Sikorsky SB-1 flies for first time
Only two flights in a month. Not an impressive demonstration pace.
This guy is struggling to make the program sound viable. Really not enthusiastic about what he is spinning.
This guy is struggling to make the program sound viable. Really not enthusiastic about what he is spinning.
Thanks for the link! I hadn't heard they had a second flight. Not sure I agree that he was struggling to make the program sound viable, but I don't think he is very knowledgeable about the technology.
The X-59 36 Years ago
I had an opportunity to fly the X-59 with the two J60 engines (3000 lbs. thrust each) installed in March of 1983. It was a short 45 minute flight that began with a short running takeoff followed by what would be categorized as a maximum performance climb at 45 degrees pitch up. Once leveled off we made a level speed run at just under 250 KIAS. As we rotated during the take off roll the torque from the PT-6 twinpac (1800 ESHP) reduced to 0%. The rotor system operated as an autogyro from takeoff rotation until we slowed for our descent to approach for landing. The PT-6s smoothly re-engaged providing power for hover and landing. The short end of the story is, the X-59 flew more than 100 hours and achieved a pretty significant flight envelope 36 years ago. It required a combined 6000 lbs. of thrust from the two J-60’s to push this little 11,000 lb. aircraft out to a maximum of 263KIAS. I have to believe that the SB-1 Defiant will require more than a T-55 engine to meet its goals. To say that the vibrations during my flight were significant would be an understatement.
JC
From Bell site:
That is 275 kts which indicates with enough thrust even a conventional helicopter can get to high speeds. Like the -59 this test bed had no range and shook like hell.
From Bell site:
Bell Helicopter's compound research helicopter, a highly modified Bell UH-1, attains a speed of 316 mph in level flight. This is an unofficial speed record and has remained unchallenged.
Jack,
When I was recruited to design and build the X2 FBW I spent a lot of time studying the ABC and talking to the old timers. Everything you say about the ABC is true. The X2 and its successors are different in two respects. The blade planform is a leap way beyond what you had on the ABC. The drag is way lower even without the nifty inter-rotor fairing. Also due to the driveline, speed of the main rotor is controllable. It doesn't autorotate away like the ABC, even at flat pitch. The ABC was a cool aircraft, and it advanced the state of the art of blade construction, but still seemed to be designed around hover. You probably remember the twist of the blades. What is good for low speed is bad for high speed, and visa versa. Time will tell for the Defiant, numbers don't lie.
Bryan Cotton
When I was recruited to design and build the X2 FBW I spent a lot of time studying the ABC and talking to the old timers. Everything you say about the ABC is true. The X2 and its successors are different in two respects. The blade planform is a leap way beyond what you had on the ABC. The drag is way lower even without the nifty inter-rotor fairing. Also due to the driveline, speed of the main rotor is controllable. It doesn't autorotate away like the ABC, even at flat pitch. The ABC was a cool aircraft, and it advanced the state of the art of blade construction, but still seemed to be designed around hover. You probably remember the twist of the blades. What is good for low speed is bad for high speed, and visa versa. Time will tell for the Defiant, numbers don't lie.
Bryan Cotton
IFMU
There are always compromises. Having enough blade twist to a achieve hot high hover capabilities while achieving reasonable cruise speeds and range is challenging.
There are always compromises. Having enough blade twist to a achieve hot high hover capabilities while achieving reasonable cruise speeds and range is challenging.
The aerodynamic benefits of the ABC rotor are significant but they come at considerable cost.
If you look at the installed power required for high speed flight, you are more than covered. Also with 8 blades there is enough solidity to absorb the power required for high/hot even without all the twist.
Right, I'm speaking from a "first principles" textbook point of view, the full problem is certainly more complex, but unlikely in a positive way. Question is, can that AVC clean up the vibes to a production level across an entire flight envelope? I'm sure the Army will be interested in that answer.
Right, I'm speaking from a "first principles" textbook point of view, the full problem is certainly more complex, but unlikely in a positive way. Question is, can that AVC clean up the vibes to a production level across an entire flight envelope? I'm sure the Army will be interested in that answer.
AVC a Flight Critical System on Defiant and Raider?
I have been wondering for a while. Is the AVC system on the Defiant and Raider considered a flight critical system? By that I mean, is it like a flyby wire flight control system where redundancy is required and complete system failure can result in loss of the aircraft?
However, that said, if vibrations on a rigid rotor can be significant, and I believe math and available evidence says they can be, then an AVC system has to be suitably powerful. An active system capable of (nearly) canceling large vibrations is technically capable of nearly doubling them with incorrect system operation. It might not need to be strictly flight critical, but it could well be mission critical.
From what I have been told, PIO from severe vibration can be a concern. At least with FBW with notch filters this can be addressed. This may allow AVC loss to be only mission critical.
Paxing All Over The World
As a rank outsider who knows nothing about Helis and had never heard of this machine until deciding to browse this forum:
Looking at the machine, I have to ask, why would anyone do that? As far as I am aware, the Osprey is not a runaway success and this machine looks like it's trying to tackle the same problem from a slightly different angle.
Looking at the machine, I have to ask, why would anyone do that? As far as I am aware, the Osprey is not a runaway success and this machine looks like it's trying to tackle the same problem from a slightly different angle.
