Tractor Cat aka PushyCat Modification Notes

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There are some build photos and an RCGroups Thread.

Initial Notes 20 September 2008

Seems like CG is wrong at 100-105mm., more like 130(10%SM). The wiring from the elevator is a problem as I could not bring myself to taping servo wires to the surface of the wing - surely a duct of some sort in the kit would have been better. The horizontal stabiliser is cut along the grain where it plugs into the fins. I added bamboo pins to give at least some strength as well as using them to lock the tail booms in place. Slicing into the covering film on the wing to glue the booms in place is risky as it is easy to also nick the wing sheeting. The foam core of the wing is VERY fragile crumbling easily and so I used some white glue to stabilise it when widening the hole for my two wing servos. The Rx is velcroed to the wing assembly leaving one lead only (throttle) to the fuselage. The motor mount box is made of some rather weak wood which I strengthened using some ply. I removed the decals except for Sniper EP.

I will probably build a top hatch for battery loading etc as I don't intend using an undercarriage. Hand launching may change my mind on this however although I could simply mount the fuselage under the wing for a different look and for something to hang onto. It will also give the wing some more ground clearance.

Booms limit prop to 9" so will use an overpitched Aeronaut 9x7 folder and a Turnigy 2213/20.

First Flight 24 September 2008

So the first flight was too tentative given the rear propellor and nowhere to hang onto. The aircraft failed to launch and upon hitting the ground, fairly gently, the horizontal stabiliser fell off. This was a combination of poor balsa and almost zero adhesion to the laser cut holes in the tail-booms. The laser leaves a chared coating on the balsa which is not porous and so the white glue I used had failed to adhere. In addition the balsa spigots split along the grain (no surprise) leaving only the bamboo pegs. Without the horizintal stabiliser one of the tail-booms deflected and was hit by the propellor.

Tractor Configuration 25 September 2008

So having thought about this for a few minutes and having run the CG computations I will convert the PushyCat to a tractor configuration - the current configuration is not worth the risk and frankly I could not be bothered with bungees. Once its in the air no one can see the propellor anyway so repairs first then off with its nose.

Servo Issues 7 October 2008

Tractor configuration finished with CG at 130mm with a 2000mAH LiPo pack fully aft! Cheap HXT900 servoes on elevons not centering properly - very annoying - torque rods not helping. Test flight in a week or so.

Broken 16 October 2008

A combination of torque rod slop, stiff aileron hinges and bad servo centering led to PIO (Pilot Induced Oscillation) and a major crash while attempting to land after one circuit. Launch was difficult as the aircraft was not at flying-speed from a hand launch for 10M given the marginal power available. Once up to speed it flies quick just takes time to get there.

Rebuild finished 15 November 2008. Probably will run as elevon-only control after some initial flights with elevator.

Slope Soaring 16 November 2008

First flight interesting. Not enough elevator available to counter motor induced pitch up. Very frisky tip stalling off left wing followed by spiral dive recovered just before outlanding. After some diagnostics by Ray Cooper CG was moved forward to 120mm behind LE from 130mm. Aileron throw was increased and differential mix removed leaving mechanical differential. Much improved and several flights followed easily hooking into moderate slope lift. Elevator extremely useful on the slope so elevon configuration abandoned. Distinctly asymetric behaviour on loops and subsequent investigation showed slight washin on left wing difficult but possible to fix on balsa sheeted foam core wing. Yaw oscillation evident cause unknown but possibly connected to washin Likes to be flown fast with only 100mm tip chord. Landed with neutral elevator.

A good result.

Shorter Nose 10 June 2009

Hacked about 3cm off the nose removing the yaw oscillation flight. Tip stalls easily but exciting to fly.

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