Forward CG Experience

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

Koopas Ly wrote:

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

It will in my Maule.

George Patterson
They say nothing's certain except death and taxes. The thing is, death
doesn't get worse every time Congress goes into session.

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

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

I submit that you may want to find a different forum, if you have found my
posts defensive or gratuitiously stern.

Do you also post in rec.aviation.student?


Alex

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.

Pappy Gunn did not install any 75mm cannon's if I remember correctly.
He felt that the firepower of the .50 caliber machine guns was
adaquate, but more than that, he felt that it was necessary to
saturate the defenses with a dense volume of bullets to make them keep
their heads down while the bombers made their runs to the target.

The 75mm installation was done at the North American factory. Gunn
never liked it much. The fire rate was slow, it was inaccurate and
the recoil and flash were problematic. Most of the 75mm models had
their cannon removed from the airplane and replaced with more machine
guns once out to the war zone.

The skip bombers and the B-25 strafers actually developed side by
side, but independant of each concept. Initially, the skip bombing
technique was worked up by guys flying four engine bombers, mostly the
B-17. They practiced the run-in on a wreck out in Port Moresby's
harbor. Kenney always felt the bombers were too unwieldy for this
role and about the time a convoy of Japanese ships was detected
heading for New Guinea across the Bizmark Sea, he decided to attack it
using all his air forces.

Several B-17's did make attacks on the transports, but Australian
forces made attacks as well. The main thing though was that the B-25
strafers came into their own during this battle. They proved to be
extremely effective with their withering fire as they bore in at
wavetop height with all their machine guns blazing away. They'd
perfected the skip bombing technique by that time, which involved
dropping the bombs one by one in quick intervals, usually in a salvo
of four. This ensured that at least one would be at the right height
to penetrate the hull and detonate inside.

The Japanese literally had no counter for this tactic, which has got
to be one of the most successful field developed attack techniques of
WWII. So deadly was this technique that even the best destroyer
captains lost sleep pondering how to counter it, as nothing seemed to
work. See "Destroyer Captain" by Hara.

It must have been a truly terrifying situation to be in for the
Japanese as the B-25's normally attacked in pairs which limited the
maneuvering options of the target, no matter how fast and maneuverable
it was. The pilots split up and attacked from either side which split
the target's AA counterfire. But it did not split the attackers fire.

When the B-25's opened up, as many as 8 forward firing heavy machine
guns (ten if the top turret was swiveled to fire forward) poured an
absolute hail of bullets against the ship which caused even the
bravest sailer to flinch or duck for cover.

It wasn't all gravy for the B-25's though. Low level attacks like
this were extremely dangerous as any battle damage put the airplanes
into the ocean or jungle almost immediately. Many were lost.

Corky Scott

If you're in the front of the power curve, your drag will also
increase with the higher airspeed.

Yes.

Unless your nose-up trim change upped the angle of attack...

Yes.

Do you use the door trick to induce more drag and increase your
descent path as if you're you're adding more flaps?

No, the door thing is to bank the aircraft. I presume it deflect that
air upwards toward the underside of the wing, increasing its AOA.

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"

Corky

The Skip bombing carried over into the P-51's. The technique taught
was to drop short of the vessel and let the bomb
skip off the water into the side. Fuse was a short delay to let
aircraft clear the explosion. By dropping early if the pilot made a
mistake and actually dropped late, he would drop directly into the
side of the vessel which was a good hit.

One skip was ideal but I've see some dropped at high speed and skipped
several times before hitting. Remember all pilots felt that speed was
a life saver when being shot at in combat.

Big John

On Mon, 17 Nov 2003 14:39:42 GMT,
(Corky Scott) wrote:

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.

Pappy Gunn did not install any 75mm cannon's if I remember correctly.
He felt that the firepower of the .50 caliber machine guns was
adaquate, but more than that, he felt that it was necessary to
saturate the defenses with a dense volume of bullets to make them keep
their heads down while the bombers made their runs to the target.

The 75mm installation was done at the North American factory. Gunn
never liked it much. The fire rate was slow, it was inaccurate and
the recoil and flash were problematic. Most of the 75mm models had
their cannon removed from the airplane and replaced with more machine
guns once out to the war zone.

The skip bombers and the B-25 strafers actually developed side by
side, but independant of each concept. Initially, the skip bombing
technique was worked up by guys flying four engine bombers, mostly the
B-17. They practiced the run-in on a wreck out in Port Moresby's
harbor. Kenney always felt the bombers were too unwieldy for this
role and about the time a convoy of Japanese ships was detected
heading for New Guinea across the Bizmark Sea, he decided to attack it
using all his air forces.

Several B-17's did make attacks on the transports, but Australian
forces made attacks as well. The main thing though was that the B-25
strafers came into their own during this battle. They proved to be
extremely effective with their withering fire as they bore in at
wavetop height with all their machine guns blazing away. They'd
perfected the skip bombing technique by that time, which involved
dropping the bombs one by one in quick intervals, usually in a salvo
of four. This ensured that at least one would be at the right height
to penetrate the hull and detonate inside.

The Japanese literally had no counter for this tactic, which has got
to be one of the most successful field developed attack techniques of
WWII. So deadly was this technique that even the best destroyer
captains lost sleep pondering how to counter it, as nothing seemed to
work. See "Destroyer Captain" by Hara.

It must have been a truly terrifying situation to be in for the
Japanese as the B-25's normally attacked in pairs which limited the
maneuvering options of the target, no matter how fast and maneuverable
it was. The pilots split up and attacked from either side which split
the target's AA counterfire. But it did not split the attackers fire.

When the B-25's opened up, as many as 8 forward firing heavy machine
guns (ten if the top turret was swiveled to fire forward) poured an
absolute hail of bullets against the ship which caused even the
bravest sailer to flinch or duck for cover.

It wasn't all gravy for the B-25's though. Low level attacks like
this were extremely dangerous as any battle damage put the airplanes
into the ocean or jungle almost immediately. Many were lost.

Corky Scott

Great story, Thanks Big John and Corky Scott.

Man it must have sucked to be on either side during this attack. To go back
on topic, I guess letting this quantity of lead loose, it surely would
change the Forward CG experience.

Pat Thronson


"Big John" wrote in message
...
Corky

The Skip bombing carried over into the P-51's. The technique taught
was to drop short of the vessel and let the bomb
skip off the water into the side. Fuse was a short delay to let
aircraft clear the explosion. By dropping early if the pilot made a
mistake and actually dropped late, he would drop directly into the
side of the vessel which was a good hit.

One skip was ideal but I've see some dropped at high speed and skipped
several times before hitting. Remember all pilots felt that speed was
a life saver when being shot at in combat.

Big John

On Mon, 17 Nov 2003 14:39:42 GMT,
(Corky Scott) wrote:

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.

Pappy Gunn did not install any 75mm cannon's if I remember correctly.
He felt that the firepower of the .50 caliber machine guns was
adaquate, but more than that, he felt that it was necessary to
saturate the defenses with a dense volume of bullets to make them keep
their heads down while the bombers made their runs to the target.

The 75mm installation was done at the North American factory. Gunn
never liked it much. The fire rate was slow, it was inaccurate and
the recoil and flash were problematic. Most of the 75mm models had
their cannon removed from the airplane and replaced with more machine
guns once out to the war zone.

The skip bombers and the B-25 strafers actually developed side by
side, but independant of each concept. Initially, the skip bombing
technique was worked up by guys flying four engine bombers, mostly the
B-17. They practiced the run-in on a wreck out in Port Moresby's
harbor. Kenney always felt the bombers were too unwieldy for this
role and about the time a convoy of Japanese ships was detected
heading for New Guinea across the Bizmark Sea, he decided to attack it
using all his air forces.

Several B-17's did make attacks on the transports, but Australian
forces made attacks as well. The main thing though was that the B-25
strafers came into their own during this battle. They proved to be
extremely effective with their withering fire as they bore in at
wavetop height with all their machine guns blazing away. They'd
perfected the skip bombing technique by that time, which involved
dropping the bombs one by one in quick intervals, usually in a salvo
of four. This ensured that at least one would be at the right height
to penetrate the hull and detonate inside.

The Japanese literally had no counter for this tactic, which has got
to be one of the most successful field developed attack techniques of
WWII. So deadly was this technique that even the best destroyer
captains lost sleep pondering how to counter it, as nothing seemed to
work. See "Destroyer Captain" by Hara.

It must have been a truly terrifying situation to be in for the
Japanese as the B-25's normally attacked in pairs which limited the
maneuvering options of the target, no matter how fast and maneuverable
it was. The pilots split up and attacked from either side which split
the target's AA counterfire. But it did not split the attackers fire.

When the B-25's opened up, as many as 8 forward firing heavy machine
guns (ten if the top turret was swiveled to fire forward) poured an
absolute hail of bullets against the ship which caused even the
bravest sailer to flinch or duck for cover.

It wasn't all gravy for the B-25's though. Low level attacks like
this were extremely dangerous as any battle damage put the airplanes
into the ocean or jungle almost immediately. Many were lost.

Corky Scott