Pulldog Tow Plane

[Al Clark]

Thanks, Marc. You're welcome!

[Al Clark]

Fuselage Assembly Part 3

Glue the two 3/16 balsa mounts to the ESC plate and install into the fuse as shown on the plan. Put a thin coating of epoxy on the plate so the Velcro will stick well.

After test running the Power 160 motor on the bench with the 20 inch prop I realized I needed to use an arming switch. This motor has a lot of power and could do major damage to persons or property with an inadvertent bump of the throttle stick. Fortunately Castle Creations provides a nice arming switch (for free, no less!) that works with a 4^th wire on the HV80 ESC. Installation is simple. Bore a hole through the fuse side (location shown on the plan) that will clear the switch jack assembly. Make a 1/8 plywood disc that fits into the hole, and drill a hole in the disc for the jack to mount to. Glue the disc into the fuse flush with the outer surface and mount the jack. If all fits as expected, remove the arming switch for installation after the fuse is covered.
Cut some ¼ X ½ spruce to length for the two servo rails. Glue them into the fuse using the upper half of the servo rail mounts to properly locate them. Install the servos in the exact positions shown on the plan.

Cut the 5/16 balsa fill-in pieces (see plan for template) and glue to the inside of the fuse sides in front of F1.
Photo captions:

1. Hole and parts for arming switch mounting
2. 1/8 plywood disc glued in
3. Interior view of 1/8 plywood disc installed
4. Arming switch installed
5. Exterior view of installed arming switch
6. Servo rails installed showing upper half of rail mount
7. View showing location of servos on rails
8. Another view. Tow release servo can be seen below.
9. 5/16 balsa nose fill-ins installed

[Al Clark]

Fuselage Assembly Part 4

Canopy/hatch assembly is next. Edge glue 5 pieces of 5/16 thick X 4 wide X 5.375 long balsa, sand, then cut to final size which is 5.25 wide (check the fuse top width for the exact dimension) X 18.836 long. This will be the base for the canopy/hatch. Use a sharpened brass tube to make the holes in the bottom for the 1/8 thick X 3/8 diameter magnets, making sure these are accurately located.

Glue on the two 3/16 balsa canopy sides in the exact position shown on the plan. Add the 5/16 square balsa cross members. Edge glue six 1/8 X 3 X 5.375 balsa pieces together and sand the surfaces smooth. Bevel the front edge to match the plan and trim and bevel the aft edge so it exactly meets the 5/16 base sheet, then glue onto the 3/16 balsa canopy sides and cross bracing. Sand the edges flush with the 3/16 balsa canopy side pieces.

Check the fit of the 1/16 plywood tongue – it should fit snugly between the fuse doublers at the front of the canopy/hatch. Glue the tongue to the canopy/hatch base. Cut a piece of 5/16 square basswood to fit snugly between the fuse doublers near F3, and glue to the bottom of the canopy/hatch base where shown on the plan. A good way to glue these pieces is to place them between the fuse doublers in their exact positions, add three small spots of CA+ to each piece, then carefully set the canopy/hatch base on top of the fuse making sure the edges are aligned with the fuse. Wait a couple minutes, pull the canopy/hatch off and finish gluing the pieces with CA.

Add the two 5/16 square basswood stiffeners to bottom front of the canopy/hatch, making sure they are located to fit just inside the fuse doublers. These stiffeners will need to be notched at the front to clear the 1/16 plywood tongue. Rough up the edge and one face of each magnet and glue them in place with epoxy. Check the fit of F3A to the fuse and glue in the two magnets, making sure they are oriented properly to attract the canopy/hatch magnets. Then glue F3A into the fuse.

Put the canopy/hatch in place on the fuse. Cut three pieces of 5/16 balsa to cover the top front of the fuse. There should be a gap of about 1/64 inch at the front and rear of the canopy/hatch. Edge glue the 5/16 balsa pieces, cut to length, and then glue them to the fuse. If you plan to use a digital readout voltage meter, cut a hole for it, located about over the top of the ESC mount. Don’t forget to glue on the two scrap balsa fill-in pieces to the fuse sides at the top front.

Photo captions:

1. 3/16 balsa canopy sides glued to the 5/16 balsa base, and 5/16 square balsa cross braces installed
2. 1/8 sheeting glued onto the 3/16 canopy sides, and 1/16 plywood tongue installed
3. Aft end of canopy and base
4. Bottom view of canopy/hatch showing the 5/16 sq. basswood cross piece, 1/16 plywood tongue, 5/16 sq. basswood stiffeners, and magnets. Note these magnets were later replaced by larger ones as shown on the plan.
5. Close-up of stiffeners
6. Close-up of aft cross piece and magnets
7. Top front 5/16 sheeting. Note hole for digital readout voltage meter.
8. Front edge of the top sheeting and scrap balsa fill-ins
9. F3A and magnets. Note these magnets were later replaced by larger ones as shown on the plan.

[stihac]

Great build! Thanks for taking the time to post it

Petr

[Al Clark]

Thanks Petr!

[Al Clark]

Fuselage Assembly Part 5

Study the tailwheel mounting plate on the plan and then cut the 1/8 O.D. nylon tube slots. Check the fit of the nylon tube before gluing for the correct angle, then glue the tubes into the tailwheel mounting plate. The front end of the tubes will be glued to the fuse later after the cables are installed.

Cut the slot on top of the fuse for the rudder pushrod (see plan for location). Glue the fin into the fin slot (you can attach the stab temporarily to check for perpendicularity). Looking from underneath you will see a gap between the fin post and F4. Cut a piece of ½ wide spruce to fit the gap and glue in place. Check fin perpendicularity again before the glue sets.

Make the rudder pushrod per the details on the plan. Cut down a large red servo arm to match the one shown on the plan. Install the pushrod, add the clevis and horn at the rudder and check the fit. Some slight bending of the aft 4-40 rod might be required for smooth operation.

Attach the tailwheel assembly to the fuse. Make the tailwheel steering cables per the plan details and attach so the tailwheel steering springs are stretched a bit. Now the front of the 1/8 nylon tubes can be glued to the fuselage frame so they align with the steering cables. Once everything is correct the rudder, rudder pushrod, and tailwheel assembly can be removed (leave the cables
attached to the rudder servo arm and let the ends hang loose near the tailwheel).

Photo captions:

1. 1/8 O.D. nylon tubes glued into tailwheel mounting plate. Note the fuse cross member has to be notched a bit for clearance.
2. Rudder pushrod slot on fuse top
3. Close-up of gap between fin post and F4
4. ½ inch wide spruce fit to fin post gap
5. ½ inch wide spruce piece glued between fin post and F4
6. Tailwheel mounted and steering cables attached
7. Close-up of tailwheel steering cable springs
8. Rudder and elevator servo pushrod and cable attachments
9. Close-up of rudder servo arm (cut down from heavy duty 4 way arm) showing 1/16 music wire pushrod with Z bend and tailwheel steering cable adjusters
10. Pushrod at rudder

[Al Clark]

Fuselage Assembly Part 6

Make up the elevator pushrod per the plan details. Use a heavy duty servo arm on the elevator servo as shown on the plan. Use a Sullivan S591 4-40 aluminum ball connector on the aft end. Install the 4-40 ball onto the elevator control horn (ball goes on port side of horn). Attach the horizontal tail, hook up the elevator pushrod, and then adjust the length. I made up a simple tool that makes connecting the Sullivan aluminum ball connector a bit easier – it is shown at bottom right on the fuse plan.

Make the tow release plate from 1/8 aluminum as shown on the plan. Cut a piece of 3/16 plywood to 5/16 X 1, and glue to the fuse top (see fuse side view and F3 details for position). Move the 3/32 diameter tow release rod to its extended position, set the tow release plate onto the rod, center the rod in the hole on the aluminum plate, and tack the aluminum plate to the 3/16 ply block with CA. Drill and tap the two holes for 4-40 screws, install the screws, and check for free movement of the tow release rod. Remove the aluminum plate before covering the fuse, and re-install later.

This is a good point to round off all the edges (except under the stab) on the fuselage to a radius of 3/32 – 1/8 inch.

Photo captions:

1. 4-40 ball attached to elevator control horn
2. Sullivan 4-40 aluminum ball connector attached to elevator control horn
3. Aft view of elevator pushrod attached to control horn
4. Elevator pushrod hook-up at servo. Note heavy duty servo arm.
5. Tow release plate, 3/16 ply block, and 4-40 screws
6. Aluminum tow release plate tacked in place and drilled holes being tapped for 4-40 screws
7. Side view of installed tow release plate
8. Top view of installed tow release plate
9. Typical radius sanded onto the edge of the upper basswood longeron

[Al Clark]

Fuselage Assembly Part 7

I mounted the switch for the receiver battery on the left side of the fuse, below the canopy. There is only the 1/8 lite plywood doubler here, so a spaced out frame needs to be made for the switch to mount to. The frame is a piece of 1/16 plywood with two ¼ thick balsa spacers glued underneath. Cut a hole through the 1/8 lite plywood fuse doubler big enough to clear the switch body. Glue the frame into place and check the fit of the switch.

Get some ¼ - 20 threaded nylon rod and ¼ -20 nylon wing nuts from McMaster Carr. Cut two pieces off the rod, each 1.375 long. These will be used later to hold the wings in place on the fuse.
Photo captions:

1. Switch frame and clearance hole in left side fuse doubler
2. Switch frame mounted
3. Fit check of switch
4. ¼ - 20 nylon stud and nylon wing nut
5. Nylon wing nut on ¼ - 20 nylon stud

[Al Clark]

Fuselage and Tail Ready for Covering

That’s it for the fuse construction except for final sanding prior to covering. Here are some photos of the fuse framework with the horizontal tail bolted on and LG and wheels installed.

[Al Clark]

Wing Assembly Part 1

I started with the right wing panel. Glue the wing socket tube doublers to the W1 and W2 ribs. Make sure to place them on the correct side. Check the fit of the spar caps and the phenolic wing tube and sand if required.

Pin the lower TE spar cap to the plan. Use ribs W2 and W 13 to locate the lower wing spar cap and pin in place with 3/16 scrap shims under the wing spar cap. Glue ribs W2 – W14 to the wing spar cap and TE spar cap. Note the wing spar cap will have a slight aft tilt, so make sure it fits into the rib notches well before gluing. Carefully position W1 and set the angle with the W1 angle gauge before gluing.

Cut some phenolic wing socket tube slightly long and glue into ribs W1 –W3. Make sure the angle on W1 remains correct. Sand the end of the Phenolic wing socket tube flush with the outer edge of W3 and glue on the plywood socket tube end cap. Cut, fit, and glue all the vertical grain balsa webs from W3 to W14, noting the positions of the three different thicknesses of webs. Glue the upper TE spar cap to all the ribs. Check the fit of the upper wing spar cap and sand the rib notches if required. Glue the top wing spar cap on using epoxy to fill any slight gaps there might be between the webs and the wing spar cap. Fit the plywood webs from ribs W1 to W3 and epoxy to the wing spar caps.

Use a straightedge along the front of all ribs to see which ones need to be trimmed slightly. There might be a few ribs that need to have a small amount of balsa added on the front. Cut the false LE from 1/8 balsa and glue to the front of the ribs. Sand the top of the false LE down to the top of the ribs at the angle shown on the plan. You might want to put some painter’s tape on the top of the ribs while sanding the false LE to avoid sanding flat spots on them.

Photo captions:

1. Wing socket tube doublers glued to right wing ribs W1 and W3
2. Angle gauge used to set angle of rib W1
3. Ribs glued to lower wing spar cap and lower TE spar cap. Note 3/16 shims under the lower wing spar cap.
4. Another view of the glued wing ribs
5. Phenolic wing socket tube glued to ribs W1 – W3
6. Wing socket tube end cap glued to outer side of rib W3
7. Balsa webs installed from W3 – W14. Upper TE spar cap has also been installed.
8. Another view of the webs.
9. Upper wing spar cap has been installed, along with the plywood webs from W1 – W3

[Al Clark]

Wing Assembly Part 2

Unpin the wing panel from the building board and turn it upside down, then sand the bottom of the false LE flush with the ribs at the angle shown on the plan.

Before the wing D-tube can be sheeted, the width of the 3/32 balsa D-tube sheets will need to be extended. Make up 4 D-tube sheets by gluing a 3/4 inch wide strip to a 4 inch wide sheet. Cut the edges of the sheets and strips straight before gluing. It’s best to put a strip of masking tape down one side of the joint, open the joint, add some Titebond glue, close the joint, clean of the excess glue, and pin or weight the sheet down while the joint dries. Sand smooth after the Titebond dries. Once all four D-tube sheets are made you can lay them over the ribs for a size check and trim them slightly oversize in width.

Glue the D-tube sheet onto the bottom of the wing frame. Note the D-tube sheeting begins at the mid-point of the spar cap. Also glue on the bottom and top TE sheeting. Turn the wing right side up and pin the wing back down to the plan with 3/16 shims under the wing spar area. Make sure it is pinned down well. Install the 5/16 balsa gusset at the front of W1. I will describe the method I use to install the top D-tube sheeting; you might be more comfortable with a different method. Apply Titebond on the tops of ribs W2 – W13, then position the D-tube sheet and glue it to the upper wing spar cap with CA. Then starting at rib W7 pull the sheet down tight over the rib and spot glue it to the false LE with CA. Do the same for every other rib, going from side-to-side working your way out from rib W7. Make sure the sheeting is contacting the top of each rib well before spot gluing to the false LE. When you get to the ends, CA the sheeting to rib W1 and rib W14. At this point the D-tube can no longer twist so the wing can be unpinned from the building board and you can finish gluing the D-tube sheeting to the false LE. Sand the excess D-tube sheeting flush with the false LE at the top and bottom.

Photo captions:

1. Bottom D-tube sheeting and TE sheeting installed
2. Top TE sheeting installed
3. Corner gusset installed
4. Top D-tube sheeting installed

[Al Clark]

Wing Assembly Part 3

Glue in the ¼ X ½ and ¼ X ¼ spruce servo rails for the spoiler and aileron servos. Sheet the aileron servo area and install the balsa border strips at the spoiler servo area. Cut the 3/32 plywood spoiler servo hatch and drill the holes for the four #2 screws. The spoiler servo hatch will need to be thinned a bit (with a sanding block) along the edges to fit flush with the bottom of the wing.

Cut the 3/16 brass rear wing tube to length and sand the outside. Glue to ribs W1 and W2, and install the 1/8 balsa webs. Crush the outer end of the tube a bit.

Glue the large and small wing bolt doublers to W1 (see plan for location). Using the pilot hole in W1, drill through and tap with a 4-40 tap. Glue the 1/16 plywood cap onto the outer side of the small wing bolt doubler. The ¼ - 20 nylon wing bolt studs will thread into this tapped hole.

Photo captions:

1. Aileron and spoiler servo rails and aileron bay sheeting
2. Aileron bay sheeting installed; spoiler bay balsa border installed; and 3/32 plywood spoiler bay hatch with #2 screws
3. Rear 3/16 O.D. brass wing tube and balsa webs
4. Bottom cap strips and sheeting from W13 to W14 installed
5. Close-up of sheeting from W13 to W14
6. Close-up of area around aileron and spoiler servo bays
7. Top of wing showing bevel on bottom sheeting from W13 to W14
8. Wing bolt doublers installed and hole being tapped with 4-40 tap
9. 1/16 plywood cap on wing bolt doublers
10. ¼ - 20 nylon wing hold-on stud with wing nut

[Al Clark]

Wing Assembly Part 4

Sheet the area around the spoiler opening as shown on the plan. Install cap strips from W4 to W12. Install sheeting from W13 to W14.

Glue the Molex connector shell into rib W1 so it is flush with the outside surface. Make sure the holes are oriented up. Use servo extensions with the male end cut off to make the leads going from the Molex connector to the spoiler and aileron servos. Route the leads through the rib holes. Solder the leads to the Molex contacts and snap the contacts into the connector shell.

Photo captions:

1. Cap strips and sheeting around spoiler opening
2. Sheeting around spoiler opening
3. Servo leads installed
4. Ends of servo leads at aileron bay and spoiler bay
5. Use a tie-wrap to keep the leads tight, and put some 3M plastic tape around the leads at the large rib holes to prevent wear
6. Close-up of 3M plastic tape around leads at the large rib holes
7. Close-up of Molex connector shell with contacts snapped into place
8. Outside view of Molex connector at rib W1. Note order of leads – you don’t want the plus and minus pins adjacent to each other.

[Al Clark]

Wing Assembly Part 5

Make the spoiler blades from 3/8 thick balsa that is cut to just over 1.5 width and planed/sanded down to 3/32 thick at the aft edge. Fit the blade to the spoiler opening so there is 1/32 clearance all around the edges. Sand the top surface of the spoiler blade to match the curved shape of the ribs at each end. Cut a slot in the middle of the blade to fit a cut-down Du-Bro #105 control horn (see detail on plan), and glue the control horn into the spoiler blade. Center the blade in the spoiler opening and put a couple pieces of tape along the front edge to act as a temporary hinge. Tape a piece of covering material to the bottom of the blade on each end, close the spoiler, and glue a piece of 3/16 balsa scrap on ribs W5 and W8 to support the spoiler blade flush with the upper wing surface.

Put a thin coating of epoxy on the inside surface of the spoiler bay hatch where the servo will mount. Adjust the servo arm position and travel to get the range and end points as shown on the plan. Solder the spoiler linkage, attach to the spoiler horn, and attach the screw-lock connector to the servo arm. Move the spoiler servo arm to its extended position (pointing up) and temporarily put the spoiler linkage together to see where the servo will be located. Make a few locating pencil marks on the hatch if you like. Pull the servo out, clean off the case with alcohol, and attach servo tape. Put the servo back into the wing, put the linkage back together, and stick the servo down onto the spoiler bay hatch. Coil up the excess servo wire, connect the plugs (put a piece of tape around the plugs), and use a couple tie-wraps to hold the coiled wire together. I also used a small screw eye on the aft hatch rail to attach the coiled wire to. If the servo ever needs to be removed you just have to clip the tie-wraps and it will be easy to get out.

Photo captions:

1. Spoiler blade and cut off Du-Bro #105 control horn
2. Top view of blade where horn is glued in
3. Spoiler blade in opening with temporary tape hinges
4. 3/16 scrap balsa blade support. Note also the piece of covering taped to the end of the blade to get proper positioning.
5. Coiled up excess servo wire attached with tie-wraps. Note screw eye on aft hatch rail, and 3M plastic tape around plug.
6. Top view of spoiler linkage
7. Aft view of spoiler linkage. The scrap balsa block glued to the rib next to the servo case is to keep the servo wire from coming up over the servo case.
8. Another view of the spoiler linkage

[Al Clark]

Wing Assembly Part 6

The aft edges of the 3/16 X 3/8 balsa TE spar caps need to be sanded off even with the aft end of the wing ribs. Once this is done use a straightedge to check that the wing TE is straight. Cut the 3/32 balsa TE cap slightly oversize and glue into place, then sand off the top and bottom edges flush with the TE sheeting.

Sand the D-tube sheeting flush with the false LE. Use a straightedge to check that the front of the wing is straight everywhere. Cut the 1/4 hard balsa LE slightly oversize and glue to the front of the wing. Plane and sand the LE down to the D-tube sheeting on the top and bottom. Refer to the plan for the proper angles. Wait until the other wing panel is built before rounding off the LE to the final shape, so that both panels LE’s can be shaped concurrently.

Photo captions:

1. Sanding the TE spar caps flush with the end of the ribs using a long sanding block
2. 3/32 TE cap glued on and top and bottom edges sanded flush with TE sheeting
3. 1/4 LE glued on and planed/sanded even with D-tube sheeting. Final shaping will be done when other wing panel is completed.
4. Completed wing panel, except for final sanding