Soft field take-off

[Admin]

Soft field take-off

 

Soft field procedures may be applicable to muddy, waterlogged or long/wet grass surfaces. The prime aim in a soft field take-off is to reduce the extremely long ground roll, and become airborne with less than adequate initial airspeed safety margin while utilising ground effect for fast acceleration. The following procedure should not be used in turbulent or gusty conditions, as the possibility of a stall after lift-off is increased.

 

In very soft conditions the usual technique is always to keep rolling; i.e. do not taxi to the take-off position and then stop to do the take-off checks — they should be completed beforehand. When lined up, open the throttle fully and smoothly while holding the control column back. Using a maximum lift flap setting is usually highly recommended. As the elevators become effective, the nose of a nosewheel aircraft will rise. With a taildragger, the elevator pressure should be relaxed sufficiently so that the tailwheel is held off the surface but the aircraft remains firmly in a tail-down attitude. As ground speed builds, start relaxing the back pressure and the aircraft will lift itself (or more likely lurch and stagger) from the surface at its minimum unstick speed [Vmu] and at an aoa very close to the stalling aoa — so, it is vulnerable to turbulence and mishandling. Also, P-factor and slipstream effect may come into play at this time, so it is important to keep the wings level with aileron and stop any turn with opposite rudder to negate any cross-controlled skid.

 

The pilot must then smoothly reduce aoa to 5–6° and hold the aircraft just above the surface in ground effect, so that it accelerates at the maximum possible rate. Gyroscopic effect may be significant during the pitch down to the smaller aoa, which must be anticipated with rudder. The aircraft is rotated after Vy (or Vx if there are obstructions) is attained to break it out of ground effect, held for a few moments to ensure it will accelerate, and then climb-out is commenced. At the initial rotation. the aircraft will slow as induced drag increases substantially and rapidly; firstly because of the restoration of the normal induced drag as it pulls out of ground effect, and secondly because of the increased aoa. The aircraft is likely to sink back to the surface if rotation occurs before sufficient speed is built.

 

The TODR for a soft field take-off will be considerably longer than that for a normal take-off. It is most unwise to attempt take-off from an airfield that is both short and soft.

 

The following is an extract from an RA-Aus incident report:

 

The pilot intended to conduct a trial instructional flight from a grass strip in excess of 250 metres in length. Due to recent rain the strip was soft and several solo take-offs had been carried out, each clearing the fence at the end of the strip by 25–30 m.

 

 

 

After some test runs with the passenger on board the pilot's 'gut feeling' was to abandon the exercise but he elected to take-off using a short field technique. The aircraft accelerated until the nosewheel lifted off the ground and then slowed, with the nosewheel sinking back onto the ground. Because he still had what he believed to be sufficient speed in hand the pilot tried to make it over the fence — and didn't. The damage to occupants was minor but the aircraft was a write-off.

 

 

 

The pilot identified the cause of the accident as lack of experience in operations from wet fields. In his words the aircraft was 'basically stuck to the field'

 

From the Recreational Flying John Brandon's Tutorials

 

 

[rdarby]

Very much so! But the intention of the article is to describe the procedure, not to be a self help manual, I am sure. It also gives people something to go and ask their instructor about.

 

But it's important to do this with an instructor first. Getting the nose up like that and sort of hovering for a bit feels very different, and it's easy to form bad habits by not lowering the nose a bit to pick up speed in ground effect before you climb. I tried to shoot straight up and dropped about a foot before it luckily picked up flying speed. I was lucky!

 

Thanks for posting Ian. Do you have one for short field landings?

 

 

[poteroo]

A lot of other points to consider with soft surface ops. Lighten the load, reload so less weight on nosewheel, how much flap?, rolling start v's standing start, should you lower tyre pressures, and more. Need to also consider why you'd land on a place which is likely to be soft - brings in what to look for, what questions to ask of the owner.

 

happy days,

 

 

[AM397]

As I'm not a pilot yet, and have no intention of being my own teacher with no guidance, I still like this sort of articles. It helps understanding things, so that when it is demonstrated to me, I will know what he's talking about. So, in other words, I think it should go without saying that these sorts of things aren't self-help articles, but articles to help one understand.

 

The ONUS question asked a few hours ago gave me something to look up and consider as well. I guess I like learning stuff, regardless of how I explore a given topic.

 

 

[facthunter]

Unless I want to be deliberately picky I feel that the subject is covered well in the article. Tail heavy helps as the tailfeathers are helping to carry the load but this is a minor factor. With this type of operation you have to be ready to abort the take-off if the performance is not adequate. Experience ia necessary. Nev

 

 

[Ballpoint 246niner]

Very much so! But the intention of the article is to describe the procedure, not to be a self help manual, I am sure. It also gives people something to go and ask their instructor about.But it's important to do this with an instructor first. Getting the nose up like that and sort of hovering for a bit feels very different, and it's easy to form bad habits by not lowering the nose a bit to pick up speed in ground effect before you climb. I tried to shoot straight up and dropped about a foot before it luckily picked up flying speed. I was lucky!

 

Thanks for posting Ian. Do you have one for short field landings?

Hi Ryan, I'll cover both these techniques with you on Friday OK?

 

 

[rdarby]

Yes please.