February 2013

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: https://experimenter.epubxp.com/i/108002

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Page 32 of 44

aircraft with restraints that show these signs of decreased strength. With the relatively recent introduction of airbags into aircraft, the subject of their use often comes up. The "airbag seatbelt," if put into a crash-resistant structure, might have some benefit if for nothing more than reducing the tendency of the head to swing forward causing the chin to impact the upper torso. This is hazardous for two reasons. The first is that an impact to the chin can transmit forces to the base of the skull via the temporomandibular joint (TMJ), causing a fracture. This is likely how Dale Earnhardt, Sr. suffered his fatal injury. The second is that an impact of the chin against the chest can compress the anterior chest wall, causing compression or rupture-type injuries to the heart and large blood vessels surrounding it in what is called the "chin-sternumheart syndrome." like a championship bass at a fishing tournament, you can refer to the NASA biomechanics website for measurements. Using a 255- or 260-pound weight will take into account all but the largest folks in our population. If you design your cockpit around a 95th percentile man, it will feel very roomy for those of us who are not quite so large. The only concern with this would be making sure you keep the controls, instruments, and switches within reach for the smaller folks. This is where building a mock-up of the cockpit before finalizing the design can be helpful. The larger mass of the "test subject" will also help to design the restraints to be more resilient when exposed to loads of smaller occupants. Placing airbags into an airframe that will fragment or collapse will probably offer less benefit. Airbags have to be treated as a part of a comprehensive system designed to protect the occupants and not as a Band-Aid for a less-well-thought-out approach. To do so is to possibly impart a Figure 3. Layout of a well-designed restraint system. false sense of security to pilots and passengers. Probably the What is a survivable crash also tends to depend upon best use of airbags is to provide impact-lessening whom you ask. The issue is extremely complicated and effects on areas of the cockpit or cabin where clearwould take more space than I have left this month. The ance beyond the strike envelope cannot be provided issues of crash loads and energy attenuation will be because of aerodynamic considerations. discussed in the next two installments. Another point one must consider when designing a Until next month, fly safely. restraint system is something a lot of us do not consider when you say "restraint." The attachment points of the seats are just as important as any other part Stephen L. Richey is an aviation safety of the system. If the seat breaks loose, you will likely researcher who has been involved with flying overload even an optimally designed harness because for the better part of two-and-a-half decades, the harness is now the only thing trying to hold the starting with his time as a "junior hangar seat in place; and the "added" mass of the seat is not bum" with a local EAA chapter while a child in normally tolerated in a good way. Indiana in 1988. He has logged about 700 hours thus far, including time in ultralights and as I strongly recommend that when doing calculations a perennial student pilot in light singles. His that you use the biggest, "huskiest" friend you have current project is the design of a new homebuilt who could fit into your particular aircraft as the "test known as the Praetorian. case." If you do not want to grab a tape measure and ask your large friend to submit to being measured EAA Experimenter 33

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