Table 2 Touch Down Point Dispersion and Flight Path Error *
*The Flight Psth Error(rms) was calculated after capture until 100 feet height
Recommendation, problem and solution
The NASA pilot comments covered all aspects of the aircraft and will be reported on more fully in another paper. This paper will discuss only those items associated with the HUD and the Radar Guidance Systern. The NASA recommendations, the problem, and the solutions are as follows.
1. "Improve the law driving the gamma prediction symbol to remove the overshoot when marking an FPC lever input."
The overshoot of the gamma prediction symbol was a scale factor mistake in the HUD/TEL interface. It was later corrected.
2. "Reformat the display to make the gamma prediction symbol easier to find and use."
In the original format of the gamma prediction symbol it did not move laterally with wind drift. If a large drift existed, the flight path symbol and gamma prediction and gamma prediction symbol were separated making it hard to use. To correct the problem, in the Pseudo/Radar Guidance Mode, the gamma prediction was attached to the flight path symbol in order to make it easier to find. See Fig.8.
3. "Add localizer and glide-slope raw data in the Pseudo/Radar Guidance B mode or provide an automatic switch from Guidance A mode to Radar Guidance B mode switching to aid the capture of the localizer and glide-slope. It was confusing with the Mode B format alone"
The problem cause was that the radar guidance B mode could not cover lateral deviations over 0.lnm. With the B mode format alone this caused the aircraft to overshoot after the initial lateral capture. After NASA flight tests, the HUD program was changed to provide an automatic switch from Radar Guidance A mode to Guidance B mode after the capture of the localizer and glide-slope.
4. "Eliminate the jumps in the radar guidance data on the HUD when on the final approach flight path".
The shifts in the HUD radar guidance data was caused by an error grater than 10 meters developing between the filtered radar position of the complementary filter and the integrated position in HUD CSG. The error results from the inertial velocity of the complementary filter because the different delay time. between the inertial velocities of IRU and the tracking radar position yields the error at a large velocity change such as a final turn.
For solution, HUD program was changed to use directly radar position of the output of complementary filter instead of the integrated position in the HUD CSG. Although this position error existed in the guidance data during the flight tests, the pilots could still touch down very accurately. This shows that the HUD guidance system position data becomes redundant with the outside view during landing and that by using the flight path symbol against the outside view, accurate landings were possible.
CONCLUSION
The HUD guidance system was used for all the Aska flight tests. We have confirmed its performance and characteristics as follows.
