Alex Perry wrote:
> David Megginson wrote:
> > I've been wondering for a while - suppose I take a non-force
> > feedback yoke, and attach a wheel that actually moved the neutral
> > position by moving the end points of both springs backwards or
> > forwards, and use this instead of the software trim, would this be a
> > reasonably realistic approximation of elevator trim (from the pilots
> > perspective) or not?
>
> That implements the trim effect, but not the change in spring force.
The spring force isn't felt by the pilot in that scheme, or the
typical ("tab" style) aerodynamic trim. The trim changes the neutral
point of the control; all the force the pilot feels in the yoke is due
to the difference from the neutral point.
Of course, other trim systems have different properties. The MD-80
scheme I mentioned earlier has no feel whatsoever (the trim axis
doesn't connect to the pilot's controls), so feel has to be added
artificially somehow if you want the neutral-stick position to change
with trim. (I don't know if they bothered or not for the MD-80).
Then there are all sorts of "meta-trim" features in control systems.
Consider things like bob weights attached to the stick. These exert
extra stick force in situations of high-G, to prevent pilots of
aircraft with "loose" controls (or low dynamic stability) from losing
control by snapping the stick back. How do you handle *this* with a
USB joystick? :)
Control system theory is complicated, and control system simulation is
complicated by a 100 year history of pragmatic hackery. Maybe Jon or
Tony will want to jump in here. I think we're fine so long as we get
the control sense right, and render the appropriate thing on the
screen. Getting the "feel" of a control system down with PC hardware
is essentially impossible anyway.
Andy
--
Andrew J. Ross NextBus Information Systems
Senior Software Engineer Emeryville, CA
[EMAIL PROTECTED] http://www.nextbus.com
"Men go crazy in conflagrations. They only get better one by one."
- Sting (misquoted)
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