#AIRFOIL SHAPE HOW TO#
#AIRFOIL SHAPE SKIN#

This arrangement is a classic example of how to achieve dynamic STABILITY. For stable flight, the horizontal stabilizer will need to create a downwards force to push the nose back UP. This airfoil has a negative moment coefficient of -0.085, meaning the sum of forces acting about the ¼ chord of the wing is pulling the NOSE DOWN. If you set up the actual airfoil at the ideal angle of incidence of 0.85° (best L/D), this would bring the notional airfoil to about 0.25° positive incidence.įor comparison, here's a plot of a Clark Y, a classic (nearly) flat-bottomed airfoil. If you draw a chord line through a notional semi-symmetrical airfoil with a lowered flap, that notional airfoil has about 0.6° of negative incidence compared to the actual airfoil. The airfoil has a slightly larger amount of camber on the lower surface, and after looking at a plot, I'd agree with u/Knut79, it's basically a semisymmetrical airfoil with a fixed-flap trailing edge - albeit, the airfoil is upside down. This arrangement is a classic example of how to achieve dynamic INSTABILITY. For stable flight, the horizontal stabilizer will need to create an upwards force to push the nose back DOWN. A positive moment coefficient means that the sum of forces acting about the ¼ chord of the wing is pulling the NOSE UP. What is most interesting is that the airfoil has a moment coefficient of +0.017. Here's a link to a screenshot of how CompuFoil processed the data: A plot and analysis of that data is interesting. Using the picture that u/dawnkiller428 posted, I generated a coordinate set for the airfoil he's created. If you keep your speed up even on landings, just above you're discovered stall speed, you'll probably be fine and have loads of fun. Let the plane fall for 2 seconds and pull out to get a feel for how to recover from a stall and to get an idea for the stall speed.

It might be worth getting the plane at at fairly high altitude, 3-4 mistakes high, and inducing a stall. If you're high enough, you could be able to recover once you've regained sufficient airspeed, but if your low then you'll most likely to end up nose diving into the ground. This airfoil has very poor stall characteristics, and if you find yourself in a stall you will likely have a wing over where the plane seems to fall out of the sky. I suspect it will fly fine, but it does means that the plane will need to be flown at speed. It is more similar to a low-drag, super critical airfoil, much like airliners, as opposed to the a more traditional rc plane high lift airfoil. But it will fly like this, but it might be harder to me both wings identical. If he's building a plane after a video and the video shows a flat bottom, he should try to build it like that. You're applying flying wing logic to regular wings. Semi symmetrical wings will want to have some positive lift, or drop when flying inverted. Though the air and will want to be flying straight forward in the direction it's going. A fully symmetrical wing basically flies nearly neutral. High AoA is something you get on flat wings because they merely push the air. Whereas a fully symmetrical is fully acrobatic.īoth semi and fully symmetrical fly fine without high AoA. Its a type of airfoil used on trainers with some acrobatic abilities. It will fly great with slightly more lift than a fully symmetrical. This is basically a semi symmetrical airfoil. If you put that airfoil on your aircraft as shown, it will require a very large angle of attack to overcome its upside down orientation and the reflexed trailing edge (which will try to pitch the nose down). TLDR: fix the airfoil or build a new wing to plans.īackground: I’ve been designing and scratch-building RC models for 40 years. The high angle of attack will require lots of power to overcome the drag, which as previously mentioned, your model is unlikely to have.

This is partly because they are designed for slow, high-lift flight, but also because adding lots of power to such a model won’t make it go appreciably faster because of the airfoil’s high drag (lift and drag go hand in hand). Models that use flat-bottomed airfoils typically have power-to-weight ratios on the low end. While it might “fly,” I would not use that wing with a model that was designed for a different airfoil. I disagree with sentiment of other posters. In its current configuration, it looks similar to a reflexed airfoil for a flying wing, but UPSIDE DOWN. That would pull the nose down and give you a flat-bottomed airfoil.

#AIRFOIL SHAPE SKIN#

It looks like the bottom skin was intended to slide back towards the trailing edge so that the angled edges line up.

Airfoil shape