Standard temp/pressure compensation
08-03-2003 | 12:26 AM
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From: CA
Standard temp/pressure compensation
I have a turbine that is claimed to put out 13.9kilos thrust at 10deg C. I do not know at what barometric pressure (altitude) this was at.
Can someone give me the formula for calculating expected thrust at a different temp and baro pressure.
Sure would be nice for all turbine manufacturers to spec their motors at Standard Temp and Pressures.This is the only way to properly claim thrust output for the consumers (I.E. brand "a" turbine claims thrust at 30lb( S.T.P.) , brand "b" claims 30lb BUT AT 10deg C. --brand "b " isn't a true 30lb motor .)
Jake
Can someone give me the formula for calculating expected thrust at a different temp and baro pressure.
Sure would be nice for all turbine manufacturers to spec their motors at Standard Temp and Pressures.This is the only way to properly claim thrust output for the consumers (I.E. brand "a" turbine claims thrust at 30lb( S.T.P.) , brand "b" claims 30lb BUT AT 10deg C. --brand "b " isn't a true 30lb motor .)
Jake
08-06-2003 | 03:59 AM
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From: Paso Robles,
CA
Standard temp/pressure compensation
Ideal gas law is express as
PV=nRT
Where P is pressure ("Hg), V is volume (ft^3); n (moles, lbs/lbmole); M (molecular weight, lbs/lbmol); R (gas law constant = 21.85 ("Hg*ft^3/lbmol/deg R); T (deg R). However, there is much more involved!!!
What you might be looking for is an altitude density calculator. Search the Internet and you can find tons of them. My favorite is http://www.wahiduddin.net/calc/calc_hp_dp.htm
We rate JetCat engines for a standard day. The ICAO International Standard Atmosphere standard conditions for zero density altitude are 0 meters (0 feet) altitude, 15 deg C (59 deg F) air temp, 1013.25 mb (29.921 in Hg) pressure and 0 % relative humidity ( absolute zero dew point). The standard sea level air density is 1.225 kg/m3 (0.002378 slugs/ft3).
It is very difficult however to directly calculate the thrust change at different density altitude conditions. For example, the P160 is more sensitive to density altitude compared to P80s or P120s. This means the P160 is closer to the edge. This is true with many other brands. The best way I have found in testing new engine models is doing it empirically. I test them here in LA for the closest readings to a Standard Day and then send the engine to MTSS, our dealer in Denver, to test them at 5,400 feet. The differences are quite significant!
I think you will have a hard time calculating the exact thrust difference for different altitude densities.
Best of luck!
PV=nRT
Where P is pressure ("Hg), V is volume (ft^3); n (moles, lbs/lbmole); M (molecular weight, lbs/lbmol); R (gas law constant = 21.85 ("Hg*ft^3/lbmol/deg R); T (deg R). However, there is much more involved!!!
What you might be looking for is an altitude density calculator. Search the Internet and you can find tons of them. My favorite is http://www.wahiduddin.net/calc/calc_hp_dp.htm
We rate JetCat engines for a standard day. The ICAO International Standard Atmosphere standard conditions for zero density altitude are 0 meters (0 feet) altitude, 15 deg C (59 deg F) air temp, 1013.25 mb (29.921 in Hg) pressure and 0 % relative humidity ( absolute zero dew point). The standard sea level air density is 1.225 kg/m3 (0.002378 slugs/ft3).
It is very difficult however to directly calculate the thrust change at different density altitude conditions. For example, the P160 is more sensitive to density altitude compared to P80s or P120s. This means the P160 is closer to the edge. This is true with many other brands. The best way I have found in testing new engine models is doing it empirically. I test them here in LA for the closest readings to a Standard Day and then send the engine to MTSS, our dealer in Denver, to test them at 5,400 feet. The differences are quite significant!
I think you will have a hard time calculating the exact thrust difference for different altitude densities.
Best of luck!
08-06-2003 | 01:16 PM
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From: Fond du Lac,
WI
Performance vs. Density Altitude
Jake:
About 3 years ago, at Florida Jets, Vern Montgomery was recording the installed thrust of many of the jets with his homemade scale on wheels....he may still have that data...
At the time he did my engine, Rei Gonzales' engine, and another guy with a Mercury, all externally mounted on 2 HS's and a Roo, both my P-80 and Rei's 750F were at 16.5 lbs, and the Merc was just under 16.0 lbs.
I don't remember the exact atmospherics at the time, but guessing, it probably was 85 deg with dewpoint of 65 deg, ambient pressure close to 29.92 and altitude at Flagler of about 25 ft MSL....giving a density altitude of close to 2000 ft.
As Bob noted, JetCat uses STP for it's thrust calculations. AMT NL reports their thrust at STP, and you can probably use their data for AMT USA, comparing similar engines. I know Carlos at RTI has done umpteen thrust recordings on many engine types, and also is a good source of comparative data.
My own personal experience with JetCat P-80/120, AMT USA Mercury/Pegasus, and a RAM 1000, all externally mounted, is that they all put out thrust very close to what is advertised on a standard day.
Tom
About 3 years ago, at Florida Jets, Vern Montgomery was recording the installed thrust of many of the jets with his homemade scale on wheels....he may still have that data...
At the time he did my engine, Rei Gonzales' engine, and another guy with a Mercury, all externally mounted on 2 HS's and a Roo, both my P-80 and Rei's 750F were at 16.5 lbs, and the Merc was just under 16.0 lbs.
I don't remember the exact atmospherics at the time, but guessing, it probably was 85 deg with dewpoint of 65 deg, ambient pressure close to 29.92 and altitude at Flagler of about 25 ft MSL....giving a density altitude of close to 2000 ft.
As Bob noted, JetCat uses STP for it's thrust calculations. AMT NL reports their thrust at STP, and you can probably use their data for AMT USA, comparing similar engines. I know Carlos at RTI has done umpteen thrust recordings on many engine types, and also is a good source of comparative data.
My own personal experience with JetCat P-80/120, AMT USA Mercury/Pegasus, and a RAM 1000, all externally mounted, is that they all put out thrust very close to what is advertised on a standard day.
Tom
