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In 4D paper airplane model, the effect of Washout is achieved by slightly push up the shallow part of the wing along the red line shown in Fig. 5. 

Fig.2 Dihedral angle and dihedral effect.

4D paper airplane:

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Fig.5 The "Washout" in 4D paper airplane.. 

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Fig.4 Wing design with "Washout". 

Washout (aeronautics) is a characteristic of aircraft wing design which deliberately reduces the lift distribution across the span of an aircraft’s wing. The wing is designed so that the angle of incidence is greater at the wing roots and decreases across the span, becoming lowest at the wing tip. This is usually to ensure that at stall speed the wing root stalls before the wing tips, providing the aircraft with continued aileron control and some resistance to spinning. Washout may also be used to modify the spanwise lift distribution to reduce lift-induced drag.

For high-speed jet, and some times the delta-wing, the wing design often has a feature called "Washout". This is shown in Fig. 4 and explained in Wiki: 

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Fig.1 Nomenclature and function for 4D model.

Fig.3 Aileron function.

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Tip for test fly:

  • Adjust center of gravity of 4D model airplane.
  1. Most models here are based on the airplanes with engine (a most heavy part of airplane) mounted at front. So these paper models also need to add weight at front.
  2. I generally use paper for weight adjusting (see detail shown in adjusting the center of gravity for Douglas TBD-1). Add nose weight after detaching of the front fuselage. Folding the weigh paper evenly for insertion around both sides of model’s main frame, so both left and right side is balanced in weight.
  3. In general, you will need more nose weight if your plane had the upward-flight that leads to the stall and then drop. On the other hand, you may consider reducing the nose weight if your plane goes down deeply. 
  4. The precise amount of weigh-paper is depends on many factors such as the type of paper used and the manner of your launch. The heavier weight helps the faster-launcher and the longer flying distance. But if you like the “floating” fly with slower launch, less nose weigh would help.
  5. You can keep a set of balance weights and switch the weight on the same model to enjoy a different flying character.

  • Adjust lateral balance of 4D models.
  1. An aircraft use aileron to roll (movement around aircraft’s longitudinal axis). (figure 2)
  2. Based on the function of aileron, if the model roll left side, turn up the trailing edge of  the main wing at right side, and vice versa. Generally, the degree of adjustment would be very minor. If it started to roll on the opposite side, you are over adjusted.

  • To test fly, use handle (see Fig.1 Nomenclature ) to hold the model and to launch. Leave the airplane leveled when releasing. (Most of launching mistakes are throwing it too hard and the model is not allied with the forward direction when released).


(Note: The 4D model was designed with a “handle”(Fig.1), which is located at opposite side of vertical stabilizer for most models. The sole purpose of the “handle” is for easy holding and launching of the model. You can omit the handle for a better appearance.)

  • The flying character of your model may vary completely by the ways of your launch. Since speed is proportionally related with force of lift, the initial launch speed will impact the lift of your plane. (Higher speed will lift the plane. But if flights up-ward, it will lead to the stall and then drop) . It’s fun to learn your model with various ways of launch.  

  • Depend on a given 4D model and construction, every model has different intrinsic aerodynamic character. Some model is suited for higher speed launch while others are the opposite. This launch pattern is somewhat loosely related with the speed signature of the original airplane that the 4D paper airplane is based.

  • Many models use dihedral effects for the stability (Fig. 2), make sure your model's dihedral angle is correct.

  • Check the configuration of your paper model often (the alignments between fuselage, main wing, tail wing, and the horizontal stabilizer). Each landing (or long-time storage) may have impact on your model’s configuration. 

  • It always fun to know more about how airplane control its movement. More you know, more you can test aerodynamic with your 4D models.

​ Enjoy! Embrace the Beauty and Take Off!​​

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Test Fly,the moment of truth: DIY project of paper airplane

Once beautifully crafted your 4D model, it’s the time to make adjustment (such as center of gravity and lateral balance) and to test fly. The model is not yet ready to fly right after construction, so do not be disappointed at this stage. If you have solid construction, it will fly.

There are two basic adjustments: (1) the center of gravity, the 4D model must have similar location for its center of gravity as its real airplane counterpart in order to fly; (2) the lateral balance, the adjustment you will need from time to time, even it may not at beginning.  To help that and make flying 4D model a very rewarding process, there is a few thing to know about the basic aerodynamic and how airplane controls its balance in the air. (click for more of Aerodynamics)