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Balsa Grading?

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accooper

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Any one know an easy way to tell what grade balsa is? I have yet to see a label that is attached to a sheet of balsa mention the grade.

Andrew
Dark Lord Of The Scratch Builders
 

ben_ullman

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Any one know an easy way to tell what grade balsa is? I have yet to see a label that is attached to a sheet of balsa mention the grade.

Andrew
Dark Lord Of The Scratch Builders
if it
looks good A
If theres some blemishes B
Is its warped C
if its splintering D
If its expensive F

BEn
 

Stymye

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Any one know an easy way to tell what grade balsa is? I have yet to see a label that is attached to a sheet of balsa mention the grade.

Andrew
Dark Lord Of The Scratch Builders
You may be referring to "grain" there are different types of grain tho there are common "grades" of weight also
this page has a pretty good description of balsa concerning grain and weight

http://www.rcscalebuilder.com/tutorials/Balsa/balsa_1.htm
 
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MaxQ

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That weblink is as good as any....
I'm afraid real "contest grade" is hard to come by these days...(They use balsa in big supertankers IIRC)

Are you concerned about weight?
I didn't think most rocket builders were even concrned about that...unless you are building a boost glider.
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The different “grades” :

Grade
Ultra Light - “Contest” grade balsa
Light - “Contest” grade balsa
Light Medium
Medium
Medium Hard
Hard

Density in lb/cu.ft
4 - 5.4 “Contest” grade balsa
5.5 - 6.0 “Contest” grade balsa
6.1 - 7.5
7.6 - 9.5
9.6 - 12
14 +



Suggested uses of the different grades of Balsa



Ultra Light

4 - 5.4lb
Wing, tail and fuselage sheeting on models that are finished with fiberglass

Light

5.5 - 6.0lb
Sheeting covering (fuselages and wings).
Wing leading edge sheeting.
All wing and tail-plane ribs and tip blocks.
Engine cowling blocks.

Light medium

6.1 - 7.5lb
Sheeting on larger models
Large section leading and trailing edges.
All sheet tail surfaces
Sheet box constructions (fuselages).
Wing ribs.

Medium

7.6 - 9.5lb
Spacers on built up box fuselages.
Leading and trailing edges.

Medium hard

9.6 – 12lb
Wing spars of large cross-section.
Auxiliary wing spars (multi spar wings).
Fuselage longerons for open frame models.
Small section leading and trailing edges.

Hard

14+
Single main wing spars.
Fuselage longerons, 2.5mm sq and under.
Auxiliary wing spars of very small X-section.
 

powderburner

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All I remember about picking out balsa is to use your thumbnail. If you want really low density, and you can't tell by yourself by hefting the piece of material in your hand, then you can press the edge of your fingernail against the side of the balsa grain. If it creases the balsa easily (and the wood is soft) you usually have low density. You use this kind as a wing plank when you are going to sand an airfoil shape. If it barely creases at all you have high density. It is usually stronger and is good for cutting wing spars (for "built-up"-style construction) or fuselage stringers. When I was a kid you pretty much had to "learn by doing" but it really isn't that hard to figure out.

And these days, you are lucky to find any place that has balsa....period. I can't remember the last time I saw a shop with an actual range of balsa densities in the same size balsa stock.
 

o1d_dude

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The grade has to do with orientation of plank relative to the grain of the original balsa log. Actually, this is true of all wood but I digress.

If the plank has long lines running the length of it, it's "A" grain. The plank will flex across the grain.

If the plank has a mottled appearance and shows some lines going crosswise, it's "C" grain (aka "quarter sawn"). The plank will resist flexing across the grain. "C" grain is quite often warped and or skewed as well so the good stuff is hard to find.

If it the plank has some elements of both A and C grain, it's considered "B" grain. It resists flexing both length and width-wise.

For rocket fins I look for the stiffest/densest "B" grain I can find.
 

Micromeister

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Andrew:
MaxQ's list should be very helpful.
I also find the chart attached below of use in understanding were the different grades come and cuts come from.
Hope it works for you as well;)

balsa Chart_10-18-06.jpg
 

Stymye

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that chart refers to the grain...not grade.

for example with stick and tissue models "grade"(density) becomes much more important than with typical rocket construction.

however I think understanding grain is more important for typical rocket construction.so the chart is good to read/understand
 

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