By Rich Coppenbarger

April 15, 1999

A couple of years ago I was heavily involved in a project called pilot-directed guidance. It involved improving helicopter flight low to the ground, in what we call the nap-of-the-earth. The military would like to have this capability in order to avoid enemy threats. The idea was to allow the helicopter to fly as low to the ground as possible, below the treetops in order to sneak up on an enemy and remain undetected by radar. The problem with doing this is that helicopters tend to run into obstacles at low altitudes like power lines and tree branches.

We put camera sensors on the helicopters and developed guidance and control laws to basically assist the pilot in identifying what these obstacles were and maneuver away from those obstacles. I contributed by developing state of the art software called pilot-directed guidance. I think the best way to describe this is that it is kind of like a horse and a rider. If you imagine a horse kind of trotting over the ground, the horse is usually smart enough to avoid most simple obstacles with out the rider giving explicit directions to avoid a rock or tree. We wanted to make the guidance system like a smart horse. We wanted the guidance system to be able to avoid the low-level obstacles automatically. The pilot would be able to give the high level steering commands, kind of like pulling on the reigns of a horse.

I tested this out on simulations on NASA's Vertical Motion Simulator. This is the largest vertical motion simulator in the world, it can move up and down 60' and from side to side 40', more than any other simulator. Of course it's very realistic when you step into the cab. There is realistic computer-generated imagery up on the windows and it feels very much like you are actually flying a helicopter.

First we had to develop a mathematical computer model of the helicopter itself. This needs to run on the simulator and simulate the basic behavior of the vehicle you are experimenting with. In this case we were testing a UH60 helicopter called a Black Hawk. We then added pilot-directed guidance to the simulation. This involved making a pilot-directed control system interact with the vehicle and putting special displays in front of the pilot. At first we experimented with a heads-up display. This is a holographic image that you put in front of the pilot that contains various symbology. This allows the pilot to look straight out the window and pick up information like air speed, obstacles, and terrain without having to look down. I believe that even some automobiles have this type of display. I know I've seen holographic displays of speedometers on the windshield of certain automobiles.

We finally ended up using a helmet-mounted display system, which gave the pilot a lot more range for looking at different symbology. In other words the pilot could turn his head and see virtual imagery that was placed out there in the scenery.

We did many simulation runs in low visibility conditions. Typically if the fog is really dense and the visibility is below 100 feet, the pilot wouldn't be able to detect a tree that was 200 feet away. We presented the symbology by painting it on the helmet-mounted holographic display system. In a sense this allowed the pilot to see through the fog. Even without the guidance system, the advanced imagery went a long way towards improving the ability of the pilot to fly the helicopter in poor weather conditions and at low altitudes.

We worked closely with McDonald Douglas Helicopter Company on this project. They were interested in developing displays for a rotorcraft pilot associate system designed for their Apache attack helicopters. We also had pilots from Sikorsky and Boeing helicopters participate in our simulations, along with numerous military pilots.

When you first complete the simulation development, you have to test it and usually the research engineer is the first person to test the software. Unfortunately, I spent many occasions stranded in the cab of the simulator in the VMS because of software glitches. No one can encode perfectly and there are always some bugs in the software. Normally I would only be stranded for fifteen or twenty minutes while they worked out the bugs. Sometimes a software bug can cause the simulation cab to jolt, vibrate, or make loud noises that can be a little frightening for the occupant. Once the engineers have played guinea pig and ironed out the major problems and fixed the bugs, the pilots get to fly in order to carry out the research.