questions on multi-wing planforms

"pTooner" wrote in message
...

"Drew Dalgleish" wrote in message
...
Even if everything works just the way you dream it will how will you
see where you're going?

You are assuming a far more complete design than actually exists, but I
don't see why that should be a problem.

Gerry
I am fairly certain that tandem biplane designs existed in the early
days--in addition to the obvious case of the Wright Flyer.

However, I will second the suggestion to stay with one of the various
folding wing designs. Also, unless you are *very* masochistic, you probably
won't fly very ofter if you also have to tow the aircraft to and from the
airport, so the ability to be towed at highway speeds (or even street
speeds) may not be as usefull as the ease of folding and unfolding the
wings. I would suggest asking around your local airport(s) regarding the
storage cost for a folding wing aircraft--you may be able to share part of a
hangar or even get a reasonable deal from a maintenance facility if they
have permission to move the plane out of the way when they need the
workspace. Also, the way Tee-hangars are constructed at some airports,
there may be a half hangar on the end of each row--and a folding wing
airplane would only need about half of a half hangar!

BTW, depending on the size of the Tee hangars on the row, you might be able
to nose a VariEze or even a LongEze into a half hangar and still share the
back part of the hangar for storage or office space--depending on the rules
at your airport.

Also the Nesmith Cougar has a folding wing, and if you are of very small
stature there is the Stits Playmate.

I hope this helps
Peter

"pTooner" wrote in message
. ..
Firstly, I am new here although I've been reading for a few days. For
anyone with more knowledge than I, I keep considering building a small
4
wing aircraft. Not stacked, but two up front and two in the rear. I
have
read frequently of problems supposedly resulting from interference of
the
airflow between wings, but I can't seem to find anything very
specific.
I'm fairly confident that interference between the front wings (or
rear)
can be minimized by reasonable spacing and differing dihedral. I'm
not
sure what the effect of the airflow coming off the front wings will
have
on the rear set. I don't know whether I could remove most of the
problem
by having one set considerably higher (how much?) than the other set
or
if
it is reasonable to have them on more or less the same height. The
reason for the concept is trying to get a wingspan small enough to fit
into a normal garage and conceivably take off and land from streets
and
highways. I visualise something in a two place plane that would fall
into
something of the appeal category of a motorcycle or small sports car.
Any
thoughts would be appreciated.

Gerry

"Peter Dohm" wrote in message
. ..
"pTooner" wrote in message
...

"Drew Dalgleish" wrote in message
...
Even if everything works just the way you dream it will how will you
see where you're going?

You are assuming a far more complete design than actually exists, but I
don't see why that should be a problem.

Gerry
I am fairly certain that tandem biplane designs existed in the early
days--in addition to the obvious case of the Wright Flyer.

Well, I tend to think that it's only a tandem wing if both portions
contribute substantially to the list. I don't know of any of those,
although I'd like to find them for informational purposes.


However, I will second the suggestion to stay with one of the various
folding wing designs. Also, unless you are *very* masochistic, you
probably
won't fly very ofter if you also have to tow the aircraft to and from the
airport, so the ability to be towed at highway speeds (or even street
speeds) may not be as usefull as the ease of folding and unfolding the
wings. I would suggest asking around your local airport(s) regarding the
storage cost for a folding wing aircraft--you may be able to share part of
a
hangar or even get a reasonable deal from a maintenance facility if they
have permission to move the plane out of the way when they need the
workspace. Also, the way Tee-hangars are constructed at some airports,
there may be a half hangar on the end of each row--and a folding wing
airplane would only need about half of a half hangar!

Those are good ideas, but I never consider towing. Picture instead, someone
who happened to own a few acres on the dead end of a very rural florida road
that is straight as an arrow. ;-)

Gerry

Awright.

There's more to aerodynamics than that covered by your philosophy.

Area and airfoil are not really the right starting place for a new
and novel configuration.


the dimensions of your wings...

First - learn about Reynolds number.
Very few of the published airfoils work well below about 3 meg RN.

What does that mean in regard to your choices?

Well, the two-foot chord wing is going to have to move pretty fast to make
3 meg RN.

The four-foot chord wing will have twice the RN from the start.


Richard

You will, with optimization of all the variables. be lucky to get 40%
of the lift/drag ratio of an equivalent conventional planform.

Can you elaborate? I don't see why this should be true.

Well, let's see. The back wing(s) operate in the downwash of the
forward wings, there's a hit there. The upper wings operate in a flow
field affected by the lower wings, there's a hit there. Twice as many
wingtip vortices, take a hit there, and at some angles of attack, the
aft wing(s) will be operating in the vortice of the front wing(s).


But the bigger problem will be control. Pitch stability, in and out of
ground effect, will be a formidable problem, as will stall
characteristics. Compromises needed to make the handling acceptable
may make the efficiency even worse.

Well, most tandem wing aircraft are designed to make normal stall
impossible. (the rutan designs for instance)

There is a price paid in efficiency, and in landing speed in making
this NECESSARY trait possible. It's necessary because a canard or
tandem wing design is very vulnerable to an un-recoverable deep stall.
The consequence is that you cannot optimize the angle of attack for
both wings simultaneously, and that the C ell Max of the combined
system is degraded, making the landing speed higher, or the wings
bigger (which will hurt efficiency AGAIN).

Pitch stability is a problem
that I thought had been pretty well handled by airfoil design in canard
aircraft years ago. My thoughts (I wouldn't call it a design) are simply
two sets of biplane wings mounted fore and aft. Biplane wings don't
normally present much of an efficiency problem except for the bracing which
isn't stricly necessary (The hyperbipe was a pretty efficent design)

Pretty efficient for a biplane, but nowhere near as efficient as a
conventional design.

I certainly agree that handling especially in the pitch axis is the major
challenge, but I don't see why it should present a much bigger problem than
the flying flea family of aircraft where it was eventually solved
satisfactorily.

Again, by limitations that hurt efficiency. And a good half-dozen
people died before the pitch stability issue was solved. That was
actually a problem at cruise/top speed.

The transition between operating in ground effect and out of it is
pretty tricky for a equal area tandem wing airplane. This was seen in
some of the first experimental Wing In Ground effect surface skimmers.
They had tremendous pitch stability (a problem if you're trying to
rotate) until they suddenly didn't, and they would pitch up quite
violently. That's one reason the Quickies have ANHEDRAL on the forward
wing, and Dihedral on the aft wing, as well as mounting the forward
wing lower than the aft wing. In this way, with a pitch up to rotate,
both wings come out of ground effect at much closer to the same
instant, without a sharp pitch divergence.

I agree with Ernst - a low aspect ratio delta/lifting body makes more
sense. Perhaps a 2 seat Facetmobile with the outer portions folding
inward like a Dyke Delta.

Perhaps, but it's been tried many times and with very limited success.

Various low aspect ratio designs have been flow since the twenties,
it's true. The Burnellis, the Spratt, the Fike designs. The Dyke Delta
is a low aspect double delta, with the main cabin airfoil shaped. But
true lifting bodies were basically unknown until the 1960's. John
McPhee wrote about one of them in "The Deltoid Pumpkin Seed". The the
Facetmobile is, IMHO, the most successful general aviaition true
lifting body design.

"cavelamb" wrote in message
k.net...
Awright.

There's more to aerodynamics than that covered by your philosophy.

Huh???


Area and airfoil are not really the right starting place for a new
and novel configuration.

Then where WOULD be the right starting place?



the dimensions of your wings...

First - learn about Reynolds number.
Okay

Very few of the published airfoils work well below about 3 meg RN.

What does that mean in regard to your choices?

Well, the two-foot chord wing is going to have to move pretty fast to make
3 meg RN.

How fast? None of these were really choices, just random numbers for
explanation. In other words, 4 10x1 wings = 40 sq ft. or 1 20x2 wing = 40
sq ft. The most important single factor in wing design appears to be square
feet. ??

The four-foot chord wing will have twice the RN from the start.
That's built into the RN equation. What's the relevance??

I have no argument here, I'm looking for info. So far, I've gotten some
pretty good references.

Gerry

"flybynightkarmarepair" wrote in message
oups.com...


You will, with optimization of all the variables. be lucky to get 40%
of the lift/drag ratio of an equivalent conventional planform.

Can you elaborate? I don't see why this should be true.

Well, let's see. The back wing(s) operate in the downwash of the
forward wings, there's a hit there.

That's not necessarily true, it depends on many additional factors. The
same could be said for the main sail on a sloop operating in the downwash of
the jib, but it works damned well.

The upper wings operate in a flow
field affected by the lower wings, there's a hit there.

Seems I read somewhere that as long as the gap is about 1.5 times the chord
that isn''t a factor?

Twice as many
wingtip vortices, take a hit there,

Maybe - I'm not sure about that one. There are certainly other
considerations.

and at some angles of attack, the
aft wing(s) will be operating in the vortice of the front wing(s).

That strikes me as the single most important problem with this
consideration.




But the bigger problem will be control. Pitch stability, in and out of
ground effect, will be a formidable problem, as will stall
characteristics.

See above.

Compromises needed to make the handling acceptable
may make the efficiency even worse.

Please elaborate.


Well, most tandem wing aircraft are designed to make normal stall
impossible. (the rutan designs for instance)

There is a price paid in efficiency, and in landing speed in making
this NECESSARY trait possible. It's necessary because a canard or
tandem wing design is very vulnerable to an un-recoverable deep stall.
The consequence is that you cannot optimize the angle of attack for
both wings simultaneously, and that the C ell Max of the combined
system is degraded, making the landing speed higher, or the wings
bigger (which will hurt efficiency AGAIN).

Generally, I agree. OTOH, all designs are compromises of some kind.


Pitch stability is a problem
that I thought had been pretty well handled by airfoil design in canard
aircraft years ago. My thoughts (I wouldn't call it a design) are simply
two sets of biplane wings mounted fore and aft. Biplane wings don't
normally present much of an efficiency problem except for the bracing
which
isn't stricly necessary (The hyperbipe was a pretty efficent design)

Pretty efficient for a biplane, but nowhere near as efficient as a
conventional design.

The published specs don't seem to agree with you there.


I certainly agree that handling especially in the pitch axis is the
major
challenge, but I don't see why it should present a much bigger problem
than
the flying flea family of aircraft where it was eventually solved
satisfactorily.

Again, by limitations that hurt efficiency. And a good half-dozen
people died before the pitch stability issue was solved. That was
actually a problem at cruise/top speed.

Sad, but many people died to learn what we now know about aeronautics.


The transition between operating in ground effect and out of it is
pretty tricky for a equal area tandem wing airplane. This was seen in
some of the first experimental Wing In Ground effect surface skimmers.
They had tremendous pitch stability (a problem if you're trying to
rotate) until they suddenly didn't, and they would pitch up quite
violently. That's one reason the Quickies have ANHEDRAL on the forward
wing, and Dihedral on the aft wing, as well as mounting the forward
wing lower than the aft wing. In this way, with a pitch up to rotate,
both wings come out of ground effect at much closer to the same
instant, without a sharp pitch divergence.

Interesting observation that I haven't come across previously.


I agree with Ernst - a low aspect ratio delta/lifting body makes more
sense. Perhaps a 2 seat Facetmobile with the outer portions folding
inward like a Dyke Delta.

Perhaps, but it's been tried many times and with very limited success.

Various low aspect ratio designs have been flow since the twenties,
it's true. The Burnellis, the Spratt, the Fike designs. The Dyke Delta
is a low aspect double delta, with the main cabin airfoil shaped. But
true lifting bodies were basically unknown until the 1960's. John
McPhee wrote about one of them in "The Deltoid Pumpkin Seed". The the
Facetmobile is, IMHO, the most successful general aviaition true
lifting body design.

I agree.
\

pTooner wrote:
Firstly, I am new here although I've been reading for a few days. For
anyone with more knowledge than I, I keep considering building a small 4
wing aircraft. Not stacked, but two up front and two in the rear. I have
read frequently of problems supposedly resulting from interference of the
airflow between wings, but I can't seem to find anything very specific. I'm
fairly confident that interference between the front wings (or rear) can be
minimized by reasonable spacing and differing dihedral. I'm not sure what
the effect of the airflow coming off the front wings will have on the rear
set. I don't know whether I could remove most of the problem by having one
set considerably higher (how much?) than the other set or if it is
reasonable to have them on more or less the same height. The reason for
the concept is trying to get a wingspan small enough to fit into a normal
garage and conceivably take off and land from streets and highways. I
visualise something in a two place plane that would fall into something of
the appeal category of a motorcycle or small sports car. Any thoughts would
be appreciated.

Gerry
Gerry! Look up the Stinton reference I gave you, read it over a bunch
of times 'til you start getting an idea of how spacing and stagger
would affect the wing placement. Then keep in mind, this is
Experimental aviation! Try your idea in a large model; see how that
works. But don't let the nay-sayers keep you from experimenting.
There's no progress in building the same thing over and over. Your
creation doesn't have to be the most efficient thing out there. All
designs call for some compromises! Good experimenting!

"ELIPPSE" wrote in message
ups.com...

pTooner wrote:
Firstly, I am new here although I've been reading for a few days. For
anyone with more knowledge than I, I keep considering building a small 4
wing aircraft. Not stacked, but two up front and two in the rear. I
have
read frequently of problems supposedly resulting from interference of the
airflow between wings, but I can't seem to find anything very specific.
I'm
fairly confident that interference between the front wings (or rear) can
be
minimized by reasonable spacing and differing dihedral. I'm not sure
what
the effect of the airflow coming off the front wings will have on the
rear
set. I don't know whether I could remove most of the problem by having
one
set considerably higher (how much?) than the other set or if it is
reasonable to have them on more or less the same height. The reason for
the concept is trying to get a wingspan small enough to fit into a normal
garage and conceivably take off and land from streets and highways. I
visualise something in a two place plane that would fall into something
of
the appeal category of a motorcycle or small sports car. Any thoughts
would
be appreciated.

Gerry
Gerry! Look up the Stinton reference I gave you, read it over a bunch
of times 'til you start getting an idea of how spacing and stagger
would affect the wing placement. Then keep in mind, this is
Experimental aviation! Try your idea in a large model; see how that
works. But don't let the nay-sayers keep you from experimenting.
There's no progress in building the same thing over and over. Your
creation doesn't have to be the most efficient thing out there. All
designs call for some compromises! Good experimenting!


Thanks, I haven't located that book yet, but I will. And I will on the
experimenting too.
Gerry

pTooner wrote:
"Ernest Christley" wrote in message
...

pTooner wrote:

Firstly, I am new here although I've been reading for a few days. For
anyone with more knowledge than I, I keep considering building a small 4
wing aircraft. Not stacked, but two up front and two in the rear. I
have read frequently of problems supposedly resulting from interference
of the airflow between wings, but I can't seem to find anything very
specific. I'm fairly confident that interference between the front wings
(or rear) can be minimized by reasonable spacing and differing dihedral.
I'm not sure what the effect of the airflow coming off the front wings
will have on the rear set. I don't know whether I could remove most of
the problem by having one set considerably higher (how much?) than the
other set or if it is reasonable to have them on more or less the same
height. The reason for the concept is trying to get a wingspan small
enough to fit into a normal garage and conceivably take off and land from
streets and highways. I visualise something in a two place plane that
would fall into something of the appeal category of a motorcycle or small
sports car. Any thoughts would be appreciated.

Gerry

Go from 4 to 1.
The Dyke Delta JD-2 will fold up to fit in a one car garage. And it is
designed to be towed behind a car on it's own wheels; though, some have
had issues with getting trailer tags to do it legally.


I'm familiar with the plane, and it is reputed to be very difficult and
lengthy to build.

Gerry



Aren't they all? 4 years and running here. Almost ready to close up
the skins.

--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."

flybynightkarmarepair wrote:

Various low aspect ratio designs have been flow since the twenties,
it's true. The Burnellis, the Spratt, the Fike designs. The Dyke Delta
is a low aspect double delta, with the main cabin airfoil shaped. But
true lifting bodies were basically unknown until the 1960's. John
McPhee wrote about one of them in "The Deltoid Pumpkin Seed". The the
Facetmobile is, IMHO, the most successful general aviaition true
lifting body design.


I've heard this stated several times, and always found it a bit strange.

What is it that makes the Facetmobile so successful? A single prototype
that crashed, vs the Dyke Delta that has had dozens flying and about
half a dozen currently airworthy. Why is the Dyke Delta not considered
a lifting body design? The fuselage provides the majority of the lift
at cruise, according to John Dyke and verified in XPlane (if that can be
considered any sort of verification).


--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."