Great Planes Piper Cherokee

Whilst collecting some bits from my local model shop I espied this model hanging from the ceiling. It was a Piper Cherokee, built from unknown kit at the time and very well finished. It needed an engine, servos and electronics. It was a good price so I took it on. Had a really good look at the model and thought, yes, nicely built, shame that whoever built it didn't bother with adding some flaps.


I didn't like the tank that came with it or the engine mounting. Plus it had a fixed nose leg! I am not carrying it to the runway! That'll have to be changed. Initially I considered a 65 4stroke that desperately needed a home but it was not going to fit after all. What else have I got? A pre-run OS 55, which was exceptional when it was installed in my "late" CMPro Cessna Skylane which I still miss! I plumped for the OS 55 with a Pitts in cowl muffler and would change the tank for a 420cc Dubro.

My suspicions that this model was Great Planes kit and surfing the internet, finding the manual online confirmed it. There were some very slight changes but I did not know how how old the kit was, but was not a problem.

Install The Fuel Tank

On acquiring the model there was a small rectangular tank strapped on to a removable mounting shelf inside the forward fuselage. Pulled out the tank and choose a larger 420cc rectangular tank. I had to open up the firewall hole to allow the tank bung to sit in it slightly. Once the tank was strapped onto the shelf, the shelf was re-installed to verify position. Everything good! Removed the tank in readiness for the engine mounting.



Engine Installation

Stripping out the original mount and using the OS 55 and bolted to a decent mounting, I now had to make up a template so I could drill the holes in the firewall. The mounting would be secured by 4mm machine screws and spike nuts. I think the Americans call them crocodile nuts! With this done and using the pre-drilled holes of the mounting the engine sat perfectly with the drive flange a few milimeters outside the cowl. A Pitts muffler with twin pipes was fitted up temporarily in readiness for cutting the cowl exits.

For the throttle I drilled a hole in line with the carb lever and installed a Dubro snake outer sleeve as a guide. The lever would have to be repositioned later once the servo was installed and a connecting rod fitted. Thats as far as I can go with the engine install for now.

Install Steering

Rummaging through the "junk" box I found a steering kit including a nose leg. Measuring up the leg it was the same length as the original so modding needed there. After verifying the centre line of the fuslage and using the mounting as a template I drilled four 3mm holes in the firewall. Fitted the kit using 3mm machine screws and spike nuts. I then had to mark a hole for the steering rod just a little lower than the steering arm. Swinging the kit to one side I then drilled a 6mm hol and elongated it horizontally. This allows for the rod to move sideways slightly when the steering is operated.

Delving into the "junk box" once again found a length of 2mm rod and made a 90 degree bend at one end. This was then passed through the firewall and hooked to the steering arm. There was no need for a clip here because the rod now did not have enough lift to jump out again. With all necessary holes made in the firewall the tank could now be installed. With the steering rod as it came through the firewall I was unable to install the tank! Had to disconnect the rod momentarily while I install the tank.

Install of Major Components

With the tank now installed with coloured fuel lines connecteed and hanging out through the firewall, the steering rod put back in it's rightful place, it was time to position the servos on the rail. Unfortunately I found the rails were too far apart by about 3mm so had to make up some ply strips which were then glued onto the rails so that the servo screws would have something to bite into. There would have to be four servos, 1 elevator, 1 rudder, 1 steering and 1 throttle. I could not use the rudder servo for steering because the rudder wire was on the opposite side to the steering rod.

In my spares department I found 2 Spektrum A6000 digitals and two Futaba S3003's. The digitals I would use for rudder and elevator and the S3003's for throttle and steering. The wire control rods were passed through rod connectors fitted on to the servo arms. With respect for the elevator and rudder control wire guides, these were secured on to the rearmost rail, the latter had to be raised using a block of wood, so that the guides had little or no bends in them. These guides were clamped down using some plastic blocks normally used to fix landing gear wire to wings.

With power temporarily applied to the receiver, I was now able to set up the neutral positions of the control surfaces and lock the wires off. At the same time I was able to centre the steering and set this up. The steering servo was Y-leaded to the rudder output.

The wings have been filled with foam and fully sheeted. The servo extensions were preinstalled which just as well because they couild not now be replaced. The aileron servo hatches were the small plastic type so the only servos I could fit were HiTec Mighty Feathers, which are quite torquey for their size. A liitle trimming of the servo area and these servos dropped in nicely. I used 2mm spring clevises into which I wound in a length of 2mm rod which was bent at right angles at the aileron horns. Plastic rod clips were then fitted for security. Mechanical adjustment of the ailerons now just required unclipping the rods and winding either way in the clevis and locking off with nuts and re-clipping the rod ends.

Electrical System

I decided on LiPo power for the electronics, regulated by a Flight-Tec 5 amp VR. The regulator would supply a steady 5.5v current to a Spektrum AR6210 receiver and satellite receiver. I made up a little shelf for the regulator to sit on which would be glued in the fuselage just behind the tank. A cable tie would secure the VR to the shelf. A 2300mAh 7.4v LiPo pack was then wrapped in foam and slide neatly into the empty space above the tank. The battery would be secured using a hook and loop strap across it's end to stop the likelyhood of it sliding back out. In the side of fuselage I installed the fail safe switch.

The receiver was positioned in the vast empty space behind the rear servo rail using HD hook-n-loop pads and the satellite RX on to the fuselage sides at 90 degree orientation the the main receiver. We now have onboard power so it was time to verify the control surface movements and with the wing nearby connected to the RX temporarily via a 1 metre extension lead, to enable ailerons.



Engine and Cowl Set Up

Moving to the front, it was time to cut the cowl out for the cylinder head (which hardly sticks out at all), an exit aperture for the twin muffler pipes and steering. The more precsie bit is working out where the holes would have to be drilled for the main jet screw, access hole for the idling screw and pick a position for the fueling stop. Once the cowl was cut out so it could be positioned, it was time to drill the holes for the jets,etc.

Using 1/4 inch strips of white card, 6 inches long, these were taped to the fuselage and their ends aligned with the main jet and idling screw. Sliding the cowl carefuly back on, into it's final position I was now able to mark the location of the jet's access holes. Removing the cowl, I proceeded to drill 10mm holes at these marks and also a hole for the fueling stop just back from the main jet hole. The main jet is angled backwards which required slotting the hole. Now that the adjuster protrudes through the cowl all that is needed is an OS type extension to make adjusting of the jet simpler and well away from the propellor.

At this point I would proceed in starting the engine and making adjustments as required but as this engine ran perfectly in the late Cessna I did not think this necessary.

Finishing Off

I was going to us the lovely chrome spinner that originally was fitted to the Cessna and a 12 x 6 Master Airscrew prop. But next job was to fit the wing, loosely fit the spinner and prop ready for setting up the CG (centre of gravity). Strangely the GP manual shows the throws of the control surfaces but only mentions the cG. Not giving any indication of what it is supposed to be! Oh well, time to search the net for some info. Discovered that the CG is 3 1/16 inches back from leading edge next to fuselage.

Being a Piper Cherokee it wouldn't look right without wheel pants (spats) and fairings on the landing wires/legs. There wasn't any with the model but what I could do is improve the landing legs. I cut some plastic tubing which originally came from some old roller blinds, to length and using a cutting wheel carefully made a cut on the back edge. This would allow me to prise the plastic profile open enough to fit over the wire gear. I knew it may be a loose fit, so to fill this gap I used "No More Nails" double sided silicon adhesive tape. I cut two strips just wide enough lengthwise to wrap around the wire gear. It grabs the wire virtually instantly. All I had to do now was prise the plastic farings wide enough apart to go over the legs without touching the tape and when happy with their location, let them springback and squeeze them firmly on to the tape. Voila! We now have landing gear fairings.

At the time of writing I am asking around other members for any wheel pants they have spare which I can modify to fit over the wheels. Two would do, I am not too worried about the nose gear at present. I'll update this item when completed.

Applying masking tape approx in the positions, then marking with a felt tip on the tape I then proceeded to balance the aircraft. Placing it inverted on my homemade balancer I found not unexpectantly that it was tail heavy. Using a couple of known weights (old NiMh battery packs) taped to the engine mounting I found it needed 325 gms of weight. I cut some sheet lead and trimmed it the weight required and then folded it and hammered it flat. I then pressed it against the lower crankcase of the engine and shaped it to follow the castings profile. When happy with the fit I secured the lead tight to the engine mounting/crankcase using plastic cable ties. With this done I removed the wing and returned to the final fitting of the cowl because as I said before the engine was previously a happy runner.

With cowl fitted I lwas looking forward with glee to starting the Cherokee up. With the model fuelled up, switched on the TX and the models power, again checking the control movements and throttle. I had earlier when connecting the throttle control rod set the low throttle (idle) by using a piece of 1.5mm wire down the carb intake then locking off the throttle servo arm at this point. With throttle wide open and finger over exhaust outlets I rotated the engine a number times to prime it. Closed the throttle to about 1/4 throttle and applied the glow starter. Using a electric starter within a few spins the engine fired and ran. We are in business! I let it run for a few a minute then increased the throttle to halfway, hardly a splutter. Thinking of the neighbours I decided that final tweaking would need to be done up at the field.

The planned maiden on the Early May Holiday weekend was aborted due to the rather blustery winds swinging wildly from Northerly to NorWesterly. However, did get the final tuning of the engine done though. Hoping to get her airborne later in the month, so watch this space for an update.


Update:  The Cherokee was maidened and flew well although it needed a lot of up elevator. This was due to the weight of the ballast up front.  We reduced the weight by 100gms and reflew it.  Elevator is more responsive now.  Still needs a little more weight reduction so another 100 gms has been removed.  The original CG was derived from GP's website for their ARF.  It appears that the kit version does not folllow the ARF or has the same CG location. (The plans for the kit give no indication of the CG point)  Wating on suitable weather and time to retest the Cherokee.

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