wings profils

[vvs]

whether there are real examples of the use of such a profile Eppler Shen E900 or the like for keels ?

[tkettlepoint]

Went to the Wright Brothers display yesterday with my son. Those boys were smart.

If those to brother that built bikes with no know how of planes made the first one... The foil world is just starting and will go crazy in the next years

terrie B
www.jellyfishboards.com

[revhed]

Thanx for the post T K!
I have been debating making some coanda type wings like shown on the right wing camber photo, it just seems to make hydrodynamic sence and I am pretty sure the spotz R wing is using this design.
When I see birds fly I always remark the coanda camber BUT I do not see this in marine animals, they seem to be more T Speer like,have you or anyone else seen coanda camber in marine animals?
I also agree that there may be a major design break through, maybe like a certain four line stunt kite many years ago....
R H

[windfreak74]

there is a video on youtube of a sloted wing showing coanda effect.
one of the comments talks about how fish scales overlaping on top of the other creating a small void (pocket).mabe this is teh tecnology used in slipery swimming suits less friction means less drag.
So this means smaller wings with greater lift and less drag?
Pedro

[Phezulu1]

I tried running an Eppler 817 against a Speer H105 in XFLR5, the wing used exactly the same plan form, just the airfoil profiles varied. The analysis uses a constant weight loading and varies the angle of attack (alpha is independent variable). The flying speed and lift to drag ratio are calculated as dependant variables.

The conclusion is that the flying speed varies between the two for the same angle of attack (to be expected with different lift graphs) - but that the lift to drag ratio for a given velocity is pretty much identical (see the same colour blocks).

The conclusion to the conclusion is that there is no magic profile and no free lunch

Lift to drag graph -Eppler 817 vs H105 .JPG (49.37 KiB) Viewed 1842 times

[JS]

An inverted rear foil creates negative (downward) lift which must be compensated by additional lift from the main foil, thereby resulting in additional drag. To an extent, the two foils work against each other.

To minimize drag, the most efficient layout is a positive asymmetric main and rear foil (with the whole assembly moved slightly forward relative to the board to compensate for balance). This geometry minimizes the total amount of foil required to provide a specific amount of net lift.

However, with both foils providing lift, a stall will tend to affect both, leading to a "flat" drop, as opposed to a "nose" drop that the inverted-rear configuration would tend to induce.

This is analogous to the posted aircraft vector schematics. The advantage of the so-called stable designs occurs during a stall, in which case the nose will dive to regain air speed. Basically, an inverted foil creates negative lift at speed, but positive lift during a stall. This can make an aircraft safer, albeit at the cost of efficiency and performance.

I'm unsure whether or not this is a helpful or worthwhile trade-off for a foil board though.

[gmb13]

An inverted rear foil creates negative (downward) lift which must be compensated by additional lift from the main foil, thereby resulting in additional drag. To an extent, the two foils work against each other.

To minimize drag, the most efficient layout is a positive asymmetric main and rear foil (with the whole assembly moved slightly forward relative to the board to compensate for balance). This geometry minimizes the total amount of foil required to provide a specific amount of net lift.

However, with both foils providing lift, a stall will tend to affect both, leading to a "flat" drop, as opposed to a "nose" drop that the inverted-rear configuration would tend to induce.

This is analogous to the posted aircraft vector schematics. The advantage of the so-called stable designs occurs during a stall, in which case the nose will dive to regain air speed. Basically, an inverted foil creates negative lift at speed, but positive lift during a stall. This can make an aircraft safer, albeit at the cost of efficiency and performance.

I'm unsure whether or not this is a helpful or worthwhile trade-off for a foil board though.

Nicely explained

I would like to add one thing:

It is one thing to try to make the Foil as theoretically fast as possible, but the main factor of going fast around the course and especially when going for highest possible speed is CONTROL.

Especially at any speed over 30 Knots you will need to worry more about the controllability of your foils rather than drag.

So when you design Foils you need to find a balance between performance and control.

--
Gunnar

[Phezulu1]

I'm a fan of the inverted profile on the rear. At first I couldn't understand why foils need so much stabiliser wing area, then I realised that it's because the force input - the kite line attachment at the harness - is very high above the foil and tends to pull the foil over forward and you need a down force at the tail of the fuselage to counter this. It's analogous to having a plane with the propeller mounted 3 or 4 fuselage lengths above the wing axis. You can correct for it to some extent with where you place your COG, but only to a degree

I agree with Gunnar and JB above, speed is all about control and stability. The French foil forum guys call the difference between front and rear wing angle "the longitudinal V" - this is an indication of how much the foils fight each other, front lifting up - rear pulling down. More longitudinal V = increased stability + increased drag. The trick is to find the balance between the 2.

I love playing with these things!

[revhed]

An inverted rear foil creates negative (downward) lift which must be compensated by additional lift from the main foil, thereby resulting in additional drag. To an extent, the two foils work against each other.

To minimize drag, the most efficient layout is a positive asymmetric main and rear foil (with the whole assembly moved slightly forward relative to the board to compensate for balance). This geometry minimizes the total amount of foil required to provide a specific amount of net lift.

However, with both foils providing lift, a stall will tend to affect both, leading to a "flat" drop, as opposed to a "nose" drop that the inverted-rear configuration would tend to induce.

This is analogous to the posted aircraft vector schematics. The advantage of the so-called stable designs occurs during a stall, in which case the nose will dive to regain air speed. Basically, an inverted foil creates negative lift at speed, but positive lift during a stall. This can make an aircraft safer, albeit at the cost of efficiency and performance.

I'm unsure whether or not this is a helpful or worthwhile trade-off for a foil board though.

Thanx J S for this post, my inital thoughts needing just before bed time thought , as you have stimulated a concept idea I have pondered for a few years now.
Sounds simple but I bet it is not, What is the R wing REALLY doing in flight? And more importantly why?
Off to think........cool thanx again....
R H

[revhed]

An inverted rear foil creates negative (downward) lift which must be compensated by additional lift from the main foil, thereby resulting in additional drag. To an extent, the two foils work against each other.

.

VS,
I have thought about this a lot and had talks with others with different thoughts.
Lets consider a design wih 90° angles for both the straight strut to fuse and strut to board to make it easy to see, and wings sym to make it even easier.
So if you mount the F wing at 0 lift, centerline T E to L E, on the fuse and the R wing at 0 lift also with the fuse level there is no lift.
Now introduce say 5° positive A O A, now both wings are of course also +5° A O A so I would think both are generating lift.
It would seem logical to find the center of lift from the 2 wings on the fuse and mount the strut there.
If I could build a set up like this without a TON of work I would just for the fun of testing it!
Who thinks this would fly how well?
Now lets say we mount the profiled 817 front wing on its center line, not 0° lift due to the profile and the R wing also 817 BUT inverted!
Lets say it will now fly at +4 A O A but because the R wing is also +4 But inverted profile maybe its lift is much less?
But I do not see it giving any downward lift.
There are those on the french forum who are sure that R wings deflects h20 up therfore pitching the fuse to positive A O A, I do not get this? It has + A O A even if angled down 2° or so.
So the debate for me is as follows.
Even with a R wing with profile inverted AND 2 ° negitive pitch how can it add and downward input if the f Wing is + 4°and it as well, it still has + 2° A O A!
It seems to me, I am probably way off, that the R wing should be neurtral, No lift either up or down when the F wing is flying at its designed speed, it will only come into play when the F wing is outside of its optimum A O A bringing it back into trim?
I know I oversimplify but in this configuration it adds the least drag.
What am I missing?
Often now that I am so into this I wished I had studied aero, hydrodynamics so I could get my head around this better.
How can a R wing even with a profile produce down lift if the F wing is + A O A therefore it as well.
And if it does it would pitch UP the F wing as it piviots on the Strut, down in back up in front.
Is this not unlike and airplane that when down elevator, up flaps, is given the nose pitches up.
When we shim to tune our R wings with it mounted on the bottom we add more - A O A by shimming the front making the foil generate more overal lift, pitching the nose up.
I hope someone can explain this well for all of us.
If I could make simple drawings I would, maybe i will hand draw them and take picts to upload.
R H