Replacing the Motor and Gearbox in PZ UM P51

The motor and gearbox for Parkzone's Ultra Micro P51 can be easily replaced. If you plan on replacing both the gearbox and motor, you will need part# PKZ3624. The gearbox only is part# PKZ3527 and the motor only is part# PKZ3616. You can find a complete list of replacement parts for this aircraft here.

New Motor, Gearbox, Prop and Spinner From Horizon Hobby

New Motor and Gearbox Ready for Installation

To gain access to the internal components you have to take an Xacto knife and cut along the seam cutting through the decal on each side and along the rear of the top fuselage half.

Fuselage Access

Once you have access to the motor area you again take you Xacto knife and cut along the foam at along the areas shown in red below to separate the caulking used to secure the gearbox in place. You will also need to separate a couple of areas  of caulking that secure the wiring.

Once you have the gearbox, motor and wiring separated from the caulking, you will need to unplug the motor wires from the rear of the receiver. Note that the white wire is inboard and that the plug uses the out board two pins. Be sure to use tweezers to unplug the JST plug. Don't pull on the wires to remove the plug as this can break the wiring to the plug.

Photo shows the two pronged male plug removed from the reciever

Old Motor removed from the fuselage

At this point you will want to plug the new motor in and see that it runs with no problems. If so, lay down a layer of adhesive caulking along the fuselage sides where the gearbox mounts. Press the new gearbox and motor into this layer of caulk. Route motor wire along the side of the fuselage and under receiver circuit board. Plug the wiring into the the receiver and secure the wiring along the side of the fuselage with a couple of dabs of caulking. Also pull the motor wiring under the receiver to one side and secure it with a dab of caulk so that the wires are away from the aileron servo motor gear.

Put a second layer of caulking over top of the gear box flanges Allow the caulking to dry at least 24 hours before starting up the motor or putting any strain on the power system. The additional wires you see in the photos are for the navigaional lights that I added. The balsa cross members are an attempt to reinforce a badly deformed fuselage nose.

All that's left to do is put the fuselage top back on, secure it with a few pieces of Scotch tape and your motor replacement is finished.

Tags:Parkzone P51 Ultra Micro, RC, Radio Control, Airplane, Hobby

Fixing Ultra Micro Servo Problem

A problem I came across while flying my Parkzone Ultra Micro P51 RC airplane was that of a failed aileron servo. While flying the servo just locked up and the plane fell from the sky. At first the problem was intermittent, the servo would work and then just stall. Finally it locked up all together and I thought I would have to replace it.

Spektrum AS2000 Linear Servo

After doing some research, I found that other UM P51 owners had the same problem and fixed it by lubricating the screw assembly of the servo. From experience with RC helicopters, I know that it's not a good Idea to oil plastic parts. It might be a temporary fix, but in the long run, the oil will attract more dirt and cause an even bigger problem.

I found that by taking the end of my Xacto knife and carefully rotating the Screw Gear, I could get the servo to re-center and start to move again. It was still locking up each time I tried moving the ailerons, so I was pretty sure the problem was a small partial of dirt getting caught in the screw assembly and locking up the works. I broke out a blow gun and attached it to my compressor along with a small length of tubing that I attached to the nozzle of the blow gun. I then blasted air into screw assembly on either side of the linear slide all the while using my radio to move the slide back and forth. Each time the servo would lock, I could take the Xacto to the Screw gear and get it going again. After a minute or so of this, I was able to dislodge what ever was causing the problem and the servo has been operating fine ever since. This is not the cure all of servo repair, but is worth a try before going to the expense of replacing your servo.

If you think this might be your problem, but don't have an air compressor, no worry. You can buy a can of compressed air at your local office supply store. Typically sold for cleaning computer components, they come with a little spray tube nozzle that will work perfectly for cleaning your servo so you can get back in the air quickly.

Tags: Ultra Micro P51, Radio Control, RC, Airplane

Ultra Micro P51 Nav Lights

A great modification for your Parkzone Ultra Micro P51 is the addition of navigational lights. This lets you fly at dusk, a time of day when the wind typically dies down. If your daring, you could also try night flight. I found a great deal on a L.E.D. kit at S.F. Design Solutions, $15.00 includes shipping . The kit consists of red and green wing-tip nav lights with a blue or white tail light and white landing light. The lights are very easy to install, you just open up the fuselage, plug in the wiring harness, route the wires and your ready to take to the night skies.

The kit includes step by step instructions, but I've included a few photos and a detail of how I routed my wires. If you have never opened up your P51, it requires that you take a Xacto knife and cut through the decals on the fuselage sides and rear of the radio compartment so that you can remove the top to expose the motor, servos and AR6400 receiver.

Kit as received from SF Design Solutions

Below you can see where I have opened the radio compartment and plugged the lights into my receiver to see that they are working properly.

Testing the lights prior to installation

Click Image for Larger View

Pulling the tail LED out of the fuselage thru the vent hole

Tail light installed and anchored with tape

Wires for wing lights exiting thru forward vent hole

Wing wire installed and anchored with tape

Landing Light mounted at bottom of fuselage under the prop

Ready For Takeoff