Basics of Flight
At some point we all will fly a
paper airplane , if not for class maybe just for fun, but what makes that
airplane fly and what makes one paper airplane any better than any other?
Experiment Title:
What properties make for a
fantastic paper airplane?
Objective:
The objective of this experiment
is to learn about aerodynamics (the study of the motion of air) and how
understanding it can lead to flight of things even more complicated than paper
airplanes (think of all the amazing missions that NASA has done to the planets
in our Solar System because of their basic understanding of Aerodynamics!)
Background on Aerodynamics:
Unless otherwise cited information for the background on
this post was gained from NASA’s post of the Dynamics of Flight [1].
Do you remember our Buoyancy
experiment (if not you can click this link to refresh yourself), in the
Buoyancy experiment we talked about two opposing forces the force of gravity
that pushes down on something (that is why we do not fly off into space) and
the force of Buoyancy which pushes upward on something when it is in a fluid.
Now this next concept will sound a bit weird but it also super cool, air (that
is the invisible gas that surrounds us and our planet making it possible to
breath and sustain life) acts a lot like a fluid (Whoa I know, isn’t that
completely awesome!). Now that we know that did you know that air can exert a
force on an object? Think about when the wind blows outside does it just pass
through you or does it send your beach ball flying (if it not properly
secured)? In that instance wind is exerting a force on you now what if we found
a way to use the force that air exerts on us to make us fly? For the most part
we are not like the birds and cannot fly without assistance (granted birds are
specially adapted to fly over millions of years).
For centuries people from Da
Vinci to the Wright Brothers tried to get mankind’s feet off of the ground and
soaring through the air, do you know how they did it? They learned how to
generate (make) lift on something like a plane (there have been lots of other
things people have tried like jetpacks, rockets, flying cars, etc… This does
not mean you should go out and try to fly on some homemade rocket, instead you
should learn the principles of flight and build models of your idea and work
out all of the kinks then build a slightly bigger model and again work out the
kinks and by the time you have a fully working prototype you may very well be
admitted to MIT for your awesome designs).
Let’s start with one of the most
important concepts for flight: Lift. Lift can be describe as the upward force
that is acting to counteract gravity. Remember how the buoyant force pushed
against the gravity force with the egg? This is the same idea except you are
using the lift force that can be generated by creating a high and low pressure
system around an airplane wing. What does that mean? A high pressure system is
an area where the air movement is calm and relatively slow moving (like a
gentle wind) and a low pressure system is an area where the air movement is
more intense (strong winds at higher speeds, pressure of the air decreases with
higher speeds).
Figure 1: This is a NASA diagram
from their Dynamics of Flight, the white blob in the middle is symbolic of an airplane
wing.
Now a plane wing is designed with
a flat bottom (this does not disrupt the airflow and allows the air to keep
flowing in the direction it was flowing before the wing came in contact with
it) allowing for a gentle wind or high pressure system, and the top of the wing
has a curve to it (this causes the airflow to be disrupted and in order for the
air to travel to the same point in the same amount of time the air has to flow
faster over the top causing a low pressure system to form). When the two
systems are created this causes the pressure below the wing to be higher than
the pressure above the wing and overall creates a lift force against the bottom
of the wing. Here is an easy way to remember the difference between lift and
buoyancy: Buoyancy is the upward force on a stationary object (should be
relatively constant when moving through a constant density fluid) and Lift is
an upward force on an object moving through a liquid (remember we are treating
air as a liquid, even though it is a gas)[2].
To counteract the lift force we
have the force of gravity (that force that keeps us on the earth and not
floating out in space). One of the coolest things about gravity is that it can
effect how things move. Think about the oceans, have you ever heard that about
something called a tide where the water rises and falls on a beach? Well this
thing is caused by the gravitational pull of the moon on the oceans (So COOL!).
Gravity is the attraction of objects with Mass to one another, so even though
the gravitational attraction is super small compared to the earth gravity could
explain why your little brother is always drawn to you. When looking at flight
a plane will need to overcome gravity by creating a large enough lift force to
take off from the ground, the more lift the higher your plane could potentially
go (although lift will only take you as far as you can create a high and low
pressure system (no air to make that difference in pressures means no lift)).
The next force is drag, and no I
do not mean it is such a drag that I am not singing while I talk about it, by
drag I am talking about the mechanical force that that pushes against the plane
as it moves through the air. This force is not created by a field like gravity
(a force field (not from Star Trek) is a field in which an object can affect
another object without being in direct contact, think about the earth and a
bird, while a bird is flying the bird is not in direct contact with the earth
but still feels the effect of its gravity) but is created by the movement of
the plane and is known as a mechanical force (a force when exerted on a body
(plane, person, rock, etc…) that can cause a change in the motion (movement) of
that body[3]. Think about it in this way you are running outside and a big gust
of wind hits you, you react by trying to run harder and keep your pace or you
slow down possibly even stop, the wind is exerting a drag force on you making
it so that you have to change something (either your speed or direction) in
order to keep going. A plane when traveling through the air has a drag force
exerted by the air (remember air is treated like a fluid), if the plane does
not counteract the drag it will not be able to go very far and so we have one
more main force to talk about.
The thrust force is that last
main force we have on our plane. The thrust force is force generated by the
engines to move the plane through the air (when you make your own paper
airplanes the amazing engines behind them will be you!). Thrust , like drag, is
a mechanical force exerted by the plane’s engines on the air in order to
overcome the drag and the gravity force (it overcomes gravity by moving fast
enough to create a great enough pressure difference between the top and bottom
of the wing to create lift). Provided you create a fairly aerodynamic paper
airplane the more thrust you use the further potential the airplane has to fly
a greater distance (but remember we are flying through a liquid so we will
experience resistance and too much thrust and your plane will do some crazy
tricks and crash right in front of you). The key here is to throw your airplane
hard enough to overcome gravity and the initial drag force (since you are not
constantly adding energy the drag force will eventually win and your plane will
land) but not so hard that it immediately crashes.
Figure 2: This is a diagram from NASA showing the direction that each force we discussed acts in on an airplane.
Now that we know the basics of
flight let’s do something even more fun and put those dynamics into action
(let’s build some paper airplanes. Here are a few example plane designs we are
going to work off of for our experiment. The simplest one will be first and the
most difficult example will be last. You can choose from any of these plane
designs (or make your own based on the principles shown in these designs) to
create your own initial airplane. All the instructions and images are from
www.foldnfly.com an awesome website for making super cool airplanes, check it
out for more advanced designs to make at home.
The Basic [4]: this is a very
basic airplane and is great for beginners to get their feet wet
The Stable [4]: this one should
go a decent distance and can do some neat acrobatics if thrown the right way
The
Sea Glider [4]: This is a bit harder to fold but super neat once put together
If you want to learn more about
flight and the amazing things that engineers and programmers working for NASA
have done or are doing check out the NASA Kids page, has tons of awesome
information about space and different programs that NASA has created over 59
amazing years.
Materials
-
3-5 pieces of printer paper
-
Some marker if you want to decorate your awesome
creations!
Method
Prepare Experiment
- Pull the sheets of printer paper out of your stem kit and unfold them, possibly put them under a book just to make them nice and flat (don’t worry we have extra paper if you are really worried about the wrinkles on your STEM Club kit sheets)
Run Experiment
- Look at the different sample designs that we have and try to fold your own.
- Now repeat that same fold but this time try making an adjustment by increasing the point of the front of the plane or folding it so that the wings are wider rather than skinnier
- Repeat the folding process one more time but this time go through and
Analyze Data
The cool thing
about observations and experiments is that everyone has their own unique way
about going about making and doing them. Let’s all share our observations of
what happened with our planes. Which features lad to the best flight, a longer
tip or shorter tip, wider wings or narrower wings, the way in which it is
thrown? There are no wrong answers with your observations.
Conclusions
We learned about the different forces that a plane
experiences when trying to fly, then worked to build our own airplanes out of
paper. We learned that the wing design is important for getting a good distance
and decreasing drag with our nose (the front of the plane) is important.
Make It Your Own
We have done a lot to learn about flight and the forces that
are involved with it. Now go home and only with your parents permission try to
make a few more airplane designs from www.foldnfly.com.
See if you can improve upon the farthest distance or coolest tricks that you
did with your initial airplanes.
Extension Activities to do at home
Now try adding a weight to the
front of your airplane (the paperclips in your STEM Kit will be very helpful
for this), do this change how your plane flies? What if you put the paperclip
on the back of your airplane, do you have the same result or something
different? Now try making your airplane out of aluminum foil, what happens now?
Citations
[1] Dynamics of Flight, NASA Kid’s Page, 12/27/2017, https://www.grc.nasa.gov/www/k-12/UEET/StudentSite/dynamicsofflight.html
[2] Difference Between Lift Force
And Buoyant Force, Online Forum 12/27/2017, http://www.airliners.net/forum/viewtopic.php?t=771243
[3] Types of Mechanical Forces, ME Mechanical, 12-30-2017, https://me-mechanicalengineering.com/types-of-mechanical-forces/
[4] Paper Air Plane Designs, Fold N Fly, 12/30/2017, http://www.foldnfly.com/#/1-1-1-1-1-1-1-1-2
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