October 18, 201213 yr If I used the table at a high-altitude airport, say La Paz, would I then have to make a correction to the tabulated VS (or V1 or VR) based on the local air density? No...indicated airspeeds are a function of air density at sea level. V1 and Vr do change at altitude, however, due to changes in available thrust at the lower air density. Stall and V2 speeds should not be affected. I think the recreational flying is a long way off yet... lots of data collection to complete. Last night I had a happy couple of hours practising the startup routine and taking off into a couple of dozen stalls while using AFSD to log CL as an empirical way of determining CLmax ; tonight, I think I'll set up a flight for VS at different altitudes and weights. The flights should confirm the calculation. Why not just determine CLmax by simple inspection of the CL vs alpha curve in the airfile plus the add for flaps in the flap CL table? Bob Scott | President and CEO, AVSIM Inc ATP Gulfstream II-III-IV-V Sys1 (MSFS20+24/XPlane12+11): AMD 9800X3D, water 2x240mm, MSI MPG X670E Carbon, 64GB GSkill 6000/30, nVidia RTX4090FE Alienware AW3821DW 38" 21:9 GSync, 2x4TB Crucial T705 PCIe5 + 2x2TB Samsung 990 SSD, EVGA 1000P2 PSU, 12.9" iPad Pro Thrustmaster TCA Boeing Yoke, TCA Airbus Sidestick, Twin TCA Airbus Throttle quads, PFC Cirrus Pedals, Coolermaster HAF932 case Sys2 (P3Dv5/v4): i9-13900KS, water 2x360mm, ASUS Z790 Hero, 32GB GSkill 7800MHz CAS36, ASUS RTX4090 Samsung 55" JS8500 4K TV@60Hz, 3x 2TB WD SN850X 1x 4TB Crucial P3 M.2 NVME SSD, EVGA 1600T2 PSU Fiber link to Yamaha RX-V467 Home Theater Receiver, Polk/Klipsch 6" bookshelf speakers, Polk 12" subwoofer, 12.9" iPad Pro PFC yoke/throttle quad/pedals with custom Hall sensor retrofit, Thermaltake View 71 case, Stream Deck XL button box Sys3 (DCS/P3Dv4/ATS/ETS): AMD 7800X3D, MSI MPG X870E Carbon, Noctua NH-D15S, 64GB GSkill 6000/30, EVGA RTX3090 Alienware AW3420DW 34" 21:9 GSync, Corsair HX1000i PSU, 4TB Crucial T705 PCIe5 + 2TB Samsung 970Evo Plus, TM TCA Officer Pack, Saitek combat pedals, TM Warthog, TM RS300 FF wheel/pedals, Coolermaster HAF XB case
October 18, 201213 yr No...indicated airspeeds are a function of air density at sea level. V1 and Vr do change at altitude, however, due to changes in available thrust at the lower air density. Stall and V2 speeds should not be affected. Indeed. The true airspeed at which you stall will change, but the indicated airspeed will remain the same. A plane's performance is governed by the dynamic pressure (1/2 * rho * TAS = 1/2 *rho_0*EAS, where rho_0 is density at sea level). TAS is a measure of your plane's speed with respect to the surrounding air, whereas IAS / EAS is a measure of the dynamic pressure. All the above neglects compressibility, but if your plane stalls at speeds where compressibility become an issue you're flying a weird plane (or at high (cruise) altitude I suppose, but let's neglect that for now). Dave I don't know about your autism gene, but it sounds like you're doing a good job of simulating a flight test program . John-Alan Pascoe
October 19, 201213 yr Author Good morning to you all. I jotted this down last night while idling. I see you've already answered these questions, too but I'll drop the original text in here anyway-- it's nice to arrive independently at the same conclusion. At present I have to determine CLmax empirically (I can't get in to the air file) but that may change soon. While downloading the newest AFSD last night I also picked up a copy of AirEd. Yet another tangent... *** *** I think I may have cleared this up for myself at the second glass. Am I right in believing that IAS is derived from the difference between static and dynamic pressures? If so, given that the density of (ideal) air is the same at the mouth of either pitot tube, it's become evident to me that altitude will make a minimal difference. I guess, in my uneducated imagination, that less-dense air will compress more easily and, for want of a better way of putting it, that the dynamic pressure will alter the density of the air in that tube, leading to a slight error. I suppose that's where your discussion of compressibility stems from. Further, Hervé Sors has made most of my struggle redundant. I dowloaded the latest version of AFSD last night and spotted this. I subsequently discovered it was already in my older version :blush: . Clearly no powers of observation until the first glass is history. *** *** Best regards, D
October 19, 201213 yr Am I right in believing that IAS is derived from the difference between static and dynamic pressures? More accurate to say derived from total (ram) pressure minus static pressure.
October 20, 201213 yr IAS is the most reliable... Its what the airplane knows about...The Aircraft knows of no other airspeed. IAS is the only airspeed the Aircraft thinks the speed is..and what the aircraft thinks it is, it would behave as per its knowledge. Manny Manny Beta tester for SIMStarter
October 20, 201213 yr IAS is the most reliable... Its what the airplane knows about...The Aircraft knows of no other airspeed. IAS is the only airspeed the Aircraft thinks the speed is..and what the aircraft thinks it is, it would behave as per its knowledge. Manny Well technically it would be CAS. Chris Miller
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