Richard fired this volley in
m:

On 9/21/2011 5:59 PM, Sunworshipper wrote:

Sounds good and all, but I don't believe it. Loosing a trim tab
shouldn't cause multiple G forces.


SW


Doesn't matter if you believe it or not.
That's how it happens to work.

The forces involved are tremendous.

And that tiny little tab is what makes it all happen.

Think of it as the base of a transistor?
A tiny amount of current controlling a larger current.

They are, after all, just air currents!


Perhaps he doesn't understand what a trim tab does. It does NOT act as
an elevator. What it does is deflect the elevator, and the elevator's
movement would cause the aircraft to pitch.

But even if he doesn't understand that, I also don't believe it. I'm a
pilot. There is NO excursion of a trim tab one cannot properly correct
for with the stick. And one that's broken loose, so it's hanging by one
corner of one end would not act to effectively deflect the elevator
surface. You would get some "flutter", but not any severe deflection one
way or the other.

One thing that sometimes breaks trim tabs is too forceful a throw of the
stick (below or at maneuvering speed). Trim tabs are delicate. Elevator
shafts or hinges are not.

If he'd been above maneuvering speed (which is damned high on a Mustang)
when such a deflection occurred, he'd have torn off a wing at the root,
instead of a trim tab.

I don't know if the Mustang had lever controls or cables -- likely cables
to the elevator. A broken or disconnected elevator cable (it would use a
pull-pull system of two cables) would cause a rapid deflection to the
neutral position (it's most streamlined position) unless a lot of force
was being applied to the still-good half of the cable pair. THAT
wouldn't happen, because the remaining cable would act to move the
elevator in the wrong direction from that in which you wished it to go.

You can do a lot of maneuvers without a rudder, or without ailerons with
enough dihedral in the wings, and even do some pretty fancy airspeed-
controlled rate-of-descent tricks with a stuck elevator, so long as it's
stuck slightly up or neutral. But you can't control the aircraft at all
with an elevator that's just flopping around loose. And with only
'down' control, you can change the trajectory, but you cannot avoid a
crash.

I had a friend who took a newly-annual'd MU2 for its shakedown, and
forgot to check aileron throw before he rolled out. They were reversed,
and he'd already rotated and retracted the gear when he finally noticed.
He got it around the field and landed it on sheer nerve and a damn-lot
more skill than I could muster in that situation. But they were
reversed, not broken.

However, I believe those racing planes have redundant cabling to all the
control surfaces to protect against the likelihood of one letting go. So
more likely, I think he busted an elevator control horn, which would act
just like a broken cable, and he couldn't correct in the desired
direction. So he used the opposite throw to try to guide his up-scaled
lawn dart away from as many people as possible. Which, if it's proven,
would make him a hero.

LLoyd