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[SAS~Storebror]

Hello there, FMB experts!
I've been tinkering with formations in FMB on Ultrapack 3.4 "Cassie" and I've noticed something peculiar.
It seems to me that the speed setting in FMB changes its meaning depending on which waypoint it's applied to. Am I the only one who's noticed this?

Specifically, the initial speed setting (i.e., the Spawn Waypoint) appears to be True Airspeed (TAS), while all subsequent speed values are Indicated Airspeed (IAS).

For example, if I want to spawn a flight of B-29s cruising at 25k ft at a steady 215mph IAS, I need to set their spawn speed to 500kph (which is roughly the calculated TAS for that altitude) and maintain all further waypoints at 345kph (equivalent to 215mph) to ensure a smooth journey. If, on the other hand, I spawn the bombers at 345kph, they start off at 230kph IAS, causing them to plummet.

Is this just a quirk I've stumbled upon, or has it always been this way?

Additionally, when arranging multiple bomber formations with vertical spacing, the fact that the speed setting per waypoint is IAS means we need to calculate a speed offset to ensure all flights maintain the same TAS and avoid collisions.

Given that IL-2's IAS to TAS conversion doesn't quite match real-life calculations, has there ever been a tool to convert these values accurately, or are we left to our own devices to figure out the correct speed offset by height offset? It feels a bit like a guessing game at times!


Mike

[FL2070]

It's been this way since as long as I can remember. I don't remember ever seeing a tool to calculate these speeds, either. When making the B-17 intercept mission on the west front map, I had to test the speeds at each altitude to know which speeds to give to which elements in the formation.

[Kopfdorfer]

Interesting find.
I had no idea about this peculiarity despite building a boatload of missions
 - but given other mysterious methodologies in this old game's design and structure
it is not a great surpirise.
I have had reasonable luck building and keeping various formations of bombers
in FMB , but sadly my methodology has been no more than trial and error/tweak and error.
An actual effective process would be a very useful tool for an old geezer.

Sorry to not have a more constructive comment.

Following with interest , though.

Kopfdorfer

[vonofterdingen]

This is a fascinating observation. I try to always have the player takeoff, and for the last several years that a taxi-to-takeoff. But I often have other flights do air starts. In those cases, I have often noticed odd behavior at spawn time. The air spawned planes dip, lose some control, and then recover. I compensate by providing plenty of space between aircraft in order to prevent collisions until the planes right themselves. It did not occur to me that speed might be a factor.

Note: my experience is limited to BAT for the most part, but I assume this issue applies to BAT as well.

[Dimlee]

Interesting observation. I knew about IAS in FMB but didn't realize that it was TAS in the initial spawn point and considered that plummeting effect just another "bug feature". But now it makes sense.

I used online TAS/IAS calculators and haven't experienced any issues with them so far.

I have never tried to build formations with vertical separations so large that they require separate IAS calculations. This is work for a real FMB aficionado. 
Have seen B-17 and B-24 formations spread vertically by about 1 km in some online missions, a true work of art. And quite a challenge for an interceptor.

[SAS~Storebror]

When it comes to the relationship between vertical spacing and IAS difference, it’s quite fascinating how a small change can have a significant impact on large bomber formations over a considerable distance, say from the Channel coast to Cologne.

I’ve been busy setting up three groups of 16 B-29s each. Each group has a horizontal offset of about 300m and a vertical offset of 100m relative to the lead group.

Interestingly, the difference between maintaining the formation exactly as set up versus the second group (the higher one) overtaking or colliding with the lead group was a mere 0.2 kph. For the third group (the lower one), the difference was slightly larger at 0.3 kph.

It’s quite intriguing, isn’t it? It’s not just about the absolute difference, but the absolute altitude also plays a crucial role. So, there’s a lot to consider!


Mike

[tomoose]

I'll echo Kopfdorfer's response as I had no idea about the TAS/IAS issue.

I've been working my way through my customized version of the Big Bird B17 campaign and in my ignorance I've simply gone into the .mis file and changed the speed for each B17 flight to 250.00 (after they reach 3000m alt).  I also go into FMB and zoom in to the 100m x 100m grid and ensure the pairs of flights have good horizontal separation and vertical.  We're on mission 24 of 25 and the formations in all the previous missions were still hit or miss.  My biggest problem was definitely speed.  While I could get the formations reasonably close horizontally and vertically it was always a fight to match speed. 
My only solution was to use the SET command between each pair of flights and SET for the lead of one flight to the 'tail' of the next flight.  This seemed to get better results but was still unpredictable.  Formation was still usually strung out.
That said, you can see some of the efforts here in the Squadron Mission Photos (specifically Rotterdam, Tilburg and Dusseldorf) https://381st.nfshost.com/page5.html

[UberDemon]

When it comes to the relationship between vertical spacing and IAS difference, it’s quite fascinating how a small change can have a significant impact on large bomber formations over a considerable distance, say from the Channel coast to Cologne.

I’ve been busy setting up three groups of 16 B-29s each. Each group has a horizontal offset of about 300m and a vertical offset of 100m relative to the lead group.

Interestingly, the difference between maintaining the formation exactly as set up versus the second group (the higher one) overtaking or colliding with the lead group was a mere 0.2 kph. For the third group (the lower one), the difference was slightly larger at 0.3 kph.

It’s quite intriguing, isn’t it? It’s not just about the absolute difference, but the absolute altitude also plays a crucial role. So, there’s a lot to consider!


Mike

When I release my new concept of UberQuick Mission Generator, UQMG, it may help mission designers.  Each mission template is designed with 7 total sections:
* Takeoff (including Taxi, Scramble, Classic lineup, or flying) to first waypoint
* After Takeoff (where I the user can setup patrol points for formation assembly)
* Transit
* Action/Misson
* Transit back
* before landing
* last waypoint and landing

Each section can be removed, and each has its own choice of speed, altitude, and even ability to do bulk move of the entire section north/south and east/west.

But...  with the cloning algorithm, all you do is select how many flights you want copied of the original flight, then you can have as many as you want (limited by the number of regiments in IL-2).

So if the original flight is of 3 B-17s, you could add 10 copies of the flight with a single click, and you have 11 x 3 airplanes which are placed in a large formation...  I want to improve my original classic implementation of the cloning algorithm with something more interesting that allows the mission designer to chose the type of large formation.

Look here for my initial design of formation types:  https://www.sas1946.com/main/index.php/topic,71120.msg784594.html#msg784594

Oh in the patrol routine, if you have clones, it will calculate for large formations...

Say, you can have the original flight taxi and takeoff from spawn points, then you could have the clones come in waves from a standard lineup spawn point (can't reuse generic spawn points unfortunately), or you could have clones start in air... whatever.

For the patrol assembly, the first flight would do the most loops.  In our example, if there is only one clone at a time or they all spawn at the same time then the first fligt would loop for 11 times, the next 10, 9, 8 you get the idea... that is a lot of times, so an alternative would be to have a certain number of clones per wave.  Say 3 flights per wave... so that would be 9 planes spawn, then another 9, then 9, then 6 (for 33 total).  First wave would loop 4 times, then you get the idea.

UQMG classic already implemented that flights per wave concept, but I want to make it a bit better, taking advantage of patrol points to assemble formations if the user desires, or they can simply do a one time loop for all flights, or not at all.

Long story short... with the users being able to apply a different speed per section, maybe they will the desired effect.

I am hoping to make UQMG not only a quick mission generator but also a mission designer aid.

[SAS~Storebror]

Cheers, chaps! A big thank you for your input and a special nod to UberDemon for the UQMG insights.

I've been having a good old rummage around my options, particularly with Ultrapack Development in mind. We've got a new version of the formation code in Ultrapack that sorts out many of the initial hiccups. That said, a lot of what UberDemon pointed out still holds true for other game versions, especially BAT. But, Ultrapack FMB users can already enjoy pretty solid support for large formations.

On the topic of speed settings, I've given the mission builder interface a bit of a spruce up to show both TAS and IAS values for each waypoint. The game takes care of which value applies to which waypoint internally, but now you can enter your waypoint speeds using either true or indicated values. The other value will be calculated automatically as you type.

What's more, the new FMB interface also considers IAS speeds when working out the timing for each waypoint. In the past, time calculation would always treat each waypoint speed as if it was TAS, which inevitably leads to incorrect time values the further and higher you go.

Having given all these changes a whirl, I've stumbled upon another issue: AI planes, especially the big ones, don't stick to the speed setting from the waypoints they fly. In fact, they tend to fall a bit short. Plus, when you have AI fly in formation, the planes don't stick to the set altitude either.

The latter is quite straightforward to explain: In Stock IL-2 - and therefore in every mod pack - the formation leader uses an altitude offset value which isn't zero, for some reason. This offset is taken into account, and the lead AI plane will miss the set altitude accordingly. For example, a 4-ship Vic-Formation B-29 flight will end up at 7586m when you set the waypoint to 7500m. It might not seem like much, but as the speed setting is IAS and IAS depends on altitude, the difference adds up along the route.

What's worse, AI uses a power setting code which makes big planes miss the set speed by quite a bit. There's an initial power setting that depends on the ratio between waypoint speed and "VmaxH", the maximum speed at altitude from the flight model. On top of that initial power setting, the game takes the difference between waypoint speed and current IAS, multiplies it by 0.1, and subtracts the current forward acceleration multiplied by 3 from it.

For instance, I've set a flight of B-29 to cruise at 7500m, 525 kph TAS = 350.09 kph IAS (in IL-2's world), and this is the result when speed and altitude have settled:
Altitude: 7586m
Initial power setting: 58%
Adjusting by WP speed vs. IAS and fwd. accel.: +19%
Final power setting: 77%
TAS: 505.39 kph
IAS: 335.31 kph

This in turn causes AI planes to miss the "perfectly" aligned IAS speeds of given waypoints depending on the altitude difference between them, and it makes the planes miss the pre-calculated times on waypoints the further they are.

This brings us to a couple of questions:
1.) Is it worth trying to make AI meet the set IAS from waypoints? I reckon it is. Should be doable.
2.) If we do that, will it mess up existing missions? Possibly, yes, because AI planes will no longer miss the set speed, i.e. they'll travel at different speeds than the ones when the mission author tested the mission.

It's a bit of a pickle... any thoughts?


Mike

[tomoose]

Mike;
thanks for that info it helps explain some of the pain I've gone through in trying to get planes together at a rendezvous point.  In my ignorance I've simply moved waypoints around so that the time for each flight at the RV ends up being the same and adjusting speed in the .mis but when running the actual mission there can still be some discrepancies on arrivals. 

This definitely explains however why in FMB I have fighter escorts supposedly meeting bombers at the same time (according to the waypoint timing) and yet in-mission the fighters can miss the rendezvous by many minutes and be WAY ahead or WAY behind.  Quite frustrating.  The only way I've got around it is to do a test run to see what 'actually' happens.

NOTE:  I'm using HSFX for our online coop play.

[Frankiek]

That is what i have been doing trial and errors painfully adjusting the numbers until the targets setting up to the desired effect

[SAS~Storebror]

why in FMB I have fighter escorts supposedly meeting bombers at the same time (according to the waypoint timing) and yet in-mission the fighters can miss the rendezvous by many minutes and be WAY ahead or WAY behind

IIRC you see the speed of the plane you're actually watching on externals when you toggle the speed bar (lower left corner) in HUD.
That way you can see what speed your fighters are running at, and compare it to what you've set in FMB.
My suspicion is that we have plenty of A/C where the "VmaxH" value in their flight model (.fmd file) is way off, which has a direct impact on the throttle setting AI will use.
This relationship of "VmaxH" and AI speed isn't quite obvious, let alone intuitive, but it's real (real in terms of "it happens in IL2").


Mike