Posted on 02/09/2014 12:44:07 PM PST by rawhide
I wonder if that is a byproduct of the counter-roatating prop blades? I remember as a young kid seeing B-36s fly overhead. The B-36 featured counter rotating props and they sounded like God's own beehive.
I learn something every day on F/R!
Let’s see now. If knots were to be replaced it would more likely be by kph (kilometres per hour) than by mph (statute miles per hour).
Curious if the advancing blades are breaking the speed of sound and how they solved that problem. /Cue Airwolf theme
So doesn't that mean that the main rotors don't have to tilt to create forward thrust? And without such a joint, wouldn't that make the main assembly stronger (more rigid, less complex, etc)? What kind of advantages might that bring?
What airspeed is that? Indicated or true or groundspeed? 1 Kt is approximately 1.2 mph, not that hard.
Pretty cool, not very attractive though, and I saw some wearing the Chinese star, ships of our enemy?
All helos do, the best reason to land into the wind and pay attention to the H/V diagram and the PA vs PR calculations lest you find yourself with less power available than the power required for a particular maneuver.
LOL great tune!
If I remember my airforce school (after I left infantry) well enough, existing helo’s blades break the speed of sound as it is, hence the noise.
It's all in what normal folks can think with. Miles Per Hour communicates with most people because they have direct experience with that unit of measure in their daily lives.
LOL! It would make a lot more sense to ditch the mile for the knot unit of measure. A knot (aka nautical mile) is exactly 1 minute of latitude. All navigation uses trigonometry that is based on this knot definition.
Computers will use decimals but manual navigation tools and techniques are based on the formal degree:minutes:seconds. This is matches up to the clock increments the are integral to navigation, surveying and astronomical usage.
Most airmen are trained in knots for the reasons stated. MPH is usually given in stat sheets although KPH seems to have favor as well. Having lived knots I wouldn’t want to give them up.
I imagine a fair number of people will die before a type certificate is issued for such an aircraft.
This a second-gen deal and the the production model is another step. There is always a ‘blood tax’ that gets paid. The 206 is a blast to fly, once you’ve flown some other helo. It was great to come back to. I got some time on one 15 years since I had last flown it. What a difference from the first 7 or so flights in it. What made it difficult in a trainer became a joy later. I even remembered to correct for the kick in the ass when turning downwind on departure. But it is old. I’d like to fly this new bird, see the thrust controls and how flying a single mast mounted rotor feels flatfooted.
” ‘1 Kt is approximately 1.2 mph, not that hard.’
It’s all in what normal folks can think with. Miles Per Hour communicates with most people because they have direct experience with that unit of measure in their daily lives.”
If “normal folks” (i.e., people who think the English/American statute mile (5280 ft) is somehow superior) cannot think in other terms, they might give at least some consideration to the notion that they are out of date. Unless that possibility is just too lacking in comfort, too.
The nautical mile (6076 ft) corresponds to a direct measurement from the earth’s surface, as SampleMan pointed out: one minute of latitude (north/south). Thus, there are nominally 5,400 nautical miles from the equator to either pole.
The metric system began as another attempt to devise a measure of distance that could be derived from an unalterable physical quantity, observable by all: One meter was originally defined to be 1/1000000 (one millionth) of the distance between the equator and the north pole. As it turned out, they got the math wrong, but by the time the mistake was discovered it was judged too many devices and systems had already been put in place, to go to the trouble of changing again. All this went down at the time of the French Revolution, so it’s not like the metric system is some new-fangled tom-foolery, thought up on a whim a few seasons ago.
The statute mile is thus 5280/6076 or 0.869 of a nautical mile, and one nautical mile is 1.151 statute miles - pretty close to the 1.2 posted by xone.
As a matter of historical interest, US Army Air Corps began with instruments that measured airspeed in statue miles per hour; after it was formed into a separate service (USAF), that convention held for some years. The US Navy - a separate government dept until late in the 1940s - developed its own aircraft instruments on an entirely separate basis, and calibrated them in nautical miles per hour (jargon: “knots”), to stay interoperable with ship systems. The unification of all US armed services under one dept did not standardize any of the nomenclature, nor measurement units, until some decades passed.
Civil aviation in the US used statute miles per hour for many decades, but has been slowly shifting to knots.
It’s arguable that the only reason US/English measurements of distance (inches, feet, miles) and mass (grains, ounces, pounds, tons) are still around at all was because of early US/British dominance in not only aeronautical engineering, but in worldwide commercial aviation, and later space systems.
Airspeed - indicated, calibrated, equivalent, and true - is always expressed in distance units per time unit, and it does not matter what one uses (mph, knots, km/hr, ft/sec, furlongs/fortnight). But each of those terms means very different things to a flyer.
I wonder if the preeminent position occupied by Aerodynamics for Naval Aviatiors as a reference book hasn't played a big part in in the whole NM vs. SM thingy.
As an aside, I teach a meteorology course to aviation professionals. A couple of my favorite graphic winds aloft products that I like to present display velocity in meters/second. I can never get used to that.
The load is the same. In fact, they can spin slower than a single rotor would have to, because there is no worry about losing lift on the retreating side.I'm sure it takes a much larger engine to push the torque needed to turn two rotors...
A single rotor's max speed is a factor of one side losing lift as the blade speed is zeroed out by the forward speed.
I would think that this would be a fuel-efficient design, since in high-speed flight the slower single-rotor designs would spend more time generating the lift to keep the thing airborne. I was also struck by the sound; it seemed quieter than the single rotor type even though it had a different sound presumably due to the counter-rotating lower blades colliding with the downward, corkscrewing washes from the upper rotor blades (makes me speculate about the possibility of having a different number of blades in the two different rotors, so that not all lower blades would collide with the downwashes of all the blades of the upper rotor at the same time).Given the problem of the loss of lift of the retreating-side blade with increasing forward speed, has anyone tested the concept of having a “fixed” wing on the retreating side which would provide compensating lift on that side at high speed? I put “fixed” wing in scare quotes because you would undoubtedly want it to twist like the Osprey’s to produce minimum vertical drag at zero airspeed, and also provide variable lift at speed for roll control. Obviously this would be in the context of a tail rotor for yaw control - but this Sikorsky design suggests that you would like to have the tail rotor be steerable to provide forward thrust for high speed flight.It’s a thought, but I confess that as I describe it I realize that it’s not necessarily any less mechanically complex than the Sikorsky design itself. And I don’t pretend it would be as good.
Air speed is the relevant measure of performance for this vehicle.
I've also flown Hueys that have a high inertia head so in an auto you had to control the Nr with the collective to prevent an overspeed. You had lots of turns at the bottom, which is helpful having skids.
I’d love to see its flight manual.
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