BeechTalk - BT - SB-1 Defiant Helo

Username Protected · **Posted:** 23 Mar 2019, 17:46

https://arstechnica.com/information-tec ... st-flight/

[youtube]https://youtu.be/Sm-N7trI0sw[/youtube]

Username Protected · **Posted:** 23 Mar 2019, 17:59

Claims 250 kts. I wonder how they have defeated retreating blade stall in this airframe? :scratch:

Username Protected · **Posted:** 23 Mar 2019, 18:09

Looks like a nuclear sub and a Blackhawk had a love child!!

Username Protected · **Posted:** 23 Mar 2019, 18:12

I believe I read that the two rotors are counter rotating so each has a blade coming forward at all times. They also do something to the angle of attack of the retreating blade.

Username Protected · **Posted:** 23 Mar 2019, 18:12

Username Protected wrote:

Claims 250 kts. I wonder how they have defeated retreating blade stall in this airframe? :scratch:

I imagine the contra-rotating rotors compensate for that.

Username Protected · **Posted:** 23 Mar 2019, 18:13

Username Protected wrote:

Claims 250 kts. I wonder how they have defeated retreating blade stall in this airframe? :scratch:

If I had to guess, I'd say that the rotors spin in opposite directions, so instead of the retreating blade increasing the angle of attack to keep the lift centered, it just creates lift on the advancing blade and relies on the other rotor to produce lift for the opposite side using its advancing blade.

Username Protected · **Posted:** 23 Mar 2019, 18:51

From the article:
“...the Advancing Blade Concept, a design that uses a combination of rotor design and software to overcome the aerodynamic challenges that have limited helicopter airspeeds in the past. In conventional helicopter rotor designs, drag near the blade tip on the advancing side of the rotor increases dramatically at higher air speeds, resulting in shocks and vibrations in the helicopter's blade. The design of the SB-1's rotors limits the drag on the advancing blade. Software helps adjust the orientation of the closely stacked rotors to keep them from crashing into each other.”

In other words: magic.

Username Protected · **Posted:** 23 Mar 2019, 19:02

Username Protected wrote:

From the article:
“... Software helps adjust the orientation of the closely stacked rotors to keep them from crashing into each other.”

In other words: magic.

SOFTWARE!

Given the likely contribution of software to some recent high profile accidents, I would prefer software to be as far away from my main rotor blades as possible...says the guy who flys a helicopter designed in the 1940's

.

Glenn

Username Protected · **Posted:** 23 Mar 2019, 21:22

Username Protected wrote:

Claims 250 kts. I wonder how they have defeated retreating blade stall in this airframe?

The retreating blade is feathered so no lift, hence no stall. All lift is generated by the advancing blade on each side. The next speed limitation is set by compressibility on the advancing blade tip, note it is highly swept, even though they also slow the rotation speed.
http://www.propilotmag.com/archives/2012/September 12/A3_Rotor_p1.html