How can a glider or an airplane do a loop without thrust

In summary: I looked for an existing equation whether it be in polar or rectangular to aid in modeling physical behavior. Hope this helpsYes flaps in case of airplane would be involved indeed, the code I put there is just one example it's not the full code but it simulate well a rock ; (dir) is the variable for the direction I could change, isn't enough for pitch angle ?
  • #1
plaguebreath
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I have to admit I am not good on physics but I am willing to try to understand how is possible for a plane or a glide that's falling without thrust applied downward to make a loop (by changing direction or using the elevators on the tail of plane, like in this picture.
5ldgzr.jpg

I am try to write a program to simulate the motion of this object flying using this code (I consider only gravity for the moment not drag nor lift)
Code:
tempgy = g * frametime ; // acceleration of gy
tempay = ((thrust / m) * 32) * frametime * sin(degtorad(dir)) ; // acceleration of thrust y
tempax = ((thrust / m) * 32) * frametime * cos(degtorad(dir)) ; // acceleration of thrust x
y -= (vely + tempay/2 + tempgy/2) * frametime   ; // update position y
x += (velx + tempax /2)* frametime  ; // update position x
vely += tempgy + tempay; // update velocity y
velx += tempax; // update velocity x
but offcurse with this code I only consider the sin and cos of the thrust applied to glider, what you can suggest me to do ? What other force applied to the airplane that will make him loop by changing the angle of elevators ? Best regards
 
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  • #2
Look up Kinetic Energy
 
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  • #3
plaguebreath said:
What other force applied to the airplane that will make him loop by changing the angle of elevators ?
That would be lift -- a force at right angles to the current line of motion.

If you consider only gravity and thrust and if you are modelling a glider (thrust = 0), the motion you simulate will always be that of a thrown rock. A parabola.
 
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  • #4
Which control surfaces are changing at the beginning of the loop? I can see the loop occur if a change in the tail sections elevator moves upward and occurs at a rate that prevents the plane from stalling. Is the plane's flaps involved as well to generate the loop?
 
  • #5
plaguebreath said:
Code:
tempgy = g * frametime ; // acceleration of gy
tempay = ((thrust / m) * 32) * frametime * sin(degtorad(dir)) ; // acceleration of thrust y
tempax = ((thrust / m) * 32) * frametime * cos(degtorad(dir)) ; // acceleration of thrust x
y -= (vely + tempay/2 + tempgy/2) * frametime   ; // update position y
x += (velx + tempax /2)* frametime  ; // update position x
vely += tempgy + tempay; // update velocity y
velx += tempax; // update velocity x
What you have is a reasonable simulation of a rock. For a plane, you need to keep track of the pitch angle as another state variable. Then you need to assign a lift which depends on the speed and angle of attack. And you need to include drag. Note that drag necessarily increases with lift. You can't gain elevation without sacrificing some speed.
 
  • #6
A glider performing aerobatics trades Potential Energy and Kinetic Energy back and forth (with some energy lost to air resistance/drag).
 
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  • #7
Khashishi said:
What you have is a reasonable simulation of a rock. For a plane, you need to keep track of the pitch angle as another state variable. Then you need to assign a lift which depends on the speed and angle of attack. And you need to include drag. Note that drag necessarily increases with lift. You can't gain elevation without sacrificing some speed.

Yes flaps in case of airplane would be involved indeed, the code I put there is just one example it's not the full code but it simulate well a rock ; (dir) is the variable for the direction I could change, isn't enough for pitch angle ?
 
  • #8
Aerodynamic force can be a lot greater than the thrust from any engine.
 
  • #9
I looked up rose curves and polar equations for r^2 =a^2sin2theta. If the equation for that that curve was modified slightly and reflected on polar graph paper, that curve looks similar to your sketch. The line of the curve heading downward could represent the plane's angle of attack and possibly other information. I sometimes look for an existing equation whether it be in polar or rectangular to aid in modeling physical behavior. Hope this helps
 
  • #10
plaguebreath said:
Yes flaps in case of airplane would be involved indeed, the code I put there is just one example it's not the full code but it simulate well a rock ; (dir) is the variable for the direction I could change, isn't enough for pitch angle ?
I do not think you would be using flaps as control surfaces to initiate a loop. That's what the elevators are for.
 
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  • #11
I think the domain on theta needs to be limited after the reflection to [3pi/2,pi/2] or [0,pi] depending on how the graph is to be visualized. One quadrant is needed for the line entering the loop and the second quadrant representing the loop itself.
 
  • #12
I was not saying the flaps would be used to initiate the loop but in synchrony with the elevator itself. I have used flaps and the elevator together on model aircraft for loops and it worked ok. The flaps seem to help smooth the curve until the plane is upside down and returning back towards Earth and which point the flaps are level relative to the rear part of the wing. I was merely asking a question
 
  • #13
There is always scientific method to fall back on when all else fails . Perhaps a diagram showing the forces acting on the glider might clear a few things up ?
 
  • #14
+1

It would be interesting to write equations (probably simplified) for each of the four forces plus a control input and then just "let it run". The control input will need to change with time.

Aside:I've flown aerobatics in both gliders and powered aircraft. You can forget complications like flaps.
 
  • #15
Loop-the-Loop with a Flying Hoopster

Most paper airplanes are flat, but these paper hoops can really fly!

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https://www.scientificamerican.com/sciam/cache/file/9A8F3141-AEB1-4615-AE1DA6F30B4DE59D.jpg?w=590&h=393&FEC0D52A-E684-4E89-8BF2E6230BD056F0

Soar away sans wings! Try this activity to see how a simple paper craft can fly just as well as a traditional paper airplane. Credit: George Retseck
Key Concepts
Gravity
Thrust
Lift
Drag

Introduction
Paper airplanes are fun to make and fly. Most designs resemble miniature planes—made of folded paper, with wings, stabilizers and sometimes even flaps. These creations look like they are ready to soar. There are some designs, like the one you can try in this activity, however, that look so awkward one might imagine they would not fly at all. Find out if it will really soar!

Background
Although there are many different paper airplane designs, almost all of them have a flat winglike structure, which, like a traditional plane, helps create lift to keep the plane in the air. The plane in this activity, which is reminiscent of Phillip Swift's design entered in Scientific American's , gets the lift needed to glide from two rings, instead of wings. Normal wings have wing tips that generate vortices, adding drag (which isn't ideal for an object trying to stay aloft). The lift-providing rings have no wing tips and so they have less drag. The streamlined shape of the "hoopster" also makes it easy to throw accurately.

Materials

  • Scissors
  • Ruler
  • Pen or pencil (optional, for measuring out paper to cut)
  • 3-x-5-inch index card (or a file folder or some other stiff paper)
  • Piece of printer paper (or similar stiff paper)
  • Clear plastic tape
  • Stiff plastic straw (that does no have a bendy top)
  • Measuring tape (or long string)
ANADMANNI
 
  • #16
Ok, my knowledge on physics and vector algebra is quite bad so I am just learning, be patient with me.
Based on this image
Image218.gif

let's say my airplane have a direction of 15° and accelerating, then suddenly stop acceleration and point down nose of the plane, get some velocity and still without thrusting using the aileron make plane turn up again with the nose. With the formula I write before offcurse this movement will not be done because as soon I point down my nose on the plane and stop the thruster my plane will continue to fly down even if I change my variable (dir) because offcurse that's chained with the thrust part, so how can I could make chaning x and y if not thrusting with another direction controlled by tail aileron ?
Another question regarding the drag force, if my plane it's with thrust = 0 and I let it fall down it's creating velocity, so with drag added my plane tend to go backward (not considering air resistance or wind) what I'm doing wrong ?
 
  • #17
plaguebreath said:
let's say my airplane have a direction of 15° and accelerating, then suddenly stop acceleration and point down nose of the plane, get some velocity and still without thrusting using the aileron make plane turn up again with the nose. With the formula I write before offcurse this movement will not be done because as soon I point down my nose on the plane and stop the thruster my plane will continue to fly down even if I change my variable (dir) because offcurse that's chained with the thrust part

As you say, have a direction variable which models the plane's current pitch angle relative to the horizontal. You have vx and vy variables for the plane's current velocity. From these you can obtain the plane's current velocity angle relative to the horizontal. That would allow you to compute the pitch angle relative to the current velocity, aka "angle of attack".

Then you should proceed as @Khashishi has already suggested:

Khashishi said:
What you have is a reasonable simulation of a rock. For a plane, you need to keep track of the pitch angle as another state variable. Then you need to assign a lift which depends on the speed and angle of attack.

plaguebreath said:
Another question regarding the drag force, if my plane it's with thrust = 0 and I let it fall down it's creating velocity, so with drag added my plane tend to go backward (not considering air resistance or wind) what I'm doing wrong ?
If your forward velocity is not adequate, gravity will indeed slow it down and cause it to move backwards. (e.g. a "hammerhead stall"). You need enough velocity going into the loop so that you still have forward velocity left over at the top of the loop.
 
  • #18
So basically as my beautiful pic show
1o4ry1.jpg

this is correct immagining the plane with initial v0 let it fall without thrust
 
  • #19
plaguebreath said:
So basically as my beautiful pic show
1o4ry1.jpg

this is correct immagining the plane with initial v0 let it fall without thrust
What does that drawing depict?
 
  • #20
An ideal airplane or paperplane, set in space and let it fall down freeely as stated before.
 
  • #21
plaguebreath said:
An ideal airplane or paperplane, set in space and let it fall down freeely as stated before.
No. What does it say? You show a plane moving both forward and downward and diagonally backward at the same time. Is that what you intend?
 
  • #22
Sorry my drawing skill is very poor, the first plane is the step at time 0, my plane is on starting position with velocity 0 and thrust =0
The second plane is the action after 5 unit of time, my plane went backward and down because of the gravity and the drag as it get velocity but no thrust
 
  • #23
by changing direction
OP answered their own question.

This is achieved through aerodynamics such as the Bernoulli effect and the fact that air resistance is not identical against cross sections in the different axes.
 
  • #24
Are you interested in simulating a reasonable path for a piloted glider, or in simulating all the physics that would give you a path?
The first is much easier than the second because there are a lot of flight paths that are possible for a piloted glider. You have a lot of freedom and just have to keep within certain limits.
Simulating the physics would get into more detailed aerodynamics and equations of motion.
 
  • #25
plaguebreath said:
Sorry my drawing skill is very poor, the first plane is the step at time 0, my plane is on starting position with velocity 0 and thrust =0
The second plane is the action after 5 unit of time, my plane went backward and down because of the gravity and the drag as it get velocity but no thrust
If drag is backward, that means that initial velocity was forward. Accordingly, the plane will move forward. It will not move as far forward as it would have done without drag, but it will move forward.

If your step size is large enough that the plane stops and then moves backward due to drag, then either your drag formula is incorrect or your step size is too large. Drag scales with velocity. The slower you go, the less the drag. You will never stop and then start moving backward under drag alone.
 
  • #26
jbriggs444 said:
If drag is backward, that means that initial velocity was forward. Accordingly, the plane will move forward. It will not move as far forward as it would have done without drag, but it will move forward.

If your step size is large enough that the plane stops and then moves backward due to drag, then either your drag formula is incorrect or your step size is too large. Drag scales with velocity. The slower you go, the less the drag. You will never stop and then start moving backward under drag alone.

isn't drag at certain point be equal to thrust ? If drag is based on the speed, and because there is no speed increase deriving from thrust (my immaginary airplane has no starting speed) we will get that thrust = 0 so what's left is only the negative force of drag that will increase as my plane falling because it will increase the speed too right ?
 
  • #27
Your plane will have velocity changes continuously as result of acceleration due to gravity.

The air resistance and drag including all the factors as result of flaps and the shape of the glider as well as this gravity will all affect how component parts are accelerated relative to that of the centre of gravity of the object overall. The glider will maintain some speed through inertia.

The initial speed due to inertia from being pulled by the plane will grant an amount of kinetic energy in addition to the gravitational potential due to height.
This means that there is sufficient kinetic energy to move horizontally as well.
 
  • #28
plaguebreath said:
isn't drag at certain point be equal to thrust
Yes. If drag exceeds thrust, the plane slows down.
If drag is based on the speed, and because there is no speed increase deriving from thrust (my immaginary airplane has no starting speed) we will get that thrust = 0 so what's left is only the negative force of drag that will increase as my plane falling because it will increase the speed too right ?
If the plane is falling and gaining speed, that's drag plus gravity. If it is going to be looping the loop, that's lift as well.
 
  • #29
jbriggs444 said:
Yes. If drag exceeds thrust, the plane slows down.

If the plane is falling and gaining speed, that's drag plus gravity. If it is going to be looping the loop, that's lift as well.

I am just getting confused, let's see what I'm doing wrong, I take this picture:
climb.gif

Offcurse my plane is not climbing but just free fall on axis Y (my plane have angle of 0 let's say) so my plane isn't moving backward ?
 
  • #30
plaguebreath said:
I have to admit I am not good on physics...
Then you should learn the basics first, like Newton's Laws. After that you can look for some tutorials about "physics for games".
 
  • #31
plaguebreath said:
I am just getting confused, let's see what I'm doing wrong, I take this picture:
[snip]
Offcurse my plane is not climbing but just free fall on axis Y (my plane have angle of 0 let's say) so my plane isn't moving backward ?
If you have a plane that is pitched upward and is stopped dead in the air then that plane will not be airborne for long.

If you have a plane that is moving forward... Well then that plane is moving forward, not backward.
 
  • #32
Ok guess I am just looking stupid now, thank you everyone for the help.
 
  • #33
I think you can still work through this without advanced physics training. The Glenn research center slide shows some useful equations.

Here's the deal: if there is no thrust, the plane has to be pointed downward to gain horizontal momentum. Note that when pointed downward, the lift has a component that is pointed forward. It is this lift that propels the plane forward and allows it to glide. If the plane tilts up, the lift will have a component pointing backwards, so the plane is now losing horizontal momentum. If there's enough momentum to begin with, the plane can execute the loop de loop. If not, the plane loses too much momentum and starts to stall. That's because the lift depends on the forward (not necessarily horizontal) velocity squared of the plane. If you lose too much speed, you lose your lift. The instinctual action when you start dropping is to point the plane up more, but the correct action is to point it down more, so you can gain some speed and lift.
##L = \frac{1}{2} \rho v^2 S C_L##
from https://en.wikipedia.org/wiki/Lift_(force)
 
  • #34
plaguebreath said:
the first plane is the step at time 0, my plane is on starting position with velocity 0 and thrust =0
Ah, therein lies your problem. You can't fly if your velocity is zero. Point your nose down so you can gain some forward speed and hope you get enough lift before you hit the ground. (When pointed down, lift will provide horizontal acceleration. Once you've gotten enough horizontal velocity, you can start to point the nose more horizontal again, where lift will point up and start to slow your fall.) Planes have to be moving forward to work.
 

1. How is lift generated in a glider or airplane without thrust?

Lift is generated through the principles of aerodynamics. As the glider or airplane moves through the air, the shape of its wings creates a difference in air pressure above and below the wings. This difference in pressure creates an upward force, known as lift, which allows the glider or airplane to stay airborne.

2. Can a glider or airplane do a loop without any external forces?

Yes, a glider or airplane can do a loop without any external forces such as thrust. This is because the lift generated by the wings is enough to overcome the force of gravity and maintain the necessary speed and altitude to complete the loop.

3. How does the angle of attack affect a glider or airplane's ability to do a loop?

The angle of attack, which is the angle between the wing and the oncoming airflow, plays a crucial role in a glider or airplane's ability to do a loop without thrust. A higher angle of attack can generate more lift, allowing the glider or airplane to maintain the necessary speed and altitude to complete the loop.

4. What is the role of airspeed in a glider or airplane's ability to do a loop?

Airspeed is essential in a glider or airplane's ability to do a loop without thrust. The glider or airplane needs to have enough airspeed to generate sufficient lift to overcome the force of gravity and complete the loop. If the airspeed is too low, the glider or airplane may not have enough lift to maintain the loop and could stall.

5. Why is it more challenging for a glider to do a loop compared to an airplane?

A glider's ability to do a loop without thrust is dependent on its initial altitude and airspeed. If a glider does not have enough altitude or airspeed, it may not be able to complete the loop. In contrast, an airplane can use its engines to maintain the necessary airspeed and altitude to complete the loop, making it easier for an airplane to do a loop compared to a glider.

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