Static thrust

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Aeh

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Hi,
Anyone have any idea about the static thrust of the 1) O-320 2) Rotax 912 100hp
Rgds
A
 

Vigilant1

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It depends on what type and size propeller.
Yep.

I'm always surprised when folks are interested in static thrust, unless they are using the engine to dry crops. It isn't very relevant to flight.
 

Pilot-34

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Ok I will bite how would static thrust be more relevant to dryIng crops than flight ?
 

Vigilant1

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Static thrust is only germane when the aircraft isn't moving. So, helicopter designers care about it. But for those planes which depend on airflow over a fixed wing to get airborne, the performance of the engine and prop at cruise speed, climb speed, and during the takeoff roll is generally what counts. And a prop specifically designed for static thrust might do poorly at airspeeds that matter.
For drying crops, static thrust is relevant.
I suppose people measure it because it is convenient.
 

Pilot-34

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I still don’t understand how static thrust could be relevant to crop drying.
crop drying is about airflow, volume.
I’ve dried millions of pounds of crops and never once felt the need to know static thrust numbers.
 

fly2kads

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Then how 'bout we say that static thrust is relevant to blowing dust off the run-up area at the end of the taxiway?
 

MadProfessor8138

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I'm always surprised when folks are interested in static thrust, unless they are using the engine to dry crops. It isn't very relevant to flight.
Not sure why you wouldn't be interested in knowing the static thrust # of an engine & prop combination.
Yes,it is only one aspect of the total performance spectrum but it is still extremely relevant.
For individuals that are looking for STOL performance, particularly while competing,it is a main focus point for them....climb and cruise #'s are a mute point because they are only interested in using the maximum amount of static thrust available to get the mass of the airframe moving as quick as possible to get airborne.

When racing.......
Do you want hp or torque ?
Do you want to be fast or quick ?

Those questions aren't very relevant either.......if you enjoy being the first loser.

Kevin
 

henryk

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to get airborne,
a=F/m ,

a=dV/dt
V=a*t

=greater static thrust=shorter take off distance...

BTW=iff taxii acceleration (a) is big,the TAKE OFF speed (Vto) is lowered...
(Cl dynamic > Cl static !)

f.e.=low power tow ,Vto=90 km/h,
big power tow ,Vto=70 km/h ...
 
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Vigilant1

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As soon as the plane starts moving, the static thrust number becomes increasingly irrelevant. In some cases, the thrust at fairly low airspeeds/ground speeds differs considerably from the static situation.
It is relatively easy to determine static thrust, so people do it
 

Pilot-34

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It is relatively easy to determine static thrust, so people do it
ding ding ding winner winner chicken dinner

I think that’s the key is static thrust has a strong relationship to launch which is an important aspect for many.

Add easy to that and you have a often quoted statistic
 

henryk

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Dan Thomas

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The propeller's blades are airfoils. Rotating wings. They have an angle of attack just like any other wing, and that angle of attack is dependent on the propeller's pitch, the RPM, and the forward speed of the airplane. AOA falls off as forward speed increases, because the inflowing air is changing the direction of the relative wind over the propeller blades.

So we can have an engine driving a propeller that has a low pitch so that the engine can reach redline RPM when the airplane is at full throttle, brakes locked, and we get a phenomenal thrust number. Once we start rolling, though, the AoA decreases and the engine overspeeds, so fixed-pitch props are coarser than that and the static thrust numbers are lower. If we're drying crops that low-pitch prop is fine. If we want to go flying we'd better have something better, or we overspeed the engine and prop or we have to reduce throttle, reducing power right when we need it the most. And the top speed will be very low, maybe not even above stall speed.

This is why the constant-speed propeller is the best form of propeller propulsion. Its pitch changes to get the best efficiency for any speed and power setting.

1594583803306.png
 
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MadProfessor8138

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Another misguided idea. HP is the result of torque times RPM. Torque is a completely useless number on its own unless we're discussing some static condition such as the torque on a bolt or nut when it stops turning at the torque setting.
I was referencing cars,motorcycles,etc.....
I figured the reference was obvious but it may not have been.
In 1/8 - 1/4 mile runs.....
Rpm does not win races.....
Hp does not win races......
Torque wins races.....

If you don't have the torque to pull the mass off the line....you've already lost.
I know engines that will rev to the moon......they lose.
I know engines with 700-1,000 hp.....they lose.
My little Fiero with a Cadillac 4.9 v8 and upwards of 300 ft lbs of torque will walk away from almost anything on the road from a dead pull.
The engine is only 230hp,stops breathing after 4,000 rpm... but has a ton of torque all the way to 4,000 rpm.

So,pertaining to aircraft......your engine can rev exponentially......have huge hp #'s.....but if you can't change those #'s into torque/thrust with pitch at the prop..........
For STOL competition....the static thrust is what is needed to pull off the line to get airborne....they are not worried about climb or cruise numbers because they will repitch the prop after the competition.
Yes,they will over rev in climb if not careful...that's why you hear them pull the power when they get airborne.

Kevin
 
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AdrianS

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What is it with torque?
By itself it's a totally meaningless number.

Yet some people think it's the only metric that counts.




Wierd.
 

Dan Thomas

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I was referencing cars,motorcycles,etc.....
I figured the reference was obvious but it may not have been.
In 1/8 - 1/4 mile runs.....
Rpm does not win races.....
Hp does not win races......
Torque wins races.....

If you don't have the torque to pull the mass off the line....you've already lost.
I know engines that will rev to the moon......they lose.
I know engines with 700-1,000 hp.....they lose.
My little Fiero with a Cadillac 4.9 v8 and upwards of 300 ft lbs of torque will walk away from almost anything on the road from a dead pull.
The engine is only 230hp,stops breathing after 4,000 rpm... but has a ton of torque all the way to 4,000 rpm.

So,pertaining to aircraft......your engine can rev exponentially......have huge hp #'s.....but if you can't change those #'s into torque/thrust with pitch at the prop..........
For STOL competition....the static thrust is what is needed to pull off the line to get airborne....they are not worried about climb or cruise numbers because they will repitch the prop after the competition.
Yes,they will over rev in climb if not careful...that's why you hear them pull the power when they get airborne.

Kevin
You can take that 1000 hp and gear it high or gear it low and get the acceleration or the top end you want. It's still 1000 hp, and that 1000 hp is the result of RPM times torque. The engine doesn't care what you drive with it; it just produces its 1000 hp at full throttle, redline RPM, under full load.

The propeller does the same thing. The engine spins it as fast as it can, which is less than redline for the average fixed-pitch prop in takeoff and climb, but at redline at full throttle in level flight, if it's pitched right. It's like second gear: not much good for quick takeoff and not much good for fast cruise at redline RPM.

Torque alone, like I said, is useless for figuring power. It's like trying to figure amperage in a circuit without knowing voltage and resistance. Hosepower is completely dependent on both torque and RPM (turns per unit of time) just like work is completely dependent on force and distance. I can push all I want (force) on a big boulder and not move it at all. I have accomplished nothing. No work. I can put a huge wrench on the nut of a ship's propeller and hang my weight on the end of that great long wrench, putting lots of torque on it, but if it doesn't move, I have generated no horsepower. Accomplished nothing at all.

One HP is 33,000 foot-pounds of work per minute. A ten-horse engine therefore will do 330,000 foot-pounds of work in a minute. We can gear than engine way down and turn a wheel very slowly but with a lot of torque, or we can gear it up to a wheel that turns very fast but with a lot less torque. Nothing is free, and nothing happens without any motion.

We had a very long thread here on this very thing maybe three or four years ago. There seems to be a lot of folks hung up on torque, as if it's something magic that can do wonders all by itself. It can't. In fact, I can't even torque a nut without some rotation, some fraction of an RPM, or the torque applied will accomplish nothing.

I could build a huge engine that generates 2500 foot-pounds of torque at 25 RPM, but you're not going to win races with it. Lots of torque that isn't up to the job. Good for operating a big winch or something, maybe.
 
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