Prop Pilots Always Get Their Man: Winning
The Co-E Chase
writer, Leon "Badboy" Smith, takes a quick look
at a common problem in sim combat..... you're on the bandit's
six, and he's running scared. But you're juuuuust out of guns
range, so what can you do? Badboy takes a common jet tactic
and applies it to the world of prop sims. This article was
prompted by a thread on the Aces High message board, when
someone posted a similar situation.
six, and remember, that guy behind you who's diving may be
getting ready to eat you for lunch. Badboy explains more about
winning the Co-E Chase.
The technique described below is one
that Ive been aware of for some considerable time. I've
been using it myself and I use a variation of it at higher
altitude. The question being asked is how can it be correct.
However, before I offer the explanation, I would like to say
that when I first used the method and noticed that it worked,
I wasn't at all surprised. I am more familiar with modern
aircraft performance and tactical doctrine because most of
my writing has been concerned with simulations of modern fighters.
The method is well known and used for jet fighters, and so
when it worked in the prop sims, I was curious about the differences
in execution, and not with the right or wrong of it.
The diagram below is compressed due
to lack of space and shows the method for closing to within
guns range from a Co-E start. It involves diving at Zero G
for maximum acceleration for closure, followed by a zoom climb
to within guns range.
When I noticed that this worked in
a prop sim for the first time, I was actually doing what I
would have done had I been flying a jet. I never gave a second
thought to the question of the technique surviving the difference
in characteristics between jet and prop driven aircraft. I
used the technique and found it to be successful without a
thought...I just assumed it should be so because it worked
for jet-engined aircraft. Interestingly, I discovered that
the technique is not very well known, and after consistently
catching the same pilots in the online arenas, and being repeatedly
accused of cheating, or hacking the code, I thought it would
be a good idea to share.
Before I explain how such a thing
could be correct, I'd like to show you how a real fighter
pilot would approach the problem in a modern jet, because
the solution is not just surprising but useful as a datum.
Picture yourself in the cockpit of an F-15 at 20,000ft and
M0.7 making radar contact with a distant target. At that point
a real fighter pilot would have a great deal of busy work,
but high on his priority list will be the desire to enter
the fight with the highest possible energy state in the shortest
possible time. You would achieve that by selecting afterburner,
unloading to zero G, and accelerating in a dive to M0.92,
losing several thousand feet in the process. You would then
begin a climb to an altitude above the enemy if there were
What surprises most folk about this
story is the initial dive to a higher speed. That is the correct
procedure in a jet regardless of altitude, providing you are
not at sea level.
To understand why this works, take
a look at the diagram below. This diagram shows lines of constant
specific Energy (Es) in green and lines of constant specific
excess power (Ps) shown in blue. If you want to achieve the
highest energy state at the greatest rate of energy increase,
you need to maximize your Es and Ps at the same time. That
can be seen to occur where the P's curves are tangent to the
E's curves. The red line is drawn through all such points
and represents the best energy transfer line. For the F-15
that happens at M0.92 and for most jet fighters is somewhere
close to M0.9. In the diagram below, our pilot started at
A, accelerated to B than climbed to C.
The amazing thing is that in order
to get to the best possible energy advantage for the fight,
you start by diving! You increase speed to a point well above
that for minimum drag. The objective, after all, was not to
minimize drag, it was to gain the most energy in the least
time. Drag is not the only factor that needs to be considered.
Jet engines generally produce more thrust at higher speeds,
and so a higher speed can result in a greater specific excess
power...that's more Ps and thats always good! The diagram
below is typical of real jet fighters.
So the modern fighter pilot will always
begin an intercept (or a tail chase) by increasing his speed
to maximum energy transfer rate as quickly as possible, using
a zero G maneuver. How does that contrast with the aircraft
of W.W.II? Propeller and turbocharged engine combinations
were generally designed to give maximum efficiency close to
top speed at the critical altitude. So both altitude and airspeed
have an influence on the best energy transfer, just as it
does for the jets. That this technique survives the differences
between jet and prop driven aircraft is both surprising and
advantageous to those who know.
So assuming a realistic drag polar,
and properly modeled prop thrust, the energy transfer diagram
will appear similar to the one above. A wise pilot will therefore
dive to get to his maximum energy transfer speed as quickly
as possible before starting the climb that allowed him to
maintain that speed. If that placed him at a faster speed
than his opponent, he would not only be closing but also building
an overall energy advantage prior to the zoom climb.
Just as for jets, drag is not the
only concern in maximizing rate of energy transfer. If you
start a chase above the critical altitude for your supercharged
engine, diving towards that altitude would increase the available
power, resulting in higher specific excess power. That this
works in simulations like Aces High and Warbirds can be confirmed
by chasing an aircraft at high altitude. If you deliberately
stay below it, you will have more engine power and a slightly
higher air speed, resulting in closure and better energy transfer.
This is interesting enough to do properly
so I will revisit the topic and plot some genuine curves for
Aces High that will show the best energy transfer speed for
some of the aircraft. I will do that quantitative analysis
when time permits and it will be interesting to see how the
figures clock out. Meanwhile I feel very confident that the
flight models of most of the current W.W.II simulations are
close enough to reality that what happens in the sim will
agree with what real world aerodynamics predicts.
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