Tandem-wing Airplanes

"Ken S. Tucker" wrote in
:

On Feb 4, 6:53 am, wrote:
On Feb 3, 9:05 pm, "Marc J. Zeitlin"
wrote:

Any aircraft in which the CG can be ahead of the AIRCRAFT AC, but
behind the main wing AC. There are many aircraft that when flown
at rear CG positions and low speeds will have the tail producing
lift. Gliders, in particular. Off the top of my head, I don't know
of any in particular, although I remember being told that a C-172
will have an upforce on the tail at low speeds and rear CG. Can't
cite it, though.

Even with the CG at its most aft position, a 172's AC is still
behind the CG. CG range is typically 25-33% of MAC, while AC is
around 40%.



The web site I indicated:

http://www.av8n.com/how/htm/aoastab.html

explains all this.

That's a good site that I've used for more than four years. I
think we're talking about two different things here and there's a
misunderstanding that leads to argument.
I find a fairly widely-held opinion that the aft CG can be
(legally) at or behind AC. This isn't true for any "modern"
lightplane. FAR 23.173 requires that the airplane return to trimmed
speed after being slowed or accelerated using pitch inputs only and
releasing them; this won't happen in a CG-behind-AC situation. As the
wing slows its AC moves forward due to the breakup of the boundary
layer toward the trailing edge, the CG therefore ends up even farther
behind the AC, the situation gets worse as the nose rises with the
forward-moving AC, and it eventually stalls. This is what I meant by
the illegality of a lifting tail.
Here's an example of some common
miperceptions:http://answers.yahoo.com/question/index?qid=
2008
0109225927AAfYZDU
Even the first answer, the one the voters liked, says that the CG is
12" ahead of the AC even in the most-aft position, This is extreme;
it's a lot less than that, but it's still forward. Other posters
think that with the CG at the aft position the tail must produce
lift.
Dan

My experiments with models vindicate Dan's
explanation where a conventional planform is
concerned. Setting the CG = AC can cause a
screwy stall, such as nose pitch-up.

Sorry Dan, but that pretty much wraps it up. Ken agrees with you. You
need to crack the books!

Bertie

wrote in
:

On Feb 4, 8:48 am, Bertie the Bunyip wrote:
wrote
innews:dad75380-7e0e-40c6-965a-

om:

On Feb 3, 9:05 pm, "Marc J. Zeitlin"
wrote:

Any aircraft in which the CG can be ahead of the AIRCRAFT AC, but
behind the main wing AC. There are many aircraft that when flown
at rear CG positions and low speeds will have the tail producing
lift. Gliders, in particular. Off the top of my head, I don't
know of any in particular, although I remember being told that a
C-172 will have an upforce on the tail at low speeds and rear CG.
Can't cite it, though.

Even with the CG at its most aft position, a 172's AC is
still
behind the CG. CG range is typically 25-33% of MAC, while AC is
around 40%.

We're not talking about a 172.

Bertie

OK. I'll leave now.

Why? Ken likes you!

Seriously, I know what you're talking about, but your head is stuck in
the standard issue light airplane. You're not exactly wrong, but you're
missing the point. The OP is talking about putting an airplane together,
not loading one up.


Bertie

On Feb 4, 12:41 pm, Bertie the Bunyip wrote:
wrote :

On Feb 4, 8:48 am, Bertie the Bunyip wrote:
wrote
innews:dad75380-7e0e-40c6-965a-





om:

On Feb 3, 9:05 pm, "Marc J. Zeitlin"
wrote:

Any aircraft in which the CG can be ahead of the AIRCRAFT AC, but
behind the main wing AC. There are many aircraft that when flown
at rear CG positions and low speeds will have the tail producing
lift. Gliders, in particular. Off the top of my head, I don't
know of any in particular, although I remember being told that a
C-172 will have an upforce on the tail at low speeds and rear CG.
Can't cite it, though.

Even with the CG at its most aft position, a 172's AC is
still
behind the CG. CG range is typically 25-33% of MAC, while AC is
around 40%.

We're not talking about a 172.

Bertie

OK. I'll leave now.

Why? Ken likes you!

Seriously, I know what you're talking about, but your head is stuck in
the standard issue light airplane. You're not exactly wrong, but you're
missing the point. The OP is talking about putting an airplane together,
not loading one up.

Bertie

I suppose I missed the point. But it disturbs me that Ken
agrees with me. Either he's right for once or I'm way off base.

Dan

wrote
I suppose I missed the point. But it disturbs me that Ken
agrees with me. Either he's right for once or I'm way off base.

The fact that he makes this determination based on his observation of model
planes further reinforces his lack of real and tangible knowledge of the
subject at hand.

And anyway, even a stopped clock is right once (or twice) per day.

I would be disturbed, too. Don't take it too hard, though. It was a lucky
guess.
--
Jim in NC

On Feb 4, 12:09 pm, wrote:
On Feb 4, 12:41 pm, Bertie the Bunyip wrote:



wrote :

On Feb 4, 8:48 am, Bertie the Bunyip wrote:
wrote
innews:dad75380-7e0e-40c6-965a-



om:

On Feb 3, 9:05 pm, "Marc J. Zeitlin"
wrote:

Any aircraft in which the CG can be ahead of the AIRCRAFT AC, but
behind the main wing AC. There are many aircraft that when flown
at rear CG positions and low speeds will have the tail producing
lift. Gliders, in particular. Off the top of my head, I don't
know of any in particular, although I remember being told that a
C-172 will have an upforce on the tail at low speeds and rear CG.
Can't cite it, though.

Even with the CG at its most aft position, a 172's AC is
still
behind the CG. CG range is typically 25-33% of MAC, while AC is
around 40%.

We're not talking about a 172.

Bertie

OK. I'll leave now.

Why? Ken likes you!

Seriously, I know what you're talking about, but your head is stuck in
the standard issue light airplane. You're not exactly wrong, but you're
missing the point. The OP is talking about putting an airplane together,
not loading one up.

Bertie

I suppose I missed the point. But it disturbs me that Ken
agrees with me. Either he's right for once or I'm way off base.
Dan

Berties OP wasn't bad, but it's primitive.
He ignored (or is ignorant) of Rutan twisting
the main wings on his Veri-Eze 4degrees +,
at the tip. That "feeds-back" in the CL to pull
it backward to alleviate the CL going forward
when the main begins stalling at the hip, that
Dan (the BIG HEAD) described surprisingly
well.

Score +1 for BIG HEAD, Bertie -1.

What I do is calculate the CL off the geometry
of the model A/C adjust the CG and fly them.
Saves a lot of crashing and burning.
Ken

PS: Dan, you thawing out your nuts yet?

"Bertie the Bunyip" wrote:

Ken agrees with you.

Eeewww!

Usenet cooties!

On Feb 4, 1:39 pm, "Ken S. Tucker" wrote:
On Feb 4, 12:09 pm, wrote:



On Feb 4, 12:41 pm, Bertie the Bunyip wrote:

wrote :

On Feb 4, 8:48 am, Bertie the Bunyip wrote:
wrote
innews:dad75380-7e0e-40c6-965a-



om:

On Feb 3, 9:05 pm, "Marc J. Zeitlin"
wrote:

Any aircraft in which the CG can be ahead of the AIRCRAFT AC, but
behind the main wing AC. There are many aircraft that when flown
at rear CG positions and low speeds will have the tail producing
lift. Gliders, in particular. Off the top of my head, I don't
know of any in particular, although I remember being told that a
C-172 will have an upforce on the tail at low speeds and rear CG.
Can't cite it, though.

Even with the CG at its most aft position, a 172's AC is
still
behind the CG. CG range is typically 25-33% of MAC, while AC is
around 40%.

We're not talking about a 172.

Bertie

OK. I'll leave now.

Why? Ken likes you!

Seriously, I know what you're talking about, but your head is stuck in
the standard issue light airplane. You're not exactly wrong, but you're
missing the point. The OP is talking about putting an airplane together,
not loading one up.

Bertie

I suppose I missed the point. But it disturbs me that Ken
agrees with me. Either he's right for once or I'm way off base.
Dan

Berties OP wasn't bad, but it's primitive.
He ignored (or is ignorant) of Rutan twisting
the main wings on his Veri-Eze 4degrees +,
at the tip.

Correction that should be -4 degrees.
The wing tip has a REDUCED AoA.
A 1000 pardons....

That "feeds-back" in the CL to pull
it backward to alleviate the CL going forward
when the main begins stalling at the hip, that
Dan (the BIG HEAD) described surprisingly
well.

Score +1 for BIG HEAD, Bertie -1.

What I do is calculate the CL off the geometry
of the model A/C adjust the CG and fly them.
Saves a lot of crashing and burning.
Ken

PS: Dan, you thawing out your nuts yet?

wrote in
:

On Feb 4, 12:41 pm, Bertie the Bunyip wrote:
wrote
innews:da30af89-15c1-4b7b-8841-

om:

On Feb 4, 8:48 am, Bertie the Bunyip wrote:
wrote
innews:dad75380-7e0e-40c6-965a-





om:

On Feb 3, 9:05 pm, "Marc J. Zeitlin"
wrote:

Any aircraft in which the CG can be ahead of the AIRCRAFT AC,
but behind the main wing AC. There are many aircraft that when
flown at rear CG positions and low speeds will have the tail
producing lift. Gliders, in particular. Off the top of my
head, I don't know of any in particular, although I remember
being told that a C-172 will have an upforce on the tail at low
speeds and rear CG. Can't cite it, though.

Even with the CG at its most aft position, a 172's AC is
still
behind the CG. CG range is typically 25-33% of MAC, while AC is
around 40%.

We're not talking about a 172.

Bertie

OK. I'll leave now.

Why? Ken likes you!

Seriously, I know what you're talking about, but your head is stuck
in the standard issue light airplane. You're not exactly wrong, but
you're missing the point. The OP is talking about putting an airplane
together, not loading one up.

Bertie

I suppose I missed the point. But it disturbs me that Ken
agrees with me. Either he's right for once or I'm way off base.


Well, you are and you aren't. If you put a lifting stab and an aft CG in
a 172 it's not going to be a happy airplane.
You have to include the lifting stab as a wing in it's own right..


Bertie

"Ken S. Tucker" wrote in
:

On Feb 4, 12:09 pm, wrote:
On Feb 4, 12:41 pm, Bertie the Bunyip wrote:



wrote
innews:da30af89-15c1-4b7b-8841-
legroups
.com:

On Feb 4, 8:48 am, Bertie the Bunyip wrote:
wrote
innews:dad75380-7e0e-40c6-965a-



om:

On Feb 3, 9:05 pm, "Marc J. Zeitlin"
wrote:

Any aircraft in which the CG can be ahead of the AIRCRAFT AC,
but behind the main wing AC. There are many aircraft that
when flown at rear CG positions and low speeds will have the
tail producing lift. Gliders, in particular. Off the top of
my head, I don't know of any in particular, although I
remember being told that a C-172 will have an upforce on the
tail at low speeds and rear CG. Can't cite it, though.

Even with the CG at its most aft position, a 172's AC
is still
behind the CG. CG range is typically 25-33% of MAC, while AC
is around 40%.

We're not talking about a 172.

Bertie

OK. I'll leave now.

Why? Ken likes you!

Seriously, I know what you're talking about, but your head is stuck
in the standard issue light airplane. You're not exactly wrong, but
you're missing the point. The OP is talking about putting an
airplane together, not loading one up.

Bertie

I suppose I missed the point. But it disturbs me that Ken
agrees with me. Either he's right for once or I'm way off base.
Dan

Berties OP wasn't bad, but it's primitive.

Yes, it is.


He ignored (or is ignorant) of Rutan twisting
the main wings on his Veri-Eze 4degrees +,


No I didn;'t , because it's irrelevant, fjukkwit.


at the tip. That "feeds-back" in the CL to pull
it backward to alleviate the CL going forward
when the main begins stalling at the hip, that
Dan (the BIG HEAD) described surprisingly
well.



Score +1 for BIG HEAD, Bertie -1.


Just shoot yourself now Dan.

Bertie

"Ken S. Tucker" wrote in
:

On Feb 4, 1:39 pm, "Ken S. Tucker" wrote:
On Feb 4, 12:09 pm, wrote:



On Feb 4, 12:41 pm, Bertie the Bunyip wrote:

wrote
innews:da30af89-15c1-4b7b-8841-
legrou
ps.com:

On Feb 4, 8:48 am, Bertie the Bunyip wrote:
wrote
innews:dad75380-7e0e-40c6-965a-



om:

On Feb 3, 9:05 pm, "Marc J. Zeitlin"
wrote:

Any aircraft in which the CG can be ahead of the AIRCRAFT
AC, but behind the main wing AC. There are many aircraft
that when flown at rear CG positions and low speeds will
have the tail producing lift. Gliders, in particular. Off
the top of my head, I don't know of any in particular,
although I remember being told that a C-172 will have an
upforce on the tail at low speeds and rear CG.
Can't cite it, though.

Even with the CG at its most aft position, a 172's AC
is still
behind the CG. CG range is typically 25-33% of MAC, while AC
is around 40%.

We're not talking about a 172.

Bertie

OK. I'll leave now.

Why? Ken likes you!

Seriously, I know what you're talking about, but your head is
stuck in the standard issue light airplane. You're not exactly
wrong, but you're missing the point. The OP is talking about
putting an airplane together, not loading one up.

Bertie

I suppose I missed the point. But it disturbs me that Ken
agrees with me. Either he's right for once or I'm way off base.
Dan

Berties OP wasn't bad, but it's primitive.
He ignored (or is ignorant) of Rutan twisting
the main wings on his Veri-Eze 4degrees +,
at the tip.

Correction that should be -4 degrees.
The wing tip has a REDUCED AoA.


Either way, it;s irrelevant.


Bertie