Sailplanes Wing Loading?

[grampayeehaa]

I see this thing posted on the spec's of most planes call wing loading followed by a formula like 35g/dm2 in the case of the Diamond 2500. What does that mean? Another thing, what the blazes is wing loading and what does that have to do with the flight characteristics of a plane?

What the heck, as long as I am here I might as well ask another question regarding wings. It is posted that the wing area is 55 dm2. Please explain that and what does wing area have to do with the flight characteristics?

I am sure that the wing loading and wing area are important information. I would like to be able to figure them out and have an idea what all that means so I can make a more informed decision when making my next purchase.

 

[EyeStation]

I don't want to cut and paste the entire entry, so here is a link, http://en.wikipedia.org/wiki/Wing_loading

 

[pvolcko]

g = grams
dm = decimeter (10cm, or 1/10 of a meter)

So wing loading is mass per unit area, in this case grams per square decimeters.

The linked article is a good starting point to understand what this has to do with flight performance.

 

[Tony]

The lower the wing loading, the slower you can fly and the more the plane will "float". Trainers have a very low wing loading. However, on the other end, war birds, such as the P51, have a high wing loading. This just means you must keep your air speed up when taking off or landing and in a turn. As that article stated, there is a LOT more to it than that, but what I have here is the simple version of all of that math.

 

[grampayeehaa]

Ok I am trying to get my head around this. What I perceive you are saying is I take the 35g and divide it by 100sq cm giving me a value of 3.6?

 

[pvolcko]

Not quite. I don't know what the area of your model's wing is or what it's mass is. But that 35g/dm2 value is the result of a calculation like: mass / area = wing loading, which in this case equals 35g/dm2.

So you would take the weight of your model in grams and then divide it by the wing area (length x width if you are looking down on it, in decimeters, which is centimeters divided by 10) to get this value.

 

[grampayeehaa]

OMG, now I am confused. Ok, let me try this. If 35g/dm2 is more or less an end formula, then logic would dictate that the wing loading for that model would be less than a model with say an end formula of 55g/dm2. Is that correct? I am really looking for a glider that is slow and floaty as I am a flat lander looking to ride the thermals.

 

[pvolcko]

Yes, the higher the wing loading value that means less floaty, generally speaking. It means there is more weight to be supported by a given unit of wing area.

35 g/dm2 vs 55 g/dm2 means that, for the first one, for every square decimeter of wing there is 35g of weight being supported by it. The second one, there is 55g of weight being supported by every square decimeter. The first one will, all else being equal, tend to glide longer, slower, etc.

Of course, all else is not often equal. A very large, heavy model may have that 33 g/dm2 rating compared to a smaller, lighter model having the 55 rating. The size may be too much for you and your ability to transport, so you'd still want to go with the 55g/dm2 model because it is more practical or fits your budget better.

And wing shape and other factors come into play too. A wing may have low loading because it has a lot of area, but it may be so long and have such a short chord that it is very tipsy (particularly at stall) requiring a lot of careful setup and flight control to make it fly right. A better overall wing design, but with higher loading may be much more stable and offer a better overall flying experience, despite it having a "worse" wing loading value.

It is by no means the end all, be all of what determines flight characteristics, unfortunately.

 

[grampayeehaa]

Thank you pvolcko, it's starting to make some sense.

 

[grampayeehaa]

Here is my intention. I am looking for a glider with at least an 80 inch wingspan so I can become involved with a group of flyers who fly only large scale planes. It must have its own on board propulsion system. It must be reasonably stable in flight so I don't have to struggle to fly it and it would be great if it were a bit on the floaty side. I presently fly a Radian which fits all my categories except for the 80+ inch wingspan.

There are 3 planes that I have been looking at. The Masala with its 11 1/2 foot wingspanhttp://www.nitroplanes.com/23a05-masala-kit.html. The Diamond 2500 with its 98 inch wingspan http://www.nitroplanes.com/at-22093-diamond2500-rtf-24g.html. And the Airfield Giant Convertible with its 95 inch wingspanhttp://www.nitroplanes.com/95a289-giantglider-arf.html. I must say that although the Masala is huge and impressive looking, it stretches my budget to the max. I guess that I am asking for your opinion.

 

[pvolcko]

And at this point I definitely have to defer to others here. My airplane experience it practically non-existant, much less gliders.

That said, personally I like the look of the Airfield Giant. And if budget is a concern with the Masala, then it probably is with the Diamond 2500 too (only a few dollars difference). The Giant comes in significantly below the other two. Unfortunately, I can't speak to their potential flight characteristics.

 

[grampayeehaa]

Thank you for the help that you have given me. Just for information, the Masala comes as a shell, no servos, no propulsion system, no radio system and no hardware. It would cost upwards of $700.00 to get in the air. The Diamond 2500 comes with everythingpre-installed, to include TX/RX for $250.00. The Giant at $209.00 requires the purchase of a TX/RX and a 4s lipo battery and charger.

 

[pvolcko]

Ah, okay. Didn't look that closely at the "required to fly" lists. I'm assuming you already have a Tx (maybe a bad assumption?), so low channel count Rx and battery to complete the Giant... the Diamond and Giant are probably in the same ballpark.

 

[grampayeehaa]

You are correct. I do have my own TX a DX6i Spektrum. I will be using it on either plane I get because I like the ability to program the flap and elevator mix, (around 5% down elevator with down flaps). By programing in that mix, it counteracts the tendency for the plane to climb when the flaps come down. Because the Giant uses a 4s battery I will also have to purchase a charger and in the long run the Giant will cost a bit more. No big deal as either one will fit into my budget. The things that troubles me about the Giant is that it is new on the market. There is only one flight video for it and it was flown be a throttle jockey with little or no power off flying. I own an older version of the 55" Sky Surfer which appears to be a smaller clone of the Giant. My Sky Surfer flies well but it doesn't like power off. If I don't keep at least 1/4 throttle it stalls in level flight. I still have another 2 weeks to make my final decision.

 

[grampayeehaa]

At this point I am leaning more towards the Diamond

 

[pvolcko]

Sounds like you have a handle on what you afterall. Good luck, and post some vids of your flights when you get it up in the air!

 

[Chris O'Hara]

Have you already ruled out building a plane from a kit? Some of the best slow thermal duration planes are made of balsa, and they're tougher than many people might think. Very low wing loading. These can be ballasted to fly in much higher winds if the need be. An electrified OLY IIS or IISX would make a great warm liner, and the kits form Skybench are very electric conversion friendly. Very friendly flying sailplanes, and can be built with the included spoilers. Plus they are BIG! Just my .02

 

[grampayeehaa]

Thank you Chris. I have briefly considered building one but I don't have the time or space to take on the task. I built one many years ago and it took me 6 months to complete it. You are right, they are very light and surprisingly strong. It was a 2 channel that I launched with a high start and as I recall it was slow and floaty.

I just took a quick look see at Skybench site. I must admit I was impressed by what I saw. There just may be an Oly or Bird somewhere in my future.