Tandem wing for high efficiency? Case Proteus

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Grumpy Cynic
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I wonder if you could have a canard foil with a very high lift flap such as a fowler for the elevator, and at the same time be able to greatly reduce it's angle of attack so that you could get more AOA to the back wing and thus a higher overall CLmax,

Odd things happen. Some Q-2/200 use what they call a reflexor. It's a device that raises or lowers the ailerons together. It was an early fix for the pitching moment due to contaminated GU canards, mostly rain. The guys that use them generally report lower landing speeds with the reflexor in the UP position - or what one would think is less lift from the main wing. Run the 1212 airfoil through something like Xfoil with a 5 deg up flap and it actually will develop a higher CL.

Intuition doesn't always work.
 

Autodidact

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This is the very root of what makes the canard less efficient and functional than a conventional layout...
I had a feeling that i was headed up a bad path with that one. I guess we're just stuck with certain limits when it comes to canards.

Intuition seems to want to say: "Downforce on the tail adding to the wings load is inefficient.", and I guess that's why we always look for a better way.
 
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DangerZone

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It's not for me to "mind", I just thought you would get a better hearing with a new thread as that is how it is usually done and often the moderators do split something like this into a new one, keeps things organized. Whatever works out best is fine with me, though. And welcome to the forum, by the way.
Thanx again. In time, if there will be some more interest in highly efficient homebuilt ultralight tandem wing configurations I most probably will. People who post on this forum seem interesting and are definitely able to contribute to learning from each other.
 

DangerZone

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It really depends on what characteristic you're after but in general yes, you are correct. I touched upon that earlier in this discussion (see post #12). But the benefit is not so much due to mission variability but more so a benefit to agility and energy management.
That was a great post and one wonders how much the military contributed to the development of the canard configuration. It is like video games that kids play: parents buy video graphics cards for their kids to play on a computer so this gaming competition led to an evolution of excellent graphics processors that became superior to some CPUs. I get the impression that the same is with fighter jets, the military competition was pushing the canard idea so much that fighters became 'better' (conditionally, of course) than conventional designs. Can you imagine how much would the tandem wing configuration have evolved had there been some military use for it..?

True, many tandem wing and canards in homebuilt configuration were mostly optimised for flying straight and level and sometimes have shown more efficiency than conventional airplanes. But what if a tandem configuration can be used successfully to both have better efficiency at long level flights AS well as having better maneouvrability..? One planes that comes to my mind is the Beck-Mahoney Sorceress, an unconventional tandem wing design. Rutan constructed the Amsoil Racer just to try to beat it yet the Sorceress still outperformed better. So yes, I too had the impression that outside of the two classic examples of canard efficiency dominance (long level flying and military jet fighters) there are little advantages a tandem/canard wing could offer. And then the Hemiptere and the Sorceress show that maybe it isn't neccessarily so that conventional designs are more efficient but that we have not explored the idea of a tandem/canard to its maximum potential.

I guess the complexity of tandem canard configurations prevented the evolution of such designs. Thus only high tech experts mostly succeed in this and the Grippen, the Sukhoi, the Rafale and other similar designs which you mentioned are results of years and years of development. Yet that does not mean we have to quit trying and rule out the idea of making a tandem/canard that would be both more efficient in long level flights AND in aerobatics. If Arnold could do his AR-5 without the high tech support for an excellent superefficient conventional design, then isn't it just a question of time before someone builds a tandem/canard wing design which will be even more efficient..?
 

karoliina.t.salminen

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Good point. Yet, is the conventional configuration a winner because it is more efficient or because the tandem configuration is not yet explored/optimized as much as it could be..?
Nope, that is not the case. For example Scaled's planes are very optimized. They are made for a single purpose and to do that very well. Some of them have quite exotic parameters, such as one having Clmax of 4 in the forward wing according to John Roncz's presentation. I don't know how that is possible or how he made it. The airfoil nor the details of the flap mechanism is not publicly available.

It is the contrary. Traditional config usually is not better than Tandem just because GA planes nor homebuilts are not very optimized.
I have calculated Clmax based on stall speeds of a number of aircraft, and while it would be possible to achieve high Clmax with
small wing area on a conventional configuration, this is not often the case with general aviation aircraft. Many of them are in fact poor on this area and are not taking the opportunities that would be there that for example Denis is talking about. Sad thing seems to be that many modern GA aircraft are not that much if at all better in efficiency than even some of the half century old designs, even with taking some of the advantage from laminar flow with smooth surface. They drag around too much wing area to meet stall speed requirements with no better than Clmax of 1.7-1.9. When comparing configurations, it should be kept in mind, that these advantages of a single configuration are not always or even often realized in reality.

There are only few exceptions to this it seems, but generally these are not products one could buy but one-offs. It seems that there would be opportunity to do much better on this area if the aircraft is not just eyeballed together but really a result of careful multi-disciplinary analysis. Rivaling modern GA therefore should not be impossible with a tandem (in both stall speed and cruise), even with lower Clmax potential it might have simply because the conventional planes are not up to the opportunities there might be. To achieve all the benefits from conventional configuration, one needs to sacrifice simplicity and implement complex high lift systems.
 
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Autodidact

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I'd like to see an entire section of the forum devoted to canard/tandem/flying wings or any non-conventional configuration, myself. The variety of different designs that exist as experimentals would never have come about if they all had to be certified.
 

DangerZone

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I wonder if you could have a canard foil with a very high lift flap such as a fowler for the elevator, and at the same time be able to greatly reduce it's angle of attack so that you could get more AOA to the back wing and thus a higher overall CLmax,

Odd things happen. Some Q-2/200 use what they call a reflexor. It's a device that raises or lowers the ailerons together. It was an early fix for the pitching moment due to contaminated GU canards, mostly rain. The guys that use them generally report lower landing speeds with the reflexor in the UP position - or what one would think is less lift from the main wing. Run the 1212 airfoil through something like Xfoil with a 5 deg up flap and it actually will develop a higher CL.

Intuition doesn't always work.

Wasn't there some military research including UAVs which altered the airfoil profiles with flapperons transforming the cambered airfoil to a reflexed so the landing speed would be much lower..? I forgot the name of the project/s but the idea is an old one and is very practical for tandems/canards.
 

Denis

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The conventional configuration is ultimately efficient by purely physical background. The conclusion that AR-5 outperformed the EZ purely on reduced interference drag is also wrong. AR-5 still has some excess interference drag unavoidable in low-wing configurations. A far brighter example is Wittman W-10 Tailwind outracing Rutan LongEZ with the same O-320 engine and almost the same wing area.

The superiority of the conventional configuration stands on three elefants:

1. Ultimate span efficiency, even a possibility to get E>1 is now discussed.
2. Minimal trim drag, even with high Clmax and large negative pitch moment of the wing airfoil.
3. Minimal structural weight without compromises in PP 1 and 2.

The search for still better aerodinamic layout has produced a 3LS configuration. Indeed three lifting surfaces also have not helped to outperform the classics.
 

DangerZone

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Nope, that is not the case. For example Scaled's planes are very optimized. They are made for a single purpose and to do that very well. Some of them have quite exotic parameters, such as one having Clmax of 4 in the forward wing according to John Roncz's presentation. I don't know how that is possible or how he made it. The airfoil nor the details of the flap mechanism is not publicly available.

It is the contrary. Traditional config usually is not better than Tandem just because GA planes nor homebuilts are not very optimized.
What do you mean, what is not the case..? That there are homebuilt conventional planes that outperform Scaled/Rutan tandems/canards..? Hmmm, did you compare the EZ and Arnold's AR-5..?

http://www.ar-5.com/sportav93.html

And could you please be so kind to elaborate this plane "having Clmax of 4 in the forward wing according to John Roncz's presentation"..? I assume that by 'forward wing' you mean the canard or is it some other kind of configuration..?
 

autoreply

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Good point. Yet, is the conventional configuration a winner because it is more efficient or because the tandem configuration is not yet explored/optimized as much as it could be..?
What's all too often overlooked is that tandem wings or canards are nothing special. They behave exactly like normal aircraft, have the same formulas, the same air and so on. The "magic efficiency gain" that is so often expressed is just dreaming , in the end the physics don't change. As such, it immediately becomes clear that we shouldn't expect any further efficiency gains from "other" configurations, since the basic principles are known for almost a century and haven't changed.

Where we might see efficiency gains are secondary (not fundamental aerodynamic) effects. Think of the rudder/fin of the Long-EZ, the improved visibility of many pushers or the smaller wetted area since you don't need a tailboom (still need the tail/canard).

Optimize for efficiency and you end up with a flying wing, triple elliptically shaped. Has some practical drawbacks though...
 

orion

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That was a great post and one wonders how much the military contributed to the development of the canard configuration. I get the impression that the same is with fighter jets, the military competition was pushing the canard idea so much that fighters became 'better' (conditionally, of course) than conventional designs. Can you imagine how much would the tandem wing configuration have evolved had there been some military use for it..?

If Arnold could do his AR-5 without the high tech support for an excellent superefficient conventional design, then isn't it just a question of time before someone builds a tandem/canard wing design which will be even more efficient..?
One interesting side note to the fighter side - when I started work for GD/Convair in San Diego, several in my group were designers on the program that eventually became the Navy's F-14. In that competition Convair presented a double delta canard configuration that according to the design team not only met all the Navy specs but also surpassed them by a substantial margin. The design also would have had excellent carrier capabilities despite being limited in flap use - the reason behind this was the low planform loading of the double delta versus the substantial penalty the F-14 pays due to the swing wing structure and systems.

But despite the Convair design's superiority, the F-14 was selected due to the politics and prejudices of the day - the selection committee concluded that a double delta canard configuration would never be a competitive fighter. But the Convair team and configuration was later proved right: About a month after the award was given the Swedes revealed the Viggen, which went a long way to proving the claims of the Convair design. Needless to say, when the selection team was asked to comment, most were quite sheepishly silent.

Regarding the AR-5, this airplane demonstrates that when you design a plane to do only one thing well, it will most likely do so. The AR-5 was a nice effort but it demonstrates that that kind of "efficiency" will be best achieved only by paying attention to the small details and by building an airplane so small that it is pretty much useless for anything else. It doesn't take "high-tech" support to design an efficient/functional design. It just takes experience and understanding of the design process. Given that, it is extremely unlikely that a canard will be able to meet the all around goals you're discussing simply because the configurational features do not lend themselves to that function. It's sort of like trying to make a square wheel be more efficient than a round one.
 

Tom Nalevanko

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And in my early days in the air-air missile business, I had a friend whose job was to run simulations of the Convair Delta Dart F-106, against the F-14 and F-15. The 106 always came out ahead in air-air combat... Was kinda embarrassing presenting this to generals and admirals.
 

Autodidact

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Hmmm, I will say that I don't see how the 106 can beat the F-15; 35,000 fpm climb and M 2.3 against 50,000 fpm and M 2.5 doesn't add up. Perhaps the 106 could maintain energy in the turn just long enough to get in position?
 

orion

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Those are simple published numbers meant more for general knowledge than any actual evaluative purpose. They also do not equate payload, fuel, armaments, etc. A true evaluation of any fighter involves numerous scenarios and maneuvers ranging from simple speed, range, turn radii, etc., to more involved issues such as agility and energy management, target tracking, air-to-air combat, etc. These evaluations are far from cursory. Back when I was still in the mainstream industry I read just such an evaluation of an F-16 versus an upgraded and re-engined F-4 - the results were quite enlightening in that the F-4 actually out-performed and out-maneuvered the F-16 in about 80% of the criteria and the rest was a near dead heat. One aspect that really stuck out was an example where the upgraded F-4 could actually turn tighter and faster inside the flight path of the Falcon. The Falcon rolled slightly faster but overall agility went to the revamped Phantom, which in those days dollars cost less than a third of the F-16's cost.
 

Tom Nalevanko

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Thanks for Orion's comments.

One of my friends made a lot of $$$ consulting with the Navy and Air Force with his MIG-21. He could always beat the F-14 and F-15 hands-down and he was very good at it. Our aviators were surprised to have been 'killed' by old technology. Helas, the F-16 brought added thrust to weight and they could just vertically climb away from him and that was the end of his gig...

P.S. The French fighters (even the older ones) are well done also.
 

Autodidact

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I've always heard that delta wing fighters had a very good initial turn but that it came with a lot of drag and they would eventually lose energy, so the idea that the 106 could turn tightly was not out of the question in my estimation and when I saw that the engine was quite powerful too, it seemed at least within the realm of reason, especially for a good pilot. I'd love to read an evaluation like that!
 

Vigilant1

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Thanks for Orion's comments.

One of my friends made a lot of $$$ consulting with the Navy and Air Force with his MIG-21. He could always beat the F-14 and F-15 hands-down and he was very good at it. Our aviators were surprised to have been 'killed' by old technology. Helas, the F-16 brought added thrust to weight and they could just vertically climb away from him and that was the end of his gig...

P.S. The French fighters (even the older ones) are well done also.
Too much to cover here. These close-in fights don't mean very much when the F-14 and even the F-15 were designed to handle things from much farther away. And even close-in, the F-15 clearly bests the MiG-21 in all performance parameters. The only advantage the MiG-21 has is that it's harder to see, and that's not much of an advantage given the radar in the F-15 or the presence of an AWACS (and we don't go to war without 'em). RE: the added thrust-to-weight of the F-16: The thrust to weight of the F-15 is comparable, and usually better than an F-16 when loaded out for a practical A-A mission (e.g. AIM-9s, some AIM-7s or AIM-120s, and enough gas to get home from a fight that's more than one zip code away). None of this is to take anything from the MiG-21 variants, they were fine planes for their day and for their intended purpose. But nobody would pick one over an F-16 or F-15 for BVR or close-in work. Of course, in the real world force planners might have to choose between buying/maintaining 50 Mig-21-like acft or 10 F-16s, and that's where the math and modeling gets interesting.
 
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Vigilant1

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Back when I was still in the mainstream industry I read just such an evaluation of an F-16 versus an upgraded and re-engined F-4 - the results were quite enlightening in that the F-4 actually out-performed and out-maneuvered the F-16 in about 80% of the criteria and the rest was a near dead heat. One aspect that really stuck out was an example where the upgraded F-4 could actually turn tighter and faster inside the flight path of the Falcon. The Falcon rolled slightly faster but overall agility went to the revamped Phantom, which in those days dollars cost less than a third of the F-16's cost.
Some countries went that route--I think (West) Germany, Japan, and Israel did. The F-4 equipped with high efficiency turbofans and a modern look-down radar would have been quite an aircraft, and since it could have gotten by with less fuel and had more thrust, even close-in maneuvering would have been significantly improved (especially in later models with leading-edge slats). And, these converted F-4s would still have the ability to be a "bomb truck" for strike missions once the A-A work was done. Plus, the old bird could take a lot of damage and still get home, much more than a single-engine F-16 could. OTOH, those F-4s would have had to go to the boneyard due to fatigue issues a long time ago, so we'd eventually need to have replaced them with something new by now.
 
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autoreply

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OTOH, those F-4s would have had to go to the boneyard due to fatigue issues a long time ago, so we'd eventually need to have replaced them with something new by now.
Germany, Greece and Turkey still fly them operationally and quite successfully too I'm told. While our jet jockeys joked that "if the Germans were coming we would immediately hear them take-off", but got washed and tried pretty well a couple times...
Only in the coming years the first ones are running into the limits of their (upgraded) lifetime.
 
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