landing on grass?

[Crumpp]

What happens to your required landing distance on grass?

 

You are absolutely right. It is the rolling friction which what we used for distance calculations. It is still a coefficient of friction and my post was not incorrect. Taildraggers love grass because of the increased coefficient of friction.

 

Let's ask the question, "What happens to your take off distance on a grass strip?"

 

It goes up!

 

Why? The coefficient of friction is greater on dry grass than pavement.

 

Grass, snow or soft grounds increase the rolling friction and ground runs will take longer than on paved runways. Dry grass can increase take-off runs by some 20%. Long wet grass can increase this number again depending on the length of the grass and how wet it is. Aircraft wheel size and the type of aircraft can play a role too.

 

http://www.experimentalaircraft.info/flight-planning/aircraft-performance-9.php

 

 

 

 

file:///C:/Users/Owner/Downloads/Takeoff_Landing.pdf

Edited February 16, 2015 by Crumpp

[Crumpp]

You can see from the breaking action that you are also correct, btw. The difference is once the tire is rolling.

[effte]

Let's ask the question, "What happens to your take off distance on a grass strip?"

 

It goes up!

 

Why? The coefficient of friction is greater on dry grass than pavement.

 

...

 

 

No, the friction is not greater on dry grass than on pavement. The rolling resistance is. The term "rolling friction" does not refer to friction at all and those using it should be dipped in broccoli and fed to the hamsters.

 

Rolling resistance is the opposing force when a tyre rolls over the surface. Friction is the mechanism at work when you try to brake or push the tyre sideways.

 

Know what? I like your contributions in this forum, so rather than continue to argue the point, I'll humbly suggest you have look at the above, consider the wording, have a cup of coffee and, if it still isn't clear, ask someone around you whom's judgement and knowledge you trust. It will be less painful that way. Deal?

 

Summary:

 

Rolling resistance increases - Takeoff distance goes up, no effect on taildragger handling.

Friction decreases - Landing distance goes up, more forgiving taildragger handling.

[Crumpp]

I like your contributions in this forum, so rather than continue to argue the point, I'll humbly suggest you have look at the above, consider the wording,

 

I enjoy your post's. I find them well informed and well thought out. Often more so than some of mine!! :(

 

I understand exactly what you are saying and I think we are looking at two sides of the same coin.

 

As you said...hung up on wording.

 

Rolling resistance is the opposing force when a tyre rolls over the surface.

 

Absolutely! As the Mechanical Engineering text you reference, it is the ratio of tipping force to weight.

 

I was just taught it manifest's as a reduction in the static coefficient of friction.

 

Like the hyperphysics site explains:

 

Assuming that a wheel is rolling without slipping, the surface friction does no work against the motion of the wheel and no energy is lost at that point. However, there is some loss of energy and some deceleration from friction for any real wheel, and this is sometimes referred to as rolling friction. It is partly friction at the axle and can be partly due to flexing of the wheel which will dissipate some energy. Figures of 0.02 to 0.06 have been reported as effective coefficients of rolling friction for automobile tires, compared to about 0.8 for the maximum static friction coefficient between the tire and the road.

 

http://hyperphysics.phy-astr.gsu.edu/hbase/frict2.html

 

Like I said, that is how it was handled working aircraft performance problems.

 

For example:

 

Find Average Rolling Friction (lb) on Nose Tire during Landing Rollout if Rolling Coefficient of Friction = 0.2

N=25% of weight on Nose tire = (.25)(15,000)=3750 lb

fr = = .2(3750) = 750lb

 

If that is a mysnomer, then I was misinformed!!

 

:thumbup:

[sobek]

Not only does the wheel deform on grass, but the ground will too, increasing the friction losses. This will however cause a force primarily opposed to the direction of movement and not correlating with the tire orientation relative to motion.

 

Sideway force does not increase on grass.

[Crumpp]

Sobek says:

Sideway force does not increase on grass.

 

You are absolutely correct.

 

Just to be clear, I do not think anybody said that sideways force increases.

 

Grass is kind of tough to nail down because it effects change with moisture and grass length. If one "picked a side" as is typical in a less mature bulletin board crowd, one could fill it with "evidence" their point of view is correct. The otherside could do the same. Everyone would be a loser in that situation and our grass fields would simply be extremes instead of accurate.

 

When it is wet and slick it is exactly like Effte describes:

 

Effte says:

It's not increased friction which makes it easier to control conventional gear aircraft (taildraggers) on grass, but rather decreased friction. The lower (and quite different) friction allows a higher tyre slip angle (that's the sideways movement over a ground exhibited by any tyre which provides a force perpendicular to the direction in which it is rolling) for a given lateral force, which means you can get it more sideways before coming to grief. This translates into larger margins for error and much more forgiving ground handling.

 

The science behind a grass field does not make groundlooping an impossibility, it will just give you a better chance of preventing any swing from developing into a ground loop.

 

:)

[BitMaster]

These aircraft should handle landing on a grass field just fine.

 

However, a grass field (as in grass strip) is not just any plain old field you happen to find.

 

Land in an arbitrary field, and it is likely to end up in disaster. They will be too bumpy, causing you to get airborne again with too little airspeed. They will be too soft, causing the landing gear to dig in and the aircraft to nose over. The grass will not be maintained to the required standard, again likely causing too much drag and possibly a nose-over - and definitely problems taking off again, or perhaps even to get the aircraft rolling from a standstill. Piles of grass in front of the main tyres are rather effective shocks. Never brake to a stop on a grass field, especially if the grass hasn't been cut in the last few days...

 

 

It's not increased friction which makes it easier to control conventional gear aircraft (taildraggers) on grass, but rather decreased friction. The lower (and quite different) friction allows a higher tyre slip angle (that's the sideways movement over a ground exhibited by any tyre which provides a force perpendicular to the direction in which it is rolling) for a given lateral force, which means you can get it more sideways before coming to grief. This translates into larger margins for error and much more forgiving ground handling.

 

Cheers,

/Fred

 

Great Post +1

[SlipBall]

Still I think practicing landings on arbitrary field's is important training for the later use of in game play once we get a map. A designated grass field may not be close enough to you, when/if you find yourself in trouble. Just like in real life these arbitrary fields may be your only real option. Especially if forced to land on one in game and you are able to walk away from it(the wreck):P and, without being charged as a death, or as a prisoner of war if you choose the spot well...a lot of the fields in game can be landed on and then take off again with some practice

Edited February 17, 2015 by GT 5.0

[TAGERT]

I find them well informed Often more so than some of mine!! :(

Dear Diary

 

Today I fell off my chair.. End of story

[9.JG27 DavidRed]

Sideway force does not increase on grass.

 

 

but it does in dcs.

[mugen]

now trust me i'm no expert on this but i've seen a ton of footage from WWII where the aircraft would be taking off from fields rather than concrete runways, however in dcs it's pretty clear that trying to takeoff or land on any grassy area is pretty much suicide :cry: i think it would be really cool if we got some sort of grassy airfield for the WWII modules, especially with the VEAO and dcs spits coming 'round the corner, it just seems more fitting than having your home base be a modern airport :P

 

Hi pepto,

 

i did a little mission for grass strip handling.

You might want to take a look at it. Makes practicing a bit easier. :joystick:

 

 

 

http://forums.eagle.ru/showpost.php?p=2258921&postcount=122

 

greez mugen

Edited February 19, 2015 by mugen
link added

[Anatoli-Kagari9]

Great!

 

Thx!

[pepto]

many thanks mugen!

[Crumpp]

Thanks Mugen!

 

Does it work with the P51 and Dora?

[mugen]

Yes it works with all prop planes. P51 is the easiest, then the fw190. 109 is the hardest to manage (IMO).

Try to start, go around and land with all planes in one take 3 times. Quite a challenge to manage the different fm/gm in a row. I tried to record a track in one take with all planes. Still trying ...

[msalama]

:thumbup:

 

And now if someone came up with a texture of some kind for the "grass RWY" we'd get a 2 runway AF with the grass and the concrete RWYs side by side! Would do it myself but can't...

[Echo38]

also the fact that heavier aircraft like the A10 cant move at all anymore once they find themselves in the fields hints that it just didnt get too much attention by the devs yet....

 

Here's a video of what happens when an F-16 tries to taxi on short grass:

 

Granted, he was going pretty fast, hence the nosewheel collapse, but the problem of the nosewheel digging into the ground happens at any speed, hence the heavy jet fighters being unable to move on dirt. (Russian jets tend to have beefier nosewheels, as they were designed to have greater capability in this regard, but U.S. jet fighters were designed for concrete/metal runways only.)

 

As someone else pointed out, with WWII fighters, they're much lighter (and have a much better [tire area]/weight ratio) than an F-16, and so they can land on short grass or wet sand, but even these will flip over when trying to land in tall grass, which is why RL training sources for fighters such as the P-51 and Me 109 instructed pilots to land wheels-up if they had to land in tall grass or water.

[SlipBall]

so then will Edge have different vegetation lengths, or would that even matter?

[SlipBall]

The death wobble

 

contained..:P with some damage

 

Edited February 24, 2015 by GT 5.0

[Crumpp]

so then will Edge have different vegetation lengths, or would that even matter?

 

The grass length, like the moisture content has a huge effect on the coefficient of friction for grass airstrips.

 

The general rule of thumb is if the grass is more than 1/3 the height of the tire, the field is unusable. The taller the grass, the greater the friction.

[SlipBall]

So I guess we don't know anything about Edge grass yet, we know so little about Edge and the new map...I want to do one of these though, thats one tough prop! :D

 

[/url][/img]

[Crumpp]

I don't anything about edge grass effects.

 

thats one tough prop!

 

That'll buff right out. You see the pilot waiting for the ground crew to start buffing.

[MiloMorai]

The grass length, like the moisture content has a huge effect on the coefficient of friction for grass airstrips.

 

The general rule of thumb is if the grass is more than 1/3 the height of the tire, the field is unusable. The taller the grass, the greater the friction.

That is obvious to anyone who has walked on short wet grass and in long wet grass.

[SlipBall]

I don't think that we will be seeing the long grass or the crops in Edge. We see them in Clod, but they are not modeled for drag