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Altitude Density - is it modelled

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Hi folks.Had my first real flight in a single-engine prop yesterday with a fellow from work and another guy with whom he owns the plane. It was great fun (but that's beside the point).One of the things I heard in the ATIS reports was altitude density (I think that's what it was). This was NOT barometric pressure -- the effects of which I'm already familiar with. I asked the pilots what alt. density was and they explained it describes the effects of air temperature on air density. Basically, just as barometric changes have to be accounted for in your altimeter, air temperature changes on the density of the air affect the instruments and engine similarly, so both have to be taken into account.Is this effect simulated in FS2002?--Tony

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Good question. It probably depends on aircraft and I doubt FS2002 default aircraft bother to account for it considering how crude their whole flight modelling is. On the other hand some 3-rd party developers might have done it - you just have to ask them and hope for an honest answer. I know for example 767PIC does take temperature into account.Michael J.

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This is one we'll have to look into farther. It was either FS2K or FS2002 where I noticed considerably longer takeoff runs, distance wise, at various high altitude airports such as 6000-7000' msl. Of course my engine would be producing less power also. But the effect seemed quite real compared to real life. Considering MS has modeled the effect of leaning engines in "steps" in which 6000' is a major one, they may as well be simulating density altitude too... As to effects with real weather downloads, I have no real idea!L.AdamsonAnd BTW------ I've witnessed far "cruder" flight modeling than most of the defaults. I'd just rather say that they're not up to perfectionist's levels!!

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Just did a test with the default Cessna RG, since it's one of the few with original air.files that I have.With a takeoff at California's Half Moon Bay which is just above sea level, it took 14 seconds to hit 60 kias & rotate. Switching to Evanston, Wyoming (altitude 7163 msl.) & leaning the engine before takeoff for best power, it took 24 seconds to reach 60 kias.This is another reason why higher altitude general aviation airports usually have longer runways & require wider patterns. For those who are not aware, although your pattern speeds are the same as you would use in California, you're actually covering a lot more ground due to thinner air at these altitudes.Now it's off to seeing what temperature changes will do for effecting FS2002's density altitude!L.Adamson

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<>How did you go about this?Did you do it during run up and lean for about 50deg rich of peak. or from a fuel flow indication?

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>Did you do it during run up and lean for about 50deg rich of >peak. or from a fuel flow indication? Forget all that for the moment. Just start leaning until the engine starts to run rough, & then richen it a bit to highest rpm & slightly richer. There are even rules of thumb such as leaning till rough & then halfway back from that point & full rich. It at last gets you in the ballpark!Once in flight, you can start going through all the recommended leaning proceedures.................. which apparently no one can agree on, as discussed in a latest "FLYING MAGAZINE" article! :)FWIW---- Part of the accident report involving the very young female "student" pilot on a cross country marathon, reported that the "instructor" pilot of the Cessna Cardinal did NOT lean the engine in his hastly done pre-takeoff runup because of an quickly approaching storm. The airport was Cheyenne, Wyoming with an altitude of 6156' msl. In addition to being slightly over-weight the aircraft could not gain speed/altitude & had to turn away from the storm. The result was a fatal stall/spin accident. This is why leaning is SO important, but the instructor was from the Half Moon Bay airport & was not really use to leaning as a pre-takeoff check item. In fact------------- the FLYING article mentioned that some instructors tell students to NOT touch the red knob, except to start or kill the engine. "BAD ADVICE" as far as I'm concerened. They must be all sea level instructors! I fly out of a 4600' msl airport & it's standard proceedure before takeoff, as well as right after starting the engine.L.Adamson

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Actually, I find that 2K2 does a fair job of simulating DA issues. Take off from 00V (about 6900 ASL) after setting the OAT to around 85F or so (typical summer day here...) Fill your 172s tanks up and see how long your takeoff roll is compared to sea level. Then see what your rate of climb is at typical climb airspeeds. You should see a decrease in performance...Or go to LaPaz, Bolivia, (10000'+) and really get a show!!!Your leaned out 172 will not be happy up there, at least as far as climbing is concerned...Have fun,DaveKCOS

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>Or go to LaPaz, Bolivia, (10000'+) and really >get a show!!!Your leaned out 172 will not be happy up there, >at least as far as climbing is concerned... >I hope it's at least an SP (180hp) model. An older 172 with less horsepower would probably have to descend with even just a pilot aboard!! :)L.Adamson

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I'd try a 763 out of La Paz, and I nealy get used the hole +13000 feet runway before V1 (147kts)!!! CLB was about 800 feet/min. and my gross weight was 163tonnes!! Scared me a bit! temp. 10 deg. celsius

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Hi Danny,I agree with you, DA can be calculated by setting the altimeter to standard barometric pressure (29.92). Add 112 feet for each degree Celsius above ISA* *(International Standard Atmosphere - 15 degrees Celsius at sea level with a decrease of 2 degrees every 1000 feet).Example: Attempting to take off from Leadville Colorado (roughly 10000 feet)at a temperature of 28 degrees celsius.15-2x10 = -5 degrees (calculation to find ISA at this altitude)The difference betwen ISA and the actual temperature is 33 degrees (28 - minus 5).33 x 112' = 3696'Adding the 3696' to the field elevation of 10000', you get a Density Altitude of 13696' feet, which as far as I recall is above an average Cessna service ceiling.P.S. Do not forget to reset your altimeter to the correct barometric pressure (QNH) before take-off !Take careTwister

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Mr."J" Please take some time to test by yourself, it's not so difficult, take the default King Air, for examlpe, place it at an airport at sea level, set the temperature to something like 45

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>Hi folks. >>..familiar with. I asked the pilots what alt. density was and >they explained it describes the effects of air temperature >on air density. Basically, just as barometric changes have >to be accounted for in your altimeter, air temperature >changes on the density of the air affect the instruments and >engine similarly, so both have to be taken into account. >>Is this effect simulated in FS2002? >--Tony The FS atmosphere is virtually perfect. Most FS AC are not.Ron

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>Also, I mistakenly thought there would be a change in >indicated altitude,

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I guess we can conclude this issue by saying that Density Altitude is reasonably well modelled in FS2K2.Nice to know.Cheers.Twister

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Hi. I just wanted to make sure that we are all on the same page, and there is no miss understanding, since this applies to

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Be sure to catch the latest edition of FLYING magazine. A lenthly article regarding the use of mixtures & CFI's........L.Adamson

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Very nice article, avcomware, I'm sure . I just wanted to add a little comment on shooting the approaches without resetting the altimeter. Of course it's a huge mistake not to reset the altimeter with the local or if none is available the regional setting (by FSS), which leads to a difference of several hundreds of feet in your example. But there is another thing that almost nobody does : correcting the published minimas for the non-standard temperature. Imagine making an approach into a highly elevated aerodrome where the temperature is way colder than the standard temp for that pressure altitude. The altimeter will "over-read" because it's simply measuring pressure. You will however be much lower than you think, because the air being colder hence denser will be more "compact". The result is that pressure will diminish quicker with vertical distance than if the air would have been at standard density, thereby "compressing" the vertical scale of pressure altitudes. Not correcting the minimas in this case also leads to differences enough to make you hit the ground when reaching the minimums (MDA/DA). If you take an ILS approach CAT-I with a typical DH of 200 feet, and the airport is at 2500 feet of elevation, with a big enough deviation those 200 feet can easily be brought down to the terrain level ! The same applies for the glideslope check altitude at the outer marker. The published value must be corrected for non-standard temp otherwise one might think he's on a false glideslope signal. Of course, this doesn't apply to CAT-II & III approaches which use the Radio Altimeter instead of the baro altimeter to determine the minimums. Tables to correct for those deviations exist, and in fact correction is only significant from certain amount of deviation from standard atmosphere. Now actually all this is only used where the deviation is big enough to be significant. No need to correct for 10

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