Graupner Extra 300S from Hobby Lobby

The new Graupner Extra 300S was designed for glow power but easily converts to electric flight with very few changes. The Extra 300S has a large 63 wingspan, 46 overall length, 639 sq. in. wing area, and is meant to fly at around 105 oz. (6.6lbs) with glow fuel.

The .60-size Extra requires very little work to finish

The pre-built ARF model has amazing quality! The fiberglass cowl is pre-painted in three colors. The light yet strong built up balsa and ply wings has the ailerons pre-installed and each hinge is pinned for strength. The covering is quality heat shrink film with each color a separate piece (not preprinted film). The fuselage is conventional wood construction with the motor mount and pushrods pre-installed. The landing gear hardware and the wing mounting hardware are pre-installed, and the entire fuselage is already covered.

The pilot and canopy are also pre-installed. My ship has a Patty Wagstaff  figure head.

I choose to power my Extra 300S with a MaxCim 13D brushless motor. It mount easily using the 0.8oz MaxCim motor mount and the hardware that came with the plane.

Plenty of cooling openings on this huge fiberglass cowl

The wing halves are easily joined with epoxy

The stabilizers and tailwheel assembly are both solid and easy to install

My MaxCim 13D motor uses a MEC Superbox with a 3.75:1 ratio (60T/16T). My initial measurements using an APC 14x10 e-prop were about 46amps at 6400 RPMs using 14 cells of brand new HR-SC2600mAh NiMH. I believe that my new NiMH cells need a few cycles to improve and I am counting on the new high-current 1200HD Lithium pack to hold better voltage under load.


NiMH Battery Placement:

The 14-cells of HR SC2600mAh NiMH were split up into one 8-cell pack and one 6-cell pack. The two packs were then taped together and positioned just behind the firewall to balance the plane. I used some thick foam blocks to hold the packs on 3 sides and a wide Velcro strip to secure it to the wing top when installed. This kept the pack very secure for any aerobatic maneuver.

Charger Harness:

MaxCim sells an optional charger harness assembly that provides a convenient way to charge the packs while leaving them right in the plane. The fuse position is easily changed to disconnect the controller and connect the charger terminals using Sermos (Powerpole) connectors.

Lithium Battery Placement:

This is my Kokam 4s5p 1200HC pack that contains 20 cells soldered together with a circuit board from Kokam.

I easily re-configured the pack by removing one solder jumper to become a 3s5p and 1s5p combo in a single pack. This allows me to utilize the BEC system on the MaxCim controller.

It also allows me to charge it with my SC2 from Bishop Power Products.

The pack weighs 17.4oz with wires and connectors. The capacity is 6000mAh. It will replace my 14-cell HR SC2600mAh NiMH pack that weighs 32oz. That's almost 1 pound lighter and over twice the duration!

My MaxCim 13D-powered Graupner Extra 300S now weighs 112oz (7 lbs.) all up.

The Kokam 4s5p pack fit perfectly in the frame of my Graupner Extra 300S behind the firewall. Since it was a pound lighter than my 14-cell, 2600mAh NiMH pack, I needed to place it forward. The large opening in the fiberglass cowling will provide easy access to charge the pack between flights.

Tailbrace Modification:

Graupner shipped a tailbrace modification kit to all Extra 300S owners via their distributors. I received mine before I was ready for my maiden voyage. When I saw what it was for, I didn't hesitate to add it.

Ready To Fly:

Final Setup:

MaxCim 13D motor
MEC Superbox 3.75:1 ratio (60T/16T)
APC 14x10 e-prop
RTF Plane = 66 oz
RTF Wing = 28 oz
14-cell HR-SC2600 NiMH pack = 32 oz, all up at 126oz (7.9 lbs)
4s5p Kokam 1200HC LiPoly pack = 17.4oz, all up at 112oz (7.0 lbs)

*The manual claims all up glow at 3000 g (105oz) (6.6 lbs)

Pack Performance Comparison Chart

Pack Weight RPMs Current
14-cell, CP1700 NiCd 24.0oz 6400 45amps
14-cell, HR-SC2600mAh NiMH 32.0oz 6300 44amps
4s5p, 6000mAh Kokam LiPoly (using 1200HC cells) 17.4oz 6400 45amps

Flight Testing:

On the left is a take off shot of my Extra 300S maiden voyage. Note the transmitter antenna in the foreground. After a little trimming for level flight, it was knife edge time! Nothing flies like an Extra! It was a nice change to go back to a high performance aerobat after flying so many 3D planes. The plane flew great!

After discovering that my SC2 Dual Output charger would not fully charge the 3s side of my dual Lithium pack, I decided to return the pack to its original 4s5p configuration. The BEC tap on the controller for my MaxCim 13D motor can handle the worst case 4s voltage, so I can simplify the hook up by using only a single connector.

To charge the pack, I am now using the Kokam 402 Lithium charger that can handle a 4s pack on a 12v supply like a car battery.

The 4s5p pack of Kokam 1200HC cells can handle 1200*5*5 or 30amps continuous and 50-60amps peak. My 45amp maximum static draw seems to be a perfect fit.


Power Upgrade:

To facilitate a better holding knife edge, I decided to upgrade my power system a bit. By simply adding another 1s5p pack of Kokam 1200HD cells, I could switch from my 14x10 prop to a 15x10 APC e-prop and have a faster top end speed while drawing the same 45amps as before. All I needed to do was to change my pinion gear from a 16T to a 14T. What could be simpler?

I also added a high quality TruTurn aluminum spinner. The polished aluminum 2 1/2" spinner is perfectly balanced to help achieve the highest RPM output from your power system.

To build my new 1s5p Kokam 1200HCT cell pack, I started with 5 loose cells. After pulling the circuit boards up by 90, I taped the cells together. The + terminals were all soldered together using copper braid wire wick. This was repeated for the - terminals.

To finish the pack, I soldered my connector wire onto the braid and used shrink wrap to lock the cells together.

I measured 55 amps at xxxx RPMs with my new power upgrade using an APC 15x10 prop. My RTF weight was now 116oz or 7.25lbs.