172 take-off performence charts

[dudduddud]

This is to do with the surface correction factors for grass runways etc.

In the flight manual, it gives the ground roll distance and distance to 50' in respect of each pressure altitude and ambient air temperature.

At the organisation I am at, we are taught to use the 50' distance for all take-off calculations. Which makes sense.

But we are taught to apply the surface correction factor to that whole distance.

Wouldn't it be more correct to apply the surface correction factor to the stated ground roll distance and not the remaining distance to 50'?

Presumeably the runway surface does not influence the section of the take-off after actual lift-off?

Your thoughts...

[scrufflefish]

What you say is reasonable at first glance, but what if the grass is VERY long? :}

[dudduddud]

Well I would simply fire the groundsman.

But the reality of the situation is that I often take off from other peoples runways and want to be totally sure I am not 'putting them out' by using less runway than I promised.

[AussieNick]

think about it. the ground roll will obviously be longer in grass than sealed. this will also mean that your climb will begin closer to the end of the runway.

all numbers are examples;

say the T/O distance is 300m sealed and 380m on grass.
the distance to clear 50' from sealed is 350m, on grass this will be 230m. remember, you have to travel an extra 80m just to get airborne, taking you closer to the end of the runway. If there are large trees for example, this 80m ground roll increase could potentially mean that you will not be able to clear those objects at max angle climb.

so it defiantly makes sense to use surface correction on the 50' distances in my books.

now, will one of the more knowledgeable persons here let me know if i'm right or wrong?

[MCKES]

Flying 172's I can tell you that the performance is less than great in a decent bit of grass (slashed high but not mowed). Once you get going its all right and it doesn't take all that much runway and this is clearing 30ft trees roughly. As aussie nick said use the 50ft distance and then correct for grass. :ok:

[dudduddud]

Definently taking off on grass will bring you closer to the end of the runway and that is shown by adding the factor of 1.14 (in nz anyway) to the ground roll.

im just wondering once you have calculated that, if you need to also add 1.14 to the section between lift off to 50', considering you are not on the ground still? by adding the correction factor to the whole distance to 50', that is what you are effectively doing? c'est ne pas?

I know New Zealand grass is superior to Australian grass but I doubt it is long enough to effect takeoff performence once airborne?

[Capt Wally]

I like the bit about diff grasses in NZ & here, funny:)

Off track slightly but seeing as there's a fair bit of info here for the poster by now I've got a funny story re-long grass.
Many moons ago (pvt days) a friend & myself went aviating in the C150 I part owned. We ended up at Yark, NE of ML. Nice country town, tiny actually . Anyway my companion said his uncle lived right down there. We did a couple of slow/low (no other way in a C150H) passes to asses his uncles top paddock. Long enough that's for sure, few trees both ends & flat as! Dry grass looked short enough so I made an approach missed the trees & during the flair nearly had a heart attack, grass wizzing past the windows almost ! Too late to do a go-round with 40 deg flap out & little left in the way of distance from the trees at the far end. So we touched down & rolled about 2 feet! Well felt like it anyway. Forcing the doors open against the grass we stepped out. Whoooops now I've done it.

4 hrs latter with the help of a few local town folk we mowed a strip racked the long grass away & we took off usuing a LOT of real estate due still very think grass(almost as thick as the pilot!:bored:) We paced out the avail dist & checked the book, dusted off the pages first though & it showed we had enough dist for short dry grass (which we thought we had)............................moral of the story? calculate the T/O dist as per the chart & triple it !:bored:

Ah the good 'ole days

soz for the sideways drift here but it's kind of relevant:ok:



CW

[Lasiorhinus]

I often take off from other peoples runways and want to be totally sure I am not 'putting them out' by using less runway than I promised.

I really don't understand why this is a factor - unless the owners of the runway are receiving certain benefits depending on the distance your wheels stay on the ground.

If your chart says "factor by 1.14 for grass", then factor by 1.14 for grass.

If the runway is too short when you factor the whole distance, but by only factoring the ground roll then you can make the numbers "work", then your runway is still too short for comfort.

[Gundog01]

Peformance and C172.......oxymoron came to mind....

[airtags]

great story Wally - goes to reinforce whatever the tolerance/deviation is ...rwy length, crossswind, fuel reserve et al; ..... always add a little more.

No issues with the grass on my little patch (NW of MEL) - despite the rain - would love to have grass half the height of NZ!....jeez I'd even settle for a shade of jealous green! :E

AT

[Peter Fanelli]

Peformance and C172.......oxymoron came to mind....

My thoughts exactly.

[CaptainInsaneO]

Quote: "I know New Zealand grass is superior to Australian grass but...."


That's because all the Kiwi's are all over here standing on our grass!