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I saw, on National Geographic, two well built navy guys lifting a comparatively small missile to be attached on wings of an F-18 Super Hornet.

So when one missile on left wing is launched doesn't it drastically shift CoG of jet? Who copes with this shift

  1. Computer & other stuff internally adjusts the zero position of flight controls to attain level flight. In this case what is the basis of detecting shift in flight control made by pilot - the old zero or the new zero?
  2. The pilot by shifting position of flight controls, using hands & feet, in non-zeroish positions to maintain level flight despite changed CoG. If yes, isn't it detrimental to pilot's performance in a dog fight?
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  • $\begingroup$ One would also need to consider the change in lift when the departing missile effectively changes the shape of the jet's wing. $\endgroup$ – DJohnM May 31 '15 at 4:12
  • $\begingroup$ It's called roll damping and inherent stability. Yes, the cg shifts, but the aircraft will not spin out of control, but will make tiny attitude adjustments and fly on much as before. $\endgroup$ – Peter Kämpf May 31 '15 at 13:01
  • $\begingroup$ Some stores on aircraft actually have substantial G-limits on them, especially when asymmetrically loaded. In this case, those stores would be jettisoned prior to engaging another aircraft in a dogfight. $\endgroup$ – Rhino Driver May 31 '15 at 20:20
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It's kind of a mix of the two. Flight controls on aircraft have what's known as trim. All (or nearly all) airplanes have elevator trim; many also have rudder trim and aileron trim. The trimmer for each control is used to balance constant forces needed on that control.

To take an example that's more widely applicable than launching missiles: when you increase power (to climb or to reach a faster airspeed), the airplane will have a tendency to pitch up, so you might find you need to push forward on the stick to maintain the right attitude. By moving the elevator trim forward, you eliminate the needed force, effectively changing the neutral position of the stick.

On early aircraft, the trim often worked by having springs connecting the control wires to a large lever. Working the lever pulls the spring in that direction, applying a force to the controls. On modern light aircraft, there is a trim tab on each control surface. The trim tab is like a tiny control surface on the control surface. Moving the trim tab to one side or the other provides a force on it, replacing the force the pilot would provide through the controls.

Fly-by-wire aircraft, such as military jets and large passenger airplanes, have electronic trim. Since the pilot doesn't have to put much force on the controls to work them anyway, trimming just resets the neutral position of the stick as you describe. Because it's electronic, there can be different ways to control it. Some aircraft still have small levers to set the trim; some have up/down buttons in reach of the stick (such as the Su-27); and yet others simply have a single button that trims to the current position of the controls (the A-10). As Mr Çetin points out, some very modern military jets take advantage of the possibility of computer control: the aircraft is aerodynamically unstable, but a flight control system manages keeping stable flight.

Returning to the particular case of the F-18, it doesn't re-trim itself. When heavy ordnance is launched, the aircraft will roll to one side as you suspect, and the pilot has to compensate with the stick and pedals. Once he has stablised the aircraft at the desired attitude and airspeed, he can adjust the trim using a hat switch on the stick.

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    $\begingroup$ Regarding the F18, you might be surprised to know ordinance doesn't affect the aircraft much at all--other than making it a slow G-limited pig. I've never retrimmed the jet after dropping. It's a pretty incredible aircraft, the computers are magical. $\endgroup$ – Rhino Driver Jun 12 '15 at 5:17
  • $\begingroup$ @RhinoDriver that's cool man, I wish I could get some experience like you :) $\endgroup$ – RinkyPinku Jan 15 '17 at 4:28
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The F-16 Fly-By-Wire (and therefore most likely also the F-18) does actually not automatically correct for left/right CG shift due to stores load. The pilot manually has to adjust the electronic trim control (which Dan Hulme already described) to account for it. However the CG shift from releasing of one missile is relatively minimal, and would require only a tiny trim adjustment. Bombs or larger air to ground missiles is a whole different story.

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  • $\begingroup$ Can you state your source please? Or are you an (ex) fighter pilot? $\endgroup$ – CGCampbell Jun 3 '15 at 13:28
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    $\begingroup$ BMS 4.32 Dash 1 - F-16 manual for the F-16 Simulator Falcon 4.0 While not a real life manual, vast majority of systems are accurately modelled to how it works in real life. see section 1.12.7 candyparty.com/ST/Download/Checklists/BMS/Document/… $\endgroup$ – Essah Jun 4 '15 at 7:28
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The f-18 is a fly-by-wire aircraft. This means its automatic flight control system takes care of stabilizing the aircraft for cg changes, or other sudden forces (turbulence, bird strike, engine loss, etc). The controller keeps the aircraft in a balanced ("trim") state and allows the pilot to maneuver the aircraft even in the presence of these sudden changes. Therefore the pilot would probably not feel the mass leaving the aircraft, and would not have to worry about which side the Missile left (can be right or left wing).

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The Shrike (AGM-45)

Was on a training exercise where I got to launch a Shrike at a ship based radar target. It was a big missile and a lot of fun launching.

  • Weight: 390 pounds
  • Length: 10 feet
  • Diameter: 8 inches
  • Speed: Mach 1.5

I felt it come off the aircraft and made only very minor adjustments to the flight controls. I remember there being a bit of yaw, and not so much roll. I was mesmerized by its departure. It got kicked off the pylon and dropped slowly away from the wing keeping pace with me, before the rocket ignited leaving a long trail of smoke and disappeared.

The controller of the boat told me when the radar came up, and I saw the Shrike lock on. With a positive acquisition, and clearance to fire, I made a call that the missile was armed and inbound. They had an idea when it would arrive, although they were not tracking it. They had a calculated flight time and shut down the radar before impact. The missile went ballistic and missed the target.

Some pilots would fire first and then wait a few seconds before calling armed and inbound. In this way the controllers would misjudge the flight time allowing the missile to destroy the target. Since several flights used the target, it was somewhat customary for the last flight to make an early inbound call.

During the brief we went over the launch procedures and there was a warning that the pilot should not fly through the plume of the Shrike because of how hot the gas was. As the missile left the aircraft the plume ended up down the intake, I corrected quickly and looked in at my turbine outlet temperature (ToT). It was pegged, and my initial reaction was, "Holy $%&^" Then I settled down and realized it was a guage malfunction. Relieved I headed home and let maintenance know.

An Air Medal

I was briefing with one of the Cmdrs in the squadron and he was in his khakis with his ribbons on. I never kept track of those sorts of things, and yet was interested in a simple gold and blue ribbon in one of the rows. "Hey, Bagrat what is that one for?"

He told me that while in Vietnam he was out in front of the strike with 4 Shrikes on his wings. His job was to light up the SAM sights and engage them with his anti-radiation missiles. As he moved inland his ECM gear went off and he had a target acquisition warning followed by a visual of the SAM that was launched.

He launched the first Shrike and broke on the missile, while the radar that was tracking him shut down. When the Shrike lost the radar signal it went ballistic and missed the target. As the missile went by him he turned back towards the site and was picked up again by the acquisition radar. Another SAM was launched, and again he fired and broke to get away. The radar site shut down once more coming back up when the Shrike missed them. Finally, on the fourth and last Shrike, he got a hit on the site. He won the Air Medal for that engagement.

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  • $\begingroup$ inspiring words, makes me wanna be a better engineer. $\endgroup$ – RinkyPinku Jan 15 '17 at 4:29
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So when one missile on left wing is launched doesn't it drastically shift CoG of jet?

Not always. Aircraft are designed so their stores are as close to the CoG as possible specifically to reduce this. And that's true for a Cessna as much as an F-15.

Putting the stores at the CoG isn't always possible; it made swing-wing designs rather complex, for instance. In other cases, practical considerations get in the way. Many 1950s interceptors had their stores in less-than-ideal locations (cf Lightning and Avro Arrow) but the relatively light weight of the weapons made this less of a concern.

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