Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: Stoney on December 10, 2009, 12:12:07 PM
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BnZ, I keep seeing you use this term? Can you explain it please?
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BnZ, I keep seeing you use this term? Can you explain it please?
You know what wing-loading is?
Well, some wings obviously generate more lift per unit of area than others...
The aircraft with the lower power-off stall 1G stall speed is the one producing more lift in relation to its weight.
This is not *always* the aircraft with the lower basic wing-loading. Thus, "lift-loading".
If its not a proper term, sorry, but it gets the point across I think.
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You know what wing-loading is?
Well, some wings obviously generate more lift per unit of area than others...Thus "lift-loading"
If its not a proper term, sorry, but it gets the point across I think.
How do you compute it? I'm curious, since I've seen you use it as a basis for comparing aircraft.
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Check the edit. Lower 1G stall speed for a given configuration is the easiest way to compare.
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BnZs when you say "lift loading" do you mean coefficient of lift?
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BnZs when you say "lift loading" do you mean coefficient of lift?
No. I mean the ratio of the total lift the entire wing can produce to the weight of the aircraft.
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If its not a proper term, sorry, but it gets the point across I think.
It isn't a proper term and I'm guessing that it will create more confusion than anything else.
Badboy
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It isn't a proper term and I'm guessing that it will create more confusion than anything else.
Badboy
What would be the proper term to describe what BnZ is saying or is it something that isn't even calculated?
ack-ack
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No. I mean the ratio of the total lift the entire wing can produce to the weight of the aircraft.
The ratio of lift to weight is normally described using multiples of the weight of the aircraft and is called "g force". So a 7000lb aircraft generating 14000lbs of lift is at 2g. The total lift that a wing can produce increases with airspeed, and is only limited by structural strength or pilot physiology. Those limits are normally expressed in terms of the number of g, that is the ratio between the lift and weight of the aircraft.
Hope that helps...
Badboy
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What would be the proper term to describe what BnZ is saying or is it something that isn't even calculated?
ack-ack
His definition
No. I mean the ratio of the total lift the entire wing can produce to the weight of the aircraft.
is really just the maximum g.
However, the quotes below:
Well, some wings obviously generate more lift per unit of area than others...
The aircraft with the lower power-off stall 1G stall speed is the one producing more lift in relation to its weight.
sound like a description of the ability of the wing to produce lift, and that is already described by the lift coefficient.
Badboy
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It isn't a proper term and I'm guessing that it will create more confusion than anything else.
Badboy
Okay, what DO you call it when a given aircraft has a higher wing-loading in terms of pure weight/square footage but actually can produce more lift in relation to its weight? Resulting in lower stall speed, better instantaneous turn, and all that.
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It would seem much easier to just compare wing area to weight (lbs/m -- or square feet for us Yanks)
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It would seem much easier to just compare wing area to weight (lbs/m -- or square feet for us Yanks)
It is easiest yes, but does not always correct.
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Okay, what DO you call it when a given aircraft has a higher wing-loading in terms of pure weight/square footage but actually can produce more lift in relation to its weight? Resulting in lower stall speed, better instantaneous turn, and all that.
What you have just described is a situation where an aircraft has higher wing loading but also has a higher maximum coefficient of lift.
Badboy
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What you have just described is a situation where an aircraft has higher wing loading but also has a higher maximum coefficient of lift.
Badboy
Yep. Consider a wing with a higher wing loading, but with a higher AR as well, and hence potentially higher lift. Or, consider two wings of equal planform, but with two very different airfoils. Same wing loading, not so same lift. (fixing all other parameters, of course)
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What you have just described is a situation where an aircraft has higher wing loading but also has a higher maximum coefficient of lift.
Badboy
Would the P-38 be an example of such a plane, if not, what planes would be?
ack-ack
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Would the P-38 be an example of such a plane, if not, what planes would be?
ack-ack
Could be. Anybody know what the effective AR of the 38 is?
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Would the P-38 be an example of such a plane, if not, what planes would be?
ack-ack
The P-38 never had a production version that used a different airfoil, that I know of. Really, the best example would be an aircraft that had the exact same weight, same wing area, but with a different airfoil. I can't think of anything like that off the top of my head.
Stall speed is a function of Clmax and wing loading, so, in my opinion, those are the two characteristics that should be considered. For example, if you're trying to design a plane with a certain stall speed, you first look at the lift equation, and solve using the desired stall speed in the velocity term. This would provide the necessary Clmax at that stall speed. You could, if you know accurate stall speeds for two aircraft in a given configuration, compare their Clmax by using the lift equation, and solving for the lift coefficient at that stall speed. Might even give you an indication of flap efficiency if you chose to keep weight the same, and test for stall speeds at each notch of flaps; it would provide the difference in Clmax created by the flaps.
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I can't think of any WWII airplanes off the top of my head that fit the bill. In the 500 series of Cessna Citations a fair comparison can be made with the Citation II to the Citation S/II. I don't have my books in front of me but the primary differences between the II and S/II was the wing design. Replacing the inflatable boot deicing system with a weeping wing fluid system and also changing the shape of the airfoil. I only flew the S/II one time as a contractor but I do remember being surprised at how well it accelerated when you pointed it down hill when compared with a regular II. A similar wing designed was used on the Citation V and Ultra which incorporated some other improvements and weight increases so the comparison isn't quite as valid but the Vmo/Mmo of the Ultra was 292kts/.755M compared with the Citation II's 262kts/.705M IIRC. You gain an extra 30kts and .05M with what amounts to just a change to the wing.
I could dig up the weights if it was really needed but I'm just as sure they're available with a google search if such a compairson was to be made.
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What you have just described is a situation where an aircraft has higher wing loading but also has a higher maximum coefficient of lift.
Badboy
Gotcha. I thought Clmax was only correctly applied to the airfoil section, not the entire wing as a whole. Thanks!
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The P-38 never had a production version that used a different airfoil, that I know of. Really, the best example would be an aircraft that had the exact same weight, same wing area, but with a different airfoil. I can't think of anything like that off the top of my head.
Stall speed is a function of Clmax and wing loading, so, in my opinion, those are the two characteristics that should be considered. For example, if you're trying to design a plane with a certain stall speed, you first look at the lift equation, and solve using the desired stall speed in the velocity term. This would provide the necessary Clmax at that stall speed. You could, if you know accurate stall speeds for two aircraft in a given configuration, compare their Clmax by using the lift equation, and solving for the lift coefficient at that stall speed. Might even give you an indication of flap efficiency if you chose to keep weight the same, and test for stall speeds at each notch of flaps; it would provide the difference in Clmax created by the flaps.
Oh, so it's my awesome uber God like skills in the P-38 that let me turn it like a Spitfire. :aok
ack-ack
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You could define lift loading simply as
(WingArea * MaxLCO) / Weight
In which case it is a very Usefull number to compare some numbers on plane performance.
HiTech
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You could define lift loading simply as
(WingArea * MaxLCO) / Weight
In which case it is a very Usefull number to compare some numbers on plane performance.
HiTech
How this MaxLCo is relating to the wing Aspect Ratio?
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Does MaxLCO = CLmax?
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Does MaxLCO = CLmax?
I think the Hitech meant a CLmax, but is it a airfoil CLmax or wing CLmax? If later, then the aspect ration step in to the picture.
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I think the Hitech meant a CLmax, but is it a airfoil CLmax or wing CLmax? If later, then the aspect ration step in to the picture.
You guys talking about "CLimax"?
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Yes CLMax is the same as my Max Lift Coef.
We would be speaking plane CLmax which can be different then the airfoil and and wing. Basically the number is just comparing power off stall speeds of the plane.
HiTech
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I've seen the term lift loading used sometimes same way as hitech described above. Theoretically it should give a better picture of lift capability of a airframe than wing loading because the airframes can have very different Clmax values. However, the problem is that there is rarely a consensus which is a proper value of Clmax for a given airframe at given conditions.
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hitech i asked you this on another board, sort of.
are there some planes that for one reason or another much more difficult for you to get a FM that you feel very successful about?
or aspects of flight in general that are just hard to get "right" on a computer ...
i ask just because i think of some things like say "how a 38 rolls" you know "neutral" torque not on the center line etc, slat effects in the 109 ...
i just think how the @$%$ would someone approach such different aircraft in a computer representation.
nothing but sincere interest and a chance for an interesting discussion, not suggesting you have not achieved good results sir, i just think insights into the problems and problem solving would be very interesting.
i understand if you might be apprehensive with this question and or me posting it considering past discussions.
i am just interested/curious ...
Yes CLMax is the same as my Max Lift Coef.
We would be speaking plane CLmax which can be different then the airfoil and and wing. Basically the number is just comparing power off stall speeds of the plane.
HiTech
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However, the problem is that there is rarely a consensus which is a proper value of Clmax for a given airframe at given conditions.
The lift equation is the consensus. If you know the speed of an aircraft, you can compute the Clmax at any condition. Now, if you're interested in breaking out the varying components of the plane, and their contribution to lift, there are different methods used (for example, to determine the fuselages contribution) but overall, the lift equation tells you everything you need to know.
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hitech i asked you this on another board, sort of.
are there some planes that for one reason or another much more difficult for you to get a FM that you feel very successful about?
or aspects of flight in general that are just hard to get "right" on a computer ...
i ask just because i think of some things like say "how a 38 rolls" you know "neutral" torque not on the center line etc, slat effects in the 109 ...
i just think how the @$%$ would someone approach such different aircraft in a computer representation.
nothing but sincere interest and a chance for an interesting discussion, not suggesting you have not achieved good results sir, i just think insights into the problems and problem solving would be very interesting.
i understand if you might be apprehensive with this question and or me posting it considering past discussions.
i am just interested/curious ...
What you believe is difficult i.e. the 38 engines quite frankly is trivial, I am making an assumption you have never had much physics or calculus if am I wrong I apologize but to put it simply , torque is torque no mater where it is applied on an object, the net result is the same. So the engine modeling is 100% the same for a p38 or any other plane. You just change 1 +- sign and apply all forces to a different point.
The modeling of things like slats again is fairly simple, finding all the correct numbers on slats can be difficult, and when some thing is missing in the data trying to find a method to extract it from other know data points can take a lot of work.
The basic modeling system is very simple physics. You first calculate a Mass and a Moment of Inertia,(changes only with fuel consumption and expending ordinance) then start calculating and summing up forces on the object. When you have them all summed up, you use the simple equations A = R / M , V = A * T + OldV, and P = V * T + OldpP For the 6 axis and wala, you have a new plane position, rinse and repeat.
HiTech
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i just thought the torque not being on the center line would effect the roll character and wondering how you approached it. in films the 38 always seems to have a drift in its roll like a little barrel roll just different than a plane with the engine on the center line.
but those were things that struck me as seeming to be difficult, i was more asking about your problems and problem solving day to day coding work. what if anything you find more challenging than others ...
just curious ...
a little sympathy for the devil ;)
+S+
t
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i just thought the torque not being on the center line would effect the roll character
Torque not being on center line has absolutely no effect.
HiTech
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Torque not being on center line has absolutely no effect.
HiTech
yea ok, i really wasn't trying to start an argument, i just was inviting you to share the "interesting" parts of what you do.
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The reality is most of my time is not all that interesting. 95% of a programmers life is trying to figure out how we screwed up.
For instance right now I am working on the fixed pitch prop model for WWI lots of trying to find information to verify methologies. Which requires lots of reading, and again more testing and fixing what I screwed up on.
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The reality is most of my time is not all that interesting. 95% of a programmers life is trying to figure out how we screwed up.
For instance right now I am working on the fixed pitch prop model for WWI lots of trying to find information to verify methologies. Which requires lots of reading, and again more testing and fixing what I screwed up on.
I have several extra boxes of Tylenol I can send you...got them at closeout prices when a nearby pharmacy closed down... :D
Sadly no whiskey though... :cry ...none of the liquor stores seem to be having money problems these days so I can't get it cheap.
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The lift equation is the consensus. If you know the speed of an aircraft, you can compute the Clmax at any condition. Now, if you're interested in breaking out the varying components of the plane, and their contribution to lift, there are different methods used (for example, to determine the fuselages contribution) but overall, the lift equation tells you everything you need to know.
Eh... We can calculate coefficient of lift (Cl) at any condition using lift equation (altitude, speed, weight and wing area), no problem. However, we are talking about the proper value of Clmax, 1g stall speed gives some idea but it's not particularly accurate at the other conditions.
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Eh... We can calculate coefficient of lift (Cl) at any condition using lift equation (altitude, speed, weight and wing area), no problem. However, we are talking about the proper value of Clmax, 1g stall speed gives some idea but it's not particularly accurate at the other conditions.
Which other conditions? I'm not trying to be obtuse, just understand your statement. At any condition, the lift equation will tell us the necessary Cl for that condition. Obviously, its a static condition, but if we're merely comparing aircraft, and not trying to derive how much lift the wing is producing by itself, for example, it works.
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Which other conditions? I'm not trying to be obtuse, just understand your statement. At any condition, the lift equation will tell us the necessary Cl for that condition. Obviously, its a static condition, but if we're merely comparing aircraft, and not trying to derive how much lift the wing is producing by itself, for example, it works.
See above how hitech defined lift loading. It's not about what is the Cl at given flight condition but what Clmax can be reached at given conditions. As an example see page 28 in the document below.
http://naca.central.cranfield.ac.uk/reports/1946/naca-tn-1044.pdf
That example is at high altitude but same way Clmax varies also at low altitude depending on speed, power setting, flaps etc.
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The reality is most of my time is not all that interesting. 95% of a programmers life is trying to figure out how we screwed up.
For instance right now I am working on the fixed pitch prop model for WWI lots of trying to find information to verify methologies. Which requires lots of reading, and again more testing and fixing what I screwed up on.
Just out of curiosity, where do you find info such as the clmax of a particular airplane wing?
Especially for WW1 airplanes, did people actually understand that stuff back then, I thought most of that technology was developed in the 20s. I was under the impression that most early airplanes were almost, trial and error, complete with strange wing & airfoil shapes and odd control surfaces (such as wing warping, etc).
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See above how hitech defined lift loading. It's not about what is the Cl at given flight condition but what Clmax can be reached at given conditions. As an example see page 28 in the document below.
http://naca.central.cranfield.ac.uk/reports/1946/naca-tn-1044.pdf
That example is at high altitude but same way Clmax varies also at low altitude depending on speed, power setting, flaps etc.
Thanks Gripen,
Very interesting document.
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"Eh... We can calculate coefficient of lift (Cl) at any condition using lift equation (altitude, speed, weight and wing area), no problem."
What do you mean?
Cl=L/qA where L is Lift force and q is dynamic pressure and A is planform area and the L is not a simple component to determine.
http://en.wikipedia.org/wiki/Lift_(force)
However the linked document nicely represents how complex the calculation gets when the profile is also considered. Nice link, thx.
-C+
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"Eh... We can calculate coefficient of lift (Cl) at any condition using lift equation (altitude, speed, weight and wing area), no problem."
What do you mean?
Cl=L/qA where L is Lift force and q is dynamic pressure and A is planform area and the L is not a simple component to determine.
http://en.wikipedia.org/wiki/Lift_(force)
However the linked document nicely represents how complex the calculation gets when the profile is also considered. Nice link, thx.
-C+
If you know the weight of the aircraft, the speed of the aircraft, and the altitude of the aircraft, the lift equation will give you the Cl at that weight and speed. If you know the weight of the aircraft, the stall speed of the aircraft at that weight, and the altitude of the aircraft, the lift equation will give you the Clmax at that weight, regardless of aspect ratio, "e", or anything else.