MichaelNorcia
New Member
Greetings!
I am working on designing an electric ultralight. The plane will be quite light (or so is the plan); something similar to a blend of the archeopteryx ultralight sailplane (similar wing) and MIT's Daedalus (very similar fuselage layout). In conjunction and accordance with my first mission, I have a secondary goal of reducing parts count. For this reason, I am, at least for now, designing the plane to be flown 2-Axis, rudder + elevator (throttle as well of course).
Perhaps you could help me weigh the pros and cons of the 2-axis set up and answer a few aerodynamic questions?
An obvious concern with 2-axis control that I see is a lack of rudder and/or roll authority. Obviously, I could make the rudder large (as I plan on doing at ~10% of wing area with a sizeable boom) in order to have on-demand rudder response. I plan on implementing a full flying horizontal stabilizer, much like that featured in the Daedalus. I could do a similar full flying vertical stabilizer.
Which brings me to my first question: How does the CL max for a full flying surface (without trim tabs) compare to the CL max of an aggressively hinged surface (hinge line at, say 35% chord, big rudder) given the same symmetrical airfoil? Such a large flap seems well beyond X-foils capabilities, which ground my experimentation to a halt
Second question: rudder authority seems easy enough to tame. Roll authority, more difficult. What are some important things to consider when designing for roll authority? Clearly dihedral will provide some yaw-roll coupling. Beyond this, I would imagine inertia about the roll axis would be good to minimize. There are two main sources of inertia about the roll axis for my plane: the wing tip sections, and the under slung fuselage that houses much of the gross weight (the pilot). Coming from an RC sailplane background, I know light tips provide an excellent means of reading the air. In the full scale realm, are light tips advisable? I would imagine they could make for a sloshing sort of ride? What effect then will the under slung fuselage have? Unlike the wingtips, which may have a more significant effect on the moment of inertia, the fuselage will provide a strong returning force to zero roll. The restoring force will act strongly in opposition of any roll set up by the rudder at high bank angles, sort of like a twisted form of effective dihedral.
If you have any advice on any of the above, please speak up! It seems as though every time I start feeling like I have a part of the design fully understood, I come to learn of some critical new piece of wisdom. There are rather few 2-axis ultralights to compare to, and none anything like what I wish to build. One of my closest comparisons are the large (3m+ span) 2-axis (RES) RC sailplanes that are quite popular.
-Michael
I am working on designing an electric ultralight. The plane will be quite light (or so is the plan); something similar to a blend of the archeopteryx ultralight sailplane (similar wing) and MIT's Daedalus (very similar fuselage layout). In conjunction and accordance with my first mission, I have a secondary goal of reducing parts count. For this reason, I am, at least for now, designing the plane to be flown 2-Axis, rudder + elevator (throttle as well of course).
Perhaps you could help me weigh the pros and cons of the 2-axis set up and answer a few aerodynamic questions?
An obvious concern with 2-axis control that I see is a lack of rudder and/or roll authority. Obviously, I could make the rudder large (as I plan on doing at ~10% of wing area with a sizeable boom) in order to have on-demand rudder response. I plan on implementing a full flying horizontal stabilizer, much like that featured in the Daedalus. I could do a similar full flying vertical stabilizer.
Which brings me to my first question: How does the CL max for a full flying surface (without trim tabs) compare to the CL max of an aggressively hinged surface (hinge line at, say 35% chord, big rudder) given the same symmetrical airfoil? Such a large flap seems well beyond X-foils capabilities, which ground my experimentation to a halt
Second question: rudder authority seems easy enough to tame. Roll authority, more difficult. What are some important things to consider when designing for roll authority? Clearly dihedral will provide some yaw-roll coupling. Beyond this, I would imagine inertia about the roll axis would be good to minimize. There are two main sources of inertia about the roll axis for my plane: the wing tip sections, and the under slung fuselage that houses much of the gross weight (the pilot). Coming from an RC sailplane background, I know light tips provide an excellent means of reading the air. In the full scale realm, are light tips advisable? I would imagine they could make for a sloshing sort of ride? What effect then will the under slung fuselage have? Unlike the wingtips, which may have a more significant effect on the moment of inertia, the fuselage will provide a strong returning force to zero roll. The restoring force will act strongly in opposition of any roll set up by the rudder at high bank angles, sort of like a twisted form of effective dihedral.
If you have any advice on any of the above, please speak up! It seems as though every time I start feeling like I have a part of the design fully understood, I come to learn of some critical new piece of wisdom. There are rather few 2-axis ultralights to compare to, and none anything like what I wish to build. One of my closest comparisons are the large (3m+ span) 2-axis (RES) RC sailplanes that are quite popular.
-Michael
