Ukrainian 2-seat helicopter
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Nice site, Dave! That is a beautiful piece of engineering. Simple, rugged, and well designed for it's purpose. I've only had a cursory glance at the Technical Detail so far (will post more, once read). The combination of removable articulated blades has to be a winner. Wonder how it handles? 
Certainly looks like they've done all their homework properly too: Investigate the concept then prototype. Develope the prototype then produce. Refine the production then profit.
You could do far worse than basing your concepts on this machine. Identify the weaknesses then improve...
Mart
BTW regarding heli design: if "Symmetry is safer" then why is the steering of your car offset to the drivers side?
Originally Posted by From Site
Auto CAD, NASTRAN, Mechanical Desktop, Fluent, X-foil and other integrated packages.
You could do far worse than basing your concepts on this machine. Identify the weaknesses then improve...
Mart
BTW regarding heli design: if "Symmetry is safer" then why is the steering of your car offset to the drivers side?
Last edited by Graviman; 24th Mar 2006 at 21:43.
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Originally Posted by Graviman
BTW regarding heli design: if "Symmetry is safer" then why is the steering of your car offset to the drivers side?
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Off topic, but ...........
The other thread is a provocative joke, however;
Mart,
........... by eliminating lateral aerodynamic dissymmetry.
ppheli,
Perhaps the slight curve in the fuselage is an aerodynamic fix for the soon to be slighted tail-rotor.
Mart,
Identify the weaknesses then improve...
ppheli,
Perhaps the slight curve in the fuselage is an aerodynamic fix for the soon to be slighted tail-rotor.
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Dave Jackson
Yes Dave, a provocative joke, maybe only a matter of time before you get your weights tested by some our leading femme fatales.
It is a pity the flight demo didn’t have some symmetrical nodes to it, or just one or two balanced and flowing flight lines - to portray it in much better light, as another invention of beauty to us rotory nuts - however— unlike the other--;
It does present the statistics with full body detail and its T/R – M/R symmentry looks A1.
It talks about best operating RPM with no asymmetric activity, despite violent handling inputs.
It provides a good set of performance notes but lacks, as in the other, any discussion on tensile strength of the nodal points at differing periodic vibrations levels.
That was a bit unfair on Frank at least he tells you the vibration periods when things fly to pieces.
It describes a low inertia rotor, the best approach ratio in autorotation and how fast it goes down.
Then there is the Y shaped torsional plates, very flexible in the up and down mode, being compared with feeler gauges
Sound effects as well with a delightful thrumbing noise and some talk of belts, but I wont go there!!
So Dave, will you lead with the aces sport, or fold and abort?
It is a pity the flight demo didn’t have some symmetrical nodes to it, or just one or two balanced and flowing flight lines - to portray it in much better light, as another invention of beauty to us rotory nuts - however— unlike the other--;
It does present the statistics with full body detail and its T/R – M/R symmentry looks A1.
It talks about best operating RPM with no asymmetric activity, despite violent handling inputs.
It provides a good set of performance notes but lacks, as in the other, any discussion on tensile strength of the nodal points at differing periodic vibrations levels.
That was a bit unfair on Frank at least he tells you the vibration periods when things fly to pieces.
It describes a low inertia rotor, the best approach ratio in autorotation and how fast it goes down.
Then there is the Y shaped torsional plates, very flexible in the up and down mode, being compared with feeler gauges
Sound effects as well with a delightful thrumbing noise and some talk of belts, but I wont go there!!
So Dave, will you lead with the aces sport, or fold and abort?
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Here's a Sth African site for the loverly looking machine, more info than the manufacturer's
http://www.aerokopter.co.za/
TV
http://www.aerokopter.co.za/
TV
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I've had a descent read now, and seen the demo flight. Wowsers, what a machine! I suspect all that beautiful machining from billet is paid for in part by the currency exchange rate. Why the copper coated spiral bevel gears? G/box lub failure fail safe?
Clearly this machine does not suffer any handling difficulties...
The only real reason i can see for counterrotation is to avoid retreating tip stall. Symmetry does reduces interference effects, but coaxials seem to work fine. Differential pitch will, however, never offer tail rotor levels of authority.
The only way to improve stability in (for example) this helicopter would be a gyro as part of the control system. Basically pilot would fly the gyro, and gyro would fly the helicopter - thus forcing roll/pitch rate with cyclic displacement. By referencing the gyro, helicopter would become extremely stable (including hands off). By controlling the gyro directly, pilot would have absolutely undiminished authority over manouvres. Newbies would take an immediate shine, but i suspect experienced pilots would critisice the system (wondering why everyone wasn't born with heli pilot reflexes - similar criticism was leveled at the Lockheed CL475).
I agree with getting the fundamental aerodynamics right, but that really is not the problem with heli stability and control. The real thrust of aerodynamic development should be pointed squarely at machine efficiency, which you have recognised with active blade twist. In the face of overwhelming evidence (and personal testimony from the former chief test pilot of Sikorsky helicopters) only a very obstinate engineer would not concede that his understanding of the problem might be biased by personal preference.
With the evidence of flight test data for lateral symmetry hands-off stability in hover i will willingly concede that my understanding might be biased...
Mart
Clearly this machine does not suffer any handling difficulties...
Originally Posted by Dave Jackson
...by eliminating lateral aerodynamic dissymmetry.
The only way to improve stability in (for example) this helicopter would be a gyro as part of the control system. Basically pilot would fly the gyro, and gyro would fly the helicopter - thus forcing roll/pitch rate with cyclic displacement. By referencing the gyro, helicopter would become extremely stable (including hands off). By controlling the gyro directly, pilot would have absolutely undiminished authority over manouvres. Newbies would take an immediate shine, but i suspect experienced pilots would critisice the system (wondering why everyone wasn't born with heli pilot reflexes - similar criticism was leveled at the Lockheed CL475).
I agree with getting the fundamental aerodynamics right, but that really is not the problem with heli stability and control. The real thrust of aerodynamic development should be pointed squarely at machine efficiency, which you have recognised with active blade twist. In the face of overwhelming evidence (and personal testimony from the former chief test pilot of Sikorsky helicopters) only a very obstinate engineer would not concede that his understanding of the problem might be biased by personal preference.
With the evidence of flight test data for lateral symmetry hands-off stability in hover i will willingly concede that my understanding might be biased...
Mart
Last edited by Graviman; 25th Mar 2006 at 20:51.
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Mart
If you agree that dihedral provides lateral static stability for fixed-wing aircraft,
~ and ~
If you agree that the rotors of an intermeshing rotorcraft can have rigidity approaching that of a wing ['Absolutely' Rigid Rotors],
~and ~
If you agree that during hover and slower forward flight there is lateral symmetry of thrust across each rotor. [No Advancing Blade Concept utilization during slow flight]
Then you must agree with the following.
The sketch on the link
http://www.unicopter.com/UniCopter_S...eral_Stability
shows that even though the two rotors are tilted outwards the craft has a dihedral of 3-4-degrees (the red lines) during slower flight. This is because the rotors have 4-degree precones.
As the craft approaches cruise speed and ABC takes effect the dihedral will disappear.
First the theoretical data, then the flight-test data. Do you find fault with the above theory????
Dave
If you agree that dihedral provides lateral static stability for fixed-wing aircraft,
~ and ~
If you agree that the rotors of an intermeshing rotorcraft can have rigidity approaching that of a wing ['Absolutely' Rigid Rotors],
~and ~
If you agree that during hover and slower forward flight there is lateral symmetry of thrust across each rotor. [No Advancing Blade Concept utilization during slow flight]
Then you must agree with the following.
The sketch on the link
http://www.unicopter.com/UniCopter_S...eral_Stability
shows that even though the two rotors are tilted outwards the craft has a dihedral of 3-4-degrees (the red lines) during slower flight. This is because the rotors have 4-degree precones.
As the craft approaches cruise speed and ABC takes effect the dihedral will disappear.
With the evidence of flight test data for lateral symmetry hands-off stability in hover i will willingly concede .....
Dave
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Dave,
The theory is quite sound. With a rigidly centred cyclic it is possible to design for statically stable hover. The point i am trying to make is that problem with helicopter control systems is that for small/fast inputs the pilot affects pitch/roll acceleration not velocity. Larger/longer inputs will briefly control pitch/roll velocity until airspeed changes require the displacement trim with the resultant movement range. I am willing to concede that some aerodynamic tuning is possible (it works on fixed wings), but i do not believe it will cure handling complexity completely for helicopters. This means that the pilot is working very hard to figure out where the centre is, and to keep the cyclic there - naturally experience does help.
I am suggesting a gyro system, which on (for example) the Aerocopter would package neatly into the swash plate mechanism, to modify the helicopter dynamic response. The original mechanical Lockheed mechanism was self centreing, and allowed direct pitch/roll rate control with cyclic displacement. It was actually more responsive than a GA fixed wing.
Clearly the experienced demo pilot had no problem throwing the machine arround, on a clear day with a strong visual horizon. The machine had a similar head concept to the Apache Longbow and Black Shark helicopters, so i'm not suprised at the fast response to pitch/roll torque. I would be interested to know how large his cyclic inputs actually were for such fast pitch/roll rates. I suspect that many moons ago, even he had fun&games trying to keep a heli in a stationary hover.
Well, yes and no. For general aviation hands off static stability is a good thing. For an aerobatic machine the pilot doesn't want the static stability to fight his every manouvre. This is why FBW came in, which (despite the clever post Apollo computing systems) is really just a way of having the gyro fly the aircraft with the pilot flying the gyro.
Like i say, with the evidence of flight test data proving hands off hover in a symmetrical machine i will concede (i'm just a dumb engineer, trying to understand a system). Perhaps i should qualify that the machine should have "easy" flight characteristics (thus ruling out various teetering schemes from Bell and Hiller). This last point is more difficult to quantify, but linear undelayed pitch/roll rate dependence on cyclic position is not a bad start - it is how FBW machines end up.
Wasn't there a RC heli based on your symmetrical concepts?
Mart
The theory is quite sound. With a rigidly centred cyclic it is possible to design for statically stable hover. The point i am trying to make is that problem with helicopter control systems is that for small/fast inputs the pilot affects pitch/roll acceleration not velocity. Larger/longer inputs will briefly control pitch/roll velocity until airspeed changes require the displacement trim with the resultant movement range. I am willing to concede that some aerodynamic tuning is possible (it works on fixed wings), but i do not believe it will cure handling complexity completely for helicopters. This means that the pilot is working very hard to figure out where the centre is, and to keep the cyclic there - naturally experience does help.
I am suggesting a gyro system, which on (for example) the Aerocopter would package neatly into the swash plate mechanism, to modify the helicopter dynamic response. The original mechanical Lockheed mechanism was self centreing, and allowed direct pitch/roll rate control with cyclic displacement. It was actually more responsive than a GA fixed wing.
Clearly the experienced demo pilot had no problem throwing the machine arround, on a clear day with a strong visual horizon. The machine had a similar head concept to the Apache Longbow and Black Shark helicopters, so i'm not suprised at the fast response to pitch/roll torque. I would be interested to know how large his cyclic inputs actually were for such fast pitch/roll rates. I suspect that many moons ago, even he had fun&games trying to keep a heli in a stationary hover.
Originally Posted by Dave Jackson's web page
What is desired is to have the fuselage/empennage to be, constantly and without any movable controlling surface, aerodynamic attempting to hold the craft in the upright position about the X (roll) axis.
Like i say, with the evidence of flight test data proving hands off hover in a symmetrical machine i will concede (i'm just a dumb engineer, trying to understand a system). Perhaps i should qualify that the machine should have "easy" flight characteristics (thus ruling out various teetering schemes from Bell and Hiller). This last point is more difficult to quantify, but linear undelayed pitch/roll rate dependence on cyclic position is not a bad start - it is how FBW machines end up.
Wasn't there a RC heli based on your symmetrical concepts?
Mart
Last edited by Graviman; 26th Mar 2006 at 12:50.
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Mart,
Perhaps problems with stability have a lot to do with the single rotor and its lack of aerodynamic lateral symmetry?
Ref quotation of Hendrick Focke on post #30; http://www.pprune.org/forums/showthr...=219294&page=2
Dave
Perhaps problems with stability have a lot to do with the single rotor and its lack of aerodynamic lateral symmetry?
Ref quotation of Hendrick Focke on post #30; http://www.pprune.org/forums/showthr...=219294&page=2
Dave
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Originally Posted by Dave Jackson's ref
... hovering, the longitudinal oscillations .... values of 12 seconds were ascertained. With this time of oscillation of a dynamically unstable character, the helicopter could be flown without difficulty.
The Fa223 is statically and dynamically completely stable around all axes other than the longitudinal one. At traveling speed of 140 to 150 km/h all controls can be released, because longitudinal instability disappears at about 120 km/h. Then this aircraft behaves just like a normal airplane and is automatically stable.
A gyro would allow stability in all conditions. Interestingly longitudinal stability in a fixed wing suffers at high altitude, since the higher speed for same dynamic pressure results in lower elevator AOA change with pitch. Many swept wing jet-liners have put up with gyro yaw damping for a while. All modern FBW jetliners have laser gyro stabilisation on all axes - primarily to reduce the otherwise necessary aerodynamic compromises.
It has also to be said that the Fa223 has a very wide seperation between the rotors. This would adversely affect the utility function of a helicopter, since you don't want to constrain landing sites. A smaller seperation would begin to diminish lateral stability. Not sure you want the complexity of the George de Bothezat machine...
Mart
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Mart,
All the proposals at the American Helicopter Society's heavy lift design conference [mentioned on the other thread] were for multiple-main-rotor configurations. Interestingly, Sikorsky's main selling point for its coaxial configuration over the others was the ability to park more craft at San Francisco's Terminal 1, Concourse B. 
Get serious Igor. The terminal can be modified. In addition, when these large rotorcraft become a reality, the vast increase in the number of small airparks will far outweigh the penalty of spacing the terminal gates a few feet further apart.
Not too sure about that. There is no information suggesting lateral instability with this craft. http://www.luftarchiv.de/index.htm?h...uber/fl282.htm
Here is a paper on stability, written by the chief engineer of this craft http://naca.larc.nasa.gov/reports/1939/naca-tm-907/
Dave
It has also to be said that the Fa223 has a very wide separation between the rotors. This would adversely affect the utility function of a helicopter, since you don't want to constrain landing sites.
Get serious Igor. The terminal can be modified. In addition, when these large rotorcraft become a reality, the vast increase in the number of small airparks will far outweigh the penalty of spacing the terminal gates a few feet further apart.
A smaller separation would begin to diminish lateral stability.
Here is a paper on stability, written by the chief engineer of this craft http://naca.larc.nasa.gov/reports/1939/naca-tm-907/
Dave
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Originally Posted by Dave Jackson
Interestingly, Sikorsky's main selling point for its coaxial configuration over the others was the ability to park more craft at San Francisco's Terminal 1, Concourse B... Get serious Igor. The terminal can be modified.
Thanks for the paper BTW, i'll read it but i'm rushed off my feet getting our "product at the other end of the transportation spectrun" into production.
Kolibri was only ever made stable by making rotors rotate the wrong way from the point of view of higher speed aerodynamics. Accepting a gyro in the control system would have allowed the original outboard advancing rotation to have been kept. Aerodynamics is a good place to start, but the problem should be considered as a whole. Rigid rotors will definately help by reducing response delay. Longitudinal and Lateral stability can be made acceptable with a package compromise by using a gyro - in fact this is what is happening with FBW.
Mart
Last edited by Graviman; 1st Apr 2006 at 04:18.
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Mart,
That's true. It keep morphing. First the Aerocopter, then symmetry, then stability, then size.
You work on the gyro, I'll work on the rotor, then we will put it all together and have the best 'gyrorotor' in the whole damn world ...........
Dave
That's true Dave, but your missing the point.
You work on the gyro, I'll work on the rotor, then we will put it all together and have the best 'gyrorotor' in the whole damn world ...........
Dave
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Sorry TV. As prof design engineers, Dave and myself have a long standing debate about why or not helis should be symmetrical. This was just a good example of good control through use of a rigid rotor.
Agreed, it would be fantastic to see this machine in UK. The main problem would be engine, since i am not sure of it's certification for helis. It is used in the Demona/Katana fixed wing, so that may not be an issue. I notice it is being imported to S.A. as a factory built kit - so it cannot be used commercially. Pity, i think this little gem will give the R22 serious competition.
Mart
Agreed, it would be fantastic to see this machine in UK. The main problem would be engine, since i am not sure of it's certification for helis. It is used in the Demona/Katana fixed wing, so that may not be an issue. I notice it is being imported to S.A. as a factory built kit - so it cannot be used commercially. Pity, i think this little gem will give the R22 serious competition.
Mart
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Hello,
boy, you guys are giving the design a working.. that's great!! i am the US rep for the Aerokopter company and this a great thread about our little helicopter. i agree with the major factor of not being able to bring the helicopter to the US, is the engine.
Mart, could you stress the point of the engine in this thread, also why you think it would give the R22 a run for the money. any idea's you have on the helicopter, and your thoughts over the whole design. the Good people at Aerokopter are keeping an eye on this thread and i would like to get some opinions on the way people think.
here are some new pics we have of the heli. sorry for the large size.
thanks,
glyn
boy, you guys are giving the design a working.. that's great!! i am the US rep for the Aerokopter company and this a great thread about our little helicopter. i agree with the major factor of not being able to bring the helicopter to the US, is the engine.
Mart, could you stress the point of the engine in this thread, also why you think it would give the R22 a run for the money. any idea's you have on the helicopter, and your thoughts over the whole design. the Good people at Aerokopter are keeping an eye on this thread and i would like to get some opinions on the way people think.
here are some new pics we have of the heli. sorry for the large size.
thanks,
glyn