10,000' Density Altitude Departure?

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AA5Bman

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He who ironically no longer flies an AA5B
How would y'all feel about departing a 7,500' runway in a 180hp Tiger @ a density altitude of approximately 10,000'?

It would be as lightly loaded as possible, 2,095# of 2,400# gross. A DA of 10,000 is literally off the charts in the POH for takeoff performance, but it appears that conservatively extrapolating from the numbers listed at 8,000', it will take approximately 5,000 ft of runway to clear a 50' obstacle.

Makes me (again) want to upgrade to a 182...
 
I took off from a 11,400 DA at BCE a few years back in a PA28-180. I was full tanks, me, and my gear. I was probably right around your numbers for weight. I do know I was no where near that for takeoff distance.
 
I always figure it's a good idea to add 20% to the book figures...

What's the terrain around the airport? Can you climb sufficiently to avoid obstacles? What's the actual field elevation? Can you leave early A.M. when the DA is lower?
 
Field elevation is 7,100', plenty of big mountains in the area, none that you have to miss. The end of the airport is a lake (going west), and then the valley falls away after that. Can anyone guess the airport?

It's going to be hot all weekend, so the 10,000' DA is what we're going to get in the AM - an afternoon departure would be more like 11,500'.
 
Sounds like me leaving Rock Springs WY in my Tiger in 2005, except I might have been 100 lb heavier. I think your numbers are about right. As long as there's nothing after departure requiring a big climb gradient, and your engine/prop are in good shape, it's not hard. But I'd want that runway to be as long as the big one at RKS -- I wouldn't be doing that on a runway less than about 7500 feet long (150% of book 50-foot obs dist), depending on wind down the runway.

And leave when it's cool -- the differences in performance for 1500 feet higher DA are much sharper at high DA's.
 
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You're gonna be a test pilot on this adventure but you can do it safely if you work out a safe abort point and stick to it. Just don't try climbing the plane out of ground effect until you have achieved Vy or at least Vx (adjusted for the DA). If the abort point (calculated to allow landing and stopping from Vx) comes before you hit Vx then abort and reduce the weight or wait for cooler air. Keep in mind that the temp over the runway in the midday sun is likely 10-15F hotter than nearby air temp readings.
 
AA5Bman said:
Field elevation is 7,100', plenty of big mountains in the area, none that you have to miss. The end of the airport is a lake (going west), and then the valley falls away after that. Can anyone guess the airport?

It's going to be hot all weekend, so the 10,000' DA is what we're going to get in the AM - an afternoon departure would be more like 11,500'.
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Big Bear?
 
You'd be right except I made a mistake: the valley falls away going east...
 
If'n ya try it, make sure to lean for max power as part of the run-up...
 
Ron Levy said:
Sounds like me leaving Rock Springs WY
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If I remember right, Rock Springs is like an aircraft carrier... plateau with downsloping terrain off the end of the runway... that would be a major factor in my decisionmaking process.. as opposed to rising terrain in the immediate vicinity...
 
AA5Bman said:
How would y'all feel about departing a 7,500' runway in a 180hp Tiger @ a density altitude of approximately 10,000'?

It would be as lightly loaded as possible, 2,095# of 2,400# gross. A DA of 10,000 is literally off the charts in the POH for takeoff performance, but it appears that conservatively extrapolating from the numbers listed at 8,000', it will take approximately 5,000 ft of runway to clear a 50' obstacle.

Makes me (again) want to upgrade to a 182...
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Took off from LXV on a hot summer day (DA around 13,000) on a 160hp C172, full fuel with one passenger. It was a long roll, but the runway was also long with no terrain issues.
 
Just depart early AM and you will have NO DA problems!!
 
A few years back, I left Boulder Muni (BDU is at 5200ft altitude, with a 4100ft runway) on a summer afternoon that made for a DA of around 8000 feet. For the flight home, I was going to be about 100# under gross in a PA28-180.

Being a flatlander, I was worried about DA effects, so I flew a solo trip around the pattern before the luggage and my wife joined me. I was pleasantly surprised at how little runway was required before rotating. Acceleration after rotation and climb rates were of course affected significantly, but it was not as bad as I had imagined.

I suppose the big question is how well your Tiger climbs at 10k feet. If it is only 100fpm, then it's going to be a tight takeoff. If you can get at least 2-300fpm, then (IMHO) it is feasible.

Last, please remember to lean for best power during takeoff.
 
dogman said:
Just depart early AM and you will have NO DA problems!!
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I agree with an early morning departure. Any place that has that high of a DA and elevation is in the mountains. Temps fall alot during the night and first light in usually 50 degress cooler then mid afternoon. My 6am flights here in Jackson Hole Wy are flown in temps of 35-40 f. By mid afternoon it gets up to 85+. Even in my 'overpowered' experimental, high temps really eat into its performance. If you have falling terrain off the departure end and you trust your plane/motor then do as others have said. Lean agressively, stay in ground effects till VY and it will be a safe takeoff.

Tailwinds.

Ben.
www.haaspowerair.com
 
If your POH doesn't provide T/O distance for 10K D.A., you might consider using the Koch chart in conjunction with your POH for this calculation. In addition, I would also consider an abort T/O point on the runway (i.e. "I need 70% of T/O speed by the time I reach 50% of the runway length. If not, I will abort T/O.")

As already mentioned, I would also calculate climb rate to your cruise altitude, lean for best power on T/O and add 50% to your POH 50-foot obstacle distance when figuring T/O distance.
 
just Bill said:
If your POH doesn't provide T/O distance for 10K D.A., you might consider using the Koch chart in conjunction with your POH for this calculation. In addition, I would also consider an abort T/O point on the runway (i.e. "I need 70% of T/O speed by the time I reach 50% of the runway length. If not, I will abort T/O.")

As already mentioned, I would also calculate climb rate to your cruise altitude, lean for best power on T/O and add 50% to your POH 50-foot obstacle distance when figuring T/O distance.
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And if you don't have the Koch chart handy:

http://www.faasafety.gov/gslac/alc/libview_printerfriendly.aspx?id=6847

Lousy layout but what you expect from the FAA?

And if you don't want to visit the FAA, here's the chart:
 

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BTW, a 7100-foot elevation/+29C takeoff (10,000 DA) is not off the AA-5B charts. The chart goes to 8000 PA/+40C. However, leaning for peak RPM is part of the basis for that chart for takeoffs above 5000 feet.
 
midlifeflyer said:
Really? 10,000' density altitude is not a problem when it takes place in the early AM?

I want to see the performance charts with the time-of-day listing.
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Word! We left Walden, CO (33V) last weekend at 10:30AM and the DA was just shy of 10K even though it was still pretty cool. High is high no matter the time of day.

Having grown up and learned to fly at 7K+ DA, I don't really have a feel for how scary high DA must be to you low-landers. OTOH, my plane is absolutely awesome at sea-level.
 
Don't even need Springerville or mountains. Hot days on the plains in Colorado, DA is always over 9K at APA, FTG, BJC and everywhere nearby.
 
I departed the Big Bear Airport in Ca many times with a DA of 10K or more, I was just aware of the fact that the climb performance would be poor. My Mooney never liked it but we did it on 180HP and I never felt it was unsafe.
 
COFlyBoy said:
OTOH, my plane is absolutely awesome at sea-level.
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Yep. First time I went to sea level with my Cherokee 180, the deck angle on climb was alarming and I learned you can get into the yellow arc in level flight :hairraise:
 
My airplane was built before POH's and even "Owner's Manuals," so the flight data is scant.

I do know this -- any takeoff above 85 F is an exercise in tree-dodging.

The difference in performance between morning and late summer afternoon is so striking I think every pilot should experience it at least once.

So many fly fairly overpowered airplanes that make DA a mere academic curiosity. Nothing demonstrates the effect of heat on performance like an ancient 65 HP airplane.
 
Just got back from the trip. Here's the report: all went well.

I learned to fly at 5,300 feet with hot summers, so you'd think I wouldn't be so concerned, but in retrospect, maybe that's precisely why I was concerned! About departing in the morning to avoid DA: kind of tough to do when you start at 7k plus. Nights were only getting down to 55-60 degrees, so some help there, but not much.

Anyway, for anyone considering a similar trip in a 180hp bird, we were 250# shy of gross weight. Departed mid-morning with a DA of about 9,900 or so. Leaned properly, the takeoff acceleration was far from neck breaking, but we were off the ground in better than 3,000 feet, which was the number I was expecting based on POH numbers. Stayed in ground effect for quite a while to build up a margin of error, and climbed away. climbing to 9,500, we got 350 fpm. A big factor in my mind was calm winds and little in the way of vertical air movement (i.e. winds rushing over hills and through valleys, etc.

I'm sure this won't be my last trip to that location, and in the future I would be comfortable departing even hotter given calm winds, but I definitely won't be bringing more weight or a third person in particular.

Thanks for the thoughts!
 
Just saw this one. I operated my Tiger for three years outside of Denver, CO at KFTG. Went in and OUT of Leadville, CO, elevation 9,927 ft. in the summer with a heavy passenger in my Tiger without issue. Among other high DA situations, you learn to do what is right. The flight school at Leadville used a 150 HP 172 the last time I was there.
 
Rule of thumb for high-elevation airports is to keep total weight at least 10% UNDER published gross weight.

You done good.
 
My record was 12,200' DA at KLXV, and the ground roll in the 182 was 2,000 feet. 2 people and lots of bags, but partial fuel so around 3-400 pounds under gross. That's about 3x longer than normal at my home field's 887' field elevation.
 
I didn't notice the numbers at Leadville when I was there. It was May, early afternoon, 3 people, fair amount of gear, but fuel at the tabs, so I'm guessing the total weight wa something like cherokee 180, Gross:2400 Actual:2200.
 
murphey said:
I didn't notice the numbers at Leadville when I was there. It was May, early afternoon, 3 people, fair amount of gear, but fuel at the tabs, so I'm guessing the total weight wa something like cherokee 180, Gross:2400 Actual:2200.
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I departed Leadville about 10 am about a year ago (early July) and climbed out at 1,000 fpm. Gotta love the turbo and being well under max gross.
 
If you want to know how well your aircraft acts at 10,000', climb to 10.000 feet and see.

no brainer.
 
COFlyBoy said:
Having grown up and learned to fly at 7K+ DA, I don't really have a feel for how scary high DA must be to you low-landers. OTOH, my plane is absolutely awesome at sea-level.
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Oh, we have our DA issues also albeit not as "calculating". Our runways tend to be A LOT shorter.

In our case taking off from a 1600' strip on a 95dF day can be pretty interesting, even in a "performer" like my straight tail 182.

Then there's a certain one way airport in Arkansas where many of us are stupid enough to take off on a 95dF day towards a 300' bluff with a 10kt (or more) tailwind.

:goofy:


:)
 
timwinters said:
Oh, we have our DA issues also albeit not as "calculating". Our runways tend to be A LOT shorter.

In our case taking off from a 1600' strip on a 95dF day can be pretty interesting, even in a "performer" like my straight tail 182.
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True. But having been a lowlander and having flown with lowlanders since, there are differences.

For example, D-Alt affects both engine performance (about a 3%/1000' hit) and airfoil (wings and prop) performance. The result is that, to a lowlander, even one who's taken off from "high" density altitude of 2300' (your 1600' strip at 95° at sea level), the sense of "this should have been off the ground by now" is very strong. That alone has contributed to unfortunate accidents by lowlanders in these parts. Scariest time I've had as an instructor was a lowland student who insisted in maintaining his "normal' climb pitch attitude after takeoff.
 
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