canard flying boat

On 20 Jul 2005 10:27:47 -0700, wrote:



Stealth Pilot wrote:
...
fredfighter wrote:

Hmm. ISTM that a canard does not stall when the aircraft pitches
down, it stalls when the aircraft pitches up.

Correct.

picture an aircraft flying along which has a sudden brutal increase in
the resistance of the wheels (note that is hypothetical, thankfully
the snake oil plane wasnt built)
say for instance your canard clips the main wheels on the top wire of
a fence.

Or a less drastic scenario, the nosewhell plows thorugh a clump
of grass...

in that scenario, which is similar to what I predicted with the
hovercraft skirt, the sudden rotation forward and down would be
catastrophic in that the sudden downward movement of the canard would
probably increase its angle of attack beyond the stall (due to a
change in realtive wind direction).

Well, I thought that increasing the pitch (nose up) increased
the angle of attack and decreasing the pitch decreased the angle
of attack. Aren't both angles conventionally measured so that
an upward rotation of the nose of the plane is a positive change
in the respective angle?

E.g. lift increases with increasing angles until teh wing stalls.
If the canard is not stalled and then the nose of the aircraft
pitches downward the lift of the canard decreases pitching the
nose even more downward. In the air the aircraft would accelerate,
trading altitude for speed, thus increasing lift to compensate
for the reduced angle of attack. However on the ground there
is no altitude to trade for speed so the nose bounces.

Have I got it right yet?

your mental picture is a practical one but you are looking at an
aircraft with a gently changing angle of attack and your assumptions
are correct I think.

but picture if you will a *very sudden* pitchdown. the canard would
see the direction of the incident airflow change from directly ahead
to somewhere down in front of it. ...like a gust.

dont lose too much sleep over this, the scenario was hypothetical.
besides I have some more of my Turbulent's fuselage beckoning to me
for attention :-) ...and that vw engine I picked up yesterday for
converting.
Stealth Pilot

Stealth Pilot wrote:
On 20 Jul 2005 10:27:47 -0700, wrote:

...

Have I got it right yet?

your mental picture is a practical one but you are looking at an
aircraft with a gently changing angle of attack and your assumptions
are correct I think.

The only part I questioned was the algebraic sense of the direction
or rotation. E.g. which direction was an increase and which a
decrease.


but picture if you will a *very sudden* pitchdown. the canard would
see the direction of the incident airflow change from directly ahead
to somewhere down in front of it. ...like a gust.

Thinking about it, a *very sudden* pitchdown _during takeoff_ will
also re-orient the thrust line downward. Given the proximinty of
the ground during takeoff that may prove to be the dominant
consideration.

--

FF