Originally posted by Ollie
BTW, the very last sentance before figure 10 reads,"Wind tunnel tests are also difficult to interpret due to the sensitivity of CLmax to Reynolds number and even freestream turbulence levels."
I knew I'd hear from you on that.
-proves you read thru it. If you think about it though, that is more of a general disclaimer about wind tunnnel tests in general than about the particulars of the subject.
I still prefer wing loading reduction to flaps for the following reasons:
My counterpoints interspersed :
1. The results of wing loading reduction are well known and predictable rather than speculative.
As are the drawbacks - see # 2.
2. Wing loading reduction benefits virtually every flight mode rather than just takeoff and landing.
I just do not see it this way. Check out the first paragraph on the web site I posted. The wing is THE major source of drag on the airplane. If you are designing for speed, whether it's a jet or a sailplane, to much wing is a bad thing. You only want enough wing that the airplane cruises in it's drag bucket - remember I'm talking about speed tasks here. If you succeed in reducing wing loading by weight loss - there will then be gains to be had by reducing wing area.
The problem with reducing wing area is increasing stall speed, making TO and landing harder. That's where the flaps come in. The better the flaps work, the smaller your wings can be, the faster you will go at cruise.
If you want to go faster, put flaps on your design
Sounds funny, don't it?
Also, there are some tasks for which too light a wing loading makes things "skittish" Pattern fliers want thier planes "groovy" and not too responsive to gusts. Light wing loading == gust response. Not a point for flaps - just saying that light wing loading isn't a universal good.
On the other hand, my Stinger has super light wing loading - and I would never put flaps on it. Not meant to go fast - I'm
trying to do 3d with it. 3d is definitely a place where low wing loading is crucial, and landing flaps are unheard of - and flying in wind is a pain.
3. Wing loading reduction takes less design and construction effort.
Maybe, maybe not. Reducing weight may be as simple as finding lighter radio gear. Nimh batteries are wonderfull things. However, if you are actually resizing the wing - design consideration needs to be given to strength, AR, etc. And if you are actively reducing weight in the structure of the plane, that is a critical design consideration and does take effort. Proper flap design is something to learn, but no more so than good structural understanding. It all takes (a little) effort.
4. Some of the benefit of fowler flaps is consumed by the wing loading increase associated with the flap mechanism.
Actual fowler flaps do require the need for some complex mechanisms like Craig's, that will add weight. Simple single-slotted flaps though, aren't any heavier than plain flaps, and a minor addition in weight even over a hard wing. And yes, even the more complex designs make up for the weight with gains in lift and result in a slower flying airplane( TO & landing).
Of course, some of the benefit of added wing area
also is consumed by the weight of the added wing structure.
Here's a design question for you: Two cases, flaps that decrease stall speed by 10% and additional wing area that decreases stall speed by 10%. Which one adds more weight to the base configuration?
5. The complexity of the flap mechanism reduces the overall reliability of the model some.
Yep, it's another thing to look at and make sure it works. But the tradeoff here is something you don't get with a wing loading change. In flight, real-time adjustment and control authority. Being able to dial in a bit of flap for takeoff is a great thing, in that it increases the effective alpha of the wing and the downwash on the tail during roll. If you've ever seen a jet model without flaps, but with a really long nosegear, you know what I mean. It makes takeoff rotation much easier. The same effect works on my Cessna though. Also, being able to dump out a bunch of flap and really lower the L/D for landing makes spot landings alot easier on many planes, especially ones that like to float.
If you don't put much stock in flaps, etc - that's cool. I love to experiment with such things and have always had good results.
Next up - full span slotted flaps & ailerons on my F-18. Should be up & running in about 2 weeks.