Ringmaster stab

[Shorts,David]

Hi guys,
Ringmaster plan calls for 8-10# balsa 3/16".
1. I've got light and I've got heavy balsa, but no idea how that translates to 8-10#. I'm guessing something in the middle so it doesn't ding or flex.
2. Ots and classic rules allow for 5% deviations and I could all but guarantee that somebody substituted thicker or thinner balsa. I've got a ton of 1/4" balsa. Aerodynamically, would I gain anything with a thicker stab or even thinner stab?

[Tim Wescott]

It's not going to make a difference aerodynamically.

Do you have a scale that weighs in grams or ounces?  If you have a 36" x 3" sheet of 3/16" wood, weigh it in ounces.  Then divide by the thickness -- 3/16 in this case.  The result is the density in pounds per square inch.

Or just guess.

If you have any C-grain (crosscut) sheet, now is the time to use it.  Good 6 lb C-grain balsa should work just fine for a ringmaster stab.

[Colin McRae]

Hi guys,
Ringmaster plan calls for 8-10# balsa 3/16".
1. I've got light and I've got heavy balsa, but no idea how that translates to 8-10#.

Rule of thumb:

Light balsa 6-10 lbs/cuft
Med balsa  10-14 lbs/cuft
Heavy balsa  14-19 lbs/cuft

So the plans seem to recommend light 3/16" balsa.

For models of this size and type, I have been using light 3/16" for the stab/elev. IMO 1/8" is too thin strength-wise and 1/4" is too thick just adding unnecessary tail weight. And I agree C grain if you can find it.

[Dave_Trible]

Here’s a chart.   Make that pretty stiff 3/16”.

[Motorman]

With 3/16 you can just round off the edges. With 1/4 you should carve a little shape into the edge or it will look bulky. The 3/16 that came with my RSM kit was too light. I made a hand launch glider out of it. Weight to make the stab stiffer is good weight.

MM

[Dan McEntee]

Rule of thumb:

Light balsa 6-10 lbs/cuft
Med balsa  10-14 lbs/cuft
Heavy balsa  14-19 lbs/cuft

So the plans seem to recommend light 3/16" balsa.

For models of this size and type, I have been using light 3/16" for the stab/elev. IMO 1/8" is too thin strength-wise and 1/4" is too thick just adding unnecessary tail weight. And I agree C grain if you can find it.

    Light balsa that is considered contest grade, is 4 to 6 lb wood. You might extend that to 8 pound for some parts of an airplane. 8 to 12 pound would be medium and anything above that heavy and hard. Ringmasters, especially S-1 kit built versions and scratch built by the same method are usually nose heavy, so instead of adding lead to the tail to balance, make the stab from the heaviest wood you have. It will make the tail end more durable if you are still a member of the frequent crashers club. The rudder could be made from the same stuff. If all you have is light weight wood, an old British trick is to cut out slots in the stab from front to back and in lay straight grain harder strips of wood, and then sand smooth. This will help resist any warping or curling tendencies.

  Type at you later,
    Dan McEntee

[Jim Hoffman]

Dave,
Stunt Hangar has a link to a pretty good balsa density calculator.  Link on the top of the screen. 

A good gram scale is needed and incredibly worth while. About $20

[Shorts,David]

Yes, I have a gram scale I use to weigh wood. Thanks for the info.

[doug coursey]

https://stunthanger.com/smf/open-forum/ringmaster-stab/?action=post;last_msg=686588      heres a weight calculator but you have to weigh the qood in grams

[Dave_Trible]

The work is all done in the chart above-and yes it's in grams.

Dave

[Dan McEntee]

Dave,
Stunt Hangar has a link to a pretty good balsa density calculator.  Link on the top of the screen. 

A good gram scale is needed and incredibly worth while. About $20

  If you can't decide which gram scale to buy, or don't trust the electronic scales, keep your eyes peeled on Craig's List and FB Marketplace for Ohaus triple beam balance scales. I see them all the time , ranging from as little as $15 and some hopeful souls asking $150!!  I looked all over for a good deal on one when I started to build and fly indoor free flight back in the 80's and finally found one at a local scrap and resale place  for $40 and thought I got a great deal then!! I have picked up another Chinese knock off brand new in the box for $10 and a complete Ohaus  triple beam that had the add on weights that let you weigh things up to 5 pounds or more. These scales are completely adjustable and serviceable and easy to calibrate if you doubt the accuracy of one. They are dead nuts accurate and repeatable if that is important to you, and no batteries to go dead on you right in the middle of a project!! 
  Type at you later,
   Dan McEntee