Fast glass biplanes

In article ,
Jay wrote:
Hey don't give up Dave, nobody said it would be easy. You haven't
convinced me not to run the model. But you have pointed out 2 things
I will look at more carefully:

1) Will the root/tip losses from 2 wings eat up any benefit from the
shorter/lighter spans? Are there tip treatments that diminish this?

the big killer is the interaction in airflow pattern across the two
surfaces.

putting a 2nd surface "above" a lifting surface _decreases_ the available
lift from that first surface. you have a 'compression' effect on the
'ram air' passing between the two surfaces, due to the constriction from
the _reduction_ in cross-section of the space between the two surfaces,
as you proceed from leading edge of the lifting surface back to the point
of maximum rise in that surface.

To minimize these kinds of effects, the space between the surfaces has
to be relatively -large-, the velocity of the air _comparatively_ slow,
*and* you need to let that 'built-up' ram-air effect bleed off in the
only direction it can go -- i.e., _sideways_, towards the tips of the
wing(s).

2) What wing configuration can be used that minimizes mutual
interference between the 2 lifting surfaces.

One simple answer to -that- one is 'obvious' -- place them infinitely far
apart. grin

(Robert Bonomi) wrote:

In article , Dave Hyde wrote:
Jay wrote:

Okay, thanks for all that, I think you're missing some parentheses in
there because I'm getting a quad decker formula.

The formula is correct as written.

So with this theoretical wing of aspect approaching zero,
2 non-interfering wings of half span, would be essentially the
same lift and drag as one.

I think you have a fundamental misunderstanding of the basics here.
An infinte (span) wing has an aspect ratio of INFINITY, not zero.
LARGER aspect ratio is less drag.
Again, to make a successful break from the mouse-maze, you've
either got to have a sound grasp of the fundamentals or be
very lucky. Counting on luck does not instill confidence
(but sometimes produces interesting threads).

Most if not all of those X planes were R&D payed for by the you and
me, the tax payers of America. Its extremely rare for a large company
to take a "flyer" with their own money and reach very far forward.

Who pays is irrelevant. There have been and will continue to
be radical departures from the 'box' even by giants in the aerospace
industry. The simple fact that you are not aware of them does not
mean that they do not exist.

Dave 'to infinity...and beyond' Hyde

AHA! *THERE's* the proper explanation.

Twin wings, with aleph-sub-one aspect ratio _should_ out-perform a
(merely) 'infinite' AR wing. *snicker* chortle =+GUFFAW+=

You laugh, but there are planes of aleph-sub-two aspect ratio. At
least I assume that is what you need a complex rating forg.
--
Alex
Make the obvious change in the return address to reply by email.

alexy wrote:

You laugh, but there are planes of aleph-sub-two aspect ratio. At
least I assume that is what you need a complex rating forg.

And when Chuck Slusarczyk flies them as copilot they're
unstable.

Dave 'humor from the geek farm' Hyde

Aspect ratio on a wing without taper IS wingspan divided
by the chord. But few wings are strictly a rectangle. Many
have wingtips instead of being squared off. Many have
some taper, and the area covered by the fuselage is not
an extension of the taper, but figured
by straight lines connecting the left and right leading edge
points at the root and left and right trailing edge points at
the root. Not to mention airplanes with taper breaks and/or
other non-straight leading or trailing edges.

So, the easier way is to use the area and the square of the span.

Aspect Ratio (AR) is the square of the wingspan divided by
the area of the wing.

Now - to clarify the misreading of the note:

basic middle school math:
the upward arrow means to raise to the power

aero = a kindergarten form of area
also called fumble fingered the keys


Aspect Ratio is very much a part of the discussion. The biplane
has lots of area and not much span. Low aspect ratio. Inefficient.

Make the wing chord real skinny and Reynold's number comes
into play. But that's another story.





In article ,
(Jay) wrote:
Thanks Alexy,

I wasn't sure what the convention was in aero work for defining
"aspect", it doesn't really matter as long as everybody agrees on the
same definition! So I just took David's definition and went from
there.

Then in his next expresion said "span^2/aero", so I figured "AERO"
meant something that he hadn't defined, but I should have implicitly
known, and figured at this point it wasn't crucial to the discussion.

But this is the reason why I was trying to discuss relationships
before we got into botched algebra. I'm seem to be continually making
those kinds of errors so I end up doing everything 2 ways just to make
sure.


alexy wrote in message
. ..
Dave Hyde wrote:

I think you have a fundamental misunderstanding of the basics here.
An infinte (span) wing has an aspect ratio of INFINITY, not zero.
LARGER aspect ratio is less drag.
Dave, to be fair to Jay, you did type

:The _definition_ of aspect ratio is chord/span

Of course, you immediately contradicted that by typing

r span^2/aero (they're equivalent)

which should have clued anyone in that you had inverted the first
expression.

alexy wrote:
Ben Sego wrote:




But learn about scale effects, or the model work isn't useful.


Alternate responses:
1) Doh, of course. I forgot about that.
2) Well of course. I thought that was obvious.
3) Why did you assume that by RC model I meant one at other than 1:1
scale?
4) Yeah, but he was talking about wings with infinite span, so I
figured scaling didn't apply.

Honesty compels me to #1. Good catch.

Three is really good. But I think #4 is best.

B.S.

In article . net, slomo says...

Make the wing chord real skinny and Reynold's number comes
into play. But that's another story.

Boy now you did it LOL!! I was wondering when Reynolds number would be
brought up and now they are. Let's see, I bet if we build an infinate span wing
biplane flying at infinatly high reynolds we can beat the monoplane flying in
the real world. :-)

Back to lurk mode .

Chuck (that ain't syrup,it's low reynolds air) S

In article , Dave Hyde says...

alexy wrote:

You laugh, but there are planes of aleph-sub-two aspect ratio. At
least I assume that is what you need a complex rating forg.

And when Chuck Slusarczyk flies them as copilot they're
unstable.

Hell, they wuz unstable before I got in!! It ain't the instability that
bothers me, it don't hurt till the crash ......and BOY that sometimes
hurts.

Chuck ( I built a biplane glider for Junkyard wars) S


Dave 'humor from the geek farm' Hyde

Robert Bonomi wrote:

To minimize these kinds of effects, the space between the surfaces has
to be relatively -large-, the velocity of the air _comparatively_ slow,
*and* you need to let that 'built-up' ram-air effect bleed off in the
only direction it can go -- i.e., _sideways_, towards the tips of the
wing(s).


So, are we looking for a delta wing bi-plane?

--
http://www.ernest.isa-geek.org/
"Ignorance is mankinds normal state,
alleviated by information and experience."
Veeduber

Dave Hyde wrote:
snip

Biplanes are a simple,
but inefficient, way of getting more lift from wing area
when an increase in span is not feasible. The are not, nor
in general are they intended to be, "low drag."


You mentioned the interference drag, so how far do wings
need to be vertically separated for a given airfoil
and stagger for this effect to be negligable?


*negligible?* Some *large* fraction of the span. At a minimum.
snip

Dave 'usenet wind tunnel' Hyde


Here's some pretty pictures of biplane wing pressure interaction from
the CFD tool that Peter Garrison sells:

http://www.melmoth2.com/texts/CFD.htm

B.S.

On Wed, 19 Nov 2003 01:09:28 -0600, - Barnyard BOb - wrote:

Barnyard BOb - if it's a duck, it's a duck

....and if it tries to fly upside down, it quacks up....

Ron "Orville told Wilbur that one" Wanttaja