1/4ing head wind or down hill?

[landlover]

whats worse for performance? taking off up hill with a 1/4ing head wind, or down hill with a 1/4ing tail wind? to throw some more fuel on the fire, lets just say we were at 4000ft airport?

 

[gsrcrsx68]

Downhill worse by far...Assuming the uphill is slight. 4000ft will go by really fast with a tailwind and if you have to abort your GS will be fast and you'll be way less stable trying to stop with a tailwind.

I've taken off with a descent tailwind a time or two. Pretty uncomfortable to roll a plane 15knts faster than it should be on the ground(which if you think about it is 30knts faster than you'd need to be going if you took off the other way).

Then again, I've flown almost exclusively crap for planes.

 

[avbug]

This really depends on what you mean by performance. If you're talking about distance rolled, look at your performance charts and see. If you're talking about climb performance, then once you're clear, no difference. If you're talking obstacles, such as big rocks...pick the one that has the best departure path assuming no room to turn around.

I've operated from a number of one way strips, and in most all cases it was takeoff downhill land up, regardless of wind.

Given the choice, I'll always takeoff down hill, unless the wind is very strong. If you're in a turbine aircraft, you're generally restricted to a maximum of a 10 knot tailwind. Throw that into the mix when you're deciding what to do.

Mammoth, California is a good example of an airport from which you can take off in either direction, but really shouldn't. Winds seem to be generally out of the north, landing uphill, and when I have gone in there, it's always a downhill departure for me with a tailwind. The terrain is lower with the downhill takeoff...the distance might be a bit longer, but my options increase by a wide margin with the terrain falling away from me. One evening I tried it the other way and never tried it again. I've had a number of pilots tell me that taking off uphill there is no big deal, because they can outclimb the terrain...and on a good day, they're right.

On a bad day they're wrong. Always plan for the bad day.

 

[landlover]

On a bad day they're wrong. Always plan for the bad day.

http://204.108.4.16/d-tpp/0612/00297IL3.PDF
Thats the way I see it. We took off and landed downhill with a 1/4 tail wind at Ogden UT. To clearify the elevation of the airport was 4500ft, the runway was around 7500ft long for take-off. I wasn't too comfortable with this but the captain didn't see it that way. I wanted to at least land uphill with the headwind. the landing portion was fine cause we were empty and light on fuel. Also if you take off down hill(runway 3) there is some rising terrain in that direction. I wanted to use 21 for departure for the head wind and the lack of mountains. Runway 21 has a positive slope of 0.8%. Captain said the down hill of runway 3 trumps the headwind and mountains.
http://204.108.4.16/d-tpp/0612/00297IL3.PDF

 

[FL420]

Assuming your AFM has the info., use it. Headwind or tailwind component; percentage of slope uphill or downhill; density altitude; flap settings; runway condition; clutter; tire speed limitations. Get in the habit of using the book. It's a lot easier to defend your decisions, if necessary, if they're based on quantitative data pulled from the AFM.

 

[avbug]

Ogden doesn't have much of a sloping runway, and the mountains aren't very close to the airport...plenty of time to turn. The mountains aren't really an obstacle there, as you're not going to climb over them (or shouldn't try)...you're going to turn after takeoff. I've been in and out of there in some minimal performance aircraft (100 fpm max) without any worries regarding terrain (or slope, for that matter).

If you have the excess runway available, it probably isn't a big deal.

Did you calculate the performance going both ways before arguing with the captain? How much experience in type, and total experience do you have...and how much experience above sea level do you have.

Not to pry, but you sound uncomfortable flying out of a place like Ogden, which is wide open and an easy airport...you may want to do as FL420 directed and run the numbers before disagreeing with the captain. If you have good grounds, by all means speak up then. Curious about your numbers.

 

[landlover]

Ogden doesn't have much of a sloping runway, and the mountains aren't very close to the airport...plenty of time to turn. The mountains aren't really an obstacle there, as you're not going to climb over them (or shouldn't try)...you're going to turn after takeoff. I've been in and out of there in some minimal performance aircraft (100 fpm max) without any worries regarding terrain (or slope, for that matter).

If you have the excess runway available, it probably isn't a big deal.

Did you calculate the performance going both ways before arguing with the captain? How much experience in type, and total experience do you have...and how much experience above sea level do you have.

Not to pry, but you sound uncomfortable flying out of a place like Ogden, which is wide open and an easy airport...you may want to do as FL420 directed and run the numbers before disagreeing with the captain. If you have good grounds, by all means speak up then. Curious about your numbers.

since ogden's slope is very minimal is one reason i sought to use the runway with the headwind. i'll be the first to admit i don't fly in the mountains a lot, maybe 50-100 hours, yes i calculated it both ways and the numbers worked. but when we took off we maybe had 20 feet over the departure end. granted the airplane we fly is 40 plus years old and might not still be able to do what the book claims. who said there was an argument with the captain, a mere discussion. avbug i never heard of a difficult or easy airport, just difficult pilots. avbug i'll show you mine if you shom me yours

 

[A Squared]

The question as initially asked is way too vauge to give a meaningful answer. we are given values for neither the slope nor the wind speed. Makes a difference, ya know. Later it was clarified that it was Ogdon, with a 0.8% slope which isn't much slope, but it's still impossible to give a meaningful answer without the wind speed.

How about this: If there are absolutely no other considerations, the slope is 0.8 and the wind is 40 knots, I would land and take off into the wind, if the slope is 0.8% and the wind is 0.4 knots,I would land uphill and depart downhill.


On the other hand, I frequently fly into a mine strip with an 8% grade. you land uphill and depart downhill. period

 

[avbug]

avbug i'll show you mine if you shom me yours

??

 

[gsrcrsx68]

but when we took off we maybe had 20 feet over the departure end. granted the airplane we fly is 40 plus years old and might not still be able to do what the book claims.

That's what I'm talking about. That PA-200 I flew for my comm was worth 100 ft after 5000ft of rwy...POS...Nobody I flew with was willing to take that off with a tail wind. Definately wasn't living up to any Flight manual.

Fly old planes...You gotta pay somewhere...hopefully not in a ditch somewhere.

 

[MauleSkinner]

since ogden's slope is very minimal is one reason i sought to use the runway with the headwind. i'll be the first to admit i don't fly in the mountains a lot, maybe 50-100 hours, yes i calculated it both ways and the numbers worked. but when we took off we maybe had 20 feet over the departure end. granted the airplane we fly is 40 plus years old and might not still be able to do what the book claims. who said there was an argument with the captain, a mere discussion. avbug i never heard of a difficult or easy airport, just difficult pilots. avbug i'll show you mine if you shom me yours

Another question comes to mind...How did your takeoff technique compare to the technique used to determine AFM numbers? The mere fact that the airplane is 40+ years old shouldn't make a tremendous difference in performance, but it doesn't take a lot of difference in technique to throw book numbers out the window completely.

Fly safe!

David

 

[avbug]

Fly old planes...You gotta pay somewhere...hopefully not in a ditch somewhere.

Old airplanes?

I learned to fly in a 1947 J-3 Cub. It flew just as well when I learned in it as it did when it was new. I flew a 1944 PB4Y-2 into all sorts of places where performance really did become an issue (not nice flat runways)...and I don't believe for a minute that it lost it's performance over the years. Age is no excuse. If the airpalne is properly maintained, it performs. The airplane doesnt know how old it is. It knows about airflow, lift, etc...but unless your aircraft has been redesigned in the last few years, it's age is really quite irrelevant.

The numbers in your AFM pertained to the aircraft used to demonstrate the performance on a given day, followed largely by extrapolation and interpolation.

Your height over the end of the runway is really quite meaningless, unless ou have an obstacle with which to contend.

 

[gsrcrsx68]

That's a good point about the maitenance, but nobody I knew that flew that plane would agree with your point about the height over the end of the runway.

 

[avbug]

If you're not hitting something and you don't have obstacles with which to contend, then the height over the runway end is meaningless. A little like floating in the deep end of the pool. Who cares how deep the water is, if you stay on the surface? Who cares how much altitude you have at the end of the runway, if you're above the runway?

If your performance is inadequate, then consider yourself for the failure...the airplane didn't fail to gain altitude, you failed to ensure it was light enough to meet the performance standards you desired. The runway takeoff roll wasn't too long because the airplane was old...it was too long because the pilot failed to shorten it by reducing weight, waiting for a cooler day, taking off into the wind, or whatever needed to be done on a given day to meet the desired criteria. Including choosing a different airplane.

As far as height above the runway goes...I've had a heck of a lot of flights that broke ground and never climbed higher for the next hour or two, and I have a hard time getting too misty over not being able to climb at some preposterous rate. I've flown other airplanes in which I turned downwind at eighteen thousand feet, still in the traffic pattern...which is nice if that's what your mission requires on a given day. In a light piston engine airplane, clearly that kind of performance isn't going to happen. You might be used to five hundred feet per minute or a thousand feet per minute in a 172...this is a different airplane, loaded differently, flying differently, requiring different performance calculations, and must be operated accordingly.

Merely because others who have limited experience disagree about the height, is also meaningless...if I took them out for a thousand hours and worked them at six feet, they wouldn't think twice about it. The airplane isn't lacking. The experience of those making the observation is lacking, and it shows in their assessment and observation. When considering these things, keep that in mind.