This article first appeared in the April 1970 Flight Test News.
Don Evans is a rather slightly-built man, quiet and unassuming, perhaps exhibiting intensity and a trace of nervous energy, You might expect to see him on a golf course or a tennis or handball court. You might think of him as a bridge player (and you’d be right, he’s very good). But you couldn’t cast him as, say, a center or a bruising fullback. Too small for such a hazardous profession, you’d say, and he might agree.
Yet Evans is in a very hazardous job and has been for years. And for a time, his avocation was also hazard-riddled. For Evans has been a test pilot for years and one of his hobbies (until his wife coaxed him away from it) was automobile racing. The memory of those racing days, from 1962 through 1967, is so bright it appears as though a matter of the moment: mention auto racing and he smiles and his eyes light up, and he says “It was a lotta fun…”
Fun? The timid among us-and there must be millions upon millions of us-blanch a bit. Don just smiles. His attitude toward test flying is similar, and he talks of spins, rolls, stalls, yaws-and even getting shot down over Korea while flying an F-80-with apparent unconcern, in the level tone of a statistician reporting the day’s activities to his wife. The drive and fierce interest in flying comes out almost explosively, however, when he gets talking of individual planes, differences in mission-purpose, and the day-to-day work of an engineering test pilot.
No plane for all reasons
“No single plane is capable of carrying out all the types of missions that have to be performed,” Don says. “There have to be compromises, and there’s no way out of it.” He cites the U-2 (which he flew for three years), the A-6A, and the F-14 as examples: “The U-2 was a very light aircraft designed to fly at very high altitudes over very long distances. That’s all it could do. The A-6A, which I’m flying now, can’t go as high or fly for as long distances, but it can pierce the blackness of night and pinpoint an obscured target, and then either bomb the target precisely or lead a fleet of F-4s to the target. The F-14 is something o again-an air superiority fighter designed to overwhelm any other fighter in the world. It has to be faster and more maneuverable than an A-6; that’s its reason for being, fighting enemy aircraft.”
But for all of the logical and imperative differences of missions that lead to corresponding differences in aircraft design, there is, underneath it all, a set of test considerations that apply to all. Evans outlined four: structural tests, flying qualities, performance, and carrier suitability. (Because he has an Air Force background, he thought it inappropriate to talk of carrier suitability.) He spoke of the remaining three areas, mainly in terms of what the test pilot looks for when he’s putting a plane through its paces.
“You have to prove out the entire flight envelope,” said Evans, “meaning that you not only fly to the limits of what the plane is supposed to do but you push it further, to make sure it’ll live up to its billing. For example, you might roll it, do pull-ups-just about anything you can think of to find out whether it’s going to hold together. You might even overload a section of it to force it almost to flutter.”
Hazards of flight testing
Almost, in this case, is critical, for as Don points out, a real flutter can literally destroy an aircraft in less than a second! Obviously, to approach but not get flutter takes (among other things) a truly expert pilot. More important, both the pilot and the plane are heavily instrumented and every quiver, every breath, is read from equipment on the ground; and the people there can see it before you feel it. He also points out that whenever something new is put on an aircraft, such as heavy avionics gear, it could be a “new plane” and, therefore, must be test-flown. (This is one of the reasons that wind-tunnel tests of an original aircraft may not be valid after a plane has been modified.)
The question of flying qualities encompasses a number of things, such as how much stick force is needed to move a plane from one G to two Gs to three Gs. How about stalls-and are there stall warnings? “In the course of testing the plane” says Evans, “you have to stall it and spin it. You have to think of the guy who might be flying it in combat zones or under adverse conditions: He has to know exactly what he can and can’t do with that aircraft, and giving him that information is our job.”
Evans also pointed out a couple of things that “some of your readers may not know: It’s the low pressure over the wings that enables the plane to fly; and, although we have to make spins in all configurations, you can stall without spinning but you can’t spin without stalling.
Flying any modern fighter is much different, says Evans. The SAS (Stability Augmentation System) automatically smooths out a ride so effectively, he points out, it “cons the pilot” into thinking that the aircraft is more stable and easier to fly than it actually is.
“Then there’s performance testing, determining such things as fuel consumption at various altitudes, at different speeds; thrust; drag; takeoff and landing distances; climb rates; eight Mach dynamic performance testing at 30,000 feet, and so on. And, oh yes: Did I mention weapons separation? Launching a missile in flight..that’s critical.”
Back to the desk
But, as Evans had said earlier in the discussion, test flying isn’t all there is to it. “I probably spend as much as 50 or 60 percent of my time at a desk, keeping current, hashing over design or flight problems, and, mostly, writing flight reports. Really, the reports can be the bulk of the job. We have to put it all down-when we went up, under what conditions, what we were supposed to check out, what actually took place, where were the bugs and surprises-the whole thing, so that everyone with a need to know does know. That’s it.”
In a way, that is it. In another way, it isn’t it. For what is inside a man that draws him toward this extraordinarily hazardous type of work? Don smiles and shrugs his shoulders.
This article first appeared in the April 1970 Flight Test News.
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