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That makes senseThe problem is that, like I said, the torque is the result of the pressure in the cylinders (pounds per sq in acting on the piston tops) puhsing down through the connecting rods that turn the crank.
Works outSo we have a crap load of variables. If you are turning 2600rpm and using 4lbs of boost you get one pressure in the cylinders,if you are using 2600rpm and 6lbs boost you get a different pressure in the cylinders (roughly and that is the problem) 10% more pressure
How does torque vary with RPM for the same manifold pressure?if you are using 3000rpm and the same boosts the pressures will be slightly different.
Wait, I'm confused -- I thought pressure was caused by the mass of air per given area? Why would these figures vary?It gets even worse because this only works at one altitude or air density. Pressure in the manifold is related to the mass of air (weight of the air) but it is not a 100% correlation.
6lbs boost at sea level is not the same mass of air per minute as 6lb boost (or the same intake pressure ) at 10,000ft.
So would that mean if theoretical maximum thrust with 100% efficiency was 10,000 pounds and it was 80% efficient you'd get 8000 lbf? Or is it something else?I still don't know what you are trying to do with this, The best props in WW II were only about 80% efficient which means 20% of the power going to them (no matter how you measure it) was wasted.
Wait, I'm confused -- I thought pressure was caused by the mass of air per given area? Why would these figures vary?
I'm curious if there's anyway to infer thrust by the following variables: Propeller diameter, RPM, manifold pressure, altitude, TAS, rate of climb? Even if the exact figures are not stated, sometimes it's possible to infer them. After all if you have 60x = 120, it doesn't say it outright, but x = 2, and that can be inferred by dividing both sides by 60.
Is there any rule of thumb to calculate that out?Temperature. ... At 0ft the air needs less compression to reach the required MAP/boost than at 10,000ft. Even with aftercooling, the intake air temperature at 10,000ft will be higher.
Where would you either find drag & speed and altitude, or how would you compute it out?If you know the TAS and the drag at that speed and altitude, you can calculate the thrust.
FHP varies with RPM, which will impact brake torque. Track down the 'Power from fuel flow' pdf from Lycoming. That will provide some guidance from getting power from MP and RPM. The factors are going to vary, so you will need to back calculate them from known engine data.How does torque vary with RPM for the same manifold pressure?.
I was trying to get an approximation of thrust, as I was under the impression that if you know rate of climb and speed, you could determine thrust.Shortround6 said:You are trying to reinvent the wheel and take few shortcuts.
Parasitic drag is simply the drag produced by the amount of air flowing over the entire aircraft? Induced drag is drag caused by the production of lift, correct?You have to figure out how much power (or thrust) is being used just to keep the plane in the air. Best climb speed is usually about the point where parasitic drag crosses over with induced drag
What's FHP?FHP varies with RPM, which will impact brake torque.
Fascinating...Track down the 'Power from fuel flow' pdf from Lycoming. That will provide some guidance from getting power from MP and RPM.
Well, I've been collecting a bunch of test-data from WWII Aircraft Performance, and some data I've found here.For climb rates, try googling 'The Bootstrap approach to Aircraft Performance'. You will need to either test fly to obtain the parameters, or locate as much performance data that you can lay your hands on.
I do have a Mac... unfortunately, it isn't suited for the later OS...The Benchmark software appears to match what you are trying to achieve, but I have never used it. (Only for Mac) Benchmark
What is friction horsepower?FHP = friction horsepower
I assume this applies to constant speed props? The ones that weren't constant speed went faster and faster as you went up to the critical altitude...The amount of HP needed to turn the engine over at stated RPM. friction goes up with the square of the speed.
CFD = Computational Fluid Dynamics?Yep. CFD should be pretty close
Where would I find that? As for accuracy, I was basically thinking a ballpark estimate.Crane technical paper 410 will get you in the ballpark.
YesCFD = Computational Fluid Dynamics?
CRANE Technical Paper 410 US (2018) Google may find an old copy - the laws of physics don't change much. Treat the throttle plate like a butterfly valve, you will have to interpolate the ID factors as I doubt the actual ID of the carb will match a standard pipe ID.Where would I find that? As for accuracy, I was basically thinking a ballpark estimate.
Is there any ways to calculate for throttling loss?