BLR Aerospace FastFin® System Technical Briefing

[@rcafmaintainer3723]

Can increasing the cumber on the right side of the tail-boom further help? In theory speeding up the air should reduce pressure, like the topside of a wing. Sure it might look symetrical to the discerning eye.

[@OneHoof]

I absolutely love the Bell Huey. But, the Huey’s tail rotor system is a complex & some what controversial subject! 😳 Bell Helicopter Textron has had problems with creating tail rotors that aren’t effective enough with their thrust. The 206B Jetranger’s are notorious for spinning out of control because of loss of tail rotor effectiveness (LTE). I guess the Jetranger tail rotor was just too small for the amount of torque that the 206B was capable of producing. With high gross weights Jetranger pilots have to avoid right pedal turns to avoid getting into LTE. Eventually a company called Van Horn started producing more aerodynamic & effective after market composite 206B replacement tail rotor blades that greatly increased their effectiveness & safety. The original Bell UH-1 Hueys & AH-1 Huey Cobras spin their port (left) side mounted, pusher prop, tail rotors counter clockwise which is aerodynamically less efficient. Hueys are powerful helicopters, but like the Jetranger are prone to getting into Loss of Tail Rotor Effectiveness (LTE) & spinning out of control at high torque power settings & low air speeds. Bell could have fixed the Huey’s inherent anti torque design flaw in 1965 by redesigning the tail rotor gear box, remounting the tail rotor blades, & simply spinning the tail rotor blades the opposite direction (clockwise). Around that time, helicopter engineers discovered that spinning the tail rotor clockwise, & upward into the main rotor’s (MR) downwash, gave the tail rotor more bite/thrust; similar to translational lift, making the tail rotor more efficient & more effective. Unfortunately Bell helicopter did not want to pay the extra money of redesigning the Huey’s tail rotor gearboxes to fix this inherent aerodynamic problem at its original source. Instead, they started flipping the old gearbox over, & putting the tail rotor on the opposite (starboard/right) side of the vertical stabilizer. This did spin the tail rotor upwards into the main rotor’s downwash. But, it changed the tail rotor from being a pusher prop system to being a tractor system. Therefore; this induced a new aerodynamic problem because now the large vertical stabilizer was blocking maybe almost 1/4 of the tail rotor’s thrust. So, while spinning it upward into the downwash added a slight thrust advantage, this advantage was lost because the vertical fin was blocking so much of its thrust. Therefore; by switching the AH-1 Huey Cobras’ & Hueys’ tail rotors to the opposite (starboard) side in reality possibly made the Hueys’ ineffective tail rotor problem even worse! Hueys were still getting into LTE & spinning out of control & crashing when flying at high power (high torque) situations hauling heavy loads or high density altitudes. This has been a problem with the Hueys since their inception in the early 1960’s. They’re great helicopters, but they could have been even better if Bell Helicopter Textron would have spent the money to design a new gearbox to spin their tail rotors clockwise on the original port side, to keep them as a pusher system, spinning upwards into the MR downwash. In more recent years, Bell essentially tried putting a “band aid on a bullet wound “ by making the vertical fin smaller (Fast Fin), so it doesn’t block as much thrust from the starboard mounted, tractor tail rotors, hoping to increase tail rotor thrust a slight bit. Bell also started installing strakes on the left side of the tail boom to interrupt the air flow, to increase air pressure on that side & decrease airflow on the right side creating the Coandă effect, like McDonnell Douglas MD520N NOTAR helicopters. I guess this has helped increase tail rotor effectiveness in fast fin modified Hueys? The problem is, the vertical fin is designed to aerodynamically keep the helicopter from spinning if you maintain 65 knots forward speed, in the event of a tail rotor failure. Unfortunately, I don’t know if the narrower fast fin vertical stabilizer is big enough to aerodynamically prevent the Huey from spinning. So, to me, reducing the vertical fin’s size is like robbing Peter to pay Paul. Sure… it might increase tail rotor thrust of the less effective tractor system, a bit, but the vertical stabilizer might not have enough surface any longer to prevent a spin, in the event of a tail rotor failure. This just doesn’t make sense to me! Bell could have created a more effective pusher, tail rotor system by redesigning the tail rotor gearbox, to spin the tail rotor, clockwise, almost 60 years ago. But to save money they’ve engaged in shenanigans robbing Peter to pay Paul, by flipping the gearbox over, to change it to a less effective tractor system. So, whenever I see the Hueys tail rotor system brought up, it’s a frustrating topic because Bell decided to go cheap, instead of making the Huey’s tail rotor system the best it can be. The tractor system, equipped with fast fin, is a compromised system stacked onto a compromised system… to avoid fixing the root problem, of redesigning the gearbox to spin the tail rotor the opposite direction, they’ve done less effective things, to save money. 💴

[@PacoOtis]

Thanks for the video but it twice as long as it needs to be! Best of luck!