109. Lower Terrain Following Radar Ride Heights
Mod: Making the Tornado hug the terrain at lower heights.
By Frankie
Description: This mod allows you to fly at lower heights than 200 feet above ground level (AGL). Terrain-following radar (TFR) is an aerospace technology that allows a very-low-flying aircraft to automatically maintain a relatively constant altitude above ground level. It is sometimes referred-to as ground hugging or terrain hugging flight.
In DI's TORNADO simulation, you can select seven altitudes for terrain following mode: 200, 300, 400, 500, 750, 1000 and 1500 feet AGL. This is ACCURATE. Back in 1991, it was not possible for the Tornado to fly nap-of-the-earth below 200 feet AGL. During the First Gulf War in 1991, IDS Tornado pilots flew missions at altitudes as low as
100 ft AGL manually! According to the Operation Chastise entry in Wikipedia, the RAF Lancasters of Squadron 617 "flew low, at about 100 ft (30 m) altitude, to avoid radar detection", with "bombing from an altitude of 60 feet (18 meters)". So flying TFR-aided at levels below 100 feet is not uncommon. In 1995, Heinz-Bernd Eggenstein, Basil Copeland and Eric Joiner of TCSC Associates released a
Tornado Terrain Following Realism Patch. The patch swapped the TFR's 1500 feet above ground level (AGL) setting for 100 feet.
In this mod, I modified the yellow-highlighted code of AVIONICS.ASM to use the 11(!) TFR heights of 35, 50, 90, 100, 120, 150, 200, 400, 600, 800 and 1000 feet AGL. To choose a TFR level, hit F9 (to activate the TFR), followed by the Up or Down Arrow key.
The modified AVIONICS.ASM file. The modified AIRCRAFT.ASM file. There are a few things to be careful of:
- 50 feet keeps you safe only from the shorter trees.
- 90 feet keeps you safe from the taller fir-like trees.
- 150 feet keeps you safe from the dreaded power-lines. No, you can't fly under them!
I have tested flying nap-of-the-earth with 90 and 100 feet AGL and above at a speed of 600 knots. The result is the Tornado faithfully hugs the ground. Choosing TFR heights of 35 or 50 feet AGL is more problematic as at certain points of the journey, depending on the steepness of the terrain, the Tornado's B-Risk indicator can light up and the Tonka will initiate an emergency pullup. Flying on relatively level ground at 35 or 50 feet AGL poses no problems for the Tornado's TFR.
I also modified EXTRNPAN to display the value of the TFRideAlt (TFR Ride Altitude) variable on the bottom status bar of an external view. This because once the gamer selects a TFR height, it times a few moments before the Tornado's actual altitude adjusts to match the ride height. The TFRideAlt value also serves as a visual feedback to the gamer as to which ride value he has selected.
Note the currently selected Ride Height (35Ft AGL) is shown on the status bar.
The current altitude of 306 feet is yet to match the selected TFR height of 35 feet AGL. The actual altitude now matches the selected TFR height. Both show 35 feet AGL.
An extremely dangerous height to hug the terrain! The gamer may choose to fly nap-of-the-earth at these two lowest levels, with afterburners fired up, in order to avoid SAM and enemy jet fighters. However one has to be extremely alert to avoid collisions or emergency pullups. Flying at 120 or 150 feet AGL is relatively safe, except for the taller office buildings. Safest is 200 feet AGL which Tornado-out-of-the-box's standard height.
The TFR mod is action, showing the TFR ride height of 90 feet AGL being used most of the time.
Note: I used Kenneth "ICEMAN" Larsen's Tornado Time Compression TSR to speed up the real-time action. It can be found here. Digital Integration's Tornado is the only DOS combat flight simulator, that I know of, that simulates Terrain-Following-Radar with various modes of autopilot. This attention to avionics authenticity sets it apart from all other DOS combat flight simulator. I hope this mod of mine will help to extend interest and enjoyment of playing this "Blast from the Past" simulation.
Regards
Frankie Kam