Highest Density Altitude Takeoff

pcorman

pcorman

Pre-takeoff checklist
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Phil Corman
What is the highest Density Altitude that you feel comfortable departing?

I am asking as I just departed from my highest (Lake Tahoe, elev: 6260) with DA of 7600 in a Mooney M20C with 180hp O360-A1D.

I got 400-450fpm but it felt much flatter. Not sure what my limit is, but I think this is close to it.

Phil
 
Depends on the airport. Some AZ airports have a bit of a drop after the end of the runway. Climbing really isn't as much of a factor there vs sitting in a valley and having to climb out.
 
Brian Austin said:
Depends on the airport. Some AZ airports have a bit of a drop after the end of the runway. Climbing really isn't as much of a factor there vs sitting in a valley and having to climb out.
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The Supercub operators that carry skiers/climbers up to the snow on Mt. Mckinley have a 500' per Min. rate of desent going after lift off on the snow.

Climb to 10k, dump the guy, dive back down, get another load, see how many times a day you can make the cycle.
 
pcorman said:
What is the highest Density Altitude that you feel comfortable departing?

I am asking as I just departed from my highest (Lake Tahoe, elev: 6260) with DA of 7600 in a Mooney M20C with 180hp O360-A1D.

I got 400-450fpm but it felt much flatter. Not sure what my limit is, but I think this is close to it.

Phil
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Kinda depends on the terrain. I left out of Alamosa one summer afternoon with a DA over 10,000'. I had to do 4 big climbing circuits to get over the pass, but it really wasn't dangerous because it's a big flat valley with plenty of room to get up. If it was small with lots of obstacles, that might not be so good, might want to wait for night or best, first light.
 
It depends on weight, temperture and terrain. My Tiger has a similar engine to your Mooney and probably similar or slightly less climb performance. I am planning a flight to Leadville, CO, elevation 9,927 ft. Of course it will be early in the day for arrival and departure and I will be light (two people, fuel to the tabs, 38 gallons). Now, I just have to get the right weather and time to go.
 
pcorman said:
What is the highest Density Altitude that you feel comfortable departing?

I am asking as I just departed from my highest (Lake Tahoe, elev: 6260) with DA of 7600 in a Mooney M20C with 180hp O360-A1D.

I got 400-450fpm but it felt much flatter. Not sure what my limit is, but I think this is close to it.

Phil
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That's gonna depend on the wind, terrain, and percent under gross. If there's nothing but rising terrain, you could be screwed, but if you've got a way to aim for descending ground without much if any maneuvering you might get off above the plane's service ceiling.
 
lancefisher said:
That's gonna depend on the wind, terrain, and percent under gross. If there's nothing but rising terrain, you could be screwed, but if you've got a way to aim for descending ground without much if any maneuvering you might get off above the plane's service ceiling.
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Why would anybody wanna do that?
 
The highest DA I've ever operated with so far was 10500 ft, out of 7700ft long runway. The original altitude for the airport is about 5800 ft.
 
Appropriate runway, appropriate terrain, appropriate weight, I'd feel comfortable with 400fpm (heck, hot day and near gross, 172 or Warrior gets little more than that here anyway).

I do prefer more power, though, on that there can be no doubt.
 
pcorman said:
What is the highest Density Altitude that you feel comfortable departing?

I am asking as I just departed from my highest (Lake Tahoe, elev: 6260) with DA of 7600 in a Mooney M20C with 180hp O360-A1D.

I got 400-450fpm but it felt much flatter. Not sure what my limit is, but I think this is close to it.

Phil
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Just remember to do your homework, put in a safety buffer and fly the numbers you came up with before you yelled clear. 400fpm with flat or descending terrain is one thing. Climbing terrain and/or turbulence might get a little too exciting though.


Actually I haven't found my DA comfort limits yet. I take the DA+runway+terrain+WX+plane combination seriously and operate with a reasonable safety buffer based on experience. Experience is gained and the buffer is reduced a little at a time.

COS is 6183MSL. I've flown out of here with DA in the 9700ft range. Two onboard plus standard emergency supplies in a 180HP STOL CE172 in those conditions is no biggie IMHO. Two and baggage in a CE152 up here is interesting to watch though (not me, no way, no how)

We did launch out of Alamosa 7500MSL one summer morning in a Viking around 10% under gross and it was...interesting. It was planned properly however sucking the gear up asap and the image of the water tower going by at eye level is permanently etched into the inside of my skull for all eternity. Had I been PIC instead of a pilot I have complete trust in, we would have launched however the USPS package would have weighed a bit more.

I do prefer STOL kits with leading edge cuffs and as much HP as sensibly possible though. There is absolutely nothing wrong with more lift and more power and climb props IMHO.
 
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My 'personal best' was departing a 3,904 one way strip at 2,230 elev on a mid-June aftn. A no wind max performance soft field take off and I used every bit of that rwy and got >200 fpm. It took me 5 nm to climb straight out until I reached TPA. TPA was my target alt before making a 180 turn on course. This was solo in a PA-28-180, 45# baggage, < half tanks.


What made the difference was I knew what performance to expect, ie, no surprises.
 
pcorman said:
What is the highest Density Altitude that you feel comfortable departing?

I am asking as I just departed from my highest (Lake Tahoe, elev: 6260) with DA of 7600 in a Mooney M20C with 180hp O360-A1D.

I got 400-450fpm but it felt much flatter. Not sure what my limit is, but I think this is close to it.

Phil
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12,700' DA. Paced the liftoff point. Was 50' agl as we passed climbing at 700 fpm. There ain't no substitute for horsepower :yes:
 
It's all situations. Gimme a turbocharged engine and enough runway and a climb corridor, and I'll launch off the highest elevation airport you can find on the hottest day of the year. OTOH, there are sea level airports I won't take my Tiger into solo with only 10 gallons of fuel on a subzero day in January.
 
Ron Levy said:
It's all situations. Gimme a turbocharged engine and enough runway and a climb corridor, and I'll launch off the highest elevation airport you can find on the hottest day of the year. OTOH, there are sea level airports I won't take my Tiger into solo with only 10 gallons of fuel on a subzero day in January.
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You got it. T206H, 4400' at 2200 MSL. Decending terrain on departure. As good as it gets for one engine. And, actual performance beat book values by a bunch.
 
fgcason said:
I do prefer STOL kits with leading edge cuffs and as much HP as sensibly possible though. There is absolutely nothing wrong with more lift and more power and climb props IMHO.
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What are leading edge cuffs?

I am going to sound like a newbie again, but in reading all the responses, I'm trying to get a summary of factors that affect climb, and it seems the lists are all different. Is it engine power +runway + how much below gross the weight is that are the main factors? If the airplane is really light to begin with, is that better?
 
Toby said:
What are leading edge cuffs?
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Modifications to an airfoils leading edge that increase the airfoil curvature/increase lift, usually at the penalty of cruise speed. Leading edge slats do the same thing, but are movable so as to mitigate the speed penalty. Extend slats during landing/take-off and retract during cruise flight.

I am going to sound like a newbie again, but in reading all the responses, I'm trying to get a summary of factors that affect climb, and it seems the lists are all different. Is it engine power +runway + how much below gross the weight is that are the main factors? If the airplane is really light to begin with, is that better?
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Your list is somewhat confused because despite the fact that virtually everyone has listed one or more factors on your list, it isn't exactly horsepower, or weight, or runway length, or... The main criteria is really excess horsepower which pretty much equates to rate of acceleration (runway length) and rate of climb (obstacle & terrain clearance) at the given altitude & weight.
 
bbchien said:
Why would anybody wanna do that?
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Because someone was chasing me with lethal intent?

Sorry, I didn't mean to imply that taking off when conditions were near the aircraft's ceiling, just trying to show that there are lots of variables involved that can have a significant effect on the outcome.

I also intended to mention that terrain (ascending or descending) can produce downdrafts that will turn your wimpy 300 FPM (sometimes even a 2000 FPM) expected climb rate into a descent on the lee side. Plan accordingly.
 
160 HP skyhawk out of Glenwood Springs CO. 3 on board but fairly light on fuel. Reported DA was around 9000 at that time. Not much room for manuvering, as basically you come in one way and go out the other. We learned a bit of a trick though. Soft field take off. Get the plane off, and keep it down in ground effect and get some airspeed near the ground. Helped quite a bit to get it to come off at +300 FPM.

Leadville is almost always a density altitude of plus 10K, isn't it? Pattern altitude is 5 figures on any given day. The day Janet got us into and out of LXV, we had a nice new diamond star that just seemed to be able to find lift everywhere.

Jim G
 
Ed Guthrie said:
Who were those folks with the poison dipped spears?
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Don't worry about those guys, Ed. They always seem to be after Ron for some reason. What he did to offend them is another question...

-Skip
 
Ed Guthrie said:
Modifications to an airfoils leading edge that increase the airfoil curvature/increase lift, usually at the penalty of cruise speed. Leading edge slats do the same thing, but are movable so as to mitigate the speed penalty. Extend slats during landing/take-off and retract during cruise flight.



Your list is somewhat confused because despite the fact that virtually everyone has listed one or more factors on your list, it isn't exactly horsepower, or weight, or runway length, or... The main criteria is really excess horsepower which pretty much equates to rate of acceleration (runway length) and rate of climb (obstacle & terrain clearance) at the given altitude & weight.
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Excess HP (beyond that required for level flight at Vy) is directly proportional to climb rate (FPM), and power loading (HP/weight) affects the time it takes to reach lift off speed, but climb angle is also affected by aerodynamics.

I don't think it's accurate to single out any one factor, but if I had to, I'd pick the flying weight (percent under max gross) as this is one of the most significant factors that the pilot actually has control over.

Terrain, obstructions, runway length/slope, DA, and wind determine the required performance. Power (adjusted for DA), weight, airfoil characteristics, and piloting techniques determine the available performance. Margins between the two determine safety.
 
grattonja said:
160 HP skyhawk out of Glenwood Springs CO. 3 on board but fairly light on fuel. Reported DA was around 9000 at that time. Not much room for manuvering, as basically you come in one way and go out the other. We learned a bit of a trick though. Soft field take off. Get the plane off, and keep it down in ground effect and get some airspeed near the ground. Helped quite a bit to get it to come off at +300 FPM.

Leadville is almost always a density altitude of plus 10K, isn't it? Pattern altitude is 5 figures on any given day. The day Janet got us into and out of LXV, we had a nice new diamond star that just seemed to be able to find lift everywhere.

Jim G
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I flew a C-182 in and out of LXV many years ago on a warm spring day and recall that with just three on board (no bags, partial fuel) it felt like an overloaded Skyhawk on an hot day in the flatlands. The DA was probably 12-13k. Airnav says the strip is paved now, but I think it was gravel back then.
 
lancefisher said:
I flew a C-182 in and out of LXV many years ago on a warm spring day and recall that with just three on board (no bags, partial fuel) it felt like an overloaded Skyhawk on an hot day in the flatlands. The DA was probably 12-13k. Airnav says the strip is paved now, but I think it was gravel back then.
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Gravel :hairraise: Always wanted to use that little guy! It is a nice, long, recently improved paved strip now. The Diamond came off pretty well, but we WERE early in the day that day.

Jim G
 
lancefisher said:
I don't think it's accurate to single out any one factor, but if I had to, I'd pick the flying weight (percent under max gross) as this is one of the most significant factors that the pilot actually has control over.
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This is the point where we apparently differ. You suggest whittling weight off the hunting knife you have while I suggest bringing a gun to the fight.:) The aircraft is a user selected variable. I would suggest that the most prudent course would be to choose an aircraft with buckets of excess horsepower for the weight you intend to carry. Once the aircraft is selected and horsepower, aerodynamics, etc. are cast in stone, I agree, weight is the most user affected variable, followed by density altitude (wait for morning).
 
Ed Guthrie said:
This is the point where we apparently differ. You suggest whittling weight off the hunting knife you have while I suggest bringing a gun to the fight.:) The aircraft is a user selected variable. I would suggest that the most prudent course would be to choose an aircraft with buckets of excess horsepower for the weight you intend to carry.
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Yah, well sometimes it's hard to find a handy T210 to borrow at some of those mountain strips.
 
Quote:
Originally Posted by Ed Guthrie
Who were those folks with the poison dipped spears?

Skip Miller said:
Don't worry about those guys, Ed. They always seem to be after Ron for some reason. What he did to offend them is another question...
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For those unfamiliar, when asked about whether I would take off with an airplane that didn't meet airworthiness requirements, or without a preflight, or without proper planning, I always refer to the opening scenes of Steven Spielberg's "Raiders of the Lost Ark," in which the entire Horvidos tribe is chasing Indiana Jones with spears and blowguns. As Jones approaches the airplane, the pilot is showing some reticence about jumping in and cranking up, but the sight of those weapons and the mental image of his own head shrunken and stuck on a stick overcomes his devotion to safety (and fishing). As I said, it's all situations.
 
Lots of good info and ways to think about it, Lance. Thanks.
 
lancefisher said:
So the early bird gets the altitude?:D (Or is that the wise old owl?)
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I gave ya rep points for that one. Too clever not to.

Jim G
 
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