Cirrus descent rate under parachute less with wind?

[n5296s]

I really think that a flare to a safe landing from even 1300 fpm would be challenging

The Pitts I used to fly regularly comes down at about 2000 fpm power off, which is how I was taught to land it. Yes, it is. You have about a 0.25 second window to flare if you don't want either to hit the ground very hard, or flare too high, stall, and hit the ground very hard. The poor instructor, who has to give the student time to make mistakes, has maybe 0.1S to decide whether to intervene. My instructor, who had been a U2 pilot and knows a thing or two about planes which are difficult to land, says that of all the things in instructing, the one he hates the most is teaching people to land the Pitts. (The Extra 300, by contrast, is a complete pussycat, and not much harder to land than a Citabria).

One advantage of having done it is that it makes uatos seem pretty tame!

[Fl1ingfrog]

oggers, where does the increase in force come from? Surely your triangle of forces shows a decrease in the vertical impact and therefore must increase the horizontal force impact: i.e. the dry stone wall. Following the landing the drag from the surface will also form a part which will then absorb the energy further before eventually impacting with the wall, when all energy is then dissipated and comes to rest.

[cats_five]

Originally Posted by The Ancient Geek

In still air the parachute will be directly above the aircraft and both will go straight down.
In a wind the parachute will above and ahead of the aircraft and both will decend at an angle. There are 2 vectors, horizontal and vertical, the aircraft will take longer to reach the ground, simple trigonometry.

It will only take longer if the vertical vector decreases, which it doesn't

[oggers]

Originally Posted by Fl1ingfrog

oggers, where does the increase in force come from? Surely your triangle of forces shows a decrease in the vertical impact and therefore must increase the horizontal force impact: i.e. the dry stone wall. Following the landing the drag from the surface will also form a part which will then absorb the energy further before eventually impacting with the wall, when all energy is then dissipated and comes to rest.

Hi, it is a triangle of velocities not forces. The video states that the vertical speed would be reduced by drifiting in the wind - which it won't. That is what the diagram addresses, not impact forces per se. The important thing is that the vertical speed is not reduced by drifiting with the wind. It follows that the vertical acceleration experienced on hitting the ground is not reduced either.

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For anyone tempted to believe the proposition that the vertical speed of the aircraft/canopy can be reduced by drifting with the wind, simply ask yourself at what wind speed you think the whole contraption will begin to climb back up to altitude.

[Fl1ingfrog]

Originally Posted by oggers

... because wind drift is going to make the impact worse. QED

Megan I made my point because of your statement above. The speed over the ground is not really the issue,, but the force on arrival applied to terra firma is of utmost importance is you wish to survive in one piece. Megan has pointed out the forward speed assists with the landing.

To my knowledge the pilot has no control once the aircraft chute is deployed. This has always struck me as a problem. When gliding you do have control if not a lot of choices as to where you will land but you will have more than the aircraft chute offers.

[The Ancient Geek]

The chute is for use when the aircraft is uncontrollable, probably due to structural issues.
Some have been deployed when the pilot has managed to get into IMC, this should not have happened to begin with but the chute is a better option than losing control or flying into a hill.

[India Four Two]

The landing gear and the seats in the Cirrus are designed to dissipate some of the energy in a parachute landing

[Jim59]

"For anyone tempted to believe the proposition that the vertical speed of the aircraft/canopy can be reduced by drifting with the wind, simply ask yourself at what wind speed you think the whole contraption will begin to climb back up to altitude."

Your comment assumes a flat earth.

[RatherBeFlying]

Impact Angle

Horizontal velocity allows friction with the ground to dissipate kinetic energy at a gentler rate than happens with a completely vertical impact. Much depends on ground, vegetation and obstacle (rock, potholes, agricultural equipment, stone walls...) characteristics.

In the best case wheels contact an even firm surface with a vertical component that the airframe can tolerate.

[Maoraigh1]

"Horizontal velocity allows friction with the ground to dissipate kinetic energy at a gentler rate than happens with a completely vertical impact"
Friction with ground will dissipate kinetic energy parallel to the ground.
Kinetic energy perpendicular to the ground will be dissipated by deformation of the object and the ground. The latter will be over a very short time interval.

[Russell Gulch]

Pull the 'chute. Now the pilot has breathed a very heavy sigh of relief, so reducing weight. He has also shat his pants, so further reducing the all-up weight of the aircraft.

That's why they glide a longer distance. You may note I mentioned a male pilot. Now when a female pilot flies a Cirrus, there is no need for a parachute....the engine daren't fail.

[suninmyeyes]

[QUOTE=RatherBeFlying;10738439]Horizontal velocity allows friction with the ground to dissipate kinetic energy at a gentler rate than happens with a completely vertical impact.QUOTE]

Ok I agree that if a Cirrus is coming down under a parachute with a 20 knot wind it would reduce the impact force on the occupants if it could go along the ground in the same direction as the wind for a bit after impact rather than coming to an immediate stop.

However if it is coming down with no wind at the same vertical rate surely the force experienced on touchdown by the occupants in a vertical descent would be less because you have no additional sideways kinetic energy to dissipate?

[PDR1]

Originally Posted by Maoraigh1

"Horizontal velocity allows friction with the ground to dissipate kinetic energy at a gentler rate than happens with a completely vertical impact"
Friction with ground will dissipate kinetic energy parallel to the ground.
Kinetic energy perpendicular to the ground will be dissipated by deformation of the object and the ground. The latter will be over a very short time interval.

Energy is a scalar, not a vector - it has no direction. I believe you are confusing it with momentum.

PDR

[Runaway Gun]

Many of these comments scare me. Are you sure you all passed High School science?

[cats_five]

Originally Posted by Russell Gulch

Pull the 'chute. Now the pilot has breathed a very heavy sigh of relief, so reducing weight. He has also shat his pants, so further reducing the all-up weight of the aircraft.

Snip

Did he throw the pants out the window?

[PDR1]

Originally Posted by Runaway Gun

Many of these comments scare me. Are you sure you all passed High School science?

This thread is far from unique in that respect. This repeated inability to understand the difference between velocity, momentum and energy is disappointing.

PDR

[RatherBeFlying]

Originally Posted by Maoraigh1

"Horizontal velocity allows friction with the ground to dissipate kinetic energy at a gentler rate than happens with a completely vertical impact"
Friction with ground will dissipate kinetic energy parallel to the ground.
Kinetic energy perpendicular to the ground will be dissipated by deformation of the object and the ground. The latter will be over a very short time interval.

You may be surprised by how short a landing can be without damage. I once landed a glider on a sandy loam fallow field and was astonished by the sudden stop. Over some two fuselage lengths the gear dug a steadily deepening trench until the glider was sitting on the gear doors.

Admittedly, it cost me under $5 to replace a couple gear door hinges.

[Maoraigh1]

Apologies for imprecise words. What I'm try to say is that the impact force from descent into the ground will not be reduced by movement parallel to the ground as far as the descending aircraft is concerned.
​​​​​​Movement parallel to the ground will spread the force over a longer piece of ground. A shallower trench than the hole would be if no parachute.

[PaulisHome]

[QUOTE=suninmyeyes;10738675]

Originally Posted by RatherBeFlying

Horizontal velocity allows friction with the ground to dissipate kinetic energy at a gentler rate than happens with a completely vertical impact.QUOTE]

Ok I agree that if a Cirrus is coming down under a parachute with a 20 knot wind it would reduce the impact force on the occupants if it could go along the ground in the same direction as the wind for a bit after impact rather than coming to an immediate stop.

However if it is coming down with no wind at the same vertical rate surely the force experienced on touchdown by the occupants in a vertical descent would be less because you have no additional sideways kinetic energy to dissipate?

Your first statement is wrong, the second correct.

If there's a wind, we can take the view that there are two impact forces - a vertical one (same as if there was no wind) and a horizontal one where the plane needs to decelerate from the wind speed to rest relative to the ground.

So you don't reduce the impact force - you increase it. As you say in your second statement.

Paul

[Fl1ingfrog]

"So you don't reduce the impact force - you increase it. As you say in your second statement."

This is of course is true but how the impact is absorbed is important.

I attended a short course at Martin Baker many years ago. From memory they were giving a total ejection force of up to 15 G. Not many pilots survived ejection without serious injury to the spine during the early years of development. They had eventually discovered that it is not only the total G that is encountered (to a limit) but the rate it is sustained was crucial. They eventually incorporated a clockwork mechanism within the seat that, through series of stages, delayed the total G over approximately 2-3 seconds maybe less (I'm working from memory). This was from pulling the handle through to the chute being deployed. This very short period was sufficient to avoid serious injury.