Forks in the Road
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From: Vancouver, BC, Canada
Forks in the Road
When a decision in the Past results in an unnatural road in the Present, on the way to the inevitable Future.
The following excerpt is from; 'Heelicopter : pioneering with Igor Sikorsky : based on a personal account'; by William E. Hunt.
Bill Hunt was the main design engineer for Igor Sikorsky and was responsible for most of Sikorsky's advancements in rotor design.
A yearend reflection on how much more advanced today's rotorcraft would be, if only the American rotorcraft industry had continued with the German adjacent configurations.
The following excerpt is from; 'Heelicopter : pioneering with Igor Sikorsky : based on a personal account'; by William E. Hunt.
Bill Hunt was the main design engineer for Igor Sikorsky and was responsible for most of Sikorsky's advancements in rotor design.
"The entirely unexpected and unfortunate delays suffered by the prime contractor, Platt-Le Page with its XR-1 ...... suddenly thrust the Sikorsky XR-4, YR-4, R-4 into the entirely unplanned limelight."
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From: Beyond the black stump!
If they were that fabulous, how come no-one has resurrected them again? 
You seem to be the sole fan obsessing over them. Maybe you should call Eurocopter and ask them why they haven't bothered starting production again.
You seem to be the sole fan obsessing over them. Maybe you should call Eurocopter and ask them why they haven't bothered starting production again.
Thread Starter
Joined: Apr 2003
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From: Vancouver, BC, Canada
Cyclic Hotline,
Perhaps William Hunt had the answer for that also when he said;
Perhaps William Hunt had the answer for that also when he said;
"What remains so baffling to me is how consistently, when both time and resources are available, the stubborn resistance to change prevails."
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From: Australia
One can lament and feel the tug of the nostalgic heart strings when we dream of some old classics, the;
B47
DH82
DC3
are all reverent loves of our past life…!!
What is difficult to accept is that some interpreter has not resurrected their make over, so we can all drawl over and enjoy some of the true classics.
Lets just leave $$$$ aside for one passing moment.
B47
DH82
DC3
are all reverent loves of our past life…!!
What is difficult to accept is that some interpreter has not resurrected their make over, so we can all drawl over and enjoy some of the true classics.
Lets just leave $$$$ aside for one passing moment.
Joined: Jul 2003
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From: Port Townsend,WA. USA
Dave,
You could build a RC model intermesher and another standard configuration model of same size and motor. See which lifts the most. Or which is harder to fly. Or harder to build, etc. etc.
You could build a RC model intermesher and another standard configuration model of same size and motor. See which lifts the most. Or which is harder to fly. Or harder to build, etc. etc.
Thread Starter
Joined: Apr 2003
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From: Vancouver, BC, Canada
slowrotor,
A friend is currently building and comparing different configurations, with very small RC helicopters. However, he said that it is difficult to compare at these small sizes, partially due to inconsistency in the small components. His current project is a coaxial with one blade per rotor.
Here is a general comparison between an intermeshing and a single rotor configuration.
________________
The comments by William Hunt came from pages 194-196 of his book. These three pages cover his invention for an autocollective (rotor governor). If you think that the information might be of interest to you, in your search for a safer rotorcraft, just send me an email at [email protected] and I will reply with the attachments.
The technical information and the remarks on these three pages were so interesting that the whole book is now on order.
A friend is currently building and comparing different configurations, with very small RC helicopters. However, he said that it is difficult to compare at these small sizes, partially due to inconsistency in the small components. His current project is a coaxial with one blade per rotor.
Here is a general comparison between an intermeshing and a single rotor configuration.
________________
The comments by William Hunt came from pages 194-196 of his book. These three pages cover his invention for an autocollective (rotor governor). If you think that the information might be of interest to you, in your search for a safer rotorcraft, just send me an email at [email protected] and I will reply with the attachments.
The technical information and the remarks on these three pages were so interesting that the whole book is now on order.
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From: Port Townsend,WA. USA
Dave,
I have decided that sport helos are too risky for most pilots that usually fly about 20-50hrs per year. So my focus will be on a compound aircraft, half airplane and half helo, but more like an airplane and therefore easier to fly.
It will most likely have a simple fixed pitch proprotor(s). And lift control would be with variable rpm. Rpm control is not good for a helo, but should work for a vstol that will make very short running takeoffs and landings.
I have decided that sport helos are too risky for most pilots that usually fly about 20-50hrs per year. So my focus will be on a compound aircraft, half airplane and half helo, but more like an airplane and therefore easier to fly.
It will most likely have a simple fixed pitch proprotor(s). And lift control would be with variable rpm. Rpm control is not good for a helo, but should work for a vstol that will make very short running takeoffs and landings.
Thread Starter
Joined: Apr 2003
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From: Vancouver, BC, Canada
Aw! Don't give up on rotorcraft so easily. Greater difficulties require greater efforts, but a success provides greater rewards.
There is no need to reply, and perhaps this post is an imposition into your own concepts. OK that's enough politness.
When contemplating "that sport helos are too risky for most pilots" and airplanes are " easier to fly" consider the following.
Lateral Symmetry:
No tail rotor: The Kaman was used for preliminary training of helicopter pilots but was then abandoned because it was too easy. The requirement for the use of pedals should be comparable to the use of pedals on a fixed wing. In fact, crosswind landings and takeoffs may be easier in a rotorcraft with twin main rotors.
Reduced Cross-couplings: The adjacent configurations and the coaxial configuration will reduce the cross-couplings and provide a laterally symmetry similar to that of airplanes.
Auto Rotor-Governor:
No Collective: Just like a fixed wing. A torque-pitch governor, controlled by the throttle, will generate instant lift from the rotor when the engine power is increased. The increasing engine power will then maintain the rotational inertia in the two rotors.
Cyclic Response: High rotor rigidity will significantly reduce the delay between pilot input and aircraft response. In fact, it should be easy to get a faster response rate than that of an airplane.
Autorotation: The torque-pitch governor will automatically put the craft into autorotation. Unlike today's helicopter's, this arraignment requires the pilot to do something to STOP the rotors from going into autorotation.
Loss of Power:
High inertia blades, a collective that can 'squeeze' the remaining inertia out of the rotors, and/or a separate device that provides short-term variable torque control during flare.
In addition, the helicopter should have a greater opportunity to select a better landing site than an airplane.
I strongly believe that it is possible to produce a helicopter that is actually safer than an airplane. In this situation the expression 'pilot error' may really become relevant, because the pilot of this rotorcraft will be able to, and perhaps want to, place himself in closer proximity to the ground then he could in an airplane.
There is no need to reply, and perhaps this post is an imposition into your own concepts. OK that's enough politness.
When contemplating "that sport helos are too risky for most pilots" and airplanes are " easier to fly" consider the following.
Lateral Symmetry:
No tail rotor: The Kaman was used for preliminary training of helicopter pilots but was then abandoned because it was too easy. The requirement for the use of pedals should be comparable to the use of pedals on a fixed wing. In fact, crosswind landings and takeoffs may be easier in a rotorcraft with twin main rotors.
Reduced Cross-couplings: The adjacent configurations and the coaxial configuration will reduce the cross-couplings and provide a laterally symmetry similar to that of airplanes.
Auto Rotor-Governor:
No Collective: Just like a fixed wing. A torque-pitch governor, controlled by the throttle, will generate instant lift from the rotor when the engine power is increased. The increasing engine power will then maintain the rotational inertia in the two rotors.
Cyclic Response: High rotor rigidity will significantly reduce the delay between pilot input and aircraft response. In fact, it should be easy to get a faster response rate than that of an airplane.
Autorotation: The torque-pitch governor will automatically put the craft into autorotation. Unlike today's helicopter's, this arraignment requires the pilot to do something to STOP the rotors from going into autorotation.
Loss of Power:
High inertia blades, a collective that can 'squeeze' the remaining inertia out of the rotors, and/or a separate device that provides short-term variable torque control during flare.
In addition, the helicopter should have a greater opportunity to select a better landing site than an airplane.
I strongly believe that it is possible to produce a helicopter that is actually safer than an airplane. In this situation the expression 'pilot error' may really become relevant, because the pilot of this rotorcraft will be able to, and perhaps want to, place himself in closer proximity to the ground then he could in an airplane.
Joined: Jul 2003
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From: Port Townsend,WA. USA
Dave,
I like your idea for automatic rotor control. A sport pilot would need that.
But I think the autorotational ability of any helicopter is inferior at low altitude, compared with a low wing loading ultralight type airplane. An ultralight can fly at 25mph at 50ft agl and glide in with a low impact velocity, in the case of complete power loss. A helicopter pilot would not fare as well, even with an instant automatic autorotation governor.
Of course, Nick would say here " dont worry about a miniscule chance of engine failure, you are more likely to experience HTG (hit the ground) from pilot error.
Thats the point, helos can bite in many ways.
I think my chances of actual flight in a machine of my design is more likely in a fixed wing with powered lift.
Nobody is working from this angle because vtol and vstol design has always been for military missions not sport. It is a huge difference in mission.
I am not sure what market you are designing for Dave. Is it sport or military/commercial?
I like your idea for automatic rotor control. A sport pilot would need that.
But I think the autorotational ability of any helicopter is inferior at low altitude, compared with a low wing loading ultralight type airplane. An ultralight can fly at 25mph at 50ft agl and glide in with a low impact velocity, in the case of complete power loss. A helicopter pilot would not fare as well, even with an instant automatic autorotation governor.
Of course, Nick would say here " dont worry about a miniscule chance of engine failure, you are more likely to experience HTG (hit the ground) from pilot error.
Thats the point, helos can bite in many ways.
I think my chances of actual flight in a machine of my design is more likely in a fixed wing with powered lift.
Nobody is working from this angle because vtol and vstol design has always been for military missions not sport. It is a huge difference in mission.
I am not sure what market you are designing for Dave. Is it sport or military/commercial?
Thread Starter
Joined: Apr 2003
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From: Vancouver, BC, Canada
Potential problem ~ Potential solution
OK, how about eliminating total power failure.
One solution is the incorporation of two engines.
Also, a simplistic reserve fuel system for two engines
Any or all.
My thinking process has always been one of a top down approach. It is a reiterative process consisting of dreaming up the wildest concepts and then working down toward the detail levels, until an insurmountable obstacle is met.
The initial objective was similar to yours; that of building a safe recreational Ultralight helicopter, which could eventually be mass-produced. The SynchroLite was detailed to the point of starting construction. However, it became apparent that it would probably never be marketable. This is due to the fact that it's cost would be more than potential customers would be able, or willing, to pay. If interested, this is an expansion of the thinking on this subject.
My interest then was redirected toward rotorcraft in general. What are the shortcomings of current rotorcraft and what might be done to minimize these deficiencies? IMHO, the features embedded in the intermeshing UniCopter appear to be the answer for light rotorcraft, which are intended to perform in-flight work. The interleaving configuration is a similar solution for medium and heavy VTOL transport activities.
Whatever comes about; active blade twist is mandatory for significant rotor improvements, and this is the current project.
OK, how about eliminating total power failure.
One solution is the incorporation of two engines.
Also, a simplistic reserve fuel system for two engines
I am not sure what market you are designing for Dave. Is it sport or military/commercial?
My thinking process has always been one of a top down approach. It is a reiterative process consisting of dreaming up the wildest concepts and then working down toward the detail levels, until an insurmountable obstacle is met.
The initial objective was similar to yours; that of building a safe recreational Ultralight helicopter, which could eventually be mass-produced. The SynchroLite was detailed to the point of starting construction. However, it became apparent that it would probably never be marketable. This is due to the fact that it's cost would be more than potential customers would be able, or willing, to pay. If interested, this is an expansion of the thinking on this subject.
My interest then was redirected toward rotorcraft in general. What are the shortcomings of current rotorcraft and what might be done to minimize these deficiencies? IMHO, the features embedded in the intermeshing UniCopter appear to be the answer for light rotorcraft, which are intended to perform in-flight work. The interleaving configuration is a similar solution for medium and heavy VTOL transport activities.
Whatever comes about; active blade twist is mandatory for significant rotor improvements, and this is the current project.
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From: Cambridgeshire, UK
Dave,
I agree with your objectives, and the way you are tackling them (actually seeing hardware helps a lot
). I think your conclusions about general heli layout are well reasoned. However, the market for a product does not usually care how that product works as long as it does. The key for reliability, hence lower operating costs, is always simplicicty.
For this reason i have always felt that counterrotation (in all it's forms) becomes justified only as speed affects retreating blade performance. Flyability is solvable with a simple gyro in the control system of a rigid rotor - quite why this has never come to market in light helis is anyones guess (eg Lockheed CL475). I imagine that when a well trained pilot can manouvre a teetering head like Dennis Kenyon can, there is little perceived requirement.
Rather than trying to convince us all off the merits of counterrotation, and the semantics of which system when, i suggest a different line. You have convinced me that active blade twist is the next big step, but have not addressed the doubts. To my mind, the biggest is the control system required. I would like to see CAD layup of the rotor hub that allows ABT to function reliably. From the view point of cost, i am not convinced about high speed active servos for a light heli - if i'm wrong i'm wrong. I would imagine that the simplest is twin swash plates, perhaps with low speed servo trim for airspeed input.
I think the real future of light helis depends on engine technology (thanks for pointing this out, NL). I am beginning a design study on diesels adapted specifically for aeronautical usage, to scope out the potential for development. The objectives would be fast combustion (for high RPM) and high dependancy on turbo charging for high torque/displacement. From the design study the best i could ever hope for is (say) Cummins to show interest, but it would be an outcome...
Mart
I agree with your objectives, and the way you are tackling them (actually seeing hardware helps a lot
). I think your conclusions about general heli layout are well reasoned. However, the market for a product does not usually care how that product works as long as it does. The key for reliability, hence lower operating costs, is always simplicicty.For this reason i have always felt that counterrotation (in all it's forms) becomes justified only as speed affects retreating blade performance. Flyability is solvable with a simple gyro in the control system of a rigid rotor - quite why this has never come to market in light helis is anyones guess (eg Lockheed CL475). I imagine that when a well trained pilot can manouvre a teetering head like Dennis Kenyon can, there is little perceived requirement.
Rather than trying to convince us all off the merits of counterrotation, and the semantics of which system when, i suggest a different line. You have convinced me that active blade twist is the next big step, but have not addressed the doubts. To my mind, the biggest is the control system required. I would like to see CAD layup of the rotor hub that allows ABT to function reliably. From the view point of cost, i am not convinced about high speed active servos for a light heli - if i'm wrong i'm wrong. I would imagine that the simplest is twin swash plates, perhaps with low speed servo trim for airspeed input.
I think the real future of light helis depends on engine technology (thanks for pointing this out, NL). I am beginning a design study on diesels adapted specifically for aeronautical usage, to scope out the potential for development. The objectives would be fast combustion (for high RPM) and high dependancy on turbo charging for high torque/displacement. From the design study the best i could ever hope for is (say) Cummins to show interest, but it would be an outcome...
Mart
Last edited by Graviman; 27th December 2005 at 12:08.
Thread Starter
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From: Vancouver, BC, Canada
Mart,
This is the current work on the control system for active blade twist.
I think that the future of all helis depends on improving the Lift/Drag ratio.
Engine advancements will only come from outside of the rotorcraft industry.
IMNSHO, the rotorcraft industry should focus on the essence of the craft ~ the rotor.
Dave
To my mind, the biggest [next step] is the control system required
I think the real future of light helis depends on engine technology
Engine advancements will only come from outside of the rotorcraft industry.
IMNSHO, the rotorcraft industry should focus on the essence of the craft ~ the rotor.
Dave
Joined: Jul 2003
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From: Port Townsend,WA. USA
Dave,
No need to answer if your busy.... but since you brought up the subject of improving the lift drag ratio in your last post....
Why is a helo rotor so much lower in L/D than a fixed wing? In your opinion.
I assume the huge difference in rotational speed along the blade averages out to a lower L/D.
Just a thought...
Maybe multiple smaller intermeshing rotors (like 8 or 10 rotors for instance) would give a better L/D because the downwash would be more uniform. And the entire disc area would be pumping air down, not just the outer part of the disc as in a conventional rotor. Just a thought, probably whacky. Maybe that is partly why you like intermeshers!
No need to answer if your busy.... but since you brought up the subject of improving the lift drag ratio in your last post....
Why is a helo rotor so much lower in L/D than a fixed wing? In your opinion.
I assume the huge difference in rotational speed along the blade averages out to a lower L/D.
Just a thought...
Maybe multiple smaller intermeshing rotors (like 8 or 10 rotors for instance) would give a better L/D because the downwash would be more uniform. And the entire disc area would be pumping air down, not just the outer part of the disc as in a conventional rotor. Just a thought, probably whacky. Maybe that is partly why you like intermeshers!
Joined: Sep 2005
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From: US
Dave, I have 'known' you for a long time now, ever since rec.aviation.rotorcraft was very active. The beginning days of the Mini500 and all that. When will I get to see your Syncopter fly? You have great ideas, but if you wait much longer, some of us will not pass our medical and wont be able to fly your copter 
Da Monk
Da Monk
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From: KPHL
The L/D curve can be considered a sum of many individual effects. The effect that is predominant at low speed is induced drag. It increases as the speed squared decreases.
The effect that is predominant for helicopters at higher speeds is profile drag. It increases as the speed increases.
If you create a machine that is designed to operate in the low speed environment and to carry a cargo volume, then it will have a relatively high cross sectional area, leading to relatively high profile drag. This will tend to shift the max L/D point towards lower airspeeds.
A good test of this (which may just prove me wrong) is to look at helicopters that aren't designed for cargo volume such as Comanche or a clean AH-1W. Does anyone have related numbers for these machines?
Matthew.
The effect that is predominant for helicopters at higher speeds is profile drag. It increases as the speed increases.
If you create a machine that is designed to operate in the low speed environment and to carry a cargo volume, then it will have a relatively high cross sectional area, leading to relatively high profile drag. This will tend to shift the max L/D point towards lower airspeeds.
A good test of this (which may just prove me wrong) is to look at helicopters that aren't designed for cargo volume such as Comanche or a clean AH-1W. Does anyone have related numbers for these machines?
Matthew.
Thread Starter
Joined: Apr 2003
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From: Vancouver, BC, Canada
Slowrotor,
From ~ Prouty, Rotor & Wing Jan 99
"The most efficient angle of attack for an airfoil is where its lift-to-drag ratio is the highest. For most rotor airfoils, this angle is in the neighborhood of 8º.
This is part of the explanation of why a helicopter can never be as efficient as an airplane. An airplane designer can arrange things so that the entire wing is flying near the optimum angle of attack at cruise speed. The other part of the story is that we burden our aircraft with rotor masts and hubs-aerodynamically dirty things not imposed on airplanes. The overall airplane lift-to-drag ratio can be 10 to 30, depending on the configuration, whereas the maximum a helicopter can do is 4 to 6.
As you and Mathew have mentioned, the primary reasons are;
~ the different airspeeds at the different locations [azimuth & radius] about the rotor disk.
~ different angles of attack at these different locations.
Few of these locations are optimized for hover, or for cruse, or for the in-between.
This is why the ability to vary the pitch of the rotor blade at many unique azimuths [higher harmonic control etc.] and many unique radii [active blade twist] is so important to the future of rotorcraft.
TheMonk;
Well at least 'time flies'.
The SynchroLite will probably never be built, at least not by me.
The above subject represents the most productive advancement in rotorcraft IMO, and I am currently building the CNC machine to produce composite blades with active twist control.
Dave
Edited to change 'pitch' to 'twist'.
From ~ Prouty, Rotor & Wing Jan 99
"The most efficient angle of attack for an airfoil is where its lift-to-drag ratio is the highest. For most rotor airfoils, this angle is in the neighborhood of 8º.
This is part of the explanation of why a helicopter can never be as efficient as an airplane. An airplane designer can arrange things so that the entire wing is flying near the optimum angle of attack at cruise speed. The other part of the story is that we burden our aircraft with rotor masts and hubs-aerodynamically dirty things not imposed on airplanes. The overall airplane lift-to-drag ratio can be 10 to 30, depending on the configuration, whereas the maximum a helicopter can do is 4 to 6.
As you and Mathew have mentioned, the primary reasons are;
~ the different airspeeds at the different locations [azimuth & radius] about the rotor disk.
~ different angles of attack at these different locations.
Few of these locations are optimized for hover, or for cruse, or for the in-between.
This is why the ability to vary the pitch of the rotor blade at many unique azimuths [higher harmonic control etc.] and many unique radii [active blade twist] is so important to the future of rotorcraft.
TheMonk;
Well at least 'time flies'.
The SynchroLite will probably never be built, at least not by me. The above subject represents the most productive advancement in rotorcraft IMO, and I am currently building the CNC machine to produce composite blades with active twist control.
Dave
Edited to change 'pitch' to 'twist'.
Last edited by Dave_Jackson; 29th December 2005 at 19:19.
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From: Port Townsend,WA. USA
Dave,
I think you are serving the future rotorcraft builders by providing ideas, facts and inspiration. Keep it up. Perhaps Monk has not noticed that very few if any new helocraft are designed and built by individuals on this planet.
Back to L/D.
I am aware of Proutys statement about L/D. But I notice in Proutys book, he offers very little consideration for rotor tip speed, in general, anywhere in his book. I think the high tip speed is a major cause of rotor ineffiency. Even at the the most efficient angle of attack.
This is based on my experience as a motorglider owner. A glider has a much lower L/D at high speed. My motorglider has about 25 to 1 L/D at 62kt (best glide speed) and about 12 to 1 L/D at 90knots. It would have a very poor glide at 200kts, which is the average rotor speed of most helos.
slowrotor
I think you are serving the future rotorcraft builders by providing ideas, facts and inspiration. Keep it up. Perhaps Monk has not noticed that very few if any new helocraft are designed and built by individuals on this planet.
Back to L/D.
I am aware of Proutys statement about L/D. But I notice in Proutys book, he offers very little consideration for rotor tip speed, in general, anywhere in his book. I think the high tip speed is a major cause of rotor ineffiency. Even at the the most efficient angle of attack.
This is based on my experience as a motorglider owner. A glider has a much lower L/D at high speed. My motorglider has about 25 to 1 L/D at 62kt (best glide speed) and about 12 to 1 L/D at 90knots. It would have a very poor glide at 200kts, which is the average rotor speed of most helos.
slowrotor
Joined: Apr 2003
Posts: 3,012
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From: USA
slowrotor, that is because your glider is designed to climb at 80 so it can be maneuvered over a thermal at that speed/radius of turn. If you skinny down the wings and cause the best L/D speed to rise, you can get good glide at higher speed. It won't be as good because the parasite drag of the fuselage and wings will rise with speed, but the peak L/D will be at higher speed.
The vast list of power losses in a helo includes the optimum blade angle of attack, but the list is far longer and includes many aerodynamic and mechanical losses and inefficiencies that airplanes laugh at. Concentrating on the blade angle makes Dave's wonder-configuration seem better, but in truth, there are dozens more issues to be delt with if one wants a hovering craft to have the L/D of an airplane.
Were there a magic button, it would have been pressed by now!
The vast list of power losses in a helo includes the optimum blade angle of attack, but the list is far longer and includes many aerodynamic and mechanical losses and inefficiencies that airplanes laugh at. Concentrating on the blade angle makes Dave's wonder-configuration seem better, but in truth, there are dozens more issues to be delt with if one wants a hovering craft to have the L/D of an airplane.
Were there a magic button, it would have been pressed by now!
Joined: Jul 2003
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From: Port Townsend,WA. USA
Nick,
I see your point. Indeed most jetliners and business jets have about 20 to 1 L/D.
Yes, that makes jets pretty efficient at their design speed where speed at any cost is the goal. For personal craft where speed is not important, the goal is to fly with low cost, low power engines.
Actually, to be precise, my glider needs a low minimum sink rate in a thermal. L/D is not a factor in a thermal. So for a helicopter, it might be better for Dave to look at minimum sink rather than L/D. Personal aircraft that fly with low power usually have a low sink rate as well.
Minimum sink speed is just a bit above stall speed for a glider.
I see your point. Indeed most jetliners and business jets have about 20 to 1 L/D.
Yes, that makes jets pretty efficient at their design speed where speed at any cost is the goal. For personal craft where speed is not important, the goal is to fly with low cost, low power engines.
Actually, to be precise, my glider needs a low minimum sink rate in a thermal. L/D is not a factor in a thermal. So for a helicopter, it might be better for Dave to look at minimum sink rather than L/D. Personal aircraft that fly with low power usually have a low sink rate as well.
Minimum sink speed is just a bit above stall speed for a glider.