1 Attachment(s)
New Tachometer Background
With less well timed screws this time.....
.....And with a proper range on the dial.
One has to wonder why use a 4500 RPM Dial when 3000 RPM or less was the limit.
- Ivan.
Of Boost Gauges and Atmospheres
Hello Folks,
Iīm having some interesting problems trying to fine-tune a CFS1 .air for the engines of the FW200A: 9-cyl radial BMW-132A, 720 Hp at 2050 RPM, not geared, with a 1.2 ATA supercharger. Ceiling is 15000 ft because this passenger plane was not pressurized. Military versions had twice the MTOW and 2/3 more power.
Well, Googling the equivalent of 1.2 ATA, I got 35.9 inches of mercury to put into the .air file. Strangely enough, the standard German CFS ATA gauges marked 1.22 ATA, as did Ivanīs new boost gauges, but the FS98 Gauges that came with a panel for this plane marked 1.2 ATA. In FS98 they marked 1 ATA, because FS98 has no superchargers. (Power was compensated to 750 hp beause of this in the FS98 .air file). Moreover, it seems that 1 ATA is not 1 Atmosphere after all...
Consulting with Ivan, he mentioned that the equivalent value for aircraft of 1.2 ATA was 34.87 inches of mercury in the standard of measurement used for aviation engineers, but that there other standards of measurement in use... Oh deary me!, like my landlady used to say when I went to college in 1972.
Of course, entering 34.87 for Max. Manifold pressure in the .air file, this time the CFS1 gauges and Ivanīs new ones, gave correct readings.
I looked this up, and it seemed like a conspiration to drive us crazy... but Iīm not paranoid anymore... I think...
https://en.wikipedia.org/wiki/Standa...e_and_pressure
The mind boggles: There are more than a dozen standards!
Iīm sure many of you will know about that, but there are probably just as many or more less illustrated ones like me who will benefit from this. >Slap!< Ha! What one knows is not necessarily true all the time!
Just to mention a couple I found:
A) The one Google uses: Why on earth this one????
IUPAC (International Union of Pure and Applied Chemistry) since 1982:
Standard atmosphere: 750.06 mm of Hg, 14.5038 PSI or 29.530 mm Hg at Zero Degrees Centigrade or 32-F
The 35.9 inches of mercury = 1.2 ATA at Zero Degrees Centigrade seem to come from here.
B) This seems more realistic because not everyone is flying when it is freezing outside:
ICAO (International Civil Aviation Organization) and EEA (European Environment Association), and FAA:
Standard atmosphere: 760 mm of Hg, 14.6959 PSI or 29.921 in.Hg at 15 Degrees Centigrade or 59-F
So hereīs the 34.87 inches of mercury = 1.2 ATA at 15 Degrees Centigrade or 59-F, and seems the most reasonable.
A bit cold outside... but thatīs where aeroplanes fly.
C) Yet another, which we had in Physics at school, because laboratories are at room temperature - itīs more comfy.
NIST (National Institute of Standards and Technology.):
Standard atmosphere is 760 mm of Hg, 14.6959 PSI or 29.921 in.Hg at 20 Degrees Centigrade or 68-F
D) And just to top things off:
ATA is absolute atmosphere where the norm is the pressure of a 10-meter column of water.
1 at:= 10 mWater = 1 kp/cmē = 9,80665 N/cmē = 0,980665 bar = 98.066,5 Physical atmosphere
ATÜ is Overpressure above 1 atmosphere.
ATU is Underpressure for pressure below 1 atmosphere
And... there are other wierd combinations of 750 mm Hg (???) and different Temperatures used by the Gas Board and the Military...
No wonder Einstein said something about the intelligence of humans, but Iīm sure different countries use different standards to outsmart each other - that is more plausible.
What a lovely and varied world we live in!
Cheers,
Aleatorylamp