I've made appropriate changes to Readme.submodels to reflect the
variation of Cd with Mach number.
Spitfire.submodel has been changed to use the variation of Cd with Mach
number
Submodel.cxx has been changed so that the default value of Cd is the
subsonic Cd of a non-boat tailed bullet.
The calculation of submodel mass from weight has been moved from AIBallistic
to Submodel so that it is calculated only once, rather than on every
iteration as a present. The parameter <contents> has been added, primarily
so that droptanks will have the proper mass. It is the path to an
appropriate property containing a weight in lbs.
Care has to be taken with the use of <contents> because after a reset there
appears to be a delay in submodel instantiation (dt not properly reset???)
and the weight property is not always picked up before it is set to zero in
the key bindings. Slightly hard to explain. It works fine if FGFS has not
been reset though. There is a partial solution which involves the rejigging
of the fuel and gui nasal scripts, but there is still the visible delay in
instantiation to be resolved. I've nearly done the nasal fixes, which will
form part of an update to the Hunter only. I'll probably complete those
later today.
I have added <Cd> and <weight> to the input parameters in the submodels.xml
script. Raw data may be used, thus avoiding the need to guestimate <eda>.
Eda remains, but should now be used to enter the proper cross-sectional
area.
I had to reverse a number of signs to get it right. I took the opportunity
to add roll to the submodel so that droptanks will come off with the right
orientation. I have neither added the rotational speed to the submodel, nor
yaw, so if you release droptanks with significant roll rate or yaw angle on
the aircraft the submodel will not be quite right. Straight and level, or
nearly so, is fine.
The maths, so far, is now correct. Roll and pitch are now both in the
correct sense. The aircraft velocity is added correctly to the
submodel velocity, and the submodel is now visible when instantiated.
However, the velocity is measured at the aircraft centre. To be totally
correct we ought to take into account the aircraft's rotational
velocity. We have pitch rate and roll rate available, but not yaw rate
(small anyway).
Here are some things I've added to the submodel code.
First, I added a first_time value that is true when the trigger is pressed and
false when the trigger is released. The true value is also made false after
the first pass through release(). Release() then uses this to force the
first dt (per salvo) to be zero. I was hoping this would make the submodel
appear closer to the airplane, but I don't notice a difference with the
tracers. In a prior test I found that the first dt is about 2.5 times larger
than subsequent ones. Maybe this will be effective with slower submodels,
like smoke, contrails, etc.
Secondly, I updated the IC.elevation and IC.azimuth calcs to correctly add in
the yaw and pitch offsets, corrected for bank angle. Actually this is still
an estimation. A proper calculation will sum the submodels vector with the
airplane's vector. Until that's done only models which are fired forward
will have proper IC.
Testing revealed that the code was not reading y-offset - a
typo in the original code, and roll was in the wrong sense. All readily
fixable, and it now works.
I've added another parameter to the submodel - wind.
It's activated by the entry <wind>true</wind> in the ../submodel.xml file.
If true, the submodel is affected by the local wind, otherwise not. The
parameter defaults to false. This is useful for exhausts and smoke, and
possibly all objects.
Silly me. I was starting the timer at zero, so the first tracer didn't fly
until 0.25 seconds after pulling the trigger. Now the timer starts at the
same value as "delay", so the first round comes out immediately.
Also, I've added an optional configuration attribute that allows you to change
the ballistics of the submodel. This allows parachutes, or anything else
that has ballistics different from a bullet. The attribute is called "eda",
which is the equivalent drag area. Default value is 0.007, which gives the
same ballistics as the current tracers. Increasing this value gives more
drag. A value of 2.0 looks good for a parachute.
math stuff
########################################################################
The deceleration of the ballictic object is now given by:
[ (rho) (Cd) ] / [ (1/2) (m) ] * A * (V * V)
where rho is sea-level air density, and Cd and m are fixed, bullet-like
values. So the calculation is:
0.0116918 * A * (V * V)
The value "A" is what I'm calling the "eda" (equivalent drag area).
########################################################################
A parachute model will have to be built so that the parachutist's feet
are in the forward x-direction.
Here is the submodel.xml config I use for "parachutes":
<submodel>
<name>flares</name>
<model>Models/Geometry/flare.ac</model>
<trigger>systems/submodels/submodel[0]/trigger</trigger>
<speed>0.0</speed>
<repeat>true</repeat>
<delay>0.85</delay>
<count>4</count>
<x-offset>0.0</x-offset>
<y-offset>0.0</y-offset>
<z-offset>-4.0</z-offset>
<yaw-offset>0.0</yaw-offset>
<pitch-offset>0.0</pitch-offset>
<eda>2.0</eda>
</submodel>
Last night I sent these new files to Vivian to fix a problem he found. Since
we can have more than one submodel we need more than one "count" property.
The new code creates a property systems/submodels/submodel[n]/count for each
submodel. Vivian is using this count property for his sound.
Here is an update for the submodel system. This will allow submodels to be
defined for any aircraft, and there are no default submodels. To use this
submodel system you need to set up a binding (slight change in property name
from last one, but you can use any property name you like, as long as it
matches the name in the submodels.xml file, see below):
<button n="0">
<desc>Trigger</desc>
<binding>
<command>property-assign</command>
<property>/systems/submodels/trigger</property>
<value type="bool">true</value>
</binding>
<mod-up>
<binding>
<command>property-assign</command>
<property>/systems/submodels/trigger</property>
<value type="bool">false</value>
</binding>
</mod-up>
</button>
Then in your *-set.xml file you need to define a path to the configuration
file (similar to the way the electrical system is now done):
<sim>
...
<systems>
<electrical>
<path>Aircraft/Generic/generic-electrical.xml</path>
</electrical>
<submodels>
<serviceable type="bool">true</serviceable>
<path>Aircraft/FW190/submodels.xml</path>
</submodels>
</systems>
...
</sim>
Then you put the submodel configuration file in your aircraft's directory.
I've attached a file, submodels.xml, that can be used to define a gun that
works just like the former one did.
There are two things remaining to be done. One is to change the function
SubmodelSystem::transform() to properly position the submodel. This will
require some complicated matrix code that I might borrow from Yasim.
Well here's some tracer stuff. If fiddled around with submodel.cxx. It now
does what it says - you need to put this:
<!-- trial gun system -->
<systems>
<submodel>
<serviceable type="bool">true</serviceable>
<amount type="int">120</amount>
</submodel>
</systems>
In the *-set.xml file NOT within <sim></sim>. Trouble is it still defaults
to serviceable=true, but it also defaults to amount=0. Unless this bit of
code is included it wont run, so other models can't fire inappropriate
tracer. Revised submodel.cxx file attached.
I've changed to a non-billboard solution. I tried to make the viewing angle
of the tracer less than 180 degs, but failed. Close enough I think. It's
still a bit big, but a reasonable compromise. .AC file attached.
I remain concerned about the tracer colour. In practice, red is better (and
it's what I am used to) but David seems set on white, and I don't want to
upset him. I'm going to adjust the texture a bit more tomorrow.
Right now the code is not very configurable, and there is only one submodel per airplane possible. It is implemented as an SGSubSystem, just like the electrics, vacuum, etc. systems. To make it work you need to make a release binding like this (for my joystick trigger):
<button n="0">
<desc>Trigger</desc>
<binding>
<command>property-assign</command>
<property>/systems/submodel/trigger</property>
<value type="bool">true</value>
</binding>
<mod-up>
<binding>
<command>property-assign</command>
<property>/systems/submodel/trigger</property>
<value type="bool">false</value>
</binding>
</mod-up>
</button>
Then, each airplane that uses the system should have something like this added to its *-set.xml file (note that this does *not* go within the <sim></sim> tags):
<systems>
<submodel>
<serviceable type="bool">true</serviceable>
<amount type="int">70</amount>
</submodel>
</systems>
Future improvements will include:
1) more configurability, so the user can create multiple submodels, and can assign them different locations, and pitch and yaw adjustments, and nitial velocity.
2) sound?
3) a more accurate calculation of the submodels location at any pitch/roll/yaw.
4) a way to pre-load the model, so the AI code doesn't have to parse the model every time it creates an instance.
I think that's all of it.
