Trying to Understand Failsafe

[Pilotguy]

Curious how much attention you all pay to failsafes.

New failsafe positions are memorized by the receiver each time I bind, correct?

My AR620, AR410 and AR636 manuals say their are 2 types of failsafes: "SmartSafe" and "Preset".

"Smartsafe" will move the throttle to idle and all control surfaces will retain their last position at the time of loss of signal with Tx.

"Preset" will place throttle and all control surfaces in the position that I held them when I bound the Tx & Rx.

If I want to set my failsafe to put the airplane into a holding pattern I would need to set the throttle stick up a bit (say 50%) and hold the aileron stick slightly left or right. I would need to hold them in these positions BEFORE I bind and during binding.

The binding procedure in the manuals for all of my airplanes say that throttle and throttle trim must be set to lowest settings otherwise the ESC will NOT arm.

My takeawy from this is that my holding pattern failsafe idea wont work because trying to bind with the throttle stick at anything above idle position will not arm the ESC and I would not be able to fly.

Am I missing something?

[fhhuber]

I understand the real purpose of failsafe.. and I pay close attention.

What does a military weapon system failsafe do? It aborts the weapon. That means it self destructs a missile or calls a bomber back to base rather than having them continue to a target to destroy it.

So your model's failsafes should be set to prevent the model from continuing, uncontrolled, on a path that might lead to undesired harm to people or property.

For most fixed wing models that means: Throttle 0, Rudder hard over and full elevator. This will induce a spin. The model will not travel very far horizontally from point of loss of control. A spin is also a far lower energy impact than a straight dive.

Any other control settings you think might slow the model and thus reduce impact force are fine. But don't let it go in a straight line. A really slow flying plane you can set for a "free flight glide" which is a circle, near minimum airspeed. (Free flight would set for max duration, and that is usually somewhat faster than minimum to prevent stall)

Helis and quads, if you kill power they'll drop like rocks... It still meeting the idea of not letting the model go far. But could be debatable as to if its the best choice. I don't fly those types.

***************

You can set most Spektrum RXs to the hard over rudder and full elevator failsafe by rebinding holding the sticks in the apprpriate positions. See the instruction manuals for your RXs for how to over-ride any default setting.

[xviper]

I can only speak to my Lemon Rx with "failsafe". With it, I can set it to apply all sticks and switches to what I want and once signal is lost, the plane will go to those stick and switch settings. Insofar as putting the plane in a "holding" pattern, this is not a guarantee that the plane will do it. It can only work if you have some sort of GPS enabled system. Let's say you put the throttle at a certain level and you put the AIL and ELE "slightly left or right". If the plane was at an attitude that is not conducive to doing a "level" holding pattern, it will very quickly roll into a death spiral into the ground or spiral upwards until it runs out of juice and disappears, at which time, it will come back to earth. Even with the seemingly "perfect" throttel and AIL and ELE deflection, it won't go into a holding pattern. Next time you fly, try it. Give it a little AIL. If you don't let go, it will continue to roll. Unless you have some kind of GPS system that can be activated to "bring it home" at a prescribed altitude, you don't know where it will go.
I have such a system on all my sailplanes as those can and sometimes do go out of sight. If you are flying a plane so far that it loses radio contact, you will have long since lost sight of it. The range of today's 2.4GH radio systems is in the several "miles" range. For most people with average eye sight, they will lose sight of the plane at around 1/2 to 3/4 of a mile. I've been able to see my sailplane as far away as 1 km (~0.62 mile) and that's a 3 meter plane. Any smaller "normal" powered plane will be gone from sight before that, but you will still have radio contact.
On the sailplanes at our field, we have GPS enabled "Return to Home" devices on board. Generally, we don't use a failsafe Rx because as soon as we lose sight of the plane, we set the throttle and hit the RTH switch. The plane will then turn and head back to our location and circle. Almost always, we will see the plane coming home and we take over control and turn off the RTH. In only one case, where a failsafe Rx was onboard and set, did it actually save the plane. In this instance, the fellow's TX battery ran out of power and was no longer in contact with the RX. At that time, the plane went to failsafe and bumped the throttle to what he had preset it and flipped the switch to RTH. The plane came back and circled overhead. During that time, we put in a TX battery from my TX into his and he was able to re-establish contact and land the plane. This is the only case where I can see a failsafe RX working to save the plane. In the case where you are so far away that you lose radio contact, failsafe will not put it into a "holding" pattern. In such a case, it's best to shut the throttle down and have the plane spiral into the ground rather than go even further away before it comes down. You will not save it.
If you are really serious about saving a plane, get one of those RTH modules (like the Bigaole) AND a failsafe Rx, but I would suggest that the failsafe RX is NOT necessary. The RTH module has a built in stabilizer and RTH (and of course, OFF). You can fly with it OFF or use the stabilizer (which is also a limiter for the control surfaces). When you get into trouble, you can switch on the stabilizer, set the throttle and let go of the sticks. The plane will right itself and fly fairly level. If you lose sight of it, just set the throttle and throw the RTH switch. The Bigaole costs about $75.00 and is a far better "recovery" device than any of the existing stabilizers with recovery (or auto balance).

Here is a video I made some years ago with my HobbyKing SkyMule with a Turnigy T1000FC (no longer available) and "Buddy Box". The buddy box is a simple module that allows me to put the T1000 in OFF mode (so I can do aerobatics). This was the precursor to the present day Bigaole. You may not see the plane in some parts of the video, so just listen to the narration to know what I'm dong.

fhhuber posted some very good info while I was typing my response. You really don't want to go into a "holding pattern" when you can't see the plane. That's how far away it'll be when you lose radio contact.

[Pilotguy]

Great to hear the very knowledgeable advice. I was thinking of failsafe in terms of preventing/minimizing damage to people or property in the event loss of signal occurs. Thought some sort of holding pattern or orbit would potentially allow the airplane to by time in the event radio contact is re-established in just a minute or so.

It just doesnt seem to me that the default failsafe positions during binding make sense (throttle to idle & flight controls for straight & level flight) (or throttle to idle & last position of flight controls prior to loss of signal).

Side note: The 1964 movie "Failsafe" with Henry Fonda, Larry Hagman (and others) is a wonderful suspense movie sure to thrill anyone who likes airplanes/flying.

[fhhuber]

Appx 5 - 7 years ago (I think) someone thought they were covered by failsafe "hold last" using an FM PCM radio system.

In Hungary
An appx 150 cc powered biplane doing demo flights before a large crowd ran into interference with a radio station (that was broadcasting illegally) Controls locked out and the radio held last command of med-high throttle, very slight aileron, neutral elevator and proceeded to curve around into the crowd, killing 2 and sending more people to the hospital.

Previus that there were several articles regarding people hit by models after loss of control with them flying around erratically under power with no failsafe system of any kind.

I've experienced a total loss of control that had the airplane flying circles with a 26cc gas engine running. Fortunaely the airplane met trees. The crystal had fallen out of the RX. We know this because it was found in the tail which was nowhere near the RX. Put the crystal back and the radio system worked.

Set it to spin.

[Pilotguy]

hhhmmm... I bound while holding the rudder stick full right & throttle at idle. I then turned my DX6 off and left the flight battery connected but nothing happened. I was expecting to see full right rudder. I repeated the binding the same way and nothing happened again. I know the bind was successful because I heard all the proper tones. What am I missing?

[fhhuber]

To do it right:

Bind while holding the sticks in the desired positions.. Turn off airplane before TX.

Note that you have to bind in AS3X OFF(full aerobatic mode) or it will try to level the model despite the other failsafe settings.

Then try the turn on TX, then power up the airplane. Then after everything is functioning (and with the airplane firmly restrained... or prop removed) turn off TX and it shuld go to the Bind failsafe positions

If that fails... see the RX instruction manual for setting failsafes. This is just the most common method for the RXs I own.

So many versions of RXs out there.... and thus variations in how to over-ride default failsafe of either hold last or neutral. There's no way that someone who is even in tech support can remember them all.

[Pilotguy]

"see the RX instruction manual for setting failsafes". Yep, the manuals say to press the bind button, let go then press bind button again. Will try it again tomorrow. Always good advice to refer to manual.

[quitcherbitchen]

Having suffered a fly away in the past, I always set the throttle for Zero. Don't expect the plane to reconnect. That is only wishful thinking.

[Pilotguy]

I am trying to do the right thing and pro-actively set the failsafes to full left rudder, throttle idle & aileron, elevators neutral. The dog-gone thing just wont do it. I have repeated the failsafe setting binding procedure step by step about 6 times within a half hour and after each time I then turn off the Tx to test the failsafe settings and each time the rudder did NOT go to full left. What’s the deal? Is it pilot error or is it the technology? I am using a Spektrum AR620 which has a bind button in lieu of a bind plug.

[fhhuber]

Its also possible that they went dumb about failsafes and factory set all but the throttle for you and don't let you change it.

AMA/FAA made it a rule (very stupid) that controls go to throttle 0, center all others for airplanes being flown at airshows for demos. Manufacturers might see that and think its a good idea. Actually is a plan for a disaster.

Spektrum went dumb about the "virtual fence"... if you stall and fall to the wrong side of the fence, the virtual fence then keeps you from flying the airplane back.

[xviper]

Do you have someone else with you as a "helper". I just read the instructions and I find it confusing which "bind" button they are talking about in each line. How do you hold one or more sticks in the desired position, then hold the bind button (which one?), then plug in the flight battery while doing the first two things (by yourself), then something about bind buttons again but which one (RX or TX?). Maybe you're interpreting which bind button wrong. I just don't know.

[fhhuber]

Sideways way to do it...

Crank the controls mechanically over and then recenter with trims. This has a negative side effect of limiting available travel in one direction, but would get around a factory neutral (but not around factory setting for it to go into panic mode which would try to level it out anyway)

[Pilotguy]

I agree that trying to follow the instructions you really need a 3rd hand. I did my best with my 2 hands. That may very well be the issue here with these Rx that have a bind button instead of a bind plug. My Pitts & P-51 Rx have the bind button. My Corsair & PT-17 have the AR636A Rx which have bind plugs, not bind buttons however, the AR636 manual says nothing about how to set the failsafes. What to do about those 2, I don’t know.

[xviper]

I agree that trying to follow the instructions you really need a 3rd hand. I did my best with my 2 hands. That may very well be the issue here with these Rx that have a bind button instead of a bind plug. My Pitts & P-51 Rx have the bind button. My Corsair & PT-17 have the AR636A Rx which have bind plugs, not bind buttons however, the AR636 manual says nothing about how to set the failsafes. What to do about those 2, I don’t know.

From the manual of the 636A ............
SmartSafe SmartSafe™ failsafe is recommended for most aircraft. When the transmitter and receiver are turned on, the receiver connects to the transmitter and normal control of all channels occurs. If loss of signal occurs, SmartSafe moves the throttle channel to its preset failsafe position (low throttle) that was set during binding. All other channels hold their last position. When the receiver detects signal from the transmitter, normal aircraft operation resumes. Receiver Power Only • With SmartSafe technology when the receiver only is turned on (no transmitter signal is present), the throttle channel has no output, to avoid operating or arming the electronic speed control. • All other channels are driven to their preset failsafe positions set during binding.

Looks to me that one of them is pre-set and the other is set during binding.

[Pilotguy]

Yes, those are the same words written in my AR636 manual. You are correct about there being 2 different failsafes. The AR 636 manual is very unclear about that. It only talks about “Smartsafe”.

The other type of failsafe (called “Preset Failsafe” in the AR620 manual) is what’s being referred to in that very last sentence that says, “all other channels are driven to their preset failsafe positions set during binding”.

But the AR636 manual still does not give you the steps to take during binding to achieve either type (the AR636 has the bind plug, not button).

This photo is from my eflite pt-17 manual. It assumes it has the AR636 Rx installed. The very last sentence at the bottom of the page where the asterisk is has the only mention about failsafe in the whole pt-17 manual. It says, “All other channels move to actively level the aircraft in flight”. This statement probably assumes that during binding, all controls were neutral with throttle at idle which would be what the AR620 manual calls “Preset Failsafe”.

Perhaps fhhuber is right about the factories went dumb and don’t let you change it on certain receivers.