questions on multi-wing planforms

I don't want to be too negative but could I suggest that if you are
struggling with these relatively fundamental issues that such a project
might be a little beyond you. These are not issues for someone without
aerodynamic knowledge and what you describe is certainly not a design that
is likely to be successful for a first time amateur designer.

However let me give you a little insight into how to tackle the problem.

Yes you could develop your own theory based on biplane type theory (i.e. a
bound vortex respresenting each wing) and use this to predict the flow
field. Any number of aerodynamics texts will give you the basic theory but
you will need to extend that for your application.

However I wouldn't bother with this with the computational tools available.

Just get a Vortex lattice code such as the NASA VLM code or Drela's AVL (or
better still a panel code such as PMARC or Peter Garrisons CMARC) and use
this. Such an approach is far more accurate and someone who knows what they
were doing would have a good feel for the issues and probably fix most of
the major problems in less than a days work.

However please be careful there are a lot of traps for new players even with
these sorts of tools. Don't treat programs like this as a balck box .. try
to understand what is going on inside them and what the limitations are.

Once you have done your computer analysis build a large scale model and go
and fly it before you waste time building the full size airplane.




"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

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

John Roncz called a 3 surface airplane he participated in the design of
"the aerodynamicists full employment act"!

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

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.

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.

But have you looked at all the wires around most roads? Not an area I
would want to use for landing and takeoff.

"flybynightkarmarepair" wrote in message
oups.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

John Roncz called a 3 surface airplane he participated in the design of
"the aerodynamicists full employment act"!

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.

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) 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) 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.

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. I
know of NO attempt to build the 4 wing system that I envision. That seems
strange when you consider that about every imaginable combination has been
tried at one time or another. Didn't someone finally build an operable
ornithopter?


But have you looked at all the wires around most roads? Not an area I
would want to use for landing and takeoff.

Good point, but they aren't everywhere. ;-)

Gerry

You might look up all the varieties of "Flying Fleas" and the Q-200 kits for
small, multiwing aircraft.
"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

pTooner wrote:
...

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

This sounds like sort of a biplane version of the dragonfly.

...
Perhaps, but it's been tried many times and with very limited success. I
know of NO attempt to build the 4 wing system that I envision. That seems
strange when you consider that about every imaginable combination has been
tried at one time or another.

Everytime I've had an idea for some way to build an airplane that I
had never seen before it took only a few minutes on the web to find
examples of the concpet that had already been built and flown.

So I daresay if you have a novel idea that has never been flown
there is probably a very good reason why it hasn't.

If you are merely interested in being able to get the plane
easiliy into a garage, there are many folding wing designs
to choose from or adapt. In addition to the Flying Flea,
the kitfox is another.

Regardless, good luck.

Didn't someone finally build an operable
ornithopter?


There have been many small (e.g. bird-sized) ones flown. You
can buy a plastic toy ornithopter for under $50.00 and there are
plans available on the web to build a rubber-bad powered version.


But have you looked at all the wires around most roads? Not an area I
would want to use for landing and takeoff.

Good point, but they aren't everywhere. ;-)


You have legal restrictions to be concerned with on public roads,
but there are private roads.

"Robert Little" wrote in message
...
You might look up all the varieties of "Flying Fleas" and the Q-200 kits
for small, multiwing aircraft.

I have done so, thanks.
Gerry
"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

Even if everything works just the way you dream it will how will you
see where you're going?

"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

"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

"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

pTooner wrote:
"ELIPPSE" wrote in message
oups.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
Look up "Monk Factor"!

In quotes that term doesn't bring any reponse in google. Without quotes it
brings an unmanageable amount but doesn't appear to have anything to do with
aerodynamics. Can you elaborate a bit?
Gerry
Hi, Gerry! Munk factor has to do with the effect multiple wing
placement has on the induced drag of tandem wings and biplane wings.
Darrol Stinton in his book "The Design Of The Aeroplane" has an
excellent, easy to understand section on it, with lots of graphs!

"pTooner" wrote:
My basic concept/question is like this. Assuming
optimum airfoil in each case which may well be different; I could
build a 20ft span 4 ft chord wing for 80sqft or two 20span 2 ft chord
or 4 10ft span 2 foot chord and they all equal the same area. What
would be their relative lift and drag numbers? (probably pretty
close) BUT would they have strange characteristics at odd angles of
attack? (That is a semi-rhetorical question)

Since a higher aspect ratio wing generally has a better lift/drag ratio,
increasing the effective wingspan would normally be a good thing - assuming
all other variables remain constant. But clearly wing gap interference
inserts an additional variable.

Another thing you might want to look into is the "multiplane" (I couldn't
remember the proper name for the concept in my first reply, otherwise I'd
have mentioned it earlier). The concept dates as far back as 1893! Horatio
Phillips designed (and did some short test flights) of what can only be
described as "Venetian blinds" wings. Here are some web sites, with some
background info and photos (some of the photos can be clicked on to get
larger images):

http://www.centennialofflight.gov/es...lips/Tech4.htm
http://www.ctie.monash.edu.au/hargrave/phillips.html

Another nice photo of Phillips multiplane:
http://invention.psychology.msstate....ultiplane.jpeg

Lastly, you should consider getting a copy of "Simplified Aircraft Design
for Homebuilders" by Dan Raymer. (He has his own website:
http://www.aircraftdesign.com/)