The Return of the TigerCat

This is the TigerCat as I have been flying it for several years. The design is an enlargement of the TigerKitten, using the same airfoil and aerodynamic layout, but with different flying surface shapes and a different cowl. The airplane you see in flight here at our field in Olympia, WA has been flying for about ten years using an origianl brushed, geared Astro Cobalt 25 motor, runing first on NiCds, then NiMH cells, and recently on a LiPo pack. What's going to happen npw is that I'll remove the old Astro motor along with the old ESC and the entire ten-plus years old Airtronics radio system and replace it with equivalent state-of-the-art equipment.

With the cowl removed you can see the old Astro 25 motor and gearbox where they have been hard at work since the late 1990's. This motor is still capable of flying the airplane, but it's time to move up to something WAY BETTER.

Here's another look at the old installation from the back. You can see how the old motor was inserted from behind the firewall/motor mounting bulkhead and prevented from rotating under operational torque by stop blocks I added to the rear face of the firewall.

This is the motor battery pack tray/mounting area as it existed in the Astro powered airplane. This is one part of the TigerCat that will not change much.

This is the same portion of the fuselage seen from the bottom, showing the old Airtronics 72 mHz installation. That's a fifteen-plus year old Astro 207 brushed ESC at the left. The servo cables at the bottom are the aileron extension connectors.

The old astro geared motor is still inplace on the firewall/mounting bulkhead. Next to it I am holding the Cobra 4120-18 brushless outrunner (http://www.innov8tivedesigns.com/product_info.php?cPath=21_120_124&products_id=860 from Innov8tive Designs that's going to replace it. As you can see, the biggest problem I'll have to solve is how to compensate for the difference in the overall length of the two motors.

The solution to the problem of the new motor being shorter than the old one was to build an adapter mount that would make up the difference. As it turned out, a couple of measurements showed me that I needed something to fill in exactly one inch of open space that would remain between the rear of the new Cobra motor and the existing mounting bulkhead when the prop driver was in position in relation to the cowl, so that the propeller would end up in exactly the same relationship to the airplane as it had been with the old motor in place. The Cobra motor comes supplied with a rear mounting fitting that attaches with four machine screws to a flat surface, which my old mounting bulkhead provided. I designed a base plate of 1/8" plywood to mount to that, a 1/4" plywood motor mounting plate, and spaced them apart with a pair of 5/8" x 1/"4" spruce blocks. Here the motor plate is drilled out to accept the rear shaft extension and the mounting screws, ready for attachment to the base plate.

I used ZAP-A-GAP to join the motor mount assembly to the base plate.

This is the completed mount adapter i place on the existing firewall. The empty holes in the motor plate will accept 4-40 bolts and already have 4-40 blind nuts installed behind them. The other four socket head screws you see are longer 4-40's tha entend all the way through the assembly to more blind nuts inside the firewall former.

Here I have the Cobra 4120-18 outrunner mounted in place on the new adapter/spacer. One advantage of a mount like this is that it is easily adjustable for short increments of length and/or for thrust line offsets.

Here's another view of the Cobra motor in placce on the new mount, with the three power leads attached to the ESC wires with bullet connectors. Before closing up the cowl to fly the airplane, I'll safety each of those connector attachments with tape so they can NOT come loose unless I want them to.

Remember the part about easy adjustment? All my measurements were pretty close, but not close enough. The front of the molded fiberglass cowl on this airplane is designed to line up exactly with the spinner backplate;when that is accomplished the motor centerline/thrustline is correct. It turned out that I need to tweak the motor a degree or so to the right, and the best way to do that was to add a washer between the upper and lower LEFT motor mounting bolts and the motor base plate. I have loosened all the bolts to get access behind the mount and here I am inserting a washer. There's another one like it already in place under the bottom left mount ear.

In this airplane the plywood panel that forms the entire mounting surface in the middle of the fuselage is a removeable tray. This is the top side, accessible by removing the top hatch that includes the cockpit opening. The double wire with the Deans Ultra connector is the power lead from the ESC. The motor LiPo pack will attach to the dark Velcro.

I replaced the old LiPo with a new ThunderPower 45C 4400 mAh 5S pack.

Here is the new Airtronics 92824 8 channel 2.4 gHz receiver in place in front of the new rudder and elevator servos...this is a view from the underside of the airplane. The dual antenna leads are held in place with a couple strips of masking tape...off the right (the rear of the airplane) they are arranged in a 90 degree orientation to each other per the Airtronics manual.

These are the new rudder and elevator servos as seen from the top of the equipment tray.These are Airtronics 94842 Digital BB output servos which will give me a bit of overkill in terms of control power and the precise centering I want to make this "Golden Age Classic" airplane fly smoothly and gracefully.

I used a pair of Airtronics 94746 Low Profile, heavy duty digital servos for the ailerons. I wanted the extra power and durability because this airplane is set up using full span ailerons that double as flaperons, and the control forces can be substantial at higher airspeeds. I'm using dual servos to take advantage of the capabilities of my new Airtronics SD-10G transmitter to control each aileron independently in order to get precise differential throw AND to make use of individual adjustment and servo speed (delay) control when I activate the flaperon function.

I used the new Innov8tive Designs Cobra 80A ESC, which is provided with a plug-in module that permits you to set all the necessary parameters directly, without having to guess at getting transmitter stick inputs right. (http://www.innov8tivedesigns.com/product_info.php?products_id=903) This ESC includes a high capacity switching BEC (battery eliminator circuit) that will reliably power servo installations like the one in this airplane without overloading.

This is a closer look at the 92824 receiver with the Cobra ESC in place ahead of it.

This is the Cobra 4120-18 motor ready to be covered up by the cowl. You can se that I have safetied the power lead bullet connectors and tucked the wires out of the way.

The TigerCat design features a long, deep cowl that covers everything neatly. It's held in place by those little screws you see along the rear (left) edge.

I used a DuBro 2 1/2" plastic spinner. Here the backplate has been bushed to fit the output shaft of the Cobra motor for a tight fit.

I chose the Cobra 4120-18 for its ability to swing a large propeller. Here I am using a VarioProp 12C two blade hub with 15" diameter scale profile blades. I added an extension propshaft (available directly from Innov8tive Designs) to permit mounting the deeper-than-usual VarioProp hub assembly.

I painted the white DuBro spinner using an airbrush and the same Stits PolyTone Insignia Blue that you see on the cowl. The VarioProp blades are normally black...I did a careful balance job on mine, sprayed them with silver PolyTone, and added a couple of Hamilton-Standard decals just for the cool factor.

This is what it's all about. The airplane is just off the ground here, at about half throttle. I'm holding a bit of right rudder...standard practice for any high-powered taildragger...and letting the TigerCat fly itself off the grass.

This is just an easy banked turn past the strip.

Smooth, straight-and-level flight looks really good with an airplane like this, but it's not as easy as you might think. The built-in stability of this design goes a long way toward taking the work out of those long, straight fly-past maneuvers.

This airplane is capable of any and all Classic Era aerobatics you can think of, and then some, but it is NOT a 3D model. Close-in, coordinated turns like this give you the feeling that you're flying a time machine in miniature.

Let's go the other way. That old-time pilot looks pretty happy with the job he's found. As soon as my friends at Premier Balsa Kits are ready to announce production of their new kit for this airplane, I'll let you know right here at rcmodel.com.