Back    Goto next page


Doug Cronkhite's 2x2m Extra Build Thread - Page 1

These pages chronicle the building of Doug Cronkhite's Comp-ARF 2x2m Extra.

Many thanks to Dough for allowing me to post all his hard work on my site.


Over to Doug.........


OK guys, time to get started on my new Composite-ARF 2x2m Extra building. Since I'm big into the electrics stuff these days, this airplane is going to use the Comp-ARF supplied Hacker conversion kit for nice, quiet, clean, impressive power. So far the weight situation is as follows:

Fuse w/chin cowl - 30.4 ounces
Canopy (opaque, no clear available) - 4.2 ounces
Stab/elevator - 4.5 ounces each (they were identical down to the gram)
Rudder - 4.6 ounces
Wing panels - 18.5 oz right panel, 19.2 oz left panel
Landing Gear legs - 5.6 ounces total for both
Wheel pants - 2.4 ounces total
Included hardware - 16.2 ounces (not all hardware will be used as much is for glow/gas installation
Hacker conversion kit - 11.9 ounces.

Total bare airframe weight - 122 ounces. I'm guessing a full 8 ounces of stuff is for the glow/gas version but I won't take that off my weight list just yet.

Motor - 18.5 ounces
Battery - 42.7 ounces
Controller - 3.2 ounces
Prop - 4 ounces
Spinner - 2.6 ounces
Servos - 11 ounces total (5 x 2.2)
Receiver - 0.9 ounces

So now we're at 204.9 ounces (12.8 pounds) not counting any misc additional weight from assembly, glue, pushrods, etc..


OK.. here are some pictures. 1st is the chin cowl. Plenty of room here to work in and the fit is perfect. 2nd is the wing tube. Nice carbon supports inside. 3rd is the gear plate. Very sturdy. If you break this out you're doing something very wrong and 4th is the gear plate from the above.




The fuselage and chin cowl have been opened and sanded for motor installation. The firewall has also been installed using BVM Aeropoxy. Since this former sets the thrust line I've opted to install this one alone to ensure the proper angles are set. Once this has cured (tomorrow), I'll go ahead and put the rest of the formers in place at one time as they're less critical. One nice touch is this former is slightly non-symmetrical so the thrust offset places the spinner in the center of the cowl opening. I'm sure things will progress rapidly once these critical alignment steps are complete. There just isn't much to do on this airplane really!



The remaining fuselage formers are in place for the Hacker install. Again, I used BVM Aeropoxy to ensure a solid bond. The motor mount is also in place here. The idea is taken directly from Jason Shulman's F3A airplanes in that the motor is mounted to a plate, which is then mounted to F1 via rubber grommets to help isolate the noise from the gearbox. A rear plate captures the rear of the motor to help stabilize it.




The canopy mounting comes next. The rear is attached with a spring loaded pin arrangement similar to the BVM unit in function. The front end is held by a hook and groove assembly. I deviated slightly from the instructions here to ensure I didn't attach the canopy permanently




And the end result is.. a perfect fitting canopy!  Stab and elevator servo mounting comes next.



Tonight I got started on the stabs. Only thing that needed adjusting was a slight change in the anti-rotation pin alignment in the stab. Incidence and fuselage fit was perfect otherwise. Because the stab gets a bit thin at this size (compared to their bigger airplanes) the elevator servos need to go into the fuselage. Using measurements in the instructions, I cut holes in the fuse sides for JR 8411's. A pre-cut lite-ply piece provides backing and support for the servos screws. These were glued in using BVM aeropoxy after scuffing the inside glass surface.



While the elevator servo supports are curing, I started working on the rudder. Comp-ARF provides composite control horn that fits into a pre-cut slot in the rudder. The holes in the arm are such that the pivot point is exactly on the hinge line giving you perfect geometry when complete. The masking tape is put in place to protect the paint finish from any excess epoxy. The horn was glued in with BVM Aeropoxy filling the slot and then set aside to dry after removing the tape. Tomorrow I'll get the rudder/fin closed up and start on the wings.




Got back to work on the Extra this morning. I basically got the rudder installed but it's not finished yet. First up was to install the rudder servo tray under the canopy. This is a pre-cut balsa/fibreglass laminate. There are 2 ribs that lock into the slots to make it VERY stiff. Then you add the lite-ply servo screw backing like in the fuselage and then the whole piece gets installed into the fuse. I basically tacked it all together using thin CA and then went back over it all with a thin fillet of Aeropoxy. Then I tacked it into the fuselage with slow CA being VERY careful not to distort the fuse at all. This plate needs to be at least 70mm off of the fuselage floor so the rudder cables don't hit the elevator servos.


With the tray in place and curing, I went to work on the rudder post and hinging. This was a bit harder to accomplish due to the tight tolerances of the rudder to fin. This time I used a gel CA to ensure it didn't run all over the place. Basically you attach the blade hinges to the rudder post, and then put the rudder onto the assembly. This allows you to position the rudder correctly in the fuselage without guesswork. Once it's all in place and taped for proper alignment, you dribble some CA Kicker down the fuse to set the gel CA. Once set, remove the rudder and go over the entire joint with Aeropoxy.



Once it all cures, you wind up with the final assembly looking like this. I get over 45 degrees of smooth friction free rudder travel. Now it's time to get to work on the stab mounting and elevator control horns.



Goto next page