Forward CG Experience

"Koopas Ly" wrote in message
om...
However, ignoring this fact, if the airplane was originally trimmed
for level flight, I contend that you would only start experiencing a
slight descent rate at an airspeed no different than prior to the
forward c.g. shift.

If you ignore that fact, sure. But you can't ignore that fact and still
have a correct understanding of the situation. I fail to see the relevance
of a hypothetical situation in which things aren't as they actually are in
real life. It won't help you understand what's happening in real life.

It's like saying "if you ignore the fact that there's gravity, we could fly
with a lot less power required than we do now". Sure, it's a true
statement, but it's not terribly useful.

Pete

Pete,

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

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.

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.

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.

Can we agree on this?

Alex

Bob

NA turned out 406 B-25G models with one 75mm and two 50 cal in the
nose.

Navigator/Cannoneer loaded the single shot canon. Bird carried 15
rounds which weighed 15 lbs each.

NA built cannon birds started arriving Brisbane in 1943.

Gun was a 75 MM CANNON, Army type M4 (not a howitzer). Gun was
descended from the French 75 of WWI fame.

Follow on was the B-25H which had the 75 mm cannon plus eight 50 cals
in nose (all fired by pilot)
..
The only bird I know of that uses a bigger gun (105 mm) is the C-130,
Spector, Gun Ship.

Not trying to take anything away from Gunn story, just giving
additional data on the NA built Cannon equiped birds.


Big John


On Fri, 14 Nov 2003 20:46:24 -0500, "Bob Chilcoat"
wrote:

It's my understanding that after Pappy Gunn had modified a B-25 for
straffing, with six 50 Cal Brownings in the nose and a 75mm field howitzer
under the floor of the cockpit, and had used it very successfully against
Japanese shipping, North American sent an engineer out to see what this
lunatic was doing. After looking over Gunn's field modification he just
shook his head and asked "Where the hell is the center of gravity?" Gunn
just shrugged and told him "Aw, we threw that out to save weight." The
engineer went home and North American started mass producing a properly
engineered variant of Gunn's cludge, the B-25G.

"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.

"Koopas Ly" wrote in message
om...
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 submit that you may want to find a different forum, if you have found my
posts defensive or gratuitiously stern. You appear to be far too sensitive
for strictly textual communications to participate in Usenet. I have simply
attempted to answer the original question, while correcting elements of your
posts that were not true.

It is unreasonable of you to post your hypothesis, ask whether your
hypothesis is valid, and then get offended when you are told it is not.

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.


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

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.