July 29, 1996 NASA Ames Research Center Vertical Motion Simulator

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by	Michael R. Corder
	Portions of this article first appeared in the September 1995 issue of PACIFIC FLYER and are reprinted here by permission. All photos courtesy of NASA.

About the Author ... Mike Corder is a writer and computer consultant who lives in Aptos, Calif. He owns a Grumman Yankee (The Banana Slug), which has carried him to Iowa, Oshkosh (twice), Canada, Baja California and many other fun places. He is based at Watsonville, California, (WVI). He has an IFR ticket but does not consider himself an IFR pilot. His current fantasy is to build an RV-7A. He can't remember a time when he wasn't a plane nut and he has the pictures to prove it.

The folks at Moffett Field located in Sunnyvale, California, must have a thing about building things BIG. If you have ever overflown Moffett or driven past it on the Bayshore Freeway, you won't forget the size of the huge Navy blimp hangars. The largest was built to house the airship "Macon" and would swallow a whole squadron of P-3s without any effort. During Moffett's annual open house, they used to give hot air balloon rides inside the hangar!

NASA also has a big presence at Moffett called the Ames Research Center, and they also have the "build-it-big" disease. You might have seen pictures of their main wind tunnel which is the largest in the world. It has two test sections: the smaller is 40 by 80 feet and the larger is 80 by 120 feet. And, yes, this does allow them to stick an entire airplane inside and turn on the fans...all six of them!

World's largest sim

But NASA Ames also has another monster that most people have never heard of, but which is really worth seeing. This is the Vertical Motion Simulator (VMS) and it is the largest three dimensional motion simulator in the world.

You've probably seen pictures of the full-motion flight simulators that the airlines and high-end flight training companies use. FlightSafety International and American Airlines routinely feature them in their ads. They consist of a simulated airplane cockpit sitting on a platform which is itself supported by a number of hydraulic pistons to move the whole thing around. A few cables come out the side to connect the simulated cockpit up to the computers located near by. Stick a pilot in the cabin, fire up the computers, add a fiendish instructor, and you can emerge at the end of an hour dripping with sweat. (And presumably a much more proficient pilot!)

Well, the VMS is just like one of these that has been taking steroids — lots of them. Picture a big empty building that is 120 ft. high, 73 ft. wide and 36 ft. deep. Put your simulated cockpit inside this big empty space and let it move anywhere it wants to. Oh yes, don't forget to add some hydraulics to make it pitch, rotate and yaw at the same time that it is moving around inside the building. That's the VMS.

The mechanical pieces to make this all work are quite amazing. The main platform is moved vertically by two large pistons which extend 75 ft. deep into the floor below the VMS. These pistons support a large horizontal platform. On this platform is a carriage that can move from side to side across the entire building. Finally on top of all this is a structure that looks basically like the simulator we have seen in the pictures — an enclosed room that looks like an airplane cockpit once you get inside. In addition, there is a large cable assembly supplying power and moving computer signals between the simulated cockpit and the rest of the building. This entire complex is big and heavy — the motion system plus payload total about 140,000 pounds

Although the motions of the system are normally fairly restrained since it is used to simulate the movements of a real aircraft, the system is capable of some truly impressive action. During tours, the operators seem to like to show off their toy by putting it into a mode where it moves from the uppermost left-hand corner down to the lowermost right-hand corner as rapidly as possible. Then it quickly moves back to where it started.

Visitors usually wind up in open-mouthed amazement that something so big can move so fast. Folks with sensitive stomachs look away because just watching the thing can tumble your gyros. Those with more intestinal fortitude look to their tour guide and ask rather sheepishly "is anyone in there?"

(The answer is "No" for both humanitarian and safety reasons.)

Quick-change cockpits

Obviously, a piece of equipment like this represents a huge investment and you would like to keep it as busy as possible. NASA has taken an interesting approach to this problem: they've built a number of quick-change cockpit enclosures that NASA calls ICABs (Interchangeable Cabs). Four ICABs exist, and are configured to simulate different types of aircraft such as fighters, helicopters, transports and the Space Shuttle.

At any given time, one ICAB will be mounted in the VMS doing research and one or more of the remaining ICABs will be sitting on the ground nearby being configured for the next research project. In this way, the actual motion simulator is used as much as possible and each newly-configured ICAB can be largely checked out on the ground. Thus the only lost time is that used to dismount the old ICAB and mount the new one.

The ICABs are all similar but differ in the number of windows, configuration of the controls, instruments, etc. since they have to be able to represent a wide variety of current and planned aircraft.

Computers, computers ...

As you might imagine, this whole affair is driven by a large number of computers. Computers control the obvious things like how the whole thing is moving around, what the pilot sees out the window, and what the instruments are showing. But they also drive some less obvious things such as how the controls feel (remember they're not connected to anything real), generating sounds and vibrations to simulate a real aircraft, and driving experimental gear such as a HUD (heads up display). The computers used to support the VMS range from some which are a bit long in the tooth to the very latest wonders from Silicon Graphics.

One of the things that I found interesting is that the VMS features old fashioned computer rooms. You remember the kind — glass walls to keep the riff raff out, raised floors to hide all the cables, lots of air conditioning ducts in the ceiling. But the computer room I saw seemed to be empty. Lots of empty floor space with a few boxes that were several feet high seemingly arranged in a rather random pattern. The boxes looked about right to sit on. Then I realized those tiny little boxes were the computers that were making all the magic happen. It was the best demonstration I have ever seen of how fast computers have progressed in the last twenty years. Especially when you consider how many more times powerful those tiny boxes are than the computers that used to fill up the entire room not so many years ago.

Check it out ...

The purpose of all this hardware is research. Tests are performed on a wide range of problems. One of the most interesting uses of the VMS is to simulate the Space Shuttle. The VMS has databases to support the simulation of the Space Shuttle landing at Kennedy Space Center as well as Edwards, Zaragosa, Banjul, Ben Gurier, Dakar and Moron. Watching over someone's shoulder while they try to land the shuttle at the Cape gives a very good feel for just how quickly things happen and how small the margin for error would be if the pilot wasn't paying attention. The ability of the VMS to simulate alternate landing sites is a big plus because that's obviously something a shuttle pilot — flying the world's most expensive glider — will have to get right the first time!

NASA offers tours of the VMS, the wind tunnels, and several other fascinating aviation goodies that they have at Ames. Call ahead to schedule your tour, and be sure to tell them you'd like to see the VMS.