The world truly seems to be smaller today, thanks in large part to aviation. This has created a renewed interest in many of us to see what is around us, and not just to dash as quickly as possible to a new destination.
While recreational aviation certainly has its share of high-performance fast aircraft, I think that what continues to draw most of us to flying is the shear excitement, enjoyment and freedom of being at the controls of our own aircraft. The popularity of aircraft like the Piper Cub has endured and grown over the years, not only on account of nostalgia, but because these aircraft are just plain fun and easy to fly and provide good grass field capability most classic aircraft were developed in a time when paved runways were rare.
However, because of their age, many of these older designs do not offer modern improvements that most of us take for granted, such as electrical systems, side-by-side seating, all-metal construction, steerable nosewheel, etc.
And of course, classic airplanes are becoming scarce and require significant maintenance just to keep them airworthy. When we do fly cross-country, the trip is as important if not more as arriving to the destination. A STOL short take-off and landing airplane gives us the ability to go to more places, especially in remote areas, where the world becomes your runway this is an important safety feature too.
With good payload, we have the ability to haul all the bags we want camping equipmentor amphibious floats can give us the added capability and freedom to operate from water.
Today, with the knowledge accumulated for over a century on aerodynamics, structural strength, on their relation in aerolasticity flutteron ergonomics and with the ongoing development of modern, efficient, reliable and lightweight engines, it is relatively easy for almost anyone curious enough to seriously study the above fields to design a light aircraft capable of carrying two to four occupants.
As a professional light aircraft designer and engineer I have done just that … quite a few times. Thus I designed the STOL CH aircraft: It needed to offer outstanding short and rough field performance, acceptable cruise performance, good cross-wind capability, excellent visibility, comfortable side-by-side seating, and a durable all-metal airframe — that was easy to build and maintain.
The two seat STOL CH was introduced in to take advantage of the new Sport Pilot category and to provide more cabin room than the original and new engine choices. However, with form following function, a study of the unique shapes shows the inherent beauty of these aircraft in their interesting, unique and highly effective aerodynamic and design features.
Following is an explanation of the basic design concepts that I have applied in designing my STOL aircraft:. Overpowering an existing aircraft is the easiest way to achieve short take-off performance with enough power anything will take-off in a short distance!
My experience tells me that I need 60 to hp for a two-seat aircraft, or to hp for a four-seater capable of carrying 1, lbs. As an airplane designer and builder and not an engine manufacturerI design aircraft around existing and readily-available engines.
For maximum flexibility and to keep costs low, a kit aircraft must be designed to accommodate different engine types so that owners can choose among existing and new powerplants. To be practical, a STOL aircraft must be able to fly at very low speeds, yet it must also offer acceptable cross-country cruise performance.
Relatively short wings make the aircraft easier to taxi, especially when operating in an off-airport environment with obstructions, and requires less space for hangaring, while being easier to build, and stronger less weight and wing span to support.
Figure 1 — Stalled Airfoil. To delay the stall to a higher lift coefficient, many airplanes are equipped with flaps on the wing trailing edgeand a few designs use slats on the wing leading edge to further lower the stall speed. Figure 2 — Lift Coefficient vs. Airfoil Angle of Attack.Forums New posts Search forums. Media New media New comments Search media.
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Topaz Super Moderator Staff member. Log Member. With a traditional fabric-covered wing, you might as well use a traditional airfoil, as well. Even the old Clark Y has decent lift and drag, all things considered, for this kind of application. Not to mention that the GA W -1 has an absolutely horrific pitching moment.
In general, the obsession with "high lift" is misplaced with very light aircraft, such as those that tend to be fabric-covered. Remember that stall speed and cruising speed are not the only performance parameters that matter in a light airplane. Perhaps even more important are climb and glide performance, and the safety that comes with them. It's entirely possible to "over-do" the quest for high lift and a small wing, such that climb and glide performance become dangerous.Forums New posts Search forums.
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Armilite Well-Known Member. Aerowerx Well-Known Member. I'm sure others with more knowledge will answer, but That is not an easy question to answer. There are probably dozens of airfoils that will work. With part you are limited to pounds empty. With a pound pilot FAA uses pounds and 5 gallons of gas, that is pounds gross.
Your stall speed is limited to 24 knots. Then you have to consider the wing area you want. From the wing area, stall speed, and weight you can determine the over all lift coefficient, and then start looking for an airfoil that meets those requirements. As I said, there are dozens that would work.
A common one is the venerable Clark Y. It goes over the basic design process. Joined Nov 3, Messages 3, Armilite said:. Topaz Super Moderator Staff member. Log Member. How high is "high"? Most of the older Clark 'Y' and such airfoils would be fine. The Harry Riblett GA series would be very good, with the rest of the digits filled in depending on the exact mission of your ultralight.
Many, many ultralights don't have a really defined "airfoil", rather they have a consistent cross-section on the wing that's defined by stretched fabric over aluminum tube or even in the oldest examples wooden-stick "battens.
Airfoils are chosen to suit a particular set of mission needs, for a particular wing that's already been designed.The most commonly used airfoils for flying model aircraft are:.
Each family encompasses a large selection of airfoils but we use very few of them due to habit or not having a clue about how to properly select a real airfoil. By "real" I mean an airfoil that has been designed and tested by the aerospace industry.
Data on real airfoils won't apply in our realm anyway. The airfoils are tested at larger sizes than the average model and things change as size changes. However, the airfoils should scale down comparatively. For example, if one airfoil is tested to stall sooner than another airfoil, then the stall speeds may be much different when scaled down but both airfoils should still stall in the same order.
That may not always be true, but it's a good rule of thumb. If you are purpose-building something competitive that requires the best possible airfoil for the application then I can't help you. However, if you enroll at a school of Aerospace then you can probably get help there. Almost nobody who designs model airplanes would have a clue how to pick an airfoil for their design based on real airfoil data. We learn from experience knowing that the subtleties between one airfoil and another close to the same shape will make a very small difference — one that would only be noticed by an expert pilot.
These behaviors are not different enough to cause any problems in your design unless you do something like change a round leading edge to one that is razor sharp. The difference won't be something like one airfoil is "right" and the other makes your plane loop back into the ground on take-off. Again, I'm comparing airfoils that are basically the same shape within a family.
Note that there will be a huge difference between any under-cambered vs. If you want to design unique planes that fly for fun, then stay in the realm of reason and make your airfoil close to the shape of airfoils used by other planes of roughly the same type. Don't get hung up about it. If you can't decide then copy an airfoil in use on a model and scale it to the right size for your model.
I almost never use a real airfoil in my designs. I have airfoils that I've used on previous models so I know how they behave. For a new design I adjust the airfoil to behave more how I want it to on the new model. For example, I may thicken it to slow the model or make the leading edge radius smaller to allow sharper stall maneuvers. If I need an airfoil of a type I have never used before then I pull out my airfoil books and look at drawings. The data is meaningless to me. I imagine the airfoil in the application and fly it in my mind.
Watch the videos in my gallery and you'll see that it works well and I'm not seeing sport designs that fly better than mine. Because all designs represent numerous compromises you'll have to use the above to decide which characteristics are more important than others.
Select a specific airfoil using whatever information you have.The UIUC Applied Aerodynamics group has been a leader in this research area with new airfoil designs being applied to unmanned aerial vehicles, small wind turbines, model aircraft and many other applications. The airfoil performance data from these tests are have been published in several books that are available in pdf format here. Printed copies published by SoarTech Aero can still be purchased online through a donation to our ongoing wind tunnel test program see below.
Aircraft Design Comes First
Also available here online and in printed format by SoarTech Aero Publications is the book Airfoils at Low Speeds SoarTech 8which includes wind tunnel data on 54 airfoils tested at Reynolds numbers ranging from 60, toThe book contains extensive commentary and analysis.
A three-component wind tunnel force balance was designed and assembled to study the low Reynolds number aerodynamics of low-to-moderate aspect ratio wings. The balance designed is capable of measuring lift, drag and moment of wings. Please contact gavin. The first two volumes include lift and drag coefficient data while the second two volumes also include pitching moment data. For SoarTech 8 tabulated airfoil data, see link above. Additional data on the S with Gurney flaps is in Vol 5. They are semisymmetrical with an aft flat bottom for easy building.
The experimental data was publically released in thanks to the agreement of the project sponsor. Low Reynolds number airfoils are defined by having a laminar separation bubble that causes an increase in drag. This bubble can be seen by injecting smoke into the boundary layer and also by a technique called oil flow visualization [graphics downloads].
Low Reynolds Number Airfoil Publications In addition to Volssome low Reynolds number airfoil publications from our group are listed below. Wind tunnel data on 34 airfoils tested at Reynolds Numbers ranging from 30, toSelig, M. Wind tunnel data on 25 airfoils tested at Reynolds Numbers ranging from 40, toLyon, C. Wind tunnel data on 37 airfoils tested at Reynolds Numbers ranging from 60, toSix airfoils tested at Reynolds Numbers ranging fromtoWilliamson, G. D, Broughton, B.Sport Utility.
Building Info. Kit Info. Cabin Details. Engine Info. Press Reviews. Pricing Information. Builders on the Net. Factory Workshops. Folding Wings. High-Lift Design. Follow us for updates:. A short take-off and landing STOL aircraft must be able to fly at low controlled speeds, yet it must also offer acceptable cross-country cruise performance. The challenge is to design a wing with a high lift coefficient so that the wing area is as small as possible, while allowing for take-off and landing speeds that are as low as possible.
Short wings make the aircraft easier to taxi, especially when operating in an off-airport environment with obstructions. They also allow for better visibility, and require less space for hangaring, while also being easier to build and stronger less weight and wing span to support. Conventional trailing-edge wing flaps help delay the stall to a higher lift coefficient, but only with limited effectiveness.
However, by combining the use of trailing-edge flaps with leading-edge slats, the wing's lift coefficient can be effectively doubled if used on the full span of the wing. Leading edge slats prevent the stall up to approximately 30 degrees incidence angle of attack by picking up a lot of air from below, where the slot is large and accelerating the air in the funnel shaped slot venturi effect and blowing this fast air tangentially on the upper wing surface through the much smaller slot.
This effectively "pulls" the air around the leading edge, thus preventing the stall up to a much higher angle of incidence and lift coefficient. The disadvantage of leading-edge slats is that the air acceleration in the slot requires energy it creates additional drag. While many STOL designs utilize retractible leading-edge slat devices, the additional weight, complexity, reliability issues and cost of such systems minimize their feasibility for use in light aircraft and their overall effectiveness.
The wings are braced by dual steel wing struts, and are bolted to the fuselage at the cabin frame with four bolts for easy wing attachment and removal. Click here for a detailed schematic of the Slats and Flaperon Assemblies. Aero : Online community for active Zenith builders, owners and pilots. Tel: Mon - Fri, CentralComments or questions? Click Here. STOL Updates. Search zenithair.
Starter Kit.Scientific Research An Academic Publisher. Several experimental investigations on estimating the lift coefficient of airfoils in two-dimensional 2D smoke tunnels have been performed  - . The technique estimating the sectional lift coefficient from the flow visualization results in the 2D smoke tunnel was proposed by Yamana  , and it was successfully applied to the basic airfoil and the cases of flaps.
In a smoke tunnel, the streamlines can be visualized as smoke lines. The lift coefficient can be estimated by measuring the distance from several points on a specific streamline to the reference line in the middle of the test section and by applying the measured values to the circulation equation.
The origin of the coordinates is set at a quarter chord length from the leading edge of the airfoil. When a high-lift device, such as Gurney flap, is attached to an airfoil, the center of pressure displaces from the origin since effective camber varies due to the flap.
There are two calculation methods to evaluate it.
High lift airfoils compatible with fabric construction?
The first one is that measures the displacement sc of the center of pressure from the origin of the coordinate in the streamwise direction. Another is that considers the height y s where the distance from the streamline to the reference line is the largest.
Yamana et al. In the original method, a smoke line must be adjusted to intersect with the reference line at a specific distance of upstream. It requires a long test section of smoke tunnel to visualize and adjust the intersection. Yamaguchi et al. The modified method was carefully validated by conventional airfoil data. In the study, the method was applied to investigate the lift characteristics of a double-wedge airfoil and modified double-wedge airfoil .
To take into account the displacement of the center of pressure when a small high-lift device is attached to the airfoils, Kashitani et al. In comparison with the measurement of the value sc, it is expected that y s can be measured within higher spatial resolution, because it basically tends to be larger measured value. It is considered that more accurate results can be obtained by the method using y s.
Supercritical airfoils are widely used for civil transport aircraft. These airfoils first garnered attention when NASA made efforts to develop an airfoil that shows better performance in transonic flow while retaining acceptable characteristics in the low-speed flow .
Generally, supercritical airfoils in combination with flaps are considered to improve the aerodynamic performance of aircraft, especially during takeoff and landing . The supercritical airfoils have asymmetric configuration and a camber near the trailing edge. In this study, the displacement of the center of pressure is controlled by varying angle of attack and by installing a small trailing-edge flap called Gurney flap GF aiming to investigate the scope of the applicability of the method.
A Gurney flap GF is a simple and small flat plate installed at the trailing edge. The higher effective camber is obtained when the GF is installed. Studies about Gurney flaps have been performed and have demonstrated the impressive lift enhancement effect of the GF   .
The results of these studies also showed that the use of a GF significantly increases the pre-stall lift and lift-to-drag ratio at small angles of attack. Understanding the aerodynamic characteristics of transonic airfoils with Gurney flaps at low-speed flow is also useful for aircraft designs.