American Scientist

To the Editors:

Your insightful column on bird ingestion by Lee Langston (“Keeping Birds Out of Jet Engines,” Technologue, January–February) does not mention the use of an upstream screen, or mesh, to help protect the engine. A relatively wide open mesh is envisioned to protect the engine from medium or large size bird impacts. The mesh would be strong, but flexible; designed to deform rather than break. The detachable screen can then be replaced when necessary. Of course, there is a trade-off, such as drag and some inflow air reduction.

George Emanuel
Arlington, TX

Dr. Langston responds:

Screens can cause inlet flow distortion, leading to possible stall and surge. Under freezing weather conditions, screens can accumulate ice, causing spalling—where small pieces flake off, which is obviously not good for rotating blades—and more distortion. Also, a possible bird impacted on a screen could cause compressor stall conditions, which might be more serious than ingestion by the fan. Finally, the screen would need to be quite strong to survive the impact of a two- to four-kilogram bird at 200 knots without both the bird and bits of the metal screen going into the engine.