Lancair Legacy Design Flaw?

Ron Wanttaja wrote:

The problem is separating the "This is due to the aircraft being a
Lancair" issues from the "This is a high-performance aircraft" ones. The
survivability of an accident is dependent on a huge number of factors,
but a big one is the speed involved. Energy is equal to the mass times
the velocity squared.

Obviously a Zenair undershooting and hitting the trees at 35 knots is
going to be MUCH more survivable than a Lancair hitting the same trees
at 80. The fatality rate *might* be the same, if a Zenair hit the trees
at 80, but there's no way to make a fair comparison.

I had a rather sad realization after re-reading this. Bill took off
downwind on Runway 04. The closest reporting site (20 miles away) was
reporting wind at 190 degrees, 10-20 knots, and the first responders
said the winds were about the same at Parowan.

Bill's Lancair thus hit the ground 20 to 40 knots faster than if he'd
taken off into the wind. That's a LOT more energy.

It may not have ultimately made any difference...a descending left turn
after a takeoff in the other direction would have put him right in the
center of the town. But you have to wonder.

Ron Wanttaja

In article ,
wrote:

On Fri, 31 Oct 2008 12:09:27 -0700, Alan Baker
wrote:


The one thing not quite right is that there is no important difference
between tractor vs. pusher configurations with respect to directional
stability.

Like some of the early rocket designers (e.g. Goddard), you are falling
into the fallacy that somehow pulling is more stable than pushing. This
is not so.
Pusher or tractor makes virtually no difference, but the vast
majority of pilon mounted engines ARE pushers - and the pilon mounted
engine does have that nasty quirk.

Yup, but that's because the pylon (note spelling) places the thrust line
far above the centre of mass, creating a long moment arm.

--
Alan Baker
Vancouver, British Columbia
http://gallery.me.com/alangbaker/100008/DSCF0162/web.jpg

In article
,
Alan Baker wrote:

In article ,
Steve Hix wrote:

In article
,
Alan Baker wrote:

Pusher or puller doesn't affect pitch forces. What affects pitch forces
is the length of the moment arm between the centre of mass and the
thrust line.

Or center of drag vs thrust line?

The problem with that is "centre of drag" changes.

And, as it does, so would pitch resultants.

Better to take all the separate moments for the various components about
the centre of mass.

Which will change as airspeed/AOA/etc. change, right?

Come to think on it, the total moments of drag don't care about any
masses, just the shape(s) of the aircraft exterior.

On Oct 31, 2:59*pm, Alan Baker wrote:
In article
,





*BobR wrote:
On Oct 31, 2:09*pm, Alan Baker wrote:
In article
,

*BobR wrote:
On Oct 30, 5:12*pm, "Gregory Hall" wrote:
"Vaughn Simon" wrote in message

...

"Gregory Hall" wrote in message
...

It looks too much like an irresponsible, hot rod, stunt plane to me.

* Well, you sucked me in at first, so on a troll scale of zero-to-10
you
rate at least a five. *How are things in France?

Vaughn

France? *I don't live in France. I built and used to fly a Rotec Rally
2B
many years ago. It was a tail dragger with a high wing and the motor
was
mounted atop the wind with a pusher prop.

When I got it trimmed out correctly at cruise speeds I could lean
forward in
the seat to nose it down and lean back in the seat to nose it up. Even
as
well-balanced as it was at about half throttle, when the engine quit it
would pitch up immediately and drastically because the high engine
placement
and pusher prop had enough leverage so that the proper trim at the tail
counteracted the nose down force of the engine and prop. If you didn't
immediately push the stick way forward when the engine quit it was a
matter
of seconds before it would nose up fast and stall and then you would
have no
control at all from the stick until it fell for a while and the nose
dropped
(thank god for that) so you could gain speed provided you had enough
altitude to get control of it again. But it didn't glide too well being
a
single surface wing with wire bracing. Perhaps 2:1 glide ratio. But it
was
easy to land with no power but you had to come in hot and steep and at
the
last second pull back on the stick and flare it.

It looks to me like the Legacy would act pretty much the same if the
engine
quit.

--
Gregory Hall

Oh for gawd sake, you are talking about two totally different designs
and the aerodynamics of the two are totally different. *The Lancair is
NOT a pusher and the engine is mounted forward of the CG instead of on
top of it. *When the engine quits it will not pitch upward. *The plane
you flew had the engine well above the center of gravity with a pusher
prop and as a result produced a force that pushed the nose of the
aircraft down. *The two planes would not act pretty much the same at
all. *The weight of the engine on the Legacy is forward of the CG and
as a result always pulling the nose of the plane down. *The counter to
the nose down is the horizontal stabilizer and the elevator. *Look at
the angle of incedence on the Horizontal Stabilizer and you will find
a slight downward angle, not an upward angle as is common on the
wing. *This counteracts the force from the weight of the engine. *An
engine out condition will not have a significant effect on pitch until
the airspeed changes and that will result in a nose down, not nose up
pull.

The one thing not quite right is that there is no important difference
between tractor vs. pusher configurations with respect to directional
stability.

Not sure what you are replying to but I never said anything about
directional stability. *The discussion was regarding pitch forces.

Which is essentially the same thing.

Pusher or puller doesn't affect pitch forces. What affects pitch forces
is the length of the moment arm between the centre of mass and the
thrust line.



Like some of the early rocket designers (e.g. Goddard), you are falling
into the fallacy that somehow pulling is more stable than pushing. This
is not so.

--
Alan Baker
Vancouver, British Columbia
http://gallery.me.com/alangbaker/100008/DSCF0162/web.jpg- Hide quoted
text -

- Show quoted text -

--
Alan Baker
Vancouver, British Columbia
http://gallery.me.com/alangbaker/100008/DSCF0162/web.jpg- Hide quoted text -

- Show quoted text -

Again Alan, I never indicated any issue with pusher vs tractor. The
layout of the two planes being discussed is totally different. One
involved a tractor configuration with the thrust line being very near
the vertical center of gravity. The second involved an plane with the
engine mounted on a pylon with a thrust line well above the vertical
center of gravity. This configuration, rather it be a tractor or
pusher will induce nose down forces that must be countered by the
horizontal stabilizer with an upward force. This is contrary to the
standard configuration which requires a downward force to counter the
weight of the engine. The post I was replying to was trying to link
the characteristic of the pylon mounted configuration to the Legacy.

In article ,
Steve Hix wrote:

In article
,
Alan Baker wrote:

In article ,
Steve Hix wrote:

In article
,
Alan Baker wrote:

Pusher or puller doesn't affect pitch forces. What affects pitch forces
is the length of the moment arm between the centre of mass and the
thrust line.

Or center of drag vs thrust line?

The problem with that is "centre of drag" changes.

And, as it does, so would pitch resultants.

Better to take all the separate moments for the various components about
the centre of mass.

Which will change as airspeed/AOA/etc. change, right?

No. The centre of mass *never* changes (in the context of this
discussion.


Come to think on it, the total moments of drag don't care about any
masses, just the shape(s) of the aircraft exterior.

You have to take moments about something that isn't going to shift,
Steve. Centre of mass.

--
Alan Baker
Vancouver, British Columbia
http://gallery.me.com/alangbaker/100008/DSCF0162/web.jpg

In article
,
BobR wrote:

On Oct 31, 2:59*pm, Alan Baker wrote:
In article
,





*BobR wrote:
On Oct 31, 2:09*pm, Alan Baker wrote:
In article
,

*BobR wrote:
On Oct 30, 5:12*pm, "Gregory Hall" wrote:
"Vaughn Simon" wrote in message

...

"Gregory Hall" wrote in message
...

It looks too much like an irresponsible, hot rod, stunt plane to
me.

* Well, you sucked me in at first, so on a troll scale of
zero-to-10
you
rate at least a five. *How are things in France?

Vaughn

France? *I don't live in France. I built and used to fly a Rotec
Rally
2B
many years ago. It was a tail dragger with a high wing and the
motor
was
mounted atop the wind with a pusher prop.

When I got it trimmed out correctly at cruise speeds I could lean
forward in
the seat to nose it down and lean back in the seat to nose it up.
Even
as
well-balanced as it was at about half throttle, when the engine
quit it
would pitch up immediately and drastically because the high engine
placement
and pusher prop had enough leverage so that the proper trim at the
tail
counteracted the nose down force of the engine and prop. If you
didn't
immediately push the stick way forward when the engine quit it was
a
matter
of seconds before it would nose up fast and stall and then you
would
have no
control at all from the stick until it fell for a while and the
nose
dropped
(thank god for that) so you could gain speed provided you had
enough
altitude to get control of it again. But it didn't glide too well
being
a
single surface wing with wire bracing. Perhaps 2:1 glide ratio. But
it
was
easy to land with no power but you had to come in hot and steep and
at
the
last second pull back on the stick and flare it.

It looks to me like the Legacy would act pretty much the same if
the
engine
quit.

--
Gregory Hall

Oh for gawd sake, you are talking about two totally different designs
and the aerodynamics of the two are totally different. *The Lancair
is
NOT a pusher and the engine is mounted forward of the CG instead of
on
top of it. *When the engine quits it will not pitch upward. *The
plane
you flew had the engine well above the center of gravity with a
pusher
prop and as a result produced a force that pushed the nose of the
aircraft down. *The two planes would not act pretty much the same at
all. *The weight of the engine on the Legacy is forward of the CG and
as a result always pulling the nose of the plane down. *The counter
to
the nose down is the horizontal stabilizer and the elevator. *Look at
the angle of incedence on the Horizontal Stabilizer and you will find
a slight downward angle, not an upward angle as is common on the
wing. *This counteracts the force from the weight of the engine. *An
engine out condition will not have a significant effect on pitch
until
the airspeed changes and that will result in a nose down, not nose up
pull.

The one thing not quite right is that there is no important difference
between tractor vs. pusher configurations with respect to directional
stability.

Not sure what you are replying to but I never said anything about
directional stability. *The discussion was regarding pitch forces.

Which is essentially the same thing.

Pusher or puller doesn't affect pitch forces. What affects pitch forces
is the length of the moment arm between the centre of mass and the
thrust line.



Like some of the early rocket designers (e.g. Goddard), you are falling
into the fallacy that somehow pulling is more stable than pushing. This
is not so.

--
Alan Baker
Vancouver, British Columbia
http://gallery.me.com/alangbaker/100008/DSCF0162/web.jpg- Hide quoted
text -

- Show quoted text -

--
Alan Baker
Vancouver, British Columbia
http://gallery.me.com/alangbaker/100008/DSCF0162/web.jpg- Hide quoted
text -

- Show quoted text -

Again Alan, I never indicated any issue with pusher vs tractor. The
layout of the two planes being discussed is totally different. One
involved a tractor configuration with the thrust line being very near
the vertical center of gravity. The second involved an plane with the
engine mounted on a pylon with a thrust line well above the vertical
center of gravity. This configuration, rather it be a tractor or
pusher will induce nose down forces that must be countered by the
horizontal stabilizer with an upward force. This is contrary to the
standard configuration which requires a downward force to counter the
weight of the engine. The post I was replying to was trying to link
the characteristic of the pylon mounted configuration to the Legacy.

Sorry, man, but you made specific reference to the plane being a pusher
as if it was a relevant factor:

"The Lancair is NOT a pusher and the engine is mounted forward of the CG
instead of on top of it. *When the engine quits it will not pitch
upward. *The plane you flew had the engine well above the center of
gravity with a pusher prop and as a result produced a force that pushed
the nose of the aircraft down."

When you include extraneous details, you make the essence of the
situation harder to glean.

And you're doing it again. You're conflating thrust line induced pitch
changes with weight of engine. One is changing, one is constant.

The only part that you had to talk about was the fact that the thrust
line was significantly above the centre of mass. The weight of the
engine doesn't matter (in an aircraft that has it's centre of gravity
appropriately located), nor does pusher vs. puller.

--
Alan Baker
Vancouver, British Columbia
http://gallery.me.com/alangbaker/100008/DSCF0162/web.jpg

In article
,
Alan Baker wrote:

In article ,
Steve Hix wrote:

In article
,
Alan Baker wrote:

In article ,
Steve Hix wrote:

In article
,
Alan Baker wrote:

Pusher or puller doesn't affect pitch forces. What affects pitch
forces
is the length of the moment arm between the centre of mass and the
thrust line.

Or center of drag vs thrust line?

The problem with that is "centre of drag" changes.

And, as it does, so would pitch resultants.

Better to take all the separate moments for the various components about
the centre of mass.

Which will change as airspeed/AOA/etc. change, right?

No. The centre of mass *never* changes (in the context of this
discussion.

No, mass (other than fuel onboard) doesn't. But drag components can
change with changes in speed, AOA, flap positions, landing gear, cooling
flaps, etc.

Come to think on it, the total moments of drag don't care about any
masses, just the shape(s) of the aircraft exterior.

You have to take moments about something that isn't going to shift,
Steve. Centre of mass.

I know that that doesn't change (ignoring fuel burn), but things like
flaps' contribution to drag moments changes with changes in
configuration.

Else we'd never see pitch changes as we raise or lower the flaps, or
changes in speed as landing gear are retracted or extended.

In article ,
Steve Hix wrote:

In article
,
Alan Baker wrote:

In article ,
Steve Hix wrote:

In article
,
Alan Baker wrote:

In article ,
Steve Hix wrote:

In article
,
Alan Baker wrote:

Pusher or puller doesn't affect pitch forces. What affects pitch
forces
is the length of the moment arm between the centre of mass and the
thrust line.

Or center of drag vs thrust line?

The problem with that is "centre of drag" changes.

And, as it does, so would pitch resultants.

Better to take all the separate moments for the various components
about
the centre of mass.

Which will change as airspeed/AOA/etc. change, right?

No. The centre of mass *never* changes (in the context of this
discussion.

No, mass (other than fuel onboard) doesn't. But drag components can
change with changes in speed, AOA, flap positions, landing gear, cooling
flaps, etc.

Right. So take moments about the thing that doesn't change.


Come to think on it, the total moments of drag don't care about any
masses, just the shape(s) of the aircraft exterior.

You have to take moments about something that isn't going to shift,
Steve. Centre of mass.

I know that that doesn't change (ignoring fuel burn), but things like
flaps' contribution to drag moments changes with changes in
configuration.

Else we'd never see pitch changes as we raise or lower the flaps, or
changes in speed as landing gear are retracted or extended.

Right. But trying to take moments about a centre of drag that is
changing because of the very thing causing you to take the moments in
the first place is a recipe for madness.

Just take them about the centre of mass!

--
Alan Baker
Vancouver, British Columbia
http://gallery.me.com/alangbaker/100008/DSCF0162/web.jpg

In article
,
Alan Baker wrote:

In article ,
Steve Hix wrote:

In article
,
Alan Baker wrote:

In article ,
Steve Hix wrote:

In article
,
Alan Baker wrote:

In article ,
Steve Hix wrote:

In article
,
Alan Baker wrote:

Pusher or puller doesn't affect pitch forces. What affects pitch
forces
is the length of the moment arm between the centre of mass and
the
thrust line.

Or center of drag vs thrust line?

The problem with that is "centre of drag" changes.

And, as it does, so would pitch resultants.

Better to take all the separate moments for the various components
about
the centre of mass.

Which will change as airspeed/AOA/etc. change, right?

No. The centre of mass *never* changes (in the context of this
discussion.

No, mass (other than fuel onboard) doesn't. But drag components can
change with changes in speed, AOA, flap positions, landing gear, cooling
flaps, etc.

Right. So take moments about the thing that doesn't change.

Looks to me that we're in something resembling violent agreement.

The center of mass doesn't change (ignoring fuel burn).

The drag components measured from that center certainly do, however.

"Alan Baker" wrote

Right. But trying to take moments about a centre of drag that is
changing because of the very thing causing you to take the moments in
the first place is a recipe for madness.

Just take them about the centre of mass!

It matters not what you take the moments from, as long as it is from a
stationary reference on the plane.
--
Jim in NC