Tandem wing for high efficiency? Case Proteus

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TopherJA

Active Member
Re: Tandem wing for high efficiency? Case Proteus
The root of the confusion comes from aerodynamicists......
You probably could have ended your sentence right there and been right on.

Orion, exactly what I was thinking!!!

One of the things I always finds interesting is the hyper focus on induced drag reduction versus other forms of drag, when induced drag is the only one you have to live with if you don't intend on falling to the ground. Induced drag has the marvelous property that the faster you go the smaller it tends to get, and for most of the flight you want to go as fast as you can... the rest of the drag contributors are not nearly so kind.

It took me a long time to realize that detail designing parts of planes tended to result in bad planes. Keeping focused on the overall " big" picture results in planes that perform well in their intended flight profiles... which is much more impotent then wing sections that perform well in their intended Re. To phrase this more to Autoreplies liking, 3D aerodynamics of the entire plane in the flight load deflected state tell you much more about airplane performance then airfoil section l/d.

Winglets are mostly hard to design cause the wing bends... making your perfect angle of incidence less perfect in practice!

Just to add another way of looking at what is the actual end result of an aircraft passage on the air... it isn't really downwash, or vorticies, it is heat. The air doesn't go down and stay there, it bounces back up again. And the vortex(ices) does not keep spinning forever. The air just gets hotter. I have tried to generate performance equations that show what the delta temp of the air is, and maximize performance by minimizing the temp change but so far I am just not that clever. I have seen it shown that the energy in the vortex(ices) being thrown down and forward are equal to the lift and drag. So just like a water wave carries energy across water not by moving the water but by carrying energy in the form of a wave through the water, air holds the wing up not by being thrown down but by carrying energy in the form of a vortex down. A wing throws energy down... ultimately in the form of heat. (Heat just being faster random motion of air molecules, so you are sending a column of faster moving air molecules toward the ground, not sending the air molecules toward the ground.)

Hot Wings

Grumpy Cynic
HBA Supporter
Log Member
(Heat just being faster random motion of air molecules, so you are sending a column of faster moving air molecules toward the ground, not sending the air molecules toward the ground.)

Newtons Cradle - Large - 7 inches - YouTube

imagine this in 3D

TopherJA

Active Member
A video is worth a million words...;-)

topspeed100

Banned
P.S. Aircar's reply is interesting.
I agree....I wonder if he means that the trailing wing in a tandem configuration will not enjoy same kinda airflow as the front wing ?

Hot Wings

Grumpy Cynic
HBA Supporter
Log Member
I agree....I wonder if he means that the trailing wing in a tandem configuration will not enjoy same kinda airflow as the front wing ?
I don't want to put words in his mouth.

I think what he is trying to say is that at some point where the 2 wings in question are separated by enough distance (either vertical or lateral) for all practical purposes you can treat them as being discrete, completely separate wings no longer influenced by the other. At some point the little air molecules no longer care what their remote neighbors are doing and settle back down into their own self-absorbed daily lives.

Himat

Well-Known Member
I speak English everyday at work exclusively and also think in English, maybe I am reading you still wrong or something, but your
statement makes me to wonder (this whole discussion is getting rather strange imho, started from a technical question about "why's and why nots" for
a specific configuration):

Are you saying that there is something strange in reducing Cl needed (alone?)? That in other words is called reducing weight.
Reducing weight reduces drag due to lift because less lift needs to be generated. Weight can be reduced without changing AR, despite
changing AR will change the weight too, but if we consider from aerodynamic standpoint, what strange there is
to make the plane lighter? Burt Rutan has said: if you build a part, throw it into air and it comes back, it is too heavy. Well maybe only
ufos that repel gravity are light enough to meet that criteria (just kidding), but the bottom line is that; to make your plane perform better, one thing you can do
is to make your plane lighter. Also John Roncz mentioned in one of his presentations "In order to your plane to have less induced drag, you shall make it lighter".
I don't see anything strange on that and it does not have direct relation to AR (you can make the plane lighter or heavier without changing AR).
If I want to climb with our Diamond higher, (thus allow it to function with less thrust available), I will not pack it full of stuff, but try to keep it light. Talked also to Jim Price at
Oshkosh and he told that he had taken measures to reduce weight when he did his altitude record 35000 ft with his normally aspirated Long-Ez. So the Cl needed alone without change
in other parameters works based on empirical experience. I don't see anything strange on that, but I think it is strange to try to see something strange on that.

P.S. Aircar's reply is interesting.
Off guard at that point, you can change the weight of the plane, either by building a lighter plane or carry less load and enjoy a lower Cdi.
Going faster at the same weight yield the same result if you have the power to do so.

Designing a plane to carry a given load a given distance at a certain speed the aim is to do that with the lighes possible aircraft.
(The flight mission might have different phases with different speed and load, furhter complicating the problem.)

Designing a wing, span, area and AR is related. Structural weight is influenced by AR to as the strengt of an beam rises by the square of the depth.

Then, what is the optimum design?
I used the expression Cdi=Cl^2/(phi*AR*e) as an example as I have seen a lot of people focusing on the AR part and L/D number and forget the load factor. (Load factor = payload carried/ all up weight).

A glider, or maybe even better a RC model glider, is good examples of very aerodynamic efficient aeroplanes. The RC model actually have a zero load factor. No load carried, it's all structure and systems. Great fun and they win competitions, but unlike GA and most other full size aeroplanes they dont carry anything anywhere

The Proteus is one example of how the designers have optimised, as light a plane as possible for the mission. An unorthodox solution, and we discuss the merrits, straying off into other subjects.

DangerZone

Well-Known Member
HBA Supporter
Hi all, I've been following this forum for quite some time and now that you speak of tandem configurations I just had to ask if anyone has a bit more knowledge. I'm working on a project of a small ultralight homebuilt, 245kg/100HP tandem wing composite, and am interested in the decalage angles of tandem planes, the influence of this angle to the airplane's speed combined with the different airfoils.

Be it the ole Beck-Mahoney Sorceress, the Quickies, Dragonflies, LongEZs or the Berkut, they all have different decalage. Even the ancient Hemiptere had a decalage of only 3 degrees and an airfoil that was not really optimised for speed yet if outflew most of the competing planes of the era that had much lower drag. So, my question is the same as in the title: which airfoils for the wing and which for the canard with the minimal decalage would result in the fastest speed to power ratio..?

I guess many will say that I should ask the aerodynamicists working on such concepts. Yet I am interested in practical knowledge, not only theory. Is there anyone who could give me some good advice or point me in the right direction whom to ask..? Who could have some knowledge/experience to tell me for example why would some Eppler 1230 wing with a Roncz canard be better than some other configuration on a 5.1 wing and 4.5m canard with 2 degrees decalage and 2.5m chord distance..?

Any ideas would be appreciated, thnx in advance.

Autodidact

Well-Known Member
NASA Technical Reports Server

This link goes to NACA-TR-648 which is a distillation of the math into charts that predict downwash and wake charactaristics based on distance behind ("r") and distance vertical ("m") of the rear wing so that decolage or "longitudinal dihedral" , if you like, can be estimated relatively accurately. The downwash angle is dependant on coefficient of lift, aspect ratio (or is it span? According to the charts it appears to be aspect ratio. :nervous , and not the airfoil since the lift curve slope is approx. linear for most of the range and for most airfoils. Stability charactaristics in most normal flight regimes is a function of c.g. location, static margin, aspect ratio, etc. Airfoil would mainly effect drag and stall charactaristics (Clmax). Others here can add more insight than I, hopefully they will, but the above NACA technical report can be of great help to you. For canard and tandem wing configurations, particularly, since they are not what is considered "conventional", learning how to do stability calcs would be very helpful, I think.

P.S.,
Decalage when measured from the airfoils zero lift line would be more enlightening than simply decalage measured from the respective airfoils datums; the latter is dependent in the airfoils camber and doesn't tell the whole story.

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DangerZone

Well-Known Member
HBA Supporter
NASA Technical Reports Server

This link goes to NACA-TR-648 which is a distillation of the math into charts that predict downwash and wake charactaristics based on distance behind ("r") and distance vertical ("m") of the rear wing so that decolage or "longitudinal dihedral" , if you like, can be estimated relatively accurately. The downwash angle is dependant on coefficient of lift, aspect ratio (or is it span? According to the charts it appears to be aspect ratio. :nervous , and not the airfoil since the lift curve slope is approx. linear for most of the range and for most airfoils. Stability charactaristics in most normal flight regimes is a function of c.g. location, static margin, aspect ratio, etc. Airfoil would mainly effect drag and stall charactaristics (Clmax). Others here can add more insight than I, hopefully they will, but the above NACA technical report can be of great help to you. For canard and tandem wing configurations, particularly, since they are not what is considered "conventional", learning how to do stability calcs would be very helpful, I think.

P.S.,
Decalage when measured from the airfoils zero lift line would be more enlightening than simply decalage measured from the respective airfoils datums; the latter is dependent in the airfoils camber and doesn't tell the whole story.

Thank you Autodidact, that is a great old article about general pre-IIWW ideas. Yet the tandem wing and flying wing research during that war and after it revealed how important the airfoil profile is and all sorts of different approaches made the tandem and canard planes more efficient.

When it comes to canards, the wing has another component besides lift, a moment, which is pretty much determined with the airfoil profile. Actually, it is more often two moments, one near the root and another one at the wingtips which is determined by the washout just before they transition into winglets. Thus choosing the right airfoil is a pretty demanding and I prefer asking those who are more experienced and have more knowledge than just stick to the theory. So yes, the 2 degrees of decalage makes the plane stable yet more stability would just reduce the manouvrability in flight during rolls, loops and the other fun stuff in flight and the top speed since at higher speeds drag becomes too much to overcome due to this decalage angle. The best idea is to find a canard airfoil which has less drag at the speed over 300km/h yet performs great at low speeds having a mild stall. One of such examples would be the Bateleur, a canard airplane which has a stall speed of 65km/h without flaps yet a top speed of more than 300km/h with 100HP and cruises at some 250km/h with less than half the power.

Most of modern canards (and the tandem wing IS basically a canard) have some sort of reflexed airfoil as wing and a totally different airfoil as canard. So, I am looking at all possibilities, all airfoils that could be used as wing and those that could be used as the canard airfoil. There's not so many choices with the 'proven concepts', the EZs and Berkuts use the modified Eppler 1230, the Quickies and the Dragonfly use an Eppler 1212, the Ares and Proteus use some sort of Roncz airfoil which are useless for my intended speeds of up to less than 400km/h and I have no idea what the Bateleur, the Beck Mahoney Sorceress and some other tandems/canards have as airfoils. On top of that, choosing a good canard profile for such a configuration is an even harder task, if Rutan and Roncz were not satisfied with their proven canards what could I do with much less experience..? That is why I came here to see if anyone has some knowledge and would like to or could help.

So, a tandem aircraft with a 4.5m canard (3.7m2 area) and 5.1m wing (7.1m2 area) and 2 degrees decalage with the chords distance 2.5m and 100HP that should have a stall speed of no more than 65km/h and top speed over 300km/h needs an adequate wing and canard airfoil. What would the aerodynamicists say, what would be best..? What would experienced homebuilders say..? All ideas are welcome.

Autodidact

Well-Known Member
...and 2 degrees decalage...
Decalage is determined by the airfoil(s) chosen. You've essentially asked for someone to design an aircraft for you and haven't even provided the weight. The NACA paper isn't out of date and only provides a downwash angle to help you with the design decisions. I do hope someone else chimes in.

DangerZone, to get the most attention from the people you are trying to reach, I would suggest that you start a new thread rather than your question being an addendum to this older thread that is not precisely the subject that you are asking about.

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DangerZone

Well-Known Member
HBA Supporter
Decalage is determined by the airfoil(s) chosen. You've essentially asked for someone to design an aircraft for you and haven't even provided the weight. The NACA paper isn't out of date and only provides a downwash angle to help you with the design decisions. I do hope someone else chimes in.

DangerZone, to get the most attention from the people you are trying to reach, I would suggest that you start a new thread rather than your question being an addendum to this older thread that is not precisely the subject that you are asking about.

Please be so kind to let me rephrase the claim about the NACA paper: it is an excellent paper yet it has little help in the question about tandem wing efficiency. And that is what I am looking for, best efficiency for a given configuration.

The weight of 245kg is mentioned in the first post, this weight is typical for ultralight homebuilt aircraft in many countries all over the World. There's no need for anyone to design the plane or alter the decalage angle, most relevant info is in the last lines of the second post. Now when it comes to decalage it does not neccessarily have to be determined by the airfoils chosen: put on this configuration the E1230 or the E1212 and the will both fly. The question is how efficient would they be for the specified configuration and which canard would be best to obtain the 65km/h (which is a very low speed for canards) and over 300km/h at as little power as possible?

I added my question to this thread because I thought it is on topic and have seen there are people who have read quite a few books about aerodynamics. I concluded they might know more about aerodynamics and that maybe some have more experience, or see things from a different angle, a different approach... Are you sure there is need for a new thread, it would have the same title..? "Which airfoils would have highest efficiency for a tandem wing configuration?"

plncraze

Well-Known Member
HBA Supporter
For a real world example of tandem wing aircraft look at the Arsenal Delanne modified Lysander from 1942. It was a tandem wing aircraft which was built and tested. See it in Darrol Stinton's book "Designt of the Aeroplane" which also talks about the Flying Flea and its behavior and modifications.

DangerZone

Well-Known Member
HBA Supporter
For a real world example of tandem wing aircraft look at the Arsenal Delanne modified Lysander from 1942. It was a tandem wing aircraft which was built and tested. See it in Darrol Stinton's book "Designt of the Aeroplane" which also talks about the Flying Flea and its behavior and modifications.
That Arsenal which was a modified Lysander had too many conceptual flaws to be a good operational tandem plane. Firstly, it wasn't a true canard/tandem wing but a tractor Lysander with a bigger tail. So, it had neither the advantages of the canard nor the benefits of a conventional airplane. Combine that with the awful visibility and that stops being a warplane and becomes a sitting duck flying in air. That is why it never went further than a concept, at the end of WWII Arsenal started making conventional planes with dual motor, I think those were the only ones made in a bigger number than one or just a concept.

There were many canards that had a good concept, like the Brittish Miles Libelulla (forgive me if I missed the spelling) or the Japanese Kyushu Shinden in that era yet all of them are beyond what I am looking for. The flying flea is more adequate, it is in the same group of homebuilt airplanes, it weights 280kg, has a larger wingspan of 8.5m and a wing area of 17.6m2 which results with a low stall speed of 63km/h yet produces too much drag so the top speed is only 250km/h, too inefficient for a tandem/canard. By comparison the RMT Bateleur weights 250kg, has a wingspan of 6.25m, a wing area of 14m2, 65km/h stall speed but a top speed of 320km/h at similar power, maybe even less at cruise.

There's plenty of real world examples, the EZs, the Berkut, the Quickies, the Amsoil Racer or its never beaten rival the Beck Mahoney Sorceress, then the Dragonflies, Flying Fleas of all sorts or small less known tandem wings and canards, but not so many of them proved to be quite succesfull. The biggest problem was the same that Rutan faced, even with the best aerodynamicists and engineers he had trouble in finding the most efficient airfoil to use in a canard configuration. A combination of airfoils that would provide both a low stall speed and a very fast top speed, using all the advantages of the tandem/canard configuration AND have a high efficiency at the same time. So I was just wondering if there are any more people who found some good solutions to this challenge..?

Autodidact

Well-Known Member
The subject of the original post is what configuration has the best efficiency and not what airfoil, and the thread has pretty much run it course and is seen by most people as Karoliina's thread and question. I think you could get a better response by starting a new thread that concentrates on your question, which is actually quite different, i.e., "what airfoil is best" for canard/tandem wing as opposed to "what configuration is best".

On the subject of airfoils, if one has a different camber it will have a different zero lift angle and will need to be set at a different angle of incidence. As for moment, a washout of 2 or 3 degrees has little or no effect on the difference in moment produced at the tips in cruise flight. The overall moment of the rear wing on a canard will have an effect on the angle that the front wing is set at for cruise equilibrium. These are very complex questions that you are asking and they certainly deserve their own dedicated thread. Just trying to help in my limited way.

DangerZone

Well-Known Member
HBA Supporter
The subject of the original post is what configuration has the best efficiency and not what airfoil, and the thread has pretty much run it course and is seen by most people as Karoliina's thread and question. I think you could get a better response by starting a new thread that concentrates on your question, which is actually quite different, i.e., "what airfoil is best" for canard/tandem wing as opposed to "what configuration is best".

On the subject of airfoils, if one has a different camber it will have a different zero lift angle and will need to be set at a different angle of incidence. As for moment, a washout of 2 or 3 degrees has little or no effect on the difference in moment produced at the tips in cruise flight. The overall moment of the rear wing on a canard will have an effect on the angle that the front wing is set at for cruise equilibrium. These are very complex questions that you are asking and they certainly deserve their own dedicated thread. Just trying to help in my limited way.

Autodidact, I read the thread, found it interesting and still would like to discuss the highest efficiency of a tandem configuration. I am not looking for a configuration, the tandem wing IS my configuration. A question like 'Which airfoil is best?' would be inappropriate because there is no 'best' airfoil, it is always mission specific or relates to what you want your airplane to be capable of doing.

The decalage is the angle difference between the wing (you called it rear wing) chord and the canard (most if not all tandem planes are canards) chord, while the washout is the angle difference at the tips of an airfoil. Those 2 to 3 degrees of washout would not matter much at low speeds but at speeds over 300km/h would just consume your power (power would be used to overcome drag and pitching moments) and make your tandem wing airplane inefficient. Yet the decalage angle can be overcome by an appropriate canard airfoil selection making the tandem configuration more efficient. As Aircar pointed out on the first page, the tandem wing can have as little as 0.6 of the induced drag of a monoplane of the same span and area so why not explore this idea further here..? Thus, you are right, it is a complex question and I just had the impression this would be a good place to further analyze the efficiency of such a tandem wing configuration.

Maybe it would be a good idea to see opinions of other people too before I open a new thread..?

StarJar

Well-Known Member
If I'm not mistaken they use the same airfoils on the Q2's as they do on the Cozy. I would just use those airfoils, including the updated Roncz airfoil for the canard. Just set the canard at 3 degrees. It's the safest and there will be hardly any performance lost compared to 2 degrees. Just set each each wing up to carry the same percentage of the total weight as they have done on the Cozy and Quickies. Just change the wing areas to give you the take off speeds you want. Best of luck.

DangerZone

Well-Known Member
HBA Supporter
If I'm not mistaken they use the same airfoils on the Q2's as they do on the Cozy. I would just use those airfoils, including the updated Roncz airfoil for the canard. Just set the canard at 3 degrees. It's the safest and there will be hardly any performance lost compared to 2 degrees. Just set each each wing up to carry the same percentage of the total weight as they have done on the Cozy and Quickies. Just change the wing areas to give you the take off speeds you want. Best of luck.
Thank you for the good luck wishes. As I wrote in the second post in this thread, the Q2 has the Eppler 1212 airfoil while the Cozy and EZs have the modified Eppler 1230 which are two different profiles. Would you or anyone else here know the exact decalage of the Cozy, the EZs and the Berkut..?

Denis

Well-Known Member
As Aircar pointed out on the first page, the tandem wing can have as little as 0.6 of the induced drag of a monoplane of the same span and area so why not explore this idea further here..?
I doubt. Such reduction in induced drag simply mean that the eqivalent span of a monoplane is increased by a factor of 1.29. One can imagine such result only if the interaction of the downwash fields of two equal wings, producing equal lifts, is almost completely suppressed. This means that these tandem wings must be greatly displaced both vertically and horizontally, by a distance comparable with a semispan. I cannot image a practical airplane with such extreme layout.
Further, one should judge the structural weight penalty against an equivalent monoiplane wing. A single wing of twice the area, same airfoil thickness and aspect ratio most likely will be lighter than two equal tandem wings, but its span will be larger by a factor of 1.41, and the induced drag will be further reduced. A conventional configuration is again a winner.

StarJar

Well-Known Member
Thank you for the good luck wishes. As I wrote in the second post in this thread, the Q2 has the Eppler 1212 airfoil while the Cozy and EZs have the modified Eppler 1230 which are two different profiles. Would you or anyone else here know the exact decalage of the Cozy, the EZs and the Berkut..?
OK I remember I did a lot research to build a plane a few years ago, and came to the conclusion that 3 degrees was pretty standard. I tried to find the exact decalage just now on Google search but couln't find for you (of EZs Berkut and Cozy. )
However I can tell you this. Once you have the plane flying, the position of the elevator will give you a hint of if you got it right. If the elevator is down a few degrees, then you have not enough incindence.(this might equate to a very small adjustment, like .2 degrees)
So whatever you decide to incorporate, test fly the airplane, but don't mess around with slow flight untill you take a look at the elevator angle, in level normal flight. You might want to install the canard with keeping in mind you may change the angle later. In other words don't do 100 hours of glossy finish all around it.
But here's another thing which makes this less critical than you may think; If a too small of decalage causes you to use more elevator, the chances are you are going to have an even earlier trailing edge stall (on the canard) than if you had more decalage. So in my mind it all sort evens out. I screwed around with models and found it was actually very hard to make the rear wing stall first on a plane that is actually flyable. But of course you eventually want to adjust it so it has nuetral elevator in normal level flight.
I wish i could give you the exact degrees for those planes, as that would be nice. Hope the the above stuff helps.

Hot Wings

Grumpy Cynic
HBA Supporter
Log Member
Original Quickie (single seat) template level lines:

E 1212 main wing
BL-10 = 0.46 degrees positive
BL-52 = 0.22 degrees negative
BL-100 = 1.9 degrees negative

LS-1 canard
BL-10 = 1.68 degrees positive
BL-51 = 0.49 degrees positive
BL-92 = 0.0 degrees

GU canard
BL-10 = 0.07 degrees positive
BL-49 = 0.22 degrees negative
Bl-88 = 0.74 degrees negative

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