Pietenpol-List: AC 43.13-1a
Posted: Wed Oct 21, 1998 9:17 am
Original Posted By: William Conway
{p1} FIGURE 1.2 - Selection and properties of aircraft wood. ----------------------------------------------------------------------- Key: Species of wood Strength properties as compared to spruce Maximum permissible grain deviation (slope of grain) Remarks ----------------------------------------------------------------------- Spruce (Picea) Sitka (P. Sitchensis) Red (P. Rubra) White (P. Glauca). 100% 1:15 Excellent for all uses. Considered as standard for this table. Douglas Fir (Pseudotsuga Taxifolia). Exceeds spruce. 1:15 May be used as substitute for spruce in same sizes or in slightlyreduced sizes providing reductions are substantiated. Difficult to work withhand tools. Some tendency to split and splinter during fabrication andconsiderable more care in manufacture is necessary. Large solid piecesshould be avoided due to inspection difficulties. Gluing satisfactory. Nobe Fir (Ables Nobiles). Slightly exceeds spruce except 8 percent deficient in shear. 1:15 Satisfactory characteristics with respect to workability, warping, andsplitting. May be used as direct substitute for spruce in same sizesproviding shear does not become critical. Hardness somewhat less thanspruce. Gluing satisfactory. Western Hemlock (Tsuga Heterophylla). Slightly exceeds spruce. 1:15 Less uniform in texture than spruce. May be used as direct substitutefor spruce. Upland growth superior to lowland growth. Gluing satisfactory. Pine, Northern White (Pinus Strobus). Properties between 85 percent and 96 percent those of spruce. 1:15 Excellent working qualities and uniform in properties but somewhat lowin hardness and shock-resisting capacity. Cannot be used as substitute forspruce without increase in sizes to compensate for lesser strength. Gluingsatisfactory. White Cedar, Port Orford (Charaecyparis Lawsoniana). Exceeds spruce. 1:15 May be used as substitute for spruce in same sizes or in slightlyreduced sizes providing reductions are substantiated. Easy to work with handtools. Gluing difficult but satisfactory joints can be obtained if suitableprecautions are taken. Poplar, Yellow (Liriodendrow Tulipifera). Slightly less than spruce except in compression (crushing) and shear. 1:15 Excellent working qualities. Should not be used as a direct substitutefor spruce without carefully accounting for slightly reduced strengthproperties. Somewhat low in shock resisting capacity. Gluing satisfactory. ----------------------------------------------------------------------- Notes for figure 1.2. 1. Defects Permitted a. Cross grain. Spiral grain, diagonal grain, or a combination ofthe two is acceptable providing the grain does not diverge from thelongitudinal axis of the material more than specified in column 3. A checkof all four faces of the board is necessary to determine the amount ofdivergence. The direction of free-flowing ink will frequently assist indetermining grain direction. b. Wavy, curly, and interlocked grain. Acceptable, if localirregularities do not exceed limitations specified for spiral and diagonalgrain. c. Hard knots. Sound hard knots up to 3/8 inch in maximum diameterare acceptable providing: (1) they are not in projecting portions ofI-beams, along the edges of rectangular or beveled unrouted beams, or alongthe edges of flanges of box beams (except in lowly stressed portions); (2)they do not cause grain divergence at the edges of the board or in theflanges of a beam more than specified in column 3; and (3) they are in thecenter third of the beam and are not closer than 20 inches to another knotor other defect (pertains to 3/8 inch knots - smaller knots may beproportionately closer). Knots greater than 1/4 inch must be used withcaution. d. Pin knot clusters. Small clusters are acceptable providing theyproduce only a small effect on grain direction. e. Pitch pockets. Acceptable, In center portion of a beam providingthey are at least 14 inches apart when they lie in the same growth ring anddo not exceed 1-1/2 inch length by 1/8 inch width by 1/8 inch depth andproviding they are not along the projecting portions of I-beams, along theedges of rectangular or beveled unrouted beams, or along the edges of theflanges of box beams. f. Mineral streaks. Acceptable, providing careful inspection failsto reveal any decay. 2. Defects Not Permitted. a. Cross grain. Not acceptable, unless within limitations noted in1a. b. Wavy, curly, and interlocked grain. Not acceptable, unlesswithin limitations noted in 1b. c. Hard knots. Not acceptable, unless within limitations noted in1c. d. Pin knot clusters. Not acceptable, if they produce large effecton grain direction. e. Spike knots. These are knots running completely through thedepth of a beam perpendicular to the annual rings and appear most frequentlyin quartersawed lumber. Reject wood containing this defect. f. Pitch pockets. Not acceptable, unless within limitations notedin 1e. g. Mineral streaks. Not acceptable if accompanied by decay (see1f). h. Checks, shakes, and splits. Checks are longitudinal cracksextending, in general, across the annual rings. Shakes are longitudinalcracks usually between two annual rings. Splits are longitudinal cracksinduced by artificially induced stress. Reject wood containing thesedefects. i. Compression wood. This defect is very detrimental to strengthand is difficult to recognize readily. It is characterized by high specificgravity; has the appearance of an excessive growth of summer wood; and Inmost species shows but little contrast in color between spring wood andsummer wood. In doubtful cases reject the material, or subject samples to atoughness machine test to establish the quality of the wood. Reject allmaterial containing compression wood. j. Compression failures. This defect is caused from the wood beingoverstressed in compression due to natural forces during the growth of thetree, felling trees on rough or irregular ground, or rough handling of logsor lumber. Compression failures are characterized by a buckling of thefibers that appear as streaks on the surface of the piece substantially atright angles to the grain, and vary from pronounced failures to very finehairlines that require close inspection to detect. Reject wood containingobvious failures. In doubtful cases reject the wood, or make a furtherinspection in the form of microscopic examination or toughness test, thelatter means being the more reliable. k. Decay. Examine all stains and discolorations carefully todetermine whether or not they are harmless, or in a stage of preliminary oradvanced decay. All pieces must be free from rot, dote, red heart, purpleheart, and all other forms of decay. -----------------------------------------------------------------________________________________________________________________________________
{p1} FIGURE 1.2 - Selection and properties of aircraft wood. ----------------------------------------------------------------------- Key: Species of wood Strength properties as compared to spruce Maximum permissible grain deviation (slope of grain) Remarks ----------------------------------------------------------------------- Spruce (Picea) Sitka (P. Sitchensis) Red (P. Rubra) White (P. Glauca). 100% 1:15 Excellent for all uses. Considered as standard for this table. Douglas Fir (Pseudotsuga Taxifolia). Exceeds spruce. 1:15 May be used as substitute for spruce in same sizes or in slightlyreduced sizes providing reductions are substantiated. Difficult to work withhand tools. Some tendency to split and splinter during fabrication andconsiderable more care in manufacture is necessary. Large solid piecesshould be avoided due to inspection difficulties. Gluing satisfactory. Nobe Fir (Ables Nobiles). Slightly exceeds spruce except 8 percent deficient in shear. 1:15 Satisfactory characteristics with respect to workability, warping, andsplitting. May be used as direct substitute for spruce in same sizesproviding shear does not become critical. Hardness somewhat less thanspruce. Gluing satisfactory. Western Hemlock (Tsuga Heterophylla). Slightly exceeds spruce. 1:15 Less uniform in texture than spruce. May be used as direct substitutefor spruce. Upland growth superior to lowland growth. Gluing satisfactory. Pine, Northern White (Pinus Strobus). Properties between 85 percent and 96 percent those of spruce. 1:15 Excellent working qualities and uniform in properties but somewhat lowin hardness and shock-resisting capacity. Cannot be used as substitute forspruce without increase in sizes to compensate for lesser strength. Gluingsatisfactory. White Cedar, Port Orford (Charaecyparis Lawsoniana). Exceeds spruce. 1:15 May be used as substitute for spruce in same sizes or in slightlyreduced sizes providing reductions are substantiated. Easy to work with handtools. Gluing difficult but satisfactory joints can be obtained if suitableprecautions are taken. Poplar, Yellow (Liriodendrow Tulipifera). Slightly less than spruce except in compression (crushing) and shear. 1:15 Excellent working qualities. Should not be used as a direct substitutefor spruce without carefully accounting for slightly reduced strengthproperties. Somewhat low in shock resisting capacity. Gluing satisfactory. ----------------------------------------------------------------------- Notes for figure 1.2. 1. Defects Permitted a. Cross grain. Spiral grain, diagonal grain, or a combination ofthe two is acceptable providing the grain does not diverge from thelongitudinal axis of the material more than specified in column 3. A checkof all four faces of the board is necessary to determine the amount ofdivergence. The direction of free-flowing ink will frequently assist indetermining grain direction. b. Wavy, curly, and interlocked grain. Acceptable, if localirregularities do not exceed limitations specified for spiral and diagonalgrain. c. Hard knots. Sound hard knots up to 3/8 inch in maximum diameterare acceptable providing: (1) they are not in projecting portions ofI-beams, along the edges of rectangular or beveled unrouted beams, or alongthe edges of flanges of box beams (except in lowly stressed portions); (2)they do not cause grain divergence at the edges of the board or in theflanges of a beam more than specified in column 3; and (3) they are in thecenter third of the beam and are not closer than 20 inches to another knotor other defect (pertains to 3/8 inch knots - smaller knots may beproportionately closer). Knots greater than 1/4 inch must be used withcaution. d. Pin knot clusters. Small clusters are acceptable providing theyproduce only a small effect on grain direction. e. Pitch pockets. Acceptable, In center portion of a beam providingthey are at least 14 inches apart when they lie in the same growth ring anddo not exceed 1-1/2 inch length by 1/8 inch width by 1/8 inch depth andproviding they are not along the projecting portions of I-beams, along theedges of rectangular or beveled unrouted beams, or along the edges of theflanges of box beams. f. Mineral streaks. Acceptable, providing careful inspection failsto reveal any decay. 2. Defects Not Permitted. a. Cross grain. Not acceptable, unless within limitations noted in1a. b. Wavy, curly, and interlocked grain. Not acceptable, unlesswithin limitations noted in 1b. c. Hard knots. Not acceptable, unless within limitations noted in1c. d. Pin knot clusters. Not acceptable, if they produce large effecton grain direction. e. Spike knots. These are knots running completely through thedepth of a beam perpendicular to the annual rings and appear most frequentlyin quartersawed lumber. Reject wood containing this defect. f. Pitch pockets. Not acceptable, unless within limitations notedin 1e. g. Mineral streaks. Not acceptable if accompanied by decay (see1f). h. Checks, shakes, and splits. Checks are longitudinal cracksextending, in general, across the annual rings. Shakes are longitudinalcracks usually between two annual rings. Splits are longitudinal cracksinduced by artificially induced stress. Reject wood containing thesedefects. i. Compression wood. This defect is very detrimental to strengthand is difficult to recognize readily. It is characterized by high specificgravity; has the appearance of an excessive growth of summer wood; and Inmost species shows but little contrast in color between spring wood andsummer wood. In doubtful cases reject the material, or subject samples to atoughness machine test to establish the quality of the wood. Reject allmaterial containing compression wood. j. Compression failures. This defect is caused from the wood beingoverstressed in compression due to natural forces during the growth of thetree, felling trees on rough or irregular ground, or rough handling of logsor lumber. Compression failures are characterized by a buckling of thefibers that appear as streaks on the surface of the piece substantially atright angles to the grain, and vary from pronounced failures to very finehairlines that require close inspection to detect. Reject wood containingobvious failures. In doubtful cases reject the wood, or make a furtherinspection in the form of microscopic examination or toughness test, thelatter means being the more reliable. k. Decay. Examine all stains and discolorations carefully todetermine whether or not they are harmless, or in a stage of preliminary oradvanced decay. All pieces must be free from rot, dote, red heart, purpleheart, and all other forms of decay. -----------------------------------------------------------------________________________________________________________________________________