Author Topic: Area rule question.  (Read 1139 times)

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Offline aerofan

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Area rule question.
« on: November 21, 2008, 02:15:24 pm »
When the YF-102 could break the sound barrier, it was altered to incorporate area rule where the center of the fuselage is pinched in. Like those old glass Coca Cola bottles. I'm not aerodynamists or aeronautical engineer but I'd like to know if these jets had their main wings shoulder mounted, would they still require to follow the area rule? From my very basic understanding of lift, the top of the wing foil has faster moving airflow that creates the the low pressure and the bottom has the slower airflow which is of higher pressure than that of the top which results in lift. The YF-102 had the thickess part of it's wing meet at the thickess part of the fuselage which both combined enough drag to keep it from breaking the sound barrier in level flight. After the pinching in of the fuselage at that part and the addition of blisters below the vertical stabilizer / rudder as well as other alterations, the YF-102A final did break the sound barrier. Note the wing was still thick at that part and it was only the fuselage that was reduced in area to cancel the drag. This is why I'm asking that if the wings were shoulder mounted would it be necessary to still incorporate the area rule to acheive supersonice level flight?

Offline fallenphoenix

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Re: Area rule question.
« Reply #1 on: November 21, 2008, 02:42:47 pm »
Theres a couple of ways around "pinching" ie M shapped wings where the wings sweep forward before sweeping aft though I'm not sure if this has ever been done in practice (brains not quite in gear right now) alternativly having the main body of the wing being set far aft results in the mach cone crossing over the leading edge aft of the widest point of the fuselage ie. Concord. at the CoP the fusleage is already tapering to the tail cone.
Long story short though if you wwant to go super sonic you must reduce the total cross sectional are at the point at which the mach cone meets the wing in order to reduce wave drag.
Sorry if theres bits of this that are unclear or off.

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« Last Edit: November 21, 2008, 05:17:17 pm by fallenphoenix »
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Offline SSgt Baloo

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Re: Area rule question.
« Reply #2 on: November 21, 2008, 04:47:40 pm »
When the YF-102 could break the sound barrier, it was altered to incorporate area rule where the center of the fuselage is pinched in. Like those old glass Coca Cola bottles. I'm not aerodynamists or aeronautical engineer but I'd like to know if these jets had their main wings shoulder mounted, would they still require to follow the area rule? From my very basic understanding of lift, the top of the wing foil has faster moving airflow that creates the the low pressure and the bottom has the slower airflow which is of higher pressure than that of the top which results in lift. The YF-102 had the thickess part of it's wing meet at the thickess part of the fuselage which both combined enough drag to keep it from breaking the sound barrier in level flight. After the pinching in of the fuselage at that part and the addition of blisters below the vertical stabilizer / rudder as well as other alterations, the YF-102A final did break the sound barrier. Note the wing was still thick at that part and it was only the fuselage that was reduced in area to cancel the drag. This is why I'm asking that if the wings were shoulder mounted would it be necessary to still incorporate the area rule to acheive supersonice level flight?

To answer the OP, very simply yes. Shoulder-mounted wings would still require area ruling if all else was the same.
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Offline noxioux

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Re: Area rule question.
« Reply #3 on: November 21, 2008, 04:50:34 pm »
For other, less obvious applications of area rule, take a careful look at the F-14, 15 and 16.  I'm sure that all modern fighter aircraft are still applying the area rule principle. Back in the good ole Cold War days, it was pretty obvious, but the principle is still applied to modern aerodynamics.  It's just more subtle, IMO.

Offline Weaver

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Re: Area rule question.
« Reply #4 on: November 21, 2008, 05:41:28 pm »
When the YF-102 could break the sound barrier, it was altered to incorporate area rule where the center of the fuselage is pinched in. Like those old glass Coca Cola bottles. I'm not aerodynamists or aeronautical engineer but I'd like to know if these jets had their main wings shoulder mounted, would they still require to follow the area rule? From my very basic understanding of lift, the top of the wing foil has faster moving airflow that creates the the low pressure and the bottom has the slower airflow which is of higher pressure than that of the top which results in lift. The YF-102 had the thickess part of it's wing meet at the thickess part of the fuselage which both combined enough drag to keep it from breaking the sound barrier in level flight. After the pinching in of the fuselage at that part and the addition of blisters below the vertical stabilizer / rudder as well as other alterations, the YF-102A final did break the sound barrier. Note the wing was still thick at that part and it was only the fuselage that was reduced in area to cancel the drag. This is why I'm asking that if the wings were shoulder mounted would it be necessary to still incorporate the area rule to acheive supersonice level flight?

Short answer: Yes.

Long answer: Area Rule is about rate of change of cross-sectional area, i.e. it has nothing to do with where the thickest part of the wing is. Compared to the effect of span, the effect of thickness on cross-section is relatively minor anyway. I suspect that on the YF-102A, they simply pinched the fuselage in where they could get away with it. The bulges on the rear fuselage were there to "smooth out" the sudden drop in cross-section at the wing trailing edge. The fairings or "Kuchemann Carrots" seen on the trailing edge of Russian bombers are there for the same reason (they only coincidentally happen to be a good place to put the undercarriage). None of this changes if the wing is high, low or mid mounted: it's simply the rate of change of the total cross-sectional area that counts.

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Offline kitnut617

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Re: Area rule question.
« Reply #5 on: November 22, 2008, 07:54:48 am »
I'm not an aerodymanic expert, but by observing various models (which I hope represent the subject somewhat) you get to see some of this area ruling, this is what I noticed on the Mig 31 fuselage I used for my Arrow project.  Thinking about it now, it's probably all wrong for this application.

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Offline elmayerle

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Re: Area rule question.
« Reply #6 on: November 26, 2008, 08:32:49 am »
Area Rule is more about a steady change in cross-sectional area rather than thickness per se.  The idea is that if you graph cross-extional area against fuselage station, it makes a smooth curve rather than a discontinuous one; those discontinuities are where your high-speed drag comes from.  It doesn't matter if it's a high-, mid-, or low-wing, the same principles still apply.
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