Forward CG Experience

"Koopas Ly" wrote in message
om...
I can see where I set myself up nicely for your latest moral
redressing.

Not sure what you mean.

My previous description pertaining to constant airspeed with a sink
rate after the forward c.g. shift was valid only if you didn't touch
any controls.

My previous comments were with respect *only* to the increase in drag, and
resulting increase in deceleration rate. Constant airspeed and sink rate
are irrelevant to those comments.

If I understand your assertion, you want to maintain altitude without
augmenting power so I concur that you would have to reduce your
airspeed through a control input to meet the higher drag.

Not sure where you got the impression that I "want to maintain altitude".
All I "want" to do is explain why airspeed scrubs off more quickly when the
CG is farther forward.

I note that the above would be invalid on the backside of the power
curve since the increase in angle of attack further compounds the drag
accumulation. In such case, only a power augmentation could be the
remedy.

No, a decrease in angle of attack in that situation would reduce drag.

Can we agree on this?

We can agree on any number of things. But you would need to stay on topic
and not make up purely hypothetical but physically impossible situations for
us to do so, at least in this thread.

Pete

I can see where I set myself up nicely for your latest moral
redressing.

Not sure what you mean.

What I mean are your consistent unfriendly didacticisms. The
defensiveness you've displayed in your last posts is unwarranted, as
is your gratuitous stern tone. I am neither attempting to provoke you
nor challenge your knowledge. In fact, I respect it. However, for
reasons unbeknownst to me, you've set upon a course to systematically
dismiss every one of my comments without the least consideration for
merit. The gist of your reply revolves around the irrelevance of my
comments with respect to the deceleration due to drag with a forward
c.g. condition. In contrast, I believe that my subsequent comments
are very much relevant digressions that expound upon your original
thread.


My previous description pertaining to constant airspeed with a sink
rate after the forward c.g. shift was valid only if you didn't touch
any controls.

My previous comments were with respect *only* to the increase in drag, and
resulting increase in deceleration rate. Constant airspeed and sink rate
are irrelevant to those comments.


Constant airspeed and sink rate are in fact relevant to those
comments, as they succeed the latter. With no control inputs after
the forward c.g. shift, you will experience a lower pitch attitude and
a subsequent sink rate at constant airspeed.



If I understand your assertion, you want to maintain altitude without
augmenting power so I concur that you would have to reduce your
airspeed through a control input to meet the higher drag.

Not sure where you got the impression that I "want to maintain altitude".
All I "want" to do is explain why airspeed scrubs off more quickly when the
CG is farther forward.


I was wrong. I assumed that you wanted to maintain altitude, and I am
sure you know what happens when you assume.



I note that the above would be invalid on the backside of the power
curve since the increase in angle of attack further compounds the drag
accumulation. In such case, only a power augmentation could be the
remedy.

No, a decrease in angle of attack in that situation would reduce drag.


A decrease in angle of attack would change your altitude, an excursion
I was trying to prevent.


Can we agree on this?

We can agree on any number of things. But you would need to stay on topic
and not make up purely hypothetical but physically impossible situations for
us to do so, at least in this thread.

Pete

With no control inputs after the forward c.g. shift, you will
experience a lower pitch attitude and a subsequent sink rate at
constant airspeed.

Moving the CG forward, with no control inputs, will change the
equilibrium lift coefficient for the aircraft, making it smaller. The
aircraft's velocity will increase, using gravity for thrust.

You can see this in a 152. Both pilots lean forward, and the aircraft
descends and speeds up. Both pilots lean back, and the aircraft
climbs and slows down.

If you move the CG forward, and want to keep the same airspeed, you
will have to increase the tail down force, i.e., nose up trim. In
this scenario, you will have the same airspeed, but slightly higher
drag and will incur a slight descent.

With no control inputs after the forward c.g. shift, you will
experience a lower pitch attitude and a subsequent sink rate at
constant airspeed.

Moving the CG forward, with no control inputs, will change the
equilibrium lift coefficient for the aircraft, making it smaller. The
aircraft's velocity will increase, using gravity for thrust.


The increased thrust component from gravity will offset the increase
in drag due to forward c.g. The trimmed speed should not change.


You can see this in a 152. Both pilots lean forward, and the aircraft
descends and speeds up. Both pilots lean back, and the aircraft
climbs and slows down.


I've never noticed that leaning forward and back changed attitude or
airspeed.


If you move the CG forward, and want to keep the same airspeed, you
will have to increase the tail down force, i.e., nose up trim. In
this scenario, you will have the same airspeed, but slightly higher
drag and will incur a slight descent.

*****I've never noticed that leaning forward and back changed attitude or
airspeed****

That just shows a low level of knowledge and awareness. I was going to say
"perception" but I didn't want to use any advanced vocabulary on you.


Karl

My "perception" is that you feel better now, pointing out the
shortcomings in others. Glad I could make your day.


*****I've never noticed that leaning forward and back changed attitude or
airspeed****

That just shows a low level of knowledge and awareness. I was going to say
"perception" but I didn't want to use any advanced vocabulary on you.


Karl

My "perception" is that you feel better now, pointing out the
shortcomings in others. Glad I could make your day.

Koopas, Koopas, Koopas. This is not a place for the thin-skinned. Both
Karl and Pete appear to be having a bad week (month? millennium?), and can't
seem to keep their tone and conversation civil.

Just presume they were abused children, make plans to pee in their gas tanks
at OSH 2004, and cheerily move on to the next thread...
;-)
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

The increased thrust component from gravity will offset the increase
in drag due to forward c.g. The trimmed speed should not change.

I'm not talking about drag.

This is a stability/control issue. By moving the CG, you are changing
the speed for which the aircraft is trimmed.

My understanding is that hang gliders use this technique by shifting
their bodies forward and aft. I've never flown one, so I can't say
from personal experience.

I've never noticed that leaning forward and back changed attitude or
airspeed.

Well, either go try it, or trust me. g Probably takes a small
plane before the effect is noticable. I've only done it in a 152. I
will occasionally demonstrate to a student how they can climb,
descend, and turn using only body shifts and opening and closing the
doors.

On Mon, 17 Nov 2003 01:38:16 GMT, Greg Esres
wrote:

I've never noticed that leaning forward and back changed attitude or
airspeed.

Well, either go try it, or trust me. g Probably takes a small
plane before the effect is noticable. I've only done it in a 152.

I've done it in a 172, and demonstrated it to interested pax. The
pitch changes, 'cause the CG changes.

I noticed it for the first time on my long cross country, while
stretching.

Rob

--
[You] don't make your kids P.C.-proof by keeping them
ignorant, you do it by helping them learn how to
educate themselves.

-- Orson Scott Card

Greg,

Please see comments below:

The increased thrust component from gravity will offset the increase
in drag due to forward c.g. The trimmed speed should not change.

I'm not talking about drag.

This is a stability/control issue. By moving the CG, you are changing
the speed for which the aircraft is trimmed.

Alright, so to sum up the situation (please correct me if I am wrong)

1. If you have a forward shift in c.g. without touching the controls,
you'll have an imbalance in pitching moment that translates into a
pitch-down attitude. Your angle of attack is reduced, and the
airplane will speed up. If you're in the front of the power curve,
your drag will also increase with the higher airspeed. The angle of
descent will be such that the thrust provided by gravity will offset
the drag increase.

2. In a previous post, you wrote "If you move the CG forward, and want
to keep the same airspeed, you will have to increase the tail down
force, i.e., nose up trim. In this scenario, you will have the same
airspeed, but slightly higher drag and will incur a slight descent.".

My question is this: When you increase the downforce, lift must also
be increased for the balance of forces in the "vertical direction".
Since neither your angle of attack nor airspeed are changing, how do
you maintain Lift = Weight in this case? Unless your nose-up trim
change upped the angle of attack...


My understanding is that hang gliders use this technique by shifting
their bodies forward and aft. I've never flown one, so I can't say
from personal experience.

I've never noticed that leaning forward and back changed attitude or
airspeed.

Well, either go try it, or trust me. g Probably takes a small
plane before the effect is noticable. I've only done it in a 152. I
will occasionally demonstrate to a student how they can climb,
descend, and turn using only body shifts and opening and closing the
doors.

Thanks for pointing that out. I definitely will try it next time. Do
you use the door trick to induce more drag and increase your descent
path as if you're you're adding more flaps?

Alex