Sunday, October 31, 2010
Thursday, March 26, 2009
Tacoma Narrows Bridge - Addressing Misconceptions
A great paper on how most undergraduate physics texts have described the collapse of the infamous bridge erroneously, over simplifying it to a case of forced resonance. The author of the article, Robert H. Scanlan, describes how the bridge failed due to 'aeroelastic flutter' -Good read.
-k
Wednesday, March 25, 2009
Equation 16.42 - Raymer 4th Edition
I went through Raymer and a couple of other texts (Stengel, Etkin, etc.) and I it's my understanding that the negative term in eqn 16.42 represents 'propeller fin effect' (Etkin eqn.3.9,8) and is destabilizing for a conventional tractor config.
The term in question, dBp/dB, is analogous to d(alpha)p/d(alpha), which is seen is eqn 16.30 (Raymer) which is the upwash derivative if the engine is in front of the wings. Similarly, dBp/dB, is probably the sidewash derivative wrt to the prop.
For a single engine tractor configuration the vertical tail is considered far aft, so that dBp/dB is equal to one. I got this value from a colleague, so there is no text I can point to. Raymer doesn't define this term anywhere.
I'd appreciate constructive feedback.
-k
Monday, March 23, 2009
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