The Ridge Runner Glider Wing
Greetings to the Flite Test Community
Recently I have been looking around for a slope soaring glider. So I had a look through the Flite Test articles and the Flite Test store to see what I could come up with. There are a few slope soarers, it is true, but what I wanted was an agile polyhedral winged glider. Something that would fly on two channels, which was a step up from the Simple Soarer, but designed for slope soaring. Unfortunately there didn't seem to be anything that fit this set of requirements.
The Wing Design Process
The only option to pursue was to design and build a slope soaring glider completely from scratch. I did alot of research, and I mean, alot. There are many factors involved, but the fundamental issue is the profile of the wing. Foam board doesn't really lend itself easily to producing complex airfoil profiles. And especially not using simple and expedient Flite Test build techniques, which is a part of my personal build mandate for all of my designs. Indeed, to create a reasonably good slope soaring glider I was going to have to come up with a solution to producing a more complex airfoil shape using those very same simple and reproducible Flite Test techniques.
The solution, in the end, is simple and elegant once you have the answer: introduce camber into the airfoil profile. Camber in a wing is where the bottom profile of the wing is not flat, but curved, in a similar manner to the top profile. A way to think about this is if you imagine a typical flite test wing cut in section, then if you could bend the tip of the wing profile down, keep the middle section flat and then bend the rear section of the wing profile down as well. See the picture below, showing my Ridge Runner wing camber:
Camber has the wonderful effect of producing lift, and bags of it, but it can also produce drag if too much camber is designed into the wing. Camber produces more lift by moving the air from the trailing edge down, thus pushing the wing up. Camber also reduces the amount of introduced turbulence produced by the wing's passage through the air: this is a premium quality for a glider wing. To explain: turbulence created by the down directed airflow, from the top of the wing, hits air coming backwards from the flat bottom of the wing; they are moving in different directions and at different speeds, which creates turbulence. A glider wing can use camber to merge the airflows into a similar down direction; this has the effect of producing more lift and reducing lost lift energy.
Camber is not a silver bullet solution, it will not solve your lift problems without limitation. In fact there are several downsides to camber. Cambered wings can introduce very adverse yaw in ailerons, a cambered wing will also move back the centre point of lift for the wing, changing the CG and also less lift is generated at faster airspeeds than lower airspeeds, which is inefficient.
The Ridge Runner Solution
The way to introduce the correct and desirable amount of camber is to use camber formers. I have devised a set of formers, for foam board wing construction, which are pinned underneath the wing during the construction phase. The bottom plate of the folded wing has two 50% score cuts used to create a ridge, which is then folded over the formers. Hot glue seams (glue spars) are used, in exactly the same manner as for the top of the wing, to turn the ridge into permenant camber in the bottom part of the wing. The top wing section is then created as per usual, by folding it over a foam main spar. Then the formers are removed. This ridged wing gave me the inspiration for the name of this technique and the slope soarer model's name: the Ridge Runner.
The Wing Build
The Wing is not difficult to build, the main theme of the build is accuracy: cut out all of the plans pieces very carefully, so as not to introduce errors. Great care should be taken to ensure that the camber templates are drawn and cut out very accurately.
Take all of the wing components for one wing; the main body of the wing, the main spar and the camber templates
I find it easier to number the camber templates 1-5, as I cut them out, from top to bottom on the Ridge Runner plans. This way once they all get jumbled up I can figure out which template to put where.
Cut all of the 50% score cuts on the wing, there are 10 to make: 5 on the main wing and 5 on the tapered end wing.
Turn the wing over and crack the leading edge cut on both the main wing...
and the tapered wing components.
Fold both of the upper surfaces of the wing completely over and make sure that they fit neatly and precisely together.
Bevel cut each side of the leading edge fold to allow the wing to fold back creating a nice rounded leading edge.
Fold the wing out flat and use packing tape to re-enforce the leading edge fold.
Turn the wing over so that the inside is facing up. Now take your trusty BBQ skewer and open up all of the 50% score cuts, include the glue spars on the upper wing as well.
Put your hand underneath the bottom of the wing and carefully crack, all the way along, the rear camber spar...
and then all away along the front camber spar.
Now comes the part you have all been waiting for, setting up the camber formers. There are 5 camber formers:
- The No.1 camber former fits along the root edge on the bottom wing.
- The No.2 camber former fits a third of the way along the wing (15.6mm from the root of the wing).
- The No.3 camber former fits two thirds of the way along the wing (31.3mm from the root of the wing).
- The No.4 camber former fits at the end of the main wing on the edge.
- The No.5 camber former fits at the end of the bottom part of the tapered wing
In the picture below the formers are placed roughly where they will be located for ease of understanding. See the blue lines marked on the plans for the exact positioning of camber former 2 and 3.
Next attach the camber formers to the underneath of the bottom of the wing; make sure to butt the formers up against the trailing edge of the wing to ensure correct placement and that they are fully in contact with the underneath surface of the bottom of the wing. Pin them in place.
Extra detail of camber former No.1.
And extra detail of camber former No.5.
Now put hot glue into the two camber forming glue spars. Wipe away any excess hot glue.
Now glue on the main spar. Place it right in the middle of the two camber glue spars. Make sure the ends line up with the wing ends.
Now remove the pins, one by one, from their current locations, and insert the pins through the rear of the camber formers into the trailing edge of the wing to hold them in place from the back only.
Fold the wing over to impress the leading edge, into the foam, for the main wing and the tapered part of the wing.
Put hot glue on the first glue spar behind the leading edge, then the leading edge and then the front half of the main spar. Fold the wing over and press down evenly along the main spar until the glue sets.
The root of the wing should look like this below:
Now crack the rear glue spar, bend it back and run a bead of hot glue along it and then the trailing edge where the two trailing edge parts of the wing meet.
Press the top of the wing down firmly until the glue sets. Repeat the above process for the tapered part of the wing as well.
You can now remove all the pins and the camber formers; we now have a set amount of camber introduced to a foam board wing.
To complete the wing build there are a few more easy steps to complete, which if you have built the Simple Soarer will be very familiar to you. First build the other wing and complete the following tasks:
- Tape the two wings together using packing tape on the bottom of the wing
- Run a good bead of glue around all of the root chord faces
- Put the wing right side up on the work bench, place the provided dihedral gauge underneath the wing tip, whilst holding one side of the wing down
- This sets the dihedral in the middle. Hold this all in place until the glue sets - about 2-3 minutes
- Tape the top of the wing, along the central main chord glue seam, using packing tape
Secondly, you need to put in the polyhedral on the wing tips:
- Cut through the top of the wing and the main spar where the tapered wing meets the main wing
- Open up the cut with the tip of a BBQ skewer, as you would a glue spar on the wing
- Put a good bead of hot glue into the opened up seam
- Hold the main wing flat on a work bench
- Lift the wing tip and place the provided dihedral/polyhedral gauge underneath the tip of the wing
- Hold this all in place until the glue has set
Lastly glue a popsickle stick in the middle of the wing on the trailing edge. This is to strengthen the trailing edge where the rubber bands go over the wing.
The fuselage is a simple slab sided build, with the two servos mounted inside the middle of the body using a foamboard template. The control rods run down the fuselage tail and out through slots cut in the fuselage side, exactly the same as for the Simple Soarer.
The wing mounts on the central fuselage are thin popsickle sticks glued to the foam board to give a bit more strength. You could easily use pieces of balsa.
Push through some BBQ skewers to make the wing holders and re-enforce the holes with pieces of gift card or some other suitable substitute.
The nose opens up halfway along the top to allow access for the battery - re-enforce the hinge with tape.
You are going to have to put a bit of weight in the front to obtain the correct balance at the CG point. I have about 125g of extra weight in the nose. Note: weight is good for a slope soarer, it needs it to penetrate through the wind.
The tail assembly is glued together and then inserted into the rear of the fuselage, like most other Flite Test tail assemblies. As the tail is so large I added a 3mm carbon fibre spa to the front of the vertical stabiliser and then covered it in white tape. The spa goes all the way down to the bottom of the fuselage, straight through the lower part of the vertical stabiliser . You could use a BBQ skewer to acheive the same effect.
The video above demonstrates the lift potential of this type of wing. In fact, this type of wing airfoil is pretty typical for a model glider and nothing new, I have just never seen it used on a foam board glider before. There are a couple of sequences in the video where the glider is actually catching updraughts and soaring rather than just slope soaring.
This technique creates a wing which produces lift like nothing I have ever flown that was made out of foam board. I have flown this glider wing many times now and it is comparible (in my opinion) to the balsa and monokote gliders being flown on the slopes where I fly. There are, of course, a few more things I have done than to just introduce camber into the wing, I am pushing the flight envelope afterall!
The wing has a couple of other modifications, when compared to the Simple Soarer. The wing tips are angled back and tapered somewhat to allow for a faster turning wing and the wing is narrower, much narrower, it cuts through the air much more cleanly than the Simple Soarer: put the nose down now and the Ridge Runner will surge forwards through the air. Additionally the fuselage and the tail configuration have changed. The fuselage is thicker through the tail section and much more sturdy, it has to be because the vertical stabiliser and the rudder assembly are massive.
This glider is only a two channel set up, it has a polyhedral wing with no ailerons, only rudder and elevator channels, yet it will roll due to the size and configuration of the rudder. Put the Ridge Runner into a shallow dive, to build up speed, push the rudder right over and watch it roll. Put in some forward stick and then fly inverted! Fabulous! This rudder configuration allows you to fly a two channel glider like a glider with ailerons, admittedly once you have learned the slightly modified techniques.
The wing is also incredibly strong, I can hold it by wing end, with one hand, waggle it up and down and it is very solid, no flex at all. The double curve of the airfoil profile introduces a vast amount of mechanical strength, which a flat bottomed wing just cannot achieve. Flying inverted doesn't seem to distort the wing either.
Sept. 2015 - Full size A0 Ridge Runner Plans: FB Ridge Runner Plans V1.1
- Added a centimetre and an Inch scale
Oct 2015 - Full size A0 Ridge Runner Plans: FB Ridge Runner Plans V1.2
- Modified tail location slots to create a stronger join
I have attached plans for the Ridge Runner, for those of you who are interested in building the Ridge Runner slope soaring glider; this includes plans for the camber formers and the Ridge Runner Wing.
Wing Span: 1500mm.
Wing Area: 229238 mm sq.
Root Wing Chord: 174.6mm
Weight: 592g - with a 500mAh 2S 7.4V (You can literally fly for hours)
Servos: Hextronik 9g x 2
Electronics: 5-6V BEC and an Orange R610RX receiver (No ESC required)
CG: 55.5mm back from root chord leading edge
I am going to play with this glider throughout the summer, which is just about to start down here in Australia, and I will report back in another article on how well it fares in thermals. The results so far look very promising and I am hopeful it will perform well.
Happy slope soaring!
Best regards to all