dbr@odin.UUCP (10/09/84)
The two closely spaced propellors act as one device. Ideally, the rear propellor straightens out the swirling airflow from the front, improving the overall efficiency. One early use of contra-rotating propellors, and still used, is naval torpedoes. The Russian Tu20 has 4 contra-rotating turboprops.
stevel@haddock.UUCP (10/13/84)
Another reason fr contra-rotating propellers is to reduce the tourque. It's embarrassing to loose control above the stall speed because your propellers fliped the plane over.