Aces High Bulletin Board
General Forums => Wishlist => Topic started by: shift8 on February 15, 2015, 06:39:47 PM
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Structural Limits?
Ok im not sure this is a issue so this is mostly for discussion, then it can be on the wishlist if its actually a problem.
I did a load of dive tests in AH and found some strange stuff.
Most planes seem to have mach limits of .75 to .80, so no problem here.
What was weird was that at low altitudes I could greatly exceed the structural limits. For example, in the P-51 was I was able to go right up the the mach limit of .80 even below 5000ft. According to the manual 505mph indicated in the limit, but Ive hit anywhere from 550 to 570 IAS in dives without damage. Same goes for the 109. 109s and spits were both limited to about 450-460 IAS at low alt due to structural failure.
So the questions is, is AH correct on this? I would imagine that any safety limit is actually higher than the actual limit, for example the P-51 is nominally limited to 8G but is actually capable of more like 12. Same for modern jets, there max G limits are not the actual limits. But is 70mph over the limit correct?
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I AH you get a new plane every time you take off, in real life planes were used over and over.
Those limits were to prevent too much stress on the airframe that would weaken it over time.
They aren't a hard limit that suddenly causes a structural failure the first time they were exceeded.
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Every time I a A20 doing high-G dogfighting with bombs I would like to see they fall apart from structural damage.
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I don't know how accurate overloading damage is but keep in mind that structural limits are probably safe structural limits. With GA airplanes there is a load limit factor of 1.5 meaning that for an aircraft with a limitation of 6g it should not be permanently deformed or weakened by being stressed at anything less than 9g.this is not the same thing as safe to 9g, but you take my point that a limit from an operating manual has a factor of safety and bending wings is not the same as having them come off, (though very close.)
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Every time I a A20 doing high-G dogfighting with bombs I would like to see they fall apart from structural damage.
They do if you exceed the load limits silly
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Underwing bombs can in some cases help u to prevent ripping of your wings in a turn, dont know if A-20 is one of those cases. The forces on the wing from the bombs is working in opposite direction from the forces coming from lift in a high G turn. Only bombs in bomb bay is more dangerous.
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Underwing bombs can in some cases help u to prevent ripping of your wings in a turn, dont know if A-20 is one of those cases. The forces on the wing from the bombs is working in opposite direction from the forces coming from lift in a high G turn. Only bombs in bomb bay is more dangerous.
Doesn't the weight of the bombs increase the required lift for a given load factor? A 4g load factor with 2 500lb bombs adds 4000 lbs to the lift force on the wing.
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Yes it does, the turn ability will suffer since the plane is heavier. But in a hard turn the forces on the wings is pulling them upwards (inwards in the turn) ords under the wings (or fuel in them) Will add a force that works in opposite direction (outwards) and thus canceling the lift forces to some extent.
U can of cource get other problems with structural integrity when u add 6G to a 1000lbs bomb under the wing.
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You don't "cancel" the lift forces when you have a lower load factor at a greater weight. You've still increased the load on the wings, you just get less radial g as a result. Radial g is not the problem. The problem is the lift force. Radial g is just an indicator of lift force for a given weight.
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Ok, u didnt get what i mean..
Yes the lift force on the wing is the same, yes, the higher weight gives higer wing loading and decreased turn ability.
But the forces from lift cause the wings to bend upwards and if u add weight to the wing, fuel or bombs, the centrifugal force from the extra weight pulls the wing downward. And 2 forces working in opposite directions cancel each other out. Point is: Bombs under wings does not increase risk of snapping wings off. U will have the same amount of lift aviable but less strain on the wing (and poorer turn performance)
Heavy fuselage + light wings = High strain on wings
Light fuselage + heavy wing = Less strain on wings.
Turn ability is affected by the total weight of the plane but the strain on the wings is also affected by where on the plane the weight is placed.
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I got that the first time. You don't have to repeat it.
For a given radial g the load is greater when the weight increases. Since the load is greater there is more stress. I don't believe it cancels out but I haven't looked into it. It seems likely that hanging a mass under the wing increases stress for all maneuvering loads.
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Ok.... we just leave it..
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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.
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Every time I a A20 doing high-G dogfighting with bombs I would like to see they fall apart from structural damage.
Loaded the A20 will break apart more easily then unloaded.
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Loaded the A20 will break apart more easily then unloaded.
In reality it depend where the bombs are loaded (belly or wings) because it affects the distribution of the forces across the wing. In the game I suspect that the model only has a total force threshold regardless of how the weight is distributed - but I do not really know.
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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.
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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.
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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?
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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.
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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.
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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.
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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.
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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?
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I thought it was idle speculation. :D
Your example put's a .3 load factor on the wing. Think it's flexing?
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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?
(http://www.rccanada.ca/rccforum/attachment.php?attachmentid=197197&d=1364582080)
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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 (http://www.aaib.gov.uk/cms_resources.cfm?file=/15-1971%20G-AWAR.pdf)
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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.
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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
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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.
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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.
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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.
Sorry I wasn't clear. It doesn't tell us what the difference is. It just predicts a difference of unknown magnitude.