When you torque a bolt into an aircraft fitting, the washer underneath the bolt work harder than you think. It spreads the load. It also protect the surface and keeps the joint from loosening up with time. If you select wrong type and/or size, you have created a weak point that may not show up until aircraft is flying.
Aviation fasteners need to meet tighter tolerances different than the ones found at your local hardware store. There’s a whole range of washers made for specific jobs that address different issues. For instance, some are used in high-stress jobs where sizes must stay exact. Others spreads heavy loads across soft materials. Some are just for general use.
Choosing the Right Washer for Aircraft
This infographic breaks all of this down so you’ll know what kind of washer goes with what application and bolt. First up, learn about the dash numbers: These indicate size of the washer’s inner diameter; i.e., what it fits around. Knowing that makes it easier to make your other choices from there (wide vs. Standard outer diameter; light vs. It has a normal thickness. Each selection alters how much of the load travel across the joint.
Beyond size, material is important too. Aluminum washers are fine for most secondary structure because they’re lightweight. Steel washers are used on landing gear and other places subject to high shear loads like engine mounts. Near your fuel system or where things get wet you’ll use stainless steel washers which don’t corrode. Using the correct material ensure the joint will resist deforming with repeated stress.
The standard washer is simply what many builders have used out of habit. This happens until they try to clamp into thin sheet or composite and find that the bearing area isn’t large enough. In those cases, a wide washer help spread the clamp force to keep the fastener from pulling through. In practice this means fewer inspections findings and longer service life then might be expected by looking at the numbers.
For joints sensitive to fatigue like the primary structure, tolerances matter. Washers can comes tighter spec’d than others. Tighter tolerances mean they holds their size better, leading to more consistent preload. For a joint subjected to thousands of cycles, you want uniform tension to avoid failure. Remember: Torque specifications is based off having the proper size washer between the nut and the bolt head. Altering the washer alters its friction properties. Tightening to the specified value will not create right tension. Check your table prior to tightening the joint. This simple error goes undetected because it’s silent.
The washer is a detail. In the end, the washer is a small detail that protects everything around it and you should of checked first. Washers don’t require memorizing figures; rather they require knowledge of a joint’s requirements. It could be an actualy luxurius part if you want, but washers is just part of job. You must recieve the correct one to avoid problems. This moddern method works better than old way.
