Ias, gs, tas, oh my!

[mallcott]

Huh? "position and oxygen levels" have absolutely nothing to do with Indicated Airspeed.
Indicated Airspeed(IAS) is solely a function of the Pitot Tube which measures the difference in pressure of the Ram Tube vs Static Port.
That difference in pressure is displayed as IAS. Some Airspeed Indicators also have a calibration for Corrected Air Speed(CAS).
The air is thinner at FLs, so, the aircraft's True Air Speed(TAS) or Ground Speed(GS) will generally be much higher than IAS or CAS.
Because it is relative to the airframe, Indicated Airspeed tells the pilot if he has enough velocity to maintain lift...Don

Actually you are incorrect. Many aircraft display increasing inaccuracy as a consequence of increasing airspeed and angle of attack as result of the position of the the ram tube and static port relative to the wing and fuselage. It is a common factor for all flight manuals to refer specifically to the inaccuracy of pressure devices at extreme ends of the flight envelope - high and low speed.

Pressure on the measuring devices is NOT a constant save for the basic factors. Other parameters also have to be factored. Thus `position` does have an effect. And oxygen level impacts on INDICATED air speed as one of those factors - a direct cause of the pressure effect that sees IAS reduce as altitude and pressure density increases.

By all means correct me when I'm wrong. This is not one of those times.

http://www.nar-associates.com/techni...ide_screen.pdf

Provides a reasonable technical explanation of the derivation of IAS, which is a calculated result, not a simple reflection or measurement. It also specifically refers to position error.

I think on that basis I'm going to use that technical document rather than your own opinion as a correct statement of the actual state of affairs.

[fxsttcb]

You need to read the article you linked.
The Static port's "Position" on the Aircraft itself relates to calibration factors for that specific aircraft.
Because a "Free Stream" atmospheric pressure point doesn't generally exist near the airframe, for the Static port to reference, a calibration is necessary.
Look at old aircraft. Many of them placed the Static port on a long probe in front of the nose or wing to be in "Free Stream".

When a newer aircraft is built, the Static Port is located on the plane in a location that will yield the closest to a "Free Stream" result.
The instrument itself is then either mechanically or electronically calibrated. Most are considered a fixed calibration.
The calibration's offset factor/multiplier is calculated at MSL and for a mechanical ASI, is not capable of recalibration in flight.

Angle of attack of the aircraft WILL affect the IAS reading to an extent. If the pilot is attempting to fly the bird at extreme AoA the error can be considerable when nearing Stall Alpha, but, within the normal AoA range of flight it will remain very accurate.

The atmospheric composition, where the aircraft is physically located, is virtually identical at the Pressure and Static ports.
The compressibility of the atmosphere will be the same, so any minuscule difference would result in negligible error.

Bottom line; V(IAS) = Constant(Cal Factor) x Sqrt{Total Pressure(Pitot port) - Static Pressure}...Don

[mgh]

. And oxygen level impacts on INDICATED air speed as one of those factors - a direct cause of the pressure effect that sees IAS reduce as altitude and pressure density increases.

By all means correct me when I'm wrong. This is not one of those times.

Oxygen levels are irrelevant. All that matters matters is temperature, density and pressure.

What is "pressure density" that increases with altitude? Pressure and density separately decrease with altitude.

[DAVIDSTRAKA]

Well, I've never flown the 737 that high. My question is, do the airlines routinely fly a 737 at that altitude? I understand the flight dynamics. Just curious if they would ever fly it that close to the service ceiling.

[pdtsad]

I'd agree, up to a point............ But GS isn't your "real speed," but just your speed over the ground, which is affected by winds, as well as by the aircraft speed. The "real speed" is True Airspeed, that is, your actual speed in relation to the air. IAS might be thought of as a "pressure speed" since it is measuring the ram air pressure coming into the pitot tube against the static pressure measured by the static ports on the aircraft, and is certainly the number to fly by until you approach limiting mach numbers.

TAS is calculated by taking IAS (actually it should be C(alibrated)AS) and adjusting for temperature and pressure. The latter is usually achieved by using the density altitude to correct for the altitude effects.

Ok you maybe are right , it depends what are you interested for. I personally care for how long I 'll travel from here to there. So you have a tailwind -positive and your GS actually increases or you have a headwind -negative so your GS decreases. I always check my GPS for GS and this is what counts on me and I noticed different GSs in different wind speeds in identical IASs at identical FLs.
And some people state Earth rotation .Ok they maybe are also right.

About flaps. Flaps are called lift ( or high lift if you prefer) devices because they give you more lift when you operate them . But they also give you more drag. There are two basic types. Normal ( dropping) and extending. Both types increase the camber of your wing and therefore its lift AND its drag. That's why you may have to increase power. Also because they don't increase the camber of your wing only but they also change the shape of it and therefore they put the point of lift a little back, your acft nose down ( you need to trim up your elevator) .The extending type ( for example Fowler type) additionally increases your wing area ( more lift -more drag ). In many medium and heavy acft you also use slats ( leading edge of wing) as lift devices to counter , to a certain degree , the great back move of point of lift and your nose down effect. But at all types please have in mind that you have a wing that produces more lift than usual and a more than usual change in Angle of Attack gives you big changes in lift - descend or ascend ( be carefull in flare because you might climb although you want to land!!!! ) .
I think that oxygen level has nothing to do with static pressure.
Conventional acft can't fly to space because of oxygen absense.
Air/fuel mixture is a PRIME factor in the operation of all engines- internal (reciprocating) or external ( jet) combustion. There are limits , outside of , you simply don't have combustion because if you have an extremely poor ( lean) or extremely rich in fuel, air/fuel ratio the engine just stops to operate. So as you climb higher you engine lowers the amount of fuel it sends to the combustion chambers trying to maintain a specific air/fuel ratio to preserve combustion . If you climb too high simply there is not enough air to burn your fuel or if you prefer in a different way the engine sends so small amount of fuel ( due to low air density) that it can't even stay in idle operation. This is the upper limit. But I think that before your engines starve due to lack of air , your wing has already arrived in its upper limit due to the thin surrounding air and can't produce enough lift to counter the weight of your plane.
The air that enters the compressor stages of a jet engine ALWAYS has to stay BELOW the speed of sound . This is why all jet intakes are more narrow in the front side than the rear. So the acft may fly above 1 MAch but the air that enters in the compressor section stays below 1 Mach.
I have never thought that AoA affects pitot reading but it seems logical to me. Concerning static ports' position I have never heard of any differences in T-41D (Cessna R172) due to flap operation or otherwise.There are in each side of fuselage outside battery compartment.
I really appreciate FS forum becoming a ...........air university !!!!!!? I really like it.

[pdtsad]

Indicated Airspeed(IAS) is solely a function of the Pitot Tube which measures the difference in pressure of the Ram Tube vs Static Port.
That difference in pressure is displayed as IAS.

I agree

[pdtsad]

Well, I've never flown the 737 that high. My question is, do the airlines routinely fly a 737 at that altitude? I understand the flight dynamics. Just curious if they would ever fly it that close to the service ceiling.

I don't think so .I think FL 400 is the usual ceiling if you prefer check here :
http://www.flightradar24.com/