@Giga I’m sorry to tell you you’re not exactly right because you’re not taking into account that our hydrofoils are weight shift controlled flying objects and not “ordinary” planes.
@MaxMaker your intuition was right and has been proven with kitefoils.
Planes are not kitefoils and eFoils are not kitefoils. Kitefoils need an edge wereas eFoils are riding flat.
You don’t need a stabilizer to make a hydrofoil fly. That is pitch unstable but works
There are 3 ways to make a plane fly.
- traditional: positive lift front wing with negative lift stabiliser (rear wing) [UDL standing for Up Down Lift]
- tandem : positive positive (flying flea project circa 1930s) [Up Up Lift or UUL for short]
- canard (stabiliser fore = positive lift) main wing = positive lift
There is a path to investigate with stabilisers (rear W) providing a positive lift. Gong experimented this setup with their “Hellvator” kitefoils in 2016, based on a tandem setup.
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Advantages:
1 - The total surface increases and don’t sustract: instead of having , say 700cm2 +(-300)cm2, the total surface becomes 700 + (+300), so you can have a foil with 350 front and 150 rear with same lift as a +800 - 300
The drag of the front wing is therefore divided by 2 whereas the drag of the stab is also decreased.
2 - The stability increases tremendously under 20 knots especially if the rider maintains his/her CG in the first half of the plane. From 25knots, the plane becomes more pitch unstable. -
Drawbacks:
D1 - the neutral point (NP) of the plane is moved aft by 10/15 cm. (the point around which the plane rotates in flight). The rider position instead of being fore the plate becomes aft the plate, ie more towards the plane tail. The best compromise would be to move the plate 15cm more aft to keep rider position at 25% of board length. But you are under the electric box on new board designs with no to not enough thickness.
D2 - At 30 knots, the balance becomes uncertain and very pitch dependent.
As a conclusion I would say that up to 25 knots, the tandem setup is very beginner friendly and should decrease the power consumption significantly. What do we want more ?
As a start, the process is to flip bottom up the stab of an existing kitefoil, Nobile-like 600cm2 Fwing and with negative lift stabiliser. It’s not easy as a 0 to +1 degree angle has to be found and maintained. This should give the same take-off speed as a 1000 cm2 supfoil with neg lift stabilizer with same or better longitudinal stability.