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Question: I heard about an aircraft called the VFW-Fokker 614 that had its engines above the wings. What were some of the negatives and positives of this design?

— Sam, Greensboro, N.C.

Answer: The VFW-Fokker 614 is a rare airliner. I only know of one remaining; it is at the Museum in Oberschleißheim, Germany. I was fortunate to see it in the summer of 2015.

The 614 was designed to be a short range, regional airliner seating 30-40 passengers. It did not sell well. It was slow for a jet and the engine manufacturer filed bankruptcy, causing very few airlines to place orders. The engine location limited the cruising speed while the small size limited the revenue it could produce.

It lost the market to the Fokker F-28 and the BAE 146.

Q: I once took a ride in a military jet with leading edge slats. The pilot seemed to dismiss them as minor, automatic. What are they?

— Kirk, Atlanta

A: Some early jet fighters, such as the F-86 had automatic slats, they help provide lift at lower speeds. However the F-86 was a single-seat fighter.

Using similar technology, the North American Saberliner, known in the Air Force as the T-39, had automatic slats. It is possible that is the airplane in which you rode.  The slats on this model were also used to provide lift at slower speeds, but were not particularly effective.

Q: A retired Air Force Colonel told me he has flown at 60,000 feet. What plane can do that?           

— Steve Barnes, Florida

A: Some of the fighter aircraft can achieve 60,000 feet, as well as special reconnaissance planes such as the U-2 or SR-71. The only civilian airplane that could fly at 60,000 feet was the Concorde.

Q: Regarding your previous column about engine mounts: I’m a commercial engine-mount engineer who designed and analyzed the DC-9, MD-80 and MD-90 engine mounts. The DC-9 and MD-80 aft engine mounts are very stiff and do a poor job of isolating transmitted vibration from the engine (not exhaust noise).  The MD90, which is also aft end mounted, has excellent (soft) isolation and the aft end of that aircraft is just fine.  Similarly, the EMB 175 and 195, both wing-mounted, generated noise in the 175 version but not the 195 version. Noise and…