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All right, you F-16 drivers. No excuses for losing control of an F-16. This fact, though well punctuated on these pages in the past, hasn’t kept my compadres in our safety department from passing me reports of some of you losing control. In some cases, this has led to the loss of an aircraft (three in the last two years). My immediate response is to dust off some old copies of Code One and do a little clench-fisted highlighting. For those of you who’ve misplaced your back issues, here’s a refresher on maintaining control and what to do when you’ve lost it.
In the first five issues of Code One, I offered a series of articles for your enlightenment and, of course, your reading pleasure. In that series, called Semper Viper, I went into some detail about the radical design of the F-16 – its use of negative stability in particular. The airplane is designed to be negatively stable in pitch. Its computer-controlled flight control system uses all the good parts of negative stability and keeps all the bad parts in check. This was a radical departure (punintentional) in aerodynamics and flight controls, and it gives the F-16 some unique characteristics. That gets me back to the topic at hand.
The most important thing to remember about the F-16 is that it will not depart if you don't get too slow. But being slow does not guarantee a departure. You must still inject a large degree of ham-handedness before you will depart. The last thing I want to see is a knee-jerk reaction of establishing some minimum airspeed on F-16 maneuvering. While it is not too smart, tactically, to fly slow, you can continue to point the lift vector even when the airspeed is off-scale low. (It is not a very big lift vector under these conditions, but you can still point it to make the aircraft go where you want it to go. You just won't go very fast in that direction until you get some smash.)
In Semper Viper, I also went to some lengths about the limiters in the F-16 flight control system. The limiters keep an unstable aircraft under control. If you're slow (both airspeed and mentally) and you make some sort of gross or rough input, the flight control computer will try to honor your request. However, it immediately senses that the airplane will depart control as a result. Even though you keep pulling or rolling, the flight control computer has reversed the control input (sometimes all the way to the opposite stop). Because you are slow (airspeed only in this case), the control surface doesn't have enough authority to maintain the control it desires. So the aircraft departs. This situation is your fault, not the airplane's.
What are some of the cues you should be looking for? If the airplane is buffeting, you're slowing down. (The altitude or power setting doesn't matter. If you are in buffet, you are slowing down.) The airplane will fly very well deep into buffet, so don't be afraid to pull if the situation dictates. Just remember, to turn in this situation you must give away energy (airspeed). Before any of you point out that you can maintain this or that altitude/g combination, go back and take another look at that same combination and you will find that the angle of attack is too small to produce buffet. A little more alpha and buffet appears, and you start to give away airspeed. The same holds true if you are flying vertical, or near vertical. In my previous articles, I went into greater detail as to why. For now, accept the fact that you will slow down if you try to go vertical for very long. (You can't escape the laws of physics, even in an F-16. But you can come closer than in any other jet.)
So, you've been paying attention and know that you're slow (airspeed for sure, maybe mentally). It may help to sneak a peek at the HUD. Still, if you're aware of the cues peculiar to the F-16 (and I've discussed these a time or two in the past), you should never be surprised that you're slow. If you are slow and the aircraft is not going where you want it to go, it's no big deal. Simply allow the flight control limiters to do their thing, and you will get where you want to go without any undue dramatics. How? Be smoooooth.
Smoooooth (that's five o's) doesn't necessarily mean slow. There's a subtle difference between the two words. If you know that you're slow and you want to pull or roll the aircraft, then do exactly that. The input should be simply "and pull" or "and roll." (More about defining "and" in a second.) It shouldn't be "pull" or "roll." It shouldn't be "and pull/roll" or "and roll/pull." In other words, don't assault the two limiters at the same time.
Speaking of time, you might ask, "How long is an and?" The answer depends on your airspeed. At 600 knots, it might be one-thousandth of a second. At less than 100 knots, it might require almost a full second of input. You want to let the flight control system know the input is coming, allowing it to make complete use of its limiters.
Figure 1 gives you a better idea of what I'm talking about. The upper line represents any of the limiters in the flight control system. It could be the AOA limiter or the roll rate limiter. If you make a brutal input, the aircraft immediately tries to honor the request. If you have sufficient airspeed (energy) in the airflow around the control surface, you might see a slight overshoot. But the flight control system can quickly return to the desired limit. If you are slow, you'll have a gross overshoot. In this case, the negative stability takes over. All bets are temporarily off as far as controlled flight is concerned.
Take a look at the smooth input line that I describe as "and pull." If your initial input is smooth (and technically slow) for the first few nanoseconds, you can continue to accelerate your input in the desired channel. Notice that the aircraft response is different since we have given the control system a heads-up that a large input is coming. The flight control system knows the limit is there and starts backing off to avoid overshooting it. If you fly the airplane in this manner, it is nearly impossible to depart. The only exception: you are nearly vertical and the airspeed truly goes to zero. When the aircraft falls backward for a short time, it is possible to depart.
In addition to the occasional screw up with the airplane nearly vertical, you heavy handers may experience some departures due to rough control inputs at low airspeeds. Despite my words of wisdom, some of you are still going to make less-than-ideal inputs to the flight control system. Once the airplane departs, it will behave in one of four cases:
- The airplane will recover on its own. It desperately wants to recover. The flight control engineers did a good job in this respect. Even though you have just departed a negatively stable airplane, it will recover without your help more than eighty percent of the time.
- The airplane will go into an erect deep stall. Figure 2 shows that in the fifty- to sixty-degree AOA range, the total moments (read forces) on the airplane are essentially zero. Therefore, if you do something foolish to force the F-16 past the AOA limiter of twenty-nine degrees and arrive in the fifty- to sixty-degree range with little or no pitch rate, the F-16 is happy to stay there.
- The airplane will go into an inverted stall with no rotation. The other side of Figure 2 shows a location similar to Case 2 above. The aircraft will behave inverted as it does erect.
- The airplane will go into an inverted deep stall with some amount of rotation. (In Semper Viper, I went into some detail as to why.)
So, now, how do you recover?
In Case 1, do nothing. Consider yourself lucky. Go home. Take some time to explain to yourself how you screwed up and don't do it again. Share your experience with your pilot bubbas.
In Case 2, you must do something to recover the airplane. Watch what it's doing in the pitch channel – the channel that makes your eyes go straight up and down in your head. Ignore any inputs that make your eyes go left or right and ones that make them go clockwise or counterclockwise. (Usually all three motions are present in various amounts.) To recover, you must reinforce the pitch oscillations. Depending on the configuration and the conditions that produced the deep stall, the magnitude of the pitch oscillations will vary from deep stall to deep stall. But the frequency of the oscillations will be fairly constant at about three seconds from one extreme (nose high) to the other (nose low).
Find the manual pitch override, or MPO, switch. As I've mentioned in the past, you should practice locating this switch when it's less hectic in the cockpit. In other words, don't wait for a deep stall to familiarize yourself with the MPO switch location. Hold the switch outboard. When the nose is at its lowest point, pull back and hold. At the same time, the other side of your brain should start counting the seconds . . . one thousand, two thousand . . . When you think the nose has reached its highest point and has reversed its direction, push and hold the stick. (The MPO is still outboard.) Check back with the other side of your brain. If it is just completing three thousand, you're doing it right.
A common mistake is to try to do the pitch rocking too fast. (Your body clock is usually running about ten times its normal rate about now.) Another common mistake is to confuse a yaw or roll oscillation with a pitch increase. Remember what I said about your eyeballs. You should only be concerned with movements straight up and down in relation with your head. (Of course, I'm assuming you're sitting straight up. You are, aren't you?) Don't bite on yaw oscillations and pull when it's not called for.
As you push, the nose should pitch down, hesitate slightly, and then pitch farther down. You'll see the AOA gage break off the peg (32.5 plus-or-minus a little), and you'll be flying. If the nose reverses in pitch, pull the normal three seconds and repeat the process. As the nose pushes down and you've recovered, quit pushing so you don't pitch over on your back and enter a situation described in Case 3.
Case 3 is a mirror image of Case 2. Once you're sure that the airplane is indeed in an inverted deep stall (remember, it wants to recover on its own), follow the sequence described above. To review: (1) MPO outboard; (2) When the nose is at its lowest point, push and hold the MPO and begin counting; (3) When the nose is at its highest point, (inverted) and total time is three seconds, pull and hold. The nose will pitch down, and you should be flying again. Don't continue pulling and force the airplane into an erect deep stall. Just like before, don't confuse a yaw or a roll for pitch.
Some people would call Case 4 – an inverted deep stall with some rotation – a spin, but the marketing guys get upset with me when I do. Whatever you want to call it, your eyeballs will be traveling in a fairly constant direction left or right, rather than oscillating left and right. To recover, step on the opposite rudder to stop the rotation. (Pitch rocking is usually ineffective if the airplane is rotating.) The airplane will usually recover on its own when you stop the rotation. If it doesn't, you have just entered Case 3. Recover the aircraft as described above, go home, and make sure you don't do it again.
For those interested in some nontextual training, the test pilot cadre here at the fighter factory has had an offer on the table since 1978 to provide a short briefing and a one-sortie program to show you all you need to know about keeping the shiny side up all the time. The sortie was designed by the test and operational pilots of the F-16 Combined Test Force at Edwards AFB. I've already trained pilots in two foreign air forces and am scheduled to fly with a third soon. Alone, I have done more than 250 intentional deep stalls with these pilots and recovered all of them. Call me stallworthy.
The training sortie includes five maneuvers that, if you understand correctly, will ensure that you never depart the F-16. To make certain that all the bases are covered, I force the F-16 into a deep stall in four additional maneuvers so that you can recover the airplane. These maneuvers get your own references to match up with what I have been saying here about timing, sounds, sights, and so on. One sortie will ensure that you'll never lose control of your jet. Give us a call and we'll take you for a spin, or rather, an inverted deep stall with some rotation.
Check six. And remember, a departure won't improve your tactical situation.
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