Forum: General

Ok I am structures stupid... How does putting dummies on station 2 and 8 instead of 1 and 9 make that big a difference with the 341 bulkhead issues? The rails are still on the tips and more rails and weight have been added?

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The closer the stores to the fuselage, the less wing warpage and vibration. Less inch-lb (Moment) effect on the aircraft total.

I get that but instead of just having one wing with a dummy you now have two extra rails on 2 and 8 with a dummy on one of them??? Seems like adding all that weight out there would offset any benefit??? What are we talking 2 feet between 2 and 8 and tips? I get even more confused when a jet that is under watch for 341 goes out with 2 and 8, 1 and 9 hanging junk?

Is this one of those cases where the weight helps like on a heavy when you keep fuel in your outboards to reduce wing and fuselage stress?

Missiles and rails at 1,2,8, and 9 don't make much difference to the 341 bhd. And you are right, heavy weights outboard can reduce wing and fuselage stress, but not always. It depends on what the airplane is doing - turning, rolling, ejecting tanks or heavy weapons from 3,4,6, or 7, or a combination of those items, speed, altitude, etc. The most severe load on 1,2,8, and 9 is from supersonic tank jettison from 4 and 6, ejecting a 2000 lb bomb from 3 and 7 at 4g, or jet wake encounter. But those severe load cases heavily stress only the wing tip area, and do not have much effect on the 341 bhd.

Salute!

A long time ago in a galaxy far away I flew the A-37.

We had pissant 250 lb eggs on the outboard stations and bigger ones inboard. So we used the little ones as "wind bombs".

When we started to get cracks in the spars from over stressing the wings and then simply taxiing with big loads, then we got religion. Turned out most of the problem was taxiing with heavy loads.

As with the Viper, you can pull a lotta gees if you have ordnance outboard. Where do you think the stress is on the wing when everything weighs three, four, six times as much as when on the ground? The "lifties" are above the wing hardpoints. Duhhhh.

If you pull a lotta gees with nothing outboard, then the wing bends upwards. If you have something out there the wing doesn't bend as much. So in the A-37 we "rippled" the upper surface of the wing panels when yanking too hard when nothing was left outboard. Crew chiefs were pissed, and we wasted lottsa hours "fixing" things.

John-boy can add his expertise here, and is much more qualified than this old fart.

The missile loads on the wingtips always seemed to me more of a problem, as they would flip up and down a lot when we were yanking and banking. Damn wings were clearly bending up and down. You coulde also see this in the HUD when using the missile display of the seeker LOS.

Gums sends ...

Gums,
Maybe more qualified about some things, but your pilot seat descriptions of what's happening out there on the wing are much more fun to read.

Yep, those tips are moving around a lot and that screws up missile alignment. So the HUD has equations in it to correct for those deflections, so it really knows where the seeker is looking. Same thing for correcting fuselage bending between the HUD and the gun to keep gun alignment pure. And same thing for the fuselage between the radar and the HUD.

Why are the wings so flexible? Low drag! You want low drag, so the wing is thin. Thin wing is flexible wing, but that's not all bad, since the clever structures weenie can use that flexibility to his advantage and to the advantage of a flight control weenie. One way is to have the wing twist leading edge down when it is loaded at high g. That means the tip has lower flexible angle of attack than the root of the wing. That reduces wing bending moment (lighter wing) and lets the tip stall later than the root for better control. The tip is farther aft and that tends to prevent pitchup and loss of control.

Forum: General

341 bulkheads and station 2 and 8