questions on multi-wing planforms

"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

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:
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.

Theory of biplanes might provide the theoretical basis. My copy of
"Theoretical Aerodynamics" by L. M. Milne-Thomson discusses wing
interference between the wings of biplanes in chapter 8. (It's a Dover
publication, so it is still in print and inexpensive.)

Also, try a Google search on this set of search words (with or without
the search word "stagger"):
aerodynamic gap biplanes

I'm fairly confident that interference
between the front wings (or rear) can be minimized by reasonable
spacing and differing dihedral.

Staggering the wings tends to help reduce interference also.

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.

I suspect having one set high that the other would equivalent to a large
staggering angle.

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.

If you are not already familiar with it, you should browse this site,
which include planes that attempt to satisfy some of your requirements
(the Wernicke Aircar uses low aspect ratio wings to try to meet some of
your requirements):
http://www.roadabletimes.com/

All very helpful and interesting stuff. Thanks a lot.
Gerry
"Jim Logajan" 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.

Theory of biplanes might provide the theoretical basis. My copy of
"Theoretical Aerodynamics" by L. M. Milne-Thomson discusses wing
interference between the wings of biplanes in chapter 8. (It's a Dover
publication, so it is still in print and inexpensive.)

Also, try a Google search on this set of search words (with or without
the search word "stagger"):
aerodynamic gap biplanes

I'm fairly confident that interference
between the front wings (or rear) can be minimized by reasonable
spacing and differing dihedral.

Staggering the wings tends to help reduce interference also.

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.

I suspect having one set high that the other would equivalent to a large
staggering angle.

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.

If you are not already familiar with it, you should browse this site,
which include planes that attempt to satisfy some of your requirements
(the Wernicke Aircar uses low aspect ratio wings to try to meet some of
your requirements):
http://www.roadabletimes.com/

"Jim Logajan" 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.

Theory of biplanes might provide the theoretical basis. My copy of
"Theoretical Aerodynamics" by L. M. Milne-Thomson discusses wing
interference between the wings of biplanes in chapter 8. (It's a Dover
publication, so it is still in print and inexpensive.)

Also, try a Google search on this set of search words (with or without
the search word "stagger"):
aerodynamic gap biplanes

I'm fairly confident that interference
between the front wings (or rear) can be minimized by reasonable
spacing and differing dihedral.

Staggering the wings tends to help reduce interference also.

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.

I suspect having one set high that the other would equivalent to a large
staggering angle.

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.

If you are not already familiar with it, you should browse this site,
which include planes that attempt to satisfy some of your requirements
(the Wernicke Aircar uses low aspect ratio wings to try to meet some of
your requirements):
http://www.roadabletimes.com/

I am getting lots of good info from the sources you recommend and I'll try
the book store tomorrow for that book. If they don't have it I'll go to
Amazon. 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)

Gerry

"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/)

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

"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

Gerry and all,

Been following this most interesting conversation on aircraft design.
I would just point out some issues that one is to consider when
endeavouring to devise his own desin.

Then where WOULD be the right starting place?


This is the most important point. It is unwise to start thinking of
SOLUTIONS ( number of wings, biplane, delta, tandem wings...) before
posing the PROBLEM, and establishing what the aircraft will be required
to do.

I understand that this particular airplane should be small, light, and
able to take off from an unprepared stretch of private road. And it
should be storable in a garage.

There are several designs (some of them out of the US) that fulfill
these requirements, without resorting to exotic or complicated technical
solutions. And yet have outstanding handling qualities, payload and
performance on a reasonable power.

The MCR 01 two seater is one of them :
http://www.avnet.co.uk/lts/pages/mcr.htm


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.

The MCR 01 has a two foot chord wing, and the four seater we built has a
3 foot chord.


Concerning the Delta Dyke, one of my buddy owns one, and it is certainly
not an answer to the original poster's requirements. On the contrary,
it is a dog in flight, and very tricky. Deltas are definitely not a
corrrect solution to any slow airplane.

Regards,
Gilles Thesee
Grenoble, France
http://contrails.free.fr

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