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Note: Title was previously "Movable big missiles/bombs/tanks under fighter jets: conceivable?"

Example: lateral weight distribution in fighters

Fighter-bombers jets are small and lightweight in proportion to the under wings load (including payload but also external tanks) they carry which means most stuff can't be placed right below the body of plane and heavy payload (very big missiles and bombs) ends up relatively very far from the center of mass.

(Although some designs have a bay to hide payload, the bay is small compared to the maximum possible load of other fighter and they still have the option to carry under the wings.)

So here is a (possibly unworkable) idea:

Is it conceivable to mount heavy load on movable arms that can move weight left or right to adjust mass centering:

  • at under wing load installing time?
  • during fight?

The heavy load, including external tanks, would be automatically moved to preserve mass balance.

Example: longitudinal balance for cargo planes

The idea here is to move the fret of a cargo plane in the longitudinal axis, to adjust balance and minimize trim.

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  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – Federico
    Oct 29, 2019 at 13:58
  • $\begingroup$ I couldn't find the reference but I think there's a movable ballast on some military transport to restore balance after some heavy payload is air dropped. $\endgroup$
    – user3528438
    Oct 29, 2019 at 17:07
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    $\begingroup$ Lookup the concorde trim tank which is close to what you are looking for. Note that the scaling effect works against your favour on a smaller fighter jet $\endgroup$
    – Antzi
    Nov 29, 2019 at 0:31

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While I don't know of any airplanes that move load in flight for CG purposes, there are definitely airplanes that have various fuel tanks that can be used to trim the airplane during flight. Some of these systems will move the CG aft after takeoff for better performance in cruise, and then move the CG forward before landing for a more stable approach and landing.

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Why worry about any of this? In a steep turn, the best place for the underwing stores is evenly distributed about the centerline, same as in wings-level flight.

Are you trying to address the situation where some stores are dropped and others are not? Aileron trim should be be sufficient to address this issue.

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    $\begingroup$ The worry is the asymmetric load if some reason heavy bombs and long range missiles are not used in pairs. $\endgroup$
    – curiousguy
    Oct 26, 2019 at 21:08
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    $\begingroup$ And we have been trying to tell you that you can use rudder and aileron trim to compensate for asymmetric loads! If it was a serious problem the best minds in the military industrial complex would have come up with a solution sometime in the last century. $\endgroup$
    – Michael Hall
    Oct 27, 2019 at 1:55
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    $\begingroup$ @MichaelHall "Clever people would have done that already if it was a good idea" is not really a good and helpful answer in general. $\endgroup$
    – curiousguy
    Oct 27, 2019 at 2:52
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    $\begingroup$ Off the top of my head, I can only recall one airframe + munition combination where this was an issue, and that was the attempted Harrier Harpoon load-out: if I recall correctly it couldn't fit a single missile on the centerline (clearance) but it could just about lift off with two... but it couldn't land with only one under a wing (asymmetric lift), meaning it would have to bring a dummy weight or always fire both, which killed the idea. $\endgroup$
    – AEhere supports Monica
    Oct 27, 2019 at 4:01
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    $\begingroup$ @curiousguy, I didn’t answer, that was a comment. You are worrying about something that isn’t a problem. $\endgroup$
    – Michael Hall
    Oct 27, 2019 at 15:10

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