Fast glass biplanes

Apart from the Quickie group of planes why aren't there more fast
biplanes? The quickies aren't exactly biplanes I know. It would
appear that 2 short wings can be built lighter than one long one since
the moment arm is half as long for the shorter wing pair. No struts
used because of drag, just short cantilever wings. You'd have a more
compact airplane that way with less weight that had the same drag as
an equal wing area monoplane.

Jay wrote:

It would appear that 2 short wings can be built lighter
than one long one since the moment arm is half as long
for the shorter wing pair.

There are a lot of benefits to higher aspect ratio
wings that far outweigh the structural advantage of low AR
wings. Reduced drag is but one. Ever wonder why you
don't see any biplane sailplanes?

You'd have a more compact airplane that way with less
weight that had the same drag as an equal wing area monoplane.

'Fast' and 'biplane' just don't go together. Fast "biplanes"(*)
like the Quickie, Mong, etc. do not get their speed and low
drag from the fact that they have two wings, but rather in
spite of it. Induced drag decreases as aspect ratio increases,
so a longer span wing of equivalent area and wing section will
have less induced drag than two wings with a lower AR. Two wings
will also have at least double the interference drag of one,
regardless of whether or not they use interplane struts.

Dave 'dragster' Hyde


(*) Jay has already stated that he knows the
Quickie is not a true biplane. The same principles apply, however.

On 15 Nov 2003 09:17:59 -0800, (Jay) wrote:

Apart from the Quickie group of planes why aren't there more fast
biplanes? The quickies aren't exactly biplanes I know. It would
appear that 2 short wings can be built lighter than one long one since
the moment arm is half as long for the shorter wing pair. No struts
used because of drag, just short cantilever wings. You'd have a more
compact airplane that way with less weight that had the same drag as
an equal wing area monoplane.


I read once that a computer program exploring optimum biplane and
canard setups popped out the optimum setup as one where the forward
canard was 5 times the span of the rear one with the cg at 25% of the
chord of the forward canard.
I accept that that maybe an urban legend but put with the success that
mike arnold experienced with his AR5 you might just have an answer.

as well have a look at formula 1 aircraft designs. they are about as
competitive as you can get and on basically the same engine they are
now 100mph faster than 50 years ago.
havent seen a canard or biplane last very long among them.

Stealth Pilot

You're missing the point of the modern canard. They were developed to be a
stall/spin-proof alternitave to the conventional wing-tail layout. An
example: two friends built glass airplanes, one a Glasair with a 150 hp Lyc
and the other a Long-EZ with a 150 hp Lyc, both with fixed-pitch wood
props.. Flat out, the Glasair was faster, but only slightly -- 215 vs. 210
mph. Seems to me to be a small price to pay for an aircraft that won't
stall or spin. And if the engine quits, you want to be in the Long-EZ, not
the Glasair -- it glides much better.

Fred in Florida

"Stealth Pilot" wrote in message
news
On 15 Nov 2003 09:17:59 -0800, (Jay) wrote:

Apart from the Quickie group of planes why aren't there more fast
biplanes? The quickies aren't exactly biplanes I know. It would
appear that 2 short wings can be built lighter than one long one since
the moment arm is half as long for the shorter wing pair. No struts
used because of drag, just short cantilever wings. You'd have a more
compact airplane that way with less weight that had the same drag as
an equal wing area monoplane.


I read once that a computer program exploring optimum biplane and
canard setups popped out the optimum setup as one where the forward
canard was 5 times the span of the rear one with the cg at 25% of the
chord of the forward canard.
I accept that that maybe an urban legend but put with the success that
mike arnold experienced with his AR5 you might just have an answer.

as well have a look at formula 1 aircraft designs. they are about as
competitive as you can get and on basically the same engine they are
now 100mph faster than 50 years ago.
havent seen a canard or biplane last very long among them.

Stealth Pilot

On Sun, 16 Nov 2003 13:07:23 +0000, karel adams wrote:


"Fred in Florida" schreef in bericht
om...
You're missing the point of the modern canard. They were developed to
be a
stall/spin-proof alternitave to the conventional wing-tail layout. An
example: two friends built glass airplanes, one a Glasair with a 150
hp Lyc
and the other a Long-EZ with a 150 hp Lyc, both with fixed-pitch wood
props.. Flat out, the Glasair was faster, but only slightly -- 215
vs. 210
mph.

Even this surprises me, I had been led to understand that the canard
design is inherently more efficient because the canard wing, besides its
basic function as a stabiliser, also helps to generate lift; wheras the
stabiliser in a conventional design must push down. So that for every
100 lbs of weight, the main wing in a conventional design carries 110
lbs, in a canard only 90.

Have I misunderstood?
Or have the Glasir designers found a very clever trick?

Thanks for explaining!
KA

(rest snipped)

With a canard, you need to have the design details and CG such that the
main wing can never, ever stall. If you screw up and have a design such
that the main wing can stall, the aircraft will pitch up at the stall, and
will almost certainly come down in an unrecoverable deep stall. The
original Velocity design had this problem, but they made some design
changes to fix it. But there was a fatal Velocity deep stall accident
recently, and the working theory seems to be that the builder did not
incorporate the design updates.

If you need to be sure the main wing never, ever gets close to the stall,
that means that you cannot use all the lift that the wing is capable of
producing. So, if you have two aircraft that weigh the same - a
"conventional aircraft" and a canard aircraft, and you want the same stall
speed, the canard aircraft will need a much larger wing. That larger wing
has more drag, so you need a very clean design in all other respects in
order to get the desired performance.

--
Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://go.phpwebhosting.com/~khorton/rv8/
e-mail: khorton02(_at_)rogers(_dot_)com

And if the engine quits, you want to be in the Long-EZ, not
the Glasair -- it glides much better.

That's a questionable statement!!

Compare the following for survivability in an accident:
* slower touchdown speed
* deformation of the structure to absorb energy
* lack of intrusions into the crew area (survivable space)

Looks to me like the Glasair would be much more survivable... not that
I'm personally interested in running the experiments

Ed "I'm supposed to teach a class on this stuff next term" Wischmeyer

The only one I know of is the Lionheart - Semi Replica of Beech Stagger
Wing.

Fast, caries high load, round engine.


"Jay" wrote in message
om...
Apart from the Quickie group of planes why aren't there more fast
biplanes? The quickies aren't exactly biplanes I know. It would
appear that 2 short wings can be built lighter than one long one since
the moment arm is half as long for the shorter wing pair. No struts
used because of drag, just short cantilever wings. You'd have a more
compact airplane that way with less weight that had the same drag as
an equal wing area monoplane.

My take on this is that while it is true that both surfaces on a canard or
tandem wing design are lifitng surfaces, the canard cannot use all of the
available lift from the main wing - if you want the stall protection - and thus
the main wing needs to be made much larger than needed for cruising flight if
one is to expect a reasonable landing speed.

In the case of my Quickie the Eppler main wing stalls at a fairly high angle of
attack but it's peak Cl is not that good. The result is that during landing
the canard is doing more than it's share of the work. Some Quickies (all
Quickies are single seat - the 2 seaters are Q-2/200's) land as fast as the
much maligned BD-5.

Another factor to consider is just because the little wing is in the back it
must not necessarily be providing down force. It can also lift and still be
part of a pitch stable plane.


props.. Flat out, the Glasair was faster, but only slightly -- 215
vs. 210
mph.

Even this surprises me, I had been led to understand
that the canard design is inherently more efficient
because the canard wing, besides its basic function
as a stabiliser, also helps to generate lift; wheras
the stabiliser in a conventional design must push down.
So that for every 100 lbs of weight, the main wing in
a conventional design carries 110 lbs, in a canard only 90.

On Sun, 16 Nov 2003 15:57:45 +0800, Stealth Pilot
wrote:

I read once that a computer program exploring optimum biplane and
canard setups popped out the optimum setup as one where the forward
canard was 5 times the span of the rear one with the cg at 25% of the
chord of the forward canard.

Actually, that was contained in an article called "Canard Canard" in
AEROSPACE AMERICA magazine, back in the early '90s. I've posted about it
here in RAH several times, that's probably where you remember it from.
Used to have the article rattling around the office, somewhere.

Canard designs are just a different approach to the compromises necessary
for aircraft development. What they gain in eliminating the horizontal
stabilizer downforce, they lose in other areas.

Wanttaja Ron

I'm not enough of an aviation know it all/historian so the only example I can
site off the top of my head is the Quickie, Q-2/200, Dragonfly, Flying Flea
family.

While the "little wing in the rear" isn't so little the physics are the same.
As long as the moment of the 2 "wings" move aft with an increasing angle of
attack, and forward with decreasing pitch the plane will be pitch stable at one
particular speed. This can be done simply by having the tail provide a down
force, but by properly selecting the airfoils so that the lift of the rear wing
increases faster than the front with increasing angle of attack you get the
same result.

I'm not a professional aerodynamisist, maybe even a poor amateur, and not a
very good teacher - so if your just learning about all of this in your PPL
ground school it might be a bit simpler to forget all about anything but
"conventional" airplanes for a while...........or find someone that can explain
it better than me.......which shouldn't be hard.

If you really want some interesting pitch stability mental exercise think about
a flying wing with negative sweep..........


Well well I am learning again.
My PPL ground school certainly disagrees with you!
Do you have any example of such a design?

TIA,
Karel