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Wednesday, 17 July 2013 09:20

The Loop

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The loop is a vertical maneuver, which consists of making a vertical circle from straight and level flight.

 

It is one of the most basic maneuvers of aerobatics. Even so, it is not easy to do it well, since it must be a perfectly round circle and you must exit at the same altitude and speed that you had at the beginning of the maneuver.

It consists of several parts that make it work, but it is simplified greatly if you are able to begin it correctly.

Therefore, it is very important that the initial pull has to be sufficiently tight to maintain speed and to be able to fly the top part. In a good start, we should pull close to 3Gs. You have to add to that the pull has to be straight, without ailerons inputs, in order to not lose direction and to avoid the plane twisting at the topmost part of the loop.

So it is very important that the students should have a good technique to achieve the perfect 45 degree ascending lines, since the beginning is exactly the same. 

Aresti drawing of the loop

 

Performing the maneuver

Even that the technique may differ from different planes, the basic acknowledge is the same for any aircraft. In the following procedure we describe in detail how to perform the maneuver in a basic aerobatic aircraft like Cap 10B or Super Decathlon.

1: Accelerate the plane to a speed 20% higher than the cruising speed making a shallow dive, controlling. This speed will vary depending on the plane you fly. Normally, it varies between 250 and 300 km/h.

2: Raise the nose to the position that allows you to maintain the altitude

in upright and level flight. Once in this position, pick a reference point with the horizon and of altitude.

3: Pull the stick backward in a constant and straight way at 3Gs, the same as in a 45 degree ascending line.  At the same time, we apply progressively full throttle while raising the position of the nose.

4: Once you pass 45 degrees, the speed begins to fall rapidly, and the elevator loses effectiveness. Therefore, we pull a little more deeply to maintain a stick pressure similar to that which we had at the beginning, and the "pitch rate" will be the same.

At this point, we should already be looking at the reference point on the wing, seeing how we describe and draw a circle.

5: Passing from vertical line, when we see that we are beginning to push back, we begin to relax the elevator pressure on the stick little by little, since at that point if we maintain the stick pressure, the nose is going to want to fall below the horizon, and will tight the top part of the loop. 

6: Once upside down, relax the stick pressure completely in order to not close the loop. We have to allow the plane to fly the top part in ballistic flight. At this point, we will look up to find the horizon and see if we have become twisted. In case we don't arrive with the wings leveled, we can correct it by leveling up using the ailerons. “Elevator in neutral!”

7: When the nose arrives at the horizon, we begin to progressively pull again from the elevator, while reducing the power slowly in order to not accelerate too quickly and avoid the engine going above maximum RPM in case of not flying a constant speed propeller plane.

8: Arriving vertical down, we maintain the stick position, without relaxing it. At this point, the plane speed increases very rapidly, and the elevator begins to gain much effectiveness so that the plane closes the last part of the loop, while we notice how the stick pressure progressively increases.

Now, lastly, we increase the power very progressively in order to avoid the plane losing speed upon arriving at a straight and level flight position.

Vertical displacement of the nose in the initial pull (Figure 2)

 

We see how we should cut a line with the nose that is perfectly perpendicular to the horizon, avoiding being displaced to the sides. 

Comparison of stick pressure with speed. (Figure 3)

 

In the drawing at the right, we see that the speed is much greater in the bottom part of the loop, therefore we apply greater stick pressure.

 

Common errors:

The primary errors made with this maneuver are:

1. Pulling the elevator with aileron inputs, normally towards to the

left.

2.  Pulling the elevator with not enough intensity.

This will cause the plane not to have enough speed at the top part of the loop and make it “impossible” to fly it.

3. In the moment of relaxing elevator or unload, the pilot does it very suddenly.

Doing this we "set a trend" to the plane, making it fly in a straight line while having a certain speed instead of continuing to draw the loop.

4. Not beginning to recover when the nose reaches the horizon. In this point, if we don't begin to pull, the plane will begin to accelerate too quickly, impeding us from being able to draw the rest of the maneuver correctly.

5.Relaxing the elevator input in the last 1/4 of the loop. What will occur is that we go down below the initial altitude, which causes us to not draw this part correctly.

 

How we can correct the errors:

1.We correct this point in the same way as the normal 45 degree lines.  We must be sure to begin the maneuver completely straight and level. If we have not the wings level, it is very easy to begin the maneuver twisted.

Another of the causes is usually created for looking at the wing device too early. With this, we unconsciously bring the stick where we look, causing the plane to turn on the ascent.  For this reason, we should not be in a hurry in looking at our reference device on the wing.

2. Nor should this point bother you if you have good technique in ascending at 45 degrees. Similarly, you should get used to "feeling" the pressure of pull at 3Gs. Also, you can read the accelerometer at the initial pull and maintain the pitching rhythm.

3. At this point, simply do not suddenly release the elevator load.  We relax very progressively seeing how the plane continues drawing the looping. “Even we continue looking at the wing.”

4. As soon as the nose reaches the horizon, we must begin the level off; our idea is not to accelerate the plane too much. The pull should be progressive; otherwise we can enter in a stall or not be able to accelerate the plane sufficiently.  The idea is that you begin to pull at the same rate that you released in the ascent, while reducing the throttle.

5. As at this point the elevator is set to "hard," it is very easy to release the control. You should remember to maintain the position and see that the stick pressure increases progressively. Practically, you don't have to work any more until you arrive to the position.

6. It could be that if you have had to correct the position of the plane in the horizon at the top part of the maneuver, you have lost the initial direction during the ascent. When you are in the last part of the loop, look for the reference point that you had and bring the nose towards it with the ailerons in a very subtle manner.

 

Elevator errors:

-In the first drawing we see that upon pulling very kind at the beginning of the loop, we cannot reach the top part of this, since we have dissipated all of the energy of "velocity" before reaching the top part. Therefore the plane falls before it can draw it.

-In the second case, we see that the loop is closing. This is due to not relaxing the elevator force in the top part of this or pulling the stick too quickly and too soon. This is when the looping takes the form of an egg.

-In the third case, we see that the plane does not draw an arc, rather instead it continues ascending. This is due to two possible causes: Reducing the elevator pressure too quickly or pushing the stick trying to maintain the nose height. This is when the plane does not do the parabolic flight, ascending until having no speed, the result being something similar to the second case.

-In the fourth case, we see that we begin the loop from below the initial altitude. This is due to pull very late at the beginning or without the necessary intensity. With this, we lose altitude, and carried to the extreme, take the plane past its structural limits due to a higher speed at VNE or too much elevated load at the last part in an attempt to recover the horizontal flight.

-In the fifth case we see that we ended the loop above the initial altitude. This is due to we pull hard very early or with a lot of energy. With this we end the loop above where we had begun and at a lesser speed. Carried to the extreme we make the plane enter in loss due to the high angle of attack the plane is undergoing.

Aileron errors:

It is very usual for there to be a little aileron "input" without realizing it during the pull towards the reversed flight position. It is normally towards the left as noted above. “stick displacement and displacement of the arm upon looking at the reference point of the wing.”

 

-In the first drawing, we see that we arrive at the top part of the looping with the wings leveled with the horizon. It is a signal that we have ascended straight correctly.

-In the second drawing we see that we arrive turned with the right wing low. This tells us that we have made the ascent with some aileron to the left. We should correct with ailerons to the right to straighten up.

-In the third drawing, we see that we arrive turned with the left wing low. That tells us that we have made the ascent with some aileron to the right. We should correct with ailerons to the left.

“Remember that you always make the position corrections in the top part of the loop when you are in ballistic flight and not pulling. Otherwise, if you are pulling, you will divert more from the direction at which you began the figure.”

On the other hand, if you don't correct the top part of the loop and level the wings with the horizon, when you make the descent, you divert even more from the initial direction at which you began.  

 

Wind correction:

Despite flying a good loop, we can find ourselves on a day with strong wind that spoils the figure and even complicates the situation in the box in a competition program if we don't pay attention and act as is necessary.

We can find ourselves in 2 primary situations:

-We find ourselves with a strong wind parallel to the flight direction, at the front or at the tail.

-We find ourselves with a strong lateral wind, whether it be from the right or from the left.

 

- Correction with strong wind aligned in the direction of flight.

-As the following drawing shows, if we must perform a loop with a strong component of headwind, we will find that upon doing the loop with the usual technique, we don't describe a circle as we are used to. Rather, to the contrary, we describe something more "flat" since at the top part, we are displaced in favor of the wind, which causes us to be displaced at a higher speed than we are used to.

 

"We correct this pulling more gently in the first and last quarter of the loop, and we tight more the top part. With this we will try to correct the wind and draw a round loop.

-In the following drawing, we see the opposite case. If we must perform a loop with a strong tail wind, we see that performing the figure with the normal technique the first and last quarter is better, and above (upper part of the loop) we will be displaced, so that we will not draw the top part correctly.

"We correct on the contrary, we pull harder in the first and last fourth of the loop, and we try flying the top part of this as much as possible, trying to arrive with more speed than usual.

 

- Correction with strong cross wind:

 

The following drawing shows us the side displacement we experience in a loop in cross wind conditions.
It is not as visible from the ground, but it is basic for maintaining a good position in the aerobatic box and not giving the impression of flying twisted, since it can be appreciated that the plane is displaced horizontally, above all in the first part of this.The best way of correcting the side wind of the loop is to apply the same procedure as a landing with cross wind.

 


We apply a little roll to the wind and opposite foot, in this way we make a small "skid" towards the wind, avoiding displacement while showing the judges a good vertical position. 

 
 
Read 5038 times Last modified on Friday, 17 January 2014 14:50
David Membrives Aviles

- Profesional pilot, aerobatic flight instructor and competitor.

-Member of the Portuguese national team.

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