2188. The Development of a Light Weight, Dynamically Certifed Chair for Cessna Citation Jets

Paper

Abstract

ERDA, inc., located in Peshtigo, Wisconsin, is a manufacturer of custom seating for business and executive aircraft, with worldwide markets. Although relatively small in size, (in the neighborhood of 150 people), weight control and weight reduction activities are very much a prime concern. My responsibilities involve the determination of structural weight during design and then concurrently with production. Every chair that leaves ERDA is weighed. The weight is then recorded along with the chairs’ serial number for reference. In April of 1993, ERDA received a contract from Cessna Aircraft Corporation to design and construct an executive seat for their Citation Jet, model 525. (For ease of discussion, I will refer to the aircraft from this point on as the Cessna 525.) This was one of the most challenging programs that I have worked on. The requirements for this design were dictated by the Federal Aviation Administration (FAA), by invoking the Federal Aviation Regulation (FAR) part 23.562. This is a new regulation for aircraft interiors that go in new airframes. In general, all components are to be able to withstand 21g’s of force in the forward direction, and 16g’s in the down direction. It is an extremely demanding design challenge; so much that it took over 2000 engineering hours to complete the chair design. Cessna required that the seat structures weigh not more than 20 pounds each in order to keep the Cessna 525 within their weight allowance. This, as a starting point, was already eight pounds lighter than a typical ERDA chair that isn’t dynamically certified. With the award of the contract ERDA management assembled a team of engineers and designers to focus completely on the design. The initial direction was to modify an existing seat design, making components as light as possible and then beef up the parts as they failed testing. This sounds great from a weight engineering standpoint, but for a stress engineer, the thought of chasing load paths around was unfathomable. Within the first day of the project it was obvious that this was not the correct approach. A full fledged effort began designing radically different, light weight components using a variety of glass/graphite composites, high strength aircraft aluminum alloys, and honeycomb panels. From a simple design stand point the typical base, or pedestal, is engineered to be a functional, structural platform for a seat to operate on. Up to this point, a pedestal did not need to absorb energy, but only transfer the energy into the aircraft’s airframe. After several brainstorming sessions the decision was made to pursue a concept that would allow the pedestal to deform non-elastically, but not fail. The methodology was to utilize a ”legged” pedestal that would lay over and deform as the energy shock went through the chair.