Fighterpilot

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I know that wing loading (oz./sq. ft.) is a relative measurement in our warbirds. A 60 sized warbird might have an excessive wing loading at 35 oz. per sq. ft. however our 102 inch warbird would be a floater with a 35 oz. wing loading. We are currently flying three American Eagle Bearcats that have an 86 in. wing span and weigh approximately 33 lbs. They fly beautifully with about a 55 oz. per sq. ft. wing loading. I've just built an AT-6 Texan with a 102 in. span that calculates to have a 57 oz. per sq. ft. wing loading. How do we know when a wing loading is approaching a catastophic level before we fly? I know from experience that it is all relative to the size of the airplane, but does anyone out there know at which wing loading level does a certain size aircraft become a brick, unable to fly?
If I am correct, the wing loading is calculated by taking the weight of the plane in ounces, multiplying that by 144 (the number of square inches in one square foot) and dividing that by the wing area of the airplane expressed in inches.
How about some of you engineers out there, any advise.
The picture attached is of my new AT-6, ready this week for it's maiden flight. It has a 57 oz. wing loading.

Chris 540

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My gosh man....

Fighterpilot

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My gosh man....what? The 33 pounds is not an abnormally heavy airplane for this model. When you have a Quadra 75 in the nose, heavy duty retracts from Sierra Precision, B&B Smoke System, and 12 servos, two fuel tanks (gas and smoke) and two 1650 mah battery packs, things add up in a hurry.
Now can anybody reflect on the original question.
Thanks guys

Chris 540

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So you must have to use a full scale runway to take off?

Taildragger

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I believe your right on the formula but I don't know beans about how you determine the critical loading of a particular plane. That T-6 is beautiful. One of my favorite planes but for some reason have never built a scale one. I blew up a set of house of Balsa 15 size plans to a 60 size once. It was a fantastic flying Sunday flyer. I'll have to build me a Ziroli one of these days. (or just buy one, that sounds easier).

Fighterpilot

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No Chris it doesn't take that much room to take off. You would be surprised at how quickly one of these fairly heavily wing loaded warbirds gets off the ground. I've got a Sea Fury with a heavier wing loading than mentioned above and it doesn't take more than a 50 ft. roll out before breaking ground. If you try to duplicate a scale take off, you don't want to pull it off the ground and climb out at 60 degrees.
Now, the problem is not the take off, it's having enough room to land one of these things. A safe wheels landing with an idle at about 1800 rpms turning a 22X12 prop keeps you going down the runway quite a ways before things begin to slow down. On grass it's not too bad, but on a hard surface be prepared to taxi back at least 4 to 5 hundred feet from where you touch down. Head winds are a big help.
I've discussed this wing loading thing with a few pilots and a lot of wether or not a plane can carry a certain amount of weight is highly dependant on the airfoil and the lift developed by the wing; therefore, certain airfoils can carry greater weight easier than others.
I guess there is only one way to really know.... Crank it up, point it into the wind, and go for it.
We'll be doing that very soon on the Texan.
Tail Dragger, my kit is an American Eagle aircraft. It is a fiberglass fuselage with foam core wings and stabs. It goes together fairly easily, except for the cutting out of all the wheel wells, servo holes in the foam wing, and flaps. Once this is done, however, the rest is not much different from any other construction.

Rocketman612

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Good luck with a great looking plane. Pete

Rooster353

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Fighter pilot, are those real rivets on the AT-6?

Nice job.

Rooster

Big_Bird

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Fighterpilot, the proper way to determine wing loading is to divide the wing area in square inches by 144. This will give you the wing area in square feet. Now divide the weight of the plane in ounces by the area in square feet to give you the wing loading in oz/sqft.

My Ziroli Corsair weighs 36 pounds with a 93" wing span and a Brison 5.8. It is very fast and agile and with full flaps (47 degrees) lands at a very good speed. I'm sure the wing loading is way up there but it doesn't seem to hurt the performance. And I really don't intentionally plan to try any 3D maneuvers.

That's a great looking T6.

Ken

Fighterpilot

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Guys the panel lines were placed on the aircraft after painting with a fine Sharpie permanent marking pen, the rivets were then placed along the panel lines, wing ribs, and bulkheads using silver Tulip Paint. The model was then painted with a urathane clearcoat. You can purchase this paint in many different colors from either a local craft shop or Wal-mart. It is the acrylic that ladies use to mark on clothing. It comes in small plastic squeeze bottles with a nozzle tip. It really makes the job quite easy and goes pretty fast. I've been able to find all the colors used on the AT-6. I still cannot find a color close to olive drab. I've even done an airplane after it was clearcoated and amazingly the rivets are still in place. The stuff really adheres to almost anything. If you make a mistake and don't like a rivet or rivet grouping, you simply wipe them off with a wet cloth. Once they are dry, they are stuck. In the pictures posted, you really can't see the rivet lines very well, but they really do show up and accent the paint scheme.
Thanks for the compliments.

Rooster353

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Just for grins, I did some math.

The wing loading of a brick is about 144 oz/sq ft.

(Brick loading 8 x 4 (x 3) inches weighing 2 pounds
32 sq inches/144= .222222 sq ft
2 pounds = 32 oz
32 oz / .222222 sq ft = 144.014 oz/sq ft.)

The wing loading of a maxed out, full scale Grumman F6F Hellcat
is about 820 oz/sq ft.

(Max Gross F6F Hellcat 13228lbs 43ft wingspan 258sq ft wing area. 13228lb x 16 oz/lb= 211648 oz / 258sq ft = 820 oz/sq ft)

In layman's terms, "wing loading" is a measure of the amount of force that each square foot of wing area must generate in order to overcome the force of gravity to allow that particular airplane to fly.

Stall speed is proportionate to wing loading.
A 102 inch wingspan AT6 with a 35 oz/sq ft wing loading
will stall at the same airspeed as a .60 size plane with the
same wing loading. Larger airplanes just appear to be
flying slower than smaller airplanes.

The beautiful 102 inch AT6 pictured above WILL fly
IF you get it going fast enough.

Then again, so will the brick.


Rooster

Fighterpilot

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Guys, all went fabulously well on the maiden flight. Not to fear, wing loading is not excessive. The plane landed on a concrete runway and rolled no more than 175 ft. after touchdown. With flaps at about 40 degrees, it slowed quite nicely for landing.
Thanks to all that posted replies.

Sorry about the quality of the posted picture, it was a single frame from a digital video camera.

RC Pilot56

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The way one old time scratch builder (Mr. Matthews) told me how to figure out wing loading goes like this.
Weight in lbs. x 16 x 144 divided by wingarea in sq.in. will give you your wing loading. If your not convinced, find a tower hobbies magazine that tells you weight in pounds, wing area and
wing loading and give it a try, I think you might be surprised.
Example: Midwest 1/6 scale AT-6 has an 83" wingspan, weight is 15lbs. and wing area is 1000 sq.in.
15x16=240x144=34,560 divided by1000=34.56oz/sq.ft.
It works every time.

paladin

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Anyone concidered wing volume loading? I've found that it worked well regardless of the size of the model. I fly 1/12 to 1/4 scale models and they all fit on the same curve.

Annything below 300oz./ft cubed is a floter.
301-500oz./ft cubed is what I try to hit.
501-700oz./ft cubed flys heavy.
600oz./ft cubed things start to get real interesting the futher abouve this number I go.

F4u5

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Paladin is correct on wing volume. When you get into an airplane of 80 inches or larger, wing loading is really no longer an acceptable consideration, yoiu need to look at wing volume. PAt McCurry had a great article in RC Report a while back that did a nice job of explaining wing volume. He states that if you take a 60 size warbird that weighs 10 pounds and calculate the wing loading, you will come up with a figure. If you take an 80 inch plane and calculate the wing loading, you will come up with another figure. Now, if you, theoretically, take all of the structure out of the 60 size wing and filled it with water, then do the same with the 80 inch bird; now if you were to pour that water from the 60 size wing into the 80 inch wing, you would find that it would not fill it up even 1/2 full. I thought this gave a good impression of wing volume. Bascially...weight is not as critical a factor with the growth in wing volume. And I think 33 pounds for a Bearcat this size is VERY acceptable. I know of an 86 inch Ziroli that weighs 41 pounds....flies fine.

Nickrc3

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That was a very interesting article Jeff. I also had concerns with my Meister 47' when I dry-weighed it (41 lbs.) and did the wing loading math. After reviewing the article and test flying her, I realized the wing volume ( and airfoil design ) determine much of the flying characteristics. With the Meister designs and their generous wing volume, you're almost guaranteed a stable flier.

Rooster353

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wing volume?

that's a new one for me.

does that mean if i double the volume of the wing of my sweet stik, while maintaining the span and the chord, that it will fly even better? Why would that be so?

Rooster

Fighterpilot

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Interesting theory on wing volumn as opposed to wing area. I can see how the theory would work, because the thicker a wing is the more lift it develops along with corresponding drag, however. Where it is relatively easy to determine the wing area accurately, measuring the volumn of a wing would depend on an accurate measurement of the wings average thickness from root to tip, and from leading edge to trailing edge. I can see where this would be a bit difficult to figure out accurately and am always willing to learn the method another pilot uses to determine the relative ability of an airplane to carry its weight. How, do you guys determine the average thickness of a wing in order to determine volumn as in length x width x height (thickness) = volumn?

rmm

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Fighterpilot,

your plane looks great. I hope it is still alive and well. I have a question - what kit is it and where did you get it?
Just returned from Oshkosh and I am thrilled by those AT6.
I guess I alos have to look for a 18 cylinder with no muffler ;-)

Regards
Rainer

fly109

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Hi all,

F4U5 is right I did right an article on this topic, in fact I have written several, all with the same concept in mind, which is to free us modelers from the chains that have been wraped around us in terms of limitations based upon completly and utterly outdated therories concerning. . . Wing Loading!
The jist of the article that I presented is very simple. Modelers are "brought up" believing in "magic numbers" that are reputed to give us good flying results. This is pounded into our heads from the moment we begin flying at our local club fields by the club Gurus and continues being echoed by manufacturers that produce models that are aimed at the vast majority of us modelers.
Why is ounces per square foot even considered as an attribute that needs consideration when selecting a model when other attributes such as pounds per horse power are ignored? Well it all started "way back when" and I am not sure of "when" that was but I for one have experienced a few things since "then" and have come to a a few conclusions of my own.
First of all, I do not care what the wing loading of any model is, period. I have arrived at this conclusion after seeing for my self some of the numbers that are supposed to suggest catastrophe being proven completely false. Secondly, I prefer heavy models over light ones, they fly much better when you as a pilot are capable of doing so. About seven years ago I did a model review in MAN on a foriegn kit of a FW 190D9. It was from a company called VZ from the Chec. republic I think. It was a glass and foam model with a wing span of just 57 inches. I loaded the model up with details and finish and installed a Satio 90. The model weighed just shy of 13 pounds....DRY! It flew great. After flying in front of people and then telling them what it weighed they where dumbfounded and probably didn't beleive me, in fact some of you probably don't either, oh well.
I have flown models in the high 80's (ounces per square foot that is) and felt just as at home as with a 60 sized model. Some of the jets I fly would have truly excessive wing loadings compared to those unfamiliar with the type but still fly wonderfully. If full scale pilots had the same limiting criteria, I don't think aviation would be where it is today. Some full scale examples for you to think about.
I am told that a fully loaded C5A approaches 220 pounds per square foot! Thats 3520 OUNCES per square foot, or roughly 100 times more that the "Comfort Zone" we seem to think is the norm. So you may be saying "yeah but thats full scale and we're talking models here". So tell me, what is the difference? We should ask ourselves, where is the line drawn? Is it 50 feet? 200 Feet? 12 feet? 30 feet? How do we explain a Lockheed F 104 starfighter? (32 feet and and approx. same wingloading as the C5A?) And when we figure this out, lets bring our note books so we can take some notes. . . . we're gonna need em, because there is no break between model and full scale but rather a constant curve. This is where wing volume comes into play. The term we typically see as "wing loading" is a descripition of our wings size in only two dimensions. As model size and wing size is increased we are increasing these sizes in 3 dimensions. The "Magic Number" theory fails to recognise this and is therefore useless once you leave the size of model for which that assertion is based - 40 sized models. Lets grow modeling into the 21st century and leave some of the cob webs behind:-)

RC Pilot56

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There is one thing that should be addressed and that is air speed. I too believe that a heavier airplane handles better than a lighter one. Too heavy and the engine quits running, you take whatever shot you can on landing it. If one wants to figure in wing loading, thats fine but the higher the wing load the more speed it will take to fly a model airplane or real airplane in a stable fashion. When was the last time you saw a military or passenger airliner land at a crawling pace? They all need to maintain a certain air speed or they will not fly. The same holds true for model airplanes. I have several planes in the 20 lb range that slow down nicely without any bad habits because of the amount of wing area, that a 40 lb plane of the same dimensions just couldn't do at the same slow air speed without tip stalling. I guess what I'm trying to say is that wing loading, wing area and air speed are all contributing factors in what we do. Enough said.
Have a Great Day,

thunderbolt-RCU

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Pat's theory on wing loading is correct. It is figured on wing volume, not sq. inches. I now own Pat's 13 pound FW-190 and fly it in Denver's 6000 ft altitude. I have flown it when it was 100 degrees with a density altitude of about 10,000 feet. It does need a very long runway to land and slow down, but it is a rocket in the air. It has never snapped on me either. I quit flying it because Bonnie doesn't like swastikas in the car.
Take a look at both Ziroli's and Vaillencourt's P-47s. Both are 92 inch wing spans. I have seen a Vaillencourt fly at 50 pounds, you do the math. The Vaillencourt has a much thicker wing than Ziroli's, so the Vaillencourt should carry more weight. You also have to take into consideration that some fuselage shapes are lifting surfaces as well. The full size Skyraider carried as much of a payload as a B-17. Again, because of the thick wing of the full size Skyraider.
Brian

fly109

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Brian,

Thats right. you're the one that got that model from me. It is a real eye opener for the wing loading crowd isn't it.

RC PIlot 56,
WIthout a doubt the airspeed factor is always present but the point of my article, and post here is that as these models get bigger, the once relyed upon "safe Number Zone" can and should be thrown out the door and never looked back upon. I can take my 101 inch warbird with about a 56 ounce per square foot wingloading and make a shorter landing from touch down to roll out than some average sport 60 size models.
I can do this because my models wing can produce upwards of six times the amount of lift that the smaller model does with 40 inches less wing span. Nowhere in a two dimensional equation (ounces per square foot) is this taken into account, thats all I am saying.
I can take my 15 pound (18 with fuel) 61 inch trainer jet which a very similar wing to just about any 60 sized sport model and I can put that one down to a full stop in less than 100 feet on pavement with an approach speed somewhere in the high 20's. And if you are not sure how that compares to other models I can promise you it is near a crawl. At 45 ounces per square foot, this model will slow down to unbeleievably slow speeds and does not tip stall. Also, the belief that a heavy model is more prone to a tip stall is not completly accurate. A model that has a tendancy to tip stall may get worse as weight is increased but but a correctly designed and built model that is not tip stall prone will not grow this bad habit out of thin air as weight is increased it simply does not work like this.
Tip stalls occur when the airflow on the outer portion of a wing panal seperate from the airfoil while airflow further inboard is still attached and producing lift WHILE at the same time this phenominon is NOT happening to the opposite wing panel. Washout, crooked wings, improper turn rates, flaps and a host of other criteria is at the top of the list of things that cause tip stall. Weight is far down on that list and is only present when the above mentioned items are present as well.

Sorry for the long explanations but this is one of those topics I can go on for days about, I'll go away for now.

Regards,

k_sonn

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Pat:
Don't go away. Please continue to educate us.

scalefan4

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Pat, I find your post on this subject educational as well as encouraging. Did you ever discuss this with Dave Platt? I remember an article by him on this subject (wing volume) years ago. Regards