>Bob,
>
>I think his statement about control may be valid for a Mark IV Kitfox
>as it uses a trim tab (i think). But a Series 5 uses the stab for
>trim control... This stab is much more powerful than a trim tab.
>I will try to do some testing in the next week and report my findings.
Very good! That's a most valuable service.
---From another respondent:
>I think I have a reasonably fair general knowledge of flight
>characteristics even though I have not yet completed pilot training, but
>I am wondering about a comment you made in your most recent letter on
>>electric trim. You said "Trims in a mechanical limit on these airplanes
>produces a barely flyable airplane". Is it not true that trimming out an
>airplane should never require full range of operational limits?
I'd suggest that the converse argument be made. Mechnical stops
on pitch trim should be set to allow only necessary trim settings
to accomodate the airplane over it's speed/c.g. envelope.
>Or was
>that the point you were making when you were referring to the builders
>who connected the servos to the tabs? I would think it would be easy to
>design a bracket that would limit trim movement but not limit full range
>of motion for normal flying maneovers.
Exactly. One of the airplanes I'm working with was built with
6" wide tabs that run the full length of the elevators on BOTH
sides. The builders installed dual trim actuators. A common complaint
now is "Gee . . . I just barely touch the trim control and it moves
too far." Further investigation shows that the full range of
NEEDED trim is only about 10% of AVAILABLE trim. Electric actuators
on this airplane is an accident waiting for a place to happen.
Even if one sets good mechanical limits to cover the speed/c.g. envelope
it's still important to know how the airplane behaves should trim
be forced to either limit. I know that doing touch and go landings
in an A-36 can make the critter a handful if you don't give the trim
wheel about three good throws of nose down before you put power back
in for takeoff. Mechanical stops are a good thing but it's not the
whole answer . . . the whole discussiont about trim runaway is unresolvable
until the trim system is analyzed for EACH airframe.
Another ON-POINT comment:
>Most of the airplanes I've flown were still flyable with trim in both max up
>or down. The difference between the situation of Doug's and Graham's, is
>that Doug induced the situation, was expecting what would happen, and
>therefore was ready for it and was able to deal with it. In Graham's case,
>he was caught by surprise, had only milliseconds to make a decision, and
>elected to put it back on the ground. I've read several NTSB accident
>briefs that indicated that a pilot should have been able to handle a certain
>situation, ie., out of trim, etc., but for reasons of surprise and denial,
>wasn't able and either made the wrong decision or lost control of the
>aircraft. Had the pilot been expecting it the situation probably would have
>been easily overcome. I think the surprise and panic of a situation can put
>a person's brain into "lockup" momentarily which is all that it may take for
>disaster to occur. Fortunately, most of us will never be faced with having
>to find out what sort of ice we have in our veins.
>
No truer words spoken . . . see why I'm so rabid about cockpit simplicity
and architectures for Plan A/Plan B training? Look through any 100 NTSB
accident reports and compare numbers of accidents with human factors
contributions versus mechanical failures. Like people who write
regulations,
it's an easy knock-off to say we've deduced procedures or put tools in
place for every contingency . . . but you cannot regulate pilot attitudes,
perceptions and operating skills with an element of surprise. You can train
but who has the time or dollars and how many would submit to mandatory
training? Only I can take on responsability for how well I can perform.
In my limited experience in airplanes, my pucker-factor has peaked at over
100 psi on several occasions and none had anything to do with mechanics.
Bob . . .
AeroElectric Connection
////
(o o)
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