Takeoff and Landing distance graphs

[gliderman]

Hi all
I flew to a friends farm last night and landed on his grass strip. on takeoff we needed all of 2400 ft to get off the ground.
seems to be a bit long.
what do you folks think?
here is the particulars:
54 Pa22-135
full tanks( 36us) and he and i have a combined weight of 445 so total weight is about 660 lbs.
Strip is 3300 ASL ( figured out the density altitude and it was 5126 )
his grass hasn't been mowed so the grass length was about 1/3 to 1/2 up the wheel
thoughts
Shane

[dcflyer84]

Heh. First off I'd say you got lucky! Second, I'd say check what your CG actually was for that takeoff and see if it was even inside the envelope. Thirdly, the official numbers in the Piper Manual are for a paved runway with no wind. At least in my PA20 one it is so, and there is no provision for additives for non-paved surfaces. Use grass and you're on your own, it would seem to say. You can see in this thread that there are some flight tested numbers from our Aussie friends on short, dry grass, but again, no provision for additives for anything beyond those conditions.
i think if it had been I behind the yoke that day and there was any doubt in my mind about the takeoff, I would have tried a run solo to see how much runway I used before having my friend join me. In addition, maybe checking ahead of time with your friends at the strip what the condition the grass was in and maybe leaving some fuel behind at home, thus coming in a bit lighter in the load.
i think there are too many unknown variables to determine if the amount of runway you used as excessive, or not. Knowing what your airplane can do and what you can do are the most important safety factors to consider, IMHO.

[Throttle Pusher]

Max gross over 5000 ft density alt., 135 Hp, original short wing,
2400 ft run on grass, This doesn't sound excessive to me.
A rule of thumb I've used is,"go in heavy,come out light"
and 70% of your takeoff speed halfway down the runway.

Ken

[tnowak]

Gliderman,

Take a look at the UK CAA guide to landing/takeoff performance:
http://www.caa.co.uk/docs/33/ga_srg_09webSSL07.pdf

If you look at the end of the leaflet you will find all the things they suggest must be factored into account for operating off other than "standard" runways at standard temperatures/altitude etc.

I suspect the long grass was the main contributing factor to your longer take-off roll.

TonyN

[andya]

I have experienced the effect of long grass, don't know how much distance it added but it took a long time to accelerate from what happens on short grass and/or hard surface.

[Curly]

Shane - I agree with Tony - 700 odd hours towing gliders out of paddocks gave me enough frights to make sure that if I had to do a retrieve from a paddock with long grass (and halfway up the wheel is long enough) I made sure that the grass was either mown or walked down (glider pilots used to love that) before attempting a takeoff.

There is also a soft ground/long grass technique which is to pull full flap at about 45kts. This will pop you off the ground (and reduce the drag from the grass), then hold the aeroplane a foot or so above the ground and allow it to accelerate in ground effect while slowly milking the flap up until you see climb speed.

This is not something you should try for real, unless you have practiced it beforehand and feel confident in using it - but it works.

[tnowak]

My first experience of long grass was at a small French airfield many years ago. Airfield was only a few hundred feet AMSL but the grass about 3-4" high on a firm surface. On take-off my A65 Vag just wouldn't get above 50 MPH until I "dragged" it off the grass. Acceleration then back to normal and off we went. That was my first experience of "long" grass take-off and did take me by surprise.
TonyN

[gliderman]

just to alleviate everyone concerns: the runway was about 3000 ft long and a "run off" area of about 200 ft(Waist high grass) past that. but was definitely thinking of shutting her down very soon when she started to fly.
ah the learning curve......

Shane

[59pacer]

At 5000' density altitude on a 135hp engine, you would only have been getting about 110hp--about the same as a Colt at sea level. Now add the extra weight and the significant effect of the grass (+20-30%), and it starts to become 'curvature of the earth' stuff! It looks like the a/c performed perfectly--but by any objective assessment it was poor!! Another thought was that, at that density altitude, did you lean at all? All grist for the mill.

[gliderman]

Hi All

"Another thought was that, at that density altitude, did you lean at all? All grist for the mill."

in response to leaning- here in Alberta we have to lean as a matter of course as we are at 3000 ASL( we call it the "alberta mixture" lol). At the strip that evening I leaned for max rpm.

Shane