Sir - The article "Dynamic overshoot" (Flight International, 24-30 January, P30) claims that engineers "completely overlooked" the phenomenon.
I hope that this is not true, as it is not only aerospace structures, which are affected. Bridges, for example, experience dynamic overshoot, because of rolling loads.
The old-fashioned bathroom-scale example given is not strictly correct in that, to generate 100% overshoot, the person would have to be suspended, with their feet just touching the scales then suddenly released. Stepping onto the scales could result in an overshoot in excess of 100%.
All good strength-of-materials books cover this topic and it can, of course, be complicated. The actual dynamic overshoot depends on the pulse shape of the applied force, the natural frequency and inherent damping of structure. It may be lower or higher than 100% - for example, the wingtip of a taxiing aircraft can experience +/- 100G acceleration.
There is no excuse for the phenomenon to have been "overlooked", as it should form part of the education of all stress and mechanical design engineers. Any "misunderstanding" should be cleared up by a visit to the company dynamics department.
Perhaps this was a case of the "wrong type" of engineers being involved in a project.
P GAMBARDELLA
Farnborough, Hampshire, UK
Source: Flight International
