Aerodymamics...

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posted on Jul, 16 2006 @ 10:10 AM
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Why does the F-16 only have one?




posted on Jul, 16 2006 @ 10:12 AM
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IIRC i read that canting the tails outwards can also make them more effective at high angles-of-attack. Canting them in either direction also reduces the RCS.



posted on Jul, 16 2006 @ 10:47 AM
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Originally posted by gfad
IIRC i read that canting the tails outwards can also make them more effective at high angles-of-attack. Canting them in either direction also reduces the RCS.


Well that would fit in well in the picture thinking about the F-22 and stealth. I always wondered how they solved the problem.

[edit on 16-7-2006 by Figher Master FIN]



posted on Jul, 16 2006 @ 12:16 PM
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Hopefully this shows more clearly than any explanation why have 2 fins, and why have them canted - they are positioned to best utlise the vortices generated from the LERXs.



posted on Aug, 12 2006 @ 09:06 AM
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Sound

I was wondering, that after I saw an F-16 fly I was truly surprised how high it's noise is. The F/A-18 doesn't even come close even though it produces far more thrust.



posted on Aug, 18 2006 @ 05:31 AM
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Originally posted by Figher Master FIN
Sound


Uhm, there are alot of factors involved in sound production.

Its not a case of looking at two aircraft and saying A is quieter than B [unless there are large differences like one is a high BPR turbofan and the other is a turbojet]


Mostly, for clean aircraft travelling subsonically, airframe noise is negligible, the main source will be from the engine, more specificially the jet plume for a lower BPR engine and a combination of the fan, plume and compressor from a higher BPR engine.

Duct length usually has an affect on noise propagation, but I doubt military aircraft have acoustic liners, so the hard-walled ducts would provide virtually no damping.



posted on Aug, 28 2006 @ 01:01 PM
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I see, could a reason also be the "hydraulic pump". I think I read something like that in an other thread.

The Tail

If I understood correctly, the tail works like a "keel" to stabilitze the plane. But then I started wondering why the tail is in the back of the plane, couldn't it just as well be in the middle or the front. Any reasons for this?




posted on Aug, 29 2006 @ 04:17 AM
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Originally posted by Figher Master FIN
If I understood correctly, the tail works like a "keel" to stabilitze the plane. But then I started wondering why the tail is in the back of the plane, couldn't it just as well be in the middle or the front. Any reasons for this?


OK, say the aircraft is yawing - that induces a sidewash on the vertical fin which produces a force.


Unless the fin's aero centre is behind the aircraft centre of gravity it will increase the yaw angle, not reduce it.


Lookie at the Linky

[edit on 29-8-2006 by kilcoo316]



posted on Aug, 29 2006 @ 09:17 AM
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Good link thanks.


I read through that link you gave me a long time ago about high and low mounted wings. It said that high mounted wings are more stabile than low mounted, wich is totally the opposite of what we have discussed here?

-link-

[edit on 29-8-2006 by Figher Master FIN]



posted on Aug, 29 2006 @ 10:02 AM
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Originally posted by Figher Master FIN

I read through that link you gave me a long time ago about high and low mounted wings. It said that high mounted wings are more stabile than low mounted, which is totally the opposite of what we have discussed here?

-link-


Uhm, I don't see where you are getting the contradiction.


High wings are more stable than low mounted wings [without considering dihedral/anhedral]. I don't see where anyone has said otherwise.



posted on Aug, 29 2006 @ 11:46 AM
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Oh yes I'am confusing with dihedral athedral


So why doesn't the 747 have high mounted wings for better stability?



posted on Aug, 30 2006 @ 03:33 AM
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Originally posted by Figher Master FIN
Oh yes I'am confusing with dihedral athedral


So why doesn't the 747 have high mounted wings for better stability?


A higher wing tends to give a shorter take-off run, but the compromise is a slightly less efficient wing in cruise.


So for longer-range aircraft, like the 747 etc, its better to go with low wings.

Military transports go with the high wing for rough field capability [both mounting the engines higher for FOD and for the shorter field length].



posted on Aug, 30 2006 @ 08:53 AM
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I see, Any explanation why high mounted wings give a possibility for the aircraft to use a shorter runway, and way low mounted wings are more efficient?



posted on Aug, 30 2006 @ 09:44 AM
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Originally posted by Figher Master FIN
I see, Any explanation why high mounted wings give a possibility for the aircraft to use a shorter runway, and way low mounted wings are more efficient?


My above post was slightly incorrect, whoops!


A high mounted wing generates more lift across the flight regime [the suction surface/upper surface is uninterrupted by the fuselage]... but structurally requires more weight - the fuselage needs strengthening both top and bottom for wing and undercarriage [instead of just bottom for wing/undercarriage for low wing].

So while the wing might be more aerodynamically efficient, it is still generating more lift induced drag through needing to generate more lift, hence less efficient overall.


A lower mounted wing also has a cleaner fuselage by only needing fairings on the bottom, and not seperate wingbox and undercarriage fairings.



posted on Aug, 31 2006 @ 08:00 AM
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Originally posted by Figher Master FIN
I see, could a reason also be the "hydraulic pump". I think I read something like that in an other thread.

The Tail

If I understood correctly, the tail works like a "keel" to stabilitze the plane. But then I started wondering why the tail is in the back of the plane, couldn't it just as well be in the middle or the front. Any reasons for this?




probably because it is needed to stabalize the plane if the tail was not there it would start spinning back and fall so the tail prevents it originally most of the weight ought to be on the bak so the air needs to flow under the tail to stabalize ( so I heard)



posted on Oct, 22 2006 @ 10:24 AM
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What is it in the "cobra" manouver that makes it so hard to perform? Does it have to do with pressure on the wings or what? If anyone can explain I would be happy.



posted on Oct, 22 2006 @ 10:29 AM
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Originally posted by Figher Master FIN
I see, Any explanation why high mounted wings give a possibility for the aircraft to use a shorter runway, and way low mounted wings are more efficient?


The main reason for a longer take-off with low-mounted wings is because of the ground interference. I'm not sure I'm in on the "low-wing is more efficient at cruise" statement yet. I'm going to have to think about that a bit.



posted on Oct, 22 2006 @ 11:08 AM
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Originally posted by Figher Master FIN
What is it in the "cobra" manouver that makes it so hard to perform? Does it have to do with pressure on the wings or what? If anyone can explain I would be happy.

The cobra manuever would require an aircraft to turn to over a 120 degree AoA. Most planes stall far below that number which is why you have a better chance of achieveing that AoA if the aircraft is inherently unstable, such as planes as the Su-27 and F-22 and F-15. However not all unstable platforms can perform a cobra and very few acrobat stable aircraft can perform the cobra.

Things like thrust vectoring can increase an aircraft's stall AoA.

Shattered OUT...



posted on Oct, 22 2006 @ 05:47 PM
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Originally posted by Valhall
The main reason for a longer take-off with low-mounted wings is because of the ground interference. I'm not sure I'm in on the "low-wing is more efficient at cruise" statement yet. I'm going to have to think about that a bit.


Yeah sorry, dropped the ball with the low-wing/cruise statement, correction is above.



Originally posted by Flight Master FIN
What is it in the "cobra" manouver that makes it so hard to perform? Does it have to do with pressure on the wings or what? If anyone can explain I would be happy.



OK, the cobra is into deep post stall manouvering, so aircraft stall angle doesn't really matter that much. What is important, is pitch control authority.


The cobra as performed by the original Su-27 was purely momentum based. Heave back on the stick, get as much upward momentum into the nose as possible. As the aircraft pulls up sharply it stalls, as its AoA increases, the horizontal tailplanes and wing are inducing a nose down pitching moment through pure wind resistance (drag) - this is what restores the aircraft to controllable flight. Its totally outside of the pilots control beyond around 25 deg - its all momentum and wing/tail drag from then on.


However, the later aircraft, like the MiG-29 OVT and F-22 can all do controlled cobras - through use of TVC. This allows the pilot to negate the nose down moment from the tail/wing - and hold the 90/120 deg AoA - then pitch down in his/her own time.



The reasons for aircraft not being able to do the cobra are (all or some of the following):

- not enough elevator input to get the nose momentum up to sufficient levels
- not high enough polar moment of interia in the longitudinal axis
- not right wing/tail planform to get sufficient nose down moments to restore controllable flight [you can do the "cobra"... once, then yer deep in the brown stuff]
- no TVC


[edit on 22-10-2006 by kilcoo316]



posted on Oct, 22 2006 @ 11:12 PM
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Wow!! I spent 10 minutes going through this thread and am 'enlightened' in many aspects..

Keep it up FMF..





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