POH no Grass field performance documentation

[rturbett]

I'm imagining the responses already-

 

But, there is a grass strip I would like to visit- 2200 listed, 2400 actual usable.

I've often been told to RTFM, so I've made a point of studying before posting. I was surprised to see that in my POH, there is no chart in the performance section for taking off or landing on grass. The POH  issued  12-28-78, and based on the weight and balance data, has been with the plane since day 1.  (1980 M20J)

 

I've seen other high performance take off and landing posted online (scanned, difficult to interpret). I have very little concern on landing, but would love a definitive source for calculating take off, especially considering the increased density altitudes. I have excellent data on runway condition before arrival.

Any source for calculating high performance take offs on grass would be greatly appreciated.

 

Thanks,

Rob

[PT20J]

Depends on which POH you have. My 1977 M20J POH does not list takeoff performance for grass. However, my 1996 POH does. I don't know when Mooney started including it. There are a lot of variables with grass: slope, grass length, whether it is wet or dry. A sea level 2400 ft level grass strip should be no issue for an M20J.

[Fly Boomer]

2 hours ago, rturbett said:

Any source for calculating high performance take offs on grass would be greatly appreciated.

I'm a math guy, so I love calculating but, if I wanted answers to these questions, I would find a 4,000 foot turf strip with similar characteristics, and do some testing.  Even if those numbers were in your POH, no single chart can be accurate for all instances of your model.

[patrickf]

Rob,  first post in this thread will give you something to play with.

All care - no responsibility

 

regards

[patrickf]

This is a pretty usefull guide from the Aus side, I'm sure FAA has an equivalent.

https://www.casa.gov.au/guidelines-aeroplanes-mtow-not-exceeding-5-700-kg-suitable-places-take-and-land

 

[Hank]

I used to take my C into a 2000' grass strip, a bit under 600msl. But due to its (lack of) length, my personal limit was two people and half tanks (52 gal capacity). But I no longer live there.

Never had any trouble.

Next week, I'm off to a 3500' grass strip at the beach, carrying as much of my wife's cooking stuff, clothes, towels, sheets, as I can make both doors close on. It's a 3 hour flight, they have no fuel, so we pack up and leave, making a nearby (paved field) fuel stop on the way home. We go 1-2X per year for the last 17 summers, never had any problems, but once I did fly out solo a day early after walking the runway to find the shallowest water, so that we could depart heavy from a paved surface (it was a very wet summer!).

The biggest factor will be your own grass field experience and your technique.

Fly safe out there!

[PT20J]

From my 1996 M20J POH: Sea Level, ISA temp, 2740 lb, paved ground roll is 1500' and grass ground roll is about 1800'

[Hank]

7 hours ago, PT20J said:

From my 1996 M20J POH: Sea Level, ISA temp, 2740 lb, paved ground roll is 1500' and grass ground roll is about 1800'

Wow! At sea level, gross weight and 59°F, the ground roll for my C is shown as 815', with no guidance for grass fields.

[midlifeflyer]

There are some general rules of thumb and some POH even give numbers. But the problem is that unimproved runways are so variable with respect to condition that anything is really just a guess.  Dry well mowed grass will have a similar landing distance to pavement, but the numbers I’ve seen for takeoff  are to increase the numbers 10-15%. But unless I know the field, I’m thinking in terms of  double the takeoff roll.

[Oscar Avalle]

I fly regularly my M20 now E into a 3500 feet long grass runway. It works well. I am normally off about 1200 feet into the take off run. However, there are several factors worth considering that have led to some interesting expiriences:

a) is the grass wet or not... last week I landed and the grass was wet and muddy... so on take the mud slowed my run and

b) you always need to use softfield procedures... specially in a mooney with a small prop clearance,

c) keep in mind density altitude...

 

Oscar

[rturbett]

Great advice-Thank you.

Earlier this year, I went to a 3000 foot grass strip. Even though there was a good pirep on field condition, the grass was taller and wetter than I expected.

Takeoff roll was much longer than expected- I nearly aborted. I had much more fuel on board than needed.

It was a great teaching moment, hence all my questions.

Rob

[laytonl]

I live on a 3,000’ grass strip with my M20J.  I collected data for a couple of years on all the factors influencing performance.  I found that ground roll is within about 5% of a paved runway when the grass is dry and recently mowed.  Otherwise about 10% variance.  Lee

[M20F]

Just because you can, doesn’t mean you should…

[Hank]

1 hour ago, M20F said:

Just because you can, doesn’t mean you should…

That applies to so much more than landing at an unpaved airport . . . .

[M20F]

38 minutes ago, Hank said:

That applies to so much more than landing at an unpaved airport . . . .

Coldplay concert?

[Ibra]

UK CAA has a good safety leaflet, with some ballpark recomanded safety factors. However, there is a lot of variability with grass, and when it is long and soft, the takeoff factor goes to infinity (at least what I measured once: I used 3000ft of 4000ft long grass few times in C172, aquaplaning for fun ) 

https://www.caa.co.uk/media/lpwhsrfn/safetysense12-strip-flying.pdf

In M20J, I need 2100ft dry grass for landing and takeoff when it's dry and well cut, when it's wet or soft, I am not going. I also needs some wind or power to smooth touchdown if surface is rough...

A well cut dry grass adds about 10% to the requirement. However, the most important elements in discussion are 1/ have you used Mooney in "other similar grass" and 2/ have you been in "that exact grass" in C172 or car? none of these questions relate to POH data 

 

 

Edited July 21 by Ibra