"tall grass" means different things to different people. We all give pause when we see 'tall grass'
due to it's potential for hiding objects which are detrimental to our health.

But does anyone have any specific rules of thumb they've found accurate for the judgement of drag and/or nose-over
risk based on the 'average height' of the grass? Since I own the hayfield, I know I have no debris in my field,
and I don't want to mow the crop for a runway - so I'm trying to decide how tall I can get away with this until
the drag tends to lift my tail on landing so much i can't keep down. Someone must have tested this, intentionally or not

I have a two seater 800lb taildragger on 26" ABW's. My takeoff is a non issue cause my initial ground roll is on mowed lawn
for the first 100ft, and i'm off in about 100-120 typically.

Any thoughts based on percentage of tire height? or any other measureable examples or experience would be interesting - I searched 'tall grass' and similar on the forum but couldn't find any definitive replies. Thanks all!

~Brendan

I don't have any rules of thumb but I've landed in a alfalfa field that was tall enough to turn the tips of the prop green and I wouldn't do it again. I was running 6.00x6 tires at the time. The problem with alfalfa is that it is a tangled mess and the right tangled mess can slow a wheel enough to cause problems. I personally wouldn't land in a field where the hay was much taller than half the height of the tire; I want the tires to be rolling over the hay and not through it.

I know you said you don't want to cut a strip but I asked a local farmer how much profit he would lose if he kept me a 1 acre strip in his alfalfa field trimmed all summer. Said it would be about $150 but he typically only gets 4 cuts a season. Seems like cheap peace of mind to me.

I second Whee's comments:

There is more than one type of grass. No pun intended.

I have landed at Dixie Forrest before it was mowed. "Grass" was about 18" high. Just kept a little more power on a little further into the roll out, but was not a problem. Grass was thin and stringy without much resistance. Have had more trouble with shorter but WET grass and ABWs. Plane wanted to go left across the slippery wet grass even with full rudder applied. I felt pardners foot on right pedal, all he said was, "Oh, you already have it all in." Hate it when ya gotta use a little brake on take-off.

Trim

It's not super dense here yet... but the ol 'half-the-height of the tire' rule seems safe, i assume that's for dense wet grass, agreed?

The percentage of your total weight that is on your tailwheel is in my opinion one of the biggest factors. My Highlander tail is quite heavy and it lets me get away with doing things that would flip a lot of planes over. With nothing but 10 gallons of fuel in my plane there is 150 pounds on the tailwheel. I have to work a little harder to keep my tail up when I want it off the ground but I think it is a very good trade off for how much it resists flipping over.

My friend had a forced landing in a bean field that was probably 15-18" tall in his Avid. He did a great landing but the crop was all grow tangled together and before he got stopped it flipped over.

Steve

Thx Steve - your insight is appreciated. Maybe I'm better to LAND with a passenger, and takeoff without ?
if I keep my speed up and can get to the top of my 15% grade field, it opens up to that 'lawn' mowed area for my
slowest phase of groundroll, which i'd guess is the biggest risk point, yea?

I wanted to test this more as the crop grew, but between EFIS changes and the Wx has been crap,
now it's already about 8" tall and thick, with seed going up to 12-14 inches already here and there.

Whenever it's deemed to tall, i'll hangar offsite... but eveyone loves having their plane at home when possible

~B

Not to be a big downer on all the snapper mowers that posted before. New regs and AC covering prop strikes, mowing grass is now considered a prop strike!

As I have said before, we thought the Feds where being a bit over the top on the new prop strike/teardown criterion. However, since we tear down 20-30 prop strike engines a year, it is real. We are seeing subtle damage to what not have been considered a strike a few years back. Mainly damage to magneto drives and oil pumps. There will be deformation on these items from the strike, not a lot but enough to warrant replacement.

How much damage are you willing to accept to your oil pump drive gears?

Here's some tall grass...



Low and slow flyby's are key. Walking it is even more important. Dont think I would ever land in tall grass that I am uncertain about. Way to many things can be hidden. Just does not make sense.

AKT

45x2100 down the middle of my hayfield =2.16 acres ave 5 1/2 ton per acre @90/ton = $1069.20 or $50.90 per hundred feet.

For you a 300' runway would be $152.71 now what part on and airplane can you buy for $152.71

There can also be mud or very soft ground under all that nice tall grass, soft enough to put you on your back

It's like pulling 'grass' around here:) Mowing is not an option (long story), so lets skip that part of the conversation
and assume there's no mud and no obstacles and you know how high the grass is cause YOU walked it....

.....is 1/2 tire hight where most people get uncomfortable? 2/3 height? full height? If I was to take a poll, where
would YOU get uncomfortable? (using the tire as a gauge gives a lil room for comparison across tire sizes which
I assume, has the biggest effect (lets just assume taildgraggers and a reasonably well balanced aircraft front to back over
the CG). We'll also assume that I'll stop long before it's risky so all the risk/reward conversation isn't necessary, I
like my plane in one piece.

100% guaranteed to be smooth and have walked it. Let the grass grow over the wings then. Its grass. Not trees.

This is exactly like asking how deep of snow you can land on wheels. It depends, and the only sure way to find out is to to try it! You'll know when it's too tall

I don't mow my runway until I get noticeable drag on takeoff, then I wait a little more, and then when the runway is getting real short I wait a bit more, and then when I'm using pretty much all the runway to launch I mow it. Good practice and experience for other sites, plus saves needless mowing.

Just last week I was scouting out a new site, and had been 360'ing over it for 5 minutes and was ready to commit, and then I saw them: land mines, ground sharks, big ass rocks, hiding in the grass (about 12" to 15" tall), maybe the bushwheels could have handled them but I went further up the ridge and landed, then walked down to eyeball the first site, pretty ugly. I'm always amazed around here how the geology works as per where the rocks are and why, the inconsistancy is the attention getter, real good here, horrible right over there, all in the same general area, tall grass adds to the suspense for sure.

Depends on the grass... This year we have what I have been told is vetch (sp) in hay fields in the mid west that are usually just grass. This stuff has a purple flower and a deep green plant color so it is pretty but what that hides is the viney nature of the plant...beware the Navy could use this stuff for arresting gear.

Oh and if landing in Alfalfa make sure you have good length if you're landing before the dew burns off' talk about slick!

I just got back from a two week trip, and the runway was mowed about 3-4 days before I left.

But .... three weeks before that, I had my crop farmer make a past with his fertilizer buggy down the runway and we had 5 inches of rain while I was gone.

My scout is REAL HEAVY on the tail and it was packed to the max. I came in with two of us and my 31's and was surprised to have the tail come up. The grass was up to my knees and it was thick.

I made a landing last summer at Whitefish, MT, after checking with the State Aeronautics people about the condition of the runway. Their report was "it was mowed last week and dry."

The grass looked a bit tall when I overflew it, but managable. Well, it was real wet and I made the shortest landing in 40+ yrs of flying. Oh did I forget to mention that it took 2200 rpm to keep moving.

I finally got to parking. Tried to take off a couple of days later and it seemed like the runway was made of suction cups. I couldn't get enough speed to rotate.

A call to the Aeronautics people (very helpful BTW) brought a crew to mow the rwy. The equipment got stuck and they had to bring more equip in to pull the mower off the rwy. Then the X's went up.

So we got to drive the the Ryan Fly-in. Talk about getting the rasberries at Ryan Field.

The state called me and let me know the field was in better shape and that they had some gravel ready to dump on the rwy if I couldnt get airborne. I didn't need the gravel and all worked out okay.

Wet grass is very slick and the mud was a big issue in my case. As always, don't do it if you are not 100% confident that things are okay.

Rich

Maybe I'm a bit picky on terms here but being in ranch/pasture country, grass is always a stem with narrow leaves on opposing sides. Very little to tangle you up and except for hiding objects, grasses usually only make for a little more drag until it gets in the prop.
On the other hand, broadleaf flowering plants that branch like alfalfa, sweet clover and vetches and just common weeds are not grasses. The difference in their greenery is easily spotted from the air with a low pass and as stated earlier avoid these like the plague. They can and will wrap around the axle or gear and pull you in. Flipping over is a real possibility in flowering broadleaves.
My rule is if it brings you flowers, it's not because it likes you.

Here is some video of an A185F clawing its way out of long grass at "Jumboland" airstrip (Makarora, New Zealand). Some nice footage of a Super Cub too.

After he gets airborne you can see the plane being held down while he drags it out of the long grass.
http://www.youtube.com/watch?v=3mX862_h7n8

That long river grass can easily grow seed heads over a foot tall, before the strip gets mown later in summer to keep it usable.