I sent the following letter to Futaba's US importer/distributor (Great Planes) on July 26 2000.

To whom it may concern,

I have been quite happy with my Futaba 8UH radio, and have recommended the
8U and Super 8 to a number of people who are now enjoying theirs as well.  
However, the more I learn about these radios, the more concerned I am with
their shortcomings.

The 8U had some problems that were not fixed in the Super 8, and this has
caused me to wonder if perhaps everyone who noticed these problems just
assumed that someone else would tell Great Planes (I'm certainly guilty of
taking that stance) and in the end nobody at Great Planes was informed.  
This time I want to make sure that if the 'next' $500 Futaba helicopter
radio isn't the best it can be, it's not because I assumed that someone
else would address these issues.

I realize that those of us who only budget $500 for a radio system can't
expect the feature set of the $1,000+ 9Z, but there are some features of
the 8U that have been implemented in a manner that can only be described
as "broken."

Most of the 8U's problems revolve around the throttle-to-needle mixer.  
While it sounded like a good feature in theory, the implementation has
flaws that will keep anyone from actually using it for mixture control.

First, there's the matter of interaction with the throttle curves.  The
throttle-to-needle mixture is based on the throttle stick position, not
the throttle servo position.  This isn't inherently wrong in itself, but
there are three possible throttle-stick-to-throttle-servo curves (for the
normal, idle-up-1, and idle-up-2 flight modes) but only two
throttle-stick-to-mixture-servo curves (a normal curve and a shared
idle-up curve).  The upshot of all this is that if the idle-up-1 and
idle-up-2 throttle curves are different, the idle-up mixture curve will be
correct for one mode and incorrect for the other.

This problem could be addressed in one of two ways.  The simplest solution
would be to use the throttle servo position, rather than the throttle
stick position, as the 'source' of the mix.  This would allow a single
curve to work equally well in all flight modes, regardless of the throttle
curve.  A slightly more complex solution would be to use three different
different throttle-to-needle mixture curves, one each for the normal,
idle-up-1, and idle-up-2 flight modes.

Second, there's the interaction with the throttle hold switch.  When you
enter throttle hold with throttle-to-needle mixing active, the mixture
servo goes all the way to one side.  Its position can be changed only by
altering the ATVs for channel 8.  If the engine idles best with the
mixture servo is 50%, the mixture servo will still travel to 100% or 0%
when you enter throttle hold.  This is bad; a reliable idle is never more
important than when throttle hold is active, as the heli is descending
without power.  If the engine doesn't transition flawlessly to full speed,
a simple misguided auto can rapidly evolve into a disaster.  Because this
behavior is not documented in the owner's guide, I assume that it is a
bug.

Ideally, the throttle hold mode would have its own mixture setting, just
is it has its own settings for trottle and rudder position.  Failing that,
it should at least default to the same position specified by the normal
mode, low stick setting, which virtually every helicopter pilot in the
world uses for starting and idling between flights.

Third, there is the throttle-to-needle function's mixture trim adjustment,
implemented via the channel 8 knob.  As implemented now, the trim has zero
effect at low stick, with increasing effect as the stick is raised.  This
makes sense only if you rule out the possiblity of inverted flight.  This
scheme is completely inadequate for inverted flight, where low stick
brings the engine to full throttle, where it needs the same mixture as
high stick.  The problem is that the trim, like the rest of the mixture
mechanism, is based on the throttle stick position, not the throttle servo
position.  

The right way to implement this function would be to have the mixture knob
shift the entire mixture curve equally (like the rudder, elevator, and
aileron trims), or to have the mixture knob's effect vary in relation to
the throttle servo position, rather than the throttle stick position.

In the US, where virtually everyone aspires to fly "3D," the 8U's built-in
mixture adjustment mechanism is all but useless.  One might argue that
nobody uses active mixture in the US anyhow, but I would argue SOMEONE at
Futaba or Great Planes clearly thought that it was a feature worth
including.  Given that it almost always appears in the 8U's
advertisements, it's impossible to guess how many people chose the radio
based in part on that feature, but opted not to bother with it once they
realized that it isn't practical.  I would also argue that more of us
would use it, if only our radios implemented this feature in a more
practical way.

Fourth, the new Super 8's implementation of the 'gyro setting per flight
condition' is broken.  The problem stems from its interaction with the
throttle hold condition.  The Super 8 allows the user to select a
different gyro setting for normal and idle-up modes, but not for throttle
hold.  The problem is that when the user enters throttle hold, the rudder
channel's trim is determined by the throttle hold offset parameter while
the gyro mode is determined by the idle-up switch.  If the throttle hold
offset is correct for 'heading hold' gyro mode, but the user entered
throttle hold from an idle-up that was configured for 'standard' gyro
mode, or vice versa, the heli will be out of trim.  The solution here is
to include the throttle hold condition in the GYRO menu, in addition to
the normal and idle up conditions that are already included there.  JR's
8103, for example, does not have this problem - the user specifies two
gyro modes and 'assigns' one of those modes to the normal, idle-up, and
throttle hold conditions.

The rudder trim / gyro mode mismatch presents the most significant problem
with "driven-tail" helicopters like the my Futura SE, but even
non-driven-tail helicopters like my Concept SRX will be affected.  Even
though the tail isn't driven, it does have enough momentum to kick the
helicopter sideways when you first enter throttle hold.  This is the last
thing a helicopter pilot needs to deal with in the event of an unplanned
engine failure (which is exactly the situation that the throttle hold
switch is supposed to help you survive).

The funny thing is, you can build on the standard 8U's throttle->needle
mechanism to get a better 'gyro mode automation' system than the one
provided by the Super 8's GYRO menu.  It's a bit more complicated to set
up, and you have to be careful to keep the channel-8 knob set at 50%, but
you're guaranteed to get the same gyro mode every time you hit throttle
hold.

Fifth and finally, there is the Super 8's throttle hold rudder offset bug.  
This has already been thoroughly discussed and documented, so I won't
belabor the point here.  I bring it up only for the sake of completeness.

[When I wrote this message, Great Planes already had a web page describing the both problem and the workaround.]

I have long been a user of and cheerleader for the Futaba 8U, and I still
believe that it is the best value for the dollar in helicopter radios
today.  However, where I used to simply recommend the Futaba 8-channel
radios to anyone interested in starting with helicopters or upgrading old
equipement, I now do so only with the qualification that they do so if the
additional price of the JR 8103 is prohibitive.  It's slightly more
expensive, but it includes a flawless gyro mode automation mechanism and a
5-point programmable mix that makes a more useful mixture control than
the 8U's built-in throttle->needle mixer.

Please share this information with anyone inside Futaba or Great Planes
whome you deem appropriate.  It is my hope that the successor to the Super
8 will put Futaba back on top in the $500 helicopter radio market.

Thanks for your time,


Nate Waddoups
Redmond WA USA
futura(at)whatever.net
http://www.whatever.net/~nathan/frames.cgi/heli/html.Index

The response from Great Planes:

Dear Nate,

Thank you for your input and especially for your patience.  I have
reviewed your comments and appreciate the time it has taken you to put the
facts in a form that is understandable.

I have printed your comments and recommendations and will have them with
me next month when we meet with Futaba to discuss new products and
projects.  I can offer you no guarantee that all or any of our
recommendations will be acted on, but our success record is getting
better.

Again, thank you for your input and for flying Futaba.

Sincerely,

Mike Stokes
Product Manager, Futaba