Hi all,
Nobody probably remembers, but a few months ago I posited that I would conduct an extensive test in XFLR5 to produce some quantifiable information about the effects of cranked tips (aka weltensegler tips, diffuser tips) on stability and control of flying wings in order to fill the gap left by the fact that nobody seems to have any data on the subject. Back when I made that statement I had no idea how much college application work was about to hit me in the face, but I have the opportunity to start it now. Northrop's N1-M testbed produced some good anecdotal info on cranked tips and several members here can describe what the theoretical, qualitative effects are, but there's nothing solid enough to do design work with. I'm here to crank out some numbers.
I will be editing this first post with the data and analysis more or less as I complete it, and notifying the changes via posts so that the information is kept in one place above any discussion that takes place. Suggestions are welcome as I want to keep the results applicable to real-world needs, but keep in mind I'm not going to change the setup on a large scale, especially after I'm deep into the work. I've tried to select the quantities I'm testing for according to the most pressing unknowns of the configuration and the principal questions and concerns members have had about it. I've had to keep the test quite limited in some regards to manage the amount of calculation required, seeing as how I have no desire to be driven stark raving mad by this endeavor. Let me know what you all think.
So without further ado...
Abstract-
Tailless aircraft have long been relegated to the fringes of aviation due in large part due to a set of necessary compromises regarding stability and performance that degrade their usefulness for many practical applications. One such compromise, and the one that this study seeks to address, is the need to seek a balance between removing excess static directional stability at high speeds (known to cause yaw hunting) and providing sufficient static directional stability at low speeds (known to cause dutch roll) created by the inherently low tail arm of the tailless configuration. The polyhedral configuration known as cranked wingtips has been shown to alleviate or remove this compromise, but there is a pronounced lack of empirical data on its effects. This study will utilize the program XFLR5 to measure several properties of the cranked configuration in response to several geometric variables.
Variables-
Controlled:
-Scale of the simulated aircraft (set to be 6m^2 wing area and 500kg)
-Spanload (set to be that occurring with no washout and appropriate control deflections)
-Aspect ratio (set to 6)
-Skid-roll moment (set by iteration to be 0 at the zero lift angle of attack)
Independent:
-Spanwise placement of the crank point (0.6, 0.7, and 0.8 times the semi-span)
-Magnitude of the angle of crank (30, 50, and 70 degrees downward from the inboard wing panel)
-Magnitude of the wing's sweep (measured in linear offset of the wingtip, 0.3 and 0.6 times the semi-span)
-Taper ratio of the wing (0.4 and 0.8)
-Lift coefficient of operation (taken at 0.0 and 1.0, corresponding roughly to fast cruise and landing regimes of flight)
Since all combinations of variables must be tested, this setup results in 72 sets of data points to be collected.
Dependent:
-Static directional stability derivative
-Damping factor in yaw
-Damping factor in dutch roll
-Roll to yaw coupling due to aileron deflection
-Reductions in projected span and efficiency factor as compared to a straight wing
Data-
Working on it. Currently setting up the first batch of test objects. When data comes in I will start filling out my spreadsheet and link to it here.
Nobody probably remembers, but a few months ago I posited that I would conduct an extensive test in XFLR5 to produce some quantifiable information about the effects of cranked tips (aka weltensegler tips, diffuser tips) on stability and control of flying wings in order to fill the gap left by the fact that nobody seems to have any data on the subject. Back when I made that statement I had no idea how much college application work was about to hit me in the face, but I have the opportunity to start it now. Northrop's N1-M testbed produced some good anecdotal info on cranked tips and several members here can describe what the theoretical, qualitative effects are, but there's nothing solid enough to do design work with. I'm here to crank out some numbers.
I will be editing this first post with the data and analysis more or less as I complete it, and notifying the changes via posts so that the information is kept in one place above any discussion that takes place. Suggestions are welcome as I want to keep the results applicable to real-world needs, but keep in mind I'm not going to change the setup on a large scale, especially after I'm deep into the work. I've tried to select the quantities I'm testing for according to the most pressing unknowns of the configuration and the principal questions and concerns members have had about it. I've had to keep the test quite limited in some regards to manage the amount of calculation required, seeing as how I have no desire to be driven stark raving mad by this endeavor. Let me know what you all think.
So without further ado...
Abstract-
Tailless aircraft have long been relegated to the fringes of aviation due in large part due to a set of necessary compromises regarding stability and performance that degrade their usefulness for many practical applications. One such compromise, and the one that this study seeks to address, is the need to seek a balance between removing excess static directional stability at high speeds (known to cause yaw hunting) and providing sufficient static directional stability at low speeds (known to cause dutch roll) created by the inherently low tail arm of the tailless configuration. The polyhedral configuration known as cranked wingtips has been shown to alleviate or remove this compromise, but there is a pronounced lack of empirical data on its effects. This study will utilize the program XFLR5 to measure several properties of the cranked configuration in response to several geometric variables.
Variables-
Controlled:
-Scale of the simulated aircraft (set to be 6m^2 wing area and 500kg)
-Spanload (set to be that occurring with no washout and appropriate control deflections)
-Aspect ratio (set to 6)
-Skid-roll moment (set by iteration to be 0 at the zero lift angle of attack)
Independent:
-Spanwise placement of the crank point (0.6, 0.7, and 0.8 times the semi-span)
-Magnitude of the angle of crank (30, 50, and 70 degrees downward from the inboard wing panel)
-Magnitude of the wing's sweep (measured in linear offset of the wingtip, 0.3 and 0.6 times the semi-span)
-Taper ratio of the wing (0.4 and 0.8)
-Lift coefficient of operation (taken at 0.0 and 1.0, corresponding roughly to fast cruise and landing regimes of flight)
Since all combinations of variables must be tested, this setup results in 72 sets of data points to be collected.
Dependent:
-Static directional stability derivative
-Damping factor in yaw
-Damping factor in dutch roll
-Roll to yaw coupling due to aileron deflection
-Reductions in projected span and efficiency factor as compared to a straight wing
Data-
Working on it. Currently setting up the first batch of test objects. When data comes in I will start filling out my spreadsheet and link to it here.
