Who said modelling was useless?

[r988]

Found this interesting little story in my travels, some of you might be interested.

link said:

www.techwr-l.com/techwhirl/archives/9509/techwhirl-9509-00690.html TRMOAS: While writing the engine maintenance manuals, one of our customers was the Republic of Singapore Air Force. They'd taken brand-new F404 engines and dropped them into rather old A-4 Skyhawk airframes. The result was actully very good, they wound up with a very hot little airplane that could outfly most other things in their class. Our folks knew the engines very well, of course, but were far less knowledgable about the airframes. The RSAF suddenly started to register complaints about the engine, saying that they were experiencing compressor stalls. (That's a condition that arises when the engine can't handle turbulance or airflow distortions in the air flowing into the engine.) The normal symptom is a loud "bang" from the engine area (not an explosion, more like a slamming noise). There is also a momentary loss of performance, only a nusiance in peacetime but dangerous in combat. RSAF was very unhappy. The tech pubs folks heard rumors that the engine was experiencing these occasional compressor stall, but we had no data. Engineers started to look into the problem, but were stumped. I was at the bottom of the information chain, nobody told me details. About six months into the study, no answers in sight, I was sitting in a meeting when the subject came up. For the first time, I heard details on the problem. One or two pilots were experiencing the problem, and only when they made certain aerobatic maneuvers in their airplanes. "Oh." I said. "Of course. That explains it. He's flying an A-4. It's not a compressor stall, and that's why you can't duplicate it." Amazed looks from around the table. I continued "The McDonnell-Douglas A-4 Skyhawk was designed with an automatic movable wing leading edge extension. To allow proper lift and control, at specific times the leading edge is supposed to move forward, and provide a little more lift. The pilot has no control over this. But it never worked quite right, and those leading edges were well known for actuating on their own when the pilots make certain aerobatic maneuvers. It got to be so annoying that when the U.S. Navy's Blue Angels flew Skyhawks, they had to rivet the doggone things shut." The motion of the leading edge would also account for the slight change in flight pattern the pilots had reported. Apparently, that was the problem. And, as none of the engineers had the right airframe/engine integration background, it had never crossed their mind. Within a week, the issue was resolved. And I almost hate to confess where -I- found the information on the leading edge problem. It was in the instruction sheet for a plastic model kit of the Blue Angels A-4 Skyhawk.

[Le TVR]

IIRC the TigerMoth had similar automatic LE slats that would operate on their own initiative (ie approaching stall)
Riveted shut was also an accepted cure!

[Eric Mc]

Also a feature of the Messerschmitt Bf-109 and the Morane MS880 Rallye series of light aircraft.