Pilots will execute a series of turns so that during an ACMI debrief, turning circles can be assessed to demonstrate the F16s optimal turn rates (it is likely pilots will notice the difference during the flight). This is essential foundation knowledge that will support understanding of how to get the most out of the F16 in a dogfight.
Turns have two basic defining characteristics which are important to understand. The first is turn rate (measured in degrees per second) or how fast the nose of the jet is moving across the sky. The next time you exit a roundabout, note how fast the front of the car is moving past the surrounding terrain. That is your turn rate. The second characteristic of a turn is radius. Turn radius is simply how tight you are turning. In the example above, as you exit the roundabout, the road sets the turn radius. In an aircraft, however, there are no roads to follow, so the pilot sets the turn radius.
Two factors affect both turn radius and turn rate: aircraft G and airspeed. Aircraft G is how hard you are turning the aircraft, which is determined by how much you are pulling back on the stick. The more you pull back on the stick, the more G you are commanding. This increased G will lead to a tighter turn radius and a faster turn rate—most of the time.
Fighter aircraft have a limit to how much G you can pull. If you pull Gs beyond this limit, you will cause the aircraft to fail structurally or you will black out. The maximum G you can pull without breaking the jet is called max G. In older fighter jets, if the pilot pulled beyond max G, the jet might break apart. I [Pete ‘Boomer’ Bonanni, author of Falcon 4.0 manual and USAF F16 IP] have personally seen F-4 Phantom engines pulled from their mounting bolts and dropped into the engine bay due to an ‘over G’. In the F-16, the aircraft is automatically limited to 9 Gs (max G) by a G-limiter built into the flight control system.
The other factor affecting turn rate and radius is airspeed. There is a direct relationship between airspeed and G and, in combination, they affect turn rate and radius. Simply put, the F-16 has an optimum airspeed range for making the quickest (best turn rate), tightest (smallest turn radius) turn. This airspeed range is called corner velocity. At 330 knots and above in your F-16, you can pull 9 Gs (the structural limit of the aircraft). Below 330 knots, you do not have enough air going over the wings to get 9 Gs. As airspeed drops off below 330 knots, so does your ability to pull Gs. Above 330 knots, you can always pull 9 Gs.
This sounds great at first, because it appears that all we have to do to optimally turn the jet is to fly faster than 330 knots. This is not true. Above 440 knots, you can still pull 9 Gs, but your turn radius increases dramatically while your turn rate actually goes down. This is because above 440 knots, the jet’s flight control system does not allow you to pull any more than 9 Gs. The extra airspeed then only hurts your ability to turn the aircraft.
How well an aircraft can turn is a function of the turn rate and radius it generates. In the F-16, turn radius at max AOA/G is relatively constant over an airspeed range of 170 knots calibrated airspeed (KCAS) up to 330 KCAS. Above 330 KCAS, turn radius increases slightly as max G is obtained (440 KCAS). Above 440 KCAS, turn radius increases dramatically.
Because of the F-16 flight control system, the F-16 does not have a true corner velocity. It has a "corner plateau" which is an airspeed range of 330 - 440 KCAS that produces a good turn rate based on available G.
There is one other manoeuvring concept that to be addressed. This concept is called Specific Energy or PS (pronounced “P sub S”). PS is a concept that describes the energy or potential manoeuvrability of a fighter.
The PS chart (below) shows a series of fluid lines that represent specific energy states of the F-16 at an altitude of 15,000 feet and a drag index of zero. The drag index is determined by what is loaded externally on the jet. The zero PS line is the area of the chart where the jet can maintain airspeed and altitude for a specific G load. The PS lines that have negative values represent a flight regime in which the jet will lose either airspeed or altitude. The PS lines with positive numbers represent where the aircraft has the potential to gain altitude or airspeed.
- F16 Turn Performance 1.png (137.78 KiB) Viewed 1062 times
- F16 Turn Performance 2.png (34.96 KiB) Viewed 1062 times
In this turn you will see what happens to the aircraft when entering a turn at or slightly above corner speed, whilst not managing G load or energy during the turn. You will notice that while your turn rate is momentarily high and your turn radius appears to improve, the aircraft is not able to sustain this attitude. In a dogfight, this leaves a pilot vulnerable – SPEED IS LIFE!
Setup: Enter turn at A15 @400-450knts, roll jet and keep pulling full aft stick until unable to control altitude whilst pulling full aft stick.
Turn 2: Max G turn well below corner airspeed (360-degree turn).
You will see the effects of trying to turn an aircraft at low airspeed. At low airspeeds, your turn radius is small but you suffer a very big turn rate reduction. This turn rate reduction hurts your ability to point the nose and shoot at enemy fighters and also creates issues for the pilot in terms of aircraft handling whist maintaining altitude – SPEED IS LIFE!
Setup: Enter turn at A15 @ 250-300knts, roll jet and pull maximum G whilst maintaining airspeed between 200 and 250knts, continue until completing a full 360 degree turn.
Turn 3: Max G turn well above corner airspeed (360-degree turn).
You will practice max G level turns starting well above corner airspeed. This demonstrates the effects of trying to turn the jet at too high an airspeed. If you fly well above corner airspeed, the turn rate of the aircraft reduces and the turn radius increases dramatically. This poor turn rate affects your ability to point the nose, while the increased turn radius allows enemy fighters to easily fly inside your turn and stay on your tail. - THE CORRECT SPEED IS LIFE!
Setup: Enter turn at A15 at 600+knts, roll jet and maintain 9g pull until completing a full 360 degree turn or below 450knts.
Turn 4: Max G turn at corner airspeed (360-degree turn).
You to practice a max G turn starting at corner airspeed and note the effects of airspeed and G on turn rate and radius.
Setup: Enter turn at A15 at 400-440knts. Maintain 330 to 440knts while maintaining a max G turn for a full 360-degree turn.