Talk:Tandem wing

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Practical Tandem Wing CG[edit]

On the CG envelope point, IIRC, the quickie and Q200 actually have excessively poor CG ranges, and it is one of the reasons that the type has never been adapted as a four-seater. I think this has to do with the absolutely necessity that the fore-wing always stall before the aft. I'll check for my source on that before updating the entry. - ESC —The preceding unsigned comment was added by (talk) 01:09, 26 April 2007 (UTC).

Tandem stability explanation[edit]

"The difference between a tandem wing and a biplane etc..." Quite all the following text is totally wrong and out of aerodynamics; stability is a matter of CG position and lift slopes of front and aft wing, anyway canard, tandem or classic. For any of them, large or poor CG range may exist; there is no "a priori" large or poor CG configuration, each time it is a matter of design and balance. Previous text tells that Q200 has excessively poor CG range... Testing of Miles Libellula M35 gave very poor longitudinal stability (no wind tunnel testing was done before flight).Plxd (talk) 19:23, 8 October 2011 (UTC)

to me, as a non-theoretician and air-plane-model-builder, what you say is not obvious... do yourself a favor: build three basic paper-models: crease a paper V-shaped and cut out a tandem-wing - model A -, that is a structure of two crosses so to speak; stabilize the wings by giving them a slight, rounded crease (transverse to the main crease). then build another one with just one wing in the middle - mod B - , no tail. and a third with the usual small tail - mod C... let them fly, with a push, and without (just letting them fall).
mod B tends to quickly rotate around the pitch-axis. mod C tends to 'pump' (don't know if you say so too in english; I mean to say: flies in a wave-movement with the tail slumping until it almost stalls - if it doesn't stall alltogether -, falls, picks up speed, and the tail comes up again, as a consequence. you will have to adjust the cg heavily by applying strips of adhesive film to the nose to get it flying in a straight line forward - with a bad gliding angle... mod A unchanged, if let loose without a push, will tend to sink without any rotation - because of the symmetrical arrangement of the tandem-wing. if you want it to automatically fly forward you also have to load the nose, but much less than with mod C. so the gliding angle is better...
now, how do you explain that in your theoretical terms? thank you! --HilmarHansWerner (talk) 13:31, 3 February 2013 (UTC)

Basic disadvantages of the tandem-wing design?[edit]

could you please describe in non-mathematical terms the basic disadvantages of the tandem-wing-design over the 'normal' one? what comes to mind immediately is: double the amount of induced drag (unless you join the two wings to form a box-wing) because you have four wing tips instead of two (sorry, that's already mathematics... ;-) ). right? what else? in other terms: why is the tandem wing concept not normally used? just our unconcious tendency to imitate birds (next question: why don't they 'use' it?) or something else?

an interesting additional question would be if there are any aerodynamical disadvantages if you arrange the two wings in one plane (not like with the QAC Quickie where they are staggered, but rather like with the Scaled Composites Proteus)?

in the article about the Rutan Quickie it says about the advantages and disadvantages: "The absence of a tailplane both reduces drag (!) and allows the aft fuselage to be slender since it has less to support.[citation needed] The canard layout[5] provides positive lift from both pairs of wings, whereas a conventional tailplane supplies negative lift (!). Being sited much higher than the canard, the aft wing avoids being affected by its downwash (?!)." what does "downwash" mean? turbulences that affect the performance of the second wing in the wake of the first one?

thank you! --HilmarHansWerner (talk) 13:41, 3 February 2013 (UTC)

Downwash? That is the downward velocity of the air after it has passed the wing.
Aerodynamic theory, and history, have shown that supporting all the weight of an aircraft on one main wing, and then supplying a balancing and stabilizing downforce on a small horizontal stabilizer located at the rear of the main wing, is usually the most efficient configuration - minimum construction cost, minimum drag and minimum take-off/landing distances for a given payload. Why build two wings when one is sufficient?
Prior to the modern era when high-compression engines and high-strength materials like aluminum alloys became available, most aircraft were biplanes but the two wings were one above the another, not one behind the other in a tandem configuration. In the biplane configuration each wing receives airflow that has not been affected by another wing, whereas in the tandem wing configuration the rear wing lies in the wake of the front wing and is affected by its downwash; this creates problems in achieving longitudinal static stability without adding too much to drag. Designers have examined the characteristics of both configurations and almost all selected the biplane configuration rather than the tandem wing. Dolphin (t) 05:16, 4 February 2013 (UTC)
thank you very much, dolphin51, for your reply, to a lazy guy like me, who does not check out if there is an article about a notion before asking... (I now linked the term "downwash" in the article about the rutan quickie to the downwash-article...)
you ask: "Why build two wings when one is sufficient?" There may be various reasons; for patenting reasons I can not talk about all of them. but the main reason is mentioned in the quotation from the "rutan quickie"-article: " The canard layout provides positive lift from both pairs of wings, whereas a conventional tailplane supplies negative lift (!)." secondly you might want to have an airplane that can use WIG-effect, an "ecranoplan"; there a tandem-wing-design is desireable for stability-reasons.
finally I would like to ask: why do you think does a top-designer like burt rutan conceive something like the record holding Scaled Composites Proteus, with the wings even in one plane...???

Orthographically projected diagram of the Scaled Composites Proteus.

Scaled Composites Proteus.

inasmuch do you think that this plane "creates problems in achieving longitudinal static stability without adding too much to drag"?? shouldn't the downwash-stream of air coming from a front-wing go past a second one behind it beneath it??
and, by the way, nature uses the tandem wing repeatedly with insects: dragon flies, butterflies... you see them even gliding (whereas I never saw a 'monowing'-insect glide...)

Broad-bodied Chaser

A Tau Emerald (Hemicordulia tau) in midflight

thanks for another answer in advance! --HilmarHansWerner (talk) 21:41, 4 February 2013 (UTC)
Why build two wings when one is sufficient? The best way to generate the required amount of lift is with one wing of suitable wing loading, planform and aspect ratio. It is a mistake to imagine that adding a second wing will increase the amount of lift generated - lift is approximately equal to the weight of the aircraft. Making use of extra wings isn’t capable of increasing the lift, but it is certainly capable of increasing the drag!
Burt Rutan is a famous advocate of the lifting-canard configuration. He has designed a number of canard types suitable for amateur building. He has also built a number of specialist aircraft using the canard configuration. In certain roles, the lifting-canard offers some advantages. For example, bending loads in the fuselage of a lifting-canard can be made smaller than the loads in the fuselage of a conventional aircraft; this is useful because the area with the greatest bending load is usually where it is necessary to make a cutout in the fuselage to place the door! As another example, it is necessary to design a lifting-canard so it will stall before the larger, rear wing. This has the advantage of making the lifting-canard stall resistant and therefore spin resistant. However, it has the disadvantage that the larger wing never reaches its maximum lift coefficient; consequently lifting-canards have a higher minimum flight speed than you would expect from their wing loading, so takeoff and landing distances are longer than you would expect. This can be mitigated by increasing the wing area in order to lower the wing loading but extra wing area causes extra parasite drag. The lifting-canard configuration would not be the best for a short take and landing aircraft unless extra parasite drag can be tolerated.
An excellent book on this subject is The Design of the Aeroplane by Darrol Stinton (1983), published first by Granada Publishing and then by Blackwell Science. On pp.146-153 Stinton considers the performance aspects of lifting-canards. He points out that it is difficult to design a lifting-canard with wing flaps so this has an obvious disadvantage when considering takeoff and landing performance. Extra wetted wing area can be used instead of flaps but this has a disadvantage in the cruise. Stability requirements of the lifting-canard are covered on pp.389-391.
The end result is that the lifting-canard has some significant advantages for a small number of specialist roles. These are the roles for which Burt Rutan has focussed his attention. Lifting-canards are not well suited to many roles. No lifting-canard aircraft has been commercially successful. The Rutan VariEze and Long-EZ were built in large numbers but they are amateur built and not eligible for commercial operations. The Beechcraft Starship was eligible for commercial operations but only 53 were built and most have been withdrawn from service and destroyed.
I agree that many flying insects use the tandem wing configuration. These are hovering insects so drag and speed are unimportant. They operate at ultra-low Reynolds number so their aerodynamics is significantly different to the aerodynamics of manned aircraft. Dolphin (t) 06:14, 8 February 2013 (UTC)