Hello again! I’m back with the final part of my ‘How Do I…’ articles focusing on giant scale setup. First, I went over 30-45cc aircraft, then followed that with 50-70cc aircraft. This article is going to cover 100-120cc airplanes, and my experience with the World Models 30% Scale Stearman. As I have stated in the previous two articles, I do not know everything there is to know about the hobby, but I’m going to share that which I do! Hopefully, I can give some pointers to those just getting into new areas of RC airplanes. Larger, more complex aircraft such as the Stearman have different requirements than smaller planes. Before we get into the thick of this, we need to answer an important question…
What is Giant Scale?
I went over this in the previous two articles, but I’ll leave it here as well. Giant scale is defined by four simple criteria:
1) Monoplanes must have a wingspan of at least 80″.
2) Biplanes must have a wingspan of at least 60″.
3) Jets must have a combined width and length of 140″. (wingspan and length of fuselage added together must be at least 140″)
3) If none of the above is true, the airplane MUST be a true 1/4 scale.
If an airplane does not meet at least one of the four criteria above, it will most likely not be considered giant scale.
What is This Article’s Purpose?
The purpose of this article is to help build on the base of my first article. We’ll continue here with 100-120cc aircraft! Now, as much as I would love to keep going, the largest plane I’ve had to date is the 30% scale Stearman biplane. I’m going to stick to what I know…. Hopefully, I’ve got your interest piqued – if so, read on!
The first thing you’re going to want is a relatively large building/assembly area. I have a shop in my basement, and I will admit that it’s not nearly as large as I’d like, but it gets me by. Unfortunately, I am limited to 7 foot ceilings in my basement, so assembling large airplanes can get a little difficult. Many of my larger projects have their final assembly done out in my garage.
My bench is a full 4 feet wide by 8 feet long, and was made by me. The frame is made from 2×4 lumber standing on edge, with a sheet of 3/4″ OSB (chip board) on top of the 2x4s. A 1/4″ Melamine top layer makes for a nice bench top, especially for all the photo work I do. The legs are made of 2×4 lumber as well, and screwed together in an ‘L’ configuration. I’ve used this bench for close to 10 years now, and it’s still flat – If I ever need to true up the top, an additional frame member can be added with two more legs.
In my first article I used the Great Planes Avistar 30cc ARF, and the second article used my World Models 29% scale CAP 232 ARF. The Stearamn really makes the other two aircraft look small. For the 30% PT-17, some of the assembly was done in the basement, but it was just too big to complete inside. As it was, I nearly had to remove the center section of the top wing to get the large biplane up my basement stairs! A folding buffet table became my temporary work bench in the garage, making final assembly easy!
Of course, a transmitter and receiver are required, but they will vary in complexity by the model. The Stearman uses the four basic channels – Aileron, Elevator, Throttle, and Rudder, which will include all current radio gear available. For the Stearman, I used my trusty Hitec Flash 7 2.4 gHz transmitter and a Hitec Optima 9 2.4 gHz receiver. Though it’s using just the four basic channels, the Stearman gets more complex. It has two servos controlling each aileron. Let me repeat that – each aileron requires two servos for proper control. We’ll get into more setup detail in a few minutes, but I mention it here for the sake of the item in the last photo. The Power Board. Its purpose is to separate the power to the servos from the receiver. This power board has a built-in adjustable voltage regulator, meaning I can supply the perfect voltage to the servos connected to it. If you look closely, you’ll also see that there are two servo connections for each of the eight channels, allowing easy wiring for the two servos per aileron. Speaking of servos… Let’s talk a little more about them!
When you get to the point that you’re wanting to build a kit or assemble an ARF in the 50-70cc size, servo selection becomes important. While I mentioned the high torque requirements in the 30-45cc article, choosing the right servos is even MORE important now! Here’s my number one recommendation for purchasing the right servo for the job at hand – DO YOUR RESEARCH! You’re going to want to spend some time finding the correct servo for your giant scale aircraft. Depending on the airplane, you’re going to be looking for different servos. Besides the torque value, you’ll want to look at servo operating speed, operating Voltage, digital or analog operation, brand, receiver type, and of course, price. All of these factors will weigh in on which servo is right for you. Let’s break these down a bit…
- Torque – The torque value (how much force the servo can apply to the control surface) is probably the most important factor in selecting a servo for your giant scale project. This will vary depending on the project – aircraft with large control surfaces, like the CAP 232 used in the 50-70cc article, will need servos with a higher torque value than a giant scale trainer or general sport plane. Both airplanes will require servos with more torque than your standard .40-.60 sized airplane, but the CAP 232 will need more than the sport plane. For 100-120cc aircraft, you’ll probably want to look at servos with a minimum torque of 140 oz./in. This, of course, will vary with the type of airplane you’re setting up and the type of flying you intend to do. For the Stearman, 140 oz/in servos will be fine – especially with two per aileron, two on the rudder, and one for each elevator half.
- Operating Speed – Like the torque value, operating speed will vary by aircraft type – an airplane designed to perform 3D aerobatics will need a servo that operates faster than a servo for a warbird or a sport plane. Typical servo speeds are in the range of .18-.23 seconds for a 60° rotation of the servo output shaft, while a high speed servo can rotate that same distance in .13 -.17 seconds. Some servos are even faster! A large warbird or sport plane doesn’t need a servo that moves that quickly.
- Operating Voltage – This topic is becoming less of a factor, as many new servos have a larger operating Voltage range. Some servos still have an operating range of just 4.8-6.0 Volts, so you’ll want to choose the servo based on the type of receiver battery you want to use. If you’re going to use a 5 cell NiMh battery to power your receiver and servos, then a 4.8 -6.0 Volt servo will work for you. Now, since I wrote the 50-70cc article, a few pilots have suggested that I remove the 4.8 Volt battery supply from the article. I can see what they are saying, so for the sake of erring on the side of caution, go with at least a 6.0 Volt power supply for your giant scale aircraft. With newer receivers able to handle an input of 4.8-8.4 Volts, LiPo and LiFe batteries have become a very popular option for flight batteries! But, just because your receiver can handle the extra Voltage doesn’t mean the servo can, so choose accordingly. Servos that can handle the higher inputs will be labeled with ‘High Voltage’ or ‘HV’.
- Analog or Digital Servos and Receiver selection – For the most part, the only reason I’m mentioning this is because there are receivers available that will only work with digital servos. I use a lot of Hitec equipment, and they have receivers that will ONLY work with digital servos. Make sure your servos are compatible with your receiver!
- Brand and Cost – Lastly, we have brand and cost. These will go hand in hand, as many name brand servos will cost more than the lesser known brands. Now, the name on the servo doesn’t automatically mean it’s going to be a better servo – Not all of us can afford to spend $100 plus dollars per servo, but this is why you need to do your research!
I used the Hitec HS-5645MG High Torque, Metal Gear Digital Sport Servo for all control surfaces on the Stearman. They proved to be a good match for the 30% scale biplane, and provided 168 oz/in of torque at 6.0 Volts. These are great servos, and I have used them many times over the years without any issues!
RCGFusa.com sent me their new 120cc Twin Cylinder engine to review – it was a perfect match for the Stearman! The engine was paired with one of Falcon Propeller’s new Civilian scale props – this was their 27×10 two-blade Beechwood propeller, available at justmodelprops.com. I also used a pair of 7.4 Volt 5000 mAh LiPo batteries from True RC. Unfortunately, it appears as though True RC is no longer in business.
Assembly/Installation Tips and Tricks
I went into great detail about setting up the servos in the 50-70cc article using arm extensions. Like the CAP 232 used in that article, the Stearman servos are set up in the same manner. One of the nice things about the World Models aircraft is that they use a composite (plastic) servo hatch. They are molded well, and keep the servo screws tight!
After pulling the servo wire through the horizontal stabilizer, The servo hatch mounting holes were drilled. A hatch screw was then turned into and then removed from each hole, and a drop of CA was applied to the holes. THIS IS A VERY IMPORTANT TASK, AND SHOULD NOT BE OMITTED! Hardening the screw holes helps to ensure that the screws will remain secure. The control horn was then installed in the elevator half, and the pushrod was assembled and installed. Like the CAP 232, the Stearman has bearings in the servo arm extension and control horn. A small machine screw and locking nut is used to secure the clevises to the servo arm and control horn. This made for a precision fit connection that had no free play. Notice that this was just HALF of the horizontal tail – the other half was assembled in the same manner, meaning that each elevator has its own servo. I really like this setup!
The aileron servos were done in the same manner, except that there were TWO servos for each aileron. This is where setup can get a little tricky if you’ve never tackled a project like this before…
The first thing you need to do is set up two servos, but they have to have their servo arms set to the same 90° angle to the servo body. Once you have two servos that are set up the same, you have to make sure that they have the same travel distance. These two servos are identical, but that doesn’t automatically mean that their travel distance is equal. Only after verifying that they were moving the same distance and approximate speed were they installed. The control horns were both installed as well, and the pushrods were assembled, installed, and adjusted. Adjustment is critical on dual servo control surfaces – if they are not properly adjusted, you can stress one servo, causing undue power usage and potential servo burnout. With both servos connected to your radio system and centered, and the control surface set to its center position, the pushrods were adjusted until there was no servo noise from either servo. The two were then tested together by moving the transmitter stick, and watching for any differential movement in the servo arms and control horns. I also watched the aileron covering material to see if any wrinkles started appearing throughout the range of movement – this would show that the two servos were not moving together. Both servos moved in unison, so I was pleased!
When airframes start to get really long, they may be split into two or more pieces. I believe this is done to keep the shipping boxes as short as possible. In the case of the Stearman, the ‘tail cone’ was a separate part that needed to be attached to the rest of the fuselage. A good, 30-minute epoxy, like Z-Poxy made attaching the tail cone easy. Once the epoxy had cured, a strip of covering was ironed over the seam. The World Models actually included this strip of covering! The vertical stabilizer was attached using more 30-minute Z-Poxy – it was installed in a slightly different manner than smaller aircraft. Because the Stearman has removable horizontal stabilizer halves, the vertical stab is attached to a vertical plywood mount. The Rudder horn and bracing was installed, and the metal rudder hinges were secured to the vertical stabilizer using more 30-minute Z-Poxy. a drop of machine oil kept the epoxy from getting into the pivot point of the metal hinges. All of this is relatively easy to do, it’s just done a little differently than smaller aircraft, and requires more space.
The custom made 42″ elevator servo extensions were pulled through the fuselage using a pre-installed pull string. The Stearman has a fiberglass tube installed for running the wires, so they don’t flop around in the fuse – that’s a nice touch! With servo connector locks on the wires, each half of the horizontal stabilizer was slid onto an aluminum joiner and secured with a machine screw and washer. Tail wiring added additional support, and is required – they are functional support on the Stearman! Each of the aluminum brackets for the tail wiring was pre-bent, but the angles were ‘fine-tuned’ while tightening the cables.
The pull-pull rudder is controlled by a pair of servos working in tandem. Just like the ailerons servos, the pushrods AND servos must operate as a collective unit to avoid problems. Believe it or not, setting up servos in this manner is not difficult – it just takes time. The results are well worth the extra effort to make sure they work properly.
Proper engine and fuel tank installation is easy – there was plenty of room on the firewall to mount the RCGF 120cc engine. The quart-sized fuel tank was assembled (the spring clips for the fuel lines were included with the tank, as was the neoprene tubing and brass clunk) and held in place with a pair of included Zip Ties. I added the thin strips of 1/4″ DuBro protective foam rubber under the ties, and a large piece of the same foam rubber under the tank. The large Tygon fuel line is available from DuBro, and was connected to the carburetor and secured with safety wire.
Using a pair of DuBro Heavy Duty 4-40 Ball Links, and a 4-40 pushrod made mounting and connecting the throttle servo easy. The instructions say to mount the throttle servo inside the fuselage, but with the carburetor’s location it would have been nearly impossible to run a pushrod and have it slide smoothly. I had the servo mount from another airplane, so it was used to mount the servo to the bottom of the engine box. This made for a really easy pushrod connection!
The engine box has plenty of room to mount the ignition module as well – a few holes were drilled and the module was secured with Zip Ties and DuBro 1/4″ protective Foam.
Proper cooling is necessary with any internal combustion engine, so I had to make sure there was enough airflow into and out of the cowl. Two large holes were cut in the TOP side of the cowl to allow hot air to escape. The spark plug caps didn’t quite fit inside the cowl, so small clearance holes were made on each side, along with the exhaust outlet holes. If you look at the last photo, you can see that the propeller hub is well inside the cowl. I chose to keep the engine mounted close to the firewall, and had a custom propeller hub extension made to fit the engine and cowl.
In this photo, you can see the custom hub extension behind the Falcon propeller. The stock prop hub machine screws were replaced with longer screws acquired at a local tool and fastener store. This setup worked out very well!
Well, we’re closing in on the end of assembly. The Power Board has been installed and connected to the Hitec Optima 9 receiver. The Power Board can be powered by two batteries, which is why there are two 7.4 Volt 5000 mAh LiPos in the second photo. Each of the servo wire extensions is connected on the face of the board on each side of the receiver. The receiver itself is connected to the top of the board, and gets power from one three wire extension. The remaining connections to the receiver are through the signal wire. See the image below to see the wiring schematic for the Power Board.
It’s a really nice setup, and it includes an adjustable voltage regulator and electronic switch for your gas engine ignition as well!
Completed Project Photos
With assembly now complete, it’s always a good idea to take a few photos. This airplane turned out so nice! By the way, I did a lot of decal work on this plane to replicate the full scale plane in the photos. All of the decals were custom cut by a friend of mine and myself.
Firing up the engine
The RCGF 120cc twin was brand new when I hung it on the fire wall, so I wanted to give it a little run time before heading to the flying field. Check out the teaser video below for the first run of the engine!
After running a couple of tanks through the engine on the ground, the cowl was installed and I brought the Stearman out to a friend’s flying field. It was their annual scale fly in, which would normally mean no maiden flights. But, because of the nature of this airplane, the field was officially closed and the flight was permitted by the event officials. Here’s the video:
This video, and the maiden flight are a perfect example of why it’s important to have enough room to fly a giant scale airplane, and why it’s a good idea to have a plan in mind when things go less than perfect. Sure, we all want that maiden flight to be as pretty as can be, but things happen that we cannot control…
So, when you’re going to fly a giant scale plane, here’s a few pointers:
- Never fly giant scale aircraft alone. It’s always a good idea to have a fellow pilot of at least a friend with you at the field. These large airplanes, engines, and propellers can cause a lot of damage!
- Be safe, and be smart!
- Write down your assembly and pre-flight checklist – the Stearman drew a lot of attention while I assembled it at the field, and I got distracted a few times.
- Fly in an area that will give you lots of places to land if things don’t go as planned.
- Be ready, and have a plan for when things don’t go as planned.
- Stay calm and take it easy the first few flights – get a ‘feel’ for the plane before you fly it hard
- After the first flight, check the plane over for loose hardware – if all looks good, recheck after two flights.
- Have a friend ready to help you with trim adjustments, so you don’t have to take your eyes off the plane.
- Set a timer for fuel consumption – running the plane on the ground should give you a decent estimate for the length of time a tank of fuel will last.
- Don’t forget to have some fun while you’re at it! After all, isn’t that what this hobby is meant to be?
In Flight Photos
As a reviewer for RCUniverse, it’s part of my job to get in flight photos. But, for the rest of you modelers in the hobby, it’s always a good idea to get some photos of your plane flying – at least when you have someone that can take a few snapshots…
Wow! writing this article brings back some good memories linked to this airplane. From that Saturday morning when I walked outside to see THREE big boxes sitting by my garage to the landing with the stuck engine – this was a great project. One down side to these really large planes is that they take up a lot of room and take time to assemble and disassemble at the field. There’s no way I could fly the Stearman at my local field, so it found a new home. It now hangs in my uncle’s hangar, permanently on display next to the full scale plane it resembles!
Giant scale aircraft, like the Stearman, are great fun, but they can be very costly as well. With that said, I’m glad that I had the opportunity to review both the engine and the aircraft, as these would be well out of my normal price range for RC aircraft! It’s been a couple of years already since I wrote the reviews on these items, but I’d like to send out another heartfelt thank you to Airborne Models, RCGF engines, and all of the other great companies that I have worked with over the past nine plus years for giving me the opportunity to review their products! For without them, and the help of some very great friends, Scott Anderson, Jim Buzzeo, Dennis Crosby, Mike Buzzeo, my son Jonathan, and my wife Anna, None of this would have ever been possible! Thank you, all of you, for letting me do what I do!
Hopefully, you were able to take something away from my article – if so, I’m glad I was able to help. If there’s something you’d like to add, please leave a comment – I’m always open to suggestions!
That’s all for now – from my shop to yours, Happy Landings! -GB
The World Models – theworldmodels.com
Airborne Models – airborne-models.com
RCGF – rcgfusa.com
Hitec – hitecrcd.com
Zap Adhesives – franktiano.com
DuBro – dubro.com
Falcon Propellers – justmodelprops.com