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How would I determine the thrust produced by a Lycoming O-360? I have looked for conversions of horsepower to pounds of thrust but have not had any success.

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A reciprocating engine generates a power on its shaft which is measured in horsepower or Watt. That's all a reciprocating engine can do. What happens with this power depends on what is attached to the shaft.

If you attach a millstone to it then you're going to get some tons of flour per hour.

If you attach four wheels to it then you're going to get a car bringing around a couple of passengers and suitcases at some km/h.

And if you attach a propeller to it then you're going to get some thrust measured in lb or Newton. A quick and dirty estimation of the thrust produced by this propeller given the engine power can be found here.

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  • $\begingroup$ You have to include a propeller efficiency factor in front of the cube root no or is that what k is for? In this video, a Cont C-85 with a fixed pitch prop produced about 320+ lbs of actual measured static thrust. The engine would've been well below its power peak tho, so probably only about 70-80 hp until it gets rolling. youtube.com/watch?v=i_tX-U_GbI0 $\endgroup$
    – John K
    Commented Dec 30, 2023 at 3:08
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    $\begingroup$ @usual impolite downvoter: explain your doubts so that I can improve my answer, thanks $\endgroup$
    – sophit
    Commented Dec 30, 2023 at 14:47
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    $\begingroup$ Your answers get downvoted because they've little value, show little consideration for the question being asked. People are not interested in answers that promote other related answers, or another answer that seemingly answers the question, all written by you. Add value to se-aviation with answers that inform, rather than answers that provide. Teach what is going on here, power plant to thrust, show some interpersonal skills, & consideration for the poster. Such answers may take hours to craft & compose... Integrate references to other answers appropriately. We value your knowledge! $\endgroup$ Commented Dec 30, 2023 at 17:54
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    $\begingroup$ @ThomasPerry: seriously? I explained that an engine supplies power, not thrust. I explained that you have to attach a propeller to the engine in order to convert that power into thrust. I explained how to estimate that thrust from the power... Sorry but I can't do more than this. If you're so sure that my answer is garbage then just flag it and I'll delete it... $\endgroup$
    – sophit
    Commented Dec 30, 2023 at 18:29
  • $\begingroup$ Seriously! Do not delete your answer. I edited your answer, with all due respect to you, to informatively direct the answer to the question being asked. If you find the edit acceptable, then let it stand, or if you wish, edit the answer otherwise. $\endgroup$ Commented Dec 30, 2023 at 19:36
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Welcome to the club. Unfortunately, in aviation, some people are loathe to describe engine/prop output by thrust because prop efficiency, especially fixed pitch, will change with airspeed.

Generally, a fixed pitch prop is designed as a "climb prop" or a "cruise prop", with finer or coarser prop pitch, respectively.

Props generate thrust by mass acceleration as spinning airfoils, so angle of attack of the prop is critical.

What one can do is build a "thrust curve" at various speeds (a power curve if you will), by first determining the thrust requirement in level flight at various airspeed with gliding tests.

Now you see how much excess thrust (at full power) you have by climbing at those airspeeds.

level flight thrust + climbing thrust = total thrust

The level flight thrust is determined by sine glide angle × weight. The climbing thrust is determined by sine climb angle × weight.

This method will give, to an approximation, the thrust output of the engine/prop combination at various airspeeds.

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