Lancair Legacy Design Flaw?

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.

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 -

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

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.


Actually, there is some difference in stability between tractor and pusher.

It's because of the volumn necesary to envlose the engine.
And the propeller disk.

Area (volumn) ahead of the CG should be considered destabalizing.

Conversly, (expecially propellers) aft of the CG contribute to better
stability.


--

Richard

(remove the X to email)

In article ,
cavelamb himself wrote:

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.


Actually, there is some difference in stability between tractor and pusher.

It's because of the volumn necesary to envlose the engine.
And the propeller disk.

Area (volumn) ahead of the CG should be considered destabalizing.

Conversly, (expecially propellers) aft of the CG contribute to better
stability.

That's a separate issue from tractor vs. pusher. True, the layout can
influence the volume question, but one is not a function of the other.

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

Ron Wanttaja wrote:
I took a quick look at my database (which covers Jan 1999 through Dec.
2006). The results were practically a wash...36% of two-seat Lancair
accidents were fatal, vs. about 40% of Glasairs. RV-8s were right
between at 38%.

Digging a little more, RV-6s were at about 26%, RANS (all models) were
34%, Avid Flyers (all models) were 10%, and Zenairs (all models) were
22%. For anyone keeping score, about 30% of first-flight accidents
kill the pilot.

Thanks for digging through the numbers!

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?

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.

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

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

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.

Very interesting post, keep it up guys.

Monk

Gezellig wrote:
On Thu, 30 Oct 2008 19:38:03 -0700, Ron Wanttaja wrote:
This is the safest homebuilt IMO.(VariEze ). The canard makes it foolproof.
If that were the case, the Velocity would have a better safety record
than the Lancair family. Based on my statistics from 1999 through 2006,
it doesn't... the Velocity has about a 20% higher accident rate. In
fact, the Velocity has a rate almost three TIMES higher that of the RV
fleet. Which isn't doesn't use canards, either.

Ron, do you judge from this that the Velocity (or the pusher/canards in
general) have basic design issues (such as the Lancair's low speed
regime history)?

It's funny you should ask, because that was one of the questions I was
hoping to answer when I got into homebuilt accident analysis about five
years ago.

Still haven't answered it.

There are so many factors involved that I could spend years of full-time
work trying to dig them out. The fleet size of the Velocity is still
relatively low, for example, and as well all know, one or two extra
accidents can cause a disproportionate change.

I dug a bit deeper into my database, and extracted the accident-cause
data for about 20 homebuilt types. As I mentioned on my last post, the
Velocity has an accident rate generally higher than most. Yet, the
Velocity had nearly the LOWEST "stick and rudder error" rate. About 43%
of RV-6 accidents involved the pilot's handling of the aircraft, vs.
only 29% of the Velocities.

HOWEVER (geeze, there's ALWAYS a "however" when you analyze accident
statistics), the pilots in the Velocity accidents had about 25% more
flight hours than those involved in RV accidents, and *four times* the
hours than the average homebuilder involved in an accident.

Lower rates because they're easier to fly...or because more-experienced
pilots are flying them?

My analysis method is a bit different from the NTSB's, too. I look for
the first major event of the accident string, which means that if the
engine quits, I attribute the accident to the engine quitting. The NTSB
works a bit differently. If the investigator thinks the pilot should
have been able to safely land the aircraft despite the engine failure,
the cause of the accident is listed as pilot error.

So my "pilot failure" category does NOT take into account the difficulty
of handling the aircraft in an emergency situation. While my stats may
show the pilot error rate for the Velocity to be lower, the NTSB's may not.

Ron Wanttaja