I finally got around to finishing the upgrade on the Air Force. I'll jump right to the end and say it was worth it! I took it out for the maiden flight this morning and had a blast flying it। Even better, it came home in one piece.
The Modifications:
To anyone who has tried to fly the Estes 747 in its stock configuration, god help you. It is basically uncontrollable and I would not recommend it. For the upgrad, I used a Hitec 3 channel receiver, Great Planes 35 amp brushed ESC, and a Thunder Power 3S 2100 Lipo battery.
I started by finding the CG of the plane with the battery and electronics installed. You'll find the CG is roughly on the two large circles under the wing.
Next I disassembled the plane and removed the stock receiver and ESC. All that is required is to clip a few wires and the stock electronics are out. I did not bother removing the power switch.
With the electronics out, I cut the ailerons and elevator. Based of other postings on the internet, I decided not to add a rudder and have been happy with that decision so far. For the ailerons, I initially cut them 1.25 inches deep, 9 inches long, starting 3 inches in from the wingtips. After the first flight, I decided they did not have enough authority. I ended up cutting them an additional 3 inches towards the center making the total dimensions 12in X 1.25in. If I had it to do over again, I would probably cut them deeper, possibly 1.5 or 2 inches. Once the ailerons are cut out, cut approximately a 45 degree angle on the downward side to allow the ailerons to travel in both directions. I cut this angle free hand and would probably have done better to use a guide to make the cut cleaner. With the angle cut, I attached the ailerons to the wing with hinge tape available from your local hobby shop or Tower Hobbies.
For the elevator, I made two cuts straight across at 1.5 inches deep. I gave some thought to making the cut parallel to the trailing edge, but decided not to complicate things so I cut straight across. Repeat the procedure from the ailerons to cut the 45 degree angle and reattach them to the plane with hinge tape. In order to make both sides of the elevator move in unison, you need to join the two sides. I cut a short piece of servo wire and bent it 90 degrees on both ends. I pushed the servo wire thought the end of the tail and glued it in place on both sides of the elevator. So far this worked out well, though I am keeping a close eye on it before and after each fight.
The next task was to install the servos for the ailerons and elevator. The aileron servo installation was straight forward, just cut out about half the depth of the servo and glue in place. I used Dubro servo hardware and ez connectors to rig up the ailerons. I made a small slit in the wing with an exacto knife to hide the servo wire.
For the elevator servo I decided to put in on the top aft of the fuselage and rig the control wire to the top of one side of the elevator. I routed the servo wire through the inside of the fuselage. If you take cut out the rear hatch on the fuselage, you will find it is easy to route the servo wire up to the center wing area.
With three servo leads now terminated at the center wing area, it is time to rig up a wiring harness for the 4 electric ducted fans. I essentially made a pig tail connection, that is soldering all the positive wires together, then soldering them to a short wire with a standard bullet connector at the end. I did the same for the negative wires. Its not the prettiest, but it does the job. For my electronics placement, I put the receiver in the small electronics bay sandwiched in between the two wing halves. I had to enlarge it a bit to accommodate all the servo and motor wires. I put the ESC down below in the old batter slot, and covered it with packing tape for protection. I routed the battery connector side of the ESC through the top of the electronics bay which required cutting a small whole.
The last step was to find a suitable location for the battery. I can't remember the website, but I ended up using someone's idea which was to carve out a cavity in the top of the fuselage, essentially in the top bulge on the 747 (you know, where the 1st class lounge is!). I am using a 2100 lipo which meant I needed to take out quite a bit of foam to accommodate the batteries size. This step is critical as you need to place the battery in the correct location in order to get the CG balance right. I taped the battery to top of the plane, moving it forward or backward until I got the correct location. Once the CG was set, I traced around the battery and commenced melting out foam with my soldering iron. I did this is small stages, frequently checking to see if the whole was deep enough. Once the battery compartment was created, there was still one problem to solve. The forward post used to join the two wing halves is directly under the battery. In order to provide enough clearance, I again used my soldering iron to melt about half of the thumbscrew down. This seemed to work well, and everything fit together nicely. If you look in the picture above you can see where I melted down the thumb screw.
Flight Report:
For the maiden flight I chose not to use the included bungee launch system. Instead, another flier was kind enough to give it a hand launch while I worked the controls. The takeoff went well, only dipping a bit before pulling nicely in a scale like fashion into the sky. The 11.1 lipo obviously helps out, though it is certainly putting more voltage to the motors than in intended 8.4V. This can be mitigated by minimizing use of full throttle while cruising. I found 1/3 to 1/2 throttle allow you to cruise at a nice level altitude. Turns were good, though on the initial flight I found the ailerons lacked much authority, requiring a lot of deflection to bank the plane. I extended them for subsequent flights to a length of 12in which helped quite a bit. For turns all that is required is to bank the plane and use a little elevator to push the tail around. Landings are easy, I found the plane glides well and had a tendency to overshoot my landing area. Flight times with the 2100 lipo where about 10 minutes. I found on subsequent days the plane was difficult to fly in windy conditions and noticed quite a bit if horizontal wobble. All in all, this is a fun plane to fly once the proper modifications are made. The looks are great as is the sound from all 4 engines. Happy Flying!
