Effect of runway slope on ASDR

[italia458]

I did a search here but couldn't find anything with details on the effect of runway slope on ASDR.

I was thinking about calculating it out using Newton's laws of motion but it's a little more complicated than that! On a down slope runway compared to a level runway you would have an accelerate distance that would be shorter due to the higher acceleration rate and the reduced rolling resistance due to the weight of the airplane not acting perpendicular to the runway. Stopping would be longer compared to a level runway because you have to oppose the component of gravity accelerating you along the runway, less weight acting perpendicular to the surface means the wheels don't have the same contact and you would be restricted to less brake force than on a level runway. Percentage wise, when on a level runway, accelerating up to a speed takes more distance than stopping from that speed but that relationship would start going the other way with an increase in downward slope so that eventually you would have the accelerate distance shorter than the decelerate distance. What slope does that happen at? Too many factors to determine it!

Based on that I think it would be hard to accurate calculate how ASDR would be affected. Does anyone have any charts that show the effect?

Edit: I should clarify that for this example V1 is not changing. Any data for either all engines operating or one engine inop ASDR is welcome.

[FE Hoppy]

Down slope overall reduces TODR, ASDR and on a balanced field calculation V1.


Not sure about your rolling resistance and brake contact arguments given that the wheels are round!

[italia458]

Where did you get that information? I was told by a relatively reliable source that on the jet he flies, a up or down slope runway will increase the ASDR. He noted that information from calculations done by the FMS. I want to get hard data from a number of different airplane types.

Not sure about your rolling resistance and brake contact arguments given that the wheels are round!

That doesn't make any sense. Rolling Resistance (http://www.engineeringtoolbox.com/rolling-friction-resistance-d_1303.html)

[de facto]

An upward slope will:Increase your TOD and Decrease your ASD
A downward slope will decrease your TOD and increase your ASD.



The problem is in the case of an uneven runway,ie upslope then around the area of V1 , a downslope....not the best scenario for a reject if fiel limited.

[FE Hoppy]

De facto,

If you offered your answer in the current EASA ATPL exams you would be marked incorrect.

The examiner currently is of the opinion that a downslope reduces TODR and ASDR as the effect of increased acceleration and therefore earlier V1 out ways the increased deceleration distance.

With the caveat that this is not true for VMBE limited take-offs.

The reality is that for each type it will be different and for any one type the effect of slope will be tempered by other variables.

[staircase]

During the 1970's I remember watching an EC121 on a flat 8000 ft runway trying to get airborne.

First 5500 ft of runway with a slight uphill slope. Last 2500 ft had a fairly sharp downhill slope.

Average runway slope was zero. Great until the EC 121, whilst accelerating uphill, had an engine fail late in the take off roll and then tried to stop going down hill, and inevitably into the overrun.

Guess after all it is still has a bit of chance associated with it.

[de facto]

For a b737 it is correct as it is for Airbus...
Based on a b767 AFM i have in my files, a downward slope will DECREASE your Engine out TOD and 2 engine ASDR.
V1 is based on the slope corrected Engine inop TOD and corrected ASD.
I will check in the 737 AFM tomorrow.
Pfeww i dont need to pass the easa atpl:O

[rudderrudderrat]

Hi italia458,
I should clarify that for this example V1 is not changing. Any data for either all engines operating or one engine inop ASDR is welcome.
ASDRs are calculated assuming all engines are operating during the acceleration phase, and stopping after the engine failure.
Why on earth you want all engines operating ASDR?

[italia458]

RRR...

I'm looking for any data related to accelerate stop distance and runway slope.

For certification you're required to measure the accelerate stop distance using all engines operating for the full test. You might need to reject a takeoff with all engines operating. Reference CAR 525.109(a)(2)(ii) or FAR 25.109(a)(2)(ii).

Part V - Airworthiness Manual Chapter 525 - Transport Category Aeroplanes - Transport Canada (http://www.tc.gc.ca/eng/civilaviation/regserv/cars/part5-standards-525-sub-ab-1739.htm#525.109)

[rudderrudderrat]

Hi italia458,
I was thinking about calculating it out using Newton's laws of motion but it's a little more complicated than that!
Construct an excel spread sheet using SUVAT equations (e.g. Equations of motion - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Equations_of_motion))
Suggest you use diStance = (Vsqd - Usqd)/2 * Acceleration.
Assume the acceleration with all engines is say 0.4 g.
Assume the deceleration with brakes & reverser(s) is say 0.8 g.
Calculate your diStance to accel to your chosen V1 and then to stop.

With down runway slope, add to the acceleration with Sine(slope in degs)*g
and reduce the deceleration by the same amount.

Try various slopes until you get the same magnitude of acceleration as deceleration and then you'll have your answer to ....eventually you would have the accelerate distance shorter than the decelerate distance. What slope does that happen at?

[FlightPathOBN]

on a related note...

watched the balked takeoff test for the 747-8...

they even shaved the brake pads to the rivets....

interestingly enough, the tires automatically deflate, I understand why, but still...

damn!

[mutt]

they even shaved the brake pads to the rivets. I think that its 80% or 90% worn brakes... This has applied for any aircraft certified in the last 10 years of so, it also indicates that the 748 didnt get grand father rights :)

interestingly enough, the tires automatically deflate, I understand why, but still... So you mean that the fuseplugs operated correctly?

Mutt

[FlightPathOBN]

mutt,

while the fuseplugs did operate correctly, it appeared a non-issue..I mean really, a balked takeoff, and then you had the vessel on runway, DOL until you bring in and exchange like 20 tires...

seems to me like there could be a intermediate step.

[john_tullamarine]

Average runway slope was zero.

If the distances are critical, or thereabouts, some of us (when we put our Ops Eng hats on) run the calculations to account for the various sloping bits to give the more conservative result.