Hi all,
In most of the METARs or ATIS information I always hear "Density Altitude" and its calculated for you. I suppose this is a big reminder to check your performance charts - especially on hot, humid, short runway days.
All the Diamond Performance charts are based on Pressure Altitude with a temperature chart for its corresponding "density altitude performance numbers". Now I know you can simply calculate pressure altitude with a formula. For example: Let’s say the current altimeter setting is 29.45 and the field elevation is 5,000 feet. Plugging these numbers into the pressure altitude formula, you get: (29.92 – 29.45) x 1,000 + 5,000 = 5,470 feet. Which then I can use in my charts that get me to temp, and then finally to the actual performance number.
It seems that ForeFlight should also show you the pressure altitude in the METARS too so we can work it easier into these charts or if the charts showed the density altitude. (lazy I know) I also know I can use the Performance Plus in ForeFlight and look at Takeoff and Landing performance, which probably calculates humidity too and is a good check but it does take a little more setup too.
Maybe I am overthinking this ... But does anyone have any thoughts on this? What do you do when you are planning?
-Ingram
Performance Charts - Pressure Altitude conversion with Foreflight?
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- ingramleedy
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Re: Performance Charts - Pressure Altitude conversion with Foreflight?
In the NG, the variation across altitude and temps is so small that I don't give it a lot of thought. With my wife, my TO weight is basically the 2,645lb table +-50lbs. The difference between SL at 10C (home) and 6,000' at 30C (Santa Fe mid-morning) is 90fpm. I assume I'll climb at 600-700fpm.
What I try to anticipate is the potential impact of downdrafts (the updrafts are all good). While I know I'll average 650fpm, a minute of being pushed down to 200fpm can be an issue.
What I try to anticipate is the potential impact of downdrafts (the updrafts are all good). While I know I'll average 650fpm, a minute of being pushed down to 200fpm can be an issue.
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Re: Performance Charts - Pressure Altitude conversion with Foreflight?
FWIW FF does display density altitude in METARS.
FF will display your current Pressure Altitude from 2 different sources in the instruments panel if you configure one or both for display.
FF will display your current Pressure Altitude from 2 different sources in the instruments panel if you configure one or both for display.
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
- Rich
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Re: Performance Charts - Pressure Altitude conversion with Foreflight?
I've been noodling the idea of creating a more usable tool for my DA40-180 based on the performance charts. Since Density Altitude is most readily available for airports, it would start from there, rather than with PA+temperature. I haven't given it a priority, though, for a number of reasons. Mostly it's not worth worrying about unless I'm departing at high DA with obstructions around and unusually heavily loaded. If I'm really traveling any distance it'll be me and my wife with some baggage, so I'm no heavier than 2300 lb. at TO.
Another other issue is that, other than takeoff, the remaining performance charts have so much in the way of assumptions about atmospheric conditions that one can't take them for any more than approximations. I base my planning and real-time decisions on long experience.
Having said that, for those new to their plane it's worth working out some scenarios ahead of time, recognizing that there is a fairly large uncertainty envelope, especially with respect to climb.
Another other issue is that, other than takeoff, the remaining performance charts have so much in the way of assumptions about atmospheric conditions that one can't take them for any more than approximations. I base my planning and real-time decisions on long experience.
Having said that, for those new to their plane it's worth working out some scenarios ahead of time, recognizing that there is a fairly large uncertainty envelope, especially with respect to climb.
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5