F-16 Contrrol stick
Kerryn Offord
controller flight stick.
THe story I have heard is that when first introduced the pilots tended
to bend the force controller (if it isn't moving it must be jammed, lets
apply more force to overcome the jam). To counteract this, a new
joystick was introduced with a small amount of deflection (this
deflection was not used to generate digital signals, it just stopped
pilots from trying to bend the force controller).
Is there any truth in this story?
What was it like when you first flew using a force controller rather
than a normal flying yoke (or whatever you call it)?
I assume that there is no force feedback through the force controller,
whereas normal flight stick would have provided feedback. How did this
affect flying?
Ross "Roscoe" Dillon
I don't recall anyone having ever bent one - that would take
incredible strength.
As for deflections, a stick with no motion provides no tactile
feedback to the pilot which makes precise inputs difficult. The
slight motion was added to fix this.
My observation is that the stick feels "heavy", i.e. more force than
normal for the same aircraft response than a normal, fully articulated
stick.
Roscoe
USAF Flight Tester
(B-1, B-2, T-38, T-37, C-5, QF-106, F-16, F-5...)
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Craig C.
>On Wed, 05 Jan 2000 15:19:55 +1300, Kerryn Offord
><ka...@its.canterbury.ac.nz> wrote:
>>
>>Is there any truth in this story?
>>What was it like when you first flew using a force controller rather
>>than a normal flying yoke (or whatever you call it)?
>>I assume that there is no force feedback through the force controller,
>>whereas normal flight stick would have provided feedback. How did this
>>affect flying?
Phil Oestricher and Neal Anderson both had a lot of input on making
the side stick move. The original installation used a fixed stick with
just a set of strain gages to provide movement data. In working with
the human factors guys, they were able to convince them that the stick
did in fact need to have some movement. Part of the reason was that
with no movement, it was possible to hold onto the stick in such a
manner that there was unintentional roll and pitch commands, even
though the pilot was trying to not make an input.
BTW....Flight 0 was due to the control law gains being set at twice
the specified gain. Phil elected to go on and take off rather than
risk loosing the a/c as it was beginning to become quite squirrely at
that point.
Craig
Mary Shafer
> I'm curious to hear from anybody who has flown the F-16 using the
> force controller flight stick.
I don't think you will, unless someone else here has flown the NF-16D
VISTA, as I don't believe the fixed force stick, which is what you're
really asking about, ever made it to operational use. Rather, I think
it was replaced with the movable force stick in either the LWF fly-off
or the F-16 acceptance testing.
The current F-16 stick, a force stick with motion, is essentially
indistinguishable from a position stick, mostly because the FCS is
designed to make it be so.
> THe story I have heard is that when first introduced the pilots
> tended to bend the force controller (if it isn't moving it must be
> jammed, lets apply more force to overcome the jam). To counteract
> this, a new joystick was introduced with a small amount of
> deflection (this deflection was not used to generate digital
> signals, it just stopped pilots from trying to bend the force
> controller).
> Is there any truth in this story?
Like all stories, the answer is "sort of". They, the test pilots,
didn't bend the stick, as that probably isn't physically possible, but
the stick was highly unsatisfactory and the pilots did get into PIOs
flying with it. Even when the gains were reduced, they still had
problems because of the lack of proprioceptive cuing.
> What was it like when you first flew using a force controller rather
> than a normal flying yoke (or whatever you call it)?
The two possibilities are force and position, with the force
controller being fixed or movable. I've flown a fixed force stick, a
movable force stick, and a position stick in rapid succession in each
of the NF-16D VISTA, the NT-33A, and the Veridian variable-stability
Lear. These were both side sticks and center sticks, making the
comparison more equal.
The fixed force stick sucks eggs, the force stick with a small range
of motion is markedly better, and the position stick and the force
stick with a larger (but still small) range of motion are equally
excellent, if everything else about the FCS is set properly. The
things that have to be set properly are the gains and the amount of
time delay in the controller system and in the feedback FCS.
In the presence of a properly designed and implemented feel system and
FCS, the difference between the movable force stick and the position
is pretty small, particularly compared to effects of the FCS. This,
of course, assumes that both sticks are otherwise the same--comparing
a center stick to a sidestick will bias the comparison. The range of
motion required is surprisingly small, on the order of an inch in each
axis, incidentally.
I recently ran a study in which we used the four viable types of
sticks--force and position, side and center. The pilot ratings were
the same for all four sticks, although the pilot inputs weren't. It
was apparent from the data that the pilots flew the center position
stick differently from the other three, although they were not aware
of doing so. While the difference wasn't huge, the pilots were all
very experienced handling qualities test pilots who should have been
able to tell that they were using a different technique. Since they
couldn't, we assume it's an unconscious change on their part, which
was a very interesting outcome of the study. I'd begun the study with
a hypothesis that pilots flew force sticks differently than they flew
position sticks and that this, plus the difference in the command
produced by the force stick, was why our rate-limiting avoidance
algorithm worked in one previous study using the variable-stability
Lear and didn't work in a subsequent study using the
variable-stability NT-33A. However, it turned out that the real
reason for the contradictory results was the difference in sampling
rates and the presence of system noise.
It is possible to develop a pilot compensation technique, making
discrete pulses to the fixed force stick and otherwise being
hands-off, which is the technique adopted by Orbiter pilot astronauts
faced with the RHC, a force stick with a very small range of motion
and two different pivot points. I was able to fly the aircraft with
the fixed force sticks using such a technique, but it was quite
objectionable.
> I assume that there is no force feedback through the force controller,
> whereas normal flight stick would have provided feedback. How did this
> affect flying?
There is no feedback from a fixed force stick, but there is
proprioceptive cuing from the movable force stick, just as there is
from the position stick. The lack of cuing, or feedback, causes PIO.
The best-known example is the YF-16 flight 0, which started out as a
high-speed taxi test and turned into a flight when the pilot got into
a PIO in the taxi and decided to get away from the ground before he
did any more damage (scuffed wingtip and elevons, I think it was).
While a lot of the problem was excessively high gains, the fixed force
stick was also a major factor in causing the PIO.
--
Mary Shafer http://www.dfrc.nasa.gov/People/Shafer/mary.html
sha...@rigel.dfrc.nasa.gov Of course I don't speak for NASA
Lead Handling Qualities Engineer, SR-71/LASRE
NASA Dryden Flight Research Center, Edwards, CA
For non-aerospace mail, use sha...@ursa-major.spdcc.com please
Sherri Stant
Test Wing pilot managed to break off (!) his F-16's side stick inflight, at
high speed and low altitude, over the Gulf of Mexico. Happy ending: he was
in a "family model" F-16B or D and had a sharp non-pilot flight test
engineer in the back seat. To make a short story even shorter, they
sucessfully recovered the jet at Eglin, with the engineer making his first
landing ever in the back of the F-16. Nice hands!
There is a good writeup about it in the Air Force's Flight Safety magazine.
Sorry, don't have the exact date.
Speaking of broken sticks, any of you old F-106 drivers remember some story
about a guy who managed to melt (?) his control stick, and didn't write it
up, and the next guy didn't even notice it? Or was it just too many Gin and
Tonics in the Osan club... Miss Kim, another round!, and I've got the
hammer- first two or last two...
Kirk Stant
Vulture
Semi-old F-4 puke
Ross "Roscoe" Dillon wrote in message ...
>I don't recall anyone having ever bent one - that would take
>incredible strength.
>
>As for deflections, a stick with no motion provides no tactile
>feedback to the pilot which makes precise inputs difficult. The
>slight motion was added to fix this.
>
>My observation is that the stick feels "heavy", i.e. more force than
>normal for the same aircraft response than a normal, fully articulated
>stick.
>
>