Mechanics of Elevator Trim. In Detail.

On Fri, 13 Jun 2008 11:02:35 -0700 (PDT), "Ken S. Tucker"
wrote:

On Jun 12, 9:53 pm, Ron wrote:
On Thu, 12 Jun 2008 09:43:07 -0700 (PDT), "Ken S. Tucker"

wrote:
On Jun 12, 5:08 am, Tina wrote:
Yes, the time my son spent with canard aircraft brought out all sorts
of interesting information about canards and the history of trying to
scale up Rutan's original concept Beech Starship. The smaller true
canards like the Long-eze are pretty good aircraft. However there is
a reason why we don't see large (six plus passenger) true canards.
It's the relationship between CG, fuel load, payload and range.
Apparently in the scale up process there is a point where it is no
longer practical.
Ron Kelley

Hmm, how the XB-70 or this,
http://en.wikipedia.org/wiki/Boeing_Sonic_Cruiser

True, the XB-70 was a qualified success of a large canard type
aircraft. Most of it's problems were due to system failures and
trying to fly at Mach 3.0. The only control issues I know of were
related to overly sensitive pitch response to control inputs. Ref:http://www.labiker.org/xb70.html

Thanks for that link.

As far as I know the Boeing Sonic Cruiser hasn't gone beyond the
artists concept stage. I guess it's no accident that all the current
crop of passenger jets look alike. That could be partially due to the
reluctance of any large airframe manufacturer to take a gamble on
trying to certify any new "radical" design. Who knows.

Personally, I am intrigued by the three surface aircraft like the
Piaggio. They seem to have done pretty good with their design. One
wonders if given enough time, money and talent, there is some room for
improvement there.

Yes! That Piaggio is one real impressive piece of
aerodynamics, and it sounds very pilot user-friendly.
Very remarkable how they utilized the canard.

I think the aircraft business is extremely conservative.
KISS applies, also canards are difficult for the average
pilot to understand, (Hey man, you got that thar tail on
the wrong end :-).

Would it not also be true that passive stability is not as important
in larger modern airplanes? I would guess (again, I admit being
ignorant of the realities) that adding a 10% aerodynamically induced
increased load on bigger aircraft would be avoided for efficiency
reasons? It might be better to have enough fly by wire and computer
induced stability instead. I don't know enough about this stuff to
even find the back of an envelope, let alone do a calculation there.

Canards are NOT simple, I've designed quite a few,
and studied others, especially Rutan's.
I find they can be optimised for a given air speed
and are much better than the conventional lay-out.
The main problem is designing the stall.
Ken

Anyone who can design a successful canard aircraft has my respect. I
didn't learn a whole lot about the design aspects from my son (he was
in flight test, not design), but what we did learn was everything
interacted with everything else. The job was interesting, but didn't
last long.

Your son sounds like a cool dude.

Yeah, I kinda like him. ;-)

The major PITA is designing aircraft to be efficient
at cruise, but safe all the way to stalling, and
recoverable. The difficulty is the movement of the
Center of Lift forward on the main wing as stall
begins.


I seem to remember a problem they had with the fuel load and the
center of lift moving close to (ahead/behind?) the CG. They also had
a problem with getting enough fuel on board (this was a single engine
turboprop) and where to put it to get the range they wanted.

Ron Kelley