Date of Award

5-2024

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Aerospace, Physics, and Space Sciences

First Advisor

Dr. Ralph D. Kimberlin

Second Advisor

Dr. Eric D. Swenson

Third Advisor

Dr. Mary Ann Gaal

Fourth Advisor

Dr. Ratneshwar Jha

Abstract

Loss of Control (LOC) while in-flight in General Aviation (GA) has been the subject of intense research by academic institutions and regulatory agencies in recent years [4] [9] [11] [19] [20] [21]. This interest is primarily due to a disproportionate number of all aircraft accidents occurring within the GA category of flight, with 94% of accidents in 2022 occurring within GA, caused primarily by pilot LOC, with 42% of accidents having LOC as the listed cause. Research into this subject at FIT yielded the results that many common GA aircraft tend to experience a strong pitch up response after undergoing a rapid configuration change, such as lowering the flaps while preparing to land [19] [20]. This pitch response can be unexpected to pilots, and on some of the aircraft examined, take a dangerous amount of control force to maintain level flight, while still within FAA limits. Some pilots may not be able to exert this force, or this response may cause a distracted pilot to lose air speed and enter a spin or a stall while at low altitudes, making recovery difficult or impossible. Some structurally similar aircraft within the aforementioned research did not experience this pitch response, and this paper aims to determine the underlying causes of the difference in response to configuration changes. A change to a larger horizontal stabilizer is the primary difference investigated, with the hypothesis that a combination of downwash and flap-tip vortices affect the larger stabilizer more, leading to the dangerous pitch response and a higher rate of LOC accidents. To evaluate this relationship, two case studies were conducted with nearly identical models of Piper aircraft; the Cherokee C and the Challenger, and the Arrow I and Arrow II. The major difference between these aircraft is a larger horizontal stabilizer installed following a design overhaul in the early 1970s. The NTSB accident rates were analyzed for each set of aircraft from 1983 to the present, and the LOC accident rates were compared for the smaller span stabilizer to the larger. The conclusion of this analysis found that there is a statistically significant difference in the LOC accident rates for both case studies conducted, supporting the hypothesis that the larger stabilizer on these aircraft is more affected by flap-tip vortices. This confirms that the aircraft with the larger tail span are more prone to the pitch change caused by a rapid configuration change, contributing to the high rate of LOC accidents found in GA.

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