Bi-wing glider

A thought came to me the other day...

Now, I have never seen a bi-wing glider, but was thinking,
could a bi-wing glider of, say 15m wingspan, effectively
have 30m performace?

This is probably a stupid uneducated question, and
I would imagine that it hasnt been done because it
wouldnt work! But its certainly something I am interested
in.

Think of it...a bi-wing ETA giving a total of 60m performance!


JR

The main idea of long wings is to reduce the relative part of the wingtip
vortexes in the total amount of the drag.
Having 4 vortexes instead of 2 certainly doesn't help.


"Jono Richards" wrote in
message ...
A thought came to me the other day...

Now, I have never seen a bi-wing glider, but was thinking,
could a bi-wing glider of, say 15m wingspan, effectively
have 30m performace?

This is probably a stupid uneducated question, and
I would imagine that it hasnt been done because it
wouldnt work! But its certainly something I am interested
in.

Think of it...a bi-wing ETA giving a total of 60m performance!


JR

Jono Richards wrote:
A thought came to me the other day...

Now, I have never seen a bi-wing glider, but was thinking,
could a bi-wing glider of, say 15m wingspan, effectively
have 30m performace?

This is probably a stupid uneducated question, and
I would imagine that it hasnt been done because it
wouldnt work! But its certainly something I am interested
in.

Short answer: no.

The F1H competition model glider class has a maximum total *projected*
wing area limit, so some years back an ingenious chap built a bi-plane
version with no stagger so the projected area was the same as for a
monoplane but with halved wing loading. He omitted interplane struts to
minimize drag, but the model flew better with one wing removed.

The reason was that you get a lot of interference drag between the
wings. His interplane spacing was about 1.5 wing chords. Theoretical
calculations later showed that he should have used a spacing of at least
5 chords to avoid interference gap.

A sailplane with a 0.7m average chord would need an interplane gap of
3.5m and you'd still have a lot of drag from interplane struts. You'd
need step-ladders or a fork lift to rig it.

However, it would win the Ugly Trophy hands down.

--
martin@ | Martin Gregorie
gregorie. |
org | Zappa fan & glider pilot

"I have never seen a bi-wing glider"

Orville and Wilbur used to fly them.

Colin

At 14:12 21 February 2006, Colin Lamb wrote:
'I have never seen a bi-wing glider'

Orville and Wilbur used to fly them.

Colin


Colin,

Good point hadnt thought of that! Were those not kites,
rather than gliders? Or maybe I should read my history
books again...

Right so there is no benefit in havin two wings than
one? even if staggered to reduce the interference from
each?

As regards to using a fork lift to rig, no i am sure
it would be far from practical, but then again, what
would some people do in the strive for performance...!?

JR

As Martin said, "interference drag" between the two wings would be the main
culprit. High pressure under the upper wing migrating to the low pressure
area above the lower wing. Some biplane designs try to counter this with
more spacing between the wings, or more off-set (think Beech Staggerwing).

Early aircraft design embraced multiple wings partly because the box
structure was easy to make strong using external wires and struts, the
additional drag wasn't such a big deal, as they didn't fly all that fast.

bumper


"Jono Richards" wrote in
message ...
A thought came to me the other day...

Now, I have never seen a bi-wing glider, but was thinking,
could a bi-wing glider of, say 15m wingspan, effectively
have 30m performace?

This is probably a stupid uneducated question, and
I would imagine that it hasnt been done because it
wouldnt work! But its certainly something I am interested
in.

Think of it...a bi-wing ETA giving a total of 60m performance!


JR

"Jono Richards" wrote in
message ...
At 14:12 21 February 2006, Colin Lamb wrote:
'I have never seen a bi-wing glider'

Orville and Wilbur used to fly them.

Colin


Colin,

Good point hadnt thought of that! Were those not kites,
rather than gliders? Or maybe I should read my history
books again...

Right so there is no benefit in havin two wings than
one? even if staggered to reduce the interference from
each?

As regards to using a fork lift to rig, no i am sure
it would be far from practical, but then again, what
would some people do in the strive for performance...!?

JR

You probably should go back and read your history again.
The Wright's 1902 glider is probably the most important aircraft in the
history of aviation.
It's the aircraft all their patents were based on.

Tim Ward

Ok, what if one of the wings is a canard? If the elevator pushes down to
support the nose, and a canard lifts, doesn't that make a canard more
efficient?

Al


"Bert Willing" wrote in message
...
The main idea of long wings is to reduce the relative part of the wingtip
vortexes in the total amount of the drag.
Having 4 vortexes instead of 2 certainly doesn't help.


"Jono Richards" wrote in
message ...
A thought came to me the other day...

Now, I have never seen a bi-wing glider, but was thinking,
could a bi-wing glider of, say 15m wingspan, effectively
have 30m performace?

This is probably a stupid uneducated question, and
I would imagine that it hasnt been done because it
wouldnt work! But its certainly something I am interested
in.

Think of it...a bi-wing ETA giving a total of 60m performance!


JR

Ok, what if one of the wings is a canard? If the elevator pushes down to
support the nose, and a canard lifts, doesn't that make a canard more
efficient?

No. Take a look at the success of Rutan's Solitaire.

The disadvantages with a canard or a tandem wing plane is that it is
hard to use flaps, and to keep the plane pitch stable you end up with a
plane that won't develop the same maximum total lift coefficient as a
"normal" plane because you can never use the aft wing to it's full
potential. This means that you end up having a higher minimum speed
for a given wing area or need more wing for a given minimum speed.
What all this means is that the speed range for efficient operation
will be less than that of a comparable "normal" plane.

You can tune the plane to be efficient at one speed by matching the
airfoils and relative areas and this is how some of the canard
homebuilts manage to show such good cruise performance. But they all
suffer from high landing speeds.

About the only way I see to improve on the standard glider - might - be
to develop a flying wing with some kind of weight shift to increase
it's speed range.

The canard/tandem wing planform does have some advantages for powered
planes but even there I've decided that a negative stagger biplane with
a conventional empenage (Durand Mk V is an example) is more efficient
than a pure tandem wing or canard ..................... and why my Q-2
will fly with a V-tail and flaps if I ever decide to finish it.
=======================
Just my opinion
Leon McAtee

Jono Richards wrote:

Good point hadnt thought of that! Were those not kites,
rather than gliders? Or maybe I should read my history
books again...

As other people have said, all their important patents were on the
glider. They famously said they thought that making a machine fly should
not be difficult, but making it controllable would be the main problem.
Their main patents reflected this.

One point I didn't know until recently is that the 1902 glider was flown
for proficiency before they tackled the Flyer and, apparently, Orville
flew the glider fairly extensively after the Flyer was in the record books.

Right so there is no benefit in havin two wings than
one? even if staggered to reduce the interference from
each?

Not for efficiency. The big biplane advantage is that you can make a
very light, strong structure by cross-bracing it with wire.


--
martin@ | Martin Gregorie
gregorie. |
org | Zappa fan & glider pilot