Although grass landing strips are not that common, especially in the public sector, it is certainly worth giving them a try, especially as you never know when you might be obliged to land on one. The obvious thought is that because a grass surface is not as smooth as tarmac, your take off roll to get up to speed is going to take a while longer, and this would be true. On the other hand, one would suspect that landing on grass would have the similar effect of slowing down your ground roll much sooner, but this is not necessarily the case, and you will need more landing distance than you think. Let’s have a look why…
Firstly, it is important to note that grass runways can be very variable in condition, and if at all possible, it is a good idea to inspect the condition on the ground, get a report from someone based at the field, or at the very least, conduct a low level inspection of the field before attempting to land there. There are three factors that we need to consider:
The length – The longer the grass, the less traction it provides, which means that your tyres will have less contact with a stable surface in order to generate the friction required to bring the aircraft to a stop. Braking will definitely be less effective, and heavy braking can be damaging and dangerous. Generally, up to 20cm in length is acceptable, longer than this and your ground roll is going to be substantially increased.
The condition – Although a wet surface does provide some drag (most notably on take off), it definitely reduces the traction on landing. Trying to land a ‘greaser’ on a wet grass runway could be detrimental, as the longer it takes to get the weight on the wheels, the more likely you are to keep sliding along, as little friction is being generated. If puddles are visible, then avoid the landing altogether. Puddles can conceal holes of a depth that you may not know, and hitting one on landing could cause directional control problems, or even result in the nose wheel digging in, and an inevitable prop strike.
Soil type – Although this can be difficult to determine from the air, firm soil is really what you want for a grass runway, as it will be able to support the weight of the aircraft, and increase the friction required from the wheels . Soft, muddy soil can be particularly hazardous, and apart from increasing your landing distance, it can cause significant damage to your wheels and brakes.
So now that we have determined that landing on grass runways is going to increase your landing distance to varying degrees, what should you do?
- Be aware of your landing factors! The graphs in your aircraft manual are for landing distances as determined by a test pilot on dry, paved runways. For grass (up to 20cm with firm soil), multiply your landing distance by 1.15. If the grass is wet, or anticipated to be wet at your ETA then multiply by 1.15. Also take into account (as with a tar runway), the slope of the runway – while uphill is certainly helpful for reducing landing distance, a downhill could make matters worse, so factor another 5% for each 1% of down slope (check the runway slope in the AIP or appropriate airfield documentation). Lastly, for most single engine aeroplanes, or light twins, it is necessary to add 70% in order to obtain the landing distance required (by law), so multiply by 1.43
- Keep the nose wheel off the ground as long as possible, as the bumpiness of a grass runway can cause damage. Or if the surface is soft it can cause the nose wheel to dig in, and a possible prop strike.
- Spats – if the aircraft you are flying has these, be aware that these could be damaged when landing on grass, so either remove them beforehand, or be sure to check and clean them after landing.
- Keep a steady hand on the controls – Holding the controls nicely backwards will provide the best clearance for the prop, especially over bumpy ground.
- Lookout – It is always a good idea to inspect the runway, especially if it is unfamiliar. Overnight mole hills could have sprung up which could cause a loss of ground control or damage.
- Save your brakes – Do not attempt hard braking, rather use aerodynamic means of stopping as far as possible i.e full flap. If you need to use the brakes, then lightly press at short intervals.
So, why do taildragger pilots often prefer landing on grass? Not because it will slow them down quicker, but rather because grass is more forgiving when it comes to maintaining directional control in a taildragger, especially if your alignment is slightly off.
Grass landings can be fun, and a good thing to practice, giving you a different perspective, that will improve your skills. Give it a try!
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