Wooden-Effects　（テストバージョン）: 2012

Understanding the properties of Commercial Balsa

The different “grades” of the wood.

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

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.

：

about Balsa

In selecting balsa sheets for need, it is important to consider the way the grain runs through the sheet as well as the weight of the sheet as we discussed above. The grain direction actually controls the rigidity or flexibility of a balsa sheet more than the density does. The following chart illustrates the 3 basic grain types for sheet balsa and lists the most appropriate uses for each.

A-Grain

A-Grain sheet balsa has long fibers that show up as long grain lines. It is very flexible across the sheet and bends around curves easily. Also warps easily. Sometimes called “tangent cut”. This cut should be used for sheet covering rounded edges, planking, forming tubes, strong flexible spars.

B-Grain

B-Grain sheet balsa has some of the qualities of both type A and type C. Grain lines are shorter than type A, and it feels stiffer across the sheet. It is a general purpose sheet and can be used for many jobs. Sometimes called “random cut”.
Use for flat fuselage sides, trailing edges, wing ribs, formers, planking gradual curves, wing leading edge sheeting in model aircraft.

C-Grain

C-Grain sheet balsa has a beautiful mottled appearance. It is very stiff across the sheet and splits easily. But when used properly, it helps to build the lightest strongest models. Most warp resistant type. Sometimes called “quarter grain”.
Use for sheeting balsa and foam wings and tails, flat fuselage sides, wing ribs, formers, trailing edges in model aircraft.

Balsa Weight for Various Densities
Balsa is one of the lightest woods available, and in many respects has the highest strength-to-weight ratio of any wood - even oak. The chart at the right gives a comparison of a few familiar wood types.

Hobby grade balsa is harvested in the jungles of Ecuador, kiln dried, cut into large blocks, and shipped to the U.S. for final cutting and sanding. Most balsa from hobby shops is in the 8-10 lbs/ft³ realm. The rock-hard stock that nobody wants is sent to the airplane kit manufacturers ;-)

Before being discovered as an ideal source of wood for model airplanes, balsa trees were cut and assembled into raft for floating down the river. In fact, the word "balsa" is Spanish for the word "raft." Balsa has been widely used by the military for air-drop pallets, and in fact, during World War II, balsa wood for models became scarce because the Army Air Force needed it for operations. Bamboo and other reeds were tried by modelers as a substitute wood, but it never could replace balsa.

Wood Properties
Species	Weight lb/ft³	Stiffness Strength	Bending Strength	Comp- ression Strength
Balsa	8	72	70	75
Balsa	10	100	100	100
Balsa	14	156	161	149
Spruce	28	230	260	289
Yellow Pine	28	222	277	288
Douglas Fir	30	241	291	341
Hickory	50	379	638	514
Oak	48	295	430	366
Basswood	26	261	288	288
Black Walnut	37	301	506	512

The charts below for weights of standard hobby shop balsa sheets, sticks and blocks were calculated from a simple formula that takes the density of the of each piece of balsa and multiply it by the volume. For 48" lengths, multiply each 36" value by 4/3 (1.333).

Example:

A 3/16" x 3" x 36" sheet of balsa has a volume of 20.25 cubic inches (in³), which is equal to 0.01171875 cubic feet (ft³). A piece of balsa with a density of 8 lbs/ft³ is the same as a density of 128 oz/ft³. So, to find the weight of the balsa sheet, multiply 128 oz/ft³ by 0.01171875 ft³ to get 1.500 oz. A 48" length would weigh 1.500 oz. x 4/3 = 2.000 oz.

BALSA SHEETS
Weight in Ounces, Density in Pounds/Foot³

36" Length	6	8	10	12	14	16
1/32"x2" 1/32"x3" 1/32"x4"	0.125 0.188 0.250	0.167 0.250 0.333	0.211 0.313 0.417	0.250 0.375 0.500	0.291 0.438 0.583	0.333 0.500 0.667
3/32"x2" 3/32"x3" 3/32"x4"	0.375 0.563 0.750	0.500 0.750 1.000	0.625 0.938 1.125	0.750 1.125 1.500	0.875 1.313 1.750	1.000 1.500 2.000
3/16"x2" 3/16"x3" 3/16"x4"	0.750 1.125 1.500	1.000 1.500 2.000	1.250 1.875 2.500	1.500 2.250 3.000	1.750 2.625 3.500	2.000 3.000 4.000
3/8"x2" 3/8"x3" 3/8"x4"	1.500 2.250 3.000	2.000 3.000 4.000	2.500 3.750 5.000	3.000 4.500 6.000	3.500 5.250 7.000	4.000 6.000 8.000
1/16"x2" 1/16"x3" 1/16"x4"	0.250 0.375 0.500	0.333 0.500 0.667	0.417 0.625 0.833	0.500 0.750 1.000	0.583 0.875 1.167	0.667 1.000 1.333
1/8"x2" 1/8"x3" 1/8"x4"	0.500 0.750 1.000	0.667 1.000 1.333	0.833 1.250 1.667	1.000 1.500 2.000	1.167 1.750 2.333	1.333 2.000 2.667
1/4"x2" 1/4"x3" 1/4"x4"	1.000 1.500 2.000	1.333 2.000 2.667	1.667 2.500 3.333	2.000 3.000 4.000	2.333 3.500 4.667	2.667 4.000 5.333
1/2"x2" 1/2"x3" 1/2"x4"	2.000 3.000 4.000	2.667 4.000 5.333	3.333 5.000 6.667	4.000 6.000 8.000	4.667 7.000 9.333	5.333 8.000 10.667

BALSA BLOCKS
Weight in Ounces, Density in Pounds/Foot³

36" Length	6	8	10	12	14	16
1"x1" 1"x1½" 1"x2" 1"x2½" 1"x3"	2.000 3.000 4.000 5.000 6.000	2.667 4.000 5.333 6.667 8.000	3.333 5.000 6.667 8.333 10.00	4.000 6.000 8.000 10.000 12.000	4.667 7.000 9.333 11.667 14.000	5.333 8.000 10.667 13.333 16.000
2"x2" 2"x2½" 2"x3"	8.000 10.00 12.00	10.666 13.333 16.000	13.333 16.667 20.000	16.000 20.000 24.000	18.667 23.333 28.000	21.333 26.667 32.000
3"x3" 3"x4"	18.00 24.00	24.00 32.00	30.000 40.000	36.000 48.000	42.000 56.000	48.000 64.000
1½"x1½" 1½"x2" 1½"x2½"	4.500 6.000 7.500	6.000 8.000 10.00	7.500 10.000 12.500	9.000 12.000 15.000	10.500 14.000 17.500	12.000 16.000 20.000
2½"x2½" 2½"x3	12.500 15.000	16.667 20.000	20.833 25.000	25.000 30.000	29.166 35.000	33.333 40.000

BALSA STICKS Weight in Ounces, Density in Pounds/Cubic³

36" Length	Qty.	6	8	10	12	14	16
1/16"x1/16" 1/16"x3/32" 1/16"x1/8" 1/16"x3/16" 1/16"x1/4" 1/16"x3/8" 1/16"x1/2"	16 16 8 8 4 4 2	0.125 0.188 0.125 0.188 0.125 0.188 0.125	0.167 0.250 0.167 0.250 0.167 0.250 0.167	0.208 0.312 0.208 0.312 0.208 0.312 0.208	0.250 0.375 0.250 0.375 0.250 0.375 0.250	0.292 0.438 0.292 0.438 0.292 0.438 0.292	0.333 0.500 0.333 0.500 0.333 0.500 0.333
1/8"x1/8" 1/8"x3/16" 1/8"x1/4" 1/8"x3/8" 1/8""x1/2"	4 4 4 2 1	0.125 0.188 0.250 0.188 0.125	0.167 0.250 0.333 0.250 0.167	0.208 0.312 0.416 0.312 0.208	0.250 0.375 0.500 0.375 0.250	0.292 0.438 0.538 0.438 0.292	0.333 0.500 0.667 0.500 0.333
1/4"x1/4" 1/4"x3/8" 1/4"x1/2" 1/4"x3/4" 1/4""x1"	1 1 1 1 1	0.125 0.188 0.250 0.375 0.500	0.167 0.250 0.333 0.500 0.667	0.208 0.312 0.416 0.625 0.832	0.250 0.375 0.500 0.750 1.000	0.292 0.438 0.583 0.876 1.166	0.333 0.500 0.667 1.00 1.333
1/2"x1/2" 1/2"x1"	1 1	0.500 1.000	0.667 1.333	0.832 1.666	1.00 2.00	1.166 2.333	0.1333 2.667
3/32"x3/32" 3/32"x1/8" 3/32"x3/16" 3/32"x1/4" 3/32"x3/8" 3/32"x1/2"	8 8 4 4 2 2	0.141 0.188 0.141 0.188 0.141 0.188	0.188 0.250 0.188 0.250 0.188 0.250	0.234 0.312 0.234 0.312 0.234 0.312	0.281 0.375 0.281 0.375 0.281 0.375	0.326 0.438 0.326 0.438 0.326 0.438	0.375 0.500 0.375 0.500 0.375 0.500
3/16"x3/16" 3/16"x1/4" 3/16"x3/8" 3/16"x1/2" 3/16"x3/4" 3/16"x1"	2 2 2 1 1 1	0.141 0.188 0.281 0.188 0.281 0.375	0.188 0.250 0.375 0.250 0.375 0.500	0.234 0.312 0.469 0.312 0.469 0.625	0.281 0.375 0.563 0.375 0.563 0.750	0.326 0.438 0.656 0.438 0.656 0.876	0.375 0.500 0.750 0.500 0.750 1.000
3/8"x3/8" 3/8"x1/2"	1 1	0.281 0.375	0.375 0.500	0.469 0.625	0.563 0.750	0.656 0.876	0.750 1.000
3/4"x3/4"	1	1.125	1.500	1.875	2.250	2.625	3.000

販売店

specialized Balsa Wood, LLC
Specially Weighed Balsa Sticks
Balsa Wood Laser Cutting Quote
(追加料金(40～150%）でグレイン、比重の指定が可能。一番品揃えも多そう。）

http://www.lonestar-balsa.com
(追加料金でグレイン、比重の指定が可能。$25Minimum Order）

Balsa USA

http://www.dbalsa.com/
http://www.nationalbalsa.com/

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