HELP: Corner speed and turn performance
Michael Williamson
David Garza wrote:
> I am aware of the corner speed indicator on the HUD, which will display
> the optimum turning velocity at a given altitude. However, what does this
> corner speed translate into in terms of turning performance?
>
> For example, at 10,000 ft. an F-22's corner speed is 340kn and a Rafale's
> is 435kn.
>
> Does this mean that the Rafale will outturn the F-22 at this altitude
>
> If the corner speed indicator doesn't give a reliable turn performance
> vs. other aircraft, how is this information available?
The corner velocity of an aircraft may be used as a guideline, if you also
know the maximum G the aircraft can pull.
First, a bit of (somewhat simplified) background on corner velocity,
for those who may not be experienced flyers in either sims or aircraft.
An aircraft's turn performance is limited by 3 things:
1. The amount of lift its wings can generate (a function of airspeed
and wing design) before a stall occurs
2. The maximum amount of force (expressed in G's: 1 G = the force
of gravity, or straight and level flight) the aircraft can
maintain before something (such as the wings, or some part of
the airframe) breaks
3. The amount of thrust available to overcome the extra drag created
when pulling Gs. If there is less thrust than drag, then the
aircraft will slow down, creating less lift and decreasing the
maximum G available.
At corner velocity, the maximum lift which may be generated by the
wings is exactly equal to the Max G limit of the aircraft. Going slower
than this will decrease the Gs you can pull because you will stall.
Going faster will not increase the Gs- they will remain constant at the
aircraft's structural limit (so you can't break it), causing turn rate
to decrease and the turn radius to decrease.
If we assume that the two aircraft in a fight both have the same G
limit, then the aircraft with the lower corner velocity will have
better turn performace unless the airspeed is higher than the faster
corner velocity. This is because at a given speed, the aircraft with
the lower corner velocity can pull more Gs, thus turning more sharply.
Thus, in your example (F-22 corner velocity 340kn, Rafale's 435kn.)
The F-22 can outturn the Rafale below 435 kn, if the G limits are the
same. If the Max G limit is different for the two aircraft, then
this will not necessarily be the case.
This only applies to *instantaneous* turn rate, however. In many
cases, sustained turn rate is more important. This is because few
(if any) aircraft may make a continuous, maximum G turn at their
corner velocity. Doing such a turn causes a tremendous amount of
drag, which is almost certainly more than the engine can overcome.
Therefore, speed will decrease, dropping turn performance.
A constant rate turn may be flown at any airspeed. What happens
is that the pilot pulls hard enough in the turn to keep the aircraft
at a constant speed. If he pulls harder, the aircraft will turn
more sharply for a time, but the airspeed will decrease. This is
why most dogfights in simulations end up being done at low speed and
on the deck if they last long enough. The pilots continue to pull
as many G's as they can, dumping energy (altitude and airspeed)
until there isn't any left. We are then left with a low speed,
low altitude fight where neither can maneuver well.
At any given altitude, one airspeed will give the tightest constant
turn. Unfortunately, this varies based on the weight of a given
aircraft. Generally aircraft with higher thrust/weight ratios have better
rate turns, but this is not always the case. Even worse, you won't find
those speeds, or their rates, listed in most cases.
Hope this helps (somewhat). If the two aircraft have identical G limits
(which they probably do in most sims) then the aircraft will have the
same turn rates and radii for a speed above both corner velocities. Below
either corner velocity, the aircraft with the lower corner velocity will
have a better instantaneous turn rate. The sustained rate is anyones
guess, but if the weights and engine thrust are comparable, probably the
aircraft with the lower corner velocity has a better sustained turn rate.
Mike
David Garza
I have a simple question: how can one tell what airplane will outturn
another one? Specifically, I'm playing ATF, and for all of Jane's
association, there doesn't seem to be a mention of comparable turn
performance in the manual.
I am aware of the corner speed indicator on the HUD, which will display
the optimum turning velocity at a given altitude. However, what does this
corner speed translate into in terms of turning performance?
For example, at 10,000 ft. an F-22's corner speed is 340kn and a Rafale's
is 435kn.
Does this mean that the Rafale will outturn the F-22 at this altitude at
just about any speed, or only at 435kn? Or does this have nothing at all
to do with comparable turn radii?
If the corner speed indicator doesn't give a reliable turn performance
vs. other aircraft, how is this information available?
Any help with this would be very appreciated.
-- David
BTW Here's the corner speed indicators for the ATF fighter planes:
F-22 Rafale FSW-29 X-31
5000ft 290kn 340 420 510
10,000 340 435 470 500
15,000 440 440 480 480
20,000 425 425 475 520
25,000 500 500 475 500
30,000 480 485 440 480