Acceleration comparisons

[horseback]

Originally Posted by majorfailure

I'll ask again, how else do you think the wing can generate the same lift at a higher speed (e. g. plane stays level), else than decreasing AoA?

First of all, I meant it as a matter of degree; there has to be a reasonable limit of movement down as a result of the direction of thrust and limiting action of the elevator. I don't buy into the notion of an aircraft like the Thunderbolt wallowing with its nose up in the air at the speeds it travels when it enters the landing circuit or in economy cruise. It is simply exaggerated, and again, appears to be limited to that same group of fighters that there is the greatest amount of data and modern pilot reports about. We are talking about relatively straight, high lift wings across a fairly limited (by modern standards) range of speeds. We aren't talking about swept-wing jets here.

The Soviet aircraft all have a 'drop' of around a quarter of the WW gunsight circle's diameter, and it generally takes place between 370 to 400 kph ias, varying somewhat from Yak to LaGG to La. It also appears that the drop is not as great when the aircraft is in a constant speed compared to when it accelerates and that some aircraft have little or no 'drop' with acceleration or greater speed in general.

My impression so far is that aircraft like the Lightning, Corsair, Hellcat and P-47 have much greater 'drops' and that at certain speeds the nose will suddenly rise again somewhat at higher speeds. I haven't fully quantified it yet (as I have said, it takes about 45 minutes to actually make a 4 run track and at least the same amount of time to replay it and transcribe the raw data) but I think that these aircraft's noses raise and lower (and sometimes raise again) by nearly the full diameter of the WW gunsight circle, possibly more. At 100m, that puts the 'pipper' well below the horizon, while the Soviet fighters' gunsight center is just a bit above it (and at considerably higher speeds in many cases).

I contend that it is way too much variation, and plan to create a separate thread about it, but only once I have my ducks in a row. Right now I'm struggling to maintain level flight and have noticed that my key visual references are either unreliable in the case of my cockpit instrument displays or are changing on me in the case of the view of the horizon, which I could normally 'set' at a certain point in my cockpit framing to keep level. I need to (a) fly a reasonably level course while accelerating through the speed range and (b) take a series of screen shots from the track after doing so to confirm what are so far just impressions.

If I'm wrong I will say so; it won't be the first time.

cheers

horseback

[MaxGunz]

Series resistance will give you linear changes.
Rtotal = R1 + R2

Parallel resistance will give you curves and the total will be less than the smallest resistance (pot adjustment) and relative to it.
(1/Rtotal) = (1/R1) + (1/R2)

A microcontroller can use a lookup table to correct non-linearity of the sensor. There's room in a Teensy 2.0 to adjust _every_ step of all 12 10-bit analog inputs and still have room for useful code.

The most accurate stick I ever had used optical encoding. That wasn't analog at all. When the new hardware came out something changed and it wouldn't work so I sent it off to Rookie from the old Delphi FSF.

[RPS69]

Did you tried Hall efect sensors?
it is a must for home made ones. Nothing is more precise than that.

[RPS69]

Horseback, you are complaining exactly about what on trim, that it requires too much touchs to reach the desired position, that it is not working as it should, or both?

On the P38, you must be carefull with what you read. The P38 may not need rudder trim, as most other single engined, and bi motors whithout counter rotating engines did. But elevator trim may be assumed as allways needed.

In game trim management will be far better if there was a x10 adjustment, at least for those people that don't have a free axis for trim on thier joys.

[horseback]

Originally Posted by RPS69

Horseback, you are complaining exactly about what on trim, that it requires too much touchs to reach the desired position, that it is not working as it should, or both?

On the P38, you must be carefull with what you read. The P38 may not need rudder trim, as most other single engined, and bi motors whithout counter rotating engines did. But elevator trim may be assumed as allways needed.

In game trim management will be far better if there was a x10 adjustment, at least for those people that don't have a free axis for trim on thier joys.

Both, in most cases. In this game, trim is a value essentially concealed from the player, but in certain aircraft, mainly the late-war US fighters and the various Spitfire models, it is often crucial in the FM (and by most accounts, it was not nearly so important in RL) and almost impossible to apply effectively. When I try to apply it in axis form (with for instance, my CH Throttle Quad), it is almost always excessive; moving the lever the slightest bit results in the nose suddenly going up or down or in the case of rudder trim, sideways. Using button trim, I will be forcing the nose down with the my (non-FFB) stick about halfway forward while clicking repeatedly on the nose down elevator trim button without noticeable effect until the nose suddenly drops like a rock. Even in what should be level cruise, you cannot seem to get these aircraft leveled out; one click has your nose moving down, or the ball offset by half a diameter to one side and clicking trim in the other direction has the nose going up or the ball offset a bit to the other side.

On this specific group of aircraft, it almost seems as though the trim is not applied until I have clicked the button a certain minimum number of times and then it is all applied at once. It is quite similar to the visual effect of applying trim; you apply four or five clicks, and only then do you see the rudder or elevator move slightly.

As for the P-38 comment, let me say that I am almost 60 years old, and that my father retired from the US Air Force just before my 18th birthday. I have been interested in WWII’s air war since I was about seven, when we were transferred to Great Britain just after the 20th anniversary of the Battle of Britain (it was kind of a big deal over there). I’ve met a great many pilots who flew Warhawks, Lightnings, Thunderbolts, Mustangs and the naval fighters during the war over the years (strangely, only one admitted that he flew a P-39—and by the way, being curious about the aircraft your girlfriend’s Dad flew can make a big difference in what time you have to get her home), and most of them were happy to talk about flying them if not always about combat. I also read everything that I could find about those airplanes, their pilots and the air war in general once I mastered the printed page. I made hundreds if not thousands of scale models of every major fighter type that could be found in 1/72nd and 1/48th scales (including paying ridiculously high prices for the crude east of the Iron Curtain stuff that gave the only semi-accurate depictions of Sturmoviks, Yaks and LaGGs).

Back to the pilots’ testimonies:

P-40 drivers always mentioned that it was like an unruly horse that had to be tamed every time you got behind the stick (with the implication that you had to be a ‘real’ man to fly it well) and a couple mentioned the constant manipulation of the rudder trim. Thunderbolt pilots talked about how safe they felt in it and how smooth it was (the turbosupercharger gave them all of the engine’s power at any altitude, so they never felt that they had to compensate for more or less power as they climbed or dove (and their dive stories were full of superlatives), and Mustang pilots tend to go on about how you just felt in control of every little thing and how you almost automatically knew what you could get away with (one guy said that it wasn’t just that it was responsive so much as it told you how responsive it would be and let you know exactly where the limits were).

The P-38 guys talked climb, acceleration (according to the comparisons on pages 603 and 604 of America’s Hundred Thousand, at sea level the P-38F accelerated from 250 mph at 2.30 ft/sec/sec (roughly 70.7cm/sec/sec) and the P-38L would do 4.13 ft/sec/sec (or about 1.27m/sec/sec), this was about 0.15 ft/sec/sec faster than the early P-47D models or the Allison Mustangs for the F and the L was about 0.11ft/sec/sec faster than the M model Jug and 0.28 ft/sec/sec faster than the P-51D; the -1 and -4 Corsairs were well back from that among US fighters) and firepower. Like the P-47, the Lightning had the GE turbosuperchargers, which gave them all the engines’ power at any altitude. If the Lightning guy served in the Pacific, it was THE airplane; if he flew the later models in the European or Med theaters, it was a cold and unreliable SOB at high altitudes. They all said the P-38 didn’t use a lot of trim unless you were going up or going down; one guy said that it was a good thing it didn’t, because the elevator trim wheel was so hard to get at (America’s Hundred Thousand says that the 1944 Fighter Pilots’ Conference voted the P-38’s cockpit arrangement the worst of the US fighters and that the flap and landing gear controls were particularly hard to reach). From what I’ve seen, if you were wearing gloves thick enough to allow you to avoid frostbite, everything except the yoke and the rudder pedals was hard to manipulate at high altitudes in the P-38, so constantly grabbing and adjusting that tiny little knob on the wheel right next to your left knee in gloves with any precision would be hard. See the attached photo; the elevator trim wheel is that little thingie with the little wooden knob on the side of the black box; from other photos I have it seems as though the thing would be digging into your knee all the time.

All of these details have been confirmed in dozens of books, magazine articles and in some cases, the training films I’ve been able to view over the years. Only the P-40 was ever described as being hard to keep up with in terms of trim in level flight, and that is consistent with the recognition that it was an early design and that it was an adaptation of the radial engined P-36 (which is universally praised as a well-balanced fighter, if a bit slow post 1939). Every other aircraft was designed for a specific range of speeds and the idea that trim should be convenience rather than a necessity. When trim tabs are referred to as sensitive, there is usually a line about how you only need to add or subtract it in small increments in the pilot manuals. Given that Il-2 ‘46’s trim model gives you 160 clicks of trim from stop to stop, it seems to me that two or three clicks from ought to cover any need for trim for changes in speed up to 35-40kph or of 10-15% throttle/rpm in all but the most extreme cases in either rudder or elevator.

What I’m seeing is five or six clicks nose down, then two up, then a couple of clicks of rudder one way, then one or two the other direction; then wait a couple of seconds to settle and begin the whole process over again for normal level flight for this specific group. When you look at the external views of these aircraft in normal level cruise trim, the elevators are all visibly deflected down. Compared to the dozens of in-flight photos I have found of these same aircraft in apparent level flight it looks as though these do not have any appreciable deflection up or down.

If you look back from the cockpit at the Il-2 ’46 Spitfire’s elevators while in flight, most of the time the balance horn is sticking up well past the upper surface of the stabilizer. Find a video on YouTube where a guy from The Guardian is learning to fly a Spit in a two seat conversion of the Mk IX (there appear to be several): the in-flight shots of his face while he flies clearly show the elevator balance horn flicking up occasionally (without the immediate bouncing up and down that Il-2 ’46 depicts), but generally it is not constantly above or below the stabilizer while in level flight.

So trim demands for these aircraft seem to me to be excessive and at the same time, trim is impossible to track, excessive in axis form and much too small and unintuitive in button form.

cheers

horseback

[MaxGunz]

The 1 or 2 click trim that we fumble around trying to get perfect IRL means less than an ounce of force on something like a P-38 control column.

Most of use use a short toy (regardless of cost) joystick with no feedback at all let alone realistic movement and forces. The short stick multiplies every little twitch and tremor compared to a full size stick.
If that's not part of your analysis, if you get demand-y regardless then you're going to be SOL as to satisfaction.

[MaxGunz]

Originally Posted by RPS69

Did you tried Hall efect sensors?
it is a must for home made ones. Nothing is more precise than that.

Only as precise as you align the sensor and magnet.

Make sure you get linear analog Hall sensor, *not* one of many others especially the bipolar switch security type.

Being non-mechanical in operation they are preferable.

[RPS69]

Originally Posted by MaxGunz

Only as precise as you align the sensor and magnet.

Make sure you get linear analog Hall sensor, *not* one of many others especially the bipolar switch security type.

Being non-mechanical in operation they are preferable.

Agreed, aligning it could be tricky. The linear is also truth.

It also have a great advantage. You could place it at the bottom of a long stick, and still have precision, while pots moving in a very short arc are far less reliable.

To achieve that kind of precision with optics, you will need some demultiplying system.

Now... so much precision got a draw back, filtering is MANDATORY!

[RPS69]

Horseback, I agree.

A better triming interface should enter the wishlist.

Still, from your findings, I may build a guess, and it is that the coding got a min¡mum value that don't allow you to achieve a middle step, meaning that the optimal trim position can't be achieved the way it is coded, at least not allways.

Also, some of your headaches, must be related to the trim delay insert. That could make trimming any plane far more tricky than it was supposed to be. Originally implemented to avoid the "online trim exploit". A bad solution to a questionable problem.

[MaxGunz]

Originally Posted by RPS69

Agreed, aligning it could be tricky. The linear is also truth.

It also have a great advantage. You could place it at the bottom of a long stick, and still have precision, while pots moving in a very short arc are far less reliable.

Distance from the magnet is not how to get linear angle from a Hall sensor! The Hall reads only on 1 axis. You align the axis dead center over the magnet center between N and S poles. When the magnet turns, the strength of the field along the Hall axis changes. That is what you measure.
Try the other way, you will need more than 1 magnet and the fields will affect each other, merge, and you won't get good results.

To achieve that kind of precision with optics, you will need some demultiplying system.

Now... so much precision got a draw back, filtering is MANDATORY!

Optical... a lot can be done using laser-printed transparency graphics you can get printed at most any office store.

Have you ever looked at how ball mice track motion? Or used a vernier?

I have read that working with the dimensions of a Young's double-slit can yield a high number of interference bands. Perhaps diffraction from a single slit can also be used.

Really, the number of ways is a study in itself.