Misunderstood and under-used, we look at why nearly every model can benefit from a Low-Throttle Failsafe. Let's get it out on the table: Fail-safe can be one of the most misleading names ever to be applied to an R/C feature.
Why? Because to the uninitiated, the name conjures up ideas of ultimate protection and huge layers of safety - a panacea of protection for your pride-n-joy model.
The reality is that Fail-Safe doesn't provide total security. Then again, nothing can offer complete safety. But once you understand failsafe systems, you realize that they represent a simple, invaluable step toward greatly improving the safety of your model.
What is Failsafe? The Failsafe feature is found in all JR radios capable of PCM modulation. When setting up Failsafe, you program the position that you want your servos to move to should your radio's receiver lose its RF signal stream.
Failsafe Simplified: Use for Low-Throttle Only
While the feature allows users to program FailSafe on any channel, for most applications we recommend low-throttle only. Many of us at Horizon set our FS for a few ticks above idle (except in jets, where we program for full-shut off. That's an additional measure of safety necessary for the breed of aircraft.)
Why only low throttle, and not some combination of flight controls? Simple. In general, we believe it's safest for your model to use the "HOLD" feature for all other channels (which is what PCM will do without any programming). If the receiver does not get a good signal, it keeps the model doing what it was until it re-establishes a good signal. Now you could argue that "hey, that doesn't work too well if I'm pointed straight into the ground," which is true. But on the whole this situation is rather rare. How much of your total time flying is spent heading straight into the ground as opposed to the amount of time you are looping, rolling, flying level, or executing turns? In these cases, "Hold" will protect your model.
Why low-throttle?
The answer to this has several points. The first answer is simple. If you lose the RF link with your model, whatever it does, it will do it at a lower speed with low throttle FS. That means people on the ground will have more time to get out of the way and you'll have more time to re-orient your transmitter antenna. At the worst, it means the model will hit the ground with significantly less energy and thereby do less damage. Many have made the argument that low-throttle will not completely save your model. While this is true, it does make sense that things are much better with low-throttle than with high.
How can low-throttle actually "save my plane"?
John Adams, the Horizon R&D manager, once explained that in some situations, low throttle could actually save your plane. How? As we know, your PCM receiver will go into "hold" only when the number of lost packets of information is high. While in some cases the reason for those lost packets is due to external interference (someone turns on your frequency, power lines, off-frequency commercial user, etc.), more often than not the interference source exists inside our models. Noisy ignition systems, electric pump motors and more can contribute to noise that can affect your receiver. If the amount of noise builds to the point where the receiver can no longer get "good information," it will go into hold.
As John says, if a contributing factor to your noise exists inside your model, by lowering the RPM of the engine, often times you'll lower the noise, giving the radio the chance to "re-engage" once it recognizes a good signal. If your model goes into low throttle and then you regain control, good situational awareness would tell you to go to mid-low throttle and land immediately to diagnose the problem.
How can PCM FailSafe help act as an "Early Warning Detection System"?
In the early days of PCM, some brands of equipment took an excessive amount of time to regain control once they went into hold. As a result, many models went into hold and stayed there.
JR systems are vastly different. They're designed to restore control the instant they get a good signal (which could be as little as 20 ms - an amount of time most of us would never notice), so many times we'll actually fly through momentary problems. For more prolonged interference, control is re-established the instant the receiver "sees" a good signal.
This fast recovery enables another benefit that most fliers are unaware of: As you reach the outer limits of your range, the model will often "blip" to low throttle. That means you'll actually get an audible indication that you're reaching the outer limits of your range. Most guys think that when the model goes into hold, it stays there. That can be true in some instances, such as if your model is a long way out, you fly on the other side of power lines, etc. In these cases it's improbable you'll get control back. But in our experience, more often than not - especially those where the interference is partially engine related - you'll get a throttle blip and then get control back very quickly. This means you are at your range limit and need to find out what adjustments are necessary to improve the robustness of your RF link. There's nothing catastrophic about it. In fact, low throttle failsafe provides an added layer of capability and security by allowing you to analyze your radio's RF link strength.
Simple Safety
It's really quite simple to activate low throttle Failsafe. If you have any questions, you can always call our service center. But it's an easy and valuable feature to use on most JR systems.
Once you've activated the low-throttle failsafe, do a range check. With your model on the ground, simply collapse the antenna on your 8103/9303, or remove the antenna on any of the 10 channel systems. With the engine running at mid throttle, walk away from the model until the engine goes to the pre-set position. Count your paces - you should be at 60 paces or greater.
With this system, you'll be safer than ever. And you'll have a more secure feeling knowing that you've checked out your model. You'll be able to get an "early warning" as to range limitations in many cases. Naturally, this system will only be of assistance if your model's battery is functioning. So as always, make sure you cycle your batteries and check them before every flight. Nothing matters if your batteries aren't functioning properly.
As you can see, Failsafe is not a complete protection solution, but nothing is. That said, when you understand all the intricacies of Failsafe, it's a lot more comprehensive than one might imagine at first glance. Give it a shot. Both the Canadian modeling organization (MAAC) and the giant scale racing association (USRA) have made this feature mandatory. This year, the organizers at Joe Nall have done the same. Whether AMA will recommend or mandate the feature is hard to say. But it's hard to say why one wouldn't want to use this valuable feature. It provides an extra level of safety and assurance so that you can fly your model confidently.
Real situations on how failsafe saved the day
A flyer is doing loops far out over the field with a giant scale aerobatic plane. He hears the engine cut back to idle (little "blips") and comes in to land. After doing a range check the pilot finds that his range on the ground has been reduced to just 20 paces (recommended minimum is 60 paces). He tries another transmitter module and finds his ground range increased up to 80 paces. The model is solid, and the module goes back to JR for servicing - instead of the model ending up in a bag.
Another pilot is flying in a contest, doing a horizontal figure 8. Without warning, the model goes into hold - continues circling, with the model losing altitude. The flier calls out his channel number, and the culprit who mistakenly turned on, turns off. The pilot regains control, and his model is saved.
A sailplane pilot has programmed his failsafe for a crow/butterfly/landing mode with the trim set to glide slowly instead of low-throttle. At a contest, the model got too far away and was going out of sight behind a line of trees. The alert flyer turned off the transmitter, putting it in landing mode. He walked the long walk, expecting disaster, only to find the model sitting in some tall grass with zero damage.
It won't work all the time, but it certainly improves your odds of keeping your plane in one piece.
Adding Failsafe to your FM (PPM) system
While we always recommend use of PCM systems in giant scale airplanes (when 20 of 20 TOC flyers all use the same of anything, there's got to be a good reason) some fliers using FM modulation are asking: Can I adapt FailSafe to my FM system?
Fortunately, there's an easy answer. Many companies make an in-line device (such as HAN6015 Airguard) that's inexpensive and easy-to-use. You simply plug the device in between the servo and the receiver. When installed, simply push a button when your throttle is in the desired position to "memorize" the setting. Then, in normal operation, the device is along for the ride. Should it detect that the signal has interference, it overrides and sends the servo to the preset position. Obviously, the success of this and all FS devices are predicated upon having power to the servos. Also, as with any electronic device you add to your aircraft, you should range test your model after installation. Virtually every electronic device gives off some RF - check to make sure it doesn't affect your range.
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