IS 1898:1990 is the Indian Standard (BIS) for timber for aircraft construction in converted form (finished form). This standard lays down the requirements, grading, and permissible defects for timber in converted (finished) form specifically intended for use in aircraft and glider construction.
Timber for aircraft construction in converted form (finished form)
| Parameter | IS Value | International | Source |
|---|---|---|---|
| Moisture Content (at inspection) | 15 ± 2% (13% to 17%) | 12% to 15% | MIL-S-6073A |
| Slope of Grain (primary structure) | Not steeper than 1 in 15 | Not steeper than 1 in 15 | MIL-S-6073A |
| Growth Rings (Spruce) | Minimum 3 per cm | Minimum 6 per inch (approx. 2.4 per cm) | MIL-S-6073A |
| Permissible Solid Knots | Up to 6 mm diameter, under specific conditions | Up to 1/4 inch (6.35 mm) diameter, highly restricted by location | MIL-S-6073A |
| Plywood Adhesive (Waterproof) | Phenol-formaldehyde (PF) resin (Type I) | Phenolic or resorcinol resin meeting specific military specs | MIL-P-6070B |
| Primary Solid Timber Species | Himalayan Spruce, Fir, Sitka Spruce | Sitka Spruce (Picea sitchensis) | MIL-S-6073A |
| Plywood Shear Strength Test | Specifies dry and wet (72-hour cold soak) shear strength values. | Specifies dry, wet (48-hour cold soak), and post-boil (3-hour boil) shear strength values. | MIL-P-6070B |