Wipa Firecat

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(Click above for specs and pricing on the Wipa Firecat)

At first glance, the price of this balsa covered ARF seems a bit high. After you take a closer look at the quality of construction, craftsmanship, and covering, you'll see why this fun-fly, 3D aerobat isn't at all like your buddies parkflyer!

This model has a very limited instruction set so it should be build by a seasoned R/Cer with at least several other planes of experience. The Firecat review by Kevin Petrilla was very helpful in providing additional information and caution areas. Additionally, I picked up some great tips from fellow E-Zoners in a thread called Firecat Assembly.

The Wipa Firecat is built solid! This is a muscle fun-fly design that is kept relatively light using excellent balsa construction techniques. The model is meant to be a high-powered thrill ride!

My Wipa Firecat project will use several interesting new components. A rotating can "outrunner" style of brushless motor and some very light, yet very powerful Lithium Polymer "bricks" from Kokam via FMA Direct.

To give the plane plenty of power, I decided to use the AXI 282010 Rotating Can Brushless motor. This little 5.8 ounce motor is only 1.38 in diameter and 2.25 long, not counting motor shaft. Attach the front of the motor to the back side of the firewall with the 5mm prop shaft coming through the firewall. The entire motor case rotates providing a very high torque and allows this motor to drive large diameter props without using a gearbox.

(Click above for specs and pricing on the AXI 282010 motor)

I am also using the  Jeti Brushless Controller JEC403 which will operate the motor from 15 to 40 Amps. On 10-cells, the motor will spin an APC 12x6 e-prop at 8500 RPMs drawing 40amps. That's 370 watts input power!

(Click above for specs and pricing on the Jeti JEC403 ESC)

 

The motor easily screws in place on the stock Firecat mount

After the motor mount photos were taken, I added a 3rd screw at the bottom. All three screws use lockwashers.

The motor wires are fed through holes into the fuselage for isolation from the rotating can

The landing gear is epoxied into place with a spare piece of plywood filler.

A 12" prop didn't provide enough ground clearance so I was forced to use the APC 11x7 e-prop. I tested the power system using a 10-cell, Sanyo 4/5FAUP 1950mAh, NiMH pack from Diversity Model Aircraft. The 10-cell pack weighs 15oz. The power output is simply fantastic!

I will be comparing several battery technologies in this write-up for use with up to 55amp power systems.

The quality of construction is very evident from the tail assembly and alignment

I used 2 solid (but short) metal rods to connect the servos to the tail

The tail assembly was easy and fit perfectly. I used the recommended HS-55 servos because they fit perfectly in the tray. I would also adjust the control lines for minimal swing to reduce torque on the servo arm. The 3D-style elevator and rudder were very large so only a small amount of throw range was needed. To easily connect the rods to the servo arm with only a single bend, I used the HLH832 30 "Better" Swing Keepers from Hobby Lobby. The "keepers" make the links simply and solid!

The underside reveals placement of the receiver, ESC, and switch

My wing is glued onto the fuselage

The removable hatch modification allows for easier pack swapping

The custom canopy and fiberglass cowl add nice finishing touches

 

The empty Firecat weighs 23oz

My empty Wipa Firecat weighed 23oz and my 10-cell, Sanyo 4/5FAUP 1950mAh, NiMH pack weighed 15oz for an all-up weight of 38oz (2.3lbs). Below are some measurements using the APC 11x7 e-prop.

 Pack Performance Comparison Chart

Pack Weight RPMs Current
10-cell, CP1700 NiCd 16.8oz 8100 35 amps
10-cell, 1950mAh NiMH 15.0oz 7700 33 amps
3s4p, 4800mAh Kokam (using 1200HC cells) 11.7oz 8300 36 amps

I was a bit surprised with the lower current draw of my 1950mAh FAUP NiMH cells but decided that this was a new pack on its first charge and that it would only get better.

Flight Testing:

My first flight test was a blast! The Firecat went vertical after a short takeoff and trimmed out with only a few aileron clicks. I used my 10-cell, CP1700 NiCd pack for the first flight and had plenty of power for any maneuver. I could hover on a 3/4 throttle setting.

About half way through the flight, the Firecat started making a rumble noise almost like it had a glow engine inside. The performance seemed fine so we kept flying. After landing, I discovered that the front motor mount plate had broken free. I was amazed that it still flew well by pressing up against the inside of the custom cowl.

The broken motor mount gets a 4th post and additional front plywood slats

I had several more flights with my Firecat after repairing the motor mount and it held up just fine. Now it is time to test it out with the new Kokam 3s4p 1200HC pack.

Lithium Flight Testing:

As expected, when I tested my 3s4p pack of Kokam 1200HC Lithium Polymer cells, they held their voltage slightly better than the NiCd cells. I measured 36amps at a "whooping" 8300 RPMs using an APC 11x7 e-prop. If this wasn't enough benefit, I also almost tripled my flight duration over the CP1700 pack. (4800mAh / 1700mAh = 2.8). Finally, my RTF weight dropped by 5oz.

The 3s4p Kokam 1200HC pack (bottom) tripled my flight time while being 5oz lighter than the 10-cell, CP1700 NiCd pack (top)

I was now ready to fly at only 34.7oz. It was the best of both worlds!

The Firecat is "loaded with Lithium" packs

The pictures above show the placement of my 4 packs in parallel of 3s Kokam 1200HC. The packs are easily connected in parallel using the Kokam connector blocks. Up to five packs can be plugged in parallel to increase capacity and current delivery capability. You simply then solder on your output wire and connector of choice.

Kokam Connector Blocks

to be continued...