the Intermeshing Configuration is Best
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H-43:
I hear you, but doesn't the trannie have two different outputs, with the associated gearing for the opposite direction drives, extra thrust bearings, output housings, swash plates and collective mechanisms? I assume (could be wrong, won't be the first time! especially since I haven't looked inside one of those trannies ever) that all this stuff is "about equal" to the added burden of a tail gearbox system.
Regarding efficiency, I'll bet you are right, the H-43 is more efficient than an H-1. That has a lot to do with its disk area, which is great, because it was designed in the late 40's for a heavy piston engine, so low low disk loading was needed to get it off the ground. Toss in a turbine, and you have a real screamer. Not necessarily an attribute of its twin rotors, more due to the turbine slipped into the ancient design.
Dave Jackson:
The ABC was a great machine, with its counterrotating system and its very high agility. It weighed about 5% more than a single rotor helo but made that up with excellent maneuverability. Also, it could get to almost 300 MPH (with aux thrust) and pull lots of g at high speed, since retreating blade stall was not an issue.
I hear you, but doesn't the trannie have two different outputs, with the associated gearing for the opposite direction drives, extra thrust bearings, output housings, swash plates and collective mechanisms? I assume (could be wrong, won't be the first time! especially since I haven't looked inside one of those trannies ever) that all this stuff is "about equal" to the added burden of a tail gearbox system.
Regarding efficiency, I'll bet you are right, the H-43 is more efficient than an H-1. That has a lot to do with its disk area, which is great, because it was designed in the late 40's for a heavy piston engine, so low low disk loading was needed to get it off the ground. Toss in a turbine, and you have a real screamer. Not necessarily an attribute of its twin rotors, more due to the turbine slipped into the ancient design.
Dave Jackson:
The ABC was a great machine, with its counterrotating system and its very high agility. It weighed about 5% more than a single rotor helo but made that up with excellent maneuverability. Also, it could get to almost 300 MPH (with aux thrust) and pull lots of g at high speed, since retreating blade stall was not an issue.
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I do not think that the intermeshing helicopter can be equated with the coaxial when discussing induced velocity. Many of the Russian coaxials were intended for shipboard operations and therefore a small 'footprint' was advantageous. The Kaman intermeshing helicopters were promoted based on their low disk loading.
1/ The Huskie has a 23.5' radius and a 3.7' stagger. Its combined disk area is exactly 10% greater then the area of its individual disks. This represents a 10% improvement over a comparable coaxial or 4-bladed single rotor disk.
2/ The tip path of the upper blade when at 90-degree azimuth is 9'-8" above the plane of the lower blade. This is a much greater gap then a coaxial has and therefor the convergence of the upper rotor's downwash will put even more of the lower retreating blade in free air.
3/ The outer portion of the retreating blade imparts the greatest (blade element) lift and this is the portion of the blade that is operating in free air.
If the payload of a helicopter is 50% of its gross weight, then the above represents at the very least a 20% increase in payload.
Conversely, for future faster intermeshing helicopters, the total disk area and rotor drag can be proportionately smaller for a given thrust.
1/ The Huskie has a 23.5' radius and a 3.7' stagger. Its combined disk area is exactly 10% greater then the area of its individual disks. This represents a 10% improvement over a comparable coaxial or 4-bladed single rotor disk.
2/ The tip path of the upper blade when at 90-degree azimuth is 9'-8" above the plane of the lower blade. This is a much greater gap then a coaxial has and therefor the convergence of the upper rotor's downwash will put even more of the lower retreating blade in free air.
3/ The outer portion of the retreating blade imparts the greatest (blade element) lift and this is the portion of the blade that is operating in free air.
If the payload of a helicopter is 50% of its gross weight, then the above represents at the very least a 20% increase in payload.
Conversely, for future faster intermeshing helicopters, the total disk area and rotor drag can be proportionately smaller for a given thrust.
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Dave Jackson's points, in turn:
>>1/ The Huskie has a 23.5' radius and a 3.7' stagger. Its combined disk area is exactly 10% greater then the area of its individual disks. This represents a 10% improvement over a comparable coaxial or 4-bladed single rotor disk.
NL- True enough, but it also shows 90% commonality with a co-axial, clearly within the accuracy of our "PPRUNE Engineering" According to the data I looked at today (This web site makes me work on Sunday!!) the negative effects get large at 50% overlap, let alone 90%. While it would be better than a straight forward coaxial, the diffecence would not be thundering.
>>>2/ The tip path of the upper blade when at 90-degree azimuth is 9'-8" above the plane of the lower blade. This is a much greater gap then a coaxial has and therefor the convergence of the upper rotor's downwash will put even more of the lower retreating blade in free air.
NL- This takes the extreme of course, but the rotors have zero clearance at the hub, so the average is probably half that, or perhaps 5 feet, which is about what a typical coaxial uses as its separation. No points scored here, Dave, I think.
>>>3/ The outer portion of the retreating blade imparts the greatest (blade element) lift and this is the portion of the blade that is operating in free air.
NL - Sounds plausable, I wonder if there is any data to describe
>>>If the payload of a helicopter is 50% of its gross weight, then the above represents at the very least a 20% increase in payload.
NL- The data gets muddy here, mostly because there is little to quantify the one possible advantage from above. The H-43 is so very hover efficient because of its extremely low disk loading, where the 48 foot rotor(S) lift about 9000 pounds of aircraft (5 pounds per square foot for 1 rotor, 2.5 pounds for both, the reality is somewhere in between). A Bell 412 is 6.5 PSF so it would use 40% more power just because of the disk loading, not the planform.
>>1/ The Huskie has a 23.5' radius and a 3.7' stagger. Its combined disk area is exactly 10% greater then the area of its individual disks. This represents a 10% improvement over a comparable coaxial or 4-bladed single rotor disk.
NL- True enough, but it also shows 90% commonality with a co-axial, clearly within the accuracy of our "PPRUNE Engineering" According to the data I looked at today (This web site makes me work on Sunday!!) the negative effects get large at 50% overlap, let alone 90%. While it would be better than a straight forward coaxial, the diffecence would not be thundering.
>>>2/ The tip path of the upper blade when at 90-degree azimuth is 9'-8" above the plane of the lower blade. This is a much greater gap then a coaxial has and therefor the convergence of the upper rotor's downwash will put even more of the lower retreating blade in free air.
NL- This takes the extreme of course, but the rotors have zero clearance at the hub, so the average is probably half that, or perhaps 5 feet, which is about what a typical coaxial uses as its separation. No points scored here, Dave, I think.
>>>3/ The outer portion of the retreating blade imparts the greatest (blade element) lift and this is the portion of the blade that is operating in free air.
NL - Sounds plausable, I wonder if there is any data to describe
>>>If the payload of a helicopter is 50% of its gross weight, then the above represents at the very least a 20% increase in payload.
NL- The data gets muddy here, mostly because there is little to quantify the one possible advantage from above. The H-43 is so very hover efficient because of its extremely low disk loading, where the 48 foot rotor(S) lift about 9000 pounds of aircraft (5 pounds per square foot for 1 rotor, 2.5 pounds for both, the reality is somewhere in between). A Bell 412 is 6.5 PSF so it would use 40% more power just because of the disk loading, not the planform.
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Nick:
I don't know if you understood my point in saying that I think there is little difference in complexity between either the "conventional helicopter" and the "intermeshing helicopter" they both have their simplicity and complexity. You pointed out correctly that the Huskie was designed with piston power in mind and had a much bigger power plant installed. However, it still has the same power plant as the UH-1 and will still out perform the UH-1. I will also add that the Huskie is still limited to the same transmission input power as it was when the T53-L1A engine. The larger engines were simply added for more altitude performance.
Brian
I don't know if you understood my point in saying that I think there is little difference in complexity between either the "conventional helicopter" and the "intermeshing helicopter" they both have their simplicity and complexity. You pointed out correctly that the Huskie was designed with piston power in mind and had a much bigger power plant installed. However, it still has the same power plant as the UH-1 and will still out perform the UH-1. I will also add that the Huskie is still limited to the same transmission input power as it was when the T53-L1A engine. The larger engines were simply added for more altitude performance.
Brian
Slightly off the topic, the great photo links listed above by some of the contributors put me in mind of a spectacular contraption that the Americans put together quite some time ago.
It had the front ends of 4 single-rotor helicopters positioned at the corners of a large square lifting frame.
As I remember (saw a photo of it somewhere) it had four pilots all setting power on command from the chief pilot who was sitting in one of the airframes.
A brave effort to come up with a heavy lift machine, but too many problems to be successful, I think.
Does anyone have links to pictures/information about this machine, whatever it was?
Thanks.
It had the front ends of 4 single-rotor helicopters positioned at the corners of a large square lifting frame.
As I remember (saw a photo of it somewhere) it had four pilots all setting power on command from the chief pilot who was sitting in one of the airframes.
A brave effort to come up with a heavy lift machine, but too many problems to be successful, I think.
Does anyone have links to pictures/information about this machine, whatever it was?
Thanks.
The machine was the Piasecki Helistat. By attaching four H-34's (Sikorsky S-58's) to the device. I guess they figured they had a good means of removing all those old ships from the desert and putting them to use. The project was funded by the US Forest Service and US Navy 
, who believed there was a need for a new heavy lift capability.
The following is the NTSB transcript of the sole flight undertaken by the craft. Sadly one of the pilots was killed when all four machines broke loose, after they lost control of the entire device.
This Russian site (again) seems to be the sole source of a photo of this machine. http://www.russian.ee/~star/vertigo/...elistat-r.html
Frank Piasecki is still around and Piasecki Aircraft recently won a US Airforce contract to produce a compound helicopter version of the H-60 Blackhawk. (The web site above has some pictures of the evolutionary models).
Lakehurst N.J was the center of US naval airship operations (collosal airship hangars), and is probably better known in infamy, as the site of the loss of the Hindenberg.
NTSB Identification: NYC86FHD01 . The docket is stored on NTSB microfiche number 32618.
Accident occurred Tuesday, July 01, 1986 at LAKEHURST, NJ
Aircraft:PIASECKI HELISTAT 97-34J, registration: N1897Z
Injuries: 1 Fatal, 3 Serious, 1 Minor.
The helistat, a hybrid a/c with 4 H-34 main fuselages attached to a frame along with a zpg-2 helium filled envelope had just completed it first hover test flt successfully and landed. A pwr loss was noted on the No. 3 helicopter and the test was terminated and the mooring mast called for. Prior to re-mooring a wind shift caused an uncommanded left turn which the pilot could not control with the flt controls. With a tailwind, no wheel brakes or gnd steering a takeoff was attempted. The 4 main landing gear which had no shimmy dampners started to shimmy. The four helicopters started to react to the shimmy with ground resonance. As the helistat finally lifted off, the four individual helicopters broke off and fell to the ground. One pilot received fatal injuries, 3 received serious injuries and one minor injuries. The helistat was destroyed. The prw loss on the no. 3 helicopter was traced to a missing throttle linkage correlation pin. Why the pin was missing was not determined.
The National Transportation Safety Board determines the probable cause(s) of this accident as follows:-
Throttle/power lever,linkage..disconnected
Rotorcraft flight control..inadequate
Acft/equip,inadequate design..manufacturer
Acft/equip,inadequate handling/perf capabilities..manufacturer
Contributing Factors
Landing gear,main gear..vibration
Rotor system..vibration
Landing gear,normal brake system..lack of
Landing gear,steering system..lack of
[ 27 August 2001: Message edited by: Cyclic Hotline ]
, who believed there was a need for a new heavy lift capability.The following is the NTSB transcript of the sole flight undertaken by the craft. Sadly one of the pilots was killed when all four machines broke loose, after they lost control of the entire device.
This Russian site (again) seems to be the sole source of a photo of this machine. http://www.russian.ee/~star/vertigo/...elistat-r.html
Frank Piasecki is still around and Piasecki Aircraft recently won a US Airforce contract to produce a compound helicopter version of the H-60 Blackhawk. (The web site above has some pictures of the evolutionary models).
Lakehurst N.J was the center of US naval airship operations (collosal airship hangars), and is probably better known in infamy, as the site of the loss of the Hindenberg.
NTSB Identification: NYC86FHD01 . The docket is stored on NTSB microfiche number 32618.
Accident occurred Tuesday, July 01, 1986 at LAKEHURST, NJ
Aircraft:PIASECKI HELISTAT 97-34J, registration: N1897Z
Injuries: 1 Fatal, 3 Serious, 1 Minor.
The helistat, a hybrid a/c with 4 H-34 main fuselages attached to a frame along with a zpg-2 helium filled envelope had just completed it first hover test flt successfully and landed. A pwr loss was noted on the No. 3 helicopter and the test was terminated and the mooring mast called for. Prior to re-mooring a wind shift caused an uncommanded left turn which the pilot could not control with the flt controls. With a tailwind, no wheel brakes or gnd steering a takeoff was attempted. The 4 main landing gear which had no shimmy dampners started to shimmy. The four helicopters started to react to the shimmy with ground resonance. As the helistat finally lifted off, the four individual helicopters broke off and fell to the ground. One pilot received fatal injuries, 3 received serious injuries and one minor injuries. The helistat was destroyed. The prw loss on the no. 3 helicopter was traced to a missing throttle linkage correlation pin. Why the pin was missing was not determined.
The National Transportation Safety Board determines the probable cause(s) of this accident as follows:-
Throttle/power lever,linkage..disconnected
Rotorcraft flight control..inadequate
Acft/equip,inadequate design..manufacturer
Acft/equip,inadequate handling/perf capabilities..manufacturer
Contributing Factors
Landing gear,main gear..vibration
Rotor system..vibration
Landing gear,normal brake system..lack of
Landing gear,steering system..lack of
[ 27 August 2001: Message edited by: Cyclic Hotline ]
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Brian,
Not to take away from the excellent performance of the H-43, but to explain why it has it, the reason is the disk loading. The Huskie was layed out when heavy piston engines were needed so the power came at a steep empty weight. This made the designers thrifty with power, and the best way was to use big rotors that needed less power. Thus, the H-43, with a 48 foot rotor disk weighs in at about 9000 pounds. The piston engine was replaced by a turbine, which could develop the transmission rating up to high altitude, but just as inportantly, it weighs about 1/3 of the weight of the piston, so all that weight savings gets to become payload.
Another example is the S-55, which has a 53 foot rotor diameter for about 8600 pounds gross weight. The Black Hawk has the same sized disk for 24000 pounds!
The lift advantage of light disk loading is awesome. The power needs of the rotor are proportional to the square root of the disk loading, so a 6.5 pound per square foot rotor (Bell 412) needs about 40% more power than a 3 pound per square foot rotor (H-43). This means that for the same power, it lifts 40% more.
In other words, the efficiency of the H-43 is not because it is a synchropter but because it has a great big rotor!
The downside of the old machines is that they also beefed up hover performance by having skinny blades with low rotor solidity (ratio of blade area to disk area). With low solidity, the blades are near optimal lift to drag in a hover, so more weight can be lifted, but the downside is that the rotor stalls at slower speeds.
The Huskie has a max speed of only about 110 knots, if I recall correctly, which is part payment for that hover efficiency.
Not to take away from the excellent performance of the H-43, but to explain why it has it, the reason is the disk loading. The Huskie was layed out when heavy piston engines were needed so the power came at a steep empty weight. This made the designers thrifty with power, and the best way was to use big rotors that needed less power. Thus, the H-43, with a 48 foot rotor disk weighs in at about 9000 pounds. The piston engine was replaced by a turbine, which could develop the transmission rating up to high altitude, but just as inportantly, it weighs about 1/3 of the weight of the piston, so all that weight savings gets to become payload.
Another example is the S-55, which has a 53 foot rotor diameter for about 8600 pounds gross weight. The Black Hawk has the same sized disk for 24000 pounds!
The lift advantage of light disk loading is awesome. The power needs of the rotor are proportional to the square root of the disk loading, so a 6.5 pound per square foot rotor (Bell 412) needs about 40% more power than a 3 pound per square foot rotor (H-43). This means that for the same power, it lifts 40% more.
In other words, the efficiency of the H-43 is not because it is a synchropter but because it has a great big rotor!
The downside of the old machines is that they also beefed up hover performance by having skinny blades with low rotor solidity (ratio of blade area to disk area). With low solidity, the blades are near optimal lift to drag in a hover, so more weight can be lifted, but the downside is that the rotor stalls at slower speeds.
The Huskie has a max speed of only about 110 knots, if I recall correctly, which is part payment for that hover efficiency.
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Cyclic hotline,
Some background on the Helistat is that Frank Piasecki did little dynamic analysis of the big airframe, a factor which perhaps contributed to the mishap. The chief pilot he had during the development told me that virtually no computer analysis was done to study the low frequency modes of the structure, which is a big problem area on all larger machines (and a major contributer to the problems with the largest helicopter that ever flew, the V-12).
Some background on the Helistat is that Frank Piasecki did little dynamic analysis of the big airframe, a factor which perhaps contributed to the mishap. The chief pilot he had during the development told me that virtually no computer analysis was done to study the low frequency modes of the structure, which is a big problem area on all larger machines (and a major contributer to the problems with the largest helicopter that ever flew, the V-12).
Nick,
There was a published engineering report prior to the first flight, that predicted exactly what occurred.
I think it is also very revealing, as you note, that so many of these huge machines were constructed but were totally impractical and had no viable application - they simply weren't thought out thoroughly. Once it was flying, you were sometimes left with more problems to tackle than the initial design work itself!
Although I never saw this machine in real life, I do know a couple of people who did and they said that they were not surprised at the outcome just from looking at the way it was constructed.
The evolution of large helicopters was spectacular and rapid, considering the short period between the first production helicopters and some of the gargantuan models that followed. Of course, like all Aviation development, the lack of suitable powerplant's was really the controlling factor in all of these developments. The Sikorsky CH-37 (S56) was unbelievable in both complexity (and maintenance demands), but the very last of the large piston engine helicopters as they struggled through material and technological change, must have been one of the most exciting times ever in the helicopter business.
Piasecki Vertol were of course in the midst of this. During the transition period between piston and turbine engines, so huge boundaries were passed. I think that one of the most amazing looking helicopters ever produced came out at that time. Although not a success, the Piasecki YH-16 epitomises 1950's design, architecture and style. Not only does it look like something from a science-fiction (or Godzilla) movie, it clearly demonstrates the amazing resources and drive that was apparent in the post war aviation industry.
http://www.russian.ee/~star/vertigo/...ki_h-16-r.html
Not meaning to detract from Dave's original thread - amazing how these topics take on a life of their own!
There was a published engineering report prior to the first flight, that predicted exactly what occurred.
I think it is also very revealing, as you note, that so many of these huge machines were constructed but were totally impractical and had no viable application - they simply weren't thought out thoroughly. Once it was flying, you were sometimes left with more problems to tackle than the initial design work itself!
Although I never saw this machine in real life, I do know a couple of people who did and they said that they were not surprised at the outcome just from looking at the way it was constructed.
The evolution of large helicopters was spectacular and rapid, considering the short period between the first production helicopters and some of the gargantuan models that followed. Of course, like all Aviation development, the lack of suitable powerplant's was really the controlling factor in all of these developments. The Sikorsky CH-37 (S56) was unbelievable in both complexity (and maintenance demands)
, but the very last of the large piston engine helicopters as they struggled through material and technological change, must have been one of the most exciting times ever in the helicopter business.Piasecki Vertol were of course in the midst of this. During the transition period between piston and turbine engines, so huge boundaries were passed. I think that one of the most amazing looking helicopters ever produced came out at that time. Although not a success, the Piasecki YH-16 epitomises 1950's design, architecture and style. Not only does it look like something from a science-fiction (or Godzilla) movie, it clearly demonstrates the amazing resources and drive that was apparent in the post war aviation industry.
http://www.russian.ee/~star/vertigo/...ki_h-16-r.html
Not meaning to detract from Dave's original thread - amazing how these topics take on a life of their own!
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Dave Jackson,
Apologies to you, I misunderstood your real intent, I beleived you meant tandems.My hope was that your hope to start a controversy wouldn't end in slanging matches, I concur with Nick.
[ 27 August 2001: Message edited by: sling load ]
Apologies to you, I misunderstood your real intent, I beleived you meant tandems.My hope was that your hope to start a controversy wouldn't end in slanging matches, I concur with Nick.
[ 27 August 2001: Message edited by: sling load ]
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i would have thought the russian "shark" helicopter would have been the most efficient design.
should go faster because retreating blade stall being reduced by the opossing blade wake (less rotational flow) which would also help when hovering, but a stronger induced flow would be the downer.
i would think votex ring state would be less of a problem too. (less rotational flow) or do you think it would be worse? comments??
should go faster because retreating blade stall being reduced by the opossing blade wake (less rotational flow) which would also help when hovering, but a stronger induced flow would be the downer.
i would think votex ring state would be less of a problem too. (less rotational flow) or do you think it would be worse? comments??
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I think the russian shark design was pretty efficient in some regions of flight but not in all.
Big long bendy blades with not that much hinge offset.(compared to the ABC)
As forward speed increased flapping did likewise. Add some g forces to it and clearances got smaller. A low speed heavy lifter great but a high speed attack helicopter no.
A few years back I sat in a similar rotored aircraft during runup. It had a video camera setup that looked down one of the blades while it rotated. (The blade was fixed in the line of site and the horizon spun around)
The big worry was that these blades would meet each other inflight at the higher end of the envelope. Apparently that's the speculation on what happened to the russian general in the shark.
Big long bendy blades with not that much hinge offset.(compared to the ABC)
As forward speed increased flapping did likewise. Add some g forces to it and clearances got smaller. A low speed heavy lifter great but a high speed attack helicopter no.
A few years back I sat in a similar rotored aircraft during runup. It had a video camera setup that looked down one of the blades while it rotated. (The blade was fixed in the line of site and the horizon spun around)
The big worry was that these blades would meet each other inflight at the higher end of the envelope. Apparently that's the speculation on what happened to the russian general in the shark.
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I agree with tgrendl, the Shark KA-50 can't do much retreating blade stall magic, as the tip clearance problems this would induce are too much for it to handle. The ABC has very stiff blades to allow the retreating blade to get into deep stall without much motion.
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tgrendl'
Not to stay off topic, but a little trivia; and a regret.
It is my understanding that the ABC had a rotor separation of 30", and they set the minimum allowable tip clearance at 10".
Unfortunately, like the Russian helicopter, it appears that the first ABC also crashed because of blade-blade contact between the rotors.
Not to stay off topic, but a little trivia; and a regret.
It is my understanding that the ABC had a rotor separation of 30", and they set the minimum allowable tip clearance at 10".
Unfortunately, like the Russian helicopter, it appears that the first ABC also crashed because of blade-blade contact between the rotors.
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Dave Jackson,
The first ABC had a hard landing due to a combination of issues, none of which were at all associated with blade clearance. The aircraft basically ran out of longitudinal control due to very conservative rigging based on simulation data that was seriously in error.
To the best of my knowledge, blade clearance was monitored in flight test, and no close calls were ever recorded on either ABC demonstrator.
Two KA-50's have been lost so far due to blade contact, I am told. Perhaps this is due to the sporty envelope proposed for an attack helo as opposed to the relatively benign envelope of the ASW missions flown by other Kamovs.
The first ABC had a hard landing due to a combination of issues, none of which were at all associated with blade clearance. The aircraft basically ran out of longitudinal control due to very conservative rigging based on simulation data that was seriously in error.
To the best of my knowledge, blade clearance was monitored in flight test, and no close calls were ever recorded on either ABC demonstrator.
Two KA-50's have been lost so far due to blade contact, I am told. Perhaps this is due to the sporty envelope proposed for an attack helo as opposed to the relatively benign envelope of the ASW missions flown by other Kamovs.
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Dave,
Nick actually flew the ABC so I think he'd have better information than I do.
I believe part of how they solved the retreating blade stall/bending problem was with a huge hinge offset (25-30%?)and very stiff blades.
There's some other magic wrapped up in that aircraft that nick would know.
And I didn't know that it had inflight blade contact, thanks I guess and sorry several years too late.
tom
Nick actually flew the ABC so I think he'd have better information than I do.
I believe part of how they solved the retreating blade stall/bending problem was with a huge hinge offset (25-30%?)and very stiff blades.
There's some other magic wrapped up in that aircraft that nick would know.
And I didn't know that it had inflight blade contact, thanks I guess and sorry several years too late.
tom
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Dave,
Back to your intermeshing discussion,
Do you or does anyone know a valid way to model the drag effects at the combined rotor mast/ fuselage area?
I have a feeling that this region may be a "try it and see" area in your testing. I've tried thinking of ways that it might be done but have come up empty handed.
This could, of course, be due to my walnut sized brain.
Back to your intermeshing discussion,
Do you or does anyone know a valid way to model the drag effects at the combined rotor mast/ fuselage area?
I have a feeling that this region may be a "try it and see" area in your testing. I've tried thinking of ways that it might be done but have come up empty handed.
This could, of course, be due to my walnut sized brain.
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Nick,
Thanks for setting me straight about the first ABC. The information that I posted had been given to me in a telephone conversation with a retired executive in the helicopter industry, so I just assumed it was correct.
Sorry about that.
Thanks for setting me straight about the first ABC. The information that I posted had been given to me in a telephone conversation with a retired executive in the helicopter industry, so I just assumed it was correct.
Sorry about that.
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Dave,
A few people have pointed out that overlapping rotors (coaxials, intermeshing, tandem overlapping) lose some power from induced losses because of the increased induced flow. Let's talk numbers.
Since induced power losses are in the range of 60% of rotor power, with profile power taking up another 30%, the reasons for adding a second rotor need to be pretty good. Adding another rotor will increase profile power (more blade area being spun through the air), but more importantly, it will increase induced power loss--the overlap induced power loss will be up to 41% (100% overlap). Of course, an intermeshing rotor will have some separation (say 10% of rotor span) which means that the loss will be less than 41%--by my calculations approximately 33%. If you want to have a 25% span overlap then the overlap fraction is .68 and the loss in power is 23%, still quite substantial in my opinion. Add the .3*(difference in profile power) to .6*.23 (14%) and you probably have something like a 16-20% loss. This doesn't include the small (1-2%) loss due to the fact that the lift vectors are not vertical or the extra frontal and and vertical blockage of such a wide separation.
While it is true that you can get a smaller footprint and won't have to worry about dissymetry, you pay for it in power and controllability. I've never flown anything but conventional (tail rotor) helicopters, but from what I've heard the coaxials and intermeshing rotor helicopters leave something to be desired when it comes to yaw control, especially in low/no power conditions. Someone with experience please correct me if I'm wrong, but the tail rotor or fantail still seems to be the best in terms of yaw control.
As for a helicopter in everyone's driveway, I really doubt it. I don't think the lack of helicopter proliferation has much to do with simplicity of control. It's cost and insurance requirements. Why can't new pilots go out and fly turbines or get a job as a heli pilot? In the US at least, you can solo in 10 hours, get your PPL with 40 hours (less if you've got other ratings already), and have a comercial ticket in as much more (150 if you don't have any other time) and then wait until you've got 1000 hours before you can fly a turbine for hire. I really don't think that would change if everyone flew an intermeshing helicopter. Do the 1000 hour requirements of insurance companies reflect on the ability of relatively inexperienced pilots to keep a steady hover? I think it has much more to do with judgement, insight, and experience.
In any case, I'd love to see your toy if you go about developing one I just don't think there's anything that will have the effect on rotorcraft the model T had on automobiles. Good luck!
A few people have pointed out that overlapping rotors (coaxials, intermeshing, tandem overlapping) lose some power from induced losses because of the increased induced flow. Let's talk numbers.
Since induced power losses are in the range of 60% of rotor power, with profile power taking up another 30%, the reasons for adding a second rotor need to be pretty good. Adding another rotor will increase profile power (more blade area being spun through the air), but more importantly, it will increase induced power loss--the overlap induced power loss will be up to 41% (100% overlap). Of course, an intermeshing rotor will have some separation (say 10% of rotor span) which means that the loss will be less than 41%--by my calculations approximately 33%. If you want to have a 25% span overlap then the overlap fraction is .68 and the loss in power is 23%, still quite substantial in my opinion. Add the .3*(difference in profile power) to .6*.23 (14%) and you probably have something like a 16-20% loss. This doesn't include the small (1-2%) loss due to the fact that the lift vectors are not vertical or the extra frontal and and vertical blockage of such a wide separation.
While it is true that you can get a smaller footprint and won't have to worry about dissymetry, you pay for it in power and controllability. I've never flown anything but conventional (tail rotor) helicopters, but from what I've heard the coaxials and intermeshing rotor helicopters leave something to be desired when it comes to yaw control, especially in low/no power conditions. Someone with experience please correct me if I'm wrong, but the tail rotor or fantail still seems to be the best in terms of yaw control.
As for a helicopter in everyone's driveway, I really doubt it. I don't think the lack of helicopter proliferation has much to do with simplicity of control. It's cost and insurance requirements. Why can't new pilots go out and fly turbines or get a job as a heli pilot? In the US at least, you can solo in 10 hours, get your PPL with 40 hours (less if you've got other ratings already), and have a comercial ticket in as much more (150 if you don't have any other time) and then wait until you've got 1000 hours before you can fly a turbine for hire. I really don't think that would change if everyone flew an intermeshing helicopter. Do the 1000 hour requirements of insurance companies reflect on the ability of relatively inexperienced pilots to keep a steady hover? I think it has much more to do with judgement, insight, and experience.
In any case, I'd love to see your toy if you go about developing one
I just don't think there's anything that will have the effect on rotorcraft the model T had on automobiles. Good luck!