Bill Tindall
Moses apparently imported it into Autocad (how I wish I could do that) and made the measurement, which is in error by the tilt in the photograph and perhaps some parallax error. This estimate could be refined by drawing a line at what you think is parallel to the plane's long axis along the base of the ramp and then making a measurement with a protractor. It looks to be close to 30 degrees from the horizontal. Is 30 degrees reasonable from what you know about the plane?

To further refine the measurement photograph a known plane in this orientation to determine parallax corrections.