Delta Wing
Chinese sixth-generation fighter jets and Thomas Harrison Butler Yacht based on the empirical work of retired rear Admiral Turner
The importance of the sea for maritime navigation in the Mediterranean Sea
Let's look at the raked trailing edge and rudder of Thomas Harrison Butler's yacht.
From the perspective of induced drag, the temptation would be to redesign it.
Buuut the magic of this type of wing is:
1) to produce considerable lateral force, and—and here's the key—
2) to decisively shift Aft the Center of Pressure of the lift created by the vortex
A wing of this type achieves a stable equilibrium because by increasing the angle of attack (in this case Yaw/Leeway) the center of lateral pressure (the center of force) moves aft, placing itself
in the longitudinal position of the yacht's center of gravity (
Neutral equilibrium) and even
aft of the center of gravity (
Stable equilibrium)
These are the two characteristics of this type of wing:
1) generating significant lift at high angles of attack: Vortex Lift, and
2) shifting the Lift towards the rear to achieve Stable Equilibrium
Vortex-Lift
If we want to further improve the ability to shift pressure aft, then we tilt the trailing edge, as seen in sixth-generation Chinese fighter jets and Thomas Harrison Butler's yacht.
The trailing edge of the Turner-Burtler Delta Wing ...
... seems completely absurd when viewed from, say, 1979:
It creates a large vortex, which also rises, lowering the effective draft (e), and the induced drag is directly proportional to the square of the effective draft.
The confusion here is that the yacht wasn't obsessed with gaining a tenth of a knot upwind in a regatta in 1974, 1979, or 1989, but rather was sailing downwind in a real sea with Waves
prof. Kensaku Nomoto
Osaka University
hydroDynamic CLR @ 6° AoA (Yaw/Leeway) ca. 40% LWL
When we talk about a yacht's Keel, we're talking about at least three things:
1) how much force (lateral force,
Lift) it produces in relation to the angle of attack
2) how much
Drag it takes to produce that force, and
3)
Where that force is located in relation to the angle of attack.
I remember the project for a large schooner.
They spent a good amount of money on a wind tunnel and a lot of tests in a tank.
On the one hand, they rediscovered the very cheap and effective CE-Davidson estimation method using only paper and pencil.
On the other hand, they discovered the difference between a delta keel and a horizontal keel.
The importance of the sea for maritime navigation in the Mediterranean.
Davidson_CE is incredibly cheap and surprisingly accurate:
+ Foresails x
1.7
+ next aft sail (MainSail on a sloop) x
1
+ next aft sail (mizzensail) x
0.5
Curlew (Falmouth Quay Punt, 1905)
L: 8.6 m
Draft: 1.85 m (!)
BC09 – Falmouth Quay punt “Curlew” | National Maritime Museum Cornwall https://nmmc.co.uk/object/boats/falmouth-quay-punt-curlew/
...
"Curlew", i don't know if this replica has the exact same hull; but I'm including this photograph to show the original "Curlew" rigging.
These sailboats (Falmouth Quay Punt) are forged (ca. 1860-1905) in the harsh forge, hammer and anvil, of the UK's Finisterre and its triathlon:
1) Upwind
2) Hove-to
3) Downwind
