Required Fail Safe and Range Checks

 

Both are are strongly recommended in the manuals by all radio manufacturers.

  1. Carefully set the Fail Safe feature for each of your planes.  Fail Safe allows you to define the “go to” position of each servo if the receiver loses the signal, even if it is only for a few seconds.  You may not know this feature is in your radio but it very likely is.  If done correctly, when the signal is lost the throttle will go to idle, thus preventing a fly-away situation and ensuring the plane is not at high power when it comes down.  Some details below.  Spektrum, Futaba, and OpenTX based radios (FrSky, RadioMaster, Jumper) etc., all have different instructions.
     
  2. AFTER setting the fail safe, do a range check.  Again, all of the radios mentioned above have differentprocedures.  Read your manual.  I have met knowledgeable pilots that did not know that using any other brand’s procedure with a Spektrum radio is useless.

    We strongly recommend that you do an enhanced, robust version of the check in your manual by checking with the model in many orientations.   It is more likely to find a problem and, if passed, make it less likely that interference could cause your plane to crash or fly outside the boundaries.  Details below.

 

1.  Set your Fail Safe (do this first)

There are some hidden traps here.  With Spektrum, Fail Safe is always enabled.  But EVERY time you bind or re-bind the receiver to the transmitter, the Fail Safe position of each of the major controls is set to wherever the sticks are.  Therefore, if you re-bind for some reason, and accidentally leave the throttle lever at mid, or even high throttle during the bind, that is where the throttle will go when the signal is lost.

If you reverse the throttle channel, be especially careful to re-bind and set Fail Safe correctly.  If you don’t, loss of signal will cause full power instead of idle.

OpenTX based radios will also disable fail safe settings if you re-bind.  Read up on how to set the failsafe on OpenTX systems.  Most times you can set it by pressing a button on the receiver after binding or in OpenTX in the model setup page.  Lemon and Orange receivers are also unique.

After you set Fail Safe, test it very carefully.  With the plane restrained and no objects near the prop, or better yet with the prop removed, power up the radio and plane.  Move the throttle to a mid or high position – just something that is not idle.  Then after checking the airplane is restrained, turn off the transmitter.  You’ll see the throttle on the model go to the Fail Safe point you set after a few seconds.

On a gas or glow model, make sure the Fail Safe setting of the throttle is not so low that the engine quits in flight if the receiver goes into a momentary hold.

In some radios, controls can be set to a desired position in the event of loss of signal.  Some radios allow you to select whether the position should be frozen where the controls were when the signal was lost, or to the pre-programmed value.  You will have to think this through based on how you fly.

A good pre-programmed position for the elevator might be a few degrees of UP to slow the plane and have it climb slightly and temporarily (assuming it was right side up when the signal was lost) until the signal is re-acquired

 

2. Range Check

ALL BRANDS say you must do this before you fly, and after any changes to the position of radios or antennas or any addition of equipment to the plane that could block the signals to the receiver. 

Range checks all involve going some distance from the plane and checking the function of the controls. Spektrum, Futaba, , and OpenTX based radios (FrSky, RadioMaster, Jumper) etc., all have different instructions. Read your manual and don’t rely on someone’s knowledge of a different brand and apply it to your own.  As I mentioned earlier, using any other brand’s procedure with a Spektrum radio is useless.

Here’s the reality.  Any item in or on the plane that conducts electricity including carbon fiber, metallic covering or paint, batteries, wiring, switches, receiver, servos, and of course any metal (hardware, pushrods, clevises) can block the signal to your receiver antennas. 

So then why would we think that checking in just one orientation is enough?  The robust procedure we strongly recommend has an assistant change your plane from facing toward you, right side to you, left side to you, and tail to you, and the range check done for each one.  Several times I have had planes that pass in one orientation and fail in another. 

Next, have your assistant stand the airplane on its nose and do the check looking at top, side, and bottom views.  Why do the sides again you ask?  Because waves coming out of the transmitter have polarity, so an antenna may work well in one orientation, and not as well in another.

CAUTION:  Make sure your assistant keeps fingers clear of the prop and restrains the plane.  If the fail safe point for throttle is anything other than idle, and your plane fails a range check badly enough for the receiver to go into Fail Safe, then the throttle could advance quickly, possibly to full throttle.

That’s why we suggest checking your fail safe operation before doing the range test.  We don’t know why the manufacturers don’t recommend checking in many orientations, but it might be out of concern for the safety of the assistant if power comes up suddenly.  Spektrum does day to restrain the plane.  Others probably do as well.

The check is best done with an assistant because when the servos stop working correctly, they can do it in subtle ways, like hesitating or moving erratically on their way to full throw.  You won’t be able to see these behaviors from a distance.  The assistant will also be rotating the airplane to different orientation for the robust version of the check.

 

Antenna placement in the plane:  The solution to failed checks is to move the antennas in the plane to new locations until things work well in all orientations. 

Antennas must be oriented 90 degrees to one another and be as far apart as practical.  If you can’t get Spektrum’s remote antennas far enough apart, extensions are available.  It also helps to mount the receiver as far aft of motor, battery, etc as possible because these are large blockers of the signal.

 

Food for thought:  Of all the possible orientations to check, which ones might be the most important?

Tail toward you.  You want this check to pass with flying colors because you always want to be able to turn an airplane flying away to come back home.

Bottom toward you.  Come to think of it we see this view of the plane a lot when flying.

Nose toward you.  Obviously, a lousy time to lose control.

They’re all important for their own reasons.

 

Here are short summaries of what the manuals say for different brands, just to show you how different they can be.  Read your manuals for the facts.

 

Spektrum Summary:

To summarize, manuals says to restrain the airplane on the ground clear of any obstacles that could block the signal, and go 30 paces or about 90 feet.  Then the radio MUST be put into Range Check mode.  Then press the trainer/bind button to cause low transmitter power.  While holding the button down check the controls visually (best done with an assistant).

 

Futaba:

Futaba transmitters have a "Power Down Mode" for doing a ground range check.  Read your manual, as each model may have slight variations to activate the "Power Down Mode".  In the T7C, for example, hold down the Dial and then turn the transmitter switch on.  The model should operate properly in the Low Power Mode from 30 - 50 paces away from the model without losing control.  Futaba also suggest another range check (with your assistant holding the plane) while the model’s engine is running at various speeds.  The "Power Down Mode" continues for 90 seconds and automatically returns to normal transmission power.  NEVER start flying when the Low Power Mode is active.

 

OpenTX (FrSky)

Place the model at least 2 feet above a non-metal surface (a wood bench works.  One of our engine start stands can also restrain the plane from moving). Power the transmitter and model.  On the model setup page, enter Range mode.  Walk away from the model for 90 ft, monitoring RSSI signal and checking for positive control of the aircraft surfaces.  

 

First Flights

Have another pilot look over your plane.  Consider using a checklist to make sure you haven’t forgotten something.  We’ve put the pre-flight inspection checklist that we use for summer training at the end of this letter for your convenience.  Almost any of the items on the list could cause a crash by itself.

The MAR/C preflight checklist that we use during summer training before any new airplay flies is on our website.

Go to the Training and Education tab.  Scroll down to c) How Training Works and open it.  The checklist is on page 4 and 5

https://www.mar-c.org/sites/default/files/ground-school/c)%20How%20Training%20Works.pdf

 

Thoughts About Intentionally Crashing the Plane

All of the above is about making sure we never have planes fly uncontrolled outside the boundary.  But this can also happen due to disorientation.

Keep your airplane close, well within the limits of your eyesight.  Make decisions soon to turn back toward yourself before getting too far away.  Switch to slower airplanes if you are having problems in this area.

If you’re in the unhappy position that an airplane is flying away and you believe it is likely to crash or fly away, you must consider putting it down before it flies farther.  You need to put the airplane into the ground quickly to avoid having it get too far away, and you need the plane to be going as slowly as possible to minimize damage to the plane or anyone on the ground. 

Of course you would pull the throttle to idle, if for no other reason than to protect the motor on impact.

Some would say to “spike” the plane by inputting full down elevator.  But if this is done from a height, then the energy the plane can impart in a collision is of course much greater.  A better option is to input full back and full right or left on both sticks.  This causes a snap roll and a spin that slows the airplane quickly.

The hard part about this is remembering it when the need suddenly arises and making the decision.  You can practice this IF you are comfortable doing violent and unpredictable aerobatics, and high enough, and your airplane can handle the abrupt inputs, and you know how to recover.    

 

Thank you for your attention to this critical issue of always keeping our planes in bounds.