Touring Machine Company

Many POHs give the maneuvering speed at max gross weight, but the lighter the airplane , the lower V_a. A general rule is to decrease the speed by 1/2 the percentage decrease in weight.

You can find Maneuvering Speed in the POH or on the aircraft’s Type Certificate Data Sheet. For my Cessna 210 it is 135 MPH (117 Knots) at 3,800 lbs. Flying alone with full tanks the weight is about 3,000 lbs. The percentage decrease is 800/3800 = 26%. Divide by 2 to get 13%. A 13% reduction is 117 MPH (102 Kts). Empty weight on the 210 is 2,300 lbs so V_a when empty is reduced by 20% (1500/3800÷2) and is 108 a reduction of 27 MPH. Every 100 lb reduction from max gross weight is about 2 MPH reduction in V_a.

For my Cherokee 140 maneuvering speed is 129 MPH (112 Knots) at 2,150 lbs. Flying alone, with tanks at the tabs, the weight is about 1,850 lbs. The percentage decrease is 300/2150 = 14%. Divide by 2 to get 7%. A 7% reduction is 120 MPH (104 Kts). That works out to about 3 mph per 100 lbs.

A general rule of thumb then is that, in normal operations, you should reduce V_a by about 2-3 MPH for every 100 lbs below max gross weight.

If you can’t find the maneuvering speed, a general rule of thumb is that it is 1.7 times V_s1 (Clean stall speed). For the 210 V_s1 is 80 so V_a is 136 MPH. For the Cherokee V_s1 is 64 so V_a is 109 MPH. On most airplanes, this speed is around 6:30 on the airspeed indicator.

This entry was posted on Thursday, November 24th, 2011 at 11:03 am and is filed under Rules of Thumb. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.