biplane wing incidence.
09-14-2018 | 03:53 PM
#26
This is an example of what I was talking about. Here the basic wing section was given a 1 degree angle of attack at the root, this section was rotated 1 degree down for washout at the tip and positioned (up) for a 1 degree dihedral (from dead front view). All the factors are incorporated right from the very start.Of course these values are seat of the pants guesses on what will work best. The 2414 is a forgiving soft-stall airfoil to begin with so I can’t go too far wrong.(By the way, the section at the center-line is a 2414 with the rear half stretched to meet my plan view design).Now comes the hard part, trying to design these theoretical sections in wood, working with standard size stock for LE and TE, etc. Building the airfoil accurately is very hard also, especially with open frame construction.
09-15-2018 | 06:22 AM
#27
My Feedback: (29)
Divergent stab root. Notice it is thicker then the wing root.
Divergent wing root. No special airfoil, just what I thought looked good but with the high point where I wanted.
Macchi 202 pylon airplane.
Alan, since your model is an EDF and will not be required to perform anything but basic aerobatics your plan may very well work as you intend. Knowing what type of airplane and what the builders expectations are for the airplane really help determine what will or will not work. That being said, you may find that airfoils selected based on data derived from full scale testing usually do not behave the same with model RE and loading. Not that I am a big beleiver in specific airfoil selection for powered models. My last two designs also used airfoils which I designed as well. I have no aerodynamic education to rely upon in this respect, just 40 years of flying models. For the Divergent I drew out a symmetrical airfoil of the thickness and cord that I wanted at the root. I then modified that airfoil to have the same thickness at mid span but a reduced cord. Then once again modified that airfoil to suit the tip by reducing the cord, slightly reducing the thickness and bringing the highpoint forward. The result is a very stable wing with a good speed range and gentle stall characteristics. The airfoil thickness percentage actually increases as it goes from root to tip. I'm not a fan of using the same airfoil from root to tip on a tapered wing. Doing so could set up a situation where the tips will stall before in inboard section. All my designs I take efforts to get the inboard section to stall first. So far it is what works for me. My other design is a scale warbird pylon racing airplane. Very thin wings with yet another set of airfoils I designed. Again the tip airfoil I used had the high point moved forward. Very successful design. The coarse we run is two pylons spaced 150 yards from one another and we fly 10 full laps. My best time with that airplane for a 10 lap race with traffic is 1:16.2. That airplane is also very well mannered at landing speeds.
