I've always read 'static thrust' as being rated in pounds. Exactly what does this mean, and how can I personally test/determine the amount of 'thrust' being generated by any given engine?

Thanks,
Tom...

Simplest way I can think of is one of those large fish weighing scales. Devise some type of hanger around the back of the airplane that won't get burned off, or hook around the nose gear or something, and then run the engine up and watch it pull against the scale. Whatever it maxes out at is static thrust. I don't know of any way to measure dynamic thrust unless you can calculate what it would be.

static thrust is on the ground correct? so that would mean dynamic thrust is what you get while actually in the air...am i on the right track with this one?
-Erik

Seanreit,

To measure 'static thrust' of an engine, wouldn't I need to test that engine as a stand alone unit? The additional wieght of an airplane would surely have an influence on the 'scales', if my thinking is correct. Even in testing an engine by itself, there will be certain factors to consider, ie., the weight of the engine itself, the amount of friction/drag inherrent to the design of the test bed upon which the engine is mounted upon, and the means by which the pull or push is measured. Perhaps I'm using the wrong term when I say 'static' thrust. What's the difference between 'static' thrust and 'dynamic' thrust of an engine?

Tom...

Erik,
It makes sense to me, but then again. Many things that make sense to me don't make sense to others... like spending lots of money on models airplanes!

haha, that's very true tmj
-Erik

Well, you could get all fancy and do some differential pressure testing and then you have to take a lot of other factors into consideration such as temperature, pressure drops and velocity of the air. What I'm talking about is a simple down and dirty proof. I don't know how to measure dynamic thrust, however, All current forms of air breathing propulsion work by accelerating a quantity of air to a higher speed in order to generate thrust. In general the amount of thrust developed can be considered to be the product of the quantity of air accelerated and the velocity to which it is accelerated. A propeller accelerates a large quantity of air to a low speed, around 100 MPH, a ducted fan accelerates a smaller quantity of air to a higher velocity, around 200 MPH, while a turbine engine accelerates a small quantity of air to very high velocities, over 400 MPH. In general the thrust developed is proportional to the difference between the flight speed and the velocity the air is accelerated to by the engine. If a propeller powered model generates 10 pounds of thrust on the ground it would only produce around 5 pounds at 50 MPH, a ducted fan model generating 10 pounds of thrust on the ground would hit the half thrust point at around 100 MPH, while a turbine engine powered model would not hit this point until over 200 MPH. Because the turbine engine losses its thrust at a much lower rate it is necessary to fly at lower throttle settings so as to not over speed the model. * JPO

Respectfully,
Turbine engines do not create thrust by accelerating air,but by differential pressures internally by the burining of fuel and an oxdizer(air). IE in the combustion chamber there is a higher pressure vector generated foward than to the rear,as the gases are allowed to escape through the NGV and turbine blades. The difference in these overall pressure vectors is what we measure as thrust. Same type thrust as a rocket, but we have to introduce our O2 ,whereas the solid or liquid propellant in a rocket motor provides the O2. A balloon when released moves because the pressure 180 degrees from the opening is higher ,therefore the pressure moves it in the direction of highest pressure.
Someone else may explain it clearer to you.

BRG

Nat

Respectfully,

You two are both half right... Thrust, as a force comes both

= Mass times acceleration + Pressure times area.

btw.... exhaust velocity of an Olympus is
closer to 800-900 mph subsonic


Eddie Weeks
http://www.corpcomp.com/weeks1/