Sheet Metal 6.3: Aircraft wood and fabric in aviation SM6.3

• Aircraft Wood

Materials

• Wood was one of the first materials used in aircraft construction.

• Most airplanes during World War I used wood frames with fabric coverings.

• Wood was preferred for aircraft construction until the 1930s.

• The slow development of strong, lightweight metal structures contributed to the use of wood.

• A lack of corrosion-resistant materials for all-metal aircraft was also a factor.

• Many airplanes with wood as the primary structural material still exist and are in operation.

• Proper maintenance and repair are essential to keep these older aircraft airworthy and operational.

• The largest seaplane and wooden aircraft ever constructed was made of wood.

• Aircraft Fabric

• Fabric-covered aircraft have significantly impacted aviation history.

• Fabric covering provides a primary advantage for planes: lightweight.

• Disadvantages of using fabric coverings on planes include: flammability and lack of durability.

• As aviation advanced, aluminum became the main construction material.

• Aluminum and composite planes dominate modern aviation.

• Gliders, home-built aircraft, light sport aircraft, and some standard and utility aircraft still get built with fabric coverings.

• Polyester fabrics are now standard, with linen and cotton no longer used on planes certified in the U.S.

• Recovering existing fabric aircraft is an accepted maintenance procedure.

• Engine mounts

Mounts for Reciprocating Engines

• Aircraft equipped with reciprocating engines use a mount structure made of welded steel tubing.
• As engines grew, the need to absorb vibration led to the development of rubber and steel engine suspension units which are known has shock mounts.
• These mounts are secured using heat-treated steel bolts.
• The three most common engine mounts are:
  • Conical
  • Dynafocal
  • Bed Mount

Conical Mount

• Conical engine mounts were developed first, and these suits traditional aircraft and smaller engines.
• Conical mounts are strong and sturdy, having four points to fasten the engine and secure the mount to the airframe.
• They are considered the easiest for installation, repairs, and maintenance.
• Conical mounts are used if crankcase pads are flat and the mounting bolts are installed horizontally through the mount and engine.

Dynafocal Mount

• Dynafocal mounts are known as the strongest engine mounts.
• Like conical mounts, dynafocal ones also have four fastener points: a ring shape around the engine for better torque and vibration distribution.
• Dynafocal mounts use larger rubber discs to cushion vibrations more effectively than the smaller cone-shaped rubbers in conical mounts.
• The attachment locations are based on the engine's center of gravity.
• The design systems have a specific position that the mounts point toward, becoming the center of gravity for the entire system, including all additional elements of the system, the engine accessories, and propeller.
• Dynafocal engine mounts are much more difficult to design and build.

Bed Mount

• Bed mounts are common in diesel and Rotax engines.
• Unlike dynafocal and conical mounts, bed mounts have a diverged shape.
• Bed mounts still use four attachment points, but are situated under a crankcase/beneath the firewall.

Turbofan Engines

• Engine mounts for turbofan engines support the engine and manage loads imposed on the aircraft structure.

• Most turbine engine mounts are made of stainless steel.

• Some systems include two mounts supporting the forward end and a single mount at the rear end.

• Vibration isolator engine mounts support the power plants and isolate the airplane structure.

• Each power plant is generally supported by forward and aft vibration isolator mounts

• For safety, turbofan mounts are designed to break off if shear loads exceed a threshold.

• The engine-to-wing structure releases the engine during extreme forces to prevent structural damage to the wing, which could impair flight.

• The design philosophy for turbofan engines differs from safe load design and varies by aircraft.

• Connection bolts/fuse pins of engine/pylon mounts can fail in a controlled manner if loads are extremely high, which endangers aircraft structure.

• Location Numbering Systems

Overview

• Both small and light aircraft require a method to precisely locate each structural component.
• Numbering systems facilitate the location of wing frames, fuselage bulkheads, and other structural parts.
• Most manufacturers use station marking systems.
• Always review the manufacturer's numbering system and designations before locating a structural member, as these are not always the same across manufacturers.

Key Terms

• These are numbered in inches from a reference or zero point known as the reference datum.
• Buttock Line (BL): The vertical reference plane down the center of the aircraft used for left or right measurements.
• Water Line (WL): Measurement of height in inches perpendicular from a horizontal plane, usually located at the ground, cabin floor, or another easily referenced location.