John B. wrote:
On Tue, 27 Sep 2011 23:23:50 -0700, Beryl wrote:

Richard wrote:
On 9/28/2011 12:28 AM, Beryl wrote:

Explain! I haven't seen any explanations here, just claims. Richard
claims the nose must forcibly be held down at 500 mph.

The airplane is nose-heavy already, it must be held up. If it takes 200
lbs of downforce at the tail to hold the nose up at 200 mph, it also
takes 200 lbs of downforce to hold the nose up at 500 mph.

Not on this planet...
You actually think the airplanes mass balance changes with speed?!!

No an aircraft's mass changes as fuel is consumed or something falls
off. But you seem to be forgetting that lift changes. Note also that
the CL moves as lift changes.

Yes, the center of lift moves aft as speed increases. Which makes the
nose become even heavier, calling for more nose-up trim, not nose-down.
Which counters Richard's got-to-push-the-nose-down reasoning.

You seem to be thinking of a static
device when you talk about 200 lb. to hold the tail down at 200 mph
then it only takes 200 lbs at 500. That is wrong, the forces acting on
an aircraft change, rather radically, with changes in speed; among
other variables.

I'm ignoring other variables. There could be thousands, can't discuss
what they all may be doing without losing focus on what the tail
feathers do. Pressure on the canopy may force the nose down, while
pressure on the cowl forces the nose up, while pressure somewhere else
forces the nose down, while... up... down... up... etc.

If your thesis was correct there would be no need of trim tabs at all.
Just built it in and away we go.

That's Richard's thesis. He just said I should forget about the airplane
being nose-heavy. Forget that, and, as you say, the whole trim problem
dosappears, at any speed.