Force calculations

In summary: To summarize, the question is how much force is needed to force a 6000kg private jet flying at 850kph to the ground by applying a force to the nose of the aircraft. Factors such as the angle of the force and altitude must be considered. The engine thrust is largely irrelevant in this situation and the target pilot will be counteracting the force by pulling back on the stick. The angle of attack and induced drag play a role in determining the required force, and equations such as "induced drag" and "angle of attack" can be used to calculate it.
  • #1
brenan
38
0
I'm not sure this is the best forum but I'm trying to work out how to do the math
for a problem -

Imagine a small private jet of weigtht about 6000kg flying at about 850kph
If a constant force was applied to the nose of the aircraft - how much force would it take
to force it down to the ground (assuming engine thrust is constant)?

I've looked at this and suspect there may be attendant problems such as the angle
of the force applied and perhaps even the altitude?

Could someone explain how to work out such a problem and any other factors that
would need to be considered please?

Thanks
 
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  • #2
Since you've chosen to apply the downforce on the nose of the target aircraft, it seems that you expect to be able to force that aircraft to pitch down, ultimately causing it to fly into the ground at high speed and crash.

The engine thrust of the target aircraft is largely irrelevant in this situation. You will be applying a torque that tends to pitch the craft down. The target pilot (or autopilot) will be pulling back on the stick, using the elevators (the horizontal control surfaces on the tail) to apply a downforce on the tail, causing a countering torque that tends to pitch the craft back up.

If you knew the maximum force that the elevators could supply and if you knew the distance from the wings to the tail and from the wings to the nose then you could equate the two torques and solve for the required force on the nose.
 
  • #3
Thanks jbriggs444

Yes the assumption is the craft will be forced down.
I didn't realize the wing and tail position would be so relevant. (I hadn't thought of it as a turning force
... more of a straight line vector - so thanks for pointing that out - In my head I had envisioned a
simple beam on a pivot type system - but with the forward motion and wing lift it is obviously more complex)
To keep it simple for me to start with can we assume everything is stable and fixed
(no pilot intervention or fly by wire response)
Would I be right in assuming an angle would occur whereby the wings cease to provide lift?
How could that angle be calculated?
Could you (or anyone) point me at formulas for the likely sequence of events so that
I can see what force is required to do this and begin to understand the math a little?
thanks
 
  • #4
If you are after equations, you could start with Google using a search term such as "induced drag" or "angle of attack"

http://en.wikipedia.org/wiki/Lift-induced_drag; [Broken] http://en.wikipedia.org/wiki/Angle_of_attack

As you force the craft's nose down the angle of attack is reduced. That means that lift is reduced. The plane starts to lose altitude. This means that the velocity vector is no longer horizontal. This tends to increase the angle of attack, thereby restoring lift.

If you want to reduce lift to zero, you have to apply enough torque so that the plane's pitch changes fast enough that the angle of attack stays constant at near-zero while the plane describes a parabolic trajectory.

http://en.wikipedia.org/wiki/Reduced_gravity_aircraft
 
Last edited by a moderator:
  • #5
for your question. I can provide some guidance on how to approach this problem. The first step would be to identify the relevant equations and principles that govern the motion of an aircraft.

In this case, we can use the equation F=ma, where F is the force, m is the mass, and a is the acceleration. Since the aircraft is flying at a constant speed, we can assume that the acceleration is zero. This means that the net force acting on the aircraft is also zero, since there is no change in its velocity.

However, if we want to force the aircraft down to the ground, we need to overcome the force of gravity acting on it. The force of gravity is given by the equation F=mg, where g is the acceleration due to gravity (9.8 m/s^2 on Earth). Therefore, in order to force the aircraft down, we would need a force greater than or equal to its weight (mg).

To determine the exact force needed, we would need to know the angle at which the force is being applied, as well as the altitude of the aircraft. This is because the force of gravity varies with altitude and the angle of the force would affect the components of the force acting in the vertical and horizontal directions. We would also need to know the specific aircraft model and its aerodynamic properties to accurately calculate the required force.

In summary, to solve this problem, we would need to consider the equations and principles of motion, as well as the specific variables and factors that may affect the force needed to bring the aircraft down. I hope this helps to guide your calculations.
 

What is force?

Force is a physical quantity that describes the interaction between two objects, causing a change in motion or deformation of an object.

How is force calculated?

Force is calculated using the equation F = ma, where F is force, m is mass, and a is acceleration. This equation is known as Newton's Second Law of Motion.

What are the units of force?

The SI unit of force is the Newton (N), which is equivalent to 1 kg*m/s^2. Other common units of force include pounds (lb) and dynes (dyn).

How is net force calculated?

Net force is the sum of all the forces acting on an object. It can be calculated by adding all the individual forces together, taking into account their direction and magnitude.

What are some common examples of force?

Some common examples of force include gravity, friction, tension, and applied forces such as pushing or pulling an object. Forces can also be caused by magnetic, electric, and nuclear interactions.

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