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/101874
S a f e t y W ir e A good example of this is to relate how I fell of the roof of my parents' house as a kid. (Explains a lot, right?) While we are on the topic of engine mounts, another related design point to consider is your firewall. In what seems kind of counterintuitive to most when it is first mentioned, a longer deceleration path is often a better choice, assuming all other factors (velocity, impact angle, the type of surface impacted) are equal. The reason for this is that a longer slide across the ground gives more time for the energy to be expended. A good example of this is to relate how I fell off the roof of my parents' house as a kid. (Explains a lot, right?) I actually did this not once but twice, both in the name of aeronautical science while trying to figure out how those funny-looking planes designed by a guy with those epic sideburns could fly. I had seen photos of Burt Rutan's airplanes in a school library book about some air show in Wisconsin. Instead of just simply looking it up or asking someone, I called the local airport and found someone with one of those planes. He made copies of the basic plans for me, and I made a series of scale replicas and proceeded to throw them off the roof. I learned a lot from those experiments, including that my parents' Doberman could jump high enough to pose a hazard to small aircraft on approach to landing. One of the other lessons was that I possess a maximum lift coefficient (CLmax) roughly equivalent to that of an ice-covered brick. That is to say not even close to sufficient to have a decent glide ratio. Once, I impacted a concrete sidewalk, breaking some ribs and giving myself two black eyes. The second time, I landed on a wicker seat. That time I escaped with just some bruises because I had a greater distance over which to slow down and change my potential energy into work done. In this case I did that by turning that seat into splinters. How does this all relate to your firewall in a crash? If the bottom edge of the firewall is either canted forward or vertically oriented and the skin of the nose and belly are torn away, the firewall can dig in much like a soccer player's cleats (this is referred to in the crash safety community as "plowing") and cause the aircraft to come to a more abrupt stop, exposing the passengers and crew to more extreme impact forces. Taking the firewall and angling the bottom edge back at least 20 to 30 degrees can help to minimize this risk. 34 Vol.2 No.1 / January 2013 In the design I am currently working on for a lightsport aircraft, this angle is approximately 45 degrees. For those designs with a canopy, a roll bar is needed to keep the pilot's and passengers' heads from contacting the ground in the event that an aircraft winds up on its back. Ideally, there should be one of these structures in front of and behind the heads of the occupants. If you have a four-seat aircraft, there should also be a roll bar immediately behind the front seats as well, with the aft bar placed at the back of the rear seats. Even among non-canopy-equipped aircraft, such structures built into the frame can serve a vital purpose by keeping the roof from caving in should the aircraft wind up on its back. Few things express the phrase "splitting headache" quite so dramatically as what often happens when someone's head and the ground or another object get into a debate over the claim to the same bit of cabin space. I actually did this not once but twice, both in the name of aeronautical science while trying to fgure out how those funny-looking planes designed by a guy with those epic sideburns could fy. Now, I can hear the groans from a subset of builders/ owners of canopy-equipped aircraft. Some will argue that this will take away from the World War II fighterlike mystique of their plane or otherwise ruin the look they are hoping to achieve. To these folks, I suggest you ask your spouse or kids what is more important to them—you looking "cool" or you being around for as many holidays, anniversaries, birthdays, and weddings as you can be? In our next installment, we will look at why restraints are important and how their benefits can be maximized. Until then, fly safely. Stephen Richey is an aviation safety researcher who has been involved with flying starting with his time as a "junior hangar bum" with a local EAA chapter as a child in Indiana in 1988. He has logged about 700 hours thus far including times in ultralights and as a student pilot in light singles. His current project is the design of a new composite homebuilt known as the Praetorian.