Density Altitude

[DroopTip]

Hey eveyone,
Im sure there are at least a few on here that fly up in the high country. I just wanted to get some other opinions on rules of thumb for using high country strips. One that i have heard befor is add 10% to your takeoff distance for every 1000ft above sea level. I know things like temperature also make a difference, but for the sake of argument lets look at it from a standard temperature. Okay, im ready for some of your thoughts!

Josh

[Stephen]

Pacers do fine in backcountry strips. I love flying mine into some of the strips in the Idaho back country. I would be more concerned with winds.

[Glen Geller]

I have not flown from high rural strips yet, but my pals have in their PA22s, they always advise being light as possible, plan so you have minimal (but safe) gas on arrival so you can leave without excess fuel weight. And early morning departures when it is cool, just after sunup if possible.
I would suggest visiting a high elevation airport with a nice long runway and doing practice approaches, departures and go around, and with crosswind runway if possible. Learn the tactics in a reasonably safge environment where you have a margin for 'learning curve' before heading into the shorter rougher fields where you may learn the hard way.

[Homer Landreth]

Hi Josh;
There is no such thing as a "Rule of Thumb" relative to aircraft performance at high density altitudes. Your terminology of "things like temperature make a difference" is a little scary. Every takeoff and every landing procedure is DICTATED by altitude, terrain, temperature and wind. I taught mountain flying courses in the high and hot areas of Northern California and from that experience I can say that you have some severe deficiencies of knowledge that transcend just getting casual information and opinion. You may not have been properly exposed to density altitude factors, but you will need to resolve those deficiencies to fly safely. I suggest that you first get your owners manual and flight manual out and study the performance figures for the total temperature and altitude range of your aircraft. Compute your own graph for takeoff distance for all temperatures and altitude ranges and see what the totality of effect is. Look in the Sportys catalog and buy a couple of books on mountain flying and read them thoroughly. Finally, find out where AOPA will be teaching mountain flying courses and sign up to attend and get instruction. Mountain flying is a real trip, but if not done right you can break your airplane and its pilot.

[Gilbert Pierce]

If you are an AOPA member start here. http://flash.aopa.org/asf/mountainFlying/html/flash.cfm?

If you are not an AOPA member you should be.
The above interactive course will Introduce you to the things Homer alluded to. I highlighted introduce because it does not qualify you to fly in the mountains. It only points out the things that can lead to trouble.

[Stephen]

Wow! Homer, "no rules of thumb"?

I guess it's in all how one chooses to learn mountain flying.

I absolutely agree that we should thoughly study performance charts, read articles and books and take courses, but I think Josh was looking for a discussion on altitude and some general moutain flying tips. I learned mountain flying well before modern courses and most books were available and, my current plane out-performs the published performance charts. Picking up tips from experts was how I learned and still remains valuable.

One of Sparky Imeson's("Mountain Flying") rules of thumb" I was rereading the other night was "abort any mountain take-off, if you are not at 70% of flying speed by midfield".

Homer, you must have some usefull tips from you experience in the mountains of No. Cal.

Hey, anyone going to Johnson Creek, Idaho June 20-21?

[Bultaco Jim]

Sparky's book is a "must read" for sure. The good thing about the 70% by half-way rule is, it works for any plane, and is a final sure-fire check in case you mis-calculated all the "info". What's happening at Johnson Creek?

[DroopTip]

Hey homer, I apologize for using such "casual information". I should not have even put it in, and left if even more vague. Im not even going to start with trying to defend myself. I know what my abilities are. All this thread was meant to do was start some discussion about this type of flying. IT WAS MEANT TO BE VAGUE! Anyway, thanks for the input everyone, i have read sparkys book, and some of the others. I was just looking to see if anything would pop up i had not heard befor. Especially from a short wing point of view.

Because I fly in the Desert Southwest I really keep an Eye on Temperature. I have flown a 172 SuperHawk 180 HP out of the Grand Canyon Airport [6500'] on a 92 deg day with three people. I made the foolish mistake of topping the tanks before we departed for the transition corridor. I don't think I cleared the trees at the end of 9000' of runway by 25 '. I could not climb above 10800' period. With 105 hrs total at the time This experience crystalized the concept of Density Altitude. I have been afforded a few experiences that have set me back on my heels. It only takes one. This flying business is harder than it looks.

I had to correct the ellevation and runway length. Should have been 6500' elev. & 9000' of runway. Got them turned around. Temp was correct. According to my CR-1 that makes 10,000+' Density Altitude :shock:

[Stephen]

Bushangel, I think it must be a Cessna thing. I remember flying a C-172, 145hp off a grass field at sea level on a warm day with three people and going between the trees at the end of the runway. Also, a lesson I learned years ago.

I've never had that problem in my Pacer.

[Bultaco Jim]

Since you two tied the "C" word to bad experiences, Hillbilly will probably let you off the hook.

[Hillbilly]

Bushangel, I think it must be a Cessna thing. I remember flying a C-172, 145hp off a grass field at sea level on a warm day with three people and going between the trees at the end of the runway. Also, a lesson I learned years ago.
I've never had that problem in my Pacer.










Since you two tied the "C" word to bad experiences, Hillbilly will probably let you off the hook.



Don't think I wasn't paying attention Jim, but notice what he said (in bold) ....Thats what cars(must) do. If you tied the C word to a good experience its probably on a banner behind a shortwing.

I'm pretty sure it was a pilot thing. Airplanes cause a lot fewer accidents than pilots. Homer is right on - know the operating limitations of the aircraft and do the math. I also read another post that talked about "milking altitude" by climbing and leveling, climbing and leveling, which I was too inexperienced to know at the time.

One other trick an old pilot friend shared with me about hot short field takeoffs to clear the highway traffic at the end of our 1200' gravel runway in the summer. He uses 1050' and builds as much speed as he can, then pops full flaps which gives an instant 100' like an elevator ride. Still scares the hell out of the truckers on the highway since the road is about 250' from the threshold.

[Homer Landreth]

Wow! Homer, "no rules of thumb"?

Homer, you must have some usefull tips from you experience in the mountains of No. Cal.


There are a lot of experiences that lead to tips, and if you want to call them a "Rule of Thumb", that is OK too, the terminology is nothing to fall on your sword over. Something I always made sure that students understood was that in a flat land in proximity to mountains environment that your plane that was suitable for takeoff in the flat country may take you, via a very short flight, into an airport in the mountains part that you can't get out of. As example I would take a student on a departure from Sacramento and we would go to Blue Canyon. Blue Canyon is 5200 feet and some change, and maybe a 30 minute flight or so from Sacramento. Then we would sit at the end of the runway and discuss the flight a bit and then I would say OK, "lets go", every new mountain flying student I did this with would immediately go to the throttle and commence takeoff. WRONG! At that point we would stop and talk a bit where I would point out to him that his first takeoff was from an over 5000 foot in length runway at 20 feet MSL elevation and he is now at an airport where the runway is half that length, and the altitude is 5200 MSL, and the temperature is wiithin a couple degrees or so of the temperature in which he took off, and his airplane weight is at most only 50 pounds lighter. If that didn't get him religion, I would also point out this little moniker in the airport data "20 ft. tree, 750 ft. from runway, 110 ft. left of centerline, 27:1 slope to clear". Then I would ask him what his departure slope was, to which few even knew how to compute it. (What is more important, where you are going to get off the ground at or what can your plane do after you get it off the ground? The answer changes sometimes.) That naturally led to a discussion of some of the mountain flying differences such as taking off toward the downsloping terrain (even if it meant having a tail wind) and then discussing a couple of other deviations to the things that you were always told to "never do". I did this little exercise because of the number of times I had former students, sometimes years later, that tell me they always remember the day that we sat at a short, high altitude runway, in a loaded C-172, looking down the runway at a tree, and they didn't have a clue whether they could even get off the ground let alone clear the tree. That is where my fetish belief of always "running the numbers" :!: comes from.

[Stephen]

Great lesson Homer! Thanks. I wish I'd had one like that early on in my flying.

[Hillbilly]

Heh!, Homers got a fetish...

[Bultaco Jim]

Maybe we should call this thread ...." DENSE 'ty Attitude"

[Homer Landreth]

Maybe we should call this thread ...." DENSE 'ty Attitude"
? ? :?: I don't get it ? ?

?

[Bultaco Jim]

I was attempting to call Hillbilly "Dense". ....(Pot calling kettle black!)

[Hillbilly]

I was attempting to call Hillbilly "Dense". ....(Pot calling kettle black!)


You might be a redneck if; no one understands your jokes but other rednecks...
Come on down south Jim, I'll teach you'uns how to say densti awltitude.

[Homer Landreth]

OK, I will have to stay out of that one because I am Southern Challenged. I am still looking on the Sectional Chart to find a city named "Gnaw O Lens". :?

[Steve Pierce]

Good one Homer. :lol:

[Tripod]

If the following video link is a re-post, my apologies to those who have already seen this or talked about in depth. But, for those who haven't seen it, I think this worth looking at:

http://www.alexisparkinn.com/photogalle ... ersion.wmv (http://www.alexisparkinn.com/photogallery/Videos/2009-7-7-CessnaL19CrashLongVersion.wmv)

-dave