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Goldberg Ultimate 10-300 ARF

 The Ultimate Project       By Don Giandomenico                                                                                                            July 23, 2004

       I had recently purchased a Carl Goldberg Ultimate Biplane ARF from Tower Hobbies and wanted to share my experience with the kit. Having never owned a Goldberg kit before, I was unsure what to expect. I was pleasantly surprised by a box of high quality pieces that fit together with little adjustment. The 54” wingspan model has 990 square inches that put the wing loading at 19 to 23 Oz per square foot of wing. The advertised weight if 7.5 to 8.5 pounds seems to be a little optimistic but the low wing loading should make up for any deviation in weight.

       The wings came pre-assembled and all that had to be glued was the verical/horizontal stabs which needed very little truing. The hardware is all top quality including a Klett tailwheel assembly and Du-Bro mainwheels. The wheelpants are fiberglass with pre-installed plywood mounting plates that make them easy to install. The Dave Brown motor mount included is set up to accept most 120 4-stroke engines and was perfect for my Saito 180.

     The instructions were very easy to follow and I had no trouble understanding any aspect of the assembly process. The supplied carbon fiber “Y” style elevator push rod system seems to be a nice touch but I preferred to mount independent servos on my elevator halves. This arrangement also serves to counterbalance the weight of the engine better. I used Hitec HS-5625MG digital servos for the control surfaces and powered it all with a 1400 Ma NiCad battery.
       I chose to use a Saito 180 4-stroke for power as this engine is only 2 Oz heavier than the Saito 120. There were initial concerns of excessive vibration from the Saito but later proved to be acceptable. Using the supplied Dave Brown motor mount, I installed the 180 horizontally. I reinforced the fire wall with a little epoxy & milled fiberglass around the inside of the fuse for good measure. I later found a weak point on the lower wing mounting bolt block which snapped out of the fuse easily when I was handling the bird, I fixed this problem with angle stock and epoxy.
       With only the elevator servo and wing bolt block modification, the ARF was on it’s feet in about 8 hours. This of course did not mean I was finished as I wanted to add a smoke system to the bipe that would rival the one installed on my Cap 232. I used the system outlined in my
Super Smokers Part I Video and modified the stock Saito muffler into a smoke muffler. After disassembling the muffler, I fabricated a 1/8” copper preheater coil by wrapping automotive gauge tubing around a socket. The coil fit snugly inside the muffler housing as to prevent vibration from grinding away the coil.

       Once the coil was made I had to drill the muffler end plate to accommodate the exit of the tubing. I set up the coil to spray oil at the exhaust header and bolted the muffler back together.

       As outlined in my Super Smokers Video, I had to install a pressure tap on the exhaust header to create my smoke oil tank pressure needed to operate the smoke system. I drilled a hole in the steel exhaust header just big enough for a piece of 3/16” ID steel brake line to fit into. I then brazed a steel line into the exhaust header with my Map gas torch.

       I tapped the steel tubing end to accommodate a brass hose barb to connect the fuel tubing to the check valve. The check valve will capture the exhaust pressure pulses as the engine runs to drive the smoke oil through the system.

       With the exhaust system modification complete, I set up the smoke oil tank and smoke oil valve system just as I did on my Super Cub & Cap 232. Although I had to make a smoke oil tank cradle to suspend the tank below the servos, everything fit beautifully.

       I finished cutting the cowl and started to bolt the wings together. I installed the aileron push rods and tested my CG. I balanced the Ultimate with the CG 1/2” behind the recommended location. The tail weight should help with hovering but may make the bird more unstable. having nothing left to do, I charged the battery and tested the Saito in the yard. I started with a 16 X 8 Top Flite Power Point propeller for break-in and ran the Saito for a bit.
       I tested the smoke system out and was impressed with the amount of smoke that was produced. I disassembled the muffler and noticed some wear on the copper tubing as it was vibrating against the housing. I opted to change my design a little by wrapping the tubing around the muffler bolt which after testing, proved to be the ticket. I later installed a spring on the muffler bolt to keep tension against the coil which should reduce unnecessary movement.
       I also changed the location of the fuel tank pressure tap so that it was upstream from the smoke oil injection or else the smoke oil could contaminate the fuel system and cause flame-outs. I installed the tank pressure tap just next to the muffler inlet threads. I was now ready for the Ultimates first test flight.

       The finished Ultimate is a sharp looking ARF indeed !!!

       I showed up to my local flying field early in the morning and set up my equipment. I changed my propeller to a Dynathrust 18 X 6 to improve slow speed thrust and fired up the Ultimate. I rolled out and without any hesitation, she rotated and climbed out beautifully. I noticed that the roll rate was not enough but otherwise she did not need much trimming. With the smoke system activated, I tried some tail slides and was amazed at how nervous I became as the plane disappeared in smoke.
       The smoke system worked as good or better than my Cap 232 and I was very pleased. After the adrenaline rush was over I landed the fuel thirsty Ultimate at 8 minutes and found the 16 Oz tank dry! I set my transmitter timer and readjusted the aileron throw. I then installed a Top Flite Power Point 18 X 6 to see if there was any improvement in vertical performance. By now my good friend George Manning showed up at the field to help me wring out the bipe.

The smoke system cranked out some clouds !!!

       George put the Ultimate through a series of tests including vertical climbs, hovering and knife-edges. All in all the Goldberg ARF handled like a aerobatic monoplane with a lot of room for experimentation. The Saito hovered the 10.5 pound Bipe at 1/2 to 3/4 throttle which hopefully will improve with a better propeller choice and the completion of break-in. More tail weight will also be needed to improve the 3D ability.  With a little radio mixing, we corrected the rudder roll with aileron to help in knife-edge flight. some down elevator was also mixed from the rudder which helped.
       The color scheme was a little hard to see and became confusing at distance so without pushing our luck We called it a day. I went home and fixed a few things including adding some fluorescent red trim vinyl to the bottom of the plane for orientation visibility and moving the receiver pack farther back in the fuse for a better CG.
       The following day I tested her out and was super happy with her performance. The overall feel of the bipe was stable and precise. The vertical climb was incredible and the roll rate was almost scary. I was very pleased at how slow and stable the bipe landed but landing under power was needed as to reduce risk of slow speed stalling. I added exponential (50% negative) to my radio and found it much more fun to fly. I have some more fine tuning to but she is a keeper for sure.

           Be sure to see the ultimate fly in my video: Super Smokers Part II

Don Giandomenico

  Questions or comments ? Feel free to contact me - Don Giandomenico

 

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