• Main page
• Theory
  • Prolog
  • Aaerodynamics
  • Aaerodynamics emergency situation
  • Choice of engines.
  • Construction
  • Safety flying twin or multi engines model.
  • Single engine landing twin model isn’t difficult at all. /Part I.
  • Single engine landing twin model isn’t difficult at all. /Part II.
  • Master Class.
  • Epilog.
  -->
• Models
  • Dung's models/USA, Texas. Twinman's revue.
  • B-25/ Arkhangelsk
  • DC-3/ Arkhangelsk
  • DO-335/Saint Petersburg
  • Flying King(4 engines trainer)/ USA
  • Twinstar II/ Saint Petersburg
  • FW-189/Kiev.
  • Four engines sport model.
  • UltraSport twin
  • Under translation.
• Useful
  • Winter season fly.
  • Warm box for batteries.
  • Warm clothing for the transmitter.
  • Under translation.
• Leave message

Aaerodynamics emergency situation.

Below I will describe terrible things – why models fall down when one side of twin or multi models dies.

Before I want to notice that model will fall if pilot controls model wrong manner only. Itself model doesn’t fall. It falls from pilot’s inaction or wrong reaction.

Therefore it is very important to know how model flies than one side dies.

Normal mode and emergency situation. Allocation of the forces

Single engine model	Twin engine model
Normal mode

Lets through look allocation of the forces.

The black arrow (it’s sum orange one and blue one) is lift one half of wing. The orange arrow is the lift from blowing propeller. The blue one is the lift from moving wing through air (speed lift).

The total lift is sum two black arrows I did not draw because this force doesn’t interesting for us.

As you can see we do not watch any deference’s in both cases. Behavior modelesses are the same in both cases.

Switch off one engine/side (single engine in case one engine’s model). Let’s see what will happen.

The black arrows as before show sum all lifts. In case single engine’s model the black arrows equal blue (speed lift) only. Two black arrows left and right ones are equal.

In case twin model you can see difference. In the right there isn’t blow from propeller and the orange arrow (lift) disappears. We get disbalance left and right wing panels. For visibility I rest sum force and subtract the common force for both wing panels.

In case single engine model we didn’t see anything terrible. In case twin model we can’t say the same thing. The black arrow shows disbalance lift on wing panels. The green arrow is the lever of the disbalance force. If you remember Mister Archimedes, he said if he had had lever he would be able to lift the Earth.

Starting from the above we can conclude the model will rollover and fall when disbalance force produces bank when wing stops hold model in the air. I remember that lifting surface of the wing equal area of projection wing to ground. The bigger wing’s bank is the less projection to the ground and less wing’s lift.

Let’s look the force but from above only. I want to notice that in such position model will be short time after one side dies. The thrust (orange arrow on lever – green arrow) starts to turn model to the left. Model will turn until fin doesn’t stop this turn. After this, model will fly strait with some angle and probably with some bank.

Let’s see such position of the model carefully. In such position will be every model with died one side. Model has follows bad things in such position: The thrust is decreased twice. The grey colored areas of wing and stab are in the shadow from fuselage and therefore this area doesn’t produce any lift. We know what the lift lower on this side. These shadow arias increase disbalance lift on wing panels. Additional to decrease thrust the model which flies sideways has higher drag from fuselage and fin. This drag decreases model’s speed additionally.

Now you can image why twin and multi engine’s model flow down when one side dies. Sometimes this fall is called spin. But it isn’t real spin – it is spin of one (died) wing panel.

Scenario models fall.

• One side stops.
• The speed of model decreases.
• Model starts to turn to the die side. Only fin produces force to prevent this turn but fin produces additional drag braking model. The flying speed of the model gradually decreases.
• Further it is possible two scenarios. Both ones are bad as result doesn’t understand fall.
• The fin doesn’t hold model in strait fly due lack of speed (lack of force). The model starts to rotate around died side. Lift on the die side decreases, this wing panel can’t hold itself in the air. It drops – model start to fall down.
• The fin hold model in strait fly but disbalance forces turns over model.

It is all what I want to say this about.

If you decided that it is no chance to save model. This is wrong opinion. All described above for one purpose that you will be ready if such situation happens. The model will be saved with correct controls pilot always or all damages will be minimized.