Tandem-wing Airplanes

William Hung wrote in news:356251e4-f6d9-420e-a4d8-
:

On Feb 2, 11:59*am, Bertie the Bunyip wrote:
Phil J wrote in news:e5efb14f-c2c5-41c7-a127-
:



Here's another question for you engineers out there. *Traditional
airplane design has the tail pressing down, so the tail is fighting
the work that the main wing is doing. *A tandem-wing airplane in
which

both front and rear wings are lifting upward is a more efficient
design, which is one reason Bert Rutan chose the canard
configuration
for so many of his designs. *But in the canard configuration, the
front wing is smaller than the rear wing. *This is what I don't
understand. *It seems to me that a design in which the front wing
was
larger and the rear wing was smaller would be more stable in pitch.
The smaller rear wing would automatically damp pitch excursions
like
the fins of an arrow. *So why is the canard the most successful
tandem-
wing design flying?

Well, it isn't a tandem wing, for one thing. It's a canard. It's
front
"wing" is called a canard and not a wing. You could say it's a tomato
tomato thing, but that's the definition. A Bleriot could also be
called
a tandem wing aircraft if you used the same standard. It's tail
lifts.
So do most free flight models. These airplanes have very large stabs
(or
wings, if you prefer), and very far aft CGs as compared to a a
"conventional" aircraft and usually very long fuselages.
Aircraft like the Bleriot were not very stable in pitch, and RC
conversions of old time free flight airplanes with the original FF CG
are very twitchy in pitch if elevator is used.

*The basic principle is that more of the horizontal surface (
multiplied

by it's arm) has to be behind the CG to get the thing going in the
direction you want it to. Think horizontal weather vane.
That's pretty simplistic, but basically it's the way it works. The
horizontal weather vane principle also explains why conventional
aircraft get nasty when their CG is moved aft. Never mind any rubbish
Jepeson might tell you about the elevators making lift the wrong way.
.
I'm not exactly sure what the definition of a tandem wing is,
percentage
wise, but basically if it looks like one then it is one. That is, the
wings should be in the neighborhood of each other area wise.
The Flying Flea would be a good example.

Bertie

I was gonna mention the Flea. The Frogs seam to like the Fleas.

Definitely not my cup of tea, but the early ones have a funky look
that's irresistable! The French were fodn of Tandem wings period. There
was a guy named Delanne who made a few in the thirties and forties. and
there was a light plane called the Payen tht was near enough a Tndem
wing that made no difference. I don't know much about how either one
flew, but Delanne made a lot of different airplanes and I think a few
Payens were made and flew for a good few years.


Bertie

On Feb 2, 4:22*pm, wrote:
On Feb 2, 2:21 pm, Bertie the Bunyip wrote:

So, tu summarise, if you put the "smaller wing" (sic) in the back, it';s
a tail unless it;s lifting. If it's lifting it needs to be fairly large
to be useful. make it large enough and you have problems with handling,
one solutuion for this problem is to reduce the sizre of the forward
wing and move the CG aft. Voila! you have a canard!

Bertie

* * * *Seems to me that lifting tails are, and have been, illegal for
long time. The regs call for the aircraft to automatically settle into
a glide if the power should fail, to prevent stalling. A lifting tail
just won't do this. As the airplane slows it will drop, raising the
nose, and the airplane will stall, and almost certainly enter an
unrecoverable spin. If the pilot does manage to establish a glide, the
nose will drop further as glide speed increases, opposite to what we
know in our airplanes, and totally unstable. Some early airplanes were
built this way, and after they'd killed enough pilots the designers
decided to make things differently.
* *See FAR 23 (U.S.) or CAR 523 (Canadian) for the details.

* * * *Dan

OK, this makes sense. Since a small lifting tail would be a long way
from the CG (compared to the main wing), it would experience a much
higher angle of attack when the aircraft pitched up. It would be very
difficult to make the main wing stall before the tail.

Phil

Phil J wrote in
:

On Feb 2, 4:22*pm, wrote:
On Feb 2, 2:21 pm, Bertie the Bunyip wrote:

So, tu summarise, if you put the "smaller wing" (sic) in the back,
it';s

a tail unless it;s lifting. If it's lifting it needs to be fairly
large to be useful. make it large enough and you have problems with
handling, one solutuion for this problem is to reduce the sizre of
the forward wing and move the CG aft. Voila! you have a canard!

Bertie

* * * *Seems to me that lifting tails are, and have been, illegal
for
long time. The regs call for the aircraft to automatically settle
into a glide if the power should fail, to prevent stalling. A lifting
tail just won't do this. As the airplane slows it will drop, raising
the nose, and the airplane will stall, and almost certainly enter an
unrecoverable spin. If the pilot does manage to establish a glide,
the nose will drop further as glide speed increases, opposite to what
we know in our airplanes, and totally unstable. Some early airplanes
were built this way, and after they'd killed enough pilots the
designers decided to make things differently.
* *See FAR 23 (U.S.) or CAR 523 (Canadian) for the details.

* * * *Dan

OK, this makes sense. Since a small lifting tail would be a long way
from the CG (compared to the main wing), it would experience a much
higher angle of attack when the aircraft pitched up. It would be very
difficult to make the main wing stall before the tail.


Actually, it wouldn't. It's easy. You're not talking about nailing a
lifting tail to a Cessna. You're talking a bespoke design and you
wouldn't have a small stab either. A lifting stab requires an aft CG and
so a completely different config anyway.

Bertie

On Feb 2, 3:21*pm, Bertie the Bunyip wrote:
Phil J wrote in news:75220ca0-969d-4a58-8dac-
:



OK. *But why on the canards flying these days is the little wing in
front of the CG, and the big wing behind it. *It seems like it would
be more stable in pitch if the little wing was behind the CG.

Then it wouldn't be a canard.

*Putting

the little wing in front of the CG seems like it would make the
airplane inherently unstable in pitch. *Looking at Rutan's designs, it
looks like he countered this by using a swept main wing. *But that
would have been unnecessary if he had put the smaller wing in back.
The only reason I can think of to put the smaller wing out front would
be for pilot visibility, so maybe that's the explanation?

No, it's because he wanted a canard. I explained above that having a
lifitng stab, even a great big one, makes for a twitchy airplane. I'm
sure that could be managed if you wanted, but it's not ever going to be
a very happy airplane. The smaller "wing",on a canard is called a
canard. It's primarily a stabilsation surface that also contributes to
overall lift. It is not a wing
There are probably several reasons that Rutan elected to sweep the wing.
One, it gives good stability without sacrificing manueverability. two,
it expands the CG limits and in the case of this aricraft, allows a
shorter fuselage than would be the case if the weren't swept. .
So, tu summarise, if you put the "smaller wing" (sic) in the back, it';s
a tail unless it;s lifting. If it's lifting it needs to be fairly large
to be useful. make it large enough and you have problems with handling,
one solutuion for this problem is to reduce the sizre of the forward
wing and move the CG aft. Voila! you have a canard!

Bertie

OK, it's a canard if its primary function is stability rather than
lift. I guess Rutan's Quickie is more like what I was thinking
about. On that airplane the front wing contributes 60% of the lift,
so it's a true wing. And there you have the larger wing in front and
the smaller wing in back. I don't know much about the stall
characteristics of that airplane, but it definitely seems to be an
efficient design. With a 64-horsepower engine it has a 140-mph
cruise.

Phil

"Phil J" wrote in message
...
On Feb 2, 3:21 pm, Bertie the Bunyip wrote:
Phil J wrote in news:75220ca0-969d-4a58-8dac-
:



OK. But why on the canards flying these days is the little wing in
front of the CG, and the big wing behind it. It seems like it would
be more stable in pitch if the little wing was behind the CG.

Then it wouldn't be a canard.

Putting

the little wing in front of the CG seems like it would make the
airplane inherently unstable in pitch. Looking at Rutan's designs, it
looks like he countered this by using a swept main wing. But that
would have been unnecessary if he had put the smaller wing in back.
The only reason I can think of to put the smaller wing out front would
be for pilot visibility, so maybe that's the explanation?

No, it's because he wanted a canard. I explained above that having a
lifitng stab, even a great big one, makes for a twitchy airplane. I'm
sure that could be managed if you wanted, but it's not ever going to be
a very happy airplane. The smaller "wing",on a canard is called a
canard. It's primarily a stabilsation surface that also contributes to
overall lift. It is not a wing
There are probably several reasons that Rutan elected to sweep the wing.
One, it gives good stability without sacrificing manueverability. two,
it expands the CG limits and in the case of this aricraft, allows a
shorter fuselage than would be the case if the weren't swept. .
So, tu summarise, if you put the "smaller wing" (sic) in the back, it';s
a tail unless it;s lifting. If it's lifting it needs to be fairly large
to be useful. make it large enough and you have problems with handling,
one solutuion for this problem is to reduce the sizre of the forward
wing and move the CG aft. Voila! you have a canard!

Bertie

OK, it's a canard if its primary function is stability rather than
lift. I guess Rutan's Quickie is more like what I was thinking
about. On that airplane the front wing contributes 60% of the lift,
so it's a true wing. And there you have the larger wing in front and
the smaller wing in back. I don't know much about the stall
characteristics of that airplane, but it definitely seems to be an
efficient design. With a 64-horsepower engine it has a 140-mph
cruise.

Phil

"Phil J" wrote in message
...
On Feb 2, 3:21 pm, Bertie the Bunyip wrote:
Phil J wrote in news:75220ca0-969d-4a58-8dac-
:



OK. But why on the canards flying these days is the little wing in
front of the CG, and the big wing behind it. It seems like it would
be more stable in pitch if the little wing was behind the CG.

Then it wouldn't be a canard.

Putting

the little wing in front of the CG seems like it would make the
airplane inherently unstable in pitch. Looking at Rutan's designs, it
looks like he countered this by using a swept main wing. But that
would have been unnecessary if he had put the smaller wing in back.
The only reason I can think of to put the smaller wing out front would
be for pilot visibility, so maybe that's the explanation?

No, it's because he wanted a canard. I explained above that having a
lifitng stab, even a great big one, makes for a twitchy airplane. I'm
sure that could be managed if you wanted, but it's not ever going to be
a very happy airplane. The smaller "wing",on a canard is called a
canard. It's primarily a stabilsation surface that also contributes to
overall lift. It is not a wing
There are probably several reasons that Rutan elected to sweep the wing.
One, it gives good stability without sacrificing manueverability. two,
it expands the CG limits and in the case of this aricraft, allows a
shorter fuselage than would be the case if the weren't swept. .
So, tu summarise, if you put the "smaller wing" (sic) in the back, it';s
a tail unless it;s lifting. If it's lifting it needs to be fairly large
to be useful. make it large enough and you have problems with handling,
one solutuion for this problem is to reduce the sizre of the forward
wing and move the CG aft. Voila! you have a canard!

Bertie

OK, it's a canard if its primary function is stability rather than
lift. I guess Rutan's Quickie is more like what I was thinking
about. On that airplane the front wing contributes 60% of the lift,
so it's a true wing. And there you have the larger wing in front and
the smaller wing in back. I don't know much about the stall
characteristics of that airplane, but it definitely seems to be an
efficient design. With a 64-horsepower engine it has a 140-mph
cruise.

Phil

Now about that Piaggio avanti....... Pat

Phil J wrote in news:ad6eb94e-4e9e-46a8-b608-
:

On Feb 2, 3:21*pm, Bertie the Bunyip wrote:
Phil J wrote in news:75220ca0-969d-4a58-8dac-
:



OK. *But why on the canards flying these days is the little wing in



OK, it's a canard if its primary function is stability rather than
lift. I guess Rutan's Quickie is more like what I was thinking
about. On that airplane the front wing contributes 60% of the lift,
so it's a true wing.


OK, that's right. I had forgoten about them. Yeah, That's a true tandem
wing.


And there you have the larger wing in front and
the smaller wing in back. I don't know much about the stall
characteristics of that airplane, but it definitely seems to be an
efficient design. With a 64-horsepower engine it has a 140-mph
cruise.

Yeah, I kow someone who built a Q200 and it cruises at about 160 mph on
100 hp! Superb.
The decalage, as with the canards, is arranged so that the front wing
reaches critical angle first thus lowering the nose. So, they don't
realy stal in the same way that a conventinal airplane does. I've never
flown one, though I have a standing offer to fly this one if I ever get
into his neighborhood. I would have thought that the rear wing was
taking more of the load, though, but i can't find any info on that on
the net. The thing that always made me nervous about those things is the
pounding the front wing must take on the ground..

Bertie

"patrick mitchel" wrote in news:fo50mi$2bl2$1
@zook.lafn.org:

Now about that Piaggio avanti....... Pat




Canard, . And I think the reason you're confused about Canards is this: The
canard is not there to provide stability. Not in the same way as a stab on
a stadard airplane. It's there to provide control. The wing provides the
stability in the way you understand it.


Bertie

On Feb 3, 12:31*pm, Bertie the Bunyip wrote:
"patrick mitchel" wrote in news:fo50mi$2bl2$1
@zook.lafn.org:

*Now about that Piaggio avanti....... Pat

Canard, . And I think the reason you're confused about Canards is this: The
canard is not there to provide stability. Not in the same way as a stab on
a stadard airplane. It's there to provide control. The wing provides the
stability in the way you understand it.

Bertie

I think you are referring to me rather than Pat, but I understand what
you are saying. On a canard design, the main wing functions like a
stab since it is behind the CG. OTOH, trying to figure out the
Piaggio seems like a good way to get a headache. It's amazing what
they were able to do with compound curves in aluminum on that
airplane, though.

Phil



Thanks to everyone who posted on this.