Pulldog Tow Plane

[Al Clark]

Wing Assembly Part 7

Cut the lower 3/32 balsa sheet for the aileron slightly oversize in width and bevel the edge. Pin the lower sheet over the plan. Glue all the ribs to the sheet. Note the two ribs where the control horn goes are 1/8 plywood. Use the cut-down Du-Bro #105 control horn to set the exact spacing of the two 1/8 plywood ribs. Cut the upper 3/32 balsa sheet slightly oversize in width and glue to the ribs and lower sheet. Use epoxy along the TE and CA for each rib. Pin a scrap balsa strip along the aft edge with plenty of pins. After the epoxy cures, unpin the aileron and sand the sheeting even with the front edge of the ribs. Check for straightness with a straightedge. Cut a slot in the bottom sheeting at the two 1/8 plywood ribs to fit the control horn.

Cut the 1/4 balsa aileron LE slightly oversize in width. Pin the aileron down to the building board with the front edge hanging off a bit. Apply some Titebond glue to the ends of the ribs and then use CA to glue the 1/4 balsa LE onto the aileron. Unpin the aileron and sand the LE even with the top and bottom sheeting.

Refer to the plan for the location of the hinge line and mark this line on the aileron LE. Mark the position of the hinges and make the hinge slots with a #11 blade. Bevel the front of the aileron to the angles shown on the plan. Glue the cut-down control horn into the aileron.

Carefully measure and mark the location of the hinge slots on the wing TE and cut the slots with a #11 blade. Temporarily mount the aileron servo to the wing. Make up the aileron pushrod linkage per the plan and attach it to the servo. Use an aluminum arm on the servo. Dry fit the aileron to the wing with the CA hinges and adjust the aileron pushrod. Check to be sure the gap at the root and tip end of the aileron is correct and adjust if required. Remove the aileron and the servo. The servo will be re-installed after covering and the excess wire tied down similar to the spoiler servo described previously.

This completes the right wing. Repeat all the wing steps for the left wing. Then sand the wing LE’s per the plan and make sure they match each other. Also round off the edges of the wing tips.

Photo captions (sorry the photos refuse to post in the proper order so the captions are re-ordered to match the photos):
1. Ribs glued to lower aileron sheet. Only one of the two 1/8 plywood ribs is shown here at the control horn location.
9. Close-up of control horn and 4-40 clevis
8. Aileron temporarily installed with servo and linkage
7. Hinge slot in wing TE
6. End view showing bevels
5. Hinge slot and beveled LE
4. 1/4 balsa LE glued on and sanded even with the sheeting
3. Slot cut for the cut-down Du-Bro #105 control horn
2. Top sheet glued on using epoxy at the TE and CA at each rib. Note scrap balsa strip pined over the aft edge.
10. Outer end of aileron showing correct gap

[Al Clark]

Final Assembly

I will show a few photos of how I installed my radio and batteries. Before covering make up the wire harnesses that will be mounted into the fuselage and will connect with the wings for the spoiler and aileron servos. I used some left over servo leads that had been cut off servos for other model projects. Solder the leads to the male Molex connector and make them long enough to reach the receiver. Make sure you have the same order on the pins as the wings do. Put labels on the leads so you will know which ones to plug into the RX ports. Slide the wing panels onto the wing tube and wing rod, and check to see how the male Molex connectors fit to the wing connectors. Depending upon how accurately you made the connector holes in the fuselage, you might have to adjust the holes a bit, removing or adding some balsa. Once the connectors line up properly, glue the male connectors into the fuselage. I plug the male connectors into the wings when I glue them to make sure they stay aligned, leaving a slight gap between the wing and fuse. Be careful not to glue the wing to the fuse!

After the male Molex connectors are installed into the fuse you can cover the airframe. Sand everything with 220 and 400 grit paper, and vacuum the dust off. Apply your favorite covering material, then install all the CA hinges.

Mount the motor and ESC. If you plan to use a digital readout volt meter, install it into the top on the fuse. Attach the landing gear and wheels, and attach the tailwheel and hook up the steering cables. Install the elevator and rudder pushrods and the horizontal tail, and connect the pushrods. Apply a thin film of epoxy to the fuse bottom just in front of former F2. Put Velcro strips down and attach the receiver battery to the fuse floor (I use a 5 cell 2000 mah NiMH battery). Apply a thin film of epoxy on the LiPo battery plate and then attach Velcro strips and also the Velcro strap through the slots. Drill through the holes in the battery plate and fasten the plate to the rails with #2 socket head cap screws. Mount the switch, receiver, and telemetry unit if you use one.
Set up all the controls for proper direction. If you use the servos, servo arms, and control horns shown on the plans then you will end up with the proper control throws. My control throws are:

Elevator + and – .875”
Rudder + and – 1.7 “
Ailerons + and - .5”
Spoilers set up for 85 – 90 degrees when fully open.

These control throws have worked out well, but you might want to change them to suit your particular flying style.

Put the prop on the motor and adjust the position of the LiPo battery packs to get the CG within the range shown on the plan. I have mine set at 27%. Now charge up your batteries and go test fly!

Photo captions:

1. Fuselage wire harnesses for left and right side soldered to male Molex connectors
2. 5 cell NiMH receiver battery velcroed to fuse bottom in front of former F2
3. Spektrum AR9020 RX, telemetry unit, and one satellite RX all attached with Velcro
4. Switch mounted to left fuse side
5. One satellite RX mounted to right fuse side
6. Second satellite RX mounted to left fuse side just in front of F3
7. DRO (digital readout) mounted into fuse top
8. Battery plate with Velcro strips and Velcro strap. One #2 S.H.C.S. is yet to be screwed in.
9. Position of the two 5S 5000 mah 25C LiPo batteries to achieve 27% CG. Note battery position marked on left fuse side for 27% CG.

[Al Clark]

Test Flight Photos

Here are some photos from the test flight of the Pulldog, taken by a fellow club member, Bill Beasley.

In addition to being a tow plane, the Pulldog is a good aerobatic sport plane as well. It uses a NACA 2415 airfoil section, one that I have been using on many of my designs since 1971. This airfoil works well for aerobatics. And the Pulldog has plenty of power, being able to climb vertically with no problem. Loops, rolls, hammerheads, spins, and snap rolls are easy. So when you are not aerotowing, you can have some fun sport flying. The LiPo battery packs last much longer when flying with no glider attached, around 7 or 8 minutes due to the lower throttle settings typically used.

I'm looking forward to cooler weather this Fall and a lot more aerotowing with the Pulldog.