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Old Sep 26, 2009, 08:57 PM
Engineer for Christ
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Amherst, VA
Joined Jun 2006
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Mini-HowTo
Scratchbuild a performance parkflyer - with plans

This is a short tutorial on how to build an excellent flying parkflyer airplane. These airplanes have airfoil wings which increase lift and lower drag making for a smoother flight than a flat foam airplane. I will be building two airplanes in this tutorial; The Ugly Stick, and the Skimmer.

The Ugly Stick is an easy to build, easy to fly, highly durable airplane. It makes an excellent first scratchbuild project. It has an interchangeable wing which gives you two airplanes in one. It will thermal, loop, roll, and even fly inverted and flight times can go for up to an hour.

The Skimmer is a much more advanced airplane. It is fairly quick and allows for smooth coordinated turns with it's dual rudder design. It makes a good low altitude flyer. Speeds can exceed 65 mph with a 1300 mAh 3S Lipo and 2100 kV brushless motor.

Measurements:

The Ugly Stick:

Overall length: 40"
Fuselage length: 36"
Wingspan: 48"
Wing central chord: 10"
Wing tip chord: 8"
Wing type: Clark Y
AUW (all up weight): 25 oz
Speed: 15-45 mph

Skimmer:

Overall length: 30"
Fuselage length: 24"
Wingspan: 32"
Central chord: 7.5"
Wing tip Chord: 5"
Wing Type: Gottingen 438
AUW: 16 oz
Speed: 25-70 mph

So now on to the tutorial.
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Old Sep 26, 2009, 09:14 PM
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Amherst, VA
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Making the Wing - building a wing jig

I usually start my builds by making the wing. In order to make the wing a “wing jig” and a hot wire bow are used. The jig is simply wooden (hardwood) wing templates secured to a flat board. You’ll need one template for the root and one for the tip. The wing cross sections can be found all over the internet by searching for "air foil". I included the airfoil templates as an attachment to this post. You can also click on this for a huge list of all kinds of airfoils with images to copy:
http://www.ae.uiuc.edu/m-selig/ads/...database.html#U

To make the cross sections edit the picture of the airfoil so that it prints out to the dimensions of your desired wing. For my attachment, just print it up so it fits on one sheet of paper. You can use MS paint and the the resize command to make a larger or smaller template if you like. Print out the template and glue it to a piece of hardwood then cut it out with a saw. Sand the airfoil template smooth. You might also add a piece of aluminum insulating tape (for taping ventilation ducts) to make a low friction surface.

Once you have the templates, you need a bow. My bow is 32" wide with 28” of .032” stainless steel fishing leader (tension on this wire is kept by the spring) connected to an automotive battery charger. .025 or .023 welding wire for a MIG welder works well too and can be found at most hardware stores and welding supply places for cheap. I used a 1X2 and 1-1/4" drywall screws to make the bow. I simply glued two 10" legs to a 32" crossbar and then screwed it together for extra hold. Then I put one 1-1/4 drywall screw at either end of the bow legs. I attached the spring to one end and ran the wire from the spring to the other drywall screw stretching the spring about 1". Tension must be kept on the wire for an even cut.

The templates should be screwed to the outer edge of your board. Therefore you'll need to cut a board (I use plywood) 1" wider than half of your wingspan. The Ugly stick uses a 25" board and the Skimmer uses an 18".
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Old Sep 26, 2009, 09:25 PM
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Making the wing - Making the cut

Once you have your wing jig made and ready to go, you need your foam. I usually use DOW blue EPS foam insulation. It is readily available at most hardware stores for $25 for a 48X96X2" block. This makes many airplanes. I also occasionally use pink foam or white box foam. Pink foam is a little heavier, but works fine. Box foam tends to be brittle, but I have used it with success many times.

Cut a block of foam out and place it in the jig with a weight on top. For the Ugly stick cut a block 24"X11". For the skimmer, cut a block 17"X8". Place a weight on top of the foam block to hold it in place. More weight is better. I usually use 10-15 lbs.

Use the selector switch in the battery charger to adjust the heat of the bow. Some people even use a light dimmer switch to fine tune the bow heat. The heated wire is run over either end of the wing templates with the foam in the middle with a weight on it to keep the foam from moving. You will want to use as little heat as possible for the best cut. The bow should move through the foam at a rate of about 1" every 2-6 seconds. Keep downward pressure on the bow so it follows the templates. Do not force the bow through the foam or the wire will curve and the cut will not come out straight. Once one side is cut, reverse the templates on the board, flip the block and cut the other side.

You now have two wing halves ready to be glued.
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Old Sep 26, 2009, 09:40 PM
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Making the wing - Gluing the wing halves

Before you glue your wing halves together, you need to decide whether you want a flat wing or a dihedral wing. A dihedral wing makes a plane fly upright more naturally. If a dihedral wing is mounted on top of the airplane such as the Ugly Stick, no ailerons are necessary, but only rudder is needed. This makes it very easy for a beginner to fly.

To glue the wing halves together I use a mixture of Gorilla glue and white glue (wood glue works too). I mix the glues in a cup at a ratio of 4 parts gorilla glue to one part white glue. This mixture expands to 6-8 times it's size, so use it sparingly!

To make the dihedral wing, I put a moderate coating of glue mix to one both wings and tape the wing tops together. I then move the wings to the desired dihedral angle and the tape the bottom. I then place blocks under the wing tips and a weight in the center of the wing to allow the glue to fill the crack and maintain shape.

For the flat wing I simply apply a small amount of glue to both wings and then wrap tape around the seam. I then add weights to the wing so it keeps it's shape.

The Ugly stick has 3" of rise from tip to root for it's dihedral wing. The Skimmer has 1.5" from tip to root.
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Old Sep 26, 2009, 09:58 PM
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Making the wing - Stiffening the wing

Now that the wing is made it could use a little strength. This can be done with carbon fiber or 1/2" X 1/8" spruce wood (Basswood works too).

To embed the spar in the wing you must cut or melt a channel in the foam. If you opt for flat carbon, cut a slice in the TOP of the wing. If you choose a carbon rod, melt a channel with a soldering iron or a hot knife. For the spruce spar, cut two channels 1/8' apart and dig out the channel with a screwdriver.

To secure the spars, I use gorilla glue. For the dihedral wing, the spruce spar is perhaps the best choice. Make two spars (one for each wing half). Make the channels so they meet in the middle. Then mix the 4:1 ratio of gorilla and white glue and pour it into the channel. Put a little extra glue on the ends of the spars and then install them in the wing so that the spars CROSS IN THE MIDDLE! Then cover with tape and let the glue dry.

For the carbon tube, I mix the 4:1 gorrila/white glue and place it in the trough and let it expand for a minute or two until the whole trough is filled with gorilla glue, then place in my spar and tape over it. I then flip the wing over and place a weight on the wing to hold it.

For the flat carbon I squeeze a small amount of gorilla glue into the slit, then wet my spar with water and force it in the slit and let it cure. The water causes the gorilla glue to expand and cure properly.

Once your glue is dry, remove the tape and cut off excess glue. To protect the wing from damage, you may add a thin carbon rod to the leading edge of the wing with the gorilla glue mix and secure it in place with tape while the glue dries.
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Old Sep 26, 2009, 10:09 PM
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Making the wing - Covering

Now you should cover the wing. Covering adds strength and protects the wing. You can use anything from paper to Tyvek homewrap to aircraft covering. I often use Tyvek homewrap because I can find end rolls of it thrown away at construction sites which have plenty left for a few wings. it is very durable, light and waterproof. It is also paintable.

I have found the best way to secure any covering is with Super 77 spray adhesive. It can be found at most hardware stores. Spray on several thin coats of adhesive to the bottom of the wing and let the glue get tacky. Then carefully apply your covering trying to avoid wrinkles. Most times it is best to use 2 pieces and cover half the wing at a time. Cut a slit down the center of the covering if you opted for one piece covering so the covering doesn't fold for the top. Once the bottom is covered, flip the wing over and spray the glue on the top of the wing and wrap the covering around the leading edge over the wing.

I have found it best to uses different coloring schemes on the top and bottom of the wing to keep me from loosing orientation of the airplane. Sometimes I use different colors, other times I use different designs, or a combination of both. The best colors to stand out in the sky are red, pink, orange, and yellow. All contrast well with green and black.
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Old Sep 26, 2009, 10:33 PM
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Making the wing - Ailerons

Making ailerons in the wing is a fairly simple task. The ailerons should take up about 1/8-1/12 of the wing surface. Typically I make them 1/4 to 1/5 of the wingspan wide and 1/6-1/8 of the wing chord deep. Thus for a 9X48" wing such as on the Ugly Stick, the ailerons are 10"X1.75". The ailerons on the Skimmer are 8.5"X1.25"

There are two basic ways to make them. One is the "live hinge" type, and the other is the balsa strip. The balsa strip is sturdier.

Live hinge

Cut out slits in the wing where you want your ailerons to be. Then cut a slit the length of the aileron on the bottom of the wing from slit to slit going almost all the way through the foam, but not piecing the top covering. Then fold the aileron up on top of the wing and cut a beveled edge. Then place some packaging tape over the cut and fold the aileron back down.

Balsa type

This one is simple. Simply cut out the back of the wing where you want your ailerons and remove the pieces. Then cut a 1/8" thick piece of balsa wood the same size as the hole. Sand a 45 degree radius on the wing side of the aileron and tape it to the wing on the top and bottom.


Control linkage:

Once the ailerons are cut, attach a control horn to the front side of the aileron. I place it as near the center of the aileron as possible to prevent flutter.

Now you must cut a hole in the wing for the servo. Line up your servo so the arm is at least 3" away from the horn on the aileron. Trace out the contour of the servo in the wing and cut off the wing covering there. Heat up a flathead screw driver with a lighter or a torch (the kitchen stove works fine too) and melt away the foam to about 1/2" or so deep by running it through the foam.

To secure the servo, cut some double sided tape and stick it on the bottom of the servo and place the servo in the hole. Then cover the servo with clear packaging tape for extra strength. Alternatively, you can wrap you servo in masking tape and then use gorilla glue/white glue mix.

Control arms

I make my control arms from 2-56 fully threaded rods with nylon control linkages at either end. They are cheap, adjustable and they work.
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Old Sep 26, 2009, 10:49 PM
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Making the Fuselage

There are three fairly simple ways to build a good strong fuselage: balsa sheeted foam, Balsa box, and stick style.

Sheeted foam

The balsa sheeted foam is probably the easiest and is very strong. The beauty of foam inside balsa is not only stiffness, but in a hard crash, the balsa and foam break cleanly and can be glued and ready to fly again in only a few minutes with minimal added weight! To make the fuselage I cut two identical cross sections from 1/8” or 3/16” balsa and secure them to a piece of white box foam or Dow blue foam sanded to shape. I used super 77 spray adhesive on either side of the foam and on one side of each balsa piece. I aligned the balsa parts and stuck them to the foam. I then used my bow (a knife works fine if you don’t have a hot wire bow) to trim off excess foam. Once done, glue a sheet of balsa to the bottom of the fuselage and trim off the excess with a knife. I typically use CA at the balsa meeting points and try to avoid letting it touch the foam.

Balsa Box:

Perhaps the simplest fuselage is the balsa box. It is simply a 3 sided box of balsa wood. Make your cross sections of the side of the fuselage and then secure them to balsa bridges at various points along the fuselage. Once done, glue a sheet to the bottom and trim off the excess balsa with a knife. I used this method for the Skimmer airplane.

Stick Style

Very simplistic, the stick style is simply two carbon shafts glued to a 3/16" balsa sheet. The fuselage is nearly indestructible. I used Carbon arrow shafts for my carbon spars and glued them down with Gorrila/white glue mix. Shoe Goo also works very well to glue this together.

The Ugly stick uses the Stick Style fuselage. It measures 34" long X 2" wide.

For the skimmer I used the balsa box. It measures 24" long X 2" wide.

Mounting the Wing:

Ugly Stick

To mount the wing you may use nylon bolts and blind nuts or rubber bands for the Ugly Stick. I used Rubber bands over two popsicle sticks. i placed a balsa block on the back of the wing for extra wing support. I use 4 size 64 rubber bands.

Skimmer:

The Skimmer wing is simply glued in. You can also use nylon bolts if you wish.
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Old Sep 26, 2009, 11:23 PM
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Making the tail

This is perhaps the easiest part of the build. A good horizontal stabilizer (elevator assembly) will be between 1/3 and 1/10 the area of the wing. High speed planes will be around 1/8. Slow flyers and 3Ds will be closer to 1/5. The shape is up to you. I make about 1/3 of the horizontal stabilizer movable as an elevator. A good tail for most planes is about 1/5 to 1/6 the surface of the wing with ¼ to 1/3 of the area movable. Most times I make the elevator 1/3-1/4 as wide as the wingspan and 1/2-1/4 as deep as the wing chord.

For example my wing the ugly stick has a wing area of 400 square inches (48"X9"). So my elevator should be between 30 and 50 square inches. My wingspan is 48" so 16" is about right for the elevator width. My wing mean chord is 9" so 4" is a good depth for the elevator since it's a slower flyer.

The vertical stabilizer has a bit of science to it. The easy way is to make it about half the size of the horizontal stabilizer (or use some judgment). The hard way is to measure the surface area of the side of the plane in front of the wing and multiply it by ½ the distance from nose to front of the wing. Then divide that number by the distance from the back of the wing to the middle of where the rudder will be. The resulting number will be the minimum surface area your rudder should be.

For the Skimmer model I will have 6 inches of nose in front of the wings leading edge. The fuselage is 2" high.

Therefore 6 X 2 X 3 = 36. Since my fuselage is 24” and the wing is 7” chord, the distance from back of the wing to tail section is 11”

Now 36/11 ~ 3.5 so my rudder/vertical stabilizer should be a minimum of 3 sqin. However this is the minimum and would be extremely small. So I opted for 5"X3.5" stabilizer with 1.25" movable rudder.

However, in most cases, the quick and dirty way to make the rudder is simply make it half of the elevator. This works great in most cases. For example the Ugly stick has a 16X4" elevator. So the rudder could be 8X4" - Simple as that

I am using 3/16” balsa for the tail assembly as it is very rigid and performs well at higher speeds. I also cover it with aircraft coating such as monokote or ultrakote to add to the stiffness and strength. On the movable joints I sand a 45 degree bevel on the movable surface and attach it with tape. I tend to like Tyvek as it adheres better than any other tape I have used, but strapping tape works well too. The tail is glued to the fuselage with CA. I use a small balsa block on either side of the rudder to help keep it secure.

Another method is to use coroplast and remove one flute. This provides the best joint, but is the heaviest option.

Tail assemblies:

Skimmer:
Rudder - 5X3.5" dual rudder with 1.5 inch slope. 1.25" dual movable surface (Detail below)
Elevator- 10 X 3.25" - 1.25" of the elevator is movable

Ugly Stick:
Rudder 8X5" - Moveable surface is 1" at the top to 2.5" at the bottom (Detail below)
Elevator: 16X4" - 1.5" movable
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Old Sep 26, 2009, 11:46 PM
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The motor

I make my motor mounts two ways:

1: Cut a 1"X 1/16"thick strip of aluminum (available at Lowes or Home Depot) and wrap it around the fuselage and glue it on with Shoe Goo or use a nylon bolt.

2. Glue down 3/8" square spruce wood and use wood screws and the motor's original mounting plate.

Motor and prop:

Ugly Stick

Motor Power: 100-300 Watts
Propeller size: 8-10"
Motor kV: 900-1400

Some good motor choices:
Tower Pro BM2409-18D
Eflite Park 400
BP hobbies 2212-13 (also Suppo 2212-13)
Scorpion 2215-18
KA22-20L

Skimmer:

Motor Power: 80-200 Watts
Propeller size: 6-7"
Motor KV: 1500-2200

Good motor choices:
Lazer toyz Blue Monster
Tower Pro BP-21 (BM2408-21)
Suppo 2208-12
Scorpion 2212-1920
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Old Sep 26, 2009, 11:50 PM
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Center of Gravity

The center of Gravity on most airplanes is 25-30% of the wing's mean chord. I use this CG calculator to figure my CG location. To find your CG find the airplane's balance point by balancing the airplane by it's wing on your finger tips. Move your battery or add weights to acheive the correct CG. CG IS CRITICAL!!!!

CG - Ugly Stick - 3.5" back

CG - Skimmer - 2" back
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Old Sep 26, 2009, 11:53 PM
Engineer for Christ
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Final notes

A few final notes.

Landing gear for either plane can be made with music wire and some landing gear straps. I opted to leave them off the Skimmer.

The Ugly Stick is perhaps the most versatile airplane I have ever made. I have adapted it to fit a camera for aerial photography work. The plane is a great trainer and very durable.

The Skimmer works best when you mix your rudder in with your ailerons. it will teach a pilot how to make a good coordinated turn.

Have fun and let me know how your builds go. Feel free to PM or Email with any questions.

-Alex
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Old Sep 27, 2009, 03:58 PM
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United States, FL, Alachua
Joined Jul 2004
1,284 Posts
Thank You

Thank you for taking the time to make such a great build guide for two good looking airplanes! There are a LOT of great tips, hints, and shortcuts in your build guide that everyone should be able use at least a few.

Now where are the parts that I got together for my hot wire cutter. I am always getting supplies for a project and not finishing the project. Your information looks easy enough for even me to give it a try!

Thanks again,
Ray
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Old Nov 25, 2009, 11:58 AM
Robot, RC Pilot & Builder :-)
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Roanoke, VA, USA
Joined Jul 2006
4,181 Posts
Alex, Thanks!

This is a wealth of information you are sharing!

I hope to be able to build such cool, scratch-built models, like yours, one day.

Thanks for inspiring me!
Kevin
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Old Jul 11, 2010, 01:09 AM
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India
Joined Feb 2006
105 Posts
can I use 20-22L motor on the ugly stick...??

http://www.hobbycity.com/hobbycity/s...idProduct=4700

What amp battery should I use with this motor on the ugly stick...??
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