A little helicopter history
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A little helicopter history
The following link gives a brief story about the Flettner FL 282 Kolibri.
It invokes speculation as to what rotorcraft would look like today; ~ if the war had gone differently.
http://www.fiddlersgreen.net/AC/airc...2/flettner.php
Dave
It invokes speculation as to what rotorcraft would look like today; ~ if the war had gone differently.
http://www.fiddlersgreen.net/AC/airc...2/flettner.php
Dave
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Hang on Dave, you saying all helicopters would be made out of folded card? Gonna meet son of single rotor pioneer in a couple of weeks, so i'll mention it. Exciting stuff BTW - you know what they say about meeting your heros. 
Seriously, for this thread lets assume that the two technologies had been developed side by side
. Clearly X2 is where the two meet, so you could say there is already a convergence. If intermeshing had been standardised helis may have achieved higher speed sooner, but may have suffered in sidewards flight. From the handling point of view symetry is good, but single rotor control systems have evolved to produce linear rate control (SAS, AFCS, FBW etc). High rotor hub separation gives a fast response, but then so does high effective hinge offset. Efficiency of two systems is in practice probably similar (although a paper only exercise could probably prove otherwise).
On balance, i think when an engineer is confronted by contraints of cost reliability and performance he/she will go for the simplest solution to deliver. To my mind MR/TR is that solution, but it is not without compromise. As market expectations shift so will the required compromise, and i will be interested to see how X2 affects this...
Mart
Seriously, for this thread lets assume that the two technologies had been developed side by side
. Clearly X2 is where the two meet, so you could say there is already a convergence. If intermeshing had been standardised helis may have achieved higher speed sooner, but may have suffered in sidewards flight. From the handling point of view symetry is good, but single rotor control systems have evolved to produce linear rate control (SAS, AFCS, FBW etc). High rotor hub separation gives a fast response, but then so does high effective hinge offset. Efficiency of two systems is in practice probably similar (although a paper only exercise could probably prove otherwise).On balance, i think when an engineer is confronted by contraints of cost reliability and performance he/she will go for the simplest solution to deliver. To my mind MR/TR is that solution, but it is not without compromise. As market expectations shift so will the required compromise, and i will be interested to see how X2 affects this...
Mart
It invokes speculation as to what rotorcraft would look like today; ~ if the war had gone differently.
-- IFMU
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There would be hundreds of single rotor helos with Iron Crosses on them, and we would be speaking German.
My Dad was a B-17 crewman in the Eighth Air Force, maybe he helped change their minds....
My Dad was a B-17 crewman in the Eighth Air Force, maybe he helped change their minds....
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I think its fair to say he might have had something to do with it Nick
Joking aside, I read the book 'Combat Crew' by John Comer once. I really dont think I'd have had the nerve to do what those guys did week after week. Balls of pure steel.
Nothing but admiration for that generation of veterans, and although I'm not the type to be easily impressed, I feel genuinely humbled whenever I'm around any of those lot. I owe them more than a beer when I get the chance.
Joking aside, I read the book 'Combat Crew' by John Comer once. I really dont think I'd have had the nerve to do what those guys did week after week. Balls of pure steel.
Nothing but admiration for that generation of veterans, and although I'm not the type to be easily impressed, I feel genuinely humbled whenever I'm around any of those lot. I owe them more than a beer when I get the chance.
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Chuk,
I just finished "Masters of the Air" by Miller, and found it simply great.
I was just placed on the Board of Trustees of the Mighty Eighth museum in Savannah GA and am quite honored. What is simply amazing is that only 9 months after Pearl harbor, the Eighth had several bomb groups dropping bombs from England - 9 months to assemble 3 bomb groups, each with 25 complex 4 engined bombers, 2,000 total crew, with support equipment, training, building the machines, etc etc. And in March of 1945, 3 1/2 years after Pearl, of the available 26 bombing days over Germany, they launched 20 1,000 plane raids! This took a war machine of over 330,000 airmen. As an index, today is 4 years from the start of the Iraq war!
I just finished "Masters of the Air" by Miller, and found it simply great.
I was just placed on the Board of Trustees of the Mighty Eighth museum in Savannah GA and am quite honored. What is simply amazing is that only 9 months after Pearl harbor, the Eighth had several bomb groups dropping bombs from England - 9 months to assemble 3 bomb groups, each with 25 complex 4 engined bombers, 2,000 total crew, with support equipment, training, building the machines, etc etc. And in March of 1945, 3 1/2 years after Pearl, of the available 26 bombing days over Germany, they launched 20 1,000 plane raids! This took a war machine of over 330,000 airmen. As an index, today is 4 years from the start of the Iraq war!
Last edited by NickLappos; 4th Apr 2007 at 15:30.
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Serious respect to your old man, Nick, and all that flew in that conflict. Occasionally in UK you bump into ex-RAF/USAF guys of that era, and i never cease to be amazed how down to earth these guys are. Definately the real deal in the hero stakes.
Mart
Mart
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I'd speculate that they would have taken all our best helicopter engineers and had a great lineup of single rotor helicopters!
) was the one with a single blade and a solidity ratio of 1.5.Anyone want to speculate as to who the designer was?
Dave
Dave,
That would be Leonardo. But is he really the best designer? He hasn't gotten any further than you have!
-- IFMU
That would be Leonardo. But is he really the best designer? He hasn't gotten any further than you have!
-- IFMU
Originally Posted by I.I.Sikorsky
To invent a flying machine is nothing. To build it little. To make it fly is everything.
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Hardest part these days, IFMU, would be to find the cash to do it. Not so much for the endeavor itself, but for the time it would take to to do it. You'd be suprised how much a small team of dedicated engineers can accomplish, but they have to eat, sleep, pay mortgages etc.
Also a decent CAD/FEA package, and machines to run it on, is going to set you back a bit more. Then the testing and developement takes more time and cash. Sikorsky was smart to recognise a new market while he was still building the Clipper flying boats.
Mart
Also a decent CAD/FEA package, and machines to run it on, is going to set you back a bit more. Then the testing and developement takes more time and cash. Sikorsky was smart to recognise a new market while he was still building the Clipper flying boats.
Mart
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As an index, today is 4 years from the start of the Iraq war!
Im begining to think this is worse than Vietnam as at least then they would send whole units out to take care of business.
Hardest part these days, IFMU, would be to find the cash to do it.
I'm building a homebuilt plank, I have to work for a living, and I'm fairly lazy. Somebody more ambitious could do it, that's why we have Enstroms and Robinsons. So, it could be done, I would propose.
-- IFMU
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IFMU, congrats on your homebuild. Not disagreeing with you, but your machine is based on a proven design, i assume. VS-300 had many technical difficulties to overcome, not all of which were foreseen. It underwent many major revisions, and suffered several crashes, as it was introducing new ground. I'll gain better insight in a couple of weeks. 
Modern equivalent would be X2, which clearly is being taken at a sensible pace. Any future development of X2 capabilities would likewise take a similar effort - it is only prudent to plan accordingly.
Mart
Modern equivalent would be X2, which clearly is being taken at a sensible pace. Any future development of X2 capabilities would likewise take a similar effort - it is only prudent to plan accordingly.
Mart
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The VS 300-C had one attribute. All FOUR of its rotors faced upward.
However, three were used for control. Then someone told Igor that others were using main-rotor cyclic control.
"Not one successful single-main-rotor helicopter existed anywhere. It was just the type of challenge that Igor Sikorsky needed ...." ~ William E. Hunt, Sikorsky Advanced Design Staff.
Apparently, the challenge was to build something different, not necessarily build something better.
However, three were used for control. Then someone told Igor that others were using main-rotor cyclic control.
________________________
"Not one successful single-main-rotor helicopter existed anywhere. It was just the type of challenge that Igor Sikorsky needed ...." ~ William E. Hunt, Sikorsky Advanced Design Staff.
Apparently, the challenge was to build something different, not necessarily build something better.
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Dave, i realise last post was tongue in cheek, but i'm not sure i agree. Remember i've actually spent a while studying an actual FL282, and beautifully engineered it was too. Although there were control advantages at that stage, there were also vibrations introduced with the use of two blades (3 or 4 is possible of course). That site you link also shows an example of how tricky they could be to fly.
Is the MR/TR design a compromise? Yes, no doubt. At the time cyclic control had not been developed to the point where it was fit and forget, and there was no Prouty to refer to either! Sikorsky's concept was to figure a way to get a single rotor to fly in a convenient package. Since the tail is needed for a rudder device anyway, combining it with an anti-torque function is a logical step. It introduces control difficulties, true, but it works. Since at that time the objective was hover and slow forward speed, retreating stall was a necessary compromise.
Side by side designs preceeded MR/TR, including Berliner in the US, but were never really taken up by anybody. Tandem had even been flown by that time, but again was seen as too complicated a solution.
http://www.nasm.si.edu/research/aero...t/berliner.htm
A good engineer understands the problems then figures out which ideas won't work. What is left, no matter how much development is needed, is the right answer.
Mart
Is the MR/TR design a compromise? Yes, no doubt. At the time cyclic control had not been developed to the point where it was fit and forget, and there was no Prouty to refer to either! Sikorsky's concept was to figure a way to get a single rotor to fly in a convenient package. Since the tail is needed for a rudder device anyway, combining it with an anti-torque function is a logical step. It introduces control difficulties, true, but it works. Since at that time the objective was hover and slow forward speed, retreating stall was a necessary compromise.
Side by side designs preceeded MR/TR, including Berliner in the US, but were never really taken up by anybody. Tandem had even been flown by that time, but again was seen as too complicated a solution.
http://www.nasm.si.edu/research/aero...t/berliner.htm
A good engineer understands the problems then figures out which ideas won't work. What is left, no matter how much development is needed, is the right answer.
Mart
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Mart,
If you want a better understanding of Igor and his technical ability, or lack thereof, you might appreciate the semi-technical book 'Heelicopter : pioneering with Igor Sikorsky' ~ based on a personal account by William E. Hunt.
I strongly suggest that European Rotorcraft technology faltered because North America won the Second World War, economically.
Nick gives a related reason for European failure when he mentions the bombing of German plants. As a matter of fact, Flettner was bombed on three separate occasions and had to relocate on two of them.
Please differentiate between American marketing and German engineering.
If you want a better understanding of Igor and his technical ability, or lack thereof, you might appreciate the semi-technical book 'Heelicopter : pioneering with Igor Sikorsky' ~ based on a personal account by William E. Hunt.
I strongly suggest that European Rotorcraft technology faltered because North America won the Second World War, economically.
Nick gives a related reason for European failure when he mentions the bombing of German plants. As a matter of fact, Flettner was bombed on three separate occasions and had to relocate on two of them.
Please differentiate between American marketing and German engineering.
For what it's worth, I have owned a Porsche 928 for 25, trouble free, years. When looking at total cost, it is probably the cheapest car that I have ever owned. IMHO, it is STILL technologically, and perhaps aerodynamically, superior to any car that North America has ever built.
Dave
Apparently, the challenge was to build something different, not necessarily build something better.
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Dave, that 928 is a beautiful looking machine.
I have worked in Munich and can speak german (and french), and will say that i learned my outlook for engineering excellence working there. By the same token my Uncle saw the demise of the UK rocket industry to Europe, my father the demise of the UK aircraft industry to Europe, and me the demise of the UK car industry to Europe. Both my grandfathers were at D-Day, so it is a bitter pill to swallow.
I can believe that Anton Flettner spent agreat deal of time investigating various options before choosing intermeshing. I can also believe that the MR/TR concept was discarded because of the possible control problems. But that doesn't alter the fact that the MR/TR concept was developed somewhere else. Intermeshing is a good concept for particular applications, but it too is a compromise. The compromise here is limited yaw authority and sideways flight performance.
Having all the powertrain in one location is good for reliability, so it would not suprise me if we saw new intermeshing developments designed for high speed flight. However i suspect high speed helicopters will develope into coaxial for high performance military machines, intermeshing for general purpose, and tandem for transport. But for a cost effective solution MR/TR will remain, albeit limited by retreating blade stall. There will be other solutions, including the current craze for tiltrotors, but in the end the market will be drawn towards best performance for a given investment...
Mart
I have worked in Munich and can speak german (and french), and will say that i learned my outlook for engineering excellence working there. By the same token my Uncle saw the demise of the UK rocket industry to Europe, my father the demise of the UK aircraft industry to Europe, and me the demise of the UK car industry to Europe. Both my grandfathers were at D-Day, so it is a bitter pill to swallow.
I can believe that Anton Flettner spent agreat deal of time investigating various options before choosing intermeshing. I can also believe that the MR/TR concept was discarded because of the possible control problems. But that doesn't alter the fact that the MR/TR concept was developed somewhere else. Intermeshing is a good concept for particular applications, but it too is a compromise. The compromise here is limited yaw authority and sideways flight performance.
Having all the powertrain in one location is good for reliability, so it would not suprise me if we saw new intermeshing developments designed for high speed flight. However i suspect high speed helicopters will develope into coaxial for high performance military machines, intermeshing for general purpose, and tandem for transport. But for a cost effective solution MR/TR will remain, albeit limited by retreating blade stall. There will be other solutions, including the current craze for tiltrotors, but in the end the market will be drawn towards best performance for a given investment...
Mart
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IFMU,
Who? Lu?
Mart,
You mention; "The compromise here is limited yaw authority and sideways flight performance."
1/ The yaw authority during hover may very likely be weaker than that of a tail-rotor craft. However, here are 2 potential solutions, should they be required; http://www.unicopter.com/1322.html and http://www.unicopter.com/1183.html
2/ The concern about sideways flight performance is more confusing.
Quadrirotor mentioned last week "As the Flettner was not allowed to taxi, I wounder if there is any problem when you try to take off with an heavy (or moderate) crosswind." This concern is similar to your's.
Quadrirotor was unable to recall where he had come upon this information. Can you recall your source so that I can dig into it further?
Thanks,
Dave
PS.
The Prewitt Aircraft Company evaluated the FL-282 for the USAF at the end of the war.
"The lateral static stability is substantially neutral. There is, however, considerable damping to lateral roll, and lateral control presents no special problem. Directional stability is influenced by collective blade pitch angles (good at high pitch, poor at low pitch)."
More of the summary from this 147 page evaluation. http://www.unicopter.com/0474.html#Evaluation
Who? Lu?
Mart,
You mention; "The compromise here is limited yaw authority and sideways flight performance."
1/ The yaw authority during hover may very likely be weaker than that of a tail-rotor craft. However, here are 2 potential solutions, should they be required; http://www.unicopter.com/1322.html and http://www.unicopter.com/1183.html
2/ The concern about sideways flight performance is more confusing.
Quadrirotor mentioned last week "As the Flettner was not allowed to taxi, I wounder if there is any problem when you try to take off with an heavy (or moderate) crosswind." This concern is similar to your's.
Quadrirotor was unable to recall where he had come upon this information. Can you recall your source so that I can dig into it further?
Thanks,
Dave
PS.
The Prewitt Aircraft Company evaluated the FL-282 for the USAF at the end of the war.
"The lateral static stability is substantially neutral. There is, however, considerable damping to lateral roll, and lateral control presents no special problem. Directional stability is influenced by collective blade pitch angles (good at high pitch, poor at low pitch)."
More of the summary from this 147 page evaluation. http://www.unicopter.com/0474.html#Evaluation
Last edited by Dave_Jackson; 6th Apr 2007 at 03:45. Reason: Grammmer
For what it's worth, I have owned a Porsche 928 for 25, trouble free, years. When looking at total cost, it is probably the cheapest car that I have ever owned. IMHO, it is STILL technologically, and perhaps aerodynamically, superior to any car that North America has ever built.
I would dare to comment that many would agree that Germany and engineering excellence go together. I don't know if it is genetic, cultural, or if it's in the beer. I have observed in my travels that many good engineers in the states are of German descent. Part of the diverse mix that makes the States a technological powerhouse.
One question that I would pose: If Flettner was so far ahead of his time, why hasn't Germany picked up the synchrocopter torch and marched on with it? They have an excellent helicopter company (MBB, even the birds are jealous). They have excellent aerospace in general - sailplanes, bizjets, commuters, unlimited acro monoplanes. Have the current generation of Germans been so cowed by their loss in WW2 that they abandoned all things German and took up the ways of the west, i.e. single rotor helicopters and weak beer? Or have their brightest minds in the helicopter field come to a different conclusion than you have?
-- IFMU