Need help regarding speed and altitude in flight simulator


I am using cesium library in my angular application and I am working on flight simulator.

I want to get the speed, altitude, start point, end point and way points from the users.
The units for speed should be knot and for the altitude should be meters.

To simulate the flight, I am setting the following configurations:

var property = new Cesium.SampledPositionProperty();
var orientationProperty = new Cesium.SampledProperty(Cesium.Quaternion);

this.entity = this.cesiumService.viewer.entities.add({
  id: "shadow",
  name: "shadow",
  availability: new Cesium.TimeIntervalCollection([
    new Cesium.TimeInterval({
      start: startWithHeight,
      stop: endWithHeight,
  position: property,
  orientation: orientationProperty

  interpolationDegree: 2,
  interpolationAlgorithm: Cesium.HermitePolynomialApproximation,

this.cesiumService.viewer.clock.multiplier = 1.0
this.cesiumService.viewer.clock.shouldAnimate = true;

In my feature, if the user enters 120 as input for speed, it means 120 knots. In that case, I want to simulate the flight at 120 knots speed. But right now, I am not getting proper speed. On setting the value of clock multiplier at 1.0, it doesn’t change the speed as per the user inputs. I also tried to set clock multiplier value with the expression (speed * 0.51444) to convert the speed from knot to m/s, but it doesn’t reflect properly during the simulation.

I am also getting some issues with altitude. Sometimes, it renders as if the flight is moving on the ground surface and not from the altitude that I get from the users.