questions on multi-wing planforms

"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

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.

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.

"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.
\

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)."

Ernest Christley wrote:
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 an admittedly arbitrary distinction. The cabin on a Dyke Delta
is, again, IMHO, not well integrated into the fuselage/wing - MY
definition of a lifting body is that it's ALL an integrated whole.
Compare these pictures of a Dyke Delta:
http://www.pivot.net/~psi/philt2.htm
and the Facetmobile:
http://members.aol.com/slicklynne/FMX4IF1.JPG
The other piece of my arbitrary distinction is that the Dyke Delta has
discernable wings, while the Facetmobile doesn't.

I think the Dyke Delta is a great airplane; one I've loved since I read
about it in Air Progress probably nearly 40 years ago.

"flybynightkarmarepair" wrote

This is an admittedly arbitrary distinction. The cabin on a Dyke Delta
is, again, IMHO, not well integrated into the fuselage/wing - MY
definition of a lifting body is that it's ALL an integrated whole.

So, in your opinion, the Hyper Bipe is not a lifting body? It provides
substantial lift, therefore, it is a lifting body, in everyone's view,
except yours.

I submit that you are incorrect.
--
Jim in NC

Morgans wrote:

"flybynightkarmarepair" wrote


This is an admittedly arbitrary distinction. The cabin on a Dyke Delta
is, again, IMHO, not well integrated into the fuselage/wing - MY
definition of a lifting body is that it's ALL an integrated whole.


So, in your opinion, the Hyper Bipe is not a lifting body? It provides
substantial lift, therefore, it is a lifting body, in everyone's view,
except yours.

I submit that you are incorrect.

Well, so does the Tailwind.

But the trick is, alla these have - well - wings!