By Tim Bailiff
It’s interesting how much my childhood still influences me today. As an example, it seems I have always had a soft spot in my heart for simple, flying balsa planes. I can’t remember a time when I didn’t have several hangared in my bedroom. In my youth, my parents understood this and never missed an opportunity to help replenish my squadron of these wonderful little planes.
In a recent construction article, I wrote about finding a great deal on Revell, Super Stratosphere, Rubber Band Gliders. I told how these were the same little planes I enjoyed as a kid. I have never been quite sure why they call them “gliders,” nevertheless, I still love them. The Super Stratosphere has a 17½-inch wingspan and is 13½ inches long. They are constructed primarily of balsa and are simply slid together. To say they are basic would be an understatement. However, with today’s micro technology, I have found that these simple little planes provide a great platform for a variety of interesting radio control projects. This article is about just such a project. If you are an intermediate RC flyer, with even rudimentary building skills, you are going to love this unique little bird. I am sure you’ll agree, this one is a keeper!
A Little Airplane History
The Pond Racer was a twin-engine, twin-boom racing plane in which the pilot was seated in a central pod, just behind the wing. It was developed and built by Burt Rutan at the request of Bob Pond. Bob commissioned the building of this airplane to compete in the Unlimited Class at the Reno air races. His idea was to design a modern airplane to fly against the vintage war birds. His concern was that these historic aircraft were being destroyed and damaged every year. Because there was a limited number in existence, he wanted his Pond Racer to be an alternative to these rare aircraft. He wanted it to be as fast and spectacular in the air, as they were. With its unique forward-swept wings and sleek aerodynamic lines, seeing it fly really was something special. It made its debut at the 1991 Reno air races and showed tremendous promise flying at 400mph. Sadly, in 1993, while again racing at Reno, it suffered a catastrophic engine failure and was destroyed. To this day, I reminisce about that beautiful airplane with its smooth, slim lines.
What’s The Big Idea?
Well, the idea showcased in this article was born as I was toying with one of my little balsa planes. At one point, I turned a wing around and noticed it swept slightly forward. In an instant, I flashed on the Pond Racer. I quickly opened another package and slid a second fuselage onto the same wing. That’s the moment I knew what I would build. I decided to construct an electric, twin engine, twin-boom plane with a pod mounted just behind the wing. Although it is not a scale model of the Pond Racer, its resemblance is obvious. I’m sure you will agree they appear to have similar genetics. As for the name, it came to me in a moment of pure genius: the Pond E-Racer. Hey, it fits, (E for electric).
You’ll have great fun building and flying this model plane! It is unique yet really simple to construct. When finished, you’ll be surprised by just how robust this little plane actually is. I guarantee, unless you are a member of my flying club, you won’t see another plane like this anywhere.
In the Beginning
Before we actually begin to build, please allow me to clarify something. When I make a reference to the “Plans,”, I mean my drawing that accompanies this article. “Instructions” refer to the printed directions on the back of the Revell packages. That being said, I always recommend perusing the plans first. It helps put things into perspective and illustrates the reason for buying the recommended airplane packages. It will also help you quickly identify the various parts as you work through your build.
OK, time to go shopping. At the store, you will need to purchase two Revell Super Stratosphere rubber-powered planes and one smaller, Revell Jet Glider. These little planes still come packaged in plastic bags, with the instructions printed on the back. They will be found hanging together at most hobby shops and discount department stores. I happened to find mine in a local craft store. Keep in mind, they come in different colors, so consider your color scheme as you search through the packages. For this project, plan on using one entire Super Stratosphere kit plus parts from the others two kits. Be careful to purchase only those kits that have firm, undamaged balsa.
Wing and Booms
Once you have returned to your work shop, open the Super Stratosphere packages and choose a wing. Make sure it isn’t cracked or otherwise broken. Also check that it isn’t too twisted or warped. Now turn the wing around so the writing on the top faces away from you. You want your wing to sweep forward. Using the plans as a guide, cut the wingtips as shown, then lightly sand where you just cut. Next slide two fuselages/ booms, taken from both Stratosphere packages, onto the wing. Make sure they are upright. Leave 4½ inch of center wing between them. Measure and mark this on the bottom. Make sure you have positioned them squarely on the wing, parallel with each other. When satisfied with the alignment, add slow CA to the inside of each fuselage along the top and bottom of the wing. Be thorough, but no need to overdo the glue.
With both booms glued in place, wet the underside of each outboard section of wing. Do only one at a time. Allow the water time to penetrate into the wood. Next, carefully bend an airfoil shape into the wing with your fingers, as indicated on the plans. Be gentle so as to avoid cracking your wing. I suggest you use a hair dryer to speed the drying process as you continue holding the airfoil shape into the wing. As the drying progresses, sight along the wing to make sure it doesn’t twist or bow up at the tip. If you find it has, simply wet the wing again and hold it straight. Don’t forget to continue holding the airfoil shape. Be sure to use the airfoil template in the plans as a gauge. Once satisfied with that wing, move on to the next. Although this may seem tedious, take your time, and be sure your wings are straight and the same.
Next, cut out your ailerons. Do this by making a flush cut to the wing, along the outside edge of each boom, ½ inch wide. Then, using the painted lines as your guide, cut straight out to the tip keeping the ailerons ½ inch wide. Don’t hesitate to refer to the plans and pictures. When both have been cut and removed, carefully sand a 45-degree angle to the underside leading edge of each aileron. This will allow them to move down without interference. Now, use 1-inch Blenderm tape to make ailerons hing
es. First, determine how long a piece you will need. It should run from the boom to wingtip. Next, split the tape lengthwise to make (2) 1/2-inch pieces. Not only will they provide an excellent hinge, but they also add strength to your wing in general. As you tape your ailerons, remember to leave a slight gap to allow the aileron to travel down freely. Rub the tape down well, and you’ll be amazed at how it disappears. Blenderm is great stuff.
Now look at the plans. The piece needed for the horizontal stabilizer and elevator is cut from the wing of the Jet Glider. I used the area with the star centered in the piece. It looks nice when in place. Cut the stabilizer and elevator out as one piece 43⁄4 x 13⁄8 inch, and then cut this piece in half, lengthwise. The back half will be your elevator. Next, remove enough balsa from the center of the elevator so as to form two pieces with a ¼-inch gap in the middle. Using a 3⁄4-inch piece of .080 carbon fiber rod or tooth pick, glue it so that it bridges the 1⁄4-inch gap at the leading edge of the elevator halves. Notch each half slightly so you finish with a straight leading edge. Glue using slow CA. As with the ailerons, sand a 45-degree angle in the underside of the elevator leading edge. Once again, a ½-inch-wide piece of Blenderm works great for hinging. Use two pieces leaving the center and ¼ inch of the outside edges unhinged.
In the full-size pond racer, the pilot sat in a central pod behind the wing. You will make this out of the Jet Glider fuselage. Using the plans as your template, draw the shape of the pod onto your glider fuselage. One trick I use is to place wax paper over the plans and trace the outline on it first. Then simply move the wax paper to your fuselage and cut away. When finished, you will need to cut the slot at the front of the pod. This is required, as it is attached to the trailing edge of the wing here.
Next, in preparation for adding the stabilizer, you will need to realign the stabilizer slots at the back of the pod and both tail booms. Again, look at the plans. As they come out of the packages, the pod and booms have a slot at the tail with a substantial amount of up, cut into them. This needs to be changed. To do this, use your hobby knife to make a cut from the front of the existing slit, straight back and level with the bottom of the piece you are working on. Make sure you cut all the way thru. After you finish cutting, you will have a wedge shape piece of balsa. Simply lift that entire wedge shaped piece up and glue it to the top of the original slot. Do this for both booms and the pod. To clarify, you are making 3 new slots for the stabilizer, all level with no “up” cut into them. Test fit the stabilizer when done and if necessary, clean out enough balsa for a nice fit.
OK; now it’s time to put the back end of the racer together. Start by first removing the wire hooks from the underside of the booms. To do this, cut the hook portion off flush with the bottom of the boom, and then carefully push up from the bottom on the remaining bit of wire. As you see the wire rise up on the top, grab it, and slowly pull it up the remainder of the way. Now you can use one of the hooks you removed to make a tailskid.
Next, slide the stabilizer assembly into the slot you cut into the back of the pod. Once the stabilizer is positioned in the pod, slide the stabilizer tips into the slots in the tail booms. As you do so, also slide the front of the pod onto the trailing edge of the wing about ½ inch. Note the bottom of the pod will attach to more of the wing than the top. You may have to slide and rearrange the stabilizer a bit to fit both booms and pod. Once you have checked for alignment and an even fit on both booms, you will need to cut away a small piece of pod where the carbon-fiber/toothpick elevator bridge passes through. This is to allow the elevator to move up and down without binding. Check the plans and then make a mark where the balsa needs to be trimmed. Now remove the stabilizer and trim the pod as necessary. Test-fit again, and when you are satisfied that the elevator moves freely, slide the stabilizer tips back into the booms while centering the pod at the trailing edge of the wing. Once again, check the elevator movement and stabilizer alignment, and make sure the pod is centered and straight. When ready, glue using thin and slow CA. Be sure you avoid getting any glue near your elevator.
Last, add the primary and secondary vertical (or near vertical) fins. This is a very unique feature as there are three. First, cut and glue the larger primary fin in place on the pod with slow CA. Next, cut and glue the two secondary fins along the line of the horizontal stabilizer, on the outside of the both booms. These are glued at a 45-degree angle and add tons of character to this little beast. As a final touch, any remaining slots in the booms and pod can be filled in with scrap wing material.
It’s time to build you motor mounts. You have two. How cool is that? If this is your first twin, do not stress. Things were kept simple, otherwise I couldn’t have built it! These mounts will utilize two of the plastic propeller units and one set of land gear that came in the Stratosphere packs. Start by trimming off the plastic prop supports flush with the front of the mount. Recognize there is a little downthrust built in. That’s great, as we need it. Now lightly sand the front of each to make sure it’s flat with no remaining protrusions. This also roughs the plastic a bit, assuring a good glue bond.
Now, using the motor mount detail on the plans, cut two rectangular 1⁄16-inch plywood “fire wall” mounts. The brushless motors I used came with their own aluminum mounts that attach flat against the plywood. If your motor and mounts are different from mine, use them as your guide to cut the ply mounts. Now, using slow CA, glue your plywood mounts squarely to the flat front of your blue plastic pieces. When finished, the plywood should face straight ahead, with some downthrust. Now acquire some ¼ x ¼-inch balsa and fill in behind the plywood mounts. Glue to both the ply and the blue plastic. Again, first sand the plastic lightly to assure a good bond. Next, sand the balsa to match the ply mount. As you look at your plane str
aight on, you shouldn’t see any balsa protruding from around your mounts.
OK; let’s work on your landing gear. You will need one wheel per side. These are very simple, as they are made out of one set of landing gear that came with the Revell kits. Following the plans, cut the one landing gear into two pieces. The wire is fairly soft, so trimming them to length and bending them should be no problem. The idea here is to bend the top of the landing gear wire so it fits into both groves molded into plastic mount, just like the original landing gear. Test-fit by inserting the wire into the plastic mount assembly onto the front of each fuselage/boom. Make sure the mounts face directly forward and angle down the same before gluing into place using slow CA.
I am a huge fan of my local Hobby People. If they don’t have what I need, however, I have no problem using the Internet. Hobby King is the Internet site I found that has the electronics I used for the Pond E-Racer. From them I purchased, (1) Orange Rx Spektrum DSM2 Compatible 4-channel receiver, (3) Ultra Micro 1.7 gram linear servos (one left and two right), (2) Turnigy Plush 6A / 6-gram speed controllers and (2) Hextronik 5-gram 2000kV brushless motors. I purchased a Thunder Power 250mAh LiPo battery from yet another site. You will be amazed by how small all these components are and how reasonably they are priced. The transmitter I use is the Specktum DX7. It has all the mixes necessary to make this little plane fly. Obviously, if you watch the weight, you can use different equipment.
Now, if you choose to use the same servos as mine, you will need to reterminate the leads using universal servo plugs. Without going into too much detail, once reterminated, be sure the leads are in the proper location on your plug. This will be determined by the receiver you choose. Work carefully, and take your time.
The three servos are placed one on each wing and one on the central pod. Refer to the plans and pictures for proper location and positioning. Remembering you purchased right and left servos, position them on the wings so as to provide the maximum amount of slack in their leads. I hot-glued mine into place, but 5-minute epoxy is fine as well. These tiny servos have no cases, so be careful not to get glue on any moving parts. Now cut and install the (3) 1⁄16-inch plywood control horns and (3) .032-inch piano-wire push rods, as per the plans.
Motors and Controllers
First, solder one controller to each motor. Don’t forget the heat shrink tubing. Attach your motors to the plywood mounts using the aluminum mounts that came with them. Along with the motor leads, each controller has a power lead (2 wires) and a servo lead (3 wires) as well. I terminated both sets of power leads (from each controller) into a single plug, matching my battery plug. Likewise, I reterminated both sets of servo leads into one servo plug. Although the wires are cramped, these procedures are very “doable.” Again, take your time and be patient. Be sure you test for proper motor rotation before you finalize everything. In other words, don’t shrink the heat shrink tubing over your solder joints too early. Because you need counter-rotating propellers for stability, assure that from the pilot’s perspective (sitting in the pod) the right motor turns counterclockwise and the left motor turns clockwise. The idea is to have each prop rotate from over the top, then down, toward the centerline of the aircraft.
Speaking of propellers, I purchased (2) GWS 5030×3, three-blade, counter-rotating props from the Internet. I then cut them down to 3 5⁄8 inch in diameter, sanded and balanced them. I mounted them with the included prop savers. They look cute as hell!
Once satisfied, shrink the tubing over your solder joints. Now use Blenderm to tape the three motor leads to the bottom of the fuselage just behind the motor mounts. Now sweep the motor leads to the inside of the fuselage, and while holding light tension, hot-glue each controller to its perspective boom. When complete, all four sets of power and servo wires should arc toward the front center, under the wing. Look at the pictures to see what is intended. Use only a few small pieces of Blenderm to secure in place.
Receiver and Battery
I can’t say enough good things about the little 2.4GHz receiver I used. It has 4 channels, one tiny 1½-inch antenna and weighs 2.2 grams, without using the self-installed heat shrink cover that came with it. Again refer to the plans and pictures to help properly position the receiver, on the forward under section of the pod. Be sure to face the pins forward. Glue in position with hot melt or 5-minute epoxy. I positioned the antenna downward at about a 45-degree angle. I have never had a single problem with control, even while flying to the safe limits of my vision, and I have pretty good eyes.
As you connect the servos and controller leads to the receiver, keep them in a nice neat bundle. Now, tape the red/black power leads, with their single connector, facing forward.
Next, I chose to position the battery on the top of the wing just ahead of the pod. For this, I used a small piece of self-sticking Velcro. Although it’s visible, I found it didn’t really detract from the overall appearance of the plane. It actually makes for a nice, neat connection. The battery lead sweeps down, around the leading edge of the wing and plugs into the controller lead under the wing. Remember, the horizontal stabilizer lies directly behind, so neatness is important to avoid blanking out the elevator (not good)!
By the way, I have a quick solution for using two separate aileron servos with only a 4-channel receiver. You won’t even need a Y-harness. Simply plug one servo into the aileron channel and the other servo into the rudder channel. Then enable your aileron/rudder mix in your transmitter. Now, set the rudder function to 100% and the reverse settings as required for proper aileron movement. Hey, it works!
I usually set my dual rates for 100% with switches in the up position and 60% with switches down. I set all my control throws with switches up. For ailerons, you want about 3⁄8 inch of up movement and ¼ inch down. If you have placed the aileron control horns where indicated on the plans, this “differential” will happen automatically. For elevator you want about 3⁄8 inch up and ¼ inch down. That’s it!
The Pond E-Racer is a really fun plane to fly and is guaranteed to attract attention at the flying field. It has a really distinctive look both on the flightline and in the air. But the nicest thing is, even though it’s a small twin, it handles very well.
Are you ready for the first flight? OK; let’s go for it. Once again check your controls one last time. Because it has no rudder, I found the best way to launch the racer is to align it with the runway centerline and hold the tail as you slowly advance the throttle. Even if the motors start at different moments, you can hear when they are in sync. At ½ throttle, my motors are at the same rpm and pulling like crazy. At this point, you simply let go. Your racer will quickly accelerate, and with a touch of up-elevator, it will be off the ground in about 10 feet.
Your plane will climb rapidly to altitude, so be ready to start a gentle turn. Now, get the feel of how it’s flying. You may have to trim a bit, but it shouldn’t take much. You’ll also find that ½ throttle moves your Pond E-Racer around really well. At full throttle it moves out, but it’s not really a screamer. I usually throttle back quite a bit because it saves the battery and still sounds great in the air. Control is crisp but not twitchy. As you gain your confidence, try a few stunts. Rolls are axial and can be done with partial throttle. I simply pull the nose up a bit and lay the stick over. The roll rate is quick but manageable. Loops are no problem as well. I use full throttle as I climb and then back off as it come over the top. Remember, it’s flying on thin balsa wings.
Landings aren’t difficult, however, they are a little hot. This plane, with its fairly high wing loading, is no floater. That means, without power, it comes down pretty fast, so save some battery for landing. When it’s time to bring it home, line up with the runway and slowly reduce power. You’ll know if you’ve throttled back too far because your racer will begin to sink like crazy. Should this occur, get on the throttle fairly rapidly so things don’t get out of hand. Continue to increase throttle until your rate of descent will get you all the way in. Fly it right down to the runway, cut the power, and begin your flair. As you continue to hold up-elevator, the plane will slightly pitch up, and you are down. This all happens fairly quickly, so stay alert. Don’t worry if the landings are a little “plunky.” The soft landing gear and prop savers will do their job to protect your airplane. After just a few flights, you will master the landings. It’s very exciting, to say the least!
If you are like me, you’ll find flying the Pond E-Racer addicting. In fact, I bring multiple batteries so I don’t have to wait long between flights. It’s fast and maneuverable, and the twin motors sound great in the air. You’ll have a blast buzzing the tower with this one. In short, it’s a fun plane to fly and almost as much fun to watch fly. Back at your tie-down, you will have many interesting conversations about its unique appearance. But do you know what the very best thing about your racer is? It’s the price. Remember, it was born a simple “Rubber Band Glider.” I wish you many happy landings. Fun stuff
|Author / designer, Tim Bailiff, with his Pond E-Racer at Winchester Calif.|
|Top view of newly completed Pond E-Racer without battery in place.|
|Top view showing battery location on top of wing, just ahead of pod.|
Tail showing unique triple fin design on Pond E-Racer.
|Right aileron detail showing hot glued servo, pushrod and aileron horn.|
Elevator servo detail showing hot glued servo and end of pushrod.
Elevator detail showing elevator horn, pushrod attachment, and notch trimmed into fuselage to clear carbon fiber bridge, connecting elevator halves together.
Under side of racer showing completed radio installation, wire routing and control hook ups.
|Motor mount detail showing blue plastic assembly with balsa and plywood motor mount and brushless motor installation.|
|Underside detail showing installed receiver and speed controllers with servo and power leads.|
|Closer detail of receiver connections, showing both sets of controller leads (battery and servo) terminated to single connectors.|
Top view of Pond E-Racer showing back side of motor mount supports with landing gear installation visible.
Pond E-Racer performing tight left turn in blue sky above flying field at Winchester California.