ERROR IN AIRSPEED INDICATOR READING
If you read your copy of “Learning to Fly the Lazair” you’re probably aware that the Hall Brothers airspeed indicator, when mounted on the fuselage of the Lazair, provides a good relative indication of airspeed, but does not give an accurate reading in miles per hour. At take-off speed, the reading Is probably accurate within two or three miles per hour but at higher speeds, your actual airspeed will be much higher than Indicated. With a reading of 40 mph, your actual airspeed will be probably about 55 mph, and this Is the recommended maximum flying speed.
The author of this website found that the halls airspeed indicator is best mounted on the wing strut well away from the propeller thrust.