When I say “forward-swept”, I mean where the “end” of the fins leading edge is forward of the base of the leading edge…I kinda, sorta, wanna push it out a couple 2 or 3 inches…just to see what happens. Any body have any knowledge of such an experiement? Any ways, I shaped a 6’ x 24" x 3" double ender that looks suspiciously like an overgrown skim board. Its not a particularly good shaping job, nor is it a board that Ive got a lot of time or love into, so I thought I might try it but I’d like some approval before I do:-)
FWIW, in the aircraft/aerospace industry, this would be referred to as a “forward-swept” wing rather than a canard. There was an experimental fighter plane built to this configuration and allegedly it was expected to have some favorable properties. Unfortunately I don’t remember what they are.
That wing also differed from your design in that the chord length was the smallest at the root (fuselage) end of the wing, and the longest at the tip end. So the alleged benefits of that configuration may not apply to your configuration.
The major problem with the experimental plane incorporating the swept-forward design was getting the structure stiff enough since the result of any twist in the wing is to increase the AOA and thus increasing the torque and the wing twisting even more. But this probably won’t be a problem in your case as long as the fin is made of fiberglass (or the equivalent) and reasonably thick since the wing chord is a minimum rather than a maximum at the tip, and structural weight isn’t as important as on the plane.
However, you will discover that it is a great kelp catcher if you’re surfing anywhere there is kelp (or other sea weed) present.
Afoaf is right, you will get a lot of lift from that thing. The x-29 had forward swept wings, and it was able to manuever at really high angles of attack without stalling. The problem with this setup that you might have is that it is incredibly structurally unstable. Think about how the fin will flex. When the tip of the fin bends about a vertical axis (as opposed to one parallel to the stringer) the fin will produce more lift, which will then cause the fin to bend more, then more lift, then more bend until SNAP! The X-29 worked because the wing structure engineers designed the wings to bend only about an axis parallel to the fuselage using composite materials. Thus the wing was not twisting such that the wingtips angle of attack would not change leading to instability and failure. My prediction: unless you are able to make that fin incredibly stiff, or can engineer it such that it wont twist, but only bend about an axis parallel to the stringer, its gonna break.
I may have time later to illustrate what I am trying to convey here, I’ll post it if I get a chance.
I hope you prove me wrong and that it works great, let us know how it goes.
unless you are able to make that fin incredibly stiff, or can engineer it such that it wont twist, but only bend about an axis parallel to the stringer, its gonna break.
Whoa…you guys are talking way over my head. A simple yes or no will suffice…hehehe J/K:-) Seriously, I have a sheet of 3/8" G10. Think that would be stiff/strong enough. I think Ill foil it then wrap it with a couple layers of carbon. My thought was it would just tear out of the board. Who knows…I will, soon:-) I think Ill just do it for grins. At the very least it’ll turn some heads at the beach, no? Maybe I can get Alex to give this one its maiden voyage like he did the “Chicago”.
BTW, when you say “lift”, would y’all clarify what you mean. Lift what and how?
The can is open ! 3/8th inch G-10 is way stiff/strong enough. Don’t waste the carbon. Seaweed aside, that fin guarentees an abrubt initiation of turns, that will test the riders’ ability to react quickly enough to stay in the wave. The fin will fairly dive into turns. Once the turn is initiated, it will be difficult to bring it back. It will be much more managable in smaller waves, than larger. The hands-on report of aquafiend65, will be interesting to read.
sorry if i got too technical, i get a little carried away sometimes. When I (I dont know whether or not others would agree with me here) mention lift with respect to fins on a surfboard, I am talking about a fins ability to generate force from the flow of water over its surface. A wing produces lift in the upwards direction… a surfboard fin is basically just a wing attached to the bottom of a surfboard. It produces lift in exactly the same way as a wing, but due to its orientation, the lift produces some force to the left or right (as well as drag of course). But as mentioned that opens up another can-o-worms…
Also I apologize for repeating everything MTB said, I wrote my response at the same time, im just a slow writer, so he beat me to it.
That fin looks awfully close to Noel and Larry’s spitfire with forward versus vertical orientation.
If you want to experiment just put on some fins backwards in a box and try the board out. The board most likely will want to spin around.
The closest I’ve seen anyone get a forward swept design to work in a high performance way is Geoff McCoy’s Gullwing design and the Bobby Owens Football or Boomerang design that he paired up with a couple of side winglet during the early days of the “tri-fin”. Bobby rode his rather bulbous setup pretty spectacularly at Sunset and other big wave spots on the northshore with alot of success. I posted the picture on Chips thread.
McCoy’s gullwings still facinate me as does the wavegrinder design
especially on Geoff’s loaded dome bottoms
it just doesn’t look like it’ll work that well but it does
Aside from the forward sweep you have to think about where all the surface areas is. On your wood design there’s alot of surface way back onlong the base. Seems like the there would be release issues that would cause either stiffness or pivoting. Maybe a narrower design with a thicker front edge like those jet wings being shown might have a more livelier response.
……Also I apologize for repeating everything MTB said, I wrote my response at the same time, im just a slow writer, so he beat me to it.
No need to apologize! Just the luck of the draw in timing. Also you introduced additional information. I, for one, had forgotten about the X-29. The plane I had in mind preceeded the X-29 (and had the reversed planform with regard to chord). I don’t remember the model identifier, but I have a faint recollection that it might have used the fuselage from the F-84.
……That wing also differed from your design in that the chord length was the smallest at the root (fuselage) end of the wing, and the longest at the tip end. Previous mtb post #2:
……Also you introduced additional information. I, for one, had forgotten about the X-29. The plane I had in mind preceeded the X-29 (and had the reversed planform with regard to chord). I don’t remember the model identifier, but I have a faint recollection that it might have used the fuselage from the F-84.
Oops. My mistake. The plane I was thinking of was the XF-91 (Thunderceptor). It was based on the F-84 fuselage, but had a wing configuration modification where the chord at the tip of the swept wing was greater than the chord at the root of the wing (i.e. the reverse of the typical wing planform). However, contrary to my previous statements, it was swept back, not swept forward.
Seems to me like you’ll be pointing the wingtip into the stream as you turn, and I would predict spinouts, but for the base length. In other words, your effective wing vanishes (reduces) as you turn and the base becomes the only focal point for lift.
The airplane has another wing (and one with a corresponding increasing chord exposure, and slower speed through the arc as a function of being inside the turn) to rely on for lift.
The airplane has another wing (and one with a corresponding increasing chord exposure, and slower speed through the arc as a function of being inside the turn) to rely on for lift.
Are you talking about the smaller triangular winlget forward of the forward swept wing? If so, I could that, right?
No, that’s a canard wing–it stalls before the main wing, if memory serves, and in doing so, drops the nose so the flow resumes over the main.
I was talking about the left and right wings–one banks through a turn with greater relative chord exposure while the other’s (outside) is turning tip-on into the flow. It’s a weird thing…normally-swept wings give greater lift to the outside wing as they bank through a turn, which being that that wing is supposed to be higher through a turn, makes sense. I can’t figure how this other plane would be advantageous, the reality of (some aspect of) which may be why it’s not in very wide use.
I hate to be a killjoy, but between not being able to allow any torsion, having to position it way back to avoid hyper-pivotation, seaweed, leash management issues, and possibly gashing innocent heads open… swept fins work relatively really well
I was reading this post with great interest because after reading an article about a proposed X Plane (the X-29) back in the early 80’s, I too became interested in the concept. I made several fins, single, twin fins, and small tri-fins (thanks to Larry and Mike at Fibre Glas Fin Co.) The fins did make the boards very lively to say the least. Feed back from riders was positive. The turning radius was decreased as expected but the boards were not squirly.
I met Malte Simer, a windsurfer from Maui, who was working on the same concept. We traded notes when he came to the mainland and basically arrived at the same findings.
The drawbacks are obvious, you can’t use them around kelp. I believe Malte snapped a fin due to the high rate of speed that windsurfers travel.
The fins were made of fiber glass and very stiff. Uni-directional carbon is a better material for keeping the foil thin and stiff.
No, that’s a canard wing–it stalls before the main wing, if memory serves, and in doing so, drops the nose so the flow resumes over the main.
I was talking about the left and right wings–one banks through a turn with greater relative chord exposure while the other’s (outside) is turning tip-on into the flow. It’s a weird thing…normally-swept wings give greater lift to the outside wing as they bank through a turn, which being that that wing is supposed to be higher through a turn, makes sense. I can’t figure how this other plane would be advantageous, the reality of (some aspect of) which may be why it’s not in very wide use.
I hate to be a killjoy, but between not being able to allow any torsion, having to position it way back to avoid hyper-pivotation, seaweed, leash management issues, and possibly gashing innocent heads open… swept fins work relatively really well
The outside wing in a coordinated turn (and subsonic flow) is always generating more lift (and is less prone to stall) because the flow over it is faster (follows a larger diameter circle than the inside wing) no matter whether the wings are straight, swept back, or swept forward. That’s one of the reasons that it can be difficult to recover from a spin if a plane has a small rudder (or flow over the rudder is being blocked during the spin by some other part of the plane). First step in spin recovery is to stop the rotation with application of opposite rudder, then when the rotation is arrested, add back pressure to the stick/control wheel to recover from the dive]. Swept back wings can have a roll control problem at low speeds (tip stalls first). This led to the death of several test pilots during development of the Super Sabre (F-100)–there is a famous movie of an F-100 that gets into this corner of the flight envelope with the plane nose high, speed and elevation low, rolling from side to side (and ultimately resulting in a fatal crash).
You are correct, the canard on a well-designed, canard-based plane does stall before the main wing. But this is not an inherent property of a canard set-up, but rather a design objective (as you noted, it is a necessity in order to recover from a stall). The piston-powered, rear-engined Ascender (commonly referred to at the time as the A**ender) fighter plane developed during WWII had this fatal trait.
As best I remember, the original canard foil on the Vari-Eze (Rutan Aircraft Factory) had the opposite problem. If flying in heavy rain, the combination of low Reynolds number (due to the short chord of the canard), the choice of foil section, and the disturbance of the flow over the foil by the presence of water on it would reduce the lift to the point where it could become difficult to maintain level flight at slow speeds and the nose would slowly pitch down even with a full-up pitch command. Certainly something that one wants to avoid during landing! As best I recall, this problem was remedied by changing to a canard foil section that had more tolerance to surface irregularities.
FWIW, the positioning of a forward-swept wing farther aft is not to avoid hyper-rotation, but rather to put the center-of-lift in the desire fore-aft location. This has some pilot visibility and some structural advantages (carrying the main spar through the fuselage) over a swept-back design.
