Setting a failsafe for RC gliders
Why do we need a failsafe?
Setting up a failsafe for your RC glider is an easy way to minimize accidents from happening and protect the investment you've made in your gliders. But, what do we need a failsafe, and how does it help us save money and make flying RC gliders safer for everyone?
A bit of background on 2.4 GHz radio systems
Nowadays, most of us use 2.4 GHz radio systems to control our RC planes and gliders. 2.4 GHz systems come in many flavours - it could be FrSky's ACCST or ACCESS protocols, Spektrum's DSMX, Futaba's FASST, FASSTest, or FHSS, or any one of the dozens of protocols available on the market right now from the various brands. 2.4 GHz radios have made it very easy for everyone to pick up a radio and fly without seeing if anyone is using the same channel or swapping frequency crystals like in the old FM days, but it's not without drawbacks.
The biggest drawback is that 2.4 GHz systems require a visual line of sight (VLOS) to maintain a strong link between the transmitter and receiver. The connection is affected when things come between the two, which is problematic for competition-use RC gliders due to the high usage of carbon fibre. Carbon fibre effectively blocks 2.4 GHz signals. Because of this, we recommend modellers use receivers with two or more antennas so one antenna will always maintain VLOS with the transmitter; why some modellers run their antennas outside the fuselage; and why some RC gliders use fibreglass noses. All these measures minimize 2.4 GHz shielding.
The second drawback is range and interference. Under ideal conditions, many 2.4 GHz protocols can operate up to 3 km in range. However, most wifi systems use 2.4 GHz (although some are 5 GHz), and it can also be affected by cell towers. So if many pilots are flying simultaneously, or you're in the city with a lot of wifi hotspots, or even if you're just near a cell phone tower, your range will be affected. Except for ExpressLRS, Team Blacksheep's Tracer systems, and ImmersionRC's Ghost protocol, your range will usually be around 1-1.5 km in real-world situations. Depending on the location, it might be even less than that. The point is 2.4 GHz is and can be affected by many variables in the environment, and we use them in carbon RC gliders which are not ideal for installation.
So what happens if we lose the connection between the transmitter and receiver? Without a failsafe, it'd usually keep the last command received. Unless the link recovers quickly, this can lead to the model flying away or crashing. That's why we need a failsafe.
What failsafe settings should I use on an RC glider?Your radio choice determines the failsafe setup process, but the end goal is the same. Here are three different examples of common failsafe setups:
- I use this first method on most of my models, but if the signal is lost while the glider is in a thermal, there is a decent chance the model may fly away. I set up my failsafe like this, so if I enter failsafe during a contest, I still have a chance to recover and complete my flight or get my model back into the flight box for scores. There is a definite risk/reward factor. I drop my camber to around 10mm with 30% left rudder and a small amount of up elevator. This setting puts the model into a slow left turn. If the model is not in a thermal, I have time to run toward the model to re-establish the link. However, if the model is in a thermal, it might continue climbing and fly away before the connection is re-established, and if there is wind, the plane will drift downwind.
- A more popular method is to have the glider deploy full flaps with full left or right rudder and allow the glider to slowly spiral to the ground. This is the safest failsafe setting for the model because it loses lift and enters a slow, controlled fall. The steady fall reduces the time the glider is in the air to minimize drift, while it still descends slow enough to minimize potential damage.
- This last method forces the glider down in a controlled descent similar to the second method but much quicker. By using only half flaps instead of full flaps, the glider goes into a faster and steeper spiral to the ground with the least amount of drift. While this will likely damage the glider, it minimizes the potential for accidents if you are flying near a busy road or highway.
If you haven't set up a failsafe for your RC gliders yet, spend some time this weekend to dial it in. It will likely save you money sooner or later.