How does one go about measuring static thrust?

Never Knew u could measure thrust.only on turbines i thought

I've never tried, but I there's two ways I can think of:

1). If the engine is on a plane, set it on a LEVEL surface, and attach a restraint to it with a spring scale or a digital scale for weighing a fish, then measure the thrust with the engine at full throttle. The same method can be used by using a small engine test stand mounted on rollers which roll VERY easily.

2). Mount the engine on a test stand with the prop facing straight up. Place it on a weigh scale and record the weight, then record the weight when the engine is full throttle. The difference in weight is the thrust produced. Use EXTREME CAUTION! with this method. Lack of proper saftey precautions could easily result in severe damage to person & property.

This is how we were taught to measure thrust back in High School Physics class.

[QUOTE]Originally posted by strato911

2). Mount the engine on a test stand with the prop facing straight up. Place it on a weigh scale and record the weight, then record the weight when the engine is full throttle. The difference in weight is the thrust produced.

raabid

Strato911" is right on both ways to measure static thrust of props.

His #2 applies to small electric motors with pusher props and the force is 'downward onto the scale'

You should try to give a little more info when asking this type of question, it helps to know what type of engine/motor you are using.

Dan Z

Why?

Just a bit of clarification on my method#2:
I meant for the engine to be placed such that the prop-wash from the motor has time to dissipate before it reaches the weigh scale. The prop's thrust will attempt to lift the motor, reducing the weight on the scale. If the prop-wash hits the scale, it can cause false readings (it lifts the engine, but pushes down on the scale). Just make sure the engine stand is several pounds heavier than the thrust you expect the engine to produce. This should work for any size of engine.

All things considered, method #1 is easier.

Ok
not here to argue"

Actually boots, I was wondering why he wanted to measure static thrust, It was a follow on to your request for more info.

Static thrust is pretty much a meaningless measure for beginners. We deal in the realm of dynamic thrust of an unloaded propeller and a moving airplane. The stump pulling power of a stalled prop, also known as a "fan" is really only important to the high alpha/high$$ guys.

I'm not being critical, just curious.

Funny, I had the same dilemma. Solved in as follows:

I put the plane on the floor, and attach a wire to the tail. I made a see-saw contraption with two balsa sticks at 90 degrees on a pivot point in such a way that the more the aircraft pulls, the more a balsa stick pushes down on an electronic scale. Voila, thrust in ounces, pounds, kilograms, whatever you like....

Dutch engineering, I tell ya.

Hans

ctdahle
Agreed, but power/speed seems to be on a begginers agenda
I worded it the way I did, so I would not insult or inflame.
The reason was due to not enough info provided, buy the question asked.

Stratto911's #2 combimed with a beginner? could get someone HURT, as I read His FIRST post.

Your (WHY?) is a reasonable question, I did not want to just assume" and it could have gone both ways. ? static thrust OR ?? why did I 'ad' to strato911"s #2 example.

All set aside, there are many forums to ask questions in. Jets and giant aircraft would be more suited to ?what He is asking?

Dan Z

Sorry, I didn't realize the why was directed at me. I had read a few days ago that a plane's weight could not exceed 1/4 of the static thrust it produced or it would not fly, and that a 1 to 1 ratio of thrust to weight would allow you to prop stall. I am playing around with some foam and stuff, building a plane for ****s and giggles, and wanted to know how heavy it could be and still fly.

WornBoots - Naturally, I would hope anyone using that method would use EXTREME CAUTION!. Lack of proper saftey precautions could easily result in severe damage to person & property.

Method #1 (horizontal thrust measurment) is far safer and easier, but I included method #2 just for the sake of being thorough.