Forward CG Experience

[Jay Honeck]

Recently we flew with a friend who weighs over 320 pounds. With he and I
in the front seat, and just Mary in the back, we were at the very forward
limits of the allowable CG. Thanks to the Pathfinder's 1400 pound useful
load, however, we were still 250 pounds under gross, even with full tanks --
but the teeter-totter was certainly pretty far to the "teeter" side.

I was contemplating this as we came in to land. Departure had felt normal,
but I figured the flare to land would be effected, so I carried a few extra
knots on final. I also figured that the wind -- 12, gusting to 18, but
right down the runway -- would help a little, too. I opted for two notches
of flaps.

As we crossed the numbers, I noticed things just didn't "feel" right.
Pulling back on the yoke was having very little effect as far as changing
the angle of attack, yet the speed was still bleeding off. This was weird,
but -- as it was all happening in the last few seconds, there wasn't much
else to do but add a touch of power and pull back some more.

We arrived firmly, in a flat attitude. The nosewheel and mains hit nearly
simultaneously, and the end result was more like a mush into the ground than
my usual "flare, chirp, chirp, settle...". It was surprisingly smooth, but
I realized that if I hadn't given that extra burst of power, and a firmer
yank on the yoke, we might well have landed on the nose gear, with possibly
expensive consequences.

Later, on the way home, with Mary as PIC and our friend in the back seat,
things were much improved. The added weight in the back actually helped to
balance our normally slightly nose-heavy (thanks to the six-cylinder
Lycoming O-540) plane, and Mary remarked that it landed more like our old
Warrior used to.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[Wallace Berry]

In article <zR5tb.196731$HS4.1666204@attbi_s01>,
"Jay Honeck" > wrote:

> Recently we flew with a friend who weighs over 320 pounds. With he and I
> in the front seat, and just Mary in the back, we were at the very forward
> limits of the allowable CG. Thanks to the Pathfinder's 1400 pound useful
> load, however, we were still 250 pounds under gross, even with full tanks --
> but the teeter-totter was certainly pretty far to the "teeter" side.


Took a heavy friend and his tiny wife for glider flights once. He was
right on 250 lbs. Put him in the front seat of a Grob 103 (a model
famous for being nose heavy anyway). With the stick all the way back,
airspeed was 60 knots. You can bet I carried some extra speed on final.
His wife was 90 lbs. Bolted in the iron ballast plates and put a chute
on her. She was still a little under the front seat minimum. Flew her
that way since I knew the glider was a little forward CG from a repair.
That was the best that glider ever flew for me.

Now I have a little Stits homebuilt. It is somewhat forward CG solo. So,
I will have some bolt-in ballast for the rear. With anybody in the back
seat, it will be aft CG once a gallon or two of fuel burns. I will have
to add some ballast up front. The most useful ballast I can think of is
an electric starter.

[Corky Scott]

On Fri, 14 Nov 2003 14:42:39 GMT, "Jay Honeck"
> wrote:

>Recently we flew with a friend who weighs over 320 pounds. With he and I
>in the front seat, and just Mary in the back, we were at the very forward
>limits of the allowable CG.

>Jay Honeck
>Iowa City, IA
>Pathfinder N56993
>www.AlexisParkInn.com
>"Your Aviation Destination"

Jay, with your indulgence, a little military history that is on your
post's topic.

During the dark days following Pearl Harbor and the invasion of the
Phillipine Islands, a highly practical and inveterate ex Navy pilot
scrounger by the name of Paul (later called Pappy) Gunn ran a rough
house airline out of the Phillipines called PAL (Philipine Air Lines).
He his airplanes were requisitioned by the army and Pappy had various
hair raising flights and encounters with Japanese aircraft and anti
aircraft fire from both sides before he wound up in Australia and then
Port Moresby.

Cutting out a lot of his story, he ended up in charge of a provisional
transport squadron and offloaded some A-20's that had been assigned
him. He discovered that they had arrived without any machine guns.
His combat experience to date had convinced him of the need for a LOT
of forward fire power to keep the enemy's heads down on the run in to
the target so he began modifying them.

He plated over the bombardier's position and installed a row of four
50 caliber machine guns in the nose, plus two more in blisters
alongside the cockpit for a total of six forward firing machine guns.

With the machine guns, internal bracing and ammo cans and ammo, the
fully loaded A-20 was seriously nose heavy (you wondered when I'd get
to the subject?) His first takeoff, apparently wasn't. He could not
lift the nose to get airborn.

So he relocated the two machine guns in side blisters, moving them
back behind the cockpit.

At this time Gunn met up with George Kenney, who arrived in the
theater with a notion about low level attacks utilizing some parachute
equipped fragmentation bombs he'd developed, which would slow their
descent to allow the bomber to move out of danger from an explosion
once the bomb was dropped.

He saw what Gunn was doing and immediately liked the concept. He
yanked Pappy from his command in the transport squadron and placed him
in charge of modifying more attack bombers.

The A-20's were immediately extremely effective, but Pappy was unhappy
with their performance, feeling that he needed a bigger bomber with
more capacity. Enter the B-25 strafer.

I've got to stop, I could go on about this for a while longer. ;-)

Corky Scott

[Jay Honeck]

> I've got to stop, I could go on about this for a while longer. ;-)

I've seen pictures of those B-25 ground-attack strafers. I imagine they
were the "A-10 Warthogs" of their day...

Thanks, Corky!
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[EDR]

In article <zR5tb.196731$HS4.1666204@attbi_s01>, Jay Honeck
> wrote:

> As we crossed the numbers, I noticed things just didn't "feel" right.
> Pulling back on the yoke was having very little effect as far as changing
> the angle of attack, yet the speed was still bleeding off. This was weird,
> but -- as it was all happening in the last few seconds, there wasn't much
> else to do but add a touch of power and pull back some more.

Subtract the weight of the fuel burned enroute and recalculate you W&B
and C/G.
Which way does the moment move? Fore or aft?

[Peter Duniho]

"Jay Honeck" > wrote in message
news:zR5tb.196731$HS4.1666204@attbi_s01...
> Recently we flew with a friend who weighs over 320 pounds. With he and I
> in the front seat [...]

Argh! "With him and me in the front seat". Sorry, pet peeve.

Anyway, some comments:

* Wind only reduces groundspeed. It has no effect on control effectiveness
for a given airspeed.
* As you found, forward CG translates into increased drag, which means
airspeed drops off quicker than usual. You can either carry more airspeed
on final (scrubbing off to normal touchdown speed in the flare, but doing so
more quickly than normal) or you can use more power (using thrust to offset
the extra drag).

The only thing aft CG isn't good for is stability. Otherwise, it's a good
thing. I prefer to fly my airplane with the CG as far aft as practical (and
legal, of course).

Pete

[Jay Honeck]

> Argh! "With him and me in the front seat". Sorry, pet peeve.

Ooooo. That *was* bad, wasn't it? :-) Sorry.

> * Wind only reduces groundspeed. It has no effect on control
effectiveness
> for a given airspeed.

Yes. I was trying to say that the wind would help with a gentle landing by
allowing a slower touch-down speed.

As I've told my son, don't listen to what I *say*, dang it, listen to what I
*MEAN*.
;-)
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[Larry Fransson]

On 2003-11-14 06:42:39 -0800, "Jay Honeck" > said:

> I opted for two notches of flaps.

That probably did a lot to help your landing. Flaps add a nose down pitching moment - something you don't really need with a forward CG.

> We arrived firmly, in a flat attitude. The nosewheel and mains hit nearly
> simultaneously, and the end result was more like a mush into the ground than
> my usual "flare, chirp, chirp, settle...". It was surprisingly smooth, but
> I realized that if I hadn't given that extra burst of power, and a firmer
> yank on the yoke, we might well have landed on the nose gear, with possibly
> expensive consequences.

Not necessarily. Sometimes, this is as good as it gets. I've had lots of nosewheel first arrivals in a Seneca (before I figured out the little flap trick). It's only a problem if you let it get out of hand by chasing the oscillation.

[Paul Sengupta]

Hey, if you want a heavy friend to take flying, ballast and all that,
I'm available! :-) In the UK though...

I have 2 seats and 200hp so not much of a problem in my plane.
However I learned on a 172 as when I walked up first time to my
6ft 5" body builder instructor, he took one look at me, looked at
himself and said "We're going to need a bigger aeroplane"!

Grob 103. I can't even fit in the front and move the stick. I'm fine
in the back though...it's about the only glider I can fit in and
waggle the stick.

When I fly a T-tailed Arrow solo I have to a) watch how much fuel
I put in, and b) usually put a sandbag in the baggage compartment.
It still needs full back yoke to the stops on landing.

Paul

"Wallace Berry" > wrote in message
...
> In article <zR5tb.196731$HS4.1666204@attbi_s01>,
> "Jay Honeck" > wrote:
>
> > Recently we flew with a friend who weighs over 320 pounds.

> Took a heavy friend and his tiny wife for glider flights once. He was
> right on 250 lbs. Put him in the front seat of a Grob 103

[Bob Chilcoat]

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.

--
Bob (Chief Pilot, White Knuckle Airways)


"Corky Scott" > wrote in message
...
> On Fri, 14 Nov 2003 14:42:39 GMT, "Jay Honeck"
> > wrote:
>
> >Recently we flew with a friend who weighs over 320 pounds. With he and
I
> >in the front seat, and just Mary in the back, we were at the very forward
> >limits of the allowable CG.
>
> >Jay Honeck
> >Iowa City, IA
> >Pathfinder N56993
> >www.AlexisParkInn.com
> >"Your Aviation Destination"
>
> Jay, with your indulgence, a little military history that is on your
> post's topic.
>
> During the dark days following Pearl Harbor and the invasion of the
> Phillipine Islands, a highly practical and inveterate ex Navy pilot
> scrounger by the name of Paul (later called Pappy) Gunn ran a rough
> house airline out of the Phillipines called PAL (Philipine Air Lines).
> He his airplanes were requisitioned by the army and Pappy had various
> hair raising flights and encounters with Japanese aircraft and anti
> aircraft fire from both sides before he wound up in Australia and then
> Port Moresby.
>
> Cutting out a lot of his story, he ended up in charge of a provisional
> transport squadron and offloaded some A-20's that had been assigned
> him. He discovered that they had arrived without any machine guns.
> His combat experience to date had convinced him of the need for a LOT
> of forward fire power to keep the enemy's heads down on the run in to
> the target so he began modifying them.
>
> He plated over the bombardier's position and installed a row of four
> 50 caliber machine guns in the nose, plus two more in blisters
> alongside the cockpit for a total of six forward firing machine guns.
>
> With the machine guns, internal bracing and ammo cans and ammo, the
> fully loaded A-20 was seriously nose heavy (you wondered when I'd get
> to the subject?) His first takeoff, apparently wasn't. He could not
> lift the nose to get airborn.
>
> So he relocated the two machine guns in side blisters, moving them
> back behind the cockpit.
>
> At this time Gunn met up with George Kenney, who arrived in the
> theater with a notion about low level attacks utilizing some parachute
> equipped fragmentation bombs he'd developed, which would slow their
> descent to allow the bomber to move out of danger from an explosion
> once the bomb was dropped.
>
> He saw what Gunn was doing and immediately liked the concept. He
> yanked Pappy from his command in the transport squadron and placed him
> in charge of modifying more attack bombers.
>
> The A-20's were immediately extremely effective, but Pappy was unhappy
> with their performance, feeling that he needed a bigger bomber with
> more capacity. Enter the B-25 strafer.
>
> I've got to stop, I could go on about this for a while longer. ;-)
>
> Corky Scott

[Snowbird]

(Corky Scott) wrote in message >...

> The A-20's were immediately extremely effective, but Pappy was unhappy
> with their performance, feeling that he needed a bigger bomber with
> more capacity. Enter the B-25 strafer.
>
> I've got to stop, I could go on about this for a while longer. ;-)

Go ahead, Corky, it's cool!

Very fond of our local B-25 "Show Me"

Cheers,
Sydney

[Koopas Ly]

Larry Fransson > wrote in message >...
> On 2003-11-14 06:42:39 -0800, "Jay Honeck" > said:
>
> > I opted for two notches of flaps.
>
> That probably did a lot to help your landing. Flaps add a nose down pitching moment

Not necessarily. Depends whether you fly a low or high wing aircraft.

[Koopas Ly]

> * As you found, forward CG translates into increased drag, which means
> airspeed drops off quicker than usual. You can either carry more airspeed
> on final (scrubbing off to normal touchdown speed in the flare, but doing so
> more quickly than normal) or you can use more power (using thrust to offset
> the extra drag).

I would think that the only source of increased drag from a forward
c.g. condition is profile drag due to a more nose-up elevator trim tab
or elevator.

How do you see a forward c.g.'s extra drag translating into premature
airspeed bleeding? Sink rate and angle of descent would
increase...but airspeed?

Alex

[karl gruber]

******Not necessarily. Depends whether you fly a low or high wing
aircraft.****

Not necessarily. The old Piper Cherokee wing pitches down with flaps. The
newer Warrior wing pitches up with flaps.

Has NOTHING to do with wing placement!!

Karl

[Peter Duniho]

"Koopas Ly" > wrote in message
om...
> I would think that the only source of increased drag from a forward
> c.g. condition is profile drag due to a more nose-up elevator trim tab
> or elevator.

There are several factors that translate into increased drag:

* Drag from the trim, if used (as you noted)
* Drag from the elevator itself (as you noted)
* Increased induced drag from the horizontal stabilizer/elevator due to
increased lift on that airfoil
* Increased induced drag from the wings since the increase in lift on the
horizontal stabilizer translates into added weight for the aircraft, which
has the exact same increase in induced drag that adding physical weight to
the aircraft would have

> How do you see a forward c.g.'s extra drag translating into premature
> airspeed bleeding? Sink rate and angle of descent would
> increase...but airspeed?

I'm not sure I understand your question. Is this a continuation of the "why
is there increased drag?" question? Or are you asking, even if one assumes
increased drag, why does the airspeed bleed off quicker?

If the former, I hope my earlier bullet points answer your question. If the
latter, that should be obvious. For a given configuration, deceleration is
strictly related to the net difference between thrust and drag. When thrust
is greater than drag, you accelerate. When thrust is less than drag, you
decelerate.

Furthermore, the rate at which you decelerate is directly proportional to
that net difference. For a given thrust, more drag means a greater rate of
deceleration. Moving the CG doesn't affect thrust, but it does affect drag.
Moving CG forward increases drag (as noted above) and thus increases the
deceleration rate.

Pete

[Peter Duniho]

"karl gruber" > wrote in message
...
> ******Not necessarily. Depends whether you fly a low or high wing
> aircraft.****
>
> Not necessarily. The old Piper Cherokee wing pitches down with flaps. The
> newer Warrior wing pitches up with flaps.
>
> Has NOTHING to do with wing placement!!

Well, actually...

It has a little to do with the wing placement in that wing placement
certainly can affect whether flaps cause a nose-up or nose-down trim change.
Other factors are involved as well, so knowing the wing placement alone
won't tell you what flaps will do. But certainly, all else being equal,
moving the wing can change the way flaps affect trim.

Now, all that said...I don't think that's what Larry was talking about. The
trim change is usually a result of a combination of things, including
airflow over the horizontal stabilizer and elevator. But if I recall
correctly, flaps extended below the wing *also* create a pitching down
moment, always. This moment may be enhanced or obscured by other factors,
but it always exists.

Since trim changes often become negligible at lower airspeeds, this moment
can become more significant during the flare, even if the net trim change at
the normal flap extension speed would be nose-up.

At least, I think that's the point Larry was trying to make. I could very
well be wrong about what point he was trying to make, and I might have
misremembered this particular aspect of the aerodynamics of flaps.

Pete

[karl gruber]

*****> Has NOTHING to do with wing placement!!

Well, actually...

It has a little to do with the wing placement in that wing placement****


So true. I must remember, the words "nothing, always, never,...Etc" don't
get very far on usenet.

Best

[Koopas Ly]

Pete,

Comments in your text.


> > I would think that the only source of increased drag from a forward
> > c.g. condition is profile drag due to a more nose-up elevator trim tab
> > or elevator.
>
> There are several factors that translate into increased drag:
>
> * Drag from the trim, if used (as you noted)
> * Drag from the elevator itself (as you noted)
> * Increased induced drag from the horizontal stabilizer/elevator due to
> increased lift on that airfoil
> * Increased induced drag from the wings since the increase in lift on the
> horizontal stabilizer translates into added weight for the aircraft, which
> has the exact same increase in induced drag that adding physical weight to
> the aircraft would have

Agreed.

>
> > How do you see a forward c.g.'s extra drag translating into premature
> > airspeed bleeding? Sink rate and angle of descent would
> > increase...but airspeed?
>
> I'm not sure I understand your question. Is this a continuation of the "why
> is there increased drag?" question? Or are you asking, even if one assumes
> increased drag, why does the airspeed bleed off quicker?
>
> If the former, I hope my earlier bullet points answer your question. If the
> latter, that should be obvious. For a given configuration, deceleration is
> strictly related to the net difference between thrust and drag. When thrust
> is greater than drag, you accelerate. When thrust is less than drag, you
> decelerate.
>
> Furthermore, the rate at which you decelerate is directly proportional to
> that net difference. For a given thrust, more drag means a greater rate of
> deceleration. Moving the CG doesn't affect thrust, but it does affect drag.
> Moving CG forward increases drag (as noted above) and thus increases the
> deceleration rate.

I agree that your deceleration is equal to (Thrust - Drag)/mass.

Even though the airplane momentarily decelerates due to the increased
drag, I ideally presume that the airplane's trimmed angle of attack
has not changed (if you consider that the forward c.g. shift occured
in flight). The assumption is probably invalid since, as you
mentioned in your last point, the wing needs to develop more lift to
offset the increase in tail downforce. The differential lift would
require a change in either trimmed speed or angle of attack.

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.

Your thoughts?

Have a good weekend,
Alex

[Larry Fransson]

On 2003-11-14 21:55:21 -0800, "Peter Duniho" > said

> At least, I think that's the point Larry was trying to make. I could ver
> well be wrong about what point he was trying to make, and I might hav
> misremembered this particular aspect of the aerodynamics of flaps

That was my point exactly

[Greg Esres]

<<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...Your thoughts?>>

Very good!

How about this: since the increased drag leads to an increased
descent rate with the power off, you will have to increase your angle
of attack at a greater rate during your flare in order to maintain a
constant altitude above the runway. Since you're increasing your AOA
more rapidly, your airspeed will be falling more rapidly.

[Peter Duniho]

"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

[Koopas Ly]

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

[Big John]

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.

[Peter Duniho]

"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

[Koopas Ly]

> > 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

[Greg Esres]

<<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.

[Peter Duniho]

"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

[Koopas Ly]

> <<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.

[karl gruber]

*****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

[Greg Esres]

<<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.

[Robert Perkins]

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

[G.R. Patterson III]

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.

[Koopas Ly]

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

[Koopas Ly]

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

[Koopas Ly]

> 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

[Corky Scott]

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

[Greg Esres]

<<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.

[Jay Honeck]

> 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"

[Big John]

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
>
>
>

[Pat Thronson]

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
> >
> >
> >
>

[Koopas Ly]

> Koopas, Koopas, Koopas. This is not a place for the thin-skinned.

Indeed, it is not :) How do you do it?

> 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,

Wait...isn't that a line from Top Gun?


> make plans to pee in their gas tanks
> at OSH 2004, and cheerily move on to the next thread...
> ;-)

Thanks for the support. :->

[Jay Honeck]

> > Koopas, Koopas, Koopas. This is not a place for the thin-skinned.
>
> Indeed, it is not :) How do you do it?

I've always liked verbal repartee, and I'm not easily intimidated. I like
to think that I know what I don't know, and that I'm here to learn.

As I'm fond of saying, I have learned more about flying here (and on the
..owning group) than I have in all my years of hanging out at airports. We
just have to separate the wheat from the chaff once in a while.

> > Just presume they were abused children,
>
> Wait...isn't that a line from Top Gun?

It appears that they've lost that "Lovin' Feelin'", too... ;-)

> Thanks for the support. :->

From what I've read, you've got much to contribute here. Please don't let a
few barbs chase you away!
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"