stunthanger.com
Engine basics => Engine set up tips => Topic started by: Steve Fitton on September 12, 2011, 08:57:34 AM
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Watching the animated discussion about density altitude over on SSW makes me want to ask a question: Assuming I don't want to bring my barometer, hygrometer and thermometer, along with an E6-B or a calculator to the contest, what should I get to determine it? I have seen Randy playing with a small handheld device at Marietta one time, and I have also seen Kent Tysor with some sort of drag racing device that expressed air density as a %, normalized to a standard day I assume. What do you guys use to determine density alt?
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Watching the animated discussion about density altitude over on SSW makes me want to ask a question: Assuming I don't want to bring my barometer, hygrometer and thermometer, along with an E6-B or a calculator to the contest, what should I get to determine it? I have seen Randy playing with a small handheld device at Marietta one time, and I have also seen Kent Tysor with some sort of drag racing device that expressed air density as a %, normalized to a standard day I assume. What do you guys use to determine density alt?
A borrowed Kestrel 4000 weather meter.
Brett
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The Kestrel 4250 has density ratio, too, but the 4000 has heat stress index, which I may need more than the other parameters.
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I use the Kestrel, for the money it is the best machine I could find, and they have many differant models
Mine will even sit and track wind, temp, etc.. over the day
Randy
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Ouch, I see why Brett borrowed the 4000. Those things are not cheap(!)
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Assuming I don't want to bring my barometer, hygrometer and thermometer, along with an E6-B or a calculator to the contest, what should I get to determine it?
The Aussie Barometer (which is simply a piece of string hanging on a small plaque) -
IF STRING
IS SWAYING
IT'S WINDY
IF STRING
STANDS SIDEWAYS
IT'S VERY WINDY
IF STRING
IS WET
IT'S RAINING
IF STRING
IS DRY
IT'S NOT RAINING
IF STRING
IS STIFF
IT'S FREEZING
IF STRING
IS BURNING
IT'S VERY HOT
IF STRING
CASTS SHADOW
IT'S SUNNY
IF STRING CASTS
NO SHADOW
IT'S CLOUDY
IF STRING
IS INVISIBLE
IT'S NIGHT
IF STRING
IS SMOKING
FIRE RAGING
IF STRING
IS MISSING
SOMEONE HAS KNOCKED
IT OFF
:D :D Cheap as chips mate!
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http://store.bruntonoutdoor.com/instruments/altimeters-wind/pro/ (http://store.bruntonoutdoor.com/instruments/altimeters-wind/pro/)
Available from amazon for $111.00
http://www.amazon.com/Brunton-ADC-Altimeter-Barometer-2010/dp/B002IAOM04 (http://www.amazon.com/Brunton-ADC-Altimeter-Barometer-2010/dp/B002IAOM04)
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Kestral has several models available, the cheapest version I have seen is 93$ at Jegs and Summit. It does not have all the bells and whistles but it will get the job done.
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The simplest and cheapest computer for density altitude is the old E6-B military style computer pilots carried in their flight bags. You can still buy one at any airport/flight school, or on amazon for $15-$20. Used for navigation, performance and speed calculations to name a few, it is basically a circular slide rule, comes with complete instructions, has no batteries, led's, watts, amps, volts, and never needs oil. Do a google for "E6-B" and read up. Hope this is helpful.
Steve Thornton
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Here's one that Frank Williams uses. It looks reasonably simple. http://stunthanger.com/smf/index.php?topic=22408.0
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If the actual altitude is high and so is the temperature, you will have a loss in performance. That's about all you really need to know, unless your airplane & handle have some calibrated gizmos to crank the actual density altitude into.
I have a wrist watch that gives me altimeter, barometer, and temperature readings, as well as the usual date & time. But I can't see that it really tells me anything I can't just feel about temperature & humidity.
When I was flying the KC-135, we spent a lot of time getting data from the Weather Service and computing the precise density altitude. It boiled down to a few simple facts:
Up to 90 degrees you can take off at full throttle.
Below 40, you need half throttle or less.
Above 90, you might have to reduce fuel load.
Turbine engines lose a lot of thrust at high density altitude, piston engines lose some, electric motors aren't engines & don't care.
A CL model airplane that can do a 90 degree vertical eight in Wichita will do a 120 degree vertical eight in Amarillo.
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Here's one that Frank Williams uses. It looks reasonably simple. http://stunthanger.com/smf/index.php?topic=22408.0
Alas, the website says its sold out. Have to save my pennies to afford it or the Kestrel 4000 anyway...
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<snip> When I as flying the KC-135, we spent a lot of time getting data from the Weather Service and computing the precise density altitude. It boiled down to a few simple facts:
Up to 90 degrees you can take off at full throttle.
Below 40, you need half throttle or less.
Above 90, you might have to reduce fuel load.
Turbine engines lose a lot of thrust at high density altitude, piston engines lose some, electric motors aren't engines & don't care.
* I was a Crew Chief on USAF KC-135A/Q models from 1984-1988. We were taught that the water injection on the J-57's increased thrust by about 13% (if I remember right) I work with guys who crewed the original config. back in the late 50's/ early 60's - The water inj. was paired LH/RH instead of the later Inbd./Outbd. Losing water on takeoff meant you were in a world of s%#*! The current "R" models (CFM-56) were just being modded the last year I was in. Some of those planes are older than me and I'm 51!!
** I still have my E-6B from 1983. Learned to fly on a C 150M. GPS? huh?
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I agree that without some method of applying density altitude this is just interesting conversation. Are there any performance charts for our engines & fuels? Higher density altitude also effects the performance of the wing, so lap times will be faster if you have the same thrust.
My $.02 worth
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* I was a Crew Chief on USAF KC-135A/Q models from 1984-1988. We were taught that the water injection on the J-57's increased thrust by about 13% (if I remember right) I work with guys who crewed the original config. back in the late 50's/ early 60's - The water inj. was paired LH/RH instead of the later Inbd./Outbd. Losing water on takeoff meant you were in a world of s%#*! The current "R" models (CFM-56) were just being modded the last year I was in. Some of those planes are older than me and I'm 51!!
** I still have my E-6B from 1983. Learned to fly on a C 150M. GPS? huh?
With those old water-injected J-57's, we had a 3-engine peacetime takeoff weight of 256,000 pound and a 4-engine war weight of 306,000 pounds.
The "new" re-engined airplances take off at 330,000 peace-or-war and forget about the water.
We didn't even think about humidity when were were blowing three tons of water into the engines in the first two minutes.
Incidentally, those "new" Air Force engines are surplus obsolete third-generation airline engines that were removed when the airlines went up to the fourth level.