What does static thrust mean exactly

Posted by Ginyat@reddit | aviation | View on Reddit | 7 comments

I have heard some people refer to static thrust as thrust produced by an aircraft while stationary at sea level (all the usual atmospheric variables controlled too).
I have also heard some people saying that static thrust is the thrust of an engine while naked (not inside / attached to the aircraft.

Which one is the correct one? If there is none, which field use which definition?

For example, for the MiG-29, does static thrust mean that the naked engines produce \~8300 kgp, or is it the jet itself that produces \~8300 kgp while stationary at sea level?

Also, if it is for the naked engine, are they referring to a power output of a single engine, or both?

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Flame2512@reddit

Static thrust is generally defined simply as the thrust produced by an engine while stationary. You would typically infer that to mean near sea level and under standard atmospheric conditions (15°c, 101.325 kPa, etc.).

As for if the engine is installed in the aircraft or not, that can be ambiguous. Installing an engine into the aircraft will nearly limit the airflow into the engine and reduce thrust by some amount.

Most commonly quoted thrust values for the engines will have originated from the manufacturer at some point. If you are the manufacturer of an engine you would advertise it using the test bench value because:

The installed thrust will vary depending on the aircraft's design, so listing is not representative of what the engine will produce in any other aircraft (it may perform better or worse). If you give test bench thrust you are accurately stating that thrust the engine can produce under ideal conditions.
That will give you the best possible results to sell your product with. You don't want your engine to seem less good because of some other company's intake design.

Generally the only place you find the installed thrust rating listed is in the aircraft flight manual (or other aircraft specific documentation). Even then most aircraft manuals seem to just quote the manufacture specs. Some even include wording such as "uninstalled bare engine" or "on a static bench" when listing the thrust. In my experience the thrust rating of an engine is nearly always the test bench value unless explicitly stated otherwise.

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Necessary-Court-883@reddit

This is kind of absurd. dude here, thinks they operate with no oversight LMFAO! "Bro they gonan put best numbers, they want to sell". No manufacturers are out there giving best possible thrust with no correction factors. Thats who you go to prison dude. The FAA is a thing buddy, any manufacturer must adhere to FAA regulation and is tested with them.

Static thrust at sea level, standard day means this is the lowest guaranteed max thrust the engine will perform at sea level. It's a baseline thrust. Its for safety. all installation losses and anything your little mind can conjure has already been corrected. All bullshit numbers of people argue are all already accounted for. the engine is tested static, the lowest possible max thrust in extreme ambient airflow is taken

This is not rocket science. Its basic well established internationally followed regulations. Manufacturer test and must chose lowest possible thrust tested in extreme ambient conditions and add required correction factors to reflect installed in the fucking jet & done there you have it. guaranteed baseline thrust at sea for air crews to rely and calculate from.

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Flame2512@reddit

I should clarify that I am talking about military fast jet applications where the engines are usually buried inside the airframe, as opposed to civilian aircraft where engines are usually in nacelles, which likely offer smaller installation losses and may have different rules.

I stand by the point that in military applications (which is what OP was asking about) there is a distinct difference between static thrust (tested on a static test bench with no intake losses) and installed thrust (the static thrust produced once the engine is installed in the aircraft); with engine manufacturers typically using the uninstalled thrust. For example the Rolls Royce datasheet for the RB199 Mk 104 engine states it has 16,400 lb static thrust. However the Tornado F.3 flight manual lists the installed thrust as 15,736 lb.

For another example the Volvo RM8B [is quoted]https://i.imgur.com/Z4HRygC.png) as having an uninstalled static thrust of 125 kN. However according to the JA37 flight manual the installed thrust is only 110.3 kN.