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in LOMAC
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A similar situation can arise in simulations
as a result of the combined drag and thrust model that results
in a Ps = 0 curve that also rises as speed drops. An example
of an overlay for the Eurofighter and MiG-29 from the Eurofighter
Typhoon simulation is shown in Figure Two. Notice again
that the sustained turn rate actually increases as the speed
of the aircraft drops, so holding full aft stick and allowing
the speed to decay actually improves your sustained turn rate
and decreases your turn radius, a similar situation to Falcon4,
but for different reasons. In Falcon4 it was due to the Angle
of Attack limitations imposed by the control system modeling,
and in Eurofighter, and many other simulations it is due to
a combination of the thrust and drag model. However, neither
is true in LOMAC, G for brains won’t work!!
Figure Two
As an aside, notice that the Ps curves
in the Falcon3 EM diagram are slightly bumpy, while those
in Eurofighter are smooth, the reason for this is that Falcon4
uses a table based model where thrust and drag data exists
in tabular format, the steps between discrete values in the
tables and the fact that software uses linear interpolation
to determine intermediate values, is what causes those bumps.
In the Eurofighter flight model the thrust and drag values
are calculated continuously and so the curves are smooth.
There are advantages and disadvantages to both modeling methods,
but a discussion of the merits of each would probably be a
better topic for another article.
So, some simulations reward the use
of G for brains, others won’t, and LOMAC is one of the
ones that don’t. The difference lies in the flight model,
in some simulations it is due to the way that thrust and drag
are modeled, and in others due to the way the control system
has been modeled. In order to understand this situation a
little better, we need to look more closely at the slower
end of the envelope, that is for speeds below corner velocity
where we need to look at what happens as aircraft approach
their Angle of Attack (AoA) or lift limits. Continuing then
with the example of the F-16 and the MiG-29, the F-16’s
AoA limit is around 25° (It is worth noting that the characteristics
of the F-15’s control system is similar to that of the
MiG-29 according to a test pilot who has flown both types)
while the MiG-29 can safely exceed a 30° limit, providing
no roll commands are given.
In order to illustrate what happens
as these aircraft approach their AoA limits we need to examine
the next sequence of EM diagrams. These diagrams are not for
any one of these aircraft in particular, they are a generic
set of diagrams that can apply equally well to any of these
aircraft, and are intended simply for the purpose of illustrating
the point. So let’s see what happens to the same aircraft
with different AoA limits imposed on it.
Figure Three
In Figure Three you will see
the EM diagram showing the envelope with a 22° AoA limit
and you can see that the maximum sustained turn rate occurs
at a speed very close to corner velocity and that the sustained
turn rate drops slightly at lower speeds. That is typical
behavior for a jet fighter and becomes more significant as
the AoA increases. Take a look at Figure Four for an
AoA limit of 25° and you notice that as the AoA increases,
the sustained turn rate drops more dramatically.
Figure Four
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