Ultralight aircraft fly "under the radar" so to speak on many of the FAA regulations. One area they are not excused from are the necessary airspeed indicators and ratings. This is so the pilots have quick access to the needed airspeed indicators for safe flight of the particular aircraft. One such demarcation is the aircraft's Vne which is the "Never Exceed" speed. This calculation is gained via the aircraft's airspeed indicator. The aircraft's Vne is determined by the manufacturer of the plane and by the FAA testers. For the pilot and user to calculate the Vne, it is a simple matter of learning the airspeed indicator colours.
Sit in the ultralight and locate the gauge and instrument panel. This is typically in front of the pilot's stick or yoke. Look for the round dial indicating Airspeed, this is the air speed indicator. In addition to being the gauge used to indicate air speed, it is also a calculator of sorts. It has marks indicating the aircrafts levels of safe operation, including the Vne.
Read the outer edge of the dial. Notice there are several colours around the edge of the dial, a green, white, yellow and red section on the curve of the dial. These colours represent the different operation speeds for the safe operation of the aircraft. For example, operations within the green marked speeds are considered a safe operating speed without a stall, in this case represented by Vso.
Go to the first number where the red colour starts along the edge of the dial. This is the aircraft's Vne, or speed to never exceed. For example, if the aircraft's dial has the red starting at 110 knots, the Vne is not to exceed 110 knots. So, the Vne is 110. Do not fly the aircraft over the Vne red mark on the air speed dial once you have arrived at the Vne calculation.
Ultra Light aircraft require training and an FAA Sport or Recreational pilot license at minimum. Do not attempt to fly any aircraft until you have received proper training from a certified flight instructor (CFI).