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rhdudley1(at)bellsouth.ne
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 Posted: Mon Jun 25, 2007 9:18 am Post subject: Takeoff Distance vs Density Altitude |
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I have attached a graph that calculates takeoff distance increase and
climb performance decrease as a function of density altitude. I found it
in someone's POH on the internet. If valid, this would be a very
convenient inclusion in a POH.
My questions for aerodynamically knowledgeable folks are:
1. Is this a valid calculation?
2. Was this formally published somewhere? If so, where?
3. Is the percent degradation in takeoff and climb performance
independent or is it dependent on the specific aircraft parameters?
Your comments will be appreciated.
Regards,
Richard Dudley
RV-6A flying
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khorton01(at)rogers.com
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| Posted: Mon Jun 25, 2007 10:26 am Post subject: Takeoff Distance vs Density Altitude |
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On Mon, 25 Jun 2007 13:08:33 -0400
Richard Dudley <rhdudley1(at)bellsouth.net> wrote:
| Quote: | I have attached a graph that calculates takeoff distance increase and
climb performance decrease as a function of density altitude. I found it
in someone's POH on the internet. If valid, this would be a very
convenient inclusion in a POH.
My questions for aerodynamically knowledgeable folks are:
1. Is this a valid calculation?
2. Was this formally published somewhere? If so, where?
3. Is the percent degradation in takeoff and climb performance
independent or is it dependent on the specific aircraft parameters?
Your comments will be appreciated.
Regards,
Richard Dudley
RV-6A flying
|
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rhdudley1(at)bellsouth.ne
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| Posted: Mon Jun 25, 2007 10:34 am Post subject: Takeoff Distance vs Density Altitude |
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Kevin,
I appreciate your response. But, I find no content in your post. Just my original message.
Regards,
Richard Dudley
Kevin Horton wrote:
[quote] | Quote: | --> RV-List message posted by: Kevin Horton <khorton01(at)rogers.com> (khorton01(at)rogers.com)
On Mon, 25 Jun 2007 13:08:33 -0400
Richard Dudley <rhdudley1(at)bellsouth.net> (rhdudley1(at)bellsouth.net) wrote:
| Quote: | I have attached a graph that calculates takeoff distance increase and
climb performance decrease as a function of density altitude. I found it
in someone's POH on the internet. If valid, this would be a very
convenient inclusion in a POH.
My questions for aerodynamically knowledgeable folks are:
1. Is this a valid calculation?
2. Was this formally published somewhere? If so, where?
3. Is the percent degradation in takeoff and climb performance
independent or is it dependent on the specific aircraft parameters?
Your comments will be appreciated.
Regards,
Richard Dudley
RV-6A flying
|
|
[b]
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khorton01(at)rogers.com
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| Posted: Mon Jun 25, 2007 10:41 am Post subject: Takeoff Distance vs Density Altitude |
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On Mon, 25 Jun 2007 13:08:33 -0400
Richard Dudley <rhdudley1(at)bellsouth.net> wrote:
| Quote: | I have attached a graph that calculates takeoff distance increase and
climb performance decrease as a function of density altitude. I found it
in someone's POH on the internet. If valid, this would be a very
convenient inclusion in a POH.
My questions for aerodynamically knowledgeable folks are:
1. Is this a valid calculation?
2. Was this formally published somewhere? If so, where?
3. Is the percent degradation in takeoff and climb performance
independent or is it dependent on the specific aircraft parameters?
Your comments will be appreciated.
|
Opps. Different e-mail client than I normally use, and I hit the Send button by accident the first time.
I'm not sure what the pedigree of this chart is, but it looks similar to other ones I have seen aimed at common light aircraft. The effect of density altitude on take-off ground roll will be roughly the same for an RV as it would be for a Cessna, as the impact is due to reduction in engine power, and increase in TAS at lift off. So this part of the chart is probably just as accurate for our RVs as it is for a SE Cessna. Or just as inaccurate.
But the impact of density altitude on climb rate depends on excess power. RVs need less power than a Cessna 172 to maintain level flight, but they have an equal, or more power available, so they have much more excess power. A Cessna sees a significant reduction in rate of climb with DA, as it doesn't take a very big reduction in power available to bring the excess power to zero. If this graph provides an accurate prediction of reduction of rate of climb on a Cessna, it would be pessimistic on an RV. I.e. it would predict a bigger reduction in rate of climb than would actually occur. For example, that chart predicts that the rate of climb would be zero with a density altitude in the high teens. But in fact, most RVs could easily climb above 20,000 ft.
Kevin Horton
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rhdudley1(at)bellsouth.ne
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| Posted: Mon Jun 25, 2007 11:08 am Post subject: Takeoff Distance vs Density Altitude |
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Thanks, Kevin.
Regards,
Richard Dudley
do not archive
Kevin Horton wrote:
[quote] | Quote: | --> RV-List message posted by: Kevin Horton <khorton01(at)rogers.com> (khorton01(at)rogers.com)
On Mon, 25 Jun 2007 13:08:33 -0400
Richard Dudley <rhdudley1(at)bellsouth.net> (rhdudley1(at)bellsouth.net) wrote:
| Quote: | I have attached a graph that calculates takeoff distance increase and
climb performance decrease as a function of density altitude. I found it
in someone's POH on the internet. If valid, this would be a very
convenient inclusion in a POH.
My questions for aerodynamically knowledgeable folks are:
1. Is this a valid calculation?
2. Was this formally published somewhere? If so, where?
3. Is the percent degradation in takeoff and climb performance
independent or is it dependent on the specific aircraft parameters?
Your comments will be appreciated.
|
Opps. Different e-mail client than I normally use, and I hit the Send button by accident the first time.
I'm not sure what the pedigree of this chart is, but it looks similar to other ones I have seen aimed at common light aircraft. The effect of density altitude on take-off ground roll will be roughly the same for an RV as it would be for a Cessna, as the impact is due to reduction in engine power, and increase in TAS at lift off. So this part of the chart is probably just as accurate for our RVs as it is for a SE Cessna. Or just as inaccurate.
But the impact of density altitude on climb rate depends on excess power. RVs need less power than a Cessna 172 to maintain level flight, but they have an equal, or more power available, so they have much more excess power. A Cessna sees a significant reduction in rate of climb with DA, as it doesn't take a very big reduction in power available to bring the excess power to zero. If this graph provides an accurate prediction of reduction of rate of climb on a Cessna, it would be pessimistic on an RV. I.e. it would predict a bigger reduction in rate of climb than would actually occur. For example, that chart predicts that the rate of climb would be zero with a density altitude in the high teens. But in fact, most RVs could easily climb above 20,000 ft.
Kevin Horton
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[b]
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lsbrv7a(at)yahoo.com
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rhdudley1(at)bellsouth.ne
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| Posted: Mon Jun 25, 2007 2:09 pm Post subject: Takeoff Distance vs Density Altitude |
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Thanks, Sherman.
I see that it turns out to be a rather standard chart, Koch Chart, and approximation for "personal aircraft".
Regards,
Richard Dudley
do not archive
Sherman Butler wrote:
[quote] Richard,
The chart came from FAA Pamphlet P-8740-2
http://www.faasafety.gov/gslac/ALC/libview_normal.aspx?id=6847
One site for a calculator:
https://www.beaufort.usmc.mil/weather/density_altitude_calculator.htm
other charts
http://www.flynewmexico.com/densityaltitudechart.htm
http://en.wikipedia.org/wiki/Density_altitude
.
enjoy
Richard Dudley <rhdudley1(at)bellsouth.net> (rhdudley1(at)bellsouth.net) wrote:
| Quote: | I have attached a graph that calculates takeoff distance increase and
climb performance decrease as a function of density altitude. I found it
in someone's POH on the internet. If valid, this would be a very
convenient inclusion in a POH.
|
Sherman Butler
RV-7a Wings
Idaho Falls
[url=http://us.rd.yahoo.com/evt=48250/*http://searchmarketing.yahoo.com/arp/sponsoredsearch_v9.php?o=US2226&cmp=Yahoo&ctv=AprNI&s=Y&s2=EM&b=50]Pinpoint customers [/url]who are looking for what you sell. [b]
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ronlee(at)pcisys.net
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| Posted: Mon Jun 25, 2007 4:34 pm Post subject: Takeoff Distance vs Density Altitude |
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Density altitude today at 00V was 10,100' when the temp was 90 deg F.
Ron Lee
Do not archive
[quote][b]
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lsbrv7a(at)yahoo.com
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| Posted: Mon Jun 25, 2007 6:01 pm Post subject: Takeoff Distance vs Density Altitude |
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I have had some interesting take offs and landings at Meadowlake.
I also had a interesting take off at Smiley Creek (U87) week before last. Terran slopes down to the North. Wind out of the SSW between 10 and 13 kts. temperature increasing. 7100 elevation and 4900 length. We should have left, rather than walk over to the lodge for coffee. I was climbing slowly when i retracted the gear. With the Bonanza the inner gear doors open, climb is NEGATIVE!
I got out the Bonanza book by Eckalbar. He said to set-up in short field take off configuration at altitude 4500, stabilize speed at 100 trim for level flight. Increase to take-off power and time to climb from 4800 to 5200 adn record teh time to climb adn rate of climb. Repeat at 90, 80, 70, 60. Plot the tangent from 0 this will be Vx and top of the curve (slope is 0) is Vy. I plan to do this at 7000 ft to plot my actual performance as I am learning to fly in Idaho backcountry.
Arrive early and leave earlyand chose airports wisely. I need to sell this airplane, stop flying and get back to building.
Ron Lee <ronlee(at)pcisys.net> wrote:
[quote] Density altitude today at 00V was 10,100' when the temp was 90 deg F.
Ron Lee
Do not archive
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