Dive limits? Structural Limits?

[Zimme83]

On a side note, who says the main wing is the first thing to fail catastrophically. Was it the Typhoon that kept shedding tails in power dives? It kept coming apart halfway back from the cockpit. So....placing the load out on the wing might spare the spar but another piece might break.

Thats a different story. I  a dive beyond Vne there are other firces at work compare to a hard turn.

[FLS]

If you pull 4g on a loaded A-20 the wing is producing 108800 lbs of lift. It hardly seems to matter if you have 1000 lbs of bombs between the engines and the fuselage.

[Karnak]

If you pull 4g on a loaded A-20 the wing is producing 108800 lbs of lift. It hardly seems to matter if you have 1000 lbs of bombs between the engines and the fuselage.

At 4G that is 4,000lbs more the wing has to hold.  It adds up.  If you have the full 2,000lbs of bombs that is 8,000lbs more strain.  Pull six Gs and it is 12,000lbs.

What is the spar on the A-20G rated for?

[FLS]

The bomb weight is included in the 108800 lbs figure.

With a loaded weight of 27, 200 and an empty weight of 15,051 lbs every addition of 1 radial g likely adds well over 15,000 lbs to the wing load.
This is why I don't think 1000 lbs of bombs is much of an issue. My concern for high g would be the bomb shackles. I don't know what their max rating was.

[pembquist]

This thread is cracking me up. The title is what exactly?

Thats a different story. I  a dive beyond Vne there are other firces at work compare to a hard turn.

Maybe if we dialed it into "failure of wingspar due to simple overload in one direction" and imagine putting the wing on a couple of jackstands about halfway from the fuse to the wingtip. Now take 10000lb of sandbags and stack them on the fuselage, visualize the forces. Now move 2000lb of those sand bags out towards the jackstands. The bending moment at the fuselage is less.

So hang the bombs under the wings or add some lift struts.

[FLS]

This thread is cracking me up. The title is what exactly?

It appears the OP is concerned that HTC's model doesn't match the OP's understanding of load limits.

Maybe if we dialed it into "failure of wingspar due to simple overload in one direction" and imagine putting the wing on a couple of jackstands about halfway from the fuse to the wingtip. Now take 10000lb of sandbags and stack them on the fuselage, visualize the forces. Now move 2000lb of those sand bags out towards the jackstands. The bending moment at the fuselage is less.

You're assuming a lower radial g. You should add weight to the fuselage in addition to the wings.

[pembquist]

No no no, it was a joke about the title, it says "Re: dive limits? Structural Limits?" and then right below is the quote from Zimme about diving beyond vne being different

I'm sorry if the second part isn't clear. Put it this way:  The fuselage is trying to go down, the wing is trying to go up. Where the fuselage and wing intersect is basically a hinge. Turn the whole thing upside down in your head. Now the lift is a weight uniformally,(close enough,)distributed along the wing. The fuselage is in the center and now imagine its load as a single post holding the whole thing up, it is bearing 10,000lbs. Imagine the force that is trying to fold the hinge. Now take a few bombs out of the fuselage and place them along the wing, they are now additional posts holding up the wing, say each new post is bearing 1,000lbs and the center post is bearing 8,000. Imagine the hinge closing force, it is less but you are still holding up the same load.

The use of a term like radial G is confusing, just think of the frame of reference and think of it as a statics problem.

[pembquist]

I reread the thread trying to see where the confusion is creeping in. Is the disagreement that locating ordinance on the wing instead of inside the fuselage causes/does not cause there to be less stress on the wing spar at the fuselage? Or is the disagreement that despite the fact that the location of the ordinance does change the stress it isn't of a magnitude to make a significant difference vs. it is a significant difference?

[FLS]

I thought it was idle speculation.   

Your example put's a .3 load factor on the wing. Think it's flexing?

[Zimme83]

I reread the thread trying to see where the confusion is creeping in. Is the disagreement that locating ordinance on the wing instead of inside the fuselage causes/does not cause there to be less stress on the wing spar at the fuselage? Or is the disagreement that despite the fact that the location of the ordinance does change the stress it isn't of a magnitude to make a significant difference vs. it is a significant difference?

I was answering on this:

Every time I a A20 doing high-G dogfighting with bombs I would like to see they fall apart from structural damage.

By saying that underwing ord doesnt nessessarily increase stress on the wing since the weight of the bombs counter the bending cause by the lift in a high G-turn. (It could of course cause other structural problems). I didnt say anything about what happen in a high speed dive.
But i all come dome to what plane  we are talking about what effect ords have on the structure.


Question: Why is it a benefit to have tanks on wing tips on a fighter?

[pembquist]

Hey FLS .3 load factor, I'm lost.

About tip tanks the answer is easy: cause they look hip.

and also the stuff about bending and the stuff about endplate effects

is there more stuff??

Tangential but good story if you haven't heard it, accident report on Neil Williams Zlin, landing with a broken spar http://www.aaib.gov.uk/cms_resources.cfm?file=/15-1971%20G-AWAR.pdf

[FLS]

Load factor is the multiplier of weight from radial g. It tells you how much lift from the wing. A 4g turn is a load factor of 4. Your fully loaded A-20 is 27200 lbs, so a 4g turn is 108800 lbs of lift force on the wing. Your 2 bombs on the wing are about 4% of that.

The F-104 had wingtip tanks because it needed the fuel and there was nowhere else to put fuel and carry ords.

[pembquist]

Ah, I see where the misunderstanding is, my example was non specific it wasn't using the a-20 values. You can put my example in a centrifuge if you want and the difference in bending moment will scale

[FLS]

Ah, I see where the misunderstanding is, my example was non specific it wasn't using the a-20 values. You can put my example in a centrifuge if you want and the difference in bending moment will scale

That's usually the case with hypothetical examples but it doesn't tell us anything about two 500 lb bombs on the A-20 wing.

[pembquist]

With respect, it does tell you that having 2 500lb bombs under the wing reduces the bending moment at the spar/fuselage join compared to having those bombs inside the bomb bay or those bombs left behind on the ground.