Graupner Model Airplanes "Show Flyer" 60 Size 3D ARF from Hobby Lobby Int.

The Graupner ShowFlyer is a highly pre-fabricated ARF for 3D style aerobatics. It is distributed in the U.S. by Hobby Lobby Int. and is designed for a .60 size glow engine.

My wife, Kim, decided to surprise me with it for my birthday knowing that I would have a great deal of fun converting it to electric power. She was, of course, very right! The ShowFlyer is an impressive 3D performer.

A so-called “3D” plane is the new term for the original “funfly” models. They usually have thick and aggressive airfoils, lots of lift, plenty of drag, and huge control surfaces. For all their intimidating features, they are merely over-grown parkflyers that fly with great ease and stability. They can take off and land in relatively small fields or parking lots.

Specifications:

bullet Graupner ShowFlyer 60-size 3D ARF ($295)
bullet Wingspan = 60.5” (1540 mm)
bullet Wing Area = 1240 sq. in. (80 dm2)
bullet Length = 64” (1630 mm)
bullet RTF Zero-cell weight is 80oz (2268 grams).
bullet MaxCim MaxN32-13Y brushless motor
bullet MaxCim Maxμ35-25BEC Controller
bullet APC 20x11 e-prop

20-cell Setup:

bullet Ready-To-Fly (RTF) @ 112 oz. (3175 grams) with 20-cells of CP1700
bullet MEC MonsterBox geared 4.38:1 (70T/16T)
bullet 800 watts at 41 amps
bullet 180oz Thrust at 4500 RPMs

24-cell Setup:

bullet Ready-To-Fly (RTF) @ 124 oz. (3515 grams) with 24-cells of CP1700
bullet MEC MonsterBox geared 5.3:1 (96T/18T)
bullet 1100 watts at 43 amps
bullet 210oz Thrust at 4900 RPMs

For my conversion, I used the popular MaxCim 13Y brushless motor, a Model Electronics Corporation (MEC) MonsterBox 6:1 (96T spur, 16T pinion), and an APC 20x11 e-prop on 24 cells of Sanyo CP1700SCR. I had an opportunity to try the newer MaxCim Maxμ35-25BEC Controller with BEC (Battery Eliminator Circuit) for my project. Previously, for the BEC function, users were limited to the 21-cell controller. The BEC feature reduces the weight of the plane almost 4oz by eliminating the need for a receiver battery pack. Additionally, the hassle of keeping the receiver battery properly charged is also eliminated.

Design Features:

The ShowFlyer was designed as an eye-catching model that can perform extreme aerobatic maneuvers close to the ground. Additionally, the construction is both very light yet strong enough to handle a .60 size glow engine. This provides a great model to convert to electric power since attention has already been made on keeping the weight down.

The aileron servos are mounted under the wing. The elevator and rudder servos are mounted in the tail. This design allows for very short control rods between the servo and the controlling surface, which provides less slop and a crisper response.

Another nice feature of the ShowFlyer design is the removable tail stabilizer. The horizontal stabilizer is very large and the removable design can aid in storing it for travel or shipment. A tailbrace assembly comes with the kit and it is also removable by simply unhooking a few clevises.

 Mounting the Motor:

I used the standard firewall mount kit (G96307-1) from MaxCim Motors to mount my brushless motor. The motor mount kit is light yet strong. The motor is solidly secured to the mount via the included metal hose clamp. It is held to the plywood firewall by 4 screws and weighs a mere 0.8 ounces with the clamp. When using an offset gearbox like the MEC MonsterBox, the resultant footprint is very similar to the intended stock glow engine. The gearbox drive shaft can easily be aligned to the center hole of the fiberglass cowl.

To help cool the motor in flight, I drilled slotted holes into the cowl front on each side of the prop opening. I then drilled five ½” holes in the bottom of the firewall below the mounted motor. The airflow exit hole was created by simply removing the small hatch under the bottom front of the fuselage. In this manner, cooling air can flow across the motor from the nose of the cowl to the bottom hatch opening.

Tail Wheel and Linkages:

The stock tailwheel is fixed under the fuselage and works by forcing the tail around with the huge rudder. While this seemed to work ok on a grass field, I had difficulty turning the plane on pavement without obtaining excessive speed. I decided to replace the tailwheel with a steerable tailwheel assembly (RA1300) from Hobby Lobby. The assembly was easy to install on the rudder bottom and gave me excellent ground steering on both pavement and grass.

As previously mentioned, the control rods between the servo and the controlling surface are very short, providing less slop and a crisper response. The rod has a clevis on each end; one is soldered in place and the other is adjustable. I added some glow fuel line “keepers” as a safety precaution to keep the clevises from pulling off in flight during extreme maneuvers.

I choose not to use the heavy stock tail brace that weighed a full ounce and looked like something from an old Erector set. We made a new one from smaller rod and clevises. One side is soldered and the other is adjustable before screwing it down to the stabilizer.

 

Battery Removal Design:

I considered several techniques for removing my battery packs. One was through the canopy and another was by creating a removable top on the fuselage. While either way would work just fine, I typically prefer using an access through the canopy.

Since I decided to remove my battery packs through the canopy, I cut an opening just large enough to slide the packs inside the fuselage. The opening was just about where an instrument panel would go in a real plane. My two 10-cell packs sat just above the wing into existing openings in the formers. By adding a few sticky-back foam pads, both packs are held in place by friction and secured by the plywood formers. For proper CG, both CP1700 packs were touching the inside of the firewall.

Originally, my design used 20 cells split into two 10-cell packs. The top pack was secured with a GWS R4-P receiver foam pad, which measured about 4” by 2.5”. This was later replaced by an additional 4-cell pack to boost my power level to 1.1 killowatts using 24 cells. An alternate method would be to use two packs of 12-cells. Either size would fit just fine in this model.

Now that my flight packs were inserted though the canopy, I needed to eliminate the four screws that held the canopy on the stock design.

Canopy Removal Design:

My solution to easy canopy removal on the ShowFlyer incorporated a combination of wooden dowels and rare earth magnets. I wanted a secure yet easy to remove solution for swapping battery packs without removing the wing. I used 6 sets of tiny rare earth magnets from Radio Shack.

The tiny rare earth magnets are recessed into the fuselage and a matching set is epoxied onto the inside of the canopy. I drilled a hole through the canopy plastic to help the epoxy hold and then painted over it.

To help secure the canopy from lifting due to wind forces during flight, I added a double wooden dowel prong to the front that slides into matching holes on the fuselage dashboard.

I used 3 sets of magnets on each side. The combined 6 sets of magnets and wooden prong hold the canopy secure during rolls, snaps, and high speed runs.

The canopy easily removes by pulling out the sides and sliding it back until the dowel rod has cleared the holes in the dashboard.

The entire battery installation procedure was a simple series of sliding the packs and canopy into place. This required no tools and no wing removal.

Painted Pilot:

For a great finished look, I purchased a Williams Bros. #18400, 2” (1/6) scale sportsman pilot figure from Tower Hobbies. The plastic pilot figure is inexpensive and comes in various sizes.

I painted my pilot figure using water-based acrylic paints. It mounts by simply pressing it onto a glued wedge of foam on the deck. I can easily remove it to provide greater room when swapping battery packs.

Flight Report:

Initially, I used my MaxCim 13Y brushless motor on 20-cells with a 4.67:1 (70/15) gear ratio and an APC 20x11 e-prop. The plane had great power for many advanced aerobatic maneuvers. It took off in about 20’ and landed in a very short distance as well. It flew very stabile both upright and inverted. I was very happy with the flight performance.

Although the power level was excellent, I did not have enough extra power for unlimited vertical or to pull up out of a hover. I later discovered that my current draw of 36 amps was actually much lower than was predicted by the modeling software for my measured 4500 RPMs. By switching to a 16T (tooth) pinion gear, my current increased to 41 amps. My ratio was now 70/16 = 4.38:1. Although I did not try it, in theory, a 17T pinion (70/17=4.12) would yield about a 46 amp current draw. This change alone would increase my power significantly.

Although I was going to simply decrease my gearbox ratio by swapping pinion gears from a 15T to a 17T, I had received an opportunity to test the new 25-cell controller from MaxCim Motors. The new (Maxμ35-25BEC) controller also had a built-in BEC (Battery Eliminator Circuit) just like my existing 21-cell controller. This is a true controller BEC in that it provides 5.0v DC at 3 amps with a 4 amp peak capability and cuts off the motor if the input voltage drops below 4.2v DC. I decided to test the new MaxCim controller on 24 cells and measure the current draw using a 6:1 (96/16) ratio on my MEC MonsterBox. Assuming that my current draw would again be lower than predicted by my modeling software (MotoCalc), I prepared in advance to possibly use a 17T, 18T, or even 20T pinion gear. I also ordered some special 4-cell packs of CP1700 from Diversity Model Aircraft. I would then use two 10-cell packs and one 4-cell pack for my 24-cell configuration.

The new 24 cell power level was fantastic! I had more than enough power to provide long vertical runs and hover at about ¾ throttle. My current draw of 43 amps was similar to my 20-cell setup but my RPMs jumped from 4500 to 4900 using the same APC 20x11 e-prop.

Conclusion:

The Graupner ShowFlyer is a great flying plane! My conversion project to electric power was very successful and it was also a great deal of fun. By providing the ShowFlyer with a clean and quiet electric power system, I was able to fly it just down the street from my home. The advantage of not using a glow engine will allow me to increase my practice time, since I can fly it more often, and learn some new 3D maneuvers.

Although the ShowFlyer has a big 61” wingspan and weighs over 7lbs, it flies very gently and is easy to land. The ShowFlyer can be flown very slow due to its aggressive “D” tube airfoil. It can be flown close to the ground either upright or inverted. Since the model is capable of performing more maneuvers than I have the skills for, it will provide me with a great learning experience for many flights to come.

The ShowFlyer "duel" at the 2002 NEAT Fair was a blast with Dave Wenzlick's Hacker-powered model and my MaxCim-powered model. Both planes looked and flew great! Dave's flat spin maneuver made an awesome noise that impressed the crowd! He is a great pilot!

 

Lithium Power Upgrade:

40 cells are needed to create two 4s5p packs

 I decided to upgrade my ShowFlyer power system to Lithium power using the new Kokam 1500HD cells. To replace my 26-cell CP1700SCR setup with a similar weight in Lithium power, I choose to use two 4s5p packs. Each pack has the voltage of a 12-cell NiCd pack and a capacity of 7.5AH. The current delivery capability is 60amps (8C) continuous and 80amps peak short term. This was much more than my MaxCim power set-up needed so I knew that I would get the best duration possible.

The finished 20 cell pack weighs only 24oz

I didn't have enough circuit board for more than the first group of 5p cells in each pack so I used copper solder braid wick instead soldered right onto the cell tabs. The individual overall pack was created by first making individual 1s5p packs and then soldering them together back-to-back.

RC Smoke System Upgrade:

A smoke system for glow or electrics? You bet! My .60-size Graupner ShowFlyer 3D model airplane not only runs on quiet and clean electric power, it also has a remotely-activated smoke system that is safe to use. For my full review on the RC Smoke system, go here.