My winter project will be a 1/5 scale Wilga which I will use as an aero-tow tug, powered by a G-62. The kit I have was built by Fan Fly in the Slovak Republic, but I am going to do more than simply add an engine and radio before I fly it.

As the full size version of the Wilga is equipped with leading edge slots, I would like to add this enhancement to the model. The wing is of the built-up variety, with a NACA 2415 section. My inclination is to simply add a permanent extension (I am not sure what to call the piece in front of the slot!!) to form a gap about 1/4 inch wide at the top and slightly more than 1/2 inch at the bottom. The extension would be airfoil shaped with the forward-most part in line with the zero camber line of the main part of the airfoil.

Does anyone have any experience with building this sort of thing?

What are the cg considerations, and what can be expected in the way of lift changes?

What are the pitfalls?

I've attached an image, with data from Andy Lennon's book, "The Basics of R/C Model Aircraft Design", which shows the proportions.

This also gives me an opportunity to mention that I've created a set of web pages which details many kinds of high-lift devices, at http://homepage.mac.com/mikejames/rc...ite/index.html This (free and non-commercial) site already has several contributions from RCU members, and I encourage you to share your progress with us, so I can add it to the "Contributor's Pages".

Good luck!

Leading edge slots such as shown in Mikes post should have no significant effect on the cg or performance in normal flight attitudes. There will be a small (but probably not noticable) drag increase in normal flight attitudes. The slot transfers energy to the upper boundry layer which delays the stall to a higher angle of attack allowing the wing to produce more lift before stalling. It's a nice addition to be true to scale, but won't really effect the flight characteristics much.

Mike

Thanks for your post. I have been a frequent visitor to your site and it has provided me with the motivation to continue with this part of my project.

Lou W

Thanks for your input as well. As I intend to use the model as a tow plane, the performance characteristics that you describe are not sub-optimal and serve to encourage me as well.

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As I have an already made built up wing to start with - the airfoil is a NACA 2415 - my intention is to use the add-on procedure. Gordon Whitehead's book on Scale Aircraft includes the attached diagram which I see as eminently doable.

Does anyone have any experience with this particular approach, or comments on its viability?

Gudmund

What about doing an Ugly Stik sort of test model for a smaller engine size? I'm thinking of a test model that copies the wing airfoil but allows you to try various slot arrangements. It could be powered by a 25 to 40 and the fuselage would be Wilga'ish but box shaped in section. The leading edge slots could be set up to either be adjustable or repaceable so that different add on plates similar to the Fiesler type could be used to position the slot airfoil at different locations.

The towplane is a pretty sizable chunk of money and time. Seems like a little sport model to test some of this stuff would be a good idea. As a bonus you could put the flaps on as well and it would make a pretty decent little sport model in it's own right afterwards I would think.

Gudmund,

The configuration shown in your diagram should work fine. It is important that the slot form a nice channel that directs the air tangentially along the upper surface, and the configuration you show certainly does that.

banktoturn

I have seen a heavy lift model perform quite well with slots. They were full span in segments 8 or 10 inches long. There were some moments where I'd seen other similar planes tip stall where this plane only got sluggish and mushed straight ahead.

I suppose one drawback would be if you didn't get the slots matched well on each side, there could be some difference in roll trim or uneven stalling.

Also, I'm not dure why you want to use a hook-shaped flange to attach the slot-LE. I would just use something that looks more like a regular rib.

Johng

Thanks for your comments. I am, of course, hoping for a mushy stall characteristic.

The hooked flange holding the slot onto the wing is Whitehead's suggestion. I was thinking about using arrow shafts (or some similar material), but I am concerned that there may be insuficient tortional stability (ie, the slots may wobble around because of insuficient support - much the way an umbrella waves in the wind, but in this case the umbrella would be really long and would be supported by a number of poles all in a line!).

I will need to do some experiments on the attachment method, but I am pretty well set on the shape and positioning of the slot.

Gudmund

I did a lot of experiments with leading edge slots on a Balsa USA stick 40... the plane was able to fly at angles of attack in excess of 30 degrees, stall speed was reduced dramatically.. the slots just about double Cl max for the airfoil section. The only problems I encountered were controlability issues at such a high angle of attack, and high power setting.. the solution was to add vertical fin area under the horizontal stabilizers. I was also involved with a wind tunnel experiment on several different leading edge high lift devices... the slots were the most effective. The wind tunnel model (a J-3 cub with a clark y airfoil) could not be set at an agle of attack greater than about 50 degrees, at that angle the tufts on the upper surface were showing about 80-90% of the boundary layer was still attached.

Your plans look good for geometry.

Good luck, the stick was an absolute blast to fly with those slots.

Ty