IFMU
I agree in principle. Igor Sikorsky flew the Grand, a 4 engine, 5 ton machine in 1913. Sixty years later that vehicle evolved into the 747. Similarly, he flew the VS-300 in 1939. 35 years later Sikorsky flew the 35 ton CH-53E. However, some subsets of rotorcraft technology may approach physical limits due to power requirements or material limitations. To draw a slightly different analogy, I believe that the VTOL Harrier and F-35 are approaching practical limits for turbo-fan thrust born flight. Co-axial rotor systems may have just such a boundary.
Jack
Jack, your comment is spot on. The boundary you are refering to is compressibility. By opting for a counterrotating main rotor system you avoid the retreating blade stall, but the limit you now hit is the advancing blade shock wave formation. Improved modelling and damping of blade modes will allow Nr to reduce at higher speeds without fear of structural divergence. Eventually the machine will operate at speeds approaching turboprops, so Sikorsky are being sensible with a 250kias start - remember it has to work.
One day in the distant future speed might get into the turbofan arena. Much work on blade dynamics will be required - likely with active systems. This is similar to commercial fixed wing struggling to justify projects over M1...
Originally Posted by Jack Carson;
".. some subsets of rotorcraft technology may approach physical limits due to power requirements or material limitations. ... Co-axial rotor systems may have just such a boundary."
A link to this subject of; Empty Weight and Payload;
The spread between the Coaxial-ABC and the Interleaving-ABC will be even greater.
Dave
Dave,
What is the drag penalty for those two masts sticking up, with not only double the profile drag, but also interference between them? That's one thing that seems unequal.
As far as the 15% benefit with respect to disk area, how much of that is undone by the fact that the lift vectors of the synchrocopter waste some of their effort against each other, since they are inclined outwards? You could probably do a ROM estimate of the lost lift of each rotor by multiplying it by the cosine of the shaft angle.
I have read that the original ABC had big vibration problems. It had two 3-bladed rotors. How is anything with 2-blade rotors going to be better? I would bet you would have a hard time getting to respectable single rotor helicopter speeds before you lost your fillings, or busted something.
-- IFMU
What is the drag penalty for those two masts sticking up, with not only double the profile drag, but also interference between them? That's one thing that seems unequal.
The rotors on both craft are identical. Four blades each, etc., etc. The induced, profile and parasitic drags should be equal.
Quote:
As far as the 15% benefit with respect to disk area, how much of that is undone by the fact that the lift vectors of the synchrocopter waste some of their effort against each other, since they are inclined outwards?
The upper blades, which are facing outward, are the retreating blades. They produce little thrust compared to the advancing blades during cruise.
I believe that this offers an advantage over the Coaxial. A problem with the Coaxial is that on one side of the craft the low thrust retreating blades are located underneath the high thrust of the advancing blades. In addition, the Coaxial's lower retreating blades span the full length of the upper blades. This is source of strong rotor-to-rotor vibration.
I think that it has something to do with symmetry.
Quote:
I have read that the original ABC had big vibration problems. It had two 3-bladed rotors.
As far as the 15% benefit with respect to disk area, how much of that is undone by the fact that the lift vectors of the synchrocopter waste some of their effort against each other, since they are inclined outwards? You could probably do a ROM estimate of the lost lift of each rotor by multiplying it by the cosine of the shaft angle.
IFMU, in theory the intermesher will not lose efficiency since the downwashes force each other back to vertical. The rotors may actually improve the way the wake contraction is handled, although a ring rotor would offer greater benefits for coaxial only.
The main arguement for interleaving to my mind is maximising rotor area for a given weight. If you see aircraft width as a constraint, this points towards tandem layout. However, rear rotor will suffer from losses due to inflow.
This may be off base on this thread but the Sikorsky Cypher slowly faded and it was a counter-rotating vehicle, though unmanned. What ever became of it and besides not having a pusher and the noise issue, was it of any help with this new aircraft? Nick? Jack?
The Cypher fell to company decisions on where the UAV future was, back in 2001. The Cypher was small and inexpensive (so that many units had to be built and sold to make any appreciable profit) but engineering labor intensive, so it was put on the back burner.
This posting is placed here in the Sikorsky SX Coaxial thread since the following US Patent Application is including the SX coaxial configuration.
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Nick,
As you probably know, I have an interest in the concept of 'Variable Speed Rotors and Propellers', having posted this publicly displayed thread in PPRuNe five months before the filing date of the following Patent Application.
A question comes up, which I am sure you can answer.
The patent's tittle includes "...with an independently variable speed tail rotor system for a rotary wing aircraft.". In addition, Claim 2 says "... said tail rotor system at an independently variable speed relative said engine speed.", and Claim 14 says " ... and an independently speed-variable tail rotor system ...".
However, there are no details on this variable-speed tail-rotor ("transitional thrust system 18 and 18' "). In addition, the associated drawings only show a blank box.
I understand that the US Patent Office does not review the Claims in a Patent Application, but my question is why is there an 'all-encompassing' claim in the patent application?
... the Cypher UAV which expanded company knowledge of the unique aspects of flight control laws in a fly by wire aircraft that employed coaxial rotors ...
The prior art in that field is vast. The work that was documented to support that and previous patent applications dates back years before your thread (it was while I was at Sikorsky, and I left months before your thread, for example.) Not being a patent expert, I can't comment on how claims are worded or handled. Like the Michael Keaton character in "NIght Shift" I'm the idea man....
"What if you mix the mayonnaise in the can, WITH the tunafish? Or... hold it! Chuck! I got it! Take LIVE tuna fish, and FEED 'em mayonnaise! Oh this is great. [speaks into tape recorder] Call Starkist!"
Not sure how many patents do get through - especially the overunity energy claims etc. It is difficult to really invent something new, since most ideas are a new application for an old concept. Must make patenting process more difficult to control.
With the headache that patenting presents to the private inventor, the thing that seperates a good company from a bad company is finantial reward for a patent which is incorperated. This encourages thought outside the box.
Thanks for the reply. Perhaps your departure from Sikorsky resulted in the legal objectives overriding your technical objectives, when the lawyer was writing the Patent Application.
Incidentally, your Patent Application includes a coaxial configuration drawing. This drawing was used six months earlier in three coaxial-ABC Patent Applications. In your Patent Application, the lawyer, perhaps in a rush to pump out coaxial-ABC patents, didn't even reference the text to this drawing correctly.
Mart,
Times have changed.
Recently, much has been written about the growing abuse of US patent system and its inability to now serve its basic objectives.
Yesterday's article in the highly respected Globe & Mail 'Tech Crusaders Are No Match For Mighty U.S. Patent Lobby' is just one more example. The year-by-year increase in number of US patents is phenomenal. Most of these patents are insignificant drivel. However, one of the things they do is allow large corporations to use their vast wealth as the hammer, and their irrelevant patent as the excuse, to 'squash' the under-funded legitimate invention.
You may find the last line in this quote from the above article of specific interest.
"The U.S. drug industry has no interest in anything remotely approaching an overhaul. It is lobbying furiously behind the scenes to make sure this legislation dies or is seriously diluted. Joining the drug companies are a broad group of blue-chip manufacturers, including United Technologies and 3M Co."
