Posted on 02/09/2014 12:44:07 PM PST by rawhide
My comment went right over your head. And here you are trying to talk to us regular folks about airspeed measurements...
Kilometers are for eunuchs and Euro-weenies.
KPH? I'll keep my Standard English measurements, thank you.
“There sure are a lot of white males in the stands.”
Into the streets we must go to force people of color to attend these type events, then the aerospace industry won’t appear so racist.
Another non-problem solved by government decree.
Metrics, reminds me of the 46 pilot who didn't do his math on an internal load of milk. Tried to lift it, but his ass rotated over the edge of the ship so the aft head was Out of Ground Effect (OGE), crashed and milk all over the place. Apparently didn't know milk is comparable to water in weight. Ended up way over max gross.
This Sikorsky design would be better classified as “two rotor, one propeller” rather than “three rotor.” If you’re gonna have two rotors, concentric contra rotating design would seem to me to be about as mechanically simple as any other design. And what’s complicated about a propeller?The concentric design might complicate the control of upper-rotor pitch, I know; OTOH it doesn’t seem like the design would necessarily require cycling the pitch of the rotor to accommodate the difference in lift between the advancing and the retreating blade when in forward flight.
Would you think that this design would be about as mechanically reliable as any two-rotor design, possibly more so?
The two counter rotating Rotors are fixed, like a Wing.
They do not pitch so the entire control system is less complicated and there are less moving parts. The rear Propeller provides forward motion, not tilting the Rotors.
I assume vertical take off is strictly controlled by increasing Engine Power.
Another forgotten thrust option are those jet engines. Generally, helicopter turbines are designed solely for mechanical power generation, but they could be redesigned to produce direction thrust for greater forward speed and maneuvering. Then you have no tail rotor at all. But it would have to be directional to hover.
They have already built helicopters with direction exhaust in the tail, replacing the tail rotor.
Airspeed is measured in knots because distances in aviation is measure in nautical miles. The earliest aviation charts were nautical charts with distances measured in nautical miles. Had to use knots in order to make the distances on the charts understandable. Now the system is so entrenched I doubt if it could be changed.
Aviation does have several different, and at times confusing, standards of measuring. Altitude is measured in feet, visibility is measured in statute miles, feet, meters, kilometers, and using Runway Visual Range (RVR) values. Distances are measured in nautical miles (6076.11548 feet)and Distance Measuring Equipment (DME). There is even a radar mile, 6000 feet.
I’ve never got the chance to examine or fly such a setup, but I’d like to the the swashplate assembly and the control tubes for the double disc. The prop portion is somewhat straightforward, but the cockpit controls and the transmission arrangement would be interesting.
I saw the S-69 make a high speed pass over the Housatonic River at a Sikorsky open house back in the 70’s. Really glad this thing has come back to life.
They have already built helicopters with direction[al] exhaust in the tail, replacing the tail rotor.
Yes, that’s clear; if you had thrust vector control, and if you had good thrust magnitude control with enough independence of turbine mechanical power output, that should work. Of course, plumbing the exhaust all the way back to the tail for the purpose isn’t quite free . . .That would seem to offer the best way to make a really fast helicopter. Tho I suppose that rotary wings would inherently limit your max forward speed to well below Mach 1 in any case . . .
But in the other direction, the limit to any rotating blade forward is also the near-supersonic speed of the advancing blade as the copter flies forward: With two counter-rotating blades rotating at a slower rate, the whole machine can go faster forward
I take it you mean trade "the swashplate assembly and the control tubes for the double disc?"The prop portion is somewhat straightforward, but the cockpit controls and the transmission arrangement would be interesting.
I’m struck by the absence of any reference to the fact that coaxial contra rotating rotors would practically eliminate the gyroscopic precession effect of rolling or pitching the axis of rotation of the rotary wings. Has technology/autopilot eliminated that confounding effect on the operability of a chopper?
Complete thoughts are impossible without fish oil.
No, I meant I'd like to examine setup of the double disc. It looks cleaner than the Kamen, but that isn't surprising.
gyroscopic precession effect of rolling or pitching the axis of rotation of the rotary wings.
I've never experienced the phenomena. Between the flapping of the rotors, the tranny mounts and the overall normal vibratory experience of helo ops that tendency never manifested to me.
As for a helo autopilot, have at it, you couldn't get me to trust one. Systems for augmenting stability or the flight controls, yes. Hands off: no. First the track has to be right, then dampen the vibes or isolate from the autopilot. The Navy had an Doppler-coupled hover ability for its SAR aircraft H-46. Never used it and would definitely want to see it used before night overwater ops. Helos are made to hand fly. A fly by wire sounds good until every VC or hadji with an AK could be shooting at you.
Correctly stated. The first issue is loss of lift on the retreating side, the next issue is compressibility on the advancing side.
Although, I would describe the first as a limit and the second as a hurdle, as the Russians were able to make the supersonic blade configuration work on their Tu-95 aircraft.
Using standard rotor blades, there is also a minimal rotational speed (centripital) force requirement to stiffen the blades, i.e. if I lift on the blades of a parked helicopter they will snap off. So, there is a minimum rotational speed required, even if a static blade could create the required lift via forward motion of the aircraft.
Granted, although the counter-rotating configuration would mean that the lateral thrust requirement would be much, much smaller, being used only for steering versus torque offset.
I've never experienced the phenomena.gyroscopic precession effect of rolling or pitching the axis of rotation of the rotary wings.
Interesting. The hello pilot I shot the breeze with was talking about the gyroscopic action of motorcycle steering wheel when I picked up the conversation. He said that at highway speed turning the front wheel to the right actually produced a roll moment to the right, which is favorable to keeping balance going around a curve. This was a new thought to me, and we discussed it a bit. He added that the rotary inertia of the rotor of a copter also has a gyroscopic effect such that rolling the vehicle induces a pitch moment, and vice versa.Most interesting of all, he added that powerful WWII fighters manifested a gyroscopic coupling which, he opined, was the reason for a lot of trouble novice pilots had with taildraggers on takeoff roll. I was aware of the phenomenon, which was erroneously briefed as “torque”, of such planes going off the runway during takeoff runs. The book, Thunderbolt, by WWII ace Bob Johnson discussed the phenomenon without ever explaining why it happened to novices but experienced pilots were able to compensate for the so-called “torque effect” of the P-47’s big engine.
The pilot who was talking gyroscopic effect asserted that the problem was not the torque of the engine, which didn’t vary that much during a takeoff run and in any event did not obviously call for a yaw correction as briefed. He asserted that the problem was simply that gyroscopic action of the large, high-RPM propeller caused a yaw moment when the tail was lifted up during the takeoff roll. Thus, briefing that the problem was “torque” led the novice pilot to preemptively apply rudder too early, and cause him to deviate from the runway to the opposite side from where that which naturally would occur later during the roll at tail liftoff.
In such case, it might seem possible to duct the exhaust gas to each side of the fuselage - then direct it either forward or aft as desired to trim the hover position, adjust the yaw attitude, or propel the vehicle forward at high speed.
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