Graviman,
There is no "free Lunch" and I would guess the airfoil never earned its keep. This is speculation (informed, perhaps) that the airfoil actually cost more vertical drag then it gained in anti-torque.
All items on a flying machine are resolved into a universal coinage that allows the item to be comparitavely valued. That coinage is usually weight.
The airfoil itself is probably extremely light, but it creates additional download with its drag (the sideward lift it creates has a drag at 90 degrees to the lift - thus downward). Most lifting bodies have a lift-to-drag ratio of between 4 to 1 to 12 to 1. Since that airfoil is low aspect and probably operated at a high angle of attack to squeeze as much anti-torque as possible, let's guess it is in the middle somewhere, 6 to 1. If the surface has appreciable anti-torque it probably reduces payload quite a bit.
Some examples: if the helo was 10,000 lbs and uses 1000 HP to hover, its tail rotor must produce about 550 lbs. If we use the airfoil to produce 30% of that, the airfoil must produce about 200 lbs of thrust (it is inside the tail rotor, so the thrust it creates acts on a shorter lever arm, and must be proportionately larger). If the airfoil had a L/D of 6 it will reduce payload by 33 lbs, at a disadvantageous aft CG.
BTW, Sikorsky never used the strake in any model, those fits were done aftermarket by others. The flight testing we did showed no significant gain, IIRC.
Last edited by NickLappos; 11th June 2005 at 16:11.