blue_meliz

how do u calculate the max. wing loading of your rc planes?(due to wat designs issit the angle of og the wing or???)

LouW

To calculate the wing loading of a model, divide the weight of the aircraft by the wing area. To get an idea as to how it will fly, you can compare it with other aircraft of similar size.

chrischicago

The wing loading of an airplane should be less than 30 for the plane to fly good.

Geistware

My Feedback: (16)

There are a lot of factors. For a given wing loading, the wingspan will determine if it is heavy or not. I have heard that someone has worked out a formula for cubic area instead of area. I don't know the details, just remember, as the wingspan increases, the same wing loading will appear lighter to fly.


THis is not exactly correct. A 40% plane can have a wing loading of 35-40 and still fly good. A .25ci plane will be a brick at 20.

LA_JOHNSTON

I FEEL LIKE THERE WAS ONE PIECE OF INFORMATION LEFT OUT OF THIS DISCUSSION AT THE VERY BEGINNING.
WING LOADING FOR MODEL AIRPLANES IS GIVEN IN OZ PER SQ FT. THE WEIGHT MUST BE IN OZ, AND THE WING AREA MUST BE IN SQ FT. NOW, WHEN YOU DIVIDE THE TOTAL WEIGHT BY THE WING AREA, IT COMES OUT IN OZ PER SQ FT.
OTHER THAN THAT EVERY THING THAT HAS BEEN POSTED IS FINE.

Mike in DC

Another thing that may not be obvious is that the part of the fuse under (or over) the wing is also counted, as are the ailerons.

Rodney

Wing loading is not a very good indicator of how well an airplane will fly. Wing volume loading gives a much better picture. Example, a 1/2 A model with a 16 oz./Sg.Ft would be a lead sled while a 40 sized model with that wing loading would be a real floater. By using wing volume loading which is defined as (Weight of the model in ounces) divided by (wing area in sq. ft raised to the 1.5 power). A value of 7 to 10 will be a nice flying model regardless of its size. A value less than 7 is a real floater and when you get much above 10, the plane will be hot and require a very high landing speed to prevent stalls.

sigrun

There are a lot of factors.

Nope just two. Weight and wing area. By mathematical convention an aircraft's 'weight' divided by its wing area is what "wing loading" is by definition.

For a given wing loading, the wingspan will determine if it is heavy or not.

Abject nonsense.

Intention isn't to offend per se, but the gist of your entire post makes it abundantly clear that you really haven't the faintest grasp of the subject fundamentals you're attempting to talk about.

I have heard that someone has worked out a formula for cubic area instead of area.

You know what the proverb says about not believing everything you hear. How can something which is effectively a planar surface have a "cubic" area? [:-]

I don't know the details, just remember, as the wingspan increases, the same wing loading will appear lighter to fly

If you only realised how silly the above statement actually sounds.

Here's what I suspect you're grasping at. Given a fixed chord, increasing the span must by default also effect an increase in the overall area. It follows that as wing area increases, for a constant weight a reduction in wing loading is an arithmetical certainty.

Buy or borrow Kermode's "Mechanics of Flight". If you bother to read it, you'll come back and cringe when you read what you've written here.

Montague

Sigrun,
Actually, you missed the entire point. The question isn't "how do you calculate wing loading". The question is "how high can wing loading be and still fly ok".

No one has said anything that would say you calculate the conventional wingloading anyway other than what you've said.

However, I can say with absolute certainly that a wingloading of 30oz/sqft as quoted by chrischicago-RCU above might be ok for a large model, but if I tried to fly my .15 powered combat ships like that, I'd never get them off the ground. (I shoot for around 10, 12 tops, anything more doesn't fly well at that scale).

So, it's clear to anyone who has flown more than one size of model that wingloading by itself is a totally useless number. It tells you absolutely nothing about how a plane will fly. You MUST know how big the plane is to go along with that wingloading.

The various cubic forumulas (and there are several of them) all try to add a scaling factor, usually based on wing span, to adjust the wingloading for differnet sized models. And, as long as you are talking about simular types of models with simular airfoils, they do work pretty well.

However, even those cubic forumlas break down when you compare a Cub to an Extra for example.

In other words, how a plane flys at a given wing loading is determined by "a number of factors", such as the airfoil, CG, thrust, Renylds number, etc.

And that is what was being pointed out above. That there are a number of factors that determine the performace of an airplane, and the wingloading is only useful in the context of those other factors.

sigrun

Wing loading is not a very good indicator of how well an airplane will fly.

For an "apples vs apples" comparison wing loading is a most salient and excellent indicator of how a particular model in its class will manoeuvre or handle/penetrate meteorological or orographically induced turbulence.

For the confused newbies, here's a link elaborating upon the "pseudo-theoretical parameter" referred to as "wing volume loading".

http://www.genesis-rc.com/wacoymf5/wing%20loading.htm

chrischicago

Yes that's right
A warbird's wing loading can be way higher than 30 and flies pretty good because it's just the way the airplane has been done. Also, it depends on which style of flying you do. For example, if you do 3d, you'll want to have a low wing loading, but if you want to go fast, high wing loading is better.
I still recommand a wing loading under 30 for most sport planes.
Chris

JohnW

My Feedback: (6)

Wing loading is highly over-rated. Wing loading by itself gives absolutely ZERO indication of how a plane will fly. The ONLY way wing loading can give a useful comparison is if you compare two exactly identical planes in every respect, except they weigh different amounts.

I'm not sure I understand the question of the original post, but if one wants to calculate wing loading becasue they need math practice, the first response by LouW was correct, weight into area.

Any statement like you must have a wing loading of X to fly good is uninformed. Montauge had a good go at it. While caluclating "wing loading" is straight forward, calculating how "light" or "heavy" a plane will "feel" in the air is considerably more complicated.

I am guilty of throwing out the cubic loading calc on ocassion. We don't live in a linear world. While not perfect, cubic wing loading (weight into volume of wing) tells a lot more about the aerodynamics of a plane than just wing loading. True, change scale dramatially or airfoils, etc., and it all goes out the window. Sigrun's link explains this in more detail.

By "good flying plane", what we really mean is that the plane falls into a certain lift/drag range with a wing that generates X lift at Y angle of attack where the Y angle is in some acceptable range for a given flight speed Z at an airdensity of A and of course X must equal the weight of the plane.

It really comes down to full blown aerodynamic theory with lift/drag ratios, flows, Renyolds #, etc. In short, there is no cheat, rule of thumb, seat of the pants estimate, or easy way to quantify aircraft performance. With enough experience, one can guess fairly closely how a plane will fly, but to actually quantify this you really need to crank all the formulas and do tunnel testing.

Cheers

Montague

Sigrun,
"apples to apples" is exactly right. And you better have a very narrow defination of "apple". By that I mean, both planes have to have the same airfoil (including, and espeically the LE shape), the same wingspan, the same wing area, the same aspect ratio, the same taper ratio, etc.

So, if you have two 30% extra 330's, sure, go ahead, compare wingloadings. Got a 1/4 scale cub and a 1/5 scale cub? Forget wingloding, it's now useless as a way to compare those two. Heck, I'd even so far as to say that a CAP and an Extra with the same wingspan and same wingloading will fly "differently".

And that "anything below 30" is a totall laugh. I guess you've never flown a small plane? Too bad you arn't around here, I'll ballast up one of my .15 powered planes to 25oz/sq foot (well below your "anything under 30" rule), and I'll bet you $100 you can't fly it though some basic acrobatics, if you can fly it at all, I'll put $25 on a snap to the ground on launch all by itself). So, Chris, unless you qualify that with some more information, you're giving out some totally bogus information there.

southern_touch9

My Feedback: (3)

Warbirds dont fly good no matter what the wing loading

JohnW

My Feedback: (6)

Actually war birds will fly fine at very high wing loadings. Many easily fly with wing loadings in the thousands of ounces per square foot... they just happen to be full scale.

sigrun

Monty I didn't respond further yesterday as the subject was not only straying totally from the question actually asked, but presumably as actually intended by the originator of the thread. ie:"how do u calculate the - max. (sic) - wing loading of your rc planes?". He was well answered by LouW on the latter, and I added my comments primarily in response to Geistware's tangent of questionable comprehensibility.

Perhaps I'll respond further later considering the turn this thread has taken. This'll necessarily be short as I want have to leave to go flying in 30 minutes time.

Not only must it be said that that not only sounds exaggerative approaching absurdity Monty, but it's simply untrue = false (logic), model or full scale.

I think I know where you're coming from, and will discuss it further with you when I have more time. I suggest that the case for our apparently varying view is not only our differing degrees of knowledge and relative perspectives based upon that individual understanding, (see next para.) but the arithmetic and its contextual relativity.

All aeroplanes by inherent difference of design have unique handing characteristics, and I've flown and instructed, checked and trained on/in 'quite a few' in 14,000hrs ITRW and aeromodelling over the past 30 years. However aircraft of similar class with similar wing loadings will ordinarily exhibit certain and predictable characteristics in their handling. This is of course always subject to characteristics imposed by other inherent design difference, which holds true on any scale. Within a relative spectrum, wing loading can be used as a datum predictor of comparitive performance, specifically in respect of the aspects mentioned in my second post in this thread.

Read what I said specifically about wing loading's effect upon manoeuvre & inertial penetration. Of course, altering the scale, form (drag) or wing shape dramatically will have an influence upon both handling and performance. Of course understood as a given, wing loading is part of the whole (design).

I'm not really interested in discussion for (ego) gratification or argument as its own end. I suspect similarly to your good self, motivation is to educate and dispel erroneous belief and misunderstanding derived of half-understood lay knowledge endlessly perpetuated in R/C mythology. BBL..gotta' go fly now.

cheers

sigrun
OOps! Epaulettes, braid & cap left in the crew room locker with the (US)ATP, (AU)ATPL + et al

JimTrainor

Wing loading of a model typically varies with the square root of model weight. I learned that here: http://jmquetin.free.fr/tips5e.htm

If you're interested in cubic wing loading, read this over on the aerodynamics forum:
http://www.rcuniverse.com/forum/What...1175842/tm.htm

Personally, I've concluded that even cubic wing loading is questionable. It is not a number that remains constant as scale increases. I have to do my home work to verify.

Nonetheless, it's interesting to consider.

Getting well beyond beginner here.

Montague

I do think we are answering different questions to some extent.

The question was "how do I calculate MAX wingloading". Not "how do I calculate THE wingloading".

LouW pretty much answered the 2nd question, "how do you calculate the wingloading". Lou then said you can compare that to simular size airplanes for a ball park idea of performace.

I don't disagree with that at all.

But that doesn't tell you what the "MAX" wingloading of the plane is.

But most of my response wasn't aimed at Lou, it was aimed at the guys who tried to give a fixed number with no clarification, which is flat wrong. Or who implied that if all you knew was the wingloading, but not the wingspan or other metrics, that you could determine the flight performace. Your first post really implied that strongly when you said:
In the context you said that, you implied that the size of the airplane was not a factor when talking about a planes MAX wingloading. Not it's wingloading, it's MAX wingloading. Your most recent point acknowledges this, and I'm sure you knew it, but it wasn't what you said.

Now, defining "MAX" wingloading, I took to mean "highest wingloading for a plane that will still fly in a reasonale manner". It's subjective of course. I am using this definition because of the way the origional question was asked. I'm guessing a bit, but it sounds like the origional question was asked because they wanted to know if a particular plane they were working on was "too heavy" or not, and wanted a way to figure that out. I also think it's possible the origional question was also asking about possible payload capacity of a given plane.

So the question is, how high can the wingloading be, and have the plane still fly "well". I think you can get a general idea of what "well" is and isn't. You'd want to be able to ROG from a typical model field, fly some basic acrobatics such as a loop or roll, and be able to land on a typical model field at a reasonable landing speed, all with out undo risk of snapping out and spinning to the ground.

And my answer is that it's hard to determine. You could probibly calculate it out, but it would be a pain.

And my main point is that the overall design of the plan is a big factor still stands. I've had plenty of person experience with my own designs to back this up. Just changing the tip chord of a wing with out changing the over all area or the wingloading can make a big difference. In my case, adding an inch to the tip chord and taking the inch back at the root made the difference between a plane that was a snapping nightmare and a very nice flyer. Same airfoil. Same wingloading. Very different performace.

Anyway, that most recent post did actually say what I've been saying all along when you said:
However, I felt it was worthwhile, in a beginners forum, to not take anything as a "given", and not assume the readers would automatically know that design elements such as scale, wing shape, etc would have a signifigante effect to the answer. So I tried to point that out. Nice to see that we do, in fact, agree in the end.

Btw, if you want to mention false logic, how many hours you do or don't have in a full scale cockpit says nothing about your ability to design anything. Your comments about your piloting experience, while intersting, is a totally bogus addition to a discussion about wingloading. I'd have to dig up a logic book, but I believe that's usually referred to as "False Authority". And veiled attacks on me personally don't help you much either.

JohnW

My Feedback: (6)

The original question wasn't 100% clear to me. I'm not sure if the poster really wanted to calculate mamimum wing loading, but maybe they did.

If so, one could get close to caluclating maximum wing loading if they have access to specs on thier airfoil. This is probably beyound the beginners forum, but it is possible to calculate maximum loading. There are a few airfoil programs lingering on the web that estimate lift/drag AOA/lift ratios, etc. Do a search for XFoil and Eppler code. They aren't perfect and often they are way off from tunnel testing. However, for a given Renoylds, AOA and airspeed, one could still calculate with some precision the maximum lift of a particular wing. Need to keep in mind that takeoff speed is typically the limiting factor since it is typically below curise spped. Once airbone and at cruise speed, the plane can carry more becasue the wing is operating at a higher reynolds number. Of course other factors come into play, such as having enough power to obtain said airspeed at said AOA, and the structure must handle the loads.

sigrun

Hi Monty

How I detest these sorts of 'discussions'. They too frequently descend to a pointlessly puerile "Nah..nah...I'm right and you're wrong!" level, and take up an inordinate amount of what essentially amounts to wasted time. However as you've taken the courtesy to respond at length, it's only courtesy that I offer you the same consideration. If we only achieve civility as a standard and observe mutual respect, they will suffice as the goal.

I concur that WAS what the thread originator literally said. But by what he said and how he said it, it's fairly apparent that not only did he not really understand what he was saying, what he literally said was clearly not the question he intended to ask. And one can hardly blame him given the further example in here by those who should be more erudite with correct terminology by convention.

An aircraft's "maximum wing loading" is a structural limitation which presents for practical purposes only as an academic exercise in the modelling world, and is totally moot insofar as the sport flyer and beginner is concerned. I don't know of any (?) who are going to conduct the destruction tests necessary in order to determine it. Do you?

Hence we can dispense with "max. wing loading" acording to its definition by convention immediately.

As we both surmised, he was most probably really asking how to determine the 'highest wing loading beyond which performance starts to deteriorate rapidly such that a model will fly like the proverbial dog', a performance 'limitation' and point on the wing loading efficiency curve which is improperly referred here to as "max. wing loading". Failing observation of terminology convention, interpretation must be employed. I expect to have to do that with beginners or the lesser informed R/C flier, but am disappointed that it has to be clarified those who present themselves with credential importance. So any argument claiming the high ground based upon what the enquirer actually said doesn't hold a lot of water per se.

Which to reiterate, is fairly apparent he doesn't really want to know. And to wit, your reference to volumetric formulae based loading still doesn't provide. Do the math and get the sandbags out if you want to determine "max. wing loading".

OK. A few things should be clarified here.

Actually I neither said nor implied any such thing considering it in the context of what the following paragraphs should make clear, and considering the proper understanding what max. wing loading definitively represents.

Firstly, following the thread to that point and to wit I relied in that context, no mention had been made of "wing volume loading" pseudo theory. The post in which I said what you've quoted was a response to Geistware whose own post was a semi-comprehensible nonsense, with and without privy to the later introduction into the discussion of "wing volume loading".

Secondly. As it was most apparent by way of analogy the thread originator was asking about algebra without having an understanding of the basic conventions of arithmetic, it was important to establish the concept of wing loading an essential foundation in order to deny the nonsense propagated in the aforementioned post. Pretty clearly from blue_meliz's question he neither understood what wing loading was, nor what he referred to either by way of convention or in any meaningful sense.

In this I consider we have found the the common ground.

Actually its not, and therein lies the essential problem. Referring to "max wing loading" when that's not what is meant is like saying multliply when you mean add. Now that sort of thing coming from an average sport flyer or newbie is understandable in the R/C community, but hardly expected from an "Chief Flying Instructor" who should be able to tell the difference between and apple and an orange.

We all have to interpret in the case of a question as presented by blue_meliz, but despite our common interpretation of what we both surmised he was truly after, you're still incorrectly referring to it as "max. wing loading". I do however agree with your two paragraphs above, and was I interpreted what he was looking for as well.

Literally. See my previous re maximum wing loading.

No contention there. I think we've both said that, and that's an accepted known involving more than merely variance in wing loading.

No ones placing aspersion on your experience, though your understanding and observance of conventional terminology could use a brush up.

That's an aerodynamic influence unrelated to wing loading per se. For a given model of the same wing loading, changing those things will change handling characteristics yet stall speed and its related characteristics I mentioned in the previous post will remain very similar. By way of example a tendency referred to as "tip stalling" by modellers which can mean anything from the tendency to enter a violent approach config stall to an excessive throw induced snap roll can designed in by changing several aerodynamic factors such that even with the same wing loading, the model can no longer safely be flown at the same Vs+n safety speed. We can go on ad infinitum about other aspects of design such as high/low wing et al, but the bottom line is that wing loading determines certain characteristics of a model all else being equal, and as such is a useful and meaningful datum.

I think I've already covered that in the previous paragraph.

Actually not quite. I think you're misunderstanding what was saying either there, or more probably originally. Essentially and simply put, it's a given or known which should be unnecessary of elaboration in our discussion that wing loading is part of the whole (design). It is however an extremely useful predictor of certain aspects of performance and most useful datum.

To analogise it simply, talking about wing loading out of the overall context of the model design is like talking about handling performance of a motorcycle based upon its pure spec. engine power output without any consideration for its charateristic power curve, frame, suspension, brakes or tyres which you can further take it down to pressure in tyres, spring rates et al if you so wish.

I see where you're coming from. In the case of beginnners, that's accepted, however in conversation with someone such as yourself, I would have considered 'spelling out the knowns' a lesser prerequisite.

Spoken with an unexpected ignorance. But it does you see, for to get there we don't just assume an air of authority re aeodynamic theory and design. We have to prove understanding both in principle and practice.

Unlike your good self, modesty forbids me from presenting pointless self-aggrandisment beneath my nick, preferring what I have to say be taken on its merit alone. Suffice to say, you're observably now speaking well beyond your 'ken.

Ad hominem isn't my style. I think its a shame you feel it necessary to become yours. I think this not only ends further 'discussion between us, but on a rather disapointing note.

all the best

sigrun

sigrun

Thanks for those links Jim. I'm having a primary read now. The links to the article presenting Therkelsen's theorem (has a nice ring to it doesn't it? are the more salient theorum or proof I'd like to investigate, though it's got me reaching for the refresher books.

Though I'm not sure I yet agree with his reference to mass (ref: measure of quantity of matter in a body aka std kilogram of quantity of platinum-iridium alloy under standard conditions) aka "weight" in the context of wing loading, as mathematically having "volume" for the purpose of its resolution or the relevance of the property of density (mass per unit volume) (ie: m/V) in the discussion of wing loading (ie: W/A) and therefore application of n³. (ie: W=M(G) g)

Velocity (speed) is also a vector and two dimensional having both a magnitude and direction, though I still have to assess the former in overall context. Thanks for providing the links. I will have a read and probably come up with more questions than answers.

cheers