I looked through your windtunnel files and I wonder if you have a run
with the 4% spoon leech profile but this time with the spoon forward
(luff spoon) to simulate the case where one has a sharp camber near
the luff. If it looks interesting I will then modify Sailcut8 to
accomodate also that case as for the time being I limit the depth
position to 25% of the cord.
Happy new year to all
- I tested a luff spoon against a leech spoon. It is the same model, I
just turned it around.
The luff spoon has a better lift/drag ratio at low incidence angles,
but a lower (maximum) lift. It stalls a bit earlier, but has
a 'softer' stall then the leech spoon.
The model is sheet metal, and I don't know if a soft luff spoon will
hold its shape at low incidence angles.
The mast will interfere with a luff spoon when on the lee-side of the
Anyway, judging by the photos, the Chinese kept the luff quite flat.
You can find 'luff_vs_leech_spoon.jpg' in 'gurney flap'
in 'windtunnel' in the files.
--- In firstname.lastname@example.org, "sailcuter <robert.laine@s...>"
> I looked through your windtunnel files and I wonder if you have a
> with the 4% spoon leech profile but this time with the spoonforward
> (luff spoon) to simulate the case where one has a sharp camber near
> the luff. If it looks interesting I will then modify Sailcut8 to
> accomodate also that case as for the time being I limit the depth
> position to 25% of the cord.
> Happy new year to all
- Thanks Bernard,
You wind tunnel is a great tool.
It is a pitty that I am not living in Holland for the time being as I would
enjoy seeing it in operation.
The sharp luff camber is what I always used on my own racing sails but many
people did not like the look of them. That is why I kept a set of equations
giving a smoother curvature up front in Sailcut.
Do you think that a combination of luff + leech spoon would gain anything?
If any good I can write the piece of code which would give that profile in
- Hi Robert,
I have added a luff + leech spoon to 'luff_vs_leech_spoon.jpg'.
This has the high lift of the leech spoon and the low drag of the luff
The luff spoon has about half the depth of the leech spoon, its profile
looks very much like the initial sketch I made in 'Gurney_flap.jpg'.
The low drag is the result of the elimination, or at least reduction in
size, of the leading edge separation bubble by the luff spoon. But you must
not forget, this is without the presence of a mast.
When on the lee-side of the sail, the mast will press into the luff spoon,
reducing its effect.
Besides, reducing the leading edge separation bubble will expose the mast to
the airflow, with negative effects on lift and drag.
When the mast is on the windward side of the sail, the luff spoon will
increase the distance between the sail(cloth) and the mast, and this is said
to increase drag.
More tests, preferably full scale, are needed to find out if a luff spoon
has a positive effect when a mast is present.
> Do you think that a combination of luff + leech spoon would gain anything?
> If any good I can write the piece of code which would give that profile in
I'm sorry it took me a while to respond to your question.
I tested a shape with zero depth between luff and leech spoon. It behaved
rather erratic, lift and especially drag kept fluctuating at all incidence
angles from 5 to 25 degrees. I suppose this is because the flow separates
off the luff spoon in a disorderly way, creating an irregular pulsating
separation bubble. Although on average the lift/drag curve seems to fall
somewhere between that of the leech spoon and that of the luff+leech spoon,
I didn't like it very much. Either you keep the luff flat, to present a
clean, well defined separation line to the airflow, or you connect the top
of the luff spoon with a straight line to the top of the leech spoon, to
keep the flow attached as much as possible, but then the mast becomes an
obstacle when on the leeside of the sail.
----- Original Message -----
From: Robert.Lainé <robert.laine@...>
To: <b.j.slotboom@...>; <email@example.com>
Sent: Sunday, January 19, 2003 11:59 PM
Subject: Re: [junkrig] Re: luff spoon
> I looked at the luff+leech spoon and I like it. However it is a problem to
> maintain the constant depth in between the 2 spoons.
> If I may ask you for further work for your wind tunnel: can you test a new
> version with called Sailcut8 double spoon as per sketch attached.
> Essentially it is the same double spoon but in between the profile goes
> to zero depth and the luff spoon is half of the leech spoon. Each half can
> be generated by a function Y= k * (x^10-x^11) with X = 1 at the luff and
> leech and X=0 in the middle of the profile.
> k=0.32 on luff side and k=0.64 on leech side will give a luff spoon of
> at 5% of cord and a leech spoon of 4.5% at 95% of cord.
> Regards / Amitiés
> Robert Lainé
> http://www.sailcut.com Free CAD for sails and hull
> http://sailcut.sourceforge.net/ Open source code