Read a book by Jeffery Quill called Spitfire, A Test Pilot’s Story. Anybody interested in the history of the Spitfire must read this book. And if you’re thinking about making an FS flight model for a Spitfire, this book is Required Reading!
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Seems the Spitfire had a very narrow margin (fore and aft) of longitudinal stability. Primarily affected by the location of the CG, an unstable aircraft will continue pitching up or down, at an increasing rate, when elevator control is applied, and will tend to tighten into turns by itselficon_eek, if not counteracted with opposite elevator, a potentially dangerous situation indeed! Later production models, with bigger props and more propeller blades, aggravated the problem because, as Quill put it, “the blades of a propeller are aerodynamically equivalent to a fixed horizontal surface equal to their projected area. This is tantamount to having foreplane acting in reverse sense to the fixed tailplane, and is therefore essentially destabilizing.” RAF pilots initially, and wrongly, attributed this instability to insufficient elevator authority. It made “common sense”, of course, because the plane was difficult to control in pitch. As the CG shifted during flight, as fuel burned off, the problem got worse. Also, in operation, additional equipment was added with the result that some operational squadrons were taking off in Spitfires with CGs outside the Supermarine’s published CG limitations, making then dangerously unstable.
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This book is great. All this gets me wondering about FS planes and about how real we really want these things to fly!
<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com
fficeffice" /><o></o>Seems the Spitfire had a very narrow margin (fore and aft) of longitudinal stability. Primarily affected by the location of the CG, an unstable aircraft will continue pitching up or down, at an increasing rate, when elevator control is applied, and will tend to tighten into turns by itself
icon_eek, if not counteracted with opposite elevator, a potentially dangerous situation indeed! Later production models, with bigger props and more propeller blades, aggravated the problem because, as Quill put it, “the blades of a propeller are aerodynamically equivalent to a fixed horizontal surface equal to their projected area. This is tantamount to having foreplane acting in reverse sense to the fixed tailplane, and is therefore essentially destabilizing.” RAF pilots initially, and wrongly, attributed this instability to insufficient elevator authority. It made “common sense”, of course, because the plane was difficult to control in pitch. As the CG shifted during flight, as fuel burned off, the problem got worse. Also, in operation, additional equipment was added with the result that some operational squadrons were taking off in Spitfires with CGs outside the Supermarine’s published CG limitations, making then dangerously unstable.<o
></o>This book is great. All this gets me wondering about FS planes and about how real we really want these things to fly!
