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Old Jul 19, 2014, 03:13 AM
Marty Petri Sr.
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Thailand, Uttaradit, Bo Thong
Joined Jun 2007
636 Posts
Build Log
Kadet Sportster, 50% Foamie

50% Kadet Sportster Foamie
Modeled after the SIG Kadet Senior Sport (TailDragger)


Materials:

(2) 3mm foam sheet (39.5” x 23.5”)
(1) 5mm foam sheet (15” x 23.5”)
(1) 3mm lite plywood sheet (8”x5.5”)
(4) 1x3mm CF Flat strips, (2) Pushrods, 3mm Bamboo Dowels
(5) 4mm Blind nuts (optional) , (5) 4mm x 25mm Nylon Screws
Epoxy, UHU POR, Spray Adhesive, clear plastic for windows.
2830 Outrunner, 30A ESC, APC-SF 8x6 Prop, 1300mah-3S Battery, 4-7 ch Rx
(2) 1.5” dia. Wheels, (1) .5” dia. Wheel, (2) 3mm Axles, (4) control horns,
(4) 9 gm. servos, (2) 30cm servo extensions. (aileron only)

Web-O-Calc shows this combo pulling 11 Amps:
8079 RPM, Vpitch 46.2 mph, Thrust 22.1 oz, Stall 15.4 mph ...... and that's about half throttle!!!

I am budgeting 22 oz AUW, hopefully it will be less.
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Last edited by mbpetri; Jul 21, 2014 at 07:44 PM. Reason: 3mm Ply Parts Revised, 7/21/14
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Old Jul 19, 2014, 03:13 AM
Marty Petri Sr.
mbpetri's Avatar
Thailand, Uttaradit, Bo Thong
Joined Jun 2007
636 Posts
Fuselage:

Cut out the Center Support from 3mm foam. Laminate the (2) 1x3mm Carbon Fiber Flat strips to the sides of the foam using epoxy. Leave 6 inches extending forward of the center support. Where the bend is, score the CF and crack it, but try not to cut the fibers. Sand both sides of the CF strips to get a better bond.

Figure #1

Cut out former F4, Landing Gear Mount and Wing Mount from 3mm lite ply.
You can use T-Nuts (Blind Nuts), but I found that I could save 10 grams of weight by using ½”x1/2” 3mm doublers, drill and tap the hole for 4mm thread, saturate the threads with thin CA, and then re-tap the threads. You wind up with threads that are 6mm Deep. The Doublers need to be offset as shown, the center doubler on the LG mount needs to be trimmed to clear F4. Glue F4 to the LG Mount with thin CA, making sure they are perpendicular.

Figure #2

Next, cut out formers F5 thru F9 from 5mm foam. There is a top and bottom half to each former. Glue formers F5 thru F9 in place.

Figure #3

Lightly sand each former F7- F9 to set the bevel, sand all (4) sides.

Cut out the (2) side skins from 3mm foam. Sand the outside window frames to simulate ½ round molding. Use thin plastic sheet, like used for report covers, to make the windows as shown. This greatly re-enforces the window area.

Gently crease the foam using a straight edge on the inside surface to create the bend at the TE of F6.

Figure #4

Glue 1 side to the formers and Center Support. Add the F4 / LG Mount making sure it is aligned with the LE of the cabin and the LG mount is seated on the bottom of the side skin.

Figure #5

Add the 2nd side. And the Wing Mount.

Figure #6

Cut and Install the Turtle Deck, cut it oversized and trim and sand to shape, radius the edges if you desire.


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Old Jul 19, 2014, 03:15 AM
Marty Petri Sr.
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Thailand, Uttaradit, Bo Thong
Joined Jun 2007
636 Posts
Tail Feathers:

The Tail Feathers are cut from 5mm foam. You can use Flat CF strips to stiffen if you like. Use your preferred method for hinging.
The alternative that I use is to cut (2) sets of parts from 3mm foam and sandwich the CF stiffeners between them, laminating with spray adhesive.

Figure #1

I have included the design for the original SIG style tail feathers if you want to stay stock. Both designs have the same surface area. The tabs on the bottom provide correct alignment. DO NOT glue these parts at this time. You can install the control horns for the Elevator and Rudder at this time.

Figure #2

I like the Counter Balance design because it has that old-time look to it, especially if you add the Wing Struts.
In reality, the CB design has larger control surfaces allowing for better acrobatics if that is your thing.
Elevator is 29.5% Larger and Rudder is 32% larger, a significant amount.
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Old Jul 19, 2014, 03:15 AM
Marty Petri Sr.
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Thailand, Uttaradit, Bo Thong
Joined Jun 2007
636 Posts
Servo Tray:

The Servo Tray is cut from 5mm foam and extends from F5-F6, and Side to Side. The cutouts need to match the servos you use, and positioned for your linkage. The Elevator Push rod runs down the center line and exits the fuselage between the (2) sides. The control horn is located in the center of the elevator facing down. Decide which hole in the control horn you want to use and measure from the center of the hole to the bottom of the elevator surface. Make a hole in each former on the center line using that same measurement less 3mm (the thickness of the center support). Run your elevator pushrod thru the holes. I use a plastic sleeve and wire pushrod which slides thru the tube and I glue the sleeve at each former. Your method may vary, so work accordingly.

Figure #1

Cut an Access hole in the center support so you can adjust the servos
The servo try is positioned in the fuselage vertically so that the control arm of the Elevator Servo lines up with the pushrod. Glue it in place. Next the rudder pushrod is installed, trying to keep the line as straight as possible. Leave both control rods hooked up to the servos, remove the Tail Feathers and proceed to the next step.
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Old Jul 19, 2014, 03:16 AM
Marty Petri Sr.
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Thailand, Uttaradit, Bo Thong
Joined Jun 2007
636 Posts
Aft Bottom Skin:

Cut a piece of 3mm foam for the aft bottom skin, slightly over sized. There is a slight bend, crease it if necessary. Glue it in place. Trim off the excess and sand to shape, radius the edges if you like.

Figure #1
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Old Jul 19, 2014, 03:17 AM
Marty Petri Sr.
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Thailand, Uttaradit, Bo Thong
Joined Jun 2007
636 Posts
Landing Gear:

The Landing Gear is fashioned from .062” Aluminum.
Landing Gear:
The Landing Gear is fashioned from .062” Aluminum.

Figure #1

All (4) bends are 45 degrees. The holes for the axles need to be sized for the part you are using. The landing gear is attached to the fuselage with (3) 4mm x 25mm nylon screws, the excess length can be cut off.

You can use standard axles and wheel collars, or 3x30mm HexBolts, hex nuts, flat washers and locking nuts.
I used 1.5" dia. Foam Wheels

Figure #2
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Old Jul 19, 2014, 03:17 AM
Marty Petri Sr.
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Thailand, Uttaradit, Bo Thong
Joined Jun 2007
636 Posts
Mounting the Motor:

Mount the motor to the firewall using blind nuts, use ply washers (small) if the blind nuts are too long. The fire wall is designed to have 6 degrees of down thrust and 3.5 degrees of right thrust. Temporarily install F1, but do not cut out the interior at this time. You want the centering hole intact. The motor shaft is inserted thru the centering hole, and the fire wall is bucked up against the CF strips and should be flush with the fuselage sides. The distance from F1 depends on the motor you selected. Glue the firewall with epoxy and re-enforce where you can with triangle stock.

Figure #1

When satisfied with the motor setup, finish the bottom sheeting from the Landing Gear Mounting Block to the LE of F1. Trim and sand, radius the edges if you like.

An option here is to add an air box, it will help with cooling and looks cool too.

Figure #2

This view shows with the cowl installed, we’ll get to that in a few steps.
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Old Jul 19, 2014, 03:18 AM
Marty Petri Sr.
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Thailand, Uttaradit, Bo Thong
Joined Jun 2007
636 Posts
The Infamous Access Hatch:

Figure #1

Start with the frame, install the 3 formers and (2) Ply side walls. Make sure the notch is on top and facing forward. The last former will need to be trimmed slightly to accommodate the side walls.
Next, add the Top Brace and Mount. You can use CA to join the ply pieces.

Figure #2

Next add the top skin. I used a length of 2” PVC pipe to roll the foam.

Figure #3

Add (2) foam side fillers and shape to windshield contour.
Add the windshield made from thin clear plastic or Lexan.

Figure #4

The Top crown will be added later and shaped to the wing contour.
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Old Jul 19, 2014, 03:19 AM
Marty Petri Sr.
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Thailand, Uttaradit, Bo Thong
Joined Jun 2007
636 Posts
The Wing:

The Wing consists of (2) wing halves.
Note: I show the LE as already being shaped in the following views, actually it will be shaped after the Top Skin is installed.
Start with the LE, 10mm x 8mm x 20” Balsa. A 5mm x 3mm notch is cut length wise.

Figure #1

Cut the Bottom Skin from 5mm Foam to the correct measurements. Taper the TE of the bottom skin on the dashed line to a sharp edge. You can cut the notches at the LE & TE at the Root later for a tight fit.

Figure #2

Note: You need to decide if you want flaps, if not, then omit the “F” slot.
The LE Balsa is glued to the Bottom Skin. I actually did this after the wing was built because I didn't have the servos at build time. I did not use flaps, but they can be added later.

Figure #3

Cut the LE close to the Bottom Skin at the Tip, leaving enough extended to accommodate the 45 degree angle. Lightly sand the Tip of the bottom skin and LE to a 45 degree angle.

Figure #4

Now raise the tip of the bottom skin ½”, setting the dihedral, and lightly sand the root of the bottom skin, setting the dihedral angle.

Figure #5
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Old Jul 19, 2014, 03:21 AM
Marty Petri Sr.
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Thailand, Uttaradit, Bo Thong
Joined Jun 2007
636 Posts
Main Spar:

The Main Spar is a solid foam piece measuring 1” x 3/4” x 20”. You can also laminate layers of foam if you don’t have a solid block. Make (2) Parts.
Setup a Hotwire or Sanding Jig using the (2) Plywood Ribs. Shape the Top Contour of the Spar.

Figure #1

Sand the same dihedral angle as above at the root end of the spar.
Set the Spar in place between the guide lines, offset from the Root by 8mm. Cut and Sand the Spar for a 45 degree angle at the Tip.

Figure #2

On the top and bottom surfaces, make a slot 1mm wide, 3mm deep, the full length on the center line.
Make a 2nd Spar for the other wing panel. Make sure you have a left and a right part. Mark the LE Face so you know which is which.
Sand (2) 1mm x 3mm CF Flat on both sides for a good bond.
Insert a CF Flat into the bottom slots using epoxy. The CF should extend 3mm beyond the root of the spar and cut flush with the tip at a 45 degree angle.
Glue the Spar on the bottom panel using the guide lines, setback 3mm from the root edge.

Figure #3

Now glue the Ply rib in place.

Figure #4

Cut a 45 degree angle on the bottom face of the Tip Base.

Figure #5

Now Glue the Tip Base in place.

Shape the top face of the Tip Base to match the airfoil contour, following the ply rib and the spar as your guides. Basically yo are setting another 45 degree angle for the top skin to sit on.

Figure #6, Figure #7

Next, you will cut the top skins, oversized, Roll the airfoil shape, Set in place on the wing. Pin it in place, Sand bags or whatever you have for weights, mark some reference points and then Sand the dihedral angle at the root edge. Set the skins aside for now.

At this point, you should have both wing panels built to this level, and top skins set aside.
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Old Jul 19, 2014, 03:21 AM
Marty Petri Sr.
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Thailand, Uttaradit, Bo Thong
Joined Jun 2007
636 Posts
Join the Wing Halves:

Temporarily join the 2 panels together. In the Root Ribs, there are (2) 3mm holes. These are for alignment pins, go ahead and stick 2 3mm dowels thru the holes.
Use clamps to hold the 2 ply ribs tightly together.
Now insert the (2) 6” Wing Joiners thru the rectangular slots. The Joiners should be centered. Add some clamps on the joiners.
Glue the Foam Wing Joiner DOUBLERS in place on the sides of the Spar.
When you are satisfied with your setup, remove the clamps, separate the wing halves, and re-assemble again with 30 minute epoxy. Use plenty of clamps and let it cure. Make sure you have both Wing Tips Raised ½”.

Figure #1

Next, set the wing assemble on the fuselage. Make sure it is straight and well seated on the wing saddle. Weight it down with sand bags or whatever you have.
Use (2) 3mm Bamboo skewers or wood dowel with a very sharp point on 1 end.
Insert both dowels thru F1 and up against the spar. Make sure the dowels are very straight, parallel to the wing and ribs. Gently insert the sharp points into the Spar. This gives you a center point. Now work the dowels completely thru the spar and then remove again. Cut off the sharp points, make a slight chamfer and insert again. Just before entry into the spar, coat the last 1” of the dowel with epoxy and insert so that it slightly protrudes out the rear of the spar. Let the epoxy cure, then remove the wing from the fuselage.
Cover F1 and the Fuselage Wing Mount with some cellophane wrap so the epoxy can’t stick to it. Make holes for the dowels and screws to pass thru the cellophane.
Slide the Front Wing Brace onto the dowels and in place over the bottom sheeting, adjusting the foam as necessary. Epoxy the brace to the foam, dowels and both ribs. Re-install the wing and make sure the brace is against F1 and set a couple of clamps, let the epoxy cure.

Figure #2

The wing mount is installed using (2) 3mm Nylon Screws. Make sure you have a good fit of the mount to the foam, When satisfied, epoxy it in place and install both screws. Make sure the wing has plent of weights to hold it in place while the epoxy cures.

Figure #3

Remove the wing and re-enforce the bottom seam with fiberglass tape and epoxy. I use the Thin Fiberglass Mesh Tape used for drywall seams. It comes in 1” wide rolls and is very cheap.
Next install your servos, wiring, pushrods for the ailerons and flaps. Make an small access hole in the bottom sheet , over the cockpit area near the Rx location.
Make sure the servos are both mechanically and electrically centered. Final adjustments must be done at the control horn, so I use linkage stoppers at the horn.

Figure #4

You will notice that the aileron servos are in opposite orientation, while the flap servos have the same orientation. This eliminates the need for a servo reverser.
Make sure your servo arms are long enough. As you can see, not much extends below the wing.

Figure #5

Install ply control horn doublers if you are using the type of control horn that mounts with screws. I use old servo arms for control horns and just epoxy them in place.
Next we attach the top skins, trim and sand as appropriate.
Add a filler over the Wing Mount Area and blend it to the Top skins. Use a skewer to locate the mounting holes from the bottom side.
Shape the LE Balsa and Foam to make a nice straight airfoil shape.
Cutout the Flaps and Ailerons then sand, hinge and install. Adjust the Control horn linkages as required.

Note: I like to get as much mechanical throw as possible and then tone it down using the programmable settings on my Tx. This way, when I’m feeling the need, I can have a very acrobatic plane.
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Old Jul 19, 2014, 03:22 AM
Marty Petri Sr.
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Thailand, Uttaradit, Bo Thong
Joined Jun 2007
636 Posts
Wing Struts:

I used 3mm Balsa 1/2" wide x 9" long. I grooved 1 side using a piece of 3mm piano wire. Then I epoxied a 3mm CF Tube.

Figure #1

Next I shaped the balsa to an airfoil shape.

Figure #2.

I used 1mm Piano Wire bent at a right angle. There is a 1" side and a 1/2" side.
I epoxied the 1" side into the CF Tube. I made the attachment hinge from 3mm CF Tube 1/2" long. I wrapped the Attachment with 1"x1/2" Fiber Glass Mesh Tape making a Tab.

Figure #3

Later I found that any pressure on the CF Tube would cause it to split, so I wrapped the Strut with Fiber Glass Mesh Tape also.

The Tab that inserts into the spar has a 1mm notch to handle the CF Flat in the bottom of the Spar.

Figure #4
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Old Jul 19, 2014, 03:31 AM
Marty Petri Sr.
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Thailand, Uttaradit, Bo Thong
Joined Jun 2007
636 Posts
Final Assembly As-Built Photos
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