This is all very interesting, but it is still obvious that the elevators on all of these aircraft are far too sensitive and that trim displacement is disproportionately ineffective compared to other aircraft modeled on the basis of old data and reputation. “Easily trimmed” means easily trimmed no matter how you want to parse it. If an aircraft has “sensitive tabs” I would expect it to mean that the elevator and rudder require fairly minor displacement to wash out higher stick or pedal forces over a wide range of speeds. When one aircraft type is clearly identified by everyone who flew it as excessively demanding of trim and other aircraft types are specifically identified as needing very little or no trim adjustment by the same group of people I tend to think that I should need to adjust the one type fairly regularly and the others considerably less.
Let’s try to put ourselves in the 1930s-era high performance aircraft designer’s shoes. Aircraft are starting to exceed level speeds of 300mph (480kph), and if you didn’t place and design the control surfaces just right, control forces became greater than the average pilot could exert. The vast majority of trim tabs were on the rudders of monoplanes, usually big ones like the Martin B-10 until the mid-30s, at which point the technical issues appear to have been largely overcome and they start showing up on the rudders and elevators of an expanding variety of aircraft (and the ailerons of aircraft that had wing tanks).
The best pilots of the era tended to be drawn from the physical elites not least because you still had to exert fine control at a high force and because the buyers of high-performance military aircraft tended to be skeptical of depending upon new-fangled trim adjustment to keep the aircraft controllable. With good reason; changing trim was often clumsy and slow, unable to keep up with the higher speeds and acceleration of the modern monoplane fighters, so the designer/manufacturer was still expected to minimize the need (as opposed to the option) for trim for small speed variations. Trim was all mechanical, based on cables, pulleys, rods and screws motivated by human muscle and it was much slower than the digitally sensed and controlled systems we take for granted today, which were originally developed for high speed jets and found their way into civilian aviation, once they became cheap enough.
Simply put, trim adjustment in the late 1930s and early 1940s was considered a necessary evil to be avoided where possible and emphatically NOT a desirable convenience that obviates the need to exert even more (expensive) fineness in design and execution of the aircraft’s wings and control surfaces. It added weight and complexity to the aircraft, as well as cost.
So a wide range of speed change without requiring an adjustment in elevator or rudder was naturally going to be a primary design consideration. I would maintain that the Mustang was the most sophisticated high performance aircraft design around at the time of its introduction, and that the sophistication of its design would therefore be relatively sensitive to very minor changes.
How sensitive to change is the Mustang’s wing to minor changes? The wing was filler finished and hand polished. The upper and lower wings were covered with a surface to assure smoothness of the airfoil sections. The metal covered ailerons are statically, dynamically and aerodynamically balanced, and the wing’s efficiency is well known to be adversely affected by nicks, dents and scratches on the surface. Look at any shot of a Mustang in flight taken from above, and check out the wings—you will see nothing like the panel lines and obvious distinct panels of the fuselage on those wings (I think of all the Mustang models I built over the years and the care with which I ‘detailed’ those wing panels for the sake of ‘authenticity’…), even on aircraft that were in constant combat operations. I can picture the engineering officer responsible for maintaining those aircraft ordering 55 gallon drums of putty and reams of sandpaper to the bemusement of his buddies whose squadrons flew P-47s.
How adversely? It was found during factory tests that with a strip of wire 1/16 of an inch (roughly 1.6mm) taped along the leading edge of the wing, the aircraft would not leave the ground. America’s Hundred Thousand and every pilot I've ever read or talked to on the subject reports that the Mustang needed very little trim adjustment throughout its performance range and that tabs had to be applied with care; if the wings were that sensitive to minor changes, I would expect the elevators and rudder to be in very nearly the same class, that is, that very small adjustments would have great effect, and that they would not be necessary until a great deal of change in speed or power had taken place.
Is that consistent with what we see in the Il-2 Sturmovik ’46 Mustangs? Are the other aircraft I've mentioned treated in proportion?
cheers
horseback
|