RV-9A's wing with Rotax 914?

Regarding earlier comment...
A tight rope walker uses a 30' balance pole, not a 2' pole. The large
moment makes everything happen slower, disruption AND correction.
Think of the stability of an arrow vs. a badmitton birdy. The birdy
always points into the wind, but any little disturbance causes it to
wiggle, like your C150 with the engine 3' from the CG, when you hit
rough air, the tail bobs around.

Regarding the fus. area in front of the CG, the Rotax engine is
smaller than the Lycoming its replacing, so you could make the cowling
smaller. And we're really only talking about 2' max on the extension.

Dave,
I think we're saying the same thing, moving a lighter weight out
further from the CG will increase the moment of inertia.



"nauga" wrote in message thlink.net...
Jay wrote:

And yes the longer moment arm will increase the time
required for spin recovery, but it will also make it a more stable IFR
platform in pitch and yaw.

Whoa there. A longer nose moment arm will _decrease_
stability, not increase it. As for spin recovery, increasing
or decreasing depends on the weight of the engine and the
moment arm (or arm^2, technically).

Dave 'sluggo' Hyde

"Jay" wrote in message
om...
Regarding earlier comment...
A tight rope walker uses a 30' balance pole, not a 2' pole. The large
moment makes everything happen slower, disruption AND correction.
Think of the stability of an arrow vs. a badmitton birdy. The birdy
always points into the wind, but any little disturbance causes it to
wiggle, like your C150 with the engine 3' from the CG, when you hit
rough air, the tail bobs around.

Regarding the fus. area in front of the CG, the Rotax engine is
smaller than the Lycoming its replacing, so you could make the cowling
smaller. And we're really only talking about 2' max on the extension.

Dave,
I think we're saying the same thing, moving a lighter weight out
further from the CG will increase the moment of inertia.



You're right about the moment of intertia, but that is only one of the
forces here. Don't forget about aerodynamically destabilizing effect of
adding that surface area forward of the CG (The plug you need to add to the
forward fuselage adds, right?). Heck, Van's used to be concerned about the
impact of adding wider than stock gear leg fairings, and we're talking a
relatively small area, located near the CG...

KB

On Thu, 04 Mar 2004 09:52:34 -0800, Jay wrote:

Regarding earlier comment...
A tight rope walker uses a 30' balance pole, not a 2' pole. The large
moment makes everything happen slower, disruption AND correction. Think of
the stability of an arrow vs. a badmitton birdy. The birdy always points
into the wind, but any little disturbance causes it to wiggle, like your
C150 with the engine 3' from the CG, when you hit rough air, the tail bobs
around.

Regarding the fus. area in front of the CG, the Rotax engine is smaller
than the Lycoming its replacing, so you could make the cowling smaller.
And we're really only talking about 2' max on the extension.


You are confusing inertia with stability. They are not the same thing at
all. You need to learn what stability means before you can deduce what
effect a particular modification is likely to have on the stability of
the aircraft.

Read and understand the info at the following links, then we can have a
useful discussion. It is not possible to have a productive discussion
when one party does not understand the terminology used.

http://142.26.194.131/aerodynamics1/...ity/Page3.html
http://142.26.194.131/aerodynamics1/.../Negative.html
http://142.26.194.131/aerodynamics1/...y/Neutral.html
http://142.26.194.131/aerodynamics1/.../Positive.html
http://142.26.194.131/aerodynamics1/...ity/Page4.html

--
Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://go.phpwebhosting.com/~khorton/rv8/
e-mail: khorton02(_at_)rogers(_dot_)com

Kevin Horton wrote...

It is not possible to have a productive discussion
when one party does not understand the terminology used.

My hovercraft is full of eels.

Dave 'tobacconist' Hyde

"nauga" wrote in message thlink.net...
Kevin Horton wrote...
It is not possible to have a productive discussion
when one party does not understand the terminology used.

My hovercraft is full of eels.
Dave 'tobacconist' Hyde


??? 'tobacconist' think you misspelt 'obfuscationist'?

Sydney

After control system theory in engineering school and designing PID
systems for work I know what stability means, but thanks for the links
anyway. I wasn't talking about the engineering definition, I was
referring to what lay people usually refer to as a feeling they call
"stability". I didn't want to bore people defining terms when we're
really talking about how something feels to a pilot.

Jay wrote...

I wasn't talking about the engineering definition, I was
referring to what lay people usually refer to as a feeling they call
"stability". I didn't want to bore people defining terms when we're
really talking about how something feels to a pilot.

Regardless of how you intended to refer to it,
more area in front of the CG will reduce both the
stick force per g and the stick force per unit
airspeed deviation. Both of these effects are
detrimental to handling in IMC (for an airplane
that's originally suited for it), and neither
are effected by the mass distribution other than
the effect that distribution has on CG. Inertia
doesn't enter into the picture in these effects.

What _hasn't_ been said here is that if you
add more aerodynamic are in front you can compensate
by moving the CG forward, but (a) that's not always
easy, and (b) you then effectively lengthen the
tail arm, which has a similar effect on handling.

Dave 'TANSTAAFL' Hyde

On Fri, 05 Mar 2004 13:24:05 -0800, Jay wrote:

After control system theory in engineering school and designing PID
systems for work I know what stability means, but thanks for the links
anyway. I wasn't talking about the engineering definition, I was
referring to what lay people usually refer to as a feeling they call
"stability". I didn't want to bore people defining terms when we're
really talking about how something feels to a pilot.

OK, if you don't want to talk about stability, try to find some other
words to describe what you want to say. Otherwise if what you are trying
to mean doesn't match the words you use it is like trying to have a
discussion with my wife when she gets in one of those moods. It ends up
with a lot of words being said, but no communication occurring.

There is a very good relationship between quantitative measures of
stability and how the aircraft will "feel" to the pilot. Adding area
forward to accommodate a lighter engine on a longer engine mount will make
the aircraft a worse IFR platform, as there will be less of a tendency
for the aircraft to return to the trimmed condition if it is disturbed in
pitch or yaw. There will also be lower stick force cues if you get off
the trimmed speed, which will increase the workload when trying to fly a
desired speed, like when you are on final approach.

--
Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://go.phpwebhosting.com/~khorton/rv8/
e-mail: khorton02(_at_)rogers(_dot_)com

Kevin

Do you think my wife and yours came from the same family tree?

BJ

On Sat, 06 Mar 2004 03:12:07 GMT, Kevin Horton wrote:

----clip----

----clip---- Otherwise if what you are trying
to mean doesn't match the words you use it is like trying to have a
discussion with my wife when she gets in one of those moods. It ends up
with a lot of words being said, but no communication occurring.

----clip----

Jay wrote:

After control system theory in engineering school and designing PID
systems for work I know what stability means, but thanks for the links
anyway. I wasn't talking about the engineering definition, I was
referring to what lay people usually refer to as a feeling they call
"stability". I didn't want to bore people defining terms when we're
really talking about how something feels to a pilot.

This IS a fairly technical forum.

What the great unwashed masses think about aerodynamic stability
would probably confuse me badly...

Richard