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Dienstag, 20. Oktober 2009, 21:08

Interesting Analysis: F16 vs F 18


A Navy Test Pilot's Perspective

As a Navy test pilot on an Air Force exchange tour, I have the best job in the world: I get to fly the F-16 Viper and the F/A-18 Hornet. Last summer, I completed Viper conversion training at the 310th Fighter Squadron at Luke AFB, and the first thing they teach is the single-engine, single-seat mindset-a new concept for a twin-engine fighter pilot. The Viper has only one engine and pilots quickly learn the "Iguana stare," which is when one eye constantly monitors the engine instruments, and the other scans everything else. Some USAF pilots have labeled the F-16 a "lawn dart," as it has one of the highest accident rates in the Combat Air Force. It's a myth that the high accident rate is caused by the lack of redundancy inherent to a single-engine fighter. The reality is that most F-16 mishaps occur because of factors other than engine failure. Running into things (the ground or other airplanes) accounts for more than three-quarters of F-16 mishaps.

After 50 hours in the jet, I've come to consider the aircraft at least a close acquaintance, and we're working toward becoming good friends. During that time, I've formed some opinions and impres- sions of the Viper compared with my normal mount: the F/A-18 Hornet.
When compared with the Hornet's, the Viper's cockpit is more compact and is very comfortable. The ejection seat's fixed, 20-degree recline angle is great for all phases of flight except air-combat maneuvering (ACM). During a fight, the pilot has to constantly lean forward to look over a shoulder or check six, and at 7 or 8G, the fixed recline angle produces a sore neck and back in nothing flat. A flight surgeon once told me that 90 percent of all fighter pilots suffer from chronic neck and back pain and Viper drivers suffer the most. The single-piece bubble canopy is one feature that I wish the Hornet had. The glass comes down to the elbows and wraps around the pilot; it provides great six o'clock and over-the-nose visibility without a canopy bow or heads-up-display (HUD) post to obstruct the view.

The main instrument panel is centrally located, compactly organized and easy to scan. The Viper is a fly-by-wire electric jet, but it still has what are considered old-fashioned, round airspeed and altitude dials, tape gauges for vertical speed indicator (VSI) and angle of attack (AoA) and an analog attitude indicator. These are the primary flight instruments because the HUD is technically not certified for IFR (instrument flight). In the Hornet, I use the HUD as my main information source and crosscheck the steam gauges during instrument approaches. The Viper HUD gives the same data as the Hornet HUD does, but the format's different. Adapting was easy except for one important item: the angle of attack bracket. The two indicators look exactly alike, but they work exactly opposite; when landing, one tells the pilot to pull when he should push, and vice versa. It's potentially very confusing. Flying AoA "backward" was tough at the beginning, but I eventually figured it out. The rest of the Viper's HUD symbols are busy but easy to interpret. By flipping a few switches, the pilot can customize HUD information as needed for the mission.

The Viper's side stick and throttle are marvels of ergonomie design. For single-seat strike fighters without the benefit of a guy in the back (GIB) to operate the radar and weapons systems, the hands-on throttle and stick (HOTAS) design is key to managing the airborne workload. As its name implies, hotAS allows complete pilot control of the weapons systems with hands-on maintenance of the flight controls. The Viper has 16 hotAS controls, and all are easily actuated with minimal movement. Some of the "HOTAS-able" functions include: radar mode select, bomb pickle, gun trigger, missile pickle, chaff/flare dispense, etc.

The throttle designator control (TDC) is a feature that's found in both aircraft, and it's essentially the "mouse" of the weapons system. It's used for slewing the cross-hairs over targets detected on the radarscope or in the HUD and locking onto them. The Viper's TDC is on the throttle under the left thumb; it took some getting used to for making fine-tuning adjustments. The Hornet's TDC is a little easier to use because of its location under the left index finger. I have much more dexterity with my index finger and found sensor slewing much easier in the Hornet.

In the Viper, all radar and targeting forward-looking infrared (FLIR) pod information is presented on the two monochrome multifunction displays (MFDs). They are smaller and are of older technology than the Hornet's, but the displays are easy to read in all lighting conditions. The F/A-18 has three color MFDs with the center one being a larger digital moving-map display. The moving map, or multipurpose color display (MPCD), is the key feature that distinguishes the two strike fighters. The sheer amount of situational awareness that the Hornet's MPCD provides the pilot of threats, friendly locations, geographic references and navigational data significantly enhances combat effectiveness. Without the moving-map display, the pilot's mental workload doubles, and some of the more senior pilots, including myself, will "down" the aircraft and not fly it if the map display fails. Some newer block Vipers have display upgrades that mirror the current capability of all Hornets, but those are exceptions. Avionics in the Hornet are far superior to those found in almost anything I have flown. The one exception is the Super Hornet; it has two additional displays that improve on the Hornet's design.
The F-16 consoles aren't as well organized as the Hornet's; some switches are hard to reach. For the most part, that doesn't affect normal operations but could delay pilot reaction time during an emergency. For example, the Viper's throttle obstructs access to the engine control switch with afterburner selected. This switch is used to back up the electronic engine control during certain failures; reaching around the throttle could delay completing the critical action procedures if the engine gets sick right after takeoff.

The Hornet's consoles are logically grouped by systems. The environmental control system control panel, electrical control panel and lighting control panel are separate units. Conversely, the Viper's left console has flight-control switches mixed with the electrical switches and fuel transfer switches; they're clustered together. After about a dozen simulations and flights, I was able to adapt to the F-16 normal and emergency procedures checklists, but the Viper's cockpit layout appears to be a product of evolution, whereas the Hornet's cockpit layout has changed little since day one.

Both the Hornet and Viper use fly-by-wire flight-control systems, which means aircraft response is governed by a set of programmed flight-control laws that "live" in the flight-control computers, which I affectionately refer to as "George." In other words, the pilot isn't flying the airplane, George is. The pilot tells George he wants the airplane to do something, and George then zips through the math to figure out which flight-control surfaces should be moved to fulfill the pilot's request. The big difference (and it is a big one) is that the Hornet uses a conventional center stick, and the computer senses stick position to interpret what the pilot wants. The Viper uses a side stick, and the computer senses stick force from pilot input.
Flying a side-stick control takes a while to get used to, but once you do, it's a joy. The conformai stick's shape feels very natural (it fits in the hand like a melted candy bar), and it allows easy access to nine of the 16 hotAS controls. Two fully adjustable forearm rests on the right cockpit bulkhead stabilize and isolate the pilot's arm and wrist, so when rattling around the cockpit during turbulence or going after the bad guy, the pilot's arm won't accidentally move and initiate unwanted control inputs. In its original design, the Viper's control stick didn't move at all; it just measured pressure from the pilot's hand. However, after initial F-16 flight tests, a ¼ inch of stick movement was incorporated to give a small dead band and a nominal breakout force to give better "feel" of a neutral stick because otherwise it was entirely too sensitive. The control harmony is quite good (the pressures required for pitch and roll mix well), but without the capability to physically position the stick, it's easy to contaminate roll inputs with unwanted pitch inputs, and vice versa.
My first Viper instructor predicted that I would over-rotate on takeoff and drop the right wing; he was right. The over-rotation occurs because a pilot is used to "moving the stick and then something happens" at rotation speed. When I reached 145 knots and pulled back, of course the stick didn't move but a scant ¼ inch, so I pulled more. The inexperienced have no way of knowing how hard to pull, so I pulled probably twice as hard as was necessary. After a half-second delay, the nose abruptly responded to my input and pitched up to about 10 degrees, while at the same time the right wing dipped to about 10-degrees wing down. I released back-stick pressure, and the aircraft held 10-degrees pitch as I gently leveled the wings. According to my instructor Lt. Col. Dan Levin, who has more than 3,000 Viper hours, pilot-induced-oscillations (PIO) are very common on takeoff for transition pilots.

End of Part I

"When my time on Earth is gone, and my activities here are past, I want they bury me upside down, and my critics can kiss my ass."Bob Knight

Those who would give up essential Liberty, to purchase a little temporary Safety, deserve neither Liberty nor Safety.."
(Benjamin Franklin)


Dienstag, 20. Oktober 2009, 21:13


In my opinion, the Viper's biggest strength is its brute force: it has lots of horsepower. The biggest kick in the pants-next to a catapult shot off an aircraft carrier-is the kick from stroking full afterburner in a General Electric-powered, bigmouth Viper on a cold winter morning. With a greater than 1.2:1 thrust-to-weight ratio at takeoff gross weight, it takes all of 1,200 feet to get airborne at 160 knots, and the jet can be supersonic just two miles later, if it's left in burner. The acceleration is unbelievable! If there weren't a 7G restriction on a fueled centerline tank, I would easily have 9G available to pull straight into the vertical and accelerate on the way up. Of course, I've done the "quick climb" to 15,000 feet, and after level-off, I still have 350 knots. The Viper can out-accelerate most anything in the air, including the Hornet.
To accurately compare the Hornet's performance to the Viper's, I took off from the same runway. The Hornet needed 200 feet more than the Viper to get airborne at about the same speed, and at the end of the runway it had only 330 knots versus the Viper's 500-plus. The best climb angle that I could get out of the Hornet before airspeed started to decay was 45 degrees, and I leveled off with 200 knots; the Viper's climb took one minute less. The Hornet's lack of thrust seems to be where all the critics linger, and that's valid-to a point. When a pilot flies into battle, lots of thrust is nice to have and is definitely fun to have, but it isn't necessarily a must-have-depending on the aircraft's other attributes. Like the Viper, the Hornet has different engine versions in inventory, but even with two "big motors," the GE-404-402 has 18,000 pounds of maximum thrust each, and in a drag race, the Hornet would be no match for the Viper.

When the wheels are in the well, the Viper flight controls change from takeoff and landing gains (it automatically changes modes, as it requires different pressures for the same reaction) to cruise gains. This reduces the PIO tendency in pitch when the aircraft is slower and near the ground. The acceleration in after-burner seems to build with airspeed, and it's really a kick! The faster I go, the faster I go; this is primarily because of the fixed-geometry inlets that become more efficient as airspeed increases. Canceling afterburner (AB) at 300 knots and 2,000 feet AGL does not stop the amazing acceleration. Even in military power, the Viper easily slips above the 350-knot climb speed in a 15-degree climb. On the other hand, the Hornet has a smooth and steady acceleration and quickly reaches the standard climb profile of 300 knots in a 15-degree climb at military power. In the Hornet, the nose must be lowered to about 5 degrees at 10,000 feet for it to accelerate and maintain a 350-knot climb speed.
Once in the air, the Viper pilot can drill around all day at 350 to 400 knots and still have fuel to spare. If there's a concern about fuel conservation, the Hornet works best in the 300- to 350-knot speed regime. Roll performance in the Viper is slightly faster than the Hornet's. A full-deflection aileron roll is eye watering in a clean Viper (about 360 degrees per second) and very impressive in a slick Hornet (about two-thirds the speed of a Viper). One nice feature of the side-stick controller is the capability to rapidly capture a precise bank angle by simply releasing the stick. The jet's controls essentially freeze when the pilot lets go of the stick, even when whipping around at maximum rate roll. This is real handy in rolling in on a target (both air-to-air and air-to-ground). The Hornet's roll control is equally precise, but it requires a bit more finesse. Its flight-control system in cruise is a "G-command" flight-control system; it continuously trims to IG flight regardless of aircraft attitude. If a pilot rolls inverted in a Hornet and lets go of the stick, the jet "pulls" IG and enters a gradual dive to maintain IG. Doing the same in the Viper causes the pilot to get light in the seat; the jet doesn't feel any pilot input, so it continues to head straight and inverted. The Hornet's G-command has bitten a few transition pilots during ACM when they were confronted with very nose-high, low-speed attitudes. Tomcat drivers learning the Hornet typically release the controls, as that is what they were used to doing in the F-14, which stops flying around 100 knots. In the Hornet, this just leads to a further nose-high attitude, as the Hornet reverts to pulling and placing IG on the airplane.

The Viper rolls well, but it is easy to inadvertently add G during rolling maneuvers because it takes some concentration to prevent accidentally applying backstick pressure while exerting side pressure in for the roll. I encountered this early in my training. It was challenging, at first, to perform a pure, constant IG maximum-rate aileron roll: nose up and then fly a gentle arc up and then down while rolling so the seat of my pants stays in the seat all the way through. My tendency was to load the roll to 2G halfway through by applying too much backpressure. The next time, I overcompensated and got light in the seat, as I saw about O.SG. Again, the learning curve is steep; eventually, I could max-perform in roll without inadvertently pulling or pushing G.
In the beginning of the training, it's difficult to yank the nose around in a minimum-radius, maximum-G level turn without accidentally introducing aileron in it that isn't wanted. On my first few attempts at a 9G level turn, I tended to ratchet the wings back and forth from one bank angle to another. The side stick feels only the first 25 pounds of pilot input in the longitudinal axis, at which time it gives all 9G (or whatever's available at that speed). Apparently, I must have also inadvertently applied a small amount of lateral-stick force, and that caused unintended bank-angle changes and the subsequent ratcheting. After a few more tries at a 9G level turn, I learned that by using a smooth, gradual G buildup and by toning down the amount of pull, I could nail a 9G, 360-degree turn while maintaining constant altitude within 100 feet.
This jet can hurt you because it has absolutely no problem holding 9G, especially down low. The Hornet is limited to 7.SG by the flight-control software, even though the airframe can handle 9G; in fact, some foreign versions were going to be sold as 9G jets. The tradeoff is fatigue life. When dogfighting in a Hornet, I rarely see 7.SG, and if so, it's momentary because I'm usually closing to guns after the second merge and am trading airspeed for nose position.
There's no better performing fighter in the close-in, slow speed, knife-in-the-teeth dogfight than the F/A-18 Hornet, except maybe, of course, a Super Hornet. But that's another story. The Hornet flies very comfortably at AoAs of up to 50 degrees and has great pitch, roll and yaw authority between 25 degrees of AoA and the lift limit of 35 degrees of AoA. Most crowds are amazed when the Blue Angels perform the Hornet low-speed pass, which is around 120 knots and only 25 degrees of AoA. There are no nasty departures to worry about, and if the pilot happens to lose control, the best recovery procedure is to grab the towel racks (two handgrips on the canopy bow used during cat shots). On the other hand, a Viper has a 25-degree AoA limiter built into its software, and even fewer degrees of AoA are available if it's carrying air-to-ground goodies on the hard points. Up against the limiter, the nose stops tracking; in that case, it's time to drop the hammer and use the big motor to get the knots back, which by the way, happens in a hurry.

The Hornet, however, will stand on its tail, hold 100 knots and 35-degrees AoA and swap ends in a maneuver called "the Pirouette," which looks like a jet fighter doing a hammerhead with a quarter roll. To the spectator and the participant, it looks and feels impossible. The Hornet gets slower (high-energy bleed rate) quicker than anything I've flown, and it gets faster (low acceleration performance) slower than anything I've flown. In a Hornet, it's difficult not to get the first shot in a close-in dog-fight that starts from a perfectly neutral merge (going opposite directions at the same altitude). My Viper buddies tell me there is very little room for error when they fight the Hornet. The best way to handle the situation is to get the Hornet to slow down, while they maintain energy so the Viper's superior thrust-to-weight will out-zoom the Hornet and then they can shoot at it from above. As a Hornet driver, I have never lost to a Viper guy that I saw, but I have run into Viper drivers that said the same thing about their jet.
As I dirty up for landing (lowering the gear handle is the only pilot action, all other configuration changes are automatic), the Viper becomes a blended-rate command, AoA-command flight-control system. I can trim the aircraft hands-off to the approach AoA of 11 degrees, and the flight-control system should maintain that AoA. In my experience, the Viper is very pitch-sensitive-especially in the flare.

Landing the Viper is easy, but landing the Viper while making it look good is far from easy. The airspeed is controlled with the throttle, and the glideslope is controlled with the stick (at least on the front side of the power curve). The pilot must use the throttle very judiciously on final; with the huge General Electric motor, it's easy to gain excess airspeed rapidly and then float a quartermile down the runway. If the pilot misjudges and gets slow, he can scrape the tailpipe or prang the landing gear, with a bounce back into the air below flying speed (very bad).
The Hornet, by contrast, is very easy to land. The aircraft is trimmed for on-speed, and the glideslope is flown with the throttles until touchdown at 650 to 700fpm. Both aircraft have a HUD flight-path marker (FPM) to tell the pilot where the jet is going. The pilot places the FPM on the piece of runway he wants to touch down on, and that's where he'll land. In the Hornet, the throttle is the primary control for the FPM; in the Viper, it's the stick. The vertical-G load on an average trap at the boat is about 2.7G. The longitudinal deceleration from grabbing an arresting cable is about 4G. That landing is actually a precisely controlled crash. It's easy to nail the glideslope in the twin-engine Hornet by adjusting one throttle at a time by "walking the throttles." Precise glide-slope control is really handy when landing on the boat. As a Navy carrier pilot, I'm not the best at flaring the Viper; I usually bounce once or twice, which I'm told isn't bad.
I am often asked, "Which one do you like the best?" The answer is easy, and I reply with this analogy: the F-16 Viper is like the Dodge Viper, and the F/A-18 Hornet is like a Lexus. If I want to cruise around town and experience pure acceleration performance, I would drive the Viper. If I want to cruise in total luxury on a long road trip with all the amenities and Gucci displays, I would drive a Lexus.

It's definitely more fun to fly the Viper, but the Hornet is the aircraft that I would want to take into combat. The primary deciding factors are the superior ergonomics in the Hornet's cockpit design, and its avionics controls and displays. The only jet that I've flown that is better is the F/A-18E/F Super Hornet. Another major consideration is the Hornet's capability to take a surface-to-air missile (SAM) up one tailpipe and still make it home on the other engine, as was demonstrated in the 1991 Gulf War.

Speed is nice to have, and 1 wish the Hornet had more, but my confidence in the jet that I grew up in is high. However, the more exposure I get to the various Viper upgrades and different blocks, the more I appreciate its capabilities. The real bottom line is this: if I were a bad guy, I would hate to go up against either one.



"When my time on Earth is gone, and my activities here are past, I want they bury me upside down, and my critics can kiss my ass."Bob Knight

Those who would give up essential Liberty, to purchase a little temporary Safety, deserve neither Liberty nor Safety.."
(Benjamin Franklin)


Dienstag, 20. Oktober 2009, 21:20

The featured article was first published in 2003.
Technical improvements in military aviation are tremendous in the timespan from 2003 to the present day
Enjoy reading this pilot report! :winke:

"When my time on Earth is gone, and my activities here are past, I want they bury me upside down, and my critics can kiss my ass."Bob Knight

Those who would give up essential Liberty, to purchase a little temporary Safety, deserve neither Liberty nor Safety.."
(Benjamin Franklin)


Mittwoch, 21. Oktober 2009, 08:51

Sehr interessant, vielen Dank Balu! :tag:


Mittwoch, 21. Oktober 2009, 22:34

Sehr interessant, vielen Dank Balu! :tag:

You´re welcome! :winke:

"When my time on Earth is gone, and my activities here are past, I want they bury me upside down, and my critics can kiss my ass."Bob Knight

Those who would give up essential Liberty, to purchase a little temporary Safety, deserve neither Liberty nor Safety.."
(Benjamin Franklin)