A little balsa glider with a good yield
To build a paper, cardboard or balsa glider is not difficult. Many Web
pages explain the basic aerodynamic rules you have to follow. You will
most often succeed to make a glider that really flies. Worst case, ask
an experienced friend to tune it. But such a glider generally does not
fly very far. It rather gracefully falls to the ground. Some
rocket-shaped paper gliders seem to fly straight in the air
but only on a short distance. They behave like an arrow: once their
initial impulse is over, they will gracefully fall to the ground too.
It took me years to build a little balsa glider that flies straight
through my room, seemingly on a horizontal path. This page proposes the
plans of that glider. I will try to explain the rules I followed to
build it. The exact shape of the glider doesn't matter. What
matters is to understand the rules and reasonings behind and to be able
to adapt them to other shapes and purposes. The explanations assume you
have an elementary
knowledge of toy gliders aerodynamics. If you want some insight in
flight physics then maybe try this page: Basics
Here are drawings of the glider:
The Wing span is 300 mm. The Wing chord is 50 mm. The wing is made out
of a 2 mm balsa plate (fibers parallel with the span). The wing
incidence is about 7°. The leading
edge of the wing is made round while the upper side of the trailing
edge is sandpapered:
The front of the vertical mast has a height of 10 mm. The rear of the
vertical mast has a height of 3 mm (which leads to the 7° incidence of
the wing). It is made out of 2 mm balsa plate
(fibers vertical). The front of the vertical mast is situated 70 mm
the front of the body.
(Jeffrey Reed pointed out that these measures actually yield an
incidence of 7.97°, which is 8°. You will be closer to 7° if you use a
height of 4 mm instead of 3 mm at the rear of the vertical mast. The
ideal height would be 3.86 mm...)
The body is a 250 mm rod of 3 x 3 mm pine
wood. The front end is a little hemisphere of hot glue. The rear end
has been cut out a little bit at the bottom. The front weight is made
out of say 1 mm diameter solder wrapped around the rod. The exact
weight doesn't matter. What matters is that the center of gravity be
situated 1/4 chord behind the leading edge, that is in this case about
12 mm from the leading edge, like
drawn below. Best way to get the center of gravity at the right place
is to add solder carefully. Start wrapping a fair length of solder at
the rod's front end. (Possibly now add the hemisphere of glue at the
top.) Test the center of gravity and remove or add little lengths of
solder. Till the center of gravity shows to be at the right place:
What really matters is that the glider flies well. If when you throw
clearly shows to need some more or some less front weight, just do that.
The rear stabilizers are made of 0.3 mm cardboard (from a pack of
organic rice wafers). The vertical stabilizer has a height of 35 mm
and a chord of 25 mm. The horizontal stabilizer is so to say made out
of two vertical stabilizers.
The glider's weight is about 10 grams.
A much heavier glider will fly perfectly yet faster (provided it is
rigid enough to keep its shape). A much lighter glider may fail to fly
correctly because it will fly too slowly. Indeed a too low airspeed
changes the way the air moves around the wing (Reynolds number...)
Solutions for low speeds can be to use turbulators, to increase the
wing chord and/or to use flatter wings. A friend was afraid to throw
the glider so I made a copy of it for him, much lighter, out of very
thin balsa sheets. It flies correctly but clearly I reached the limit.
A lighter version would need either turbulators or a longer wing
chord. Note that a heavier-faster version of this glider is not
farther than a lighter-slower version. Speed does not imply distance.
There will be differences in
flight distance between faster and
slower versions but they are not supposed to be tremendous.
To download a printable plan of the glider, a template of the wing
shape and the drawings of the glider in vector format, click here. The format is
OpenOffice.org 1.x Draw. Open
is free software, available for most computer operating systems. To get
the same drawings in Open Document format, click here. To get
just the plan and the wing template in standard printable Poscript
format, click here.
Why a flat wing profile?
For years I heard friends sweat and dream about their wing profiles.
They exchange profile drawings like if they were treasures. They spend
weeks, even months, assembling wings that match the chosen profile with
a precision up to a tenth of a millimeter. After reading through many
texts I found out that a simple flat profile was the best solution.
out the easiest to build. Its aerodynamic yield is close to the maximum
you can expect. Just give it an angle of attack of about 7°.
Apart from a good aerodynamic yield, flat profiles have a simpler
in the air. They are easier to cope with because they create less
instability than curved/cambered profiles. They are reliable and
The main advantage of a cambered profile, apart from the
facts that it has some more yield and can be more rigid, is that it
requires far less wing surface to
create an equal lift. Conversely, a flat wing will require much more
chord to create the same lift than a cambered wing (for a same span).
Hence, and this quite important: a flat profile can allow a glider to
fly slower, because for a
same span and lift a flat profile implies more chord.
Why such a thin wing profile?
A balsa plate of 2 mm is enough to get a rigid and lasting wing. So why
use a thicker one? There are a few reasons not to do so. First, a
thicker profile would mean a heavier glider. It would fly the same way
yet faster. I prefer a slow speed, to have the time to enjoy the
glider's flight. Second, At low speed and short chord, thin profiles
are commonly a better choice (whether they be flat or cambered). You
more easily the air to follow the wing shape neatly.
Basically, thin profiles allow for lower flight
speeds (whether they be flat or cambered).
You need a higher flight speed to get the air move correctly around a
thick profile. This is why the first airplanes had very thin profiles.
This too is one reason why they were biplanes; because you can't build
strength into a very thin wing. So one solution is to assemble two
wings to get a rigid structure. I was told early airplane builders
could have used thick profiles but I have no proof thereof. I'm a bit
puzzled by this. Ultralight aircrafts exist that use quite thick wing
profiles. Their slowest flight speed matches the highest speed of the
Wright Brother's Flyer... On the other hand my own
little gliders with thick wings didn't fly very well... Maybe the first
people experimenting with aerodynamics noticed that they got good
performances only with thin profiles, because they were using little
experimental wings and very slow airspeeds. But the much bigger
airplanes they were building could have used thicker profiles... I've
Advantages of thick
wings in today airplanes is that they are more rigid for a given
they can contain more fuel and hardware...
Why a wing incidence of 7°?
I read in papers that this angle provides the best aerodynamic yield
real-size airplanes. So I tried it out on my glider. Maybe another
angle would be even better. Since I got the near
horizontal flight path I was seeking for, I did no further experiment.
Many low-cost balsa gliders have a wing incidence that seems to be
0° (compared to the rear horizontal stabilizer). This doesn't mean
much since the horizontal stabilizer is not the only part of the glider
that participates into imposing the angle of attack in flight. The
weight at the front of the glider body matters too. Furthermore the
downwash created by the wings tends to push down slightly the
horizontal stabilizer, inducing an angle of attack on the wings. Such
low-cost gliders won't fly far anyway. Yet they often fly correctly.
Update: look at this record-breaking glider: http://hosted.schnable.net/amaglider/assets/indoor-gliders/handlaunch-gliders/nifkin_by_bob_romash_plans.html
. At first glance my glider can be seen as a simplified version. But
there is at least one key difference: it has no wing incidence...
Try out the renowned FoilSim Java applet from NASA: http://www.grc.nasa.gov/WWW/K-12/airplane/foil3.html
. It yields that for a flat wing profile, the optimal angle of attack
is around 3°. This leads to think that, if my glider flies optimally,
then its nose is pitched down say 3° during flight, so that with a
built-in wing incidence of 7°, the angle of attack during flight would
be say 4°, like suggested in the drawing below. The red line would be
the flight path. The horizontal tail would be pitched down a few
degrees, which yields stability. Then the body does not fly parallel to
the airstream but this would have not too much consequences because it
is quite thin. This flight attitude was not my intention and the glider
would be optimal by chance.
On the contrary,
maybe the Nifkin glider mentioned the paragraph above, flies with its
nose pitched upwards. Indeed its aim is not to fly the furthest but to
hang in the air the longest possible while. Hence it needs to get the
most possible lift out of its curved wing profile, so long this causes
not too much drag proportionally.
This is all why experienced model glider builders keep the incidences
tunable, of both the wings and the horizontal stabilizer. You don't
know in advance what the best wing angle of attack is, neither what
angle you must give to the horizontal stabilizer to get that optimal
angle of attack of the wings. If you also tune the front weight (to
displace the center of mass), then you get a hectic three variables
Why such wide wings?
An airplane keeps flying because its wings constantly blow air
downwards. Just like an helicopter does. Yet an helicopter stays at the
same place and moves its wings/propeller through the air by rotating
them, while an airplane passes its wing through the air by moving
itself through the air. The air that an airplane's wings blow downwards
does not travel all the way towards the ground. Instead it rotates
sideways and you get two slow and huge turbulences/vortexes; one
each wing. This is kind of an invisible trail left by the airplane.
Now, according to the laws of mechanics, the more volume of air the
wings make rotate every second, the slower that air will move and the
less energy the airplane will have to spend. That's one reason why
gliders have very long wings; in order to span over a huge volume of
air. The least
the air moves once a glider went through it, the better that glider's
Why such short wings?
Wings also leave little turbulences behind them,
just like a rod that you swing through the air. The swoosh noise that
can hear is generated by the turbulences. Turbulences mean drag and
loss of energy. A wing is kind of a streamlined rod, that tries to
generate as few turbulences as possible. This is the second reason why
glider's wings are long and have a narrow chord: a longer chord would
generate more turbulences. But balsa gliders have the opposite problem:
their wings are so narrow (a few centimeters) and their flight speed is
so slow, that the air barely manages to follow the wing profile
correctly. The slower a glider flies, the more you have to increase its
wing chord, so the wings can wing properly. Conversely, for a same wing
surface, you get a shorter wing. (But, if you would increase
the chord far too much, then you would get another problem: the wings
now generate turbulences, which is the problem of big gliders.)
Why those wing tips shaped like shark fins?
air shears towards and past the glider wings it will rise up,
accelerate and decelerate (turn around the wing profile and pull it
upwards just like a stone in a swing pulls on the cords), go into both
huge and microscopic
turbulences... What matters is that behind the glider the air "closes
and stays immobile as much as possible. In other words: the air may do
around the glider, provided it's fluent and has a way to close down
neatly behind the glider. The enemies to this are the aerodynamic
turbulences and instabilities. One cannot avoid them but they can be
lowered to a minimum. The more you
increase the span of the wings of an airplane, the huger become the two
main vortexes, the slower they turn and the better the airplane's yield.
The wing tip of a bare rectangular wing generates a strong local
The air just
before and especially behind the wing tip will go on turning round in
turbulence for several seconds. That turbulence carries away a part of
the energy of the glider. Hence it brakes the glider. To decrease that
turbulence several solutions exist:
- Use a
wing. That is a wide span and a narrow chord.
That's called a "high aspect ratio wing". In such a wing, the wing tips
are minute compared to the rest of the wing surface. Hence the
turbulences they generate are weak compared to the glider size. Other
good reasons exist to use such wings. But I didn't, for two reasons.
all such a wing is difficult to manufacture. You cannot cut out a
narrow strip of balsa wood and expect it to be perfectly flat and
rigid. Second, a problem with little and low speed gliders is that if
chord is too narrow, the
air simply no more travels properly around the wing. You get no more
"wing" effect. Thats due to the "Reynolds number". Below a given
"Reynolds number" the air no more follows the wing shape. To gain back
the wing effect and its lift force, you must either increase the flight
speed or the wing chord. (Turbulators can help too but they add a
little braking.) For my glider I was thus obliged to use a comfortable
chord and hence to limit the span. (On the opposite, real gliders rely
on a little chord to lower their wing profile Reynolds number, because
at very high Reynolds numbers you get strong air turbulences all over
the trailing surface of the wing.)
- Use winggrids.
tips to lower the turbulences.
Some birds use this system. I heard it's a very effective system.
It allows to build compact wings, with a low aspect ratio, yet with a
high aerodynamic yield. I didn't choose this solutions for several
reasons. First, I needed to make experiments to check out this
solution. Second, on my glider the chord of the little wings would be
below the Reynolds limit (turbulators would help...) Third, a winggrid
on a little glider would
both take a lot of time to assemble and be quite fragile, hence
the lifetime of the glider would be very short.
- Use a biplane or triplane
wing structure. I you intend to build a low-speed and big airplane, a
biplane structure is an excellent solution. It allows to build
a very lightweight, wide span and rigid wing structure. It can even
have both a rather short span and a good aerodynamic yield, provided
you put the lower wing behind the upper wing. That way you get sort of
a huge winggrid, like in the Flying
Flie. I didn't use a biplane or triplane structure because my 2 mm
balsa wing was already rigid enough and because I feared some
intellectual aerodynamic and structural fuss building a biplane.
Besides, why try to make an even more lightweight wing? To allow the
glider to fly slower? I'm already close to the lower speed limit...
- Use a trapezoidal
shape. So the wing has a strong chord at the middle and a
little chord at the tips. Hence the turbulences generated at the tips
are lower. This solution is used on quite a lot of big airplanes. I
didn't use it because The angle of the trapeze has to be under 10°.
On a wing with a short span like that of my glider, this does not allow
for a much shorter chord at the tips. So the benefit would be real yet
- Use wing tips salmons.
effective to lower the
turbulence. It is widely used on RC planes and gliders, often
associated to a trapezoidal wing shape. I didn't use standard salmons
because I believed their effect would not be sufficient for my aims.
Though we are coming close to the solution I finally choose. The wing
tips of my glider can be seen as "some sort of huge salmons" or "a
short and fluent transition between trapezoïdal wings and salmons".
- Use an elliptical wing shape. That is the wing shape of the
legendary WW II Spitfire
fighter plane. It is seen as sort of "optimized to the extreme": the
air pressure and angle of attack is the same all over the wing span,
the air streams follow
quite parallel paths all over the wing span, the wing tips turbulences
are kept to the minimum, the wing span is short enough to get a
swiftly maneuverable aircraft... it is smooth, homogeneous and optimal.
Yet it has one big disadvantage: when the aircraft makes steep turns
the lift force may disappear suddenly all over the wing inside the turn
path. (The wing profile was actually slightly changed so the pilot got
warning vibrations before the real stall would occur.) (Critics
the wing of the Messerchmitt BF-109 were as effective as that of
Spitfire but it had a more conventional shape and it was far easier to
build.) Now my glider is
not meant to make steep turns. It's not even meant to turn at all. So
why not use this ideal shape? Well, the shape I choose is quite close
the ellipse. You may argue it's closer to an ellipse cut in two.
Actually what matters is the chord length. The chord length over the
span has to obey the formula of the ellipse. No matter those chords are
pushed backwards to align with a straight trailing edge or pushed
forwards to align with a straight leading edge. In the Spitfire wing,
the chords are put just a little bit forwards (this has some structural
and aerodynamic justifications). The four shapes beneath would all be
called elliptical wings. The upper left one is a mathematical ellipse.
The upper right one approaches the wing of the Spitfire. The lower left
one approaches the wing of my glider (so I was quite confident in
its qualities). The lower right one feels to me to be an aerodynamic
nightmare. I managed to make some little balsa gliders fly correctly
with that wing shape. Anyway it was clear this is not an optimal shape
(see the end of the text for counterexamples).
- Copy a bird. That's what I did (go to the end of this text to
read why I actually didn't) (I left the rest of this paragraph intact
so you get a good example of a wrong reasoning, though the last part,
about the vibrations, is excellent). I used the shape of a seagull
wing, just a little shorter (lower aspect ratio). A seagull wing is a
very complicated structure made of bones, muscles, tendons,
articulations, skin and feathers. So simply using its rough main shape
on a flat wing is not guaranteed to yield an optimal result. But I was
sure I wouldn't get a bad result either, since the seagull wing shape
was close to the elliptical wing shape of the Spitfire and to the
trapezoid + wingtip salmon shape of good RC planes and gliders. The
main difference is that the central part of the wing has parallel
inclined for such parallel borders because I read a page
from a top balsa glider builder who explains that he simply hates the
elliptical shape. He prefers parallel borders and wide rounded wing
tips. Like the Westerner 2 RC model near the bottom of this page.
Furthermore I thought this was a mathematical best choice in order to
keep the wing chord to a maximum nearly all over the span (remember at
low speeds the chord needs to be as wide as possible). Next, why stick
to the seagull shape even for the shark fin-shaped wing tips? For three
reasons. The first one is not very important: because it is the closest
one to the successful salmon wing tip shape. The second reason is that
read in books that this shark fin shape generates the least braking and
turbulences. It's the shape that most suits a fluent air circulation.
The third reason is really and excellent one: I tried out and checked
that this shape really yields the least turbulence. I made two wings,
identical: one with the shark fin tip shape and the other with rounded
tip shape (close to the Westerner
shape mentioned above). I hold them in my hand and sheared
them in the air around me. The wing with the rounded wing tips produced
weak vibrations I could feel in my hand. The wing with the shark
fin-shaped tips produced no vibrations at all. It did glide through the
air like if there was no air at all except for the lift force. So the
seagull wing shape was adopted.
- Use winglets.
difficult to design. A random design, even an aesthetic one, is said to
brake the plane more than using no winglets. Besides, winglets are
usually meant for the tip of narrow ending wings, which is not my case.
I once saw a prey bird gliding. The tip of his wings was round shaped,
with no winggrids. The tip of his outermost feather made an upwards
bend to form a quite little yet beautiful winglet. So maybe little
winglets can enhance a little bit the yield of this glider. Maybe I
should give it a try but I know their effect will be negligible. I've
no way to
verify their usefulness. I won't add to my glider something that I
check to be worth the effort.
Why pretend that the wing profile is flat though only the upper
the trailing edge was sandpapered, which creates a very slightly curved
Well right, the profile is not perfectly flat. But I'm quite sure this
doesn't change much of the glider's flight characteristics. Such a thin
wing with the upper and downside trailing edge sandpapered
symmetrically won't change much to the glider's behavior. Sandpapering
only the upper side makes the manufacture easier.
Note that if you sandpaper the
downside of the trailing edge, you no more need a tail horizontal
stabilizer. This is a "flying
wing" shape. (Such a flying wing may benefit from a very little tail
horizontal stabilizer anyway, just to avoid pitch oscillations.)
Why such a little horizontal stabilizer?
This is a key feature. Many beginners (like me) boldly believe the rear
stabilizers of an airplane behave like the stabilizers of an arrow. So
the bigger the stabilizers, the more stable the glider's flight will
be... That's wrong.
In first approximation, a glider with a flat wing profile almost does
a horizontal stabilizer. I made such a tail-less glider and it
flies quite correctly (the build tip is to sandpaper only the downside
of the trailing edge; see data about flying wings to know why).
stability of the glider arises first of all from the interaction
between the weight in front of the glider and the tendency of the wing
to flip upwards. It's sort of a battle between the two forces. While in
flight, the wing experiences an aerodynamic torque that tends to
make the glider pitch upwards. But the center of gravity of the glider
placed slightly frontwards, which tends to
make the plane pitch downwards. The two forces equilibrate and the
aircraft flights straight. Why such a fragile equilibrium between two
forces of different natures? Well because it is not fragile at all.
quite stable and the speed regulation of the glider relies upon it.
Indeed the weight in front of the glider is constant. It doesn't change
when the speed changes. It always tends to make the glider pitch
downwards with the same force. On the contrary, the aerodynamic upwards
torque on the wings depends on the glider's speed. The faster, the
more torque. The slower, the less torque. So, should the glider fly too
slowly, the upwards aerodynamic torque decreases and the front weight
makes the glider
tend to dive, which makes it gain speed. Should the glider fly too
the aerodynamic torque will supersede the front weight, the glider will
pitch upwards and tend to climb, so it will loose speed. The result is
that the glider flies at a nearly constant speed. A huge rear
horizontal stabilizer would supersede this phenomenon and make the
glider less stable.
Then, why put a little horizontal stabilizer anyway? For two reasons.
First, The regulation phenomenon explained above tends to make the
glider oscillate. That's often a problem you get, when two forces
and the system has some inertia. The tail-less glider I made flies that
way: oscillating. It's cute to see but I bet it participates in the low
yield of that glider. The horizontal rear stabilizer tends to prevent
the oscillation. It wears away the energy of the oscillation, like the
dampers of a car suspension. Second, when I said this speed regulation
system is stable I was boasting a little bit. On a plane with a
standard curved (cambered) wing profile there is a clear instability.
the plane pitches a little upwards, the upwards aerodynamic torque will
increase a little bit. So, if the plane pitches upwards it will tend to
pitch even more upwards. And if it pitches downwards it will tend to
even more downwards. It diverges. The forces implied are not very
strong yet they
make the plane unstable, unable to fly straight. The purpose of the
rear horizontal stabilizer is to dominate this phenomenon and make the
plane fly straight. But only a quite little horizontal stabilizer is
necessary for this... (As written above, airplanes with a flat wing
profile are quite
in regard of this phenomenon. They don't tend to increase an upwards or
downwards pitch. They don't tend to stabilize it either. Only special
wing profiles intended for flying wings do.) Third, I have few
confidence in the wing to willingly adopt the 7° angle of attack
I choose. The horizontal stabilizer helps it conform to my
wishes. I'm quite sure the wing actually does not fly with an exact
angle of attack of 7°. Conversely I doubt the horizontal stabilizer
flies with an angle of attack of exactly 0° through the air. Anyway the
system seems to come globally rather close to my wishes.
So, the purpose of the horizontal stabilizer is not to impose the
flight attitude of the glider. It is rather to compensate for some weak
and secondary disorders and instabilities. Therefore it does not need
to have a huge surface. Actually it must
not have a huge surface, in
order not to dominate the main speed regulation phenomenon.
Why such a little vertical stabilizer?
The reasoning is quite close to that for the horizontal stabilizer. But
I don't master it. Specifically, with a huge vertical stabilizer the
glider gets two problems. First, it will tend to oscillate sideways; it
has a yaw
instability. Perhaps because the vertical stabilizer is caught
alternatively by the left and right main wing vortexes. Second, it
makes the glider gradually go in a spiral dive; the much hated
phenomenon that killed many pilots.
The first prototype of this glider had a quite bigger vertical
stabilizer and it didn't have a beautiful flight. The instabilities
made the glider loose a lot of energy while flying. It was falling fast
while flying. But I knew about the problem and I made a haircut to
it. Once the vertical stabilizer got little, the glider's flight became
wonderful. So smooth and straight. Especially, it flew much more
horizontally, like I wished it to.
I was told about an even better place to put the vertical stabilizer
avoid the instabilities: below the plane body. A few airplanes and
drones have such an inverted tail. The problem is that this makes the
aircraft more fragile or even dangerous during take-off and landing.
Even on a little balsa glider this can yield problems since a downwards
vertical stabilizer will be hit more often and hence be damaged. I
would have adopted this layout anyway if it had been necessary. But I
got what I wanted just by using a little vertical stabilizer.
Then again, why not simply remove the vertical stabilizer? I tried it
out and got the glider fly sideways, with obviously a lower yield. A
vertical stabilizer is needed.
I believe the seagull wing shape itself offers some stability to avoid
a sideways flight, anyway not enough.
Why not use a dihedral?
Because I didn't understand the dihedral. I did read the explanation
available in popular books but I felt it was wrong. So I preferred to
no dihedral and that was OK.
There are two ways to stabilize the roll of a glider / keep the wings
Obviously my glider relies on the second method.
- Put the center of mass below the wings.
The lower the wings are implanted on the airplane body (hence the
higher the center of mass is situated above them), the more a dihedral
will be necessary to keep the airplane stable in flight. Conversely,
airplanes with wings implanted very high may be too stable (or
oscillate), then a slight anhedral will be necessary to compensate (an
anhedral is a reversed dihedral; the wings pointing downwards).
I want to adopt the seagull wing shape for my own gliders, with
different aspect ratios. What's the build seed?
Consider that the wing is made out of four equal parts. Then cut out
outer parts in the shape of a quarter of an ellipse:
Actually, sea bird wings have the inner rectangles maybe 50% wider. Yet
anyway we are not copying a seabird wing, since their wings have a
strong curvature in the inner part. (See further at the bottom of this
Why use such a thin body?
The thinner, the less aerodynamic drag. Though this is not the most
optimized shape. I should have bend the body so that it follows the
and downwards movement of the air around the wings. Maybe on a next
A lot of little balsa gliders use a
plate of balsa wood to be the body. Clearly those gliders do fly.
But I would have been afraid to use that design. Because to me such a
body is sort of a giant vertical stabilizer smeared all along the plane
body. A conceptual nightmare.
Can I build a more lightweight exemplary anyway?
Yes. I build one two times more lightweight, using 1
mm balsa plate for the wing and stabilizers and a 4 x
4 mm balsa rod for the body. But this is the limit. I made one
even a little more lightweight and it simply fell to the ground. I had
increase its weight to get it flying properly.
If you want to build an even more lightweight glider, so it can fly
then you must build a bigger one so the wing chord increases, decrease
the wing ratio (again to get more chord), or use turbulators.
Some build tips and data?
I used standard hobby water-based white glue.
For some assemblings I put one or two loose drops of hot glue to latch
the two parts. During the few seconds the glue cools down I hold the
pieces in their correct positions. Then I smear a little quantity of
white glue all along between the two pieces. Hours later, when the
white glue is dry, I remove the hot glue drops.
Maybe best cut out a wider wing, sandpaper the trailing edge, then cut
out the wing shape:
The wing tips are fragile. So I "painted" them with a thin layer of
If the glider assembly lacks symmetry it will turn in flight.
Canonically the way to compensate for this is to make the outer rear
parts of the wings go a little bit upwards and downwards. This will
create a roll
force to compensate the asymmetry. But tuning the balsa wings may be
difficult and produce an ugly result. So if the asymmetry is not too
important and the tendency to turn is quite weak, best is to create a
force using the rear horizontal stabilizer. Bend it a little bit so the
outer rear part of one half goes a little bit upwards and the outer
rear part of the other half goes a little bit downwards. Give it a
smooth gradual curved bend. Do not bend the vertical stabilizer.
When assembling two perpendicular pieces of balsa, a common practice is
to spread a little glue on the edge of one of the pieces and press the
two together. This yields a fragile link. You get a far better result
by smearing a thick little joint of white glue along the interface
between the pieces. Say 2 up to 3 mm thick. This takes at least half a
day to dry up but you get a really strong result. Of course to put glue
on the edge of the piece is a good practice, this will add to the
resistance. But the main resistance will come from the joints on the
Did you invent this glider shape?
My pride is that I managed to understand most choices and aerodynamic
reasonings when conceiving this glider. Yet the result is quite
identical to the canonical airplane shape. This simply means I got some
understanding of this wonderful invention that took centuries to grow
in the successive brains of hundreds of inventors and scientists. The
fact that the glider
flies quite well is the ultimate and necessary proof.
This page shows the "Feather Shooter", a glider that resembles: http://xoomee.com/feather.htm
This page shows the "Epsilon 2M" glider: http://www.nesail.com/detail.php?productID=3066
A plane shape depends on its purpose. This page:
shows quite a lot of different airplane shapes. All are near optimal
choices in regard of the plane's operational needs.
So your glider is optimal?
Reasonably. Yet this does not mean that a better glider cannot be
Of course it can. I've got some ideas to do that.
Part of my reasonings were inaccurate. Globally they were good
since the glider glides. For sure the reasonings behind the building of
the glider can be enhanced.
Roughly halfway the present text I compare four elliptical wing shapes
and explain that the one with the straight leading edge is the worst.
my friend Didier Bizzarri build a successful very low speed indoor
glider that approximately uses that kind of wing shape. To view it click here. Also, flying fishes
use nearly exactly the same wing shape as my glider but reversed; with
the longest edge forward. (If you check for photographs of flying
fishes on the Web, be careful to get pictures of flying fishes in
flight. Or at least pictures that show the wings fully deployed. If a
dead flying fish lays on a table or is lousily held by hands, its
quite a different shape.) I don't know if the "reversed" wing feels
stable to the flying fish. As the fish "pilots" its flight, a less
stable wing is not a problem. It is quite probable that the straight
edge's purpose is to resist impacts. The wings of the Wright Flyer tend
end in this shape too.
Most prominent error till now is that I thought I shaped a bird's wing.
is totally wrong:
- While the shape viewed from above does match that of a sea bird,
a real sea bird wing is cambered at its root and the camber
decreases towards the tip. To get the same lift at the root as such a
cambered bird wing, my flat
wing should have had a much longer chord, maybe two times longer.
Halfway the bird wing, the camber is milder. So, to have a chance to
mimic the lift of a bird wing (with my
flat wing) I should
have used kind of a delta wing or a trapezoidal wing. Actually, real
delta wings on
military airplanes are quite flat... I suppose this is not a
coincidence. (Some of the best WWII fighters use a strong camber at the
root, down to flat wing tips.)
- The incidence of a bird wing changes along the span. Maybe to
adapt to the changes in airflow, maybe simply because a change in
curvature also changes the optimal angle of attack.
- The bird's tail adds itself to the chord of the bird's wing.
November 17 2003
till January 5 2011