Extra (260) wing loading
 

I have just built a 27% Extra 260 from a kit, foam core simmetrical wing. Then, at the end of construction with everything installed, I have put the plane on a scale and calculated the wing loading. I found an unexpected 35 ounces per square foot!!
Calculation is correct, beyond any doubt, and now the problem is how to make her fly. Through the radio setting, I have got the option to use the flaperons since I expect that I need to ease and slow down landings somehow.
What could the proper flaperons throw be for this plane? Or else, any other suggestion here?

RE: Extra (260) wing loading
 

Wing loading in oz./sq.ft. are not very meaningful on larfer airplanes. You should use wingvolumeloading which is calculated as follows:
(weight of model in ounces) devided by the wing area in square feet raised to the 1.5 power i.e. weight/area^1,5
If that value is 10 or lower the plane will fly fine. If 11 to 12 it means you have to watch out for tip stall on landing (keep the speed up). If more than 12 you probably have a lead sled. A value of 7 or less says you will have a real floater on your hands. This formulae works well for anything from 8 oz. electrics up to the 40 pound giants and is a formulae proposed by a Mr. Reynold's in the Sept 1989 issue of Model Builder.

RE: Extra (260) wing loading
 

Hi Rodney,

thanks a lot for your hint, even though it is 17 years old I didn't know it and it sounds very logical to me. Actually, as you say, the plane size matters and large designs can fly at higher wing loading indeed. Now the question is how high the wing loading can be.
Mr. Reynold's formulae should be the answer if I was able to calculate 9,98 sq.ft. raised to the 1.5 power.
Yesterday I have been spending 2 hours in looking for the logaritmic chart (assuming that 9,98 is almost 10) in my high school books but too much time has passed and my brain got rusted too.
Ok, here are the data:
Weight (at flying condition) = 352 oz
Wing area = 9.98 sq.ft.
Do you think this plane is a floater? If not, since our field is short, how can I slow down its landing speed? Will I be able to fly only on windy days? Is applying flaperons the solution?

RE: Extra (260) wing loading
 

Yes, it will be a floater, WVL is somewhere between 5 and 6. Depending on your power, wind should not be problem, you will just have to fly it down to the ground, not glide down under low power. Just fly it down until it is only inches above the ground then cut your power to idle. Incidently, your computer (if using microsoft software) should have a calculator at your fingertips, if so, you should have scientific notation available on it.

RE: Extra (260) wing loading
 

I calculated the wing loading WVL according to the Reynold's formulae, after I had found a scientific calculator ;), and I found that it is something above 11.
To be exact, 352 oz divided by 31.5 (9.98^1.5) = 11.17
It won't be a floater.
By the way I really wonder why no adv in the magazines mentions WVL, when indicating the wing loading of their products, even though it makes much more sense that the mere oz/sq.ft.

RE: Extra (260) wing loading
 

The old wing loading formula is just fine -properly applied
the 27% EXTRAS - are best in the 24-28 range your 35 number is is fine ---for a 35-40% aerobat
your wing are if correct is aprox 1150 squares -the 40% stuf is 2000--2600 typically .
the flying iron (warbirds) - typically run much higher numbers ---- depends on what you want the plane to do.

RE: Extra (260) wing loading
 

If you don't have a scientific calculator handy, raising a number to the 1.5 power is the same as multiplying a number by its sqare root. For example, 4^1.5 = 4 X the square root of 4 = 4 X 2 = 8
A lot of simple calculators have a square root key.

RE: Extra (260) wing loading
 

The old wingloading formula will likely remain the favorite - it is easy to do and like inches and pounds - is pretty well accepted by the public -her in the hew ess hay
A "better" method may NOT be better to those who simply want a quick easy approach.
If metrics were truly better - for everone -why isn't it the prevailing approach in all countries
because many people simply would rather go with tradition -it's easy and for them "good enough".
Crikey -be glad things are not measured in furlongs per fortnight.

RE: Extra (260) wing loading
 

Here is a simple basic program to figure your wing volume loading.
10 'TITLE: WNGVOLLD.BAS which stands for wing volume loading
20 'as defined by a Mr. Reynold's in September 1989 issue
30 'of Model Builder.
40 'where WVL=Wing Volume Loading which is defined as
50 ' (Weight of model in ounces) devided by
60 ' (Wing area in square feet raised to the 1.5 power)
70 '
80 'Let K=Weight in pounds
90 ' A=Wing area in square feet
100 ' then WVL=(K*16)/(A^1.5)
220 input "what is the weight in pounds? ";K
230 input "what is the area in square inches? ";sqa
240 A = sqa/144
320 WVL=(K*16)/(A^1.5)

335 PRINT "Wing volume loading is "; WVL
340 print "for a ";K; " pound model having a wing area of ";sqa;" square inches."
print

If you will note, your wing volume loading for an 8 pound model with 1150 square inches area is 5.67--a real floater.

RE: Extra (260) wing loading
 

One would think that the "wing Volume " formula would have quickly caught on and become widely accepted .
Did it ?
Nope
why

takes more figuring (I also have good HP Scientific Calc ) .
take an electric aerobatic 3D model weighing 24 ounces and having 400 square inches
now take another one weighing 16 ounces - both with same power .
Both possible -I have one of each
Run both thru volume formula .
what do you discover ?
Both are "light "
so what did the extra math accomplish?
I know what the formula is supposed to do - take into account the factors involved with size of any flying object
The results are not straight line
But when we get into specialized areas - then we need more guidelines -
for example a 24 ounce ,400 sq in electric is a great outdoor aerobat which is very stable and will land at a crawl - but as an indoor model - worthless - the 16 ouncer is far better .

The value of an idea is really only as good as it's acceptance .

RE: Extra (260) wing loading
 

Wing volume loading does a good job for the same reason that wing loading does a good job.

They both give you a number that you then apply to the list that tells you what the number means. TELLS YOU WHAT THE NUMBER MEANS...... The number actually doesn't mean anything, it's the subjective interpretation that matters. Since both systems rely on a subjective interpretation, who cares which one you use. And it matters little what the number is that gets you the prediction that says the loading is light, medium, or heavy. We're after the word after all, not the number.

RE: Extra (260) wing loading
 

yeh - try this on for size - a really good indoor electric precision model, has a wingloading of under 4 ozs /sq ft. some I have seen are at 3 .
a good outdoor, small electric pattern 3d can go up to 10 oz/sq ft .

why?
in the electrics - one can change the power loading by huge amounts .
all of them are floaters by standards for glow models 20-30 years ago
the flight character tho is completely different
these can all stop -start and to the casual eye appear to simply hang motionless -in any attitude.
The power available and extremely low weight and high strength , have bypassed the accepted rule books on safe controllable flight.

RE: Extra (260) wing loading
 

Just for fun, let's go the other way and apply the wing volumn loading and wing loading formulas to the full scale Extra 260.

Dry weight is 1150 pounds, throw in Patty Wagstaff and about 30 minutes worth of fuel and I estimate the all up flying weight to be between 1300 and 1350 pounds. I'm not about to ask her how much she weighs exactly so let's say the all up flying weight is 1325 pounds or 21,200 ounces.

I came up with 137 square feet of wing area based on reverse scaling the 9.98 square ft of the 27% Extra to 100%. I tried to google the actual wing area but was unsuccessful.

This gives us a wing loading of 155 ounces per square foot.

The wing volumn loading is 13.2

Which of these formulas do you think better predicts the flying qualities of the full scale Extra 260?

RE: Extra (260) wing loading
 

Why? Because people like you make comments like that.

Why not accept it since it's actually MUCH simpler than trying to remember acceptable wing loading ranges for different size planes. One simple formula can apply to any model. How is that more complex? Just because it hasn't caught on doesn't mean it's not a better idea - inertia is king.

I've been using volume loading to estimate performance since September '89 and it's a pretty good first approximation method. Full-scale aerodynamic formulae take volume loading into account, so the problem is avoided (in other words, they've known about it for many years). Seems only some modelers have trouble accepting the idea.

Why do you so steadfastly oppose those who offer better (or just different) approximations than those you proffer? Sure, your methods are good enough for your purposes, but that doesn't mean someone can't be satisfied using different methods to achieve the same results.

RE: Extra (260) wing loading
 

I am not trying to change anyone's mind. just noting what has happened
If you prefer it -use it .

RE: Extra (260) wing loading
 

8 pound (128 oz) on a 8 sq.ft. wing?? This more than a floater, this is the ultimate glider! My Extra is way much heavier than that! It is 22 pounds.
Maybe I didn't get what you meant...
Anyway, I agree with you when you say that a formula generates numbers but I disagree about the subjective interpretation. When a plane flies like a clothes iron, that cannot be subjective.
Here we are trying to establish a co-relation between an aerodynamic formula and a physical phenomenum indeed.
You may say that the best formula for you is going to the flying field, kick your plane in the sky and see what happen. Fine to me, I respect your opinion but I was actually expecting another kind of answer.
I said that the flield I use is short and that the wing loading predicts high speed landings. If there is no wind (head wind of course) to slow my plane down, how will I aerodynamically reduce its stall attitude?
Have you guys ever tried to use airbrakes or flaperons (radio option) for this purpose?
If yes, can you suggest any throw setting?

RE: Extra (260) wing loading
 

a 27% Extra is about 8 sq ft projected wing area and decent weight range is about 12-15 pounds.
My 22 lb model of EDGE (bout the same model really ) is 11.5 sq ft an that is lower end of envelope which once it his 25 lbs -all th shiny character is pretty well gone. It has 50 ++ lbs static thrust -
actually more -the prop- a Mejzlic , 27x10 spins over 6600 static and unloads to 7200 in level flight
at 4300 ft on a 70 degree day - you tell me what the thrust is. It is 'nuff.

RE: Extra (260) wing loading
 

Stall speed is related to wing loading regardless of airplane size. A simplified estimate of stall speed is 4 times the square root of the wing loading in ounces per square foot. Thus, if your wing loading is 35 ounces per sqare foot, your stall speed is approximateley 4 X 35^.5 or about 23.7 mph. Flaps only lower this number slightly. The real benefit of flaps is that it lets you safely approach this speed without risking a tip stall in addition to making the plane a little more draggy for a steeper glide slope.
This formula predicts the stall speed of even full scale aircraft with surprising accuracy.

While big birds may fly more smoothly than small model aircraft, they do fly faster even if it doesn't look like it. That's the reason I try to talk newbies out of making a giant scale model their second plane. They may be smooth and easy to do "grease job" landings with, but, because of their higher touchdown speeds, a pranged landing will mean major repairs, not just bending the landing gear straight again.

RE: Extra (260) wing loading
 

I don't know your construction technique neither the EDGE kit (or ARF) you bought but, to me, your weight to surface ratio sounds like very little.
22 lb on 11.5 sq ft, have I understood well? In addition to that you say that the engine provides 50++ lb static thrust, spinning a 27x10 prop @ 6600 rpm (7200 in the air).
Wow, I am just astonished.
My kit is from BETTINI (some of you should know it) and the design should be something around 27% of an Extra 260, as the box states.
I believe the engineers have taken some liberties here. I have put the plane together by the book and, at worst, I could have caused it to be 1 pound heavier than expected.
I have installed a ZDZ 60RV and a wood prop that works it out @ 6500 rpm static (some other members told me that I have to burn a couple of gallons of fuel more before the engine will give out the best).
In short, I have 22 pounds of balsa, ply and foam, ++ on 9.9 sq ft wing (including the fuselage section in between)and I have estimated the engine static thrust to be something around 30 lb.
If I look at your plane numbers I just get to realize that there is something wrong.

RE: Extra (260) wing loading
 

1425 sq inches on your model - that is above 27% of scale of the EXTRA 260-
but many kits are interpretations of scale, not scale per se.
My own version of a Giles 202 model , was 1500 sq in and of a Dalotel was 1550 sq in both were 18 lbs aprox and both used ZDZ60 on 24x10 props (MenzS )running at 6400 rpm - both excellent performers . 22 lbs will give mor scale like performance --few very few full scale planes will hang on the prop - a local guy has a Pitts 12 which will -but not accelerate from that position.
somewhere around these numbers with the ZDZ60 will deliver a really good performance combo.
The clipped wing EDGE (a H9 kit and piped ZDZ80 J ) I call "Godzdzilla " really does have good power to weight - the static thrust is as noted but the best part is that reserve thrust at cruise speed is also instant . Net result is that any maneuver from any attitude can be accelerated . Just like a good foam/electric setup.

RE: Extra (260) wing loading
 

Is WVL taking into account the lift generated from other parts of the plane like the whole of the fuselage and the tail? Not just the wings?

Is this why larger planes like 40 percenters fly so light despite not having such great wing loading?

RE: Extra (260) wing loading
 

no - bigger stuff simply displaces more air --
The Reynold's numbers formula (look it up) explains this nicely

RE: Extra (260) wing loading
 

I ended up doing a few calcs with a spreadsheet on some currently available planes. It seems to explain why bigger planes fly "lighter". If you are familiar with a given group of planes, say 50cc class planes, the wing loading number may be sufficient, because you aleady know what is a high wing load. But if you try to apply that same wing loading criteria to say 100cc class, then the simple wing loading fails. These planes have higher wing loading than the 50cc planes but have similar or less WVL.

Unfortunatley, my GP Yak don't look so good in comparison [&o]. Even if I lose a bit of weight it doesn't seem to help a whole lot. The money I could spend reducing weight I could use to buy a new plane with bigger wings.

I think if you are simply discussing the problem, then WL is OK. But if you are about to shell out some bucks for a new plane, or trying to get a better handle on an existing planes limitations, then doing a little extra calculating is worth while. Acually I set up a spreadsheet to automatically calc both WL and WVL by just inputting the posted vendors WA and Weights.

RE: Extra (260) wing loading
 

Here's another way to look at the effect of wing loading relative to larger airplanes:

When we fly a model, our perception of speed comes down to how many "fuselage-lengths-per-second" it appears to travel. So if you take two models, one 24" long and one 48" long, but traveling at the same speed, the bigger model only appears to be going half as fast. And, you can let the bigger model get twice as far away before it seems too far out to control easily. You can check this out for youself by watching a large airliner come in to land. They seem to fly impossibly slow compared to a model.

In addition to the visual size effect, there is the damping effect. If we go back to the two models, one 24" and the other 48", both at the same wing loading, the larger model will be more heavily damped in all axes by the air that flows around it. Thus, the model is visually and physically easier to fly.

Now, how much heavier does the 48" airplane have to be in order to fly at the same "fuselage-lengths-per-second" as the smaller airplane? It works out that you have to increase the weight (and thus wing loading) by the square of the scale ratio in order to make the twice as large airplane fly twice as fast. So the 48" airplane would have to be: 2 squared, or 4 times as heavy to appear to fly at the same speed.

Am I discounting Reynold Number effects? Definitely not. The higher Rn is pure icing on the cake for making larger models fly better.

To cite some personal experience on this scaling business, here is an experiment that I was involved in back in the late 1960's: I was working on an unmanned flight test vehicle at Edwards AFB which would be flown by a pilot in a ground based cockpit, much like the Predator drones of today. The only problem was that we didn't have forward looking TV in those days and so the decision was made to transfer control to a regular RC pilot for the landing. Somehow I was appointed the RC landing pilot.

Since this was a very expensive test article, we did not enter into the enterprise carelessly. One of the preparatory exercises was to evaluate my ability to percieve height, speed, turning radius, etc. of a faster and larger aircraft while standing at the planned landing site. I positioned myself alongside one of the drylake runways with a communications radio. Then an airplane was flown into my vicinity from which I directed the pilot in turning and power adjustments to guide him down to my planned touchdown spot. I did this with a B-52, an F-111, and an OV-10 in order to evaluate a range of aircraft sizes and wing loadings. You don't even want to think about the wing loading of an F-111, by the way. Anyhow, the result was that all three of the evaluation aircraft could be easily be "flown" to the planned touchdown spot, including the flare. In all cases, a typical sport/pattern model seemed faster than the big airplanes.

Did the test program work out? Yes, but we only got to make one flight with the final vehicle before we lost our launch aircraft. We had borrowed an SH-3 helicopter from NASA Houston for our launcher and somehow they wanted it back for final water rescue training of some guys who planned to go to the moon.

Dick Fischer