Acceleration comparisons

[Mustang]

Great Post Horseback !!

Thats take long time to do.

But now...
what aircraft are OP ? vs RL

[horseback]

Originally Posted by JG27CaptStubing

Interesting to see what TD did to some of the FWs... No wonder you can easily get caught with your pants done

To be fair, this set of tests were done at just about the worst possible height for the FW; 3000m is quite close to the alt at which its supercharger moves from low to high blower, so the engine is not at its best here. I've just started doing the sea level (100m) tests, which should be more flattering to the Wurger.

cheers

horseback

[IceFire]

Probably a good idea to point out that context is extremely important. As these acceleration tests were all done at the same altitude. Some aircraft will be better and others worse at this altitude... nothing stays the same across the range. It's not one acceleration level that extends from 0 to 10,000 meters.

You have to know your plane. I know that the Tempest V between 3000 and 4000 meters is less capable against the FW190D-9 (which I consider to be its chief rival) as the stage 1 supercharger starts to run out of steam and you're just about to switch to the stage 2. Depending on the D-9 model year... this is the worst altitude to fight at. Take it lower or higher and the Tempest is faster and more able. Context!

[MaxGunz]

I would have problems with a plane that didn't get noticeably more lift for a 6 mph speed increase.

Check around, there are 10-turn and IIRC 20-turn pots in various ranges.

Less fine-adjusting but oh so desirable, check the unit price:
http://www.futurlec.com/PotSliding.shtml
There is a shipping charge but that can be as low as $4 to $5.
http://www.futurlec.com/Delivery.shtml
The package comes from Hong Kong so expect about 2-3 weeks wait.

Something else you could do is put a 10k or smaller pot in series with a 100k pot (or a 1k and 10k) and have both coarse and fine adjustment knobs on the same circuit.

[majorfailure]

Originally Posted by horseback

The real P-38 needed NO elevator (or rudder) trim for speed and throttle variations (per America’s Hundred Thousand), but the Il-2 Sturmovik Lightning will go literally straight up when you push the throttle forward without shoving the stick three quarters of the way forward at the same instant and punching the elevator trim button constantly for as long as the speed continues to increase. (and it's a lot slower than the real thing was)

That makes no sense, as this would mean the P-38s wing would generate the same lift all over its speed range. But compared to http://www.wwiiaircraftperformance.org/ data its speed seems fine.

Originally Posted by horseback

The real life P-47 needed no elevator trim for initial acceleration, but the in-game version does the same thing as the Lightning, with the added entertainment value of needing a ton of right rudder as well, and like the Corsair, the nose tends to dip as speed increases in the level plane; by this I mean that the angle of attack varies significantly with speed, something I've never read or heard about in these aircraft in over 45 years of reading, modeling or personally talking to men who flew these aircraft (you'd think that somebody would have mentioned it...).

And how else if not with changing AoA should a plane regulate its lift when changing speed? Faster plane - wings generate more lift with same AoA, to keep the plane level AoA needs to decrease.

Originally Posted by horseback

As for the Spitfire, I have no documentation or discussions of its trimming requirements at all, which would indicate to me that it was fairly well-behaved by the standards of the day (it was well-enough known as an easy aircraft to fly that even German pilots would say "Anyone can fly a Spitfire," which implies to me that they considered themselves more manly because they had tamed the 109...). Yet the Il-2 Sturmovik Spitfires demand a lot of trim adjustment, about the same degree as the Mustang, although with the added difficulty of that hard to read Turn and Bank needle arrangement.

I'd think the reference that anyone could fly a Spit does not mean the plane is trimmed easily, but it is easy to fly in combat maneuvres, and it does not stall viciously and recovers good (I'd think the IL-2 Spitfire meets all those criteria).

Originally Posted by horseback

In short, in this simulation these specific aircraft are much harder to trim and control than the real ones were, particularly when measured against the other WWII fighters depicted in this sim, and all of them demand un-historic trim adjustment in the form of multiple button presses for relatively minor variations in speed and throttle settings, as well as climb or diving conditions, and it is next to impossible to roll your trim settings to a set position in anticipation of a sudden change in speed or throttle, as the real-life pilots did regularly.

Yes, we need some indicator or gradation or whatever to see where trim currently is, and how much we apply. Then one could remember:
SpitIX, 90%, 3.5k alt, left 7 (or 1.5° or whatever) trim, down 34 (or XX° or whatever) trim - flies straight. Currently we can only do this if we reset trim to 0 and then apply trim settings, but this is counterproductive, 'cause except at landing speed a Spit with neutral trim severly noses up.

[horseback]

The following paragraphs are taken whole out of America’s Hundred Thousand by Francis Dean. These are the complete sections labeled Trimming with nothing left out. Bear in mind that these are all American fighters, and any comparisons the pilots quoted herein are to other American fighters, not the Zero, not the Spitfire, not the Lavotchkin and not the Bf 109. This is just part of the picture the author paints; the sections on Ground Handling, Takeoff & Climb, Dive & Recovery, Maneuvering, Approach & Landing, Stalls & Spins, and the Gun Platform and Weapon performance paint a pretty complete picture of how these aircraft flew from a generally American perspective. Most tend to reinforce the picture painted in the Trimming sections. I have underlined or italicized key words or phrases in some cases.

I simply lack the time and patience to transcribe all these in full, even assuming that it would not violate some copyright rules. I would recommend however, that anyone who wishes to argue the point transcribes at least the full paragraph that he is citing instead of engaging in the usual cherry picking.

One interesting note: The second paragraph in the P-40’s Maneuvering section starts with “…P-40 airplanes were very maneuverable for US Army fighters, some said better than a P-51.”

Trimming Sections from America’s Hundred Thousand:

P-38

The P-38 could be trimmed out to be pleasant to fly, and trimmability was rated good to fair by the majority of pilots in one survey. No adjustment of rudder or elevator trim was required with power or speed changes.

P-39

P-39 trimmability was good. Elevator tab action allowed stick force to be trimmed to zero throughout the speed range. Aileron trim changes with speed or power were negligible to 400 mph IAS. Above that speed, there was an erratic trim force change, possibly caused by aileron fabric bulging. There were directional trim changes in climbing and diving, but they were not extreme.

P-40

A major aspect of flying the P-40 series airplane was handling trim changes from power and speed changes. A veteran AAF pilot stated “The trim changes with speed were more than in other contemporary fighters.” Typical of many single engine propeller fighters, the vertical tail fin was slightly offset to counter propeller slipstream effect at cruising speed. In a dive, as speed increased, more and more left rudder had to be added; slowing down in a climb some right rudder was needed. One pilot said “—a drawback was having to virtually stand on the left rudder pedal to keep the ball centered—it could be a real handful in a loop” (where trim reversed from dive to climb and then back again). Although directional trim tab power was available to zero out pedal force, left rudder trim could not be rolled in fast enough with high dive acceleration. No matter what P-40 version was involved, it was the same: “In the air, the Tomahawk tended to yaw considerably with speed changes”, needing directional trim, and for the P-40E/H87A: “Every power and speed change brings an immediate trim change which the pilot must either counteract or trim out”. The H87 was, if anything, worse than the H81 Tomahawk.

On the P-40E lowering the landing gear made the aircraft slightly nose heavy; there was no appreciable trim change with flap positioning. Dropping a belly tank resulted in minor tail heaviness. The elevator trim system could take care of these effects as well as longitudinal variations due to speed and power changes.

P-47

There were some differences in trimmability between models. “The P-47D-25 trimmed harder than the D-15” but generally longitudinal and lateral trimmability was satisfactory on the P-47, and the tabs were very sensitive. There was very little trim change with gear retraction and initial acceleration; dropping flaps made the airplane slightly nose heavy. Longitudinal trim changes with power and speed changes were small, and elevator tab power was sufficient to trim stick forces to zero at all speeds and all normal center of gravity locations. The aileron trim tab action was sufficiently powerful for all flight conditions, and the rudder tab could trim pedal forces to zero at all speeds above 120 mph IAS in the power on clean condition. But as with other fighters, like the P-40, the rudder trim force change with changing power or speed was objectionably high.

P-51

ALLISON powered Mustangs were particularly notable for lack of required trim changes. Power or flap setting changes gave only small trim variations, and the same was true of gear retraction. The changes in tab settings for climbing and diving were negligible. Tab controls were sensitive and had to be used carefully.

Trimmability was also quite good in MERLIN Mustangs, and tabs were sensitive. In these versions directional trim changed more with speed and power changes. When the rudder trim system was changed and rigged as an anti-balance tab to give opposite boost, a resulting disadvantage was more tab was required to trim the aircraft from a climb into a dive.

Along with trimming the airplane for longer term steady flight conditions, some pilots trimmed their aircraft almost continuously to wash out any high stick or pedal force during maneuvering in combat.

F4U

The Corsair was easy to trim out for climb. Trim changes from landing gear and flap retraction were minimal, and those for speed and power changes were quite handleable. In cruise condition the airplane could be trimmed for hands and feet off flying with little trouble. Pilots almost universally rated F4U-1C and -1D trimmability as good. In a dive, as with some other US fighters, a considerable amount of rudder trim was required to zero out pedal force which was high if this was not done.

F6F

There were nose up trim changes with gear and flap retraction, though they were minimal, and the same was true of initial acceleration into climb. In general, there were substantial trim changes both directionally and laterally with speed and power changes, but tab action allowed trimming out control forces to zero except for the rudder. At low speed and high power rudder pedal force could not be trimmed out fully. Most pilots thought trimmability was generally good, though some made the following comments ‘Lack of trimmability”, Excess rudder trim change”, and “Aircraft requires excessive trim” (three pilots). It was noted that in a dive control forces could not be trimmed out quickly enough.

MY COMMENTS:

P-38: the in-game model forces you to apply a LOT of nose down pressure and trim when you apply power, which contradicts the description from Dean. It is also quite a bit slower to accelerate than the in-game P-51B/C, which just doesn’t make sense, if you look at the test records, even those comparing the early P-51Bs without the fuselage overload tank. From the descriptions from several wartime pilots’ memoirs and historical reports as well as from America’s Hundred Thousand, I expected that the Lightning would ‘dither’ for a tiny split second before surging almost straight ahead when full power is applied, but the in-game version will immediately head almost straight up when 100% prop pitch and full power is applied if you don’t anticipate it and force the stick/yoke well forward immediately and start punching in nose down elevator trim with your eyes fixed closely on the climb & dive indicator. I expected to dial in some trim as speed increased, but I didn't expect to have to bang the stick almost all the way forward just to stay level.

P-39:A bit of a shock when I read Dean’s comments on the Airacobra; I thought it would be a bit of a trim hog, but instead the real thing seems to have trimmed out fairly easily at most level speeds. The problems it had were apparently not due to trimming issues so much as the sensitivity of its controls compared to other fighters of its time—I assume that unless the pilot had fully mastered its (several) unique quirks, he could get himself in trouble if he fell back on ‘muscle memory’ acquired in other types. The in-game ‘Cobra is a bit twitchy (you always feel like you are balancing on the head of a pin) and at the same time a bit too good if you don’t remember that the ‘Cobra’s issues with the USAAF in the Pacific in 1942-43 were more because of poor maintenance and field reassembly of hurriedly shipped in aircraft due to a lack of experience and documentation rather than to poor design or quality of production at the factory.

P-40: The Tomahawk and Warhawk were considered to be among the most maneuverable of the Western built fighters in WWII as long as they stayed below 15,000 ft, but it took a very good pilot (and a strong one, at that) to get the most out of it. It was not a good aircraft for persons with attention deficit disorders, because it was notorious for needing constant trim and engine adjustments—nobody relaxed in a Warhawk unless it had been on the ground with the engine off for a good twenty minutes. After mastering the P-40, most WWII pilots would find almost any other fighter of the period relatively easy to control and exploit (the P-38 was easy to fly but hard to master, but veteran combat groups in the Pacific transitioned into it seamlessly from the P-40). I was well aware that the P-40 series was considered very tricky to take off and land, and that taxiing it was considered a bit of a trial, so the Il-2 Sturmovik Forgotten Battles/’46 depiction has always seemed far too user friendly to me. In-game, it requires much less trim adjustment than even the P-39, and is one of the easiest fighters in the game to master. It is by far the most charitable depiction out of all the American built fighters depicted in the game.

P-47: This one is like the P-38 in some ways; in-game, the elevator trim is consistently excessive, and the rudder is fairly easy (too easy, if Dean is to be believed) to adjust. In-game, at 270kph/170 mph, it wallows like a pig and is seriously unstable with a pronounced nose high attitude, which hardly makes sense for a range of speeds that was commonly used for economy cruise and landing approach. In addition, the angle of attack will lower significantly as speed rises, which makes it hard for the pilot to judge whether he is actually keeping anything like level flight, and will complicate your firing solution when diving on an opponent. Like the P-38, the in-game P-47 wants to go sharply up the moment power is applied, and it also wants to turn left because of torque and p factor; if you don’t apply significant nose down pressure on the stick and kick in a LOT of right rudder as you punch the throttle and prop pitch forward, you’re going to waste all that power going in the wrong direction. Again, given the weight of the Thunderbolt, I would expect a slightly longer ‘dither’ than the Lightning, but it should surge more straight ahead than up, at least at first. Also, my reading leads me to believe that the P-47 was pretty fast in a straight line, even if it took a while to get there (especially with the early ‘toothpick prop’ versions) at lower altitudes, while Il-2 Sturmovik ‘46’s depiction makes it not only slow to reach top speed (and very prone to overheat) at 10,000 ft, but that top speed seems a bit short of what it should be.

P-51C: The Mustang should be the easiest US fighter in the game other than the P-38 to trim in almost any conditions by a fairly wide margin, if we are to believe Dean and testimony from pilots of the era. The consensus seems to be that the in-game Mustang demands elevator and rudder adjustments for every 10kph/5mph variation in speed. To put it lightly, that is bogus; Dean’s description says that the Merlin Mustang’s trimmability was “also quite good” in obvious reference to the standard of the Allison powered versions which needed almost no trim adjustments for speed or power changes.

The flight models of both the DCS Mustang and the Wings of Power P-51D for FSX tell me that the rudder trim requires slight adjustments for power increases of 10-15% (5-8 inches of added manifold pressure)or speed increases in the 25-35 mph (40-55 kph) range and that the elevator trim hardly needs touching at all, which is consistent with wartime reports and comparisons that suggest to me that the Mustang was rated more highly in maneuverability than it might have technically deserved because it was much more easily flown with precision than its contemporaries;; i.e., a Mustang pilot could take his aircraft to its limits with more confidence right away than the pilots of other high performance fighters of the period—there was considerably less of an exploratory period needed for it.

The in-game version’s extra acceleration, which is clearly superior to the much lighter Spitfire Mk IX, seems like an attempt to mollify those players who know that the Mustang was one of the all-time great fighter aircraft—the difficulty of bringing your guns to bear because of oversensitive elevator and rudder trim (added to the sheer unreliability of the needle and ball the microsecond you stray from the straight and level) or of achieving coordinated maneuvers are supposed to be excused by the old song and dance about superior training & numbers, plus the—(“See? See? We didn’t really nerf it.”)—speed and range.

F4U:This one is treated a lot like the Mustang in that it has been given almost spectacular speed, but it needs an awful lot of trim adjustment to maintain its E advantages. The moment you start to roll into a turn or pull up into a climb, you will be out of trim and bleeding energy in arterial spurts. Again, this seems to be contrary to the historical record. It is also like the P-47 in that the angle of attack in level flight changes radically (it seems like a drop of several degrees, but if we use the gunsight circle as the standard, it is about half to two-thirds the circle’s diameter down from the 270kph starting speed) during acceleration, but not so much at the same speeds when flying back to the starting point. At certain speeds, it will seem to drop suddenly (or else I’ve been very consistent about over-applying the nose down trim), and the pilot has to pull up on the stick sharply but very precisely in order to stay level.

F6F: With this one, you are almost constantly adding and subtracting trim; three clicks nose down to get it to react, then one or two up to correct, wait two seconds and then repeat the process. Again, once the initial rudder trims are made, it seems to stabilize directionally (which seems to me to contradict Dean's description). Bear in mind that we are talking about speed changes of 10 kph, or a bit over six miles an hour; there's quote in the P-40 Comments section where one pilot complains that he had to make adjustments for every ten miles an hour, or about 16 kph. If adjusting for 16 kph variations in speed are excessive, what does that make adjustments (and I mean absolutely necessary adjustments; if your attention wanders for two or three seconds, your altitude can change by two or three hundred feet at those speeds) for speeds of less than two thirds of that?

In every case except for the P-40 (which appears to be sort of a charity case), the trim requirements are grossly excessive. Compared to say, the Ki-43 or Ki-61 (or any late-model Soviet fighter), the elevator trim requirements in particular for late model American fighters (and the Spitfire, for that matter) are cartoonish, especially for the Mustang and the P-47. In fact, I would class the trim modelling for the Mustang, P-47 and Hellcat about one and a half to two times what should be required for the P-40 in the context of this sim.

The 'straight up' when accelerating tendency in the P-47 and P-38 is counter-intuitive; these were big heavy fighters, and as Dean confirms, should surge almost straight ahead at first, especially the P-47, which like the P-40, was well-known to almost resist entering a climb from level flight. The AOA thing is particularly troubling in aircraft that need to land on a carrier. I could accept some drop in the nose as speed increased, but not to that degree. Of all the fighters of WWII that I have read any amount of information about, only the Focke-Wulf was acknowledged as having a lowered AOA with cruising/combat speed (and I recall some howling over the Il-2 Sturmovik/Forgotten Battles Butcherbirds lacking that feature).

In my test runs so far, the FW doesn't seem to dip as much as the Corsair, Hellcat or P-47; I'm going to have to take a few screenshots for comparison while I do my sea level tests, since the horizon will make it easier to judge.

As I have said, anyone should be able to duplicate my results and see for themselves what I am describing. If you normally place your stick on a keyboard tray, I would recommend that you make sure that you have enough clearance from the desk edge so that you won't lose the skin off your knuckles when you have to shove your stick forward after you punch the throttle.

cheers

horseback

[Woke Up Dead]

Hey Horseback, in your Soviet planes chart you have two for the La-5FN; I assume the slower one is actually the La-5?

[horseback]

Originally Posted by MaxGunz

I would have problems with a plane that didn't get noticeably more lift for a 6 mph speed increase.

That might be appropriate for a general aviation private plane with a maximum speed of 170 knots, but for a fighter capable of advanced acrobatics with an engine spinning twice as many blades three times as long (& at least five times as heavy) and hosting five to ten times as many horses?

cheers

horseback

[horseback]

Originally Posted by Woke Up Dead

Hey Horseback, in your Soviet planes chart you have two for the La-5FN; I assume the slower one is actually the La-5?

The two La-5FN data lines are the same; apparently, I managed to double select its data for the chart somehow. There is a separate line for the La-5F (a rather attractive sky blue, I believe), and yes, it is slower than the La-5FN.

cheers

horseback

[MaxGunz]

Originally Posted by horseback

That might be appropriate for a general aviation private plane with a maximum speed of 170 knots, but for a fighter capable of advanced acrobatics with an engine spinning twice as many blades three times as long (& at least five times as heavy) and hosting five to ten times as many horses?

cheers

horseback

Still the same only more so. Lift is by speed squared, AOA and constant factors aspect ratio and wing area. As speed increases, AOA must decrease to keep level flight.

However the tailplane part of the airplane balancing act also has a lift and it's own AOI relative to the main wings which must affect need for trim.

If the P-38 tailplane actually forces the nose down more with increasing speed then the COL moving back as critical mach is approached would turn that into a bad thing... which may or may not be part of the P-38 death dive phenomenon.

I would be very careful pulling text out of books and treating everything with a key word as if on an equal basis with every other. Those comments come from people with different backgrounds and if filtered through yet another party with another background and then evaluated by a reader with a completely different background it's all too easy to end up in a subjective mess especially if the last person tries to use unqualified statements as hard references.

Ie, stick with controlled test data or have your experts on hand to qualify and explain just what they mean.
Don't play at guessing to arrive at your own conclusions even when you have some facts to go with the guessing. I have facts about lift and balance but only questions and not conclusions about the FM to make from those.

If the P-38 didn't need trim then why is it there? Did that quote about not needing trim with power of speed changes apply to small changes or to the full safe operating range? We all know that at some speeds that use of trim and slowing down did become needed, don't we?

BTW, what do you think of using 2 pots for coarse and fine adjustment? I've never seen such but series resistances do add.