Experimenter is a magazine created by EAA for people who build airplanes. We will report on amateur-built aircraft as well as ultralights and other light aircraft.
Issue link: http://experimenter.epubxp.com/i/307497
EAA Experimenter 29 UNDER THE COWL WHEELS AND BRAKES ARE useless in flight—mere dead weight and often drag. Reno Air Race pilot Kevin Eldredge said that extending the gear on his NXT, Relentless, doubles the drag. But, once we're on the ground, wheels and brakes are our best friends. The basics matter when choosing the right wheels and brakes for your aircraft. What is the airplane's gross weight, landing weight, and speed? Is it being flown off a hard-sur- face runway, gravel, or grass? These determine what tires are necessary. Everything else follows from accommodating the required tire. Buyers of experimental light-sport aircraft (E-LSA) and amateur-built kits have options. While kit manufacturers obvi- ously have selected systems based on their own engineering, operational, and cost criteria, many kit manufacturers will test and approve a customer's rational requests. Kit providers can opt to sell their airframes without wheels, etc. Many kits are sold in stages. In response, wheel and brake manufacturers often develop complete systems for LSA and amateur-built kits. Design solutions are as varied as the manufacturers— magnesium or aluminum alloy or sand-cast, die-cast, spin- cast, and full-machined wheels, with open ball and tapered roller or sealed ball bearing wheels. Fixed-disc, floating-cal- iper or floating-disc, fixed-caliper brakes; single- and mul- ticaliper, carbon, iron, or stainless-steel discs; and single- or multi-piston calipers—are fed by flexible or monolithic tubing. Hundreds of master cylinders are on the market. And complicating all this are two incompatible fluids. Disclaimer: This discussion is brief and necessarily gen- eralized to fit in the space of one article. W HEEL S A ND T IRE S Aircraft wheels are cast or machined. Forged wheels are not available in our aviation market, and stamped wheels are found in specialized applications only. Cast aluminum (several different methods of casting are used) has moderate weight and moderate strength, takes paint well, and is low cost. Cast magnesium corrodes fast, has very low weight and relatively high cost, and is com- paratively brittle. Cast wheels can be porous, so they usually require tubes or special sealant coatings. Machined ("billet") aluminum wheels, properly engi- neered, are strong, shiny, and relatively expensive. They can be much lighter than cast, rivaling magnesium in weight. Machined aluminum can be anodized for protection and beauty. Aluminum is also much less brittle and less corro- sion-prone than magnesium, and paints adhere better to aluminum; so "alloy" wheels can look better longer. Nick Kacludis, engineering manager at Cleveland Wheels & Brakes, said, "Don't be seduced by exotic materials and their promise of a few ounces [of weight] savings. Look at the operating environment and match your equipment to it. Magnesium is lighter than aluminum but is more susceptible to corrosion. Fix nicks in the paint right away. [Cleveland's online manual details how to do it.] There is a touch-up for corrosion: polish, clean, prime, paint." But he added, "If you Choosing Wheels and Brakes Comparing the options BY TIM KERN Stress concentration is shown on this Beringer wheel. Knowing where the stresses are allows engineers to optimize strength versus weight. Photography courtesy of Beringer Wheels and Brakes E A A E X P _ M a y 1 4 . i n d d 2 9 EAAEXP_May14.indd 29 5 / 5 / 1 4 3 : 1 9 P M 5/5/14 3:19 PM