Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: Wilbus on September 11, 2002, 06:17:39 AM
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Just wanted to know what it really was so looked it up.
NASA (http://www.grc.nasa.gov/WWW/K-12/airplane/geom.html)
Basicly, if I've undrestood it right, the HIGHER aspect ratio a plane has, the less drag it has, or have I missunderstood?
If I've understood right, that means that a plane, with, let's say aspect ratio 4 will have more drag then a plane with aspect ratio 8, right?
When it comes to drag, a plane with less drag, should maintain E and accelerate better, right?
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I think you are mostly right
But accelaration is mostly affected by Power loading (as is climb)
Weight divided by Power = Power loading (I think :)
As for retaining E I think your absolutly right.
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Thank you :)
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Wilbus,
Aspect ratio is slightly over rated sometimes I believe.
It only lowers induced drag or drag caused by lift not parasite drag or drag caused by sheer bulk.
Aspect ratio is most used in A/C that need to fly long distance and create allot of lift and need to cruise a long distance. IE an airliner or spy plane like a U-2.
If you want to really maintain speed through turns and then go fast you will find that A/C with a very low aspect ratio are ideal. Ala the F8F Bearcat or any of the A/C racing at Reno. The first thing they do is chop the wing tips lowering the aspect ratio. If a high aspect ratio was ideal they would add wing span, not reduce it.
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Ok, how about maintaining E in the vertical?
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Btw, does it mean that they climb very good with high aspect ratio as they need to create much lift?
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I heard that high aspect ratio wing is better maneuverability than lower one in vertical.
Takeo Doi, Ki-61 Tony's designer fitted Ki-61's wing with that.
He gave importance to "Span Loading".
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Also higher aspect wing has large lift-drag ratio.
it gives good rate of climb, long endurance, good performance at takeoff.
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Thanks, reason I am asking, is partly that the Ta152 had a very high aspect ratio wing, spit had about 5.6-5.7 while the Ta152 has got about 6.5.
Should be better in the vertical in such case. P51 had about 6.0.
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6.5?
I think Ta152H-1's wing aspect ratio is 8.94...
(14.5)^2 / 23.5 = 8.94
Ta152H1's wing span: 14.5m
wing area: 23.5m^2
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Wilbus,
Another advantage of high aspect ratio is lift at high altitutudes. A/C that operate at extreme alt often have high aspect ratio.
Takeoff and climb are affected by aspect ratio however they are a small part. Take a look at any Carrier fighter and it's aspect ratio. They are all lower than there Army counter parts and they need better low speed hadling and short takeoff run.
Various aspect ratios
F8F-1 = 4.1
F4U = 5.4
F6F = 5.5
P-51 = 5.9
P-38 = 8.3
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Yes Mitsu, thought there was something wrong with my calculations as my book say 8.93.
Anyway, should the Ta152 keep energy very well in a zoom as the drag is very low?
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No lift needed in vertical -> no induced drag -> aspect ratio doesn't matter.
"Keeping energy" is a function of drag AND thrust so you have to look at both if you want that answer.
Aspect ratio is important for induced drag, but equally important is Oswald's efficiency factor (a function of planform shape). More important though is wingloading, because induced drag increases with the square of wingloading for a given speed and turn rate. A good aspect ratio won't help much if you have a high wingloading.
Good discussion here:
http://142.26.194.131/aerodynamics1/Drag/Page6.html
http://142.26.194.131/aerodynamics1/Drag/Page7.html
http://142.26.194.131/aerodynamics1/Drag/Page8.html
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Funked beat me to it :).
Also - It's an oversimplification to only use AR as a key predictor of induced drag. Keep in mind that induced drag varies also with angle of attack (or the amount of lift generated). You can see it in this relationship:
Coeff-ind-drag = Coeff-lift (or AoA) / pi*span eff.*AR
E.g. - Compare the P-51D and Spitfire9 in level flight. The P-51D has more induced drag than the Spitfire9 though the P-51 has a higher AR. The reason is the P-51 has a higher wing-loading (more weight to wing area)--> more lift needed --> more AoA --> more induced drag.
Tango, XO
412th FS Braunco Mustangs
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Uhmmm, ok, so what is the meaning of aspect ratio? :)
Will go read those 3 links, thanks guys :)
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Large ascpect ratio...
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Yup, I know that gliders and similair have large aspect ratio but why? I should read up on aerodynamics, darnit, flying gliders my self...
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if you want to compare the effect of two wings with different aspect-ratios you need to keep the wing-area constant, IMO.
other factors like crosssection and general shape matter too, so you can't really compare a spit's eliptic wing to a thin rectangular ta152 wing.
the only thing high aspect ratio buys you is a smaller wingtip turbulance (but just try rolling with a glider...).
but I'm no aero-engineer.
Bozon
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Originally posted by Wilbus
Yup, I know that gliders and similair have large aspect ratio but why? I should read up on aerodynamics, darnit, flying gliders my self...
The higher the aspect ratio, the more you have a 1-dimensional airflow over the wing. The air flow is pushed away over the wing, and sidewards. The air pushed away sidewards causes losses without lift. Furhtermore you have - like bozon mentioned - a pressure equalization at the wingtips. Again, the higher the aspect ratio, the lower the losses are relativ to total lift. So a high aspect ratio increases the total lift efficiency. If you look at the wingtips of the sailing plane, those little vertical fins show up on many aircraft recently. They probably increase the efficiency because they prevent the pressure equalization and force even more a 1-dimensional air flow over the wing.
The fuselage too is a disturbing factor, the farer away the wing section is from the fuselage, the lower the influence.
niklas
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Ok so as the lift is greater, the climb should be greater aswell, right? Or is it just that the lift is greater so the plane can stay up in lower speeds?
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What Niklas said petty much hits the point. Higher aspect ratio increases the total lift efficiency of the wing. But its just one factor regarding lift and drag, Wing loading and span loading also have to be taken into account.
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remind me of the Hurel Dubois 34
(http://www.aviafrance.com/images/1811.jpg)
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Woooooo Straffo, can I have? :)
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only 7/8 were build :(
sadly as I know there is no flyin HD34 now :(
(http://perso.wanadoo.fr/pegase-meeting/divers/normales/Img_2282.jpg)
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Ok so as the lift is greater, the climb should be greater aswell, right? Or is it just that the lift is greater so the plane can stay up in lower speeds?
to test a theory, my physics teacher taught me to look at an extream case:
a helicopter - is a plane with no wings (no lift) that climbs on it's propeller thrust only, and can stay up at 0 speed.
therefor climb-rate depends on other things as well.
to achive max (sustained) climb-rate, it's easier to consider energy balance. the engine produces energy that is devoured by the drag - what ever is left is going into potential energy - alt (while keeping speed constant).
so to climb at maximum rate you need to fly at a speed that gives minimum drag.
to cut things short, since you are interested in aspect-ratio:
high aspect ratio increaces the efficiency of the wing in high attack-angles (by reducing wingtip turbulance). they will tend to move the "minimum drag" point to a slower speed.
so in general you can say that high aspect-ratio is better for slow speeds / high angles-of-attack flying than a low aspect-ratio of the same area & general shape wing.
there are so many other factors to consider that saying more than that would require writing a book.
Bozon
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Rgr Thanks :)
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Wilbus:
To put it simply rate of climb is a function of excess power and not lift.
You are correct however in saying that more lift could translate into an aircraft having a lower level stall speed.
Tango, XO
412th FS Braunco Mustangs
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thanks again :)
Straffo, what was it used for???
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oups ... forgot this thread :)
I was used for "cartographie" aka making map the IGN (*) used it
(*) institut géographique national
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Originally posted by bozon
to test a theory, my physics teacher taught me to look at an extream case:
a helicopter - is a plane with no wings (no lift) that climbs on it's propeller thrust only, and can stay up at 0 speed.
therefor climb-rate depends on other things as well.
Helicopters do have wings bozon theyre called rotary wings :D
The collective changes the angle of the blades to create more lift.
The cyclic makes the blade go up and down during the rotation to create more or less lift wich allows you to change direction.
P.S: Am I fishing or did you use it as an example only and already know all this :D
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imp:
P.S: Am I fishing or did you use it as an example only and already know all this
hehe, it was just an analogy :)
I have a few hours in bel-206 jetranger.
Bozon