Welcome to week 2 of Project Rosetta Stone. This time, we look at the parts we need to build out S800. There are also some pointers about putting it all together.

Building the plane: The strategy of the build

There was a point when you hit the buy button for a plane that you had some expectations about how it would perform. When you look through your collection and find planes that you haven’t flown in quite a while, why not? Did they fail to perform? Why? Is it your fault or was it just a bad design?

I’ve seen quite a few examples of poorly designed planes that have hit the market within the past couple of years. And yet, what may be more common is someone trying to hit a price point. They need the planes to fit into small, commonly found boxes in order to keep the price down. What may have been a good design turns into a compromise. If you build it at face value, you may be disappointed.

The S800 always seemed to me to be such a plane, some very good ideas that somehow didn’t get executed as well as they should have been. Buy the PNP and you may not be impressed. But, with a few mods it can be your goto plane that you always take along with you to the field. The few things wrong with the S800 are entirely outweighed by what is right about the S800. The S800 was selected not because it was a good plane that is easy to build. It’s a marginal plane that can be vastly better with a few mods and some attention to detail when it comes to building the plane.

The tilting bicycle

Have you ever had carry a heavy bag or box while riding a bicycle? You know that it is difficult. Which ever hand the bag or box is in, means that when you turn that direction you have to prevent yourself from falling over. The question is, what can we do to your bicycle to help prevent this?

These are the kinds of questions we get in the INAV Fixed Wing Group. Asking for help with a flight controller to solve an issue that is clearly a problem with the build process of the plane. Thus, please don’t just rush through this assuming that things can be adjusted after the fact. Pay attention to weight, CG and side to side CG. If one side is heavier than the other, use a counter weight so they are both equal

The motor

The thrust requirements for the S800 means that many, many quad motors will work fine for this plane. You wont’ be out of pocket a huge sum of money just to get this plane capable of a bit of performance. Anything around a 2205 should work.

Also there are motor extensions for sale at Banggood that take the motor out further back. This helps to get the prop further away from the foam. It’s certainly a worthwhile and underrated mod.

Motors are one of the hardest things to understand with planes for a variety of reasons. The first is that there is no common reference. A 2826 is similar if not the same as a 2212. Bit how do they relate to Park 480?

The second thing that you have to keep in mind about a motor is the weight. Small amounts in increase in motor weight often means that you have to counterbalance the plane with more weight which in turns makes the plane heavier. Extra weight isn’t always a bad thing. But, you need to be sure that this is the direction you intend to go. It will also mean that your plane may require more thrust to take off and may come in hotter. Thus, you should be reluctant to add weight to your plane; unless this is part of your overall plan.


Efficiency of your motor is part of a combination of battery, prop and motor combinations. The best way to clearly see what is going on is to put a meter on your plane and watch the energy consumption at different amounts of power. I did exactly this with two motors and 4 props. Across the board, when a motor went from a throttle position of 1400 to 1600 this is where the greatest amount of amp draw increase happened. What I’ve seen is that motors tend to deliver a certain amount of thrust in a linear relationship but when they get to a certain point they fall off the cliff and amp draw continues to climb but additional thrust isn’t that great.

What you are looking for is to have your plane function well at a cruise throttle that is below this threshold. Instead of setting up elaborate thrust monitoring stations in your garage the best way to tell is to take your plane up with INAV with your Amp and Watt draw displayed in your OSD. Get a good feel at what the cruise throttle amp draw may be. You may want to fly this plane many times over the course of a month or two in different conditions to get a feel for where it may be. Then you can start changing props and batteries to see if you can find a way to lower the Amp and Watt draw. Pay attention to Watts in particular. Because if you put in a battery with more volts the amps will drop but the wattage may not change.

Brands and motor choice

When it comes to brands and beliefs in certain motors over others, I have a bit of a more simplistic view. When you’re building a plane. you have no idea if this will be your go to plane, or sometime that is a shelf queen. If you don’t care for the way it flies, convincing you to drop another $100 in parts doesn’t make sense. I figure you can start cheap and upgrade or sell off the plane as a used plane to someone else, but new foam and start a premium build. Of course, the goal of Project Rosetta Stone is for you to have a plane that will fly great.


Look at the image to the right. If you don’t have any inclination to buy something greater than the EMAX ESO8MD II, stick with these. It will make a difference in how INAV 3.0 will perform.

If the label is on the side that gets glued, remove it first. If there is none on the other side, move it to the other side. You want to make certain that the only thing that comes between the plane and your servo is glue.

Speaking of adhesive, which one is best? If you use a very strong adhesive like a 30-minute epoxy, I can assure you, your servos won’t ever move. And I can assure you that they won’t ever come out. Even when you really want to remove them. A good adhesive is E6000. It’s strong enough to make sure your servos don’t move, but weak enough to allow you to remove them.

Speed controller

The S800 doesn’t have the space for a RC Plane ESC with built in BEC. Some people have carved in space for the larger RC plane speed controller. If you’re dealing with INAV this may be a good time stop using the plane speed controllers. The suggested speed controller is any BLHeli32 speed controller around 35 amps to 50amps, depending on your motor. Many of the PDBs have superior voltage regulators than the ones in the BEC for the RC plane ESC. The ESCs are smaller and thus take up less space. There is also a really nice set of settings you can use in the BlHeli Suite; that will easily help you set the brake and calibrate the throttle. You can also update the firmware if needed. With the non-plane ESCs, it’s good to go up a size, as they don’t all have heat sinks.


Check out Andrew Newton’s build video.

Along with the assembly of the plane, you will need to use a servo tester to center the servos, then install them (remove the label from the glue side of the servo). Get the control horns working and linkage working. Work the control surfaces up and down fairly aggressively 20 times before fitting the linkage installation. You’ll want the control surfaces to move up and down on their own, freely without binding and without the tendency to want to move on their own. The control horns go in front of the carbon rods. So that the holes in the control horns line up with the elevon hinge.

You install the 2204, 2205. or 2306 size 2300KV motor on the motor mount extension’s plate only. You will need to use a thread-locker like LocTite to ensure that vibrations won’t loosen the mount. Install the motor onto the plane, but not the propeller.

You will need to start thinking of how you plan to attach your VTX and RX. Each may have as many as four wires running back to the flight controller. There are also 3D Prints for grommets for the antenna. I’d highly suggest a small antenna, like a Foxeer Lollipop 3. You will need a VTX that fits in the space allotted in the wing. Darren Lines said

Most (VTxs) will fit fine. The key is the position of the antenna output on the VTx. Ideally, this wants to be on one side, as then it will line up with the provided hole. I’d actually recommend a TrueRC Canada AXII Side Feed and sink it in to the foam. It’s a much cleaner look and better aero.

Also, a standard ESC may be too large to work in the confined space where the ESC sits next to the motor. You’re much better off using some flavor of BLHeli ESC, 30A-40A. Don’t worry about finishing the final wiring just yet. You will want to keep the build as clean as possible. Instead of holding the wires down with duct tape, use E6000 glue. You may need to order some additional parts to finish. 

Think long and hard about your build.

On my build, I put the GPS way out on one wing, and then the receiver in the bay of that wing. On the other wing I put in the VTX and antenna. I will make sure the wings balance, side to side. The S800 is more like a custom build, forcing you to use long runs of wire and think about placement. Take your time, this is going to take around 8 weeks to get this plane flying. Good placement now will make tuning a lot easier.

Winglet files for the S800 (we will be sharing the winglet file)

The S800 is by no means a perfect plane. But, it does have a solid following from people who have figured out how to get the most from the plane. Keep it simple, and try and keep it light. Stick to light motors. You may not have the proper wire needed for this plane. Stick with 22AWG or thinner wire. You also want to avoid large VTX antennas sticking from the top of the plane. At the very least, get a Foxeer Lollipop 3. The Lollipop has a small footprint. It’s also crucial that you balance the side to side weight.

Follow Andrew’s build video, you will need to cut parts off and do sand them down before attaching. Uhu Por is a fantastic glue for gluing foam.

Cheap vs primo builds

Every year a new it plane comes out and everybody rushes to buy the plane. The Reptile S800 had it’s 15 minutes of fame. The AR 900 stole the spotlight and never gave it back.

The S800 is really a race-wing, and is actually a lot better than most give it credit. If you try to make a budget build, you may be happy with it. But if you let yourself wander a bit with the build it can be very compelling. That doesn’t mean putting in top shelf servos and a $100 motor. It means doing things like adding balsa elevons and sprucing it up with 3D printed parts. The assembling foam aspect of the build is fairly straightforward.