Soft-Field Landing and the Flight Test Guide

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photofly
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Re: Soft-Field Landing and the Flight Test Guide

#26 Post by photofly » Tue Aug 22, 2017 8:03 pm

CpnCrunch wrote: Perhaps it should be. Anyway, I'm more interested in having a good technique for actual soft-field landings on beaches and grass strips rather than just trying to do the minimum necessary to pass the flight test.
I'm happy to leave the technique "for real" to your and others' discretion, although on very many landings on unprepared surfaces I've personally never felt the need to land with the power on to touch down softly; but in the context of the thread title "Re: Soft-Field Landing and the Flight Test Guide" I'm happy to answer the question that was specifically asked. If you can't even achieve the minimum required to complete the exercise, you're not going to get the opportunity to land on beaches and grass strips!
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Re: Soft-Field Landing and the Flight Test Guide

#27 Post by digits_ » Tue Aug 22, 2017 8:13 pm

All it means is: don't let the nosewheel slam down on the ground after landing. But that's something you shouldn't do on any surface really. You always try to lower it gently. You just try to be extra gently on "soft runways".

Don't worry about the main wheels, if they dig in, it's going to be too late anyway and you shouldn't have been landing there in the first place.

A lot of that grass stuff is taking on mythical proportions. A lot of people learn to fly on short grass runways, in all kinds of weather. It's really not that big of a deal. While a "soft field" technique is required for the flight test, and it will decrease the maintenance costs on the airplane, it is not *that* critical. Soft grass just makes the consequences of incorrect landing techniques a bit worse: eg landing on the nose wheel, bouncing, porpoising, ... but those are things you shouldn't do on any runway.

If you are planning on moving on to bigger planes: it gets more and more important to not let the nose wheel slam down as the mains touch. For example navajos and metros are especially sensitive to that, 2 types the Canadian CPL might encounter in the beginning of their career.
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Re: Soft-Field Landing and the Flight Test Guide

#28 Post by photofly » Tue Aug 22, 2017 8:16 pm

digits_ wrote:All it means is: don't let the nosewheel slam down on the ground after landing. But that's something you shouldn't do on any surface really. You always try to lower it gently. You just try to be extra gently on "soft runways".

Don't worry about the main wheels, if they dig in, it's going to be too late anyway and you shouldn't have been landing there in the first place.

A lot of that grass stuff is taking on mythical proportions. A lot of people learn to fly on short grass runways, in all kinds of weather. It's really not that big of a deal. While a "soft field" technique is required for the flight test, and it will decrease the maintenance costs on the airplane, it is not *that* critical. Soft grass just makes the consequences of incorrect landing techniques a bit worse: eg landing on the nose wheel, bouncing, porpoising, ... but those are things you shouldn't do on any runway.
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Re: Soft-Field Landing and the Flight Test Guide

#29 Post by CpnCrunch » Tue Aug 22, 2017 8:27 pm

Agreed that the most important thing is to keep the nosewheel off. Still, if you're landing on sand or something that could actually be soft, I think it's probably a good idea to put the main wheels down gently too. Here's one example I found:
According to the accident report, a pilot was performing takeoffs and landings on a river sandbar without incident until the last landing. At this point, a main landing gear wheel separated after an attachment weld sheared and according to witnesses, the wheel rolled towards them and then into the river.
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Re: Soft-Field Landing and the Flight Test Guide

#30 Post by trey kule » Tue Aug 22, 2017 8:42 pm

In reading the whole thread, I have to ask why so many posts equate grass with soft fields.
I have landed literally hundreds of times on grass that was not soft at all.

Wet and soggy grass, yes, but using a special techique just because youbare landing on grass is a bit unjustified....my opinion.
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Re: Soft-Field Landing and the Flight Test Guide

#31 Post by PilotDAR » Wed Aug 23, 2017 7:50 am

I equate "soft" as to mean "not known to be firm, approach with caution". Maybe after great soft field technique, you find the surface great - nice surprise! In the mean time, the techniques of soft field landing and takeoff can be extended beyond what the flight test guide says, and flight manual recommended practices. Aircraft are routinely landed on wheels on unusual surfaces, after training and practice - "soft" techniques are often a part of that.

A part of the soft technique is a touchdown from which a go around would still be possible if the surface were too soft. Landing skis into unbroken snow would be an example of this. With correct soft technique (and yes, carrying power) you judge the softness of the surface, before you commit to stopping from the landing, lest you might not be able to take off again.
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Re: Soft-Field Landing and the Flight Test Guide

#32 Post by crazyaviator » Wed Aug 23, 2017 8:59 am

A rookie mistake I made once was to land on the edge of a sand island in the Mackenzie river ( I was previously landing on the edge of the beaches in Tofino ) Well, this was the exact wrong thing to do ( needed to land in the centre away from the water ) I went down quickly after stopping and had to lift the entire A/C out of the quicksand with driftwood poles , then build a trail to the ctr of the island. My biggest mistake, not doing a touch and go, then over flying to check the tire impression depth !
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Re: Soft-Field Landing and the Flight Test Guide

#33 Post by pelmet » Thu Aug 24, 2017 9:02 pm

trey kule wrote:In reading the whole thread, I have to ask why so many posts equate grass with soft fields.
I have landed literally hundreds of times on grass that was not soft at all.

Wet and soggy grass, yes, but using a special techique just because youbare landing on grass is a bit unjustified....my opinion.
I sincerely hope that this advice is ignored and strongly recommend that whenever landing on grass, that a soft field technique of minimizing downward force on the nosegear be utilized. There are many reasons for this. The "wet and soggy' grass/ground situation could be one reason to prevent the nosegear from digging in. I have seen an example of this once many years ago where a pilot flying a skydive C182 decided to taxi over somewhat softer ground at a fairly fast rate in the idea that he would pass over this area quickly and therefore lessen the risk. The prop left a nice arc in the ground.

But what about on a surface that is not wet and soggy and is in fact dry and firm. How do you know that there is not a groundhog hole or a not uncommon indentation in the ground. The grass may have been wet and soggy in the past when an aircraft or vehicle passed over it leaving wheel tracks at an angle to the runway that will knock your nosegear right off. By keeping the nosegear in the air during the takeoff or landing roll(or lightening it), you may end up having that unseen danger pass underneath with no damage. Even if relatively smooth, many suitable grass strip are still causing stress on the nosegear that is easily avoided. I recommend that even while taxiing on a surface that is not paved in a light tricycle gear aircraft to keep the elevator fully aft.
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Re: Soft-Field Landing and the Flight Test Guide

#34 Post by photofly » Thu Aug 24, 2017 9:13 pm

I keep the elevator fully aft on paved surfaces, too.
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Re: Soft-Field Landing and the Flight Test Guide

#35 Post by trey kule » Thu Aug 24, 2017 10:27 pm

Sort of plus 1, but there are GA aircraft where the up elevator does nothing at normal taxi speeds.
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Re: Soft-Field Landing and the Flight Test Guide

#36 Post by PilotDAR » Fri Aug 25, 2017 5:00 am

but there are GA aircraft where the up elevator does nothing at normal taxi speeds.
Yeah.... but for the vast majority which are not T tailed, use nose up elevator as much as possible during ground maneuvering, it costs nothing, and could result in damage prevention.
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Re: Soft-Field Landing and the Flight Test Guide

#37 Post by JasonE » Fri Aug 25, 2017 7:13 am

Cherokee requires a touch of power to hold the nose wheel off. Once the mains touch, the nose goes into "auto land" mode and drops.
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Re: Soft-Field Landing and the Flight Test Guide

#38 Post by pelmet » Fri Aug 25, 2017 7:48 am

I have had the same problem with the PA-28. The nosewheel just cannot be held off after touchdown the way it can be done on a Cessna. I am not sure for the reason why. And this is not a t-tail aircraft so there must be another reason.
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Re: Soft-Field Landing and the Flight Test Guide

#39 Post by PilotDAR » Fri Aug 25, 2017 6:50 pm

so there must be another reason.
Consider the following: Excepting the Cessna 177 Cardinal series, all of the others have a combination of stabilizer and elevator, compared to the PA-28 series, which like the Cardinals, have stabilators. When you pull all the way back on the elevator of a Cessna, not only do you get the effect of the deflection of the elevator, but the H tail as a whole is made more effective at lifting (down) because its camber is also increased - it became a thicker airfoil = more lift. Whereas, the more simple stabilator has no camber change, simply angle of attack/incidence (depending upon how you see that). It's ability to create lift (down) based upon deflection is limited - AoA yes, camber no. I have in past times experimented with a Cherokee 180, and got it stuck in ground effect. I did this on a very large stretch of ice on Lake Simcoe, so landing back was low risk. After a scare right seat in an Arrow, I formulated this concern. Indeed, I was just able to stall the stabilator, producing so much drag, that the plane could barely power its way out to accelerate after takeoff. But lowering the nose to relieve this drag put you back on the surface - okay if there's a good surface under you, but if you've struggled off the end of the runway in this difficult situation - trouble. In the afore mentioned Arrow, it was my daring to retract the gear that made the difference, and we struggled away.

The very early Cardinals did not have the slot in the stabilator, which is now common to all, and I understand were "challenged". I believe that they were retrofitted by Cessna after some problems. The slot delays the stall of the fully deflected stabilator, so, I presume, provides the required pitch control. Any Cardinal I've flown has been fine.

So, yes, PA-28 series will be less good at carrying the nosewheel light, but it's still worth the attempt!
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Re: Soft-Field Landing and the Flight Test Guide

#40 Post by photofly » Fri Aug 25, 2017 7:10 pm

That's a very interesting distinction, but I don't believe your analysis makes sense.
it became a thicker airfoil = more lift.
First of all a thicker airfoil doesn't generate any more lift than a thin one. Airfoil thickness doesn't appear anywhere in the lift equation. But in any case, the thickness isn't changed by moving the elevator anyway. (Which is so obvious it leads me to believe you just picked the wrong word to describe what you mean, so - never mind, let's move on.)

Deflecting the elevator does change the camber of the stabilizer-elevator assembly, but lift doesn't depend at all on camber per se. A Pitts wing is symmetric and has no camber at all, but still generates plenty of lift.

However deflecting the elevator also changes the AoA by moving the trailing edge, and it is that which changes the lift.

The extra curvature also changes the critical angle of attack - a stabilizer-elevator surface with a more deflected elevator can be flown at a higher AoA without stalling than one with a less deflected elevator. Which is just as well, as the act of deflection per we increases the AoA.
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Re: Soft-Field Landing and the Flight Test Guide

#41 Post by JasonE » Sat Aug 26, 2017 3:25 pm

I've personally experienced the stalling of the stabilator on PA-28. It was early in my flight training, and didn't quite understand back then what happened! I did end up back on the runway.....with a successful take off a bit further down. I've since played with full deflection to get a better feel for what was going on.
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