think you can go with any or all of the ways that Kurt mentioned. One way to decide which direction to turn is to check the lateral balance of the model and then trim it to turn toward the heavy side. Another way is to set the model up as straight and well balanced as possible and then see which way it wants to turn. Sometimes on a catapult glider my decision about R-R pattern or R-L pattern is made according to what the glider wants to do.

  ----- Original Message -----
  From: torqueburner
  To: Indoor_Construction_at_yahoogroups.com
  Sent: Friday, June 30, 2006 11:39 AM
  Subject: [Indoor_Construction] Re: Possibly interesting balsa test


  Hi, Bill - I found this quite interesting.

  --- In Indoor_Construction_at_yahoogroups.com, "Bill Gowen" <b.gowen@...> wrote:
>
>. . . One piece was .130 x .245 x 12" . . .It buckled toward the thin side at 180g and
>toward the thick side at something over 500g. . . .The final diameter was .195". The
>buckling load for this piece was 360g. . .

  Do I remember correctly that the buckling resistance is proportional to the square of the
  dimension parallel to the buckling force? That seems to fit your measurements for the
  rectangluar piece pretty closely (the larger dimention would buckle at (.245/.13) squared
  *180, which is about 640 g.

  Using these numbers, a piece with a height of about .18" would buckle at 360 g, same as
  the round one. And since the round piece is only .195 in the center, with a decreasing
  "height" as you move outward, it has an overall effective height that is less than .195"
  Does this make sense?

  It would be interesting to test a piece that is .18" high and see if it buckles somewhere
  around 360 g.

  Dave Drummer



   

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Received on Fri Jun 30 2006 - 11:08:51 CEST