Question For The Experts.

[Sunfish]

As you all know, airfield slope has an effect on takeoff performance.

Those of you who have flown into YARK - Arkaroola, will know that the strip is tastefully draped over a little rise, so that it's highest point is roughly in the middle and it has about a 1.5 - 1.7 percent grade towards each end.

How would one calculate the effects of that? My guess is that takeoff distance is increased slightly, but not as much as if it was a constant upward grade.

And before anyone jumps on me, I've been in and out of it a few times and my safety factor on takeoff roll distance, there not being any obstacles to clear at either end, is already slightly over two.

I'd just like to know if there is any formula or rule of thumb for dealing with this calculation.

[Enema Bandit's Dad]

Use a helicopter and you won't have to worry! :)

[nick2007]

A very rough rule of thumb might be to look at the net change in slope over the estimated length of the takeoff run (i.e. difference in heights at either end, then work out % gradient). Such detailed data isn't published, so you'd need to sit down and work it out on paper.
Of course it isn't quite as simple as this, but I'm guessing that approach would probably give a reasonable answer.

[Bendo]

First off, assume that you will stop in the "up-slope" portion.

Calculate at that % up-slope. Will you pull up before you go down the other side?

... if "yes", good.

If "no", surely you will be going pretty slow by the time you do? Just stand on the picks harder :} :eek: :ouch:

...hope you're not planning to fly a 206 full of grog in there Sunny :E

[Capt Wally]

with a thread heading like that sunfish how can we not pull up hard & pop on in to see how we can help:E

I believe that if you need to calculate that accurate the up/dwn slope of any rwy for the purposes of ldg or T/off then you are too close for comfort especially in pvt ops. Still having said that you did pose a sensible Q for which I have the following answer.
Take the LDA for Eg, if you need it all then a 'hump' in the middle pretty much cancels out each other any +/- of slope/s. What you gain upon ldg uphill you loose on the downside. Same goes for T/off.

That's what I believe to be the case, others will no doubt have a far more complex answer

CW:ok:

[john_tullamarine]

Not a question for a simple answer ... for heavy ops, the ops engineering folk would consider the match of a specific Type to the centreline profile and massage the calculations to provide a conservative answer. If you had a suitable model, the takeoff/landing calculations could integrate the distance for the varying slope but that isn't the normal approach to the problem out in the jungle.

The OEM doesn't address this sort of thing as there is no requirement for it.... fortunately most routine strips have a half decently sort of uniform slope so it's not too bad in those cases.

[dabz]

Wouldn't know how to accurately calculate that but for legal take off for p91 or p135 all you need to do is the appropriate performance calc with the slope from the back of the aerodrome chart :ok: