True Altitude?

[KG26_Alpha]

I use Pilotwizz app on my Iphone

[Soldier_Fortune]

Originally Posted by KG26_Alpha

I use Pilotwizz app on my Iphone

Good!

That app has many of the features of an E6-B... and surelly with it you can compute faster than me.

However to recreate the enviroment of the '40s, for me my E6-B, a printed map, a pair of pencils, my plotter, and a song of Glenn Miller or the Andrews Sisters, are essential. LOL

The main difference between the app and the E6-B is you can use your iPhone inflight, wihile I must pause the game for to make my calculations, because I need my two hands to handle the E6-B.

Please, when you can, have a look at the links I've posted before.

[KG26_Alpha]

Im very familiar with the Wizz Wheel E6B

I just find it so obsolete (slow) for IL2 1946, with "Pilotwizz" I can use it on the fly very quickly

Also

The test maps from earlier in this thread >>> http://forum.1cpublishing.eu/showthread.php?t=40740 I used are showing @ -5' temp at @ 4000m

This still calculates from the tables as I have been using for years.

270kph ias
330kph tas
4000m alt
OAT -5'C

So somethings making them drop long if all the calculations are correct...........What inputs are the AI using for their bombing routines, as they don't seem to have a problem ?





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[Soldier_Fortune]

Originally Posted by KG26_Alpha

Im very familiar with the Wizz Wheel E6B
...
Also

The test maps from earlier in this thread >>> http://forum.1cpublishing.eu/showthread.php?t=40740 I used are showing @ -5' temp at @ 4000m

This still calculates from the tables as I have been using for years.

270kph ias
330kph tas
4000m alt
OAT -5'C

So somethings making them drop long if all the calculations are correct...........What inputs are the AI using for their bombing routines, as they don't seem to have a problem ?

.

Hi KG26.

After reading your last post, I've conducted a test for each of both maps mentioned in that treath: Crimea and Moscow1 (winter).
I've done them with a B-25J because this aircraft is equipped with all the relevant guages for these tests: OAT, IAS/TAS, and Altimeter.

The payload were 2 x 1000 lbs bombs, being the targets:
- Crimea: a ring target placed in the air base of Simferopol (altitude = 800 ft =243 m ASL).
Moscow: the same type of target at the same altitude ASL, placed in the air base near to Vyazma.

The following data were obtained from the gauges readings (none was calculated, except the speeds in km/h):
CRIMEA:

- Wind speed = 0
- OAT at GL: 25 ºC
- Altitude during final approach to target: 13050 ft = 3970 m
- OAT at level bombing: 0ºC (should be -1 ºC)
- IAS = 160 mph = 258 km/h
- TAS = 200 mph = 323 km/h

MOSCOW WINTER:

- Wind speed = 0
- OAT at GL: -17 ºC
- Altitude during final approach to target: 13615 ft = 4150 m
- OAT at level bombing: -40ºC (should be -44 ºC)
- IAS = 160 mph = 258 km/h
- TAS = 186 mph = 300 km/h

Comparing this readings with the IAS/TAS charts, the data of the Crimea map are quite similar to them. The reason: the OAT at that altitude presents an irrelevant difference (-1 ºC).
But the outcomes obtained in the Moscow Winter map are too different when they are compared with the charts, due to the OAT differences as at GL as well as at flight altitude, like it is expected IRL.

I've engaged the Autopilot to have complete freedom for to read the gauges inflight, and because I was interested to see how the AI did do it.
May be an average AI bombardier is a bit idiot...the point is that it missed its targets in both maps, with the bombs falling too short and too far.

Anyway, I think the AI uses the gauges readings as inputs for the bombsite.

I have screenshots of the gauges in both missions. Tomorrow I'll try to upload them, and also I shall perform several flights in both maps to find out what data are the best to adjust the bombsite.

We will see the results... I hope.

[Soldier_Fortune]

Well... Finally I could perform a new test today to record an 8 minutes' .ntrk file: the last week end I should fix some issues with my hardware.

I've flown a bomb raid with a B-25 in the winter map of Moscow, and I can confirm all what I've said before:

1) The inputs for the bombsight must be the 'true altitude = indicated altitude - target altitude' (as ever), and the TAS corrected by OAT.

2) The OAT is indicated by the 'Free Air Temp' guages, or (if the plane has not such gauge) it must be calculated according to the Atmosphere International Standard (AIS) regarding of the altitude and the GL temperature.

3) The IAS/TAS charts and tables made and used before the release of the patch 4.11, are useless now.

You can see it in the attached .zip file.
Note that the speed used to set the bombsight is in knots, because yet was not fixed and old issue of the B-25: the TAS in the IAS/TAS gauge is indicated in mph, but the TAS must be converted into knots before it could be used as the speed input for its bombsight.

The values used in that test were:

Indicated ALT = 13150 ft
Target ALT = 800 ft
True ALT = 12350 ft
OAT = -40 ºC
IAS = 190 mph
TAS = 220 mph = 190 KTS
Payload: 2 x 1000 lbs bombs

The red values were used as inputs for the bombsight.

The bombs were released in automatic mode. The target was missed by very few yards, as we can expect: IRL it was practically impossible to perform precision strikes with high level bombing using the '40s optical devices, and a direct impact on an intended target was a matter of good luck. For pin point strikes, it's better to use dive bombers. For medium or heavy bombers it is better to use the carpet bombing tactics.

For me, this test (together with others which I've done) is conclusive.

Perhaps now we could talk about the other factors: wind speed, wind direction and how they affect the Ground Speed in navigation and level bombing.

[KG26_Alpha]

Please repeat the test using a Russian Bombsite.


Bomb ground strike position relative to the bombsite aiming angle is the point to note also, testing shows this is wrong/different OAT air density or something is having an effect ?

If so new bombsite calculation tables are needed for v4.11 >


I have been a bit too busy to test again with new data this week but this is from a guide pre v4.11, hopefully the same theory applies to current game versions and the problem is else where.


Equations of motion
v = velocity, u = initial velocity, a =
acceleration, s = distance, t = time.
s = ut + ½at2
v = u = s/t (unaccelerated)
Fig 1.2.

The aircraft is heading from right to left at speed, v, when it releases a bomb at A.
Initially the bomb continues to move with the aircraft, but starts to drop as gravity accelerates it downwards.

The bomb follows a parabolic path, represented by the blue line.
AB is the height, h, of the aircraft and BC is the forward throw, R, of the bomb.
If the bomb takes time, t, to reach the ground, g is the
acceleration due to gravity and we ignore air resistance for the moment, then the equations of motion give us the following:

AB = h = ½gt² -- eq 1
BC = R = vt -- eq 2

We know the height, h, speed, v, and g is a constant 9.81 m/s², so we can find t from eq 1 and substitute for t in eq 2 to find the forward throw, R:

R = v 2h/g) -- eq 3

The angle between the horizontal – the dotted line in fig – and the point of impact at C is, of course,
the angle, a, from fig 1.1 above.
This is what we want to know when we come to aim the bomb and is the same angle as ACB in fig 2.
As we now know 2 sides of the triangle, AB and BC, we can find the angle:

Tan ACB = AB/BC = h/[v 2h/g)] -- eq 4


DIVE-BOMBING
In the previous example we used the height to find the time the bomb is in the air (equation 1) and
then used equation 2 to find the forward throw of the bomb.
From these two pieces of information we could deduce the angle corresponding to the amount the bomb drops from the horizontal.
We can do exactly the same when the bomb is released from a dive at an angle, degrees.
The situation is slightly more complex, however, because the bomb now has an initial downwards velocity (v.sin ) and the horizontal velocity (v.cos ) is not quite the same as the airspeed.

The equations for AB and BC now become:

AB = h = vt.sin + ½gt² -- eq 5
BC = R = vt.cos -- eq

Equation 5 results in a quadratic equation, which can be solved to find t.
Equation 6 can then give the forward throw, R, which allows us to find AB/BC and then the sight angle.

This would be quite tedious to solve for each combination of dive angle, airspeed and release height, but it is not too
difficult to produce a spreadsheet, which will do the sums for us once we enter the desired
parameters.
The dive angle, , is found by noting height, h, and range, D, to the point on the ground under the
cross hairs at the moment of bomb release.

Tan = h/D -- eq 7

Air resistance. We have not yet considered the effect of air resistance on the falling bomb.
Once the bomb leaves the aircraft it will start to slow down.
However, so long as the bomb does not produce any lift (either up or down), the drag will only act back along the bomb’s direction of travel.
The bomb will slow down and take longer to reach the end point, C in the above fig, but it will follow the same path and still reach that point.








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[Soldier_Fortune]

Hi mate.

First of all: my sincere thanks by your explanation about the parabolic motion... but I know the works of sir I. Newton also.

BTW, I must point out an error in your eq. 3. It must be written as:

R = v . SQRT (2h/g)

Basically we are talking about of 2 types of bombsight: the Norden/Lofte type(Allies/Germans), and the OKPB-1 type (Russians). Both need 2 settings: TAS (horizontal speed), and altitude. The difference between both types is the first allows automatic or manual release, and the second only allows manual release. But in both types normally the aiming angle is internally calculated (all that equations you've posted run behind the scene).
The exception is the Norden/Lofte type when a player prefers the manual release; if so, he will must perform those calculations by himself (some players made an published their charts for manual release with the Norden/Lofte type, long before the patch 4.10).

According to my tests carried out several weeks ago, it seems that all bombs have the same FM, regardless of size and country (IRL the bombs' shape and weight are relevant, as well as the launching altitude, GS, OAT, and the wind's speed & direction).
As far as I can remember, when the atmosphere model had one only air temperature, the parabolic motion was almost perfect and it was very easy to adjust and to aim the bombsight, and to hit an intended target.
But now we have an atmosphere with different OATs at SL which change with the altitude, thus changing the air density dinamically.

I.e.: according to the AIS, if the OAT at SL is 25 ºC, we'll have:

Altitude (m)___OAT (ºC)___Air density (kg/m3)
0____________25_________1.225__(1.225)
1000_________18.5_______1.115__(1.088 )
2000_________12_________1.013__(0.966)
3000_________5.5________0.919__(0.858 )
4000_________-1_________0.831__(0.762)
5000_________-7.5_______0.75___(0.676)
6000_________-14________0.675__(0.601)
7000_________-20.5______0.606__(0.533)

* (The values into brackets are the air density at different altitudes considering a constant OAT = 0 ºC).

We could supose that any bomb released from a given altitude (say 6000 m), when t = 0, will have a constant horizontal velocity v = TAS (a/c), and an increasing vertical velocity u which range from 0 up to its final value. But both velocities will change with air densitý as the bomb is falling. Therefore, its path will not be perfectly parabolic as we could expect in a 'Newtonian Universe'.

Perhaps all bombs have the same in-game's FM... but they might work in a different fashion than that known before the patch 4.11.

Another factor which produce offsets between the aiming point and the hit point is how leveled flies the aircraft. If the pilot flies with the Level Stabilizer engaged, the aircraft may be flying at a steady altitude... but if its elevator is trimmed to avoid the 'sinking', probably its Angle of Attack (AoA) is not 0. The pilot will not be noticed about how is the AoA (the pitch), because the artificial horizon doesn't work when the LS is on, and because we haven't an 'AoA gauge' like the modern aircrafts have.
Thus, with that configuration, when the bombsite is at 0 º elevation, really it will be aiming at 'AoA' elevation.

I.e.: if the AoA is +3º, this angle adds to the bombsight elevation. A bombardier aiming to a target with a BS elevation = 50º, really is like if he would be setting an elevation of 53º, and then he adjusts the TAS and/or altitude to fix the target under his crosshair according to that wrong angle... which will worsen the final outcome.
A difference of 3º may seem a small thing; but if we make same calculations according to the equations you've posted:

Wrong elevation = 53º (the bombardier believes the elevation is 50º)
tan (53º) = 1.327
Right elevation = 50º (if the aircraft would be flying perfectly leveled)
tan (50º) = 1.192

According to your eq 7,

D(53) = 5000 x 1.327 = 6635 m
D(50) = 5000 x 1.192 = 5960 m

As you know, the most of players engage the Auto Release when the elevation is about 50º. Even if the crosshair is fixed over the target (what would be rare in this case), the bombs will fall about 675 m short because of the early release.

...

Other unavoidable errors related with the type Lofte/Norden BS:

This bombsite has not a 'coarse/fine' setting, but one only mode with 2 fixed rates: one for the TAS and the other for the altitude. The rate for altitude is 50 per keystroke, and that for TAS = 10 per keystroke.

But, depending on the chosen bomber, we have the following combinations:

- German bombers: TAS rate = 10 km/h; altitude rate = 50 m.
- Allied bombers: TAS rate = 10 KTS; altitude rate = 50 ft.
- Japanese bombers: TAS rate = 10 KTS; altitude rate = 50 m.

Thus, 1 keystroke of TAS in an Allied bomber BS is almost equivalent to 2 keystrokes in a German bomber; and conversely, 1 keystroke of altitude in an German bomber BS is almost equivalent to almost 3 keystrokes in an Allied bomber.
In short: German bombers allow more accurate TAS settings than the Allied, but the latter allow more accurate altitude settings than the German.

Other errors come from the instrument readings: sometimes the pilot visually must interpolate between two marks, and can be difficult to decide if he's reading a value of 12,600, or 12,700, or 12,800...

I'm wanting to emphasize that, even if the calculations were very accurate, the game interface makes it impossible to apply them exactly.

...

This evening I'll try to perform more tests, as you've suggested: one with a Russian bomber, and other with a German bomber at least.

See you later!