Wing designs

[windywestflyer]

I have been to many differant sites trying to find out certain characteristics about wing design. I don't mean airfoils, they. I mean the characteristics of having tapered wings or rectangular wings, elliptical wings, etc. What are differant flight characteristics associated with these types of wings? Very little information is accessable so any literature or responce would help drastically.

[DT56]

A few links:

http://www.mh-aerotools.de/airfoils/

http://www.twitt.org/

http://www.b2streamlines.com/OTW.html

http://www.ef-uk.net/data/plans.htm

http://en.wikipedia.org/wiki/Category:Wing_design

http://www.desktopaero.com/appliedaero/wingdesign/wingdesign.html

[nmasters]

http://www.rcgroups.com/forums/showthread.php?t=933270

[ziomatrixacs]

I just made a chart for my own personal records a few days ago..Basically I took a few hundred 3 view drawings and compared them like animals. Long thin wings? must be a glider. Straight LE, swept TE, must be aerobatic. Swept LE and TE, must be aerobatic too. Swept LE, straight TE, must be pattern or a trainer...

[eflightray]

Problem is, the airfoil used is probably the bigger characteristic than the shape.

Especially at model sizes, we don't exactly build sweptback wing to aid Mach penetration.

Now if your looking for 'different' shapes, have a look at Early Aircraft Design (http://www.adventurelounge.com/aircraft/) just click on the thumbnail pictures, some weird and wonderful there. :D

[ziomatrixacs]

Problem is, the airfoil used is probably the bigger characteristic than the shape.

Especially at model sizes, we don't exactly build sweptback wing to aid Mach penetration.

Now if your looking for 'different' shapes, have a look at Early Aircraft Design (http://www.adventurelounge.com/aircraft/) just click on the thumbnail pictures, some weird and wonderful there. :D


I agree. On our smaller scale, the fudge factor is much forgiving. Some shapes do have some useful properties. Dihedral any one? I noticed that sweeping the leading edges back a few degrees acts like dihedral. A swept forward TE improves aerobatic ability but takes a little away from the precision side..

Its hard to say how much an airfoil helps when you have a symmetrical foil though. Thickness and chord become the variables.

[windywestflyer]

It seems that the general properties of wing designs for the most part stem from the variety of 2-d airfoils in the wing. Each individual airfoil could be taken into accout when determining the characteristics of the whole wing

[ziomatrixacs]

Thats true too. A wing with an airfoil with washout in the root and negative wash out in the tip must have some funky flight characteristics.

[eflightray]

Now how would you class this wing shape, (see picture), swept back L.E. and swept forward T.E........aerobatic?

I doubt it would be very good inverted with that section.

Regarding wing sections, (rib profiles), it's a very exacting science, that's why there are so many variations. But when it comes to model sports flying......anything goes. :)

[Brandano]

A simple taper is ideal for acrobatic flight, because it is easily predictable in pretty much every situation and can still be made to stall or spin when needed. Whether the sweep is negative or positive is usually a matter of where the weight of the engine is and where is more convenient to get the main spar to go through the fuselage. Ideally you want a mid-wing plane, but this is in contrast with the placement of the cockpit. On a pattern plane the trend is to get everything "straight", and adding a little sweep to the wing allows the trailing edge to be at an ideal 90 degrees to the airflow. regarding the difficulty of getting a bunch of different ribs for a wing, it doesn't make much of a difference whether a wing is tapered or elliptical. You will still need to make a set of different wing ribs, though you can "cheat" a little with model planes and just sand a lot of them pinned together. On a full size plane the rib profile is likely to change between the root and the wingtip, if anything to change the relative thickness, so even a straight wing might need to have several different ribs

[ziomatrixacs]

Now how would you class this wing shape, (see picture), swept back L.E. and swept forward T.E........aerobatic?

I doubt it would be very good inverted with that section.

Regarding wing sections, (rib profiles), it's a very exacting science, that's why there are so many variations. But when it comes to model sports flying......anything goes. :)

Thats easy, an Extra 300 has a roughly similar wing but much more power.
Everyone knows those old planes dont have no motor in dem' :D

You make a good point, the Citabria is a high winged aerobatic airplane.

http://www.airplanemart.com/Arlington-Northwest-EAA-Fly-In/2007-Fly-In/aircraft-images/American-Champion-7GCAA-Citabria-Adventure-N429AC.jpg

That plane, if it were scaled down to RC size and built with the right materials, Id say it would have some aerobatic capability. As a full scale plane, those flying wires are there for a purpose, it probably would fold like a book if inverted. It also probably wouldnt have enough motor power to hold the nose up during an aileron roll (If it has ailerons!)
If you put a big enough engine in that airplane, and reinforced it a lot, I would bet it could do basic aerobatics like a roll, loop, maybe a hammer head turn. I am 90% sure it would fly inverted, but it would need a high (and negative if you want to get technical) angle of attack (at that point it would be flying by newton's law) Possible but not practical.


Airfoil is the majority of the performance of the wing. Planform sections enhance the properties of the wing. Wing tip devices also enhance the performance. There are a lot of little variables, and hard to pin point them down. I just went though a ton of 3 views noting what the wing looked like and how it was meant to perform.

[Ram-It]

Through some of my own research what I have read, straight "hershy bar" wing is the most forgiving. Rear swept leading edge wing has improved roll characteristics, however loop tracking isn't as good. The wing with forward swepy trailing edge is just the opposite and a double taper is a compromise.

[JetPlaneFlyer]

Windywestflyer,

The biggest effect of taper on a wing (LE or TE or both) is to alter the spanwise lift and coefficient of lift distribution.

A parallel chord (un-tapered) wing due to an effect called downwash, caused by the parallel wing's strong tip vortexes results in the wing tips operating at an effectively lower angle of attack than the root. This means the root will stall first, this is good as the wing will resist tip stall and the ailerons will retain effectiveness even after the wing root is stalled. The bad thing is that the downwash causes induced drag so the wing is operating inefficiently. Generally then a un-tapered wing is 'safe' but not very efficient. You will see un-tapered wings used where low speed handling is considered more important than efficiency and outright performance.

An elliptical wing is the 'perfect' shape. All the wing will operate at the same angle of attack, and induced drag is minimised, therefore it's the most efficient planform. The bad news is that the stall can be very dangerous. The tip is narrower so operates at lower Raynolds number, this and any downward aileron deflection will cause the tip to stall first with potentially disastrous consequences. Elliptical wings are also harder to build... For these reasons elliptical wings though theoretically 'perfect' are not very often used.

Tapered wings can be a compromise between parallel and elliptical. The closer they get to resembling an elliptical planform the more efficient they become but the more prone to tip stall they get. Most tapered wings use a moderate taper ratio that delivers most of the efficiency benefits of the elliptical wing but keeps the safe stall behaviour of the parallel chord wing.
Tapered wings also have structural benefits over parallel chord jobs. A tapered wing has more of its area inboard therefore the bending moment on the wing is less. Also the wing is thicker near the root allowing deeper and stronger spar to be used. This results in tapered wings having a better strength/weight ratio than parallel wings.

The aerodynamic characteristics of all wing planforms can be modified by adding washout.. that is twisting the wing so that the tip operates at lower angle of attack. By using washout heavily tapered wings and elliptical wings can be made to stall 'safe'... but efficiency is reduced.

Wing sweep is another kettle of fish. Unless your model is tailless it's hard to see a good aerodynamic reason for using sweep on a model (unless on a scale model). The only real benifit of sweep is to raise the critical mach number and as models dont get anywhere near the speed of sound this does not help us at all. Sweep can potentially bring with it all sorts of problems.

Steve

[nfhill]

A couple of additional thoughts:

The most efficient shape for a wing is one which results in an elliptical spanwise lift distribution. An elliptical plan-form is one way to achieve this, but it is not the only way.

A tapered wing is not necessarily a swept wing.

Wing sweep does have a useful function for small slow airplanes like our models. Wing sweep effects roll stability. Aft wing sweep increases roll stability and unlike dihedral it doesn't change when inverted. That is why so many 'pattern' type models have swept wings with no dihedral.

Nick

[JetPlaneFlyer]

Nick,
I'd have thought that the very last thing a pattern thip wanted was dihedral effect as it would give undesirable yaw/roll couple. I always thought neutral stability was the target for such models?

But yes, rearward sweep does have a dihedral like effect which could be benificial on some models, but it's usually easier and more effective to simply add dihedral if that's what you want. Sweep also has undesirable effects such as making the wing more prone to tip stall and/or deep stall, plus it increases induced drag.

Steve

[JetPlaneFlyer]

A couple of additional thoughts:

The most efficient shape for a wing is one which results in an elliptical spanwise lift distribution. An elliptical plan-form is one way to achieve this, but it is not the only way.



Yes and no... Elliptical lift distribution IS most efficient (because downwash is evenly distributed spanwise) and yes you can achieve elleptical lift distribution with wing planforms other than elliptical (by using twist)... BUT anything other than eliptical planform will still not be as efficient because the twist that delivers eliptical lift distribution also means that large parts of the wing are operating outside their most efficient angle of attack. Also twist only delivers elliptical lift distribution at one flying speed (i.e. one AoA), any other speed and the lift distribution moves rapidly away from elliptical. An elliptical wing has elliptical lift distribution whatever the AoA.