jwmflying14
Well-Known Member
I look up to and admire Mike Arnold, his designs, and his videos. He made me question a lot of general principles, and rules of thumb that circulate the aviation community.
So, lets discuss wing fillets and intersections.
I am going to do my best to keep the original post short, and expand on a few different angles and why they matter to me. Here we go:
Part 1) It is widely accepted that in general, the right angle (straight fuselage) intersection is the best choice. Especially when mixed with a trailing edge fillet. So my primary question is, would there be any benefit to a concave intersection? What I am referring to could be confused as the area rule, but I’m coming at it from a different perspective, with no regard to transonic aircraft at all. In my mind, you would have two (general) masses of air (fuselage, and wing), the fuselage stream is trying its best to go straight, and ends up converging with the high pressure leading edge of the wing. Then, as the pressure tapers after the thickest region of the foil (generally speaking), it creates a low pressure nozzle (in Mike Arnold’s words), effectively making a vacuum. The necessitates the need for a fillet in many cases. In my mind, it would seem as if you can match the local pressure regions of the airfoil by creating a concaved “cut out” in an otherwise no-taper fuselage intersection. In essence, take the pressure region (map, if you will) of the root airfoil, and average it out over the majority of flight parameters (alpha/velocity). Take this generalization, and create a semi-concaved fuselage intersection. The basic concept is that the local flow would match in velocity, and pressure, creating a less turbulent and “cleaner” flow. Also, the primary goal on a Laminar foil would be to regain laminar flow, where as a standar intersection can ruin it down a pretty substantial portion of the wing. The idea being very similar to the F1 guys, and leading their cowl cheeks into the wing root.
Part 2) I am building a Dragonfly, and have been planning a fuselage modification/fairing. The idea is that the Dragonfly has a tapering (expanding) fuselage over the canard. This is just about the worst intersection scenario you can have, especially on a laminar foil. To make matters worse, the original cowl cheeks tapered right above the root. In my mind this would create a substantial high pressure convergence. So, I have been planning a Glasair style fix. The idea is to extend the thickest section of fuse (Ironically the trailing edge of the canard), and extend it forward to the firewall. There would be a net increase in wetted area, but hopefully the offset in intersection drag would off set it. The plane for form drag would be to add a 6” prop extension, and a gradually tapering fuse instead of the original cowl cheeks. This works in my favor, as I am opting for a Yamaha install, so no need for cooling an opposed engine as is normal.
Note: Picture 1 is a a random image of a random foil and the general pressure distribution. If you imagine the severetiy of the low pressure matched with the “curve,” you can picture the idea of the “concave cut away” in the fuse. Picture 2 a is a general depiction of my planned fuselage and cowling mod for my Dragonfly project. No concave is currently planned or pictured.
I’d love to hear your thoughts! Thanks everyone.
So, lets discuss wing fillets and intersections.
I am going to do my best to keep the original post short, and expand on a few different angles and why they matter to me. Here we go:
Part 1) It is widely accepted that in general, the right angle (straight fuselage) intersection is the best choice. Especially when mixed with a trailing edge fillet. So my primary question is, would there be any benefit to a concave intersection? What I am referring to could be confused as the area rule, but I’m coming at it from a different perspective, with no regard to transonic aircraft at all. In my mind, you would have two (general) masses of air (fuselage, and wing), the fuselage stream is trying its best to go straight, and ends up converging with the high pressure leading edge of the wing. Then, as the pressure tapers after the thickest region of the foil (generally speaking), it creates a low pressure nozzle (in Mike Arnold’s words), effectively making a vacuum. The necessitates the need for a fillet in many cases. In my mind, it would seem as if you can match the local pressure regions of the airfoil by creating a concaved “cut out” in an otherwise no-taper fuselage intersection. In essence, take the pressure region (map, if you will) of the root airfoil, and average it out over the majority of flight parameters (alpha/velocity). Take this generalization, and create a semi-concaved fuselage intersection. The basic concept is that the local flow would match in velocity, and pressure, creating a less turbulent and “cleaner” flow. Also, the primary goal on a Laminar foil would be to regain laminar flow, where as a standar intersection can ruin it down a pretty substantial portion of the wing. The idea being very similar to the F1 guys, and leading their cowl cheeks into the wing root.
Part 2) I am building a Dragonfly, and have been planning a fuselage modification/fairing. The idea is that the Dragonfly has a tapering (expanding) fuselage over the canard. This is just about the worst intersection scenario you can have, especially on a laminar foil. To make matters worse, the original cowl cheeks tapered right above the root. In my mind this would create a substantial high pressure convergence. So, I have been planning a Glasair style fix. The idea is to extend the thickest section of fuse (Ironically the trailing edge of the canard), and extend it forward to the firewall. There would be a net increase in wetted area, but hopefully the offset in intersection drag would off set it. The plane for form drag would be to add a 6” prop extension, and a gradually tapering fuse instead of the original cowl cheeks. This works in my favor, as I am opting for a Yamaha install, so no need for cooling an opposed engine as is normal.
Note: Picture 1 is a a random image of a random foil and the general pressure distribution. If you imagine the severetiy of the low pressure matched with the “curve,” you can picture the idea of the “concave cut away” in the fuse. Picture 2 a is a general depiction of my planned fuselage and cowling mod for my Dragonfly project. No concave is currently planned or pictured.
I’d love to hear your thoughts! Thanks everyone.
