Wing loadings for Thermal

[mattbroomer2000]

what number of Oz per square inch is expected for Thermal gliding, and whats the max you can get away with before it becomes more of a slope soarer?

[DLD]

It depends on the design of the plane, the flying style of the pilot, and the general thermal conditions where you fly. If you fly a floater style aircraft 5 or 6 oz/sq ft is good. A high performance, bagged glass or molded ship will usually run somewhere in the 8-13 oz/sq ft range. If you like to fly slow, or the local conditions tend to be cool and calm, a floater might be the best choice. Where I live, it tends to be cool in the morning and warm up to rather hot during mid day, and usually with some breeze, the higher wing loading ships do well. they also need to be flown faster to get the best results. My personal preference is to fly in the 11 oz/sq ft range, I like to fly a little faster and move around the sky. If you intend to fly contests, either will work, you just have to do three things 1. Practice 2. Practice 3. Practice.

Good luck,

David Layne

[Ollie]

Some thermals are weak and some are very, very strong. The lower the wing loading the better the thermal.

I had a 2-meter plane with high wing loading (14 oz per square foot). I had many thermal flights above 45 minutes to 1-1/2 hours. With the high wing loading, there are some days I couldn't work any thermals. I could not work any thermals below 200' to 300' altitude on any day.

I had another plane (3-meter span) with 6 oz. per square foot wing loading, I could find weak thermals (ant farts) almost every flight.

The best planes have low wing loading for thermal climb and very low drag for wind penetration.

A slope soarer depends on lift conditions and wing loading. In weak lift you want low wing loading. In strong lift you want higher wing loading.

In any conditions you want lowest drag (except landing). In any conditions you want strength and stiffness

[OVSS Boss]

Ollie, I agree and disagree too. I would take you to task that the lightest loaded ship is best, except, in that rare case that it is almost calm. At the Nats last summer, Tom Kiesling and I flew the same group at ~7:30pm, his 55 ounce Supra and I flew a 72 ounce Superior, he won by about 1:15 for a ten minute task. It was absolutely calm and that is when It would be nice having a really lite ship. Yap, he beat me, but not a slam. And other than that round, I would just as soon be flying my Superior as his ultra light ship since other than that round, light did not matter.

Now, 2M's are a bit more sensitive to loading, but you have less wing volume and your reynolds numbers are lower and in such cases a lower loading can help if you are comparing similar loadings from open class ships. My 2M Mantis has a loading of about 7 O/ft2, vs. my open ships that fly great at 11-12 O/ft2.

It comes down the where you fly and what you like. A lot of guys like Ava's, I think it is about the most boring thing in the sky to fly, but some love them and that is great.

Marc

[davidjensen]

Marc Please explane why you think the Ava is boring? I do not own one but am wondering how one lightly loaded ship can be more boring than another? Are the airfoils on the Ava something different? I fly an Esprit that has about 11 oz/ft loading (7037 airfoil) and sometimes it is boring and other times it can be scary. It all depends on the wind and thermal conditions.

[OVSS Boss]

The Ava I had you could literally fly it entirely on the rudder. I realize that this is my hang up. I fly a Grand Esprit in RES and NOS and love the ship and have beat all the others with it, it has massive LD and it flies bigger than an Ava to me (it flies like a bigger ship). The Ava I would guess would have been better with lead, but that is kind of defeating the purpose.

Marc

[EricSoar]

For a 2 metre thermaller I suggest 8 oz/sqft for most models an 6 oz/sqft for a clam day floater.

There is also a useful approximation to wind loading as wing span changes. It is based on the non-scientific "cubic wing loading" formula (look it up in google!). The formula is not "correct" but does a fair job of predicting sink rate. Basically if you double the wing span, you can double the wing loading and have a similar sink performance. What this means is...

A two metre thermal glider at 8 oz/sqft thermals similarly to a 12 oz/sqft 3 metre glider. The 3 metre is 50% more wing span. 50% added to 8 oz/sqft (plus 4) is 12 oz/sqft. However, the larger model will probably penetrate wind better.

There are many true scientific parameters like Reynolds number and how clean the model is that more accurately predict the performance. However, when I see similar design models for sale on the Internet and see that the 3 metre version has a wing loading 25% more than the 2 metre, that 25% does not worry me. 50% would be about equivalent and hence at 25% more wing loading, the 3 metre version will probably thermal better. My experience is that this roughly reflect reality!

I find that 3 metre models at 10 oz/sqft are real floaters. 3 metre models at 12 oz/sqft still thermal very well.

[mhodgson]

While lighter is generally better one thing you also need to consider is the wing section. Some sections perform better lighly loaded than others.
Personal experience has shown that some (like the SD7032) definitely work better at higher wing loadings.
Myself I have a 100" full house model using the HQ 3.5/10. It now has a loading of 15oz/sqft and yet will fly slowly when needed, work the tightest lift and floats very well, though I'm sure it would float better at 10oz)
I have even built a model too light and had to add weight just to get it to fly properly.
Also I think larger models tend to cope with higher loadings better.

[OVSS Boss]

Very good explanantion Eric, way more elegant then my rambles.

Marc

[histarter]

Very good explanantion Eric, way more elegant then my rambles.

Marc
I tip my hat to you guys. You are in the know. Your generaliztions are excellant. :D

There has been so much nitpicking on CL 0.8 profiles versus CL 1.2 profiles that newbies become stranded and missapply what they have in a search for better. The range in wt we are talking about is <1.5 for the extremes at max L/D reference, meaning the loading you have been discussing is totally indicitive of your pilot skill! This is the kind of skill that practice will make into a winner. :)

My arguments have been to stimulate the newbie to load up, and learn to fly under this state of affairs, that is universal regardless of profile. The "ancient" thin flat bottom profile (or Eppler 205, 207 as examples) are still viable when loaded up, and piloting skill is aquired. Learning is fun when experimenting is encouraged. Once you have mastered what you have, then moving to higher performance profiles becomes more realistic. :cool:

Most top notch pilots can take a strong OlyII load it up with ballast (the same way a top notch bare bow archer can gap shoot an arrow to compensate for distance), and take on the slight handicap of lower LD, and win (at least place)! :eek:

[Tony D.]

"Most top notch pilots can take a strong OlyII load it up with ballast (the same way a top notch bare bow archer can gap shoot an arrow to compensate for distance), and take on the slight handicap of lower LD, and win (at least place)!"


In other words it's in the thumb ;)


T.D.