This may have to go in the Flitetest made up word file.
But seriously, great episode once again guys!
I started a thread about KFm airfoils just last weekend. Ever since my first scratch build I have been consumed by thoughts of airfoils, foam, CF/FG rods, adhesives of all type. If only the power components where as cheap as it is to build a foam board aircraft.
No wait........... Where would I sleep with foamies stacked to the ceiling?
I love the KF airfoil, its easy to use and very adaptable to many different wing types. Recently I discovered a different type of foamboard wing over at RC Groups. The Armin Wing. Here is a link to a great tutorial of how to construct them:
Love the show, but I fear this was one with some technical hiccups... the diagram and the commentary trip a little and can get a little self contradictory in parts.
the flat plate - the show starts off great with the flat plate, correctly identifying that it has no lift except with an attack angle, and that with the attack angle there's drag. The diagram says poor lift and no drag. Without incidence there's no lift, and when it's lifting there's lots of drag. Even without much/any incidence flat plates still have drag. Geeky detail is that at low reynolds numbers (very small planes or small slow planes), flat plates don't do all that bad compared to the other airfoils actually.
Undercamber - identified as the most lift, and has a lot of drag. all good, although Josh B mentions that it's not a good airfoil to choose and the reason given is that it needs incidence to create lift. High lifting airfoils actually create lift at shallow negative attack angles, they certainly don't need an increased incidence to produce lift. Many high performance sailplanes use an undercamber to create lift without a positive attack angle which would ruin the efficiency by increasing drag.
Flat bottoms - little more solid. To be splitting hairs, a Clark-Y airfoil isn't actually a true flat bottom wing, but it sure is close enough, that's cool by me... and the kids can learn the name of a genuine airfoil, gravy.
Symmetrical - described in the diagram and on the show as creating lift when in fact it's the same class as the flat wing; creates zero lift until it's given an attack angle. The reason it's chosen for aerobatic planes is that it has the same characteristics upside down as the right way up, but in both attitudes provides no lift without an attack angle. You can get this without stick movement if you balance the plane the right way, but the wing itself cannot lift the plane unless it addresses the airflow with an attack angle. To further put the symmetrical and the flat plate in the same class, indoor aerobatic planes like those seen at the ETOC are flat plates or symmetrical sections. If you draw a line through the leading edge to the trailing edge and it's the same above the line as below, then it's symmetrical, and a flat plate being a really crude symmetrical section. Symmetrical is generally low drag (though there are many high drag symmetrical sections; control line pattern planes and RC "FunFly" planes as an example), but for a typical symmetrical wing it's dependent on "induced drag", or how heavy the plane is that sets the need for the attack angle which sets the amount of drag it has beyond its natural shape
KFm airfoils - a fantastic compromise on a complex airfoil, sure are easy to build
...well, that's my spiel on the tech side of this episode. I'm really not down on the show, just that this was one episode about technical details and there were some issues with the info. The show is still awesome and truly fantastic, onwards and upwards!
I made my plane with an Under-Camber airfoil, works amazing, but you can't go to fast. Just yesterday I added some paper on the underside of the wing to give it a more Flat Bottom airfoil, just to try it out. Never got to try it yet, hope to try it soon.
Guys Thanks so much for doing this! I think in one of my many nights of way too late reading last winter I sent an email asking for some explinations of airfoils.... Thanks so much It was great to see you fly a KFm3 on that also! Just got back to where I had some time online and found the forums here! Love It, just another forum to watch this winter whilst the snow flies!
Could you probably explain us or show us a picture of how a HQ13 airfoil looks like? I have googled it and barely anything useful came out there.
It seems not to be really known so I suppose not many people use HQ13. The most popular ones are the ones in the video obviously and those are the ones used most often.