Acceleration comparisons

[horseback]

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

[JtD]

Originally Posted by horseback

...but it is still obvious that the elevators on all of these aircraft are far too sensitive...

Actually, if anything is obvious, it's that the control surfaces are far too insensitive. There's a whole bunch of fighter aircraft that could reach the stall angle of attack or designed load factor with as little as 10% control input from trimmed level flight. And as trim is linked to control sensitivity, obviously, trim is too insensitive as well.

[MaxGunz]

If you can't overcontrol at high speeds or in turbulent conditions then you'll get sweet F-A control at low speeds.

Terms to look up are Maneuver Speed and V-Speeds.
Going from flight sims in the past, maneuver speed being the fastest you can pull full stick deflection on ONE AXIS is about 240-250 mph for the P-51. By 360 mph it's -probably- not safe to pull half way, I leave it to someone else to guess why.

Note that in WWII fighters the pilot can't take what the plane can. They had feel and were less prone to trying things that gamers who have no feel take for granted. Also that IL-2 is a simulation. When some G-limit (like 12 G's) is reached even momentarily it is bye-bye wings. Pilot blackout though seems to have a time element.

BTW, I just came across FreeChecklists.net. Here is the P-51 page:
http://freechecklists.net/Resources/.../P-51+Mustang/

And from the 1944 manual on page 19 under Maneuvers Prohibited:
"It is impossible to do a good snap roll with the airplane and most attempts usually end up in a power spin."

[horseback]

Originally Posted by JtD

Actually, if anything is obvious, it's that the control surfaces are far too insensitive. There's a whole bunch of fighter aircraft that could reach the stall angle of attack or designed load factor with as little as 10% control input from trimmed level flight. And as trim is linked to control sensitivity, obviously, trim is too insensitive as well.

Maybe what I should have said is that the aircraft themselves are too sensitive to speed variation and that they are insensitive to elevator or rudder trim while being oversensitive to small rudder and elevator inputs as speed changes. The point remains that constant trim adjustment is demanded over a very small range of speed and that when compared to other aircraft of the era (and especially aircraft well-known to be less aerodynamically sophisticated, as in the case of the P-40 series) the trim model is grossly out of proportion for this relatively tiny group of fighters. It seems to me that the original game was optimized for FFB sticks, and for those of us in the majority with spring tension sticks, trimming out by 'feel' is a bit impractical, because the spring tension is just as high with the stick 5 degrees out of center as it does with it 45 degrees' deflection.

It is just silly to require the Player to click the elevator trim three or four times for every speed variation of less than 20kph indicated (plus a couple of clicks of rudder trim to compensate for nose angle immediately afterwards) for aircraft that history (and multiple current examples) shows (1) didn't require it and (2) will be constantly varying in speed and angle of attack with no accurate on screen display to indicate vector/trim state.

That this group is composed almost entirely of aircraft that exist in large numbers that fly to this day leads me to wonder if their FMs are a bit too detailed for the game engine or that there might be some kind of common mathematical error somewhere, possibly as a result of the conversion from Imperial measurements to metric.

Most of the aircraft instrument panel displays are hard to read at best (always in Wide View, and often in 'Normal' view) and far too many of them are grossly inaccurate; artificial horizons that are indistinct or offset to an exaggerated degree, climb indicators that are slow and frankly, lie much of the time (when you have an indicator that measures feet of climb in feet per minute, and one deflection division mark is supposed to represent 100 feet, you shouldn't be able to change heights by 60 or more feet in less than 3 seconds with the needle just above the '0' mark, and I experienced this routinely in a great many of the aircraft I've tested so far, the notable exceptions being the Soviet and the IJA fighters).

Two changes seem obvious to me; first, the addition of a temporary trim state display similar to the ones we get when we adjust throttle, prop pitch, supercharger or radiator settings. I'd like to see something along the lines of x% up Elevator Trim, x% Right Rudder Trim, and x% Right Aileron Trim with full trim deflection being 100%.

Second, make the cockpit instrument displays consistently accurate to exactly the same standard for every aircraft; currently, there seems to be a great deal of variation in instrument accuracy and readability from inside the cockpit.

I understand that unless there is one common conversion error that is easily detected, major changes in FMs is way more work than can be fairly asked of TD, in the near or far term, but the community shouldn't pretend that the inaccuracies aren't there.

cheers

horseback