A Study of Moisture Intrusion into the Tow Missile Launch Tube.

Abstract : Twelve tests were conducted to evaluate possible moisture intrusion into the TOW launch tube during high-speed flight in a rainfall. Simulated flight speed was 176 knots and rainfall rates were the equivalent of 2 in/hr. No free water was present in the tube after the tests and moisture intrusion was generally low. The maximum moisture gain was 1.4 grams in a 1 hr. test. This occurred once. All other tests gave moisture gains of 0.58 grams or less. Damage to the diaphragm on the front of the launch tube occurred in four tests. It was limited to separation of the backing material from the polyamide film. The damage may have affected the moisture gain in only one of the tests. Installation of the mushroom eliminated damage to the diaphragms in the four tests conducted. It did not affect moisture intrusion into the tube. Fourteen additional tests were conducted to study the effects of the diaphragm hole configuration, the airstream velocity and the angle between the launcher centerline and the airstream on moisture intrusion into the TOW missile launch tube. Without the mushroom installed, moisture intrusion was found to increase with an increase in hole size and to increase with a decrease in airstream velocity. With the mushroom installed, the effect of hole size and configuration was much less pronounced. Some reduction in moisture intrusion may be gained if holes are not placed at the bottom of the diaphragm. (edc)