oriol
Well-Known Member
Hi!
Any wing ladder style structure, like the mighty Quicksilver or the Goat glider, can be analized like a typical truss type structure. Trusses are found in many introductory structures books for analysis; such as the first picture; in where the first image is the wing front view, the second is the wing top view and the third is a 3D view of the wing, with only vertical loads. A simple truss type structure like those below, has some obvious practical advantages. In particular, it is much more simple to analize than any cantilever wing; because the torsional loads are less critical.
With the diagram below, you can calculate Lift, and then consider Drag to be a 1/10 of Lift, and get some rough numbers, using a flat lift distribution. First you can calculate moments to find out the loads on the front and rear spar? Then the reactions in the attachments? Let's assume for simplicity, that there is a front and a rear strut, each parallel to the leading and rear tube, so that none of the struts carry any drag component, but only the vertical loads. Next consider drag, and compute the loads on the diagonals and tubes inside the wing? But what happens with the ribs, how do you model them?!
Frati in his book does not cover ribs, and Stress wihout tears does not analize ribs like trusses, but I am guessing that it will be possible to do it that way. It seems that a rib made of wood sticks, has a better weight strength ratio, compared to a plywood rib. So using alu rivetted tubes, instead of a sheet alu rib, ought to work as well. The question is, if it Ok to model a rib like the one in picture 2, to size it? Does an oversimplification like that is admissible?
By looking at the rib diagram in picture two, one can note that the vertical loads on node A and B, cancel each other, because the struts are located perpendicular to the wing chord. As such the only loads on the ribs are horizontal; that is Drag. However the ribs are intended to keep an airfoil shape, to withsand the pressure difference between the upper and lower part of the wing. Tthe diagonals and perpendicular tubes already handle Drag. This perhaps shows that the rib load diagram is wrong? Otoh if the load diagram is right, perhaps the pressure difference is that small, that by modeling the rib for Drag, the rib can work just fine and keep its shape?
I am guessing here, so I am afraid to jump into wrong conclusions. Any comment will be greatly appreciated!
Cheers,
Oriol
Any wing ladder style structure, like the mighty Quicksilver or the Goat glider, can be analized like a typical truss type structure. Trusses are found in many introductory structures books for analysis; such as the first picture; in where the first image is the wing front view, the second is the wing top view and the third is a 3D view of the wing, with only vertical loads. A simple truss type structure like those below, has some obvious practical advantages. In particular, it is much more simple to analize than any cantilever wing; because the torsional loads are less critical.
With the diagram below, you can calculate Lift, and then consider Drag to be a 1/10 of Lift, and get some rough numbers, using a flat lift distribution. First you can calculate moments to find out the loads on the front and rear spar? Then the reactions in the attachments? Let's assume for simplicity, that there is a front and a rear strut, each parallel to the leading and rear tube, so that none of the struts carry any drag component, but only the vertical loads. Next consider drag, and compute the loads on the diagonals and tubes inside the wing? But what happens with the ribs, how do you model them?!
Frati in his book does not cover ribs, and Stress wihout tears does not analize ribs like trusses, but I am guessing that it will be possible to do it that way. It seems that a rib made of wood sticks, has a better weight strength ratio, compared to a plywood rib. So using alu rivetted tubes, instead of a sheet alu rib, ought to work as well. The question is, if it Ok to model a rib like the one in picture 2, to size it? Does an oversimplification like that is admissible?
By looking at the rib diagram in picture two, one can note that the vertical loads on node A and B, cancel each other, because the struts are located perpendicular to the wing chord. As such the only loads on the ribs are horizontal; that is Drag. However the ribs are intended to keep an airfoil shape, to withsand the pressure difference between the upper and lower part of the wing. Tthe diagonals and perpendicular tubes already handle Drag. This perhaps shows that the rib load diagram is wrong? Otoh if the load diagram is right, perhaps the pressure difference is that small, that by modeling the rib for Drag, the rib can work just fine and keep its shape?
I am guessing here, so I am afraid to jump into wrong conclusions. Any comment will be greatly appreciated!
Cheers,
Oriol
