Tandem wing for high efficiency? Case Proteus

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by karoliina.t.salminen, Aug 13, 2011.

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  1. Sep 9, 2011 #121

    DangerZone

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    Well, comparing conventional configurations with canards is a good idea. We could look at it from another perspective, compare the Berkut and the Osprey GP-4 which have the same engine, a Lycoming 0-360. The GP-4 has a top speed of 408km/h, cruise 386km/h, stall 105km/h and a climb rate of 12m/s at 562kg while the Berkut tops at 410km/h, has a cruise speed of 397km/h, stalls at 110km/h and climbs 10m/s weighting 460kg empty. So the only ultimate physical background that I see is the one Autoreply wrote nice and clear, that you can't get more than the laws of physics allow. Yes, the Berkut is faster and yes, it cruises more efficently. But at the expense of a lower climb rate and a higher stall speed. And all those small differences do not seem that much of a superiority when you sum it all up, whichever concept it may be.

    Now when it comes to 3LS configurations it seems the Sukhoi Su-37 is pretty dominant and efficent, outperforming all classics. Also, there were 3LS homebuilts that outperformed both the classic conventional planes AND the most optimized canards. Like in the case of the Beck Mahoney's Sorceress (BTW, does anyone have info about the airfoils of that plane?) which is an example that the same supremacy of fighters can be achieved in homebuilt aircraft. The question is only whether such a homebuilt can be more efficient than any configuration in all aspects? Not only in top speed or top cruise but also in climb rate, lower stall speed, lower weight with better structure, the whole nine yards. If the military has succeeded in that, why not the homebuilts..?
     
  2. Sep 9, 2011 #122

    DangerZone

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    ...like stability and reliability..? :)

    Yes, I had the same thought for many years that we are limited by the law of physics. Then at some point when I was analyzing VTOL aircraft I saw the Custer's Channel Wing and was surprised that sometimes different concepts and designs can achieve better results using the little things we sometimes overlook. There were many good concepts in the past that get forgotten over time, excellent ideas, wonderful designs. So instead of looking at the laws of physics as limiting, we can sometimes use new/old ideas to get better results.

    Speaking of flying wings, how many people have used a flying wing airfoil on a tandem configuration..?
     
  3. Sep 9, 2011 #123

    DangerZone

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    Yeah, I was always wondering why did the US drop the concepts of Convair's double delta or the Canadians the Avro Arrow, those were great airplanes..? Was it the 'fundamentals idea', the idea that only the conventional concept is the most efficient one..?
     
  4. Sep 9, 2011 #124

    orion

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    Not necessarily more efficient but given the understanding (or lack thereof) of the day, to the selection committee the conventional configurations seemed more functional or even practical. Add to this the fact that there seems to be a mindset within the military that the more complex system will somehow be "better", the swing wing of the Tomcat seemed to address the things they wanted to see. They were unable or even unwilling to recognize the benefits of the Convair design.

    As far as the Arrow is concerned, I think that was more a political battle. I'm not sure of the details and the few TV documentaries I've seen don't really have any pat answers either. Extrapolating from the current mindset, my guess is that the Canadians did not want to be seen as, nor invest in their ability to be a measurable military power.
     
  5. Sep 9, 2011 #125

    bmcj

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    In a discussion such as this, you have to differentiate canard designs based on whether the canard is a true lifting/stabilizing surface vs one that is intended simply for flow control. Some of the modern canard (and 3LS) fighters have small canards that only energize (add vorticity to) the airflow at high angles of attack in order to keep the flow attached to the main wing.
     
  6. Sep 9, 2011 #126

    Rick McWilliams

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    A canard is a canard? If it generates a vortex it is lifting. How big does a canard wing have to get before we call the configuation a tandem wing? Then if it gets larger when do we call it conventional? How much lift does a surface need to generate before we call it a wing or tail or canard or whatever. Do wings or tails really need to have lift, positive lift or negative lift to be called wings? Are floatplanes a four lifting surface configuration? When are struts wings?

    Unconventional configurations are part of a complex continuum of configurations.
     
  7. Sep 9, 2011 #127

    Autodidact

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    That's a good question, I don't think it has been clearly defined but there is a clear difference between a midget Mustang and a Flea type with it's pitch control on the front wing and even if it has ailerons on the rear wing. Difficult to say sometimes even when you are looking at one. I'd say that if the tail is down-lifting or down and up-lifting and the ailerons are on the main plane, it's conventional, if pitch control is on the front but the front wing is larger than the rear, it's a tandem, if it's a tandem and the front wing is smaller, then it's a canard. Fly-by-wire can muddle it all up again, though. What's an F-18? Doesn't it have a lot of roll control from its elevators (elevons)?
     
  8. Sep 10, 2011 #128

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    The point made about the small vane or delta forewing energizing the flow over the main wing (starting the LE roll up in the same way that a strake or double delta does) is valid and acting quite differently to a canard that detracts from the lift on the main wing and actually increases the lift of the rear wing outboard of the canard span --by it's upwash field --that can easily trigger tip stall if not washed out or decambered . Other means to increase the mass flow by vortex generators or nose mounted vanes work in a similar fashion -- the viggen "double delta" works quite unlike the Rutan vari viggen to the extent of the mutually reinforcing delta vortex flows and any comparison to tandem wings and tandem deltas is tenuous at best.

    the major factor of "tandem versus canard" in airfoil selection is the big difference in relative chords and re Nos and this is why the -originally - man powered aircraft airfoil GU 25 (Glasgow university GU ) was used by Rutan on the Vari eze mk 2 and later Ezes . Tandem wings can have structural issues with roll damping if both wings are of longish span and only one is equipped with ailerons (eg twist the fuselage in two ) --having differential canard flap deflection though can be problematic at high Cl since the canard is operating in the non linear part of the lift curve and adding in roll can make the aircraft unstable. Rutan first tried roll control by differential canard elevators on the first Eze but found it was unsatisfactory . joined wings arose out of the structural problem of unjoined tandem wings of high aspect ratio (Wolkovitch ) and Rutan had a dislike of joined wings as a result of a seeming personality clash with Wolkovitch and a thing about missing data on one project so the compromises with the Proteus are probably best evaluated in light of the need to be able to unscrew the mid fuselage and change the length of the fuselage (with payload in external fairings )--something less easy to do if joined wings.

    there are unexploited potentials for very much greater speed range for tandem type aircraft and the physical limits spoken of for aircraft speed range are all based on fixed geometries whereas the aircraft should in fact change wing area and span according to speed and height -- no bird would work as a fixed geometry device for structural and aerodynamic reasons (variation of wing geometry at once per flap as well as with speed and in manouvering ) --any search for optimum performance will have to include in flight variable geometry to be truly optimum and the swing wing configuration is miles ahead of any fixed geometry military aircraft when loiter or long range is needed (not just transient dog fight ) which was well shown by the F 111 in Australian service -- for point defence it is possible something like an F 104 or T38 can get better ROC by lower structural weight but they are almost just jet engines with enough wing to lift it attached and the fuel held in the fuselage because there is no wing volume ( the delta wing or double delta is again diametrically different in the case of the Viggen type --very thin wing(s) as against say the Vulcan bomber or the Blended wing body airliners where VOLUME is the main attribute --housing internal engines and weapons in the case of the Vulcan and passengers in the case of airliners . Comparing big and little aircraft on the basis of configurational similarities can be misleading ubless the design drivers are considered and scaling functions like the square cube law are taken into account (and simple packaging as in the case of the canard Vari Eze with the optimum g housing of two people and an engine -- I would dispute the "equivalancy" of the Wittman tailwind and the Vari (or long)Eze as claimed and ask for a source for that claim -- the tandem Q2 flying with reflexed rear wing is also curious (landing slower) -- about the only advantage might be to cause the aircraft as a whole to fly more nose high and allow some 'powered lift' possibly or an IAS error -- again some details would be nice .
     
  9. Sep 11, 2011 #129

    Denis

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    Let us go on:

    http://www.airventure.org/news/2010/100726_avcup_timesheet.pdf

    http://www.airventure.org/news/2009/2009avcup_resulsts.pdf

    2008 AVC Results!

    http://www.rguerra.com/avcup/avcup07/avcup_results_2007.pdf

    Wittman Tailwind and Rutan Long-EZ compete in the same class, the Formula FX Red, the planes with fixed landing gear and O-320 engine. Moreover, they are directly comparable by wing span and area.

    The only remarkable achievement for canards in these races is the Vari-EZE performance, especially the results of Klaus Savier. Indeed, for the top results for a plane with O-200 engine, one should look at the Sharp Nemesis.
     
  10. Sep 11, 2011 #130

    Denis

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  11. Sep 12, 2011 #131

    DangerZone

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    When Rutan tried roll control by differential canard elevators and found it unsatisfactory, was it because of him not succeeding or due to structural complications..? Could this concept have been more successful in some other tandem aircraft, like having flapperons on the canard and ailerons on the wing..?

    There was an interesting canard concept before the Japanese Kyushu Shinden called Ambrosini SS.4 (the SS stands for Sergio Stefanutti, author of this canard design Ambrosini SS.4 - Wikipedia, the free encyclopedia) which crashed because of aileron control malfunction. Nevertheless, it was a beautiful canard and I was just thinking would it have helped if his aircraft would have had flapperons or is it impossible to construct an airplane which could overcompensate aileron control with canard flapperons..?

    My point is, could the tandem wing concept be improved by choosing a good canard profile with flapperon control or would it be a structural problem, for example if some careless pilot turns the flapperons to roll to one side and the ailerons to the other..? Could the Q2 and Dragonfly be more efficient if someone would alter them that way..?
     
  12. Sep 12, 2011 #132

    DangerZone

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    The Nemesis has a stall speed of 172km/h which doubts the pilot could land it successfully without high speed and a perfectly smooth paved platform. Then, turning sharp corners at low speed less than it's stall without loosing control would make this airplane inefficient for anything else but fast straight flying and very long turns. So yes, it is beautiful, and yes, it is fast. But is it efficient, agile, or performant? The performance should include maneouvrability and efficiency, which neccessarily means low speed control, more speed at cruise, agility in tight corners, not just the top speed.

    The mentioned Wittman seems like a nice plane. Yet, the KR-2S which is also a conventional homebuilt is more efficient. Would that make us conclude the top wing is less efficient..? I guess not, in the end it all comes to laws of physics. And those say that a top wing is more efficient and that a tandem/canard airplane can theoretically have less drag which could make such a concept more efficient.

    Just because the tandem/canard wing concept is not explored enough in homebuilt projects or the fact that those are complicated does not mean they are less efficient than conventional airplanes. In the end, it all comes to personal preferences, what you want your airplane to do and how much time you are willing to spend on the project. And the likes, too.
     
  13. Sep 12, 2011 #133

    Himat

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    Talking about light (1 to 8 person) aircraft powered by a single piston engine driving a propellor I did think the big thing with a conventinal layout was weight and balance. The conventional layout is the easiest way to make the plane balance with minimum structural weight. At the same time speed range and load range can be made satisfying.

    Optimized for one speed and one load the flying wing is most aerodynamic efficient. But there is practical flaw's with that.
     
  14. Sep 12, 2011 #134

    Denis

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    Stall speed of the Nemesis should be about 100km/h. The wing load is just 57kg/m^2, it is not a problem without flaps. KR-25 is not more efficient than Tailwind, although these two planes may have similar equivalent drag areas. The reasons why tandem and canard configurations are unable to compete with a conventional plane are well explored. Some relevant data on this subject are given by Roncz.

    The low wing layout has a serious problem of interference drag at the wing to fuselage junction. Apart from the additional drag, this interferece causes a reduction in Clmax and often a tail buffeting. This problem can be doctored only by a cost of extra wetted area.
    A back-shifted canopy (Ar-5, CEA-308) is a workable solution to match the pressure distributions of the fuselage and wing, but it results ina considerably longer nose, which in turn calls for a larger vertical tail volume.
     
  15. Sep 13, 2011 #135

    DangerZone

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    Are you sure about the Nemesis, everyone has been saying that it has a 90 knots high stall speed as a consequence of its fast airfoil profile..? So even with flaps, could that plane land/fly any slower than some 150km/h..?

    Now when it comes to competing, are you sure there's a chance that a conventional plane could beat a canard if we look at fighter jets..? I would really appreciate if you could provide some link to this relevant data of Roncz.
     
  16. Sep 14, 2011 #136

    Denis

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    I don't know how a 90kt stall speed figurefor the Nemesis has appeared. This plane has lower wing load than C-172 and the Cdmax value corresponding to those 90 knots is as small as 0.426. Being a F1 racer, the Nemesis should be able to make quite steep turns around pylons with safe margin in respect to stall and without excessive energy losses. And the wing load is so low, that even a 61kt stall speed (the FAR-23 upper limit) would require only Cdmax=0.927, even a flat plate or a less that 6% thick airfoil would be enough to get this number. With flaps the wing area of the Nemesis could be halved, but it is the F1 requirement to have not less than 66 sq. feet.

    J. Ronch has discussed the drawbacks of the canard configuration in his series on homebuilt design published in Sport Aviation. There are also several theoretical and experimental studies, which confirm the fact that the conventional configuration has minimal trim drag and highest E factor of all two-surface configurations. Moreover, it is the only configuration, which allows one to get minimal induced and trim drag being longitudinally stable.
    Indeed, this minimal drag exists at only one CG position (zero lift at tail surface), and some trim drag appears at off -design conditions at both negative and positive sides of the tail lift range.

    The following study (Kendall, 1985)

    Powered by Google Docs

    reveals that the the trim drag over the enormous CG range of 30% for a conventional plane model varies from 1.006 to 1.069, while it is no less than 1.229 (extreme aft CG) for the best canard configuration under study. This paper also deals with a three surface configuration, where the possiblity of 1.000 value (zero trim drag) at any CG position is revealed. Indeed this result is unlikely to be achieved in real aircraft due to some other adverse effects. Particularly, the trim drag reduction in 3LS layout comes wiht a penalty of increased viscous and interference drag, and the Clmax value calculated for the total area of the main wing and the canard is considerably lower than that of the convention configuration with the same main wing.
    Here is an interesting paper, which shows how a removal of the canard ina a 3LS model actually improves performance:

    http://www.google.com/url?sa=t&sour...sg=AFQjCNFWckG9OXQhIHFO5yr4Mgco3iGlyQ&cad=rja
     
    Last edited: Sep 14, 2011
  17. Sep 14, 2011 #137

    DangerZone

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    I read in some paper that the high speed of the Sharp Nemesis has a drawback of this higher stall speed, that it has a very thin airfoil profile and that it is a fast flier with many awards. I did a search on Google now and it seems only Wikipedia has the info on stall speed (90 KIAS) and the rest of the results omit the stall speed of the Nemesis. I am aware Wikipedia is not much of a source but so far it is the only one which declares its stall speed. BTW, do you know which airfoil is on the Nemesis, it might not be that hard to estimate it's stall speed..?

    Yes, I am aware there are many drawbacks of canards and I would be very happy to read about Roncz's work, yet the page you linked leads me to Google Docs home page. Every concept has some positive aspects and some drawbacks, a conventional plane has similar pros and cons so in the end it all comes down to the laws of physics and what you want your airplane to do. Now I am sure you will agree that the same principles do not apply to jet fighters, homebuilt aircraft and RC model airplanes. And basically I do see why people think that a conventional design is the most efficient even though modern fighters show quite the opposite. I was merely asking if this idea could analogically be used in homebuilt aircraft, to construct a composite tandem/canard which could be more efficient that most conventional homebuilts. Some hundred years ago many respected scientists thought humans are unable to fly yet today we know that we can fly even more efficiently than birds, and we have only slightly explored just a bit of our flying possibilities.

    This last paper is something I will look into, it is interesting how removing of canards on a 3LS RC model improves efficiency while putting a canard improved efficiency on the Sukhoi Su-37 or the American F15S/MTD, with canards they became very agile and more efficient than their base models. There were even Quickies with an added stabilizer to the vertical tail, making them 3LS and improving performance (but not efficiency). If you find any work or research on such improvements or alterations of tandem/canard homebuilts I would be very thankful if you'd point it out.
     
  18. Sep 14, 2011 #138

    Denis

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    The collection of Roncz's publications from Sport Aviation is here:

    Roncz_r1.pdf - File Shared from Box.net

    It contains mostly decriptive discussion on the nonconventional layout. The paper by Kendall I've cited provides the good analysis with numbers and clear physical background. One can find more references like this wiht the same key resilt. The math behind this analysis is obviously out of any forum. Indeed the physical background is very clear, the inferior efficeincy of everything but conventional configuration traces down to such fundamental thing as energy conservation. Therefore one may undertake any effort to build a canard or tandem, which is aimed to outperform classics, but it will be just a waste of time, money and health.

    The wing of the Nemesis shows no signs of low Clmax, and its airfoil is of medium thickness. Again, the very mission of this palne as F1 racer calls for wide airspeed range.

    The jet fighters have only few common things with our peaceful birds, the names of basic airframe parts. If the use canards, it is done in a completely different way. Such plane is typically inherently unstable and requires a dedicated stability augmentation system. A fixed front surface is always a destabilizer, it shifts the neutral point forward. The CG position is well behind of this neutral point, and the canard is controlled by the output of the active control system and not directly by pilot.principally the same agility can be achieved in a number of other configurations, including a conventional one, but a canard solution may lead to some reduction instructural weight and overall dimensions. Efficiency-wise these planes are hogs and their design principles cannot be useful for anything else.
     
  19. Sep 14, 2011 #139

    Rick McWilliams

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    The Nemesis was a winner because it was the first long wing airplane in the F1 racing fleet. Induced drag is an issue at high altitude and high G loads. I designed the extreme, 70%, laminar flow airfoil used on the Nemisis. It is 12% thick. It was designed for absolute minimum drag at a Cl of 0.1 to 0.4. Maximum lift was not a concern. The airfoil can be expected to have nasty separation at high lift. With 66ft2 and 750lbs, anything will produce enough lift for landing.

    It is interesting to note that long or large tailed airplanes have less tail loads. The aerodynamic neutral point moves aft with the tail, and the allowable center of gravity moves aft. A conventional airplane can have a lfiting tail. The long tail improves handling as it provides more damping. It is not a useful goal to have a lifting tail, wing pitching moment and fuseleage weight make this not the best choice.

    I find the 3LS configuration enticing because a small canard is an excellent angle of attack limiter. The main wing does not need any compromises with respect to stall propagation.
     
  20. Sep 14, 2011 #140

    Denis

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    Too much positive lift at the tail is also a bad thing as too much negative lift. The deviation to any side from the minimum trim drag increases the induced drag point and reduces the span efficiency of the complete airplane. Indeed these deviations at the extreme GC margins are very small, just few percent, and the corresponding shortening of the equvalent span can be little more than 1%. Interestingly the optimum point for the best span efficiency can be slightly into the negative side of the tail lift, depending on the mutual placement of the wing and tail. This is a result of constructive interference of the two surfaces, which takes place only if a smaller surface is placed behind the larger one and sees maximal downwash.

    The canard in 3LS configuration is no longer the angle of attack limiter, because the elevator at the tail still has a lot of pitch authority when the stall begins on the canard. It can bring to full stall both the canard and the main wing and put the plane into a disastrous situation. This is especiallly dangerous for a T-tail layout (P-180), which can result in pitch lock and unrecoverable stall. The two Vee ventral fins shaped like a Concorde wing under the tail of the P-180 are added to reduce this pitch-up tendency, the same way as it is done in some conventional Tee-tailed planes.

    From other hand, the conventional configuration offers far better possibilities to control the stall than any canard.
     

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