Can you have soft stand up landing on rears??

[hillson 0]

Quote

Coming in straight in? at full flight.

Not talking about big turns to gain speed/lift here.
and
Who was dumb enough to try this and tell me your story.

Yup. Saw a buddy with a broken steering line do it so I figured I should learn more. Lots of talk with the instructors, several jumps using nothing but rears until final (did a standard control check obviously...) and then a dedicated H&P at a time with sufficient wind. Granted I was controlling as many factors a I could in my favor (planning etc)...plan on doing it again in a few weeks now that I'm on a smaller Pulse.

Proper planning, coaching and instruction...

[Ron 10]

Quote

Could someone that has a clue explain the aerodynamics of the sudden stall when using the rears? Is it the difference in the rate of change of the critical angle that causes it?

Not a physics professor, but I'll give this a shot. We know a wing stalls when the angle of attack exceeds the critical angle and that is when the boundary layer separates from the rear portion of the wing and drag becomes greater than the lift.

My guess as to why it is more pronounced when using rear risers has to do with how much the angle of attack is changed between the two control inputs. Someone already touched on this when they stated that "because of the difference in how the canopy is distorted by the different control input".

You see, the toggles are attached to the very back of the canopy and when you pull them down you only really pull the rear of the canopy down... In some ways making the wing distort more almost acting like a flap and reducing stall speed due to the increase in airfoil.

But when you use rear risers you are changing the angle of attack at a much more drastic rate without any benefit of a change in airfoil.

So with rears you need less input to get more angle of attack change.

The RATE of change should not matter much in this case. A dynamic stall can occur if you quickly change the angle of attack but I don't think that is the case with rear riser stalls here. There are high speed stalls and accelerated stalls... But these are the result of increased "G" forces basically increasing the wingloading and thereby reducing the angle of attack that the wing will stall at.

I think our rear riser canopy stalls are more a factor of reaching the critical angle of attack with less room for error, and with no "flap" effect that the toggles give you.

Of course... Like I said, I am not a physics professor and I could be WAY wrong.

"No free man shall ever be debarred the use of arms." -- Thomas Jefferson, Thomas Jefferson Papers, 334

[DaVinciflies 0]

Quote

....explain the aerodynamics of the sudden stall when using the rears...

Ok - here's my attempt!

The stall occurs when there is flow separation from the top skin of the canopy causing chaotic, non-laminar flow and a loss of lift. This can be caused by giving the air flow too abrupt a change in direction to follow along the top skin (like trying to drive around a sharp corner too fast in a car).

In a rear riser stall, the pilot pulls down on all the C and D lines deflecting the back half of the canopy downwards. At a certain point the airflow over the top of the canopy can no longer follow this change in angle between the front and back halves of the canopy and flow separation occurs at the back half. The back half of the cells cease to fly and the stall occurs. This can occur quite abruptly right across the wing and you lose the lift from half your canopy.

In a toggle stall, the pilot only deflects the very back of the more outboard cells so when a stall occurs they stop flying while the center cells continue to create lift, hence the reason why the ends of the canopy deflect backwards.

[JackC1 0]

^^ that's about right.

Toggles are essentially an airbrake that distorts the outer rear section of the aerofoil, so when it stalls it tends to stall from the outer cells inwards and you get that progressive mushiness that turns into a bow tie before it collapses completely.

With a rear riser stall you are deflecting the entire rear half of the canopy which puts a step profile in the aerofoil. When the laminar flow breaks to create a stall, it does it over the entire width of the aerofoil at the same instant so the collapse is sudden and it folds up along the center span.

[DBCOOPER 5]

Thank you gentlemen. I have a better understanding of what happens now.

Replying to: Re: Stall On Jump Run Emergency Procedure? by billvon

If the plane is unrecoverable then exiting is a very very good idea.

[fcajump 164]

Quote

Coming in straight in? at full flight.

Not talking about big turns to gain speed/lift here.
and
Who was dumb enough to try this and tell me your story.

Yes. ~Jump #17, as trained, after brake line broke, performed control and flare checks at alt, chose to keep it. Only comment from the instructors was that I should have PLF'ed, though the stand-up was soft.

Soooo.... when jump #18 broke the OTHER brake line on the same student rig (rigger only changed the one), I forced myself to PLF... almost failed it and stood up anyway as the flare was so smooth.

NOTE: This was on a lightly loaded Strong? Goliath.

JW

Always remember that some clouds are harder than others...

[jacketsdb23 49]

Crossfire WL 1.8+: Yes it can be done. I used to land on rears regularly. Didn't need to, just liked to do it and I was good at it.

Velo 96 WL 2.2+: Yes it can be done. I did it regularly just for shits and grins. Then this one time at band camp, I got my RDS grommet stuck in my brake line and had to land on rears because my toggle didn't work. Worked like a charm. I even did a 90º harness turn to final, which was probably dumb.

Comp. Velo 2.5: yes it can be done. Have done it multiple times, but not regularly.

I think learning everything possible about your canopy flight (toggles, risers, harness, riser + toggle, etc.) is important.

Losers make excuses, Winners make it happen
God is Good
Beer is Great
Swoopers are crazy.

[CSpenceFLY 1]

Look up some info aerodynamics in relation to a private pilot rating. You can probably find some good diagrams.

Not directed at DB. I've said for a long time that many canopy related injuries result from no basic understanding of aerodynamics when related to the canopy. Most peoples understanding of canopy flight is I pull this to go left, I pull this to go right and I pull both when I get close to the ground.

[chuckakers 426]

Quote

Look up some info aerodynamics in relation to a private pilot rating. You can probably find some good diagrams.

Not directed at DB. I've said for a long time that many canopy related injuries result from no basic understanding of aerodynamics when related to the canopy. Most peoples understanding of canopy flight is I pull this to go left, I pull this to go right and I pull both when I get close to the ground.

+1

Spence, the jumpers you're talking about don't even understand how their gear works, let alone the science behind it.

Understanding is the foundation of safety. Too often that understanding is absent these days.

Chuck Akers
D-10855
Houston, TX

[DaVinciflies 0]

Quote

Quote

Look up some info aerodynamics in relation to a private pilot rating. You can probably find some good diagrams.

Not directed at DB. I've said for a long time that many canopy related injuries result from no basic understanding of aerodynamics when related to the canopy. Most peoples understanding of canopy flight is I pull this to go left, I pull this to go right and I pull both when I get close to the ground.

+1

Spence, the jumpers you're talking about don't even understand how their gear works, let alone the science behind it.

Understanding is the foundation of safety. Too often that understanding is absent these days.

I agree. The AFF syllabus is so light on this, it's a joke.

And we can't blame the jumpers because nobody tells them how little they know.

[normiss 854]

Sadly, you could not be more correct.

[beowulf 1]

I recognize that dropzone!!!

[theonlyski 8]

Quote

Could someone that has a clue explain the aerodynamics of the sudden stall when using the rears? Is it the difference in the rate of change of the critical angle that causes it?

Since I'm on a Bernoulli kick today (started by the Vigil fire thread) I figured I'd throw some here too.

Explanation:
http://www.youtube.com/watch?v=5wIq75_BzOQ

Video in action:
http://www.youtube.com/watch?v=WFcW5-1NP60&feature=related

I think my Sporty's DVD's have some good visuals on it too, but I don't really feel like ripping them and getting in trouble for posting them.

"I may be a dirty pirate hooker...but I'm not about to go stand on the corner." iluvtofly
DPH -7, TDS 578, Muff 5153, SCR 14890
I'm an asshole, and I approve this message

[speedy 0]

Landing a canopy on rears only is not to be taken lightly, especially for someone who has never done it before. A friend of mine broke his back stalling his canopy on rears and was lucky he was not paralyzed for life.
If you have your muscle memory well trained on flaring with the toggles you will probably find you are too aggressive with the rear input as you approach the ground. Stalling a canopy on rears at just 10ft from the ground can have serious consequences. With rears you have not bled off much of your forward speed which will lead to landing on you back (hint: A PLF does not work when your legs are in the air).
Having said that, I agree it is a useful skill to have, but not something to try out for fun. Get suitable training and practice up high first.

Dave

Fallschirmsport Marl

[theplummeter 15]

I don't think that aircraft and parachute aerodynamics translate perfectly, pulling toggles would be the equivalent of gradually adding flaps to land rather than using a separate airfoil to change the angle of attack of the main airfoil.

Landing on rears is more closely related to how an aircraft lands than toggle movements, although almost every airplane ever built uses mulitple airfoils to provide lift and control flights.

As far as what's happening to the wing however, stalls are the same in that the pilot has exceeded the angle of attack critical to lift production.

Bernoulli was full of it, even NASA is starting to admit that. For his theory to hold true air would have to be incompressible.


http://www.telegraph.co.uk/science/science-news/9035708/Cambridge-scientist-debunks-flying-myth.html

[DBCOOPER 5]

I'm well versed in the stall principles in aircraft. But a typical aircraft doesn't stall suddenly and completely like a canopy will on rears.

Replying to: Re: Stall On Jump Run Emergency Procedure? by billvon

If the plane is unrecoverable then exiting is a very very good idea.

[chuckakers 426]

Quote

Landing a canopy on rears only is not to be taken lightly, especially for someone who has never done it before. A friend of mine broke his back stalling his canopy on rears and was lucky he was not paralyzed for life.
If you have your muscle memory well trained on flaring with the toggles you will probably find you are too aggressive with the rear input as you approach the ground. Stalling a canopy on rears at just 10ft from the ground can have serious consequences. With rears you have not bled off much of your forward speed which will lead to landing on you back (hint: A PLF does not work when your legs are in the air).
Having said that, I agree it is a useful skill to have, but not something to try out for fun. Get suitable training and practice up high first.

What he said.

And again I ask - does it make sense to practice something that might hurt you just so you don't get hurt when you do it later?

Chuck Akers
D-10855
Houston, TX

[DaVinciflies 0]

Quote

And again I ask - does it make sense to practice something that might hurt you just so you don't get hurt when you do it later?

You mean like PLFs? Or skydiving?

It is perfectly possible to practice landing on rears without getting hurt.

Would you not agree that someone should fully explore the performance envelope of their canopy before downsizing? Landing on rears is part of that exploration, in my opinion.

[wolfriverjoe 1,523]

Quote

I'm well versed in the stall principles in aircraft. But a typical aircraft doesn't stall suddenly and completely like a canopy will on rears.

Can you please elaborate on this?

Most airplanes that I'm familiar with do stall suddenly and completely. There is a fair amount of warning before the stall occurrs - first the mushiness of slow flight, then the horn going off, then the buffeting. But when the plane stalls, it's usually a sharp "break" and you feel it "fall out of the sky."

Not all that different from riser stalls, it's more that you don't feel the mushiness or buffeting (and there isn't a stall horn).

And thanks to those who elaborated on the comparison between toggle input and flaps and the way that a toggle stall is progressive from the outside in. I forgot/didn't think of those.

"There are NO situations which do not call for a French Maid outfit." Lucky McSwervy

"~ya don't GET old by being weak & stupid!" - Airtwardo

[DaVinciflies 0]

Quote

Not all that different from riser stalls, it's more that you don't feel the mushiness or buffeting (and there isn't a stall horn).

Actually it is possible to detect (both visually and by feel) a degree of mushiness before a rear riser stall - but you have to have pretty fine control to hold it on that "edge" without allowing a full stall.

[rehmwa 2]

Quote

Bernoulli was full of it, even NASA is starting to admit that. For his theory to hold true air would have to be incompressible.

I'd sure enjoy a list of all those skydivers that fly at speeds where the assumption of incompressibility doesn't apply very well in practice

or even those that think that

...
Driving is a one dimensional activity - a monkey can do it - being proud of your driving abilities is like being proud of being able to put on pants

[theonlyski 8]

Quote

(and there isn't a stall horn).

Maybe not on YOUR canopy!

"I may be a dirty pirate hooker...but I'm not about to go stand on the corner." iluvtofly
DPH -7, TDS 578, Muff 5153, SCR 14890
I'm an asshole, and I approve this message

[DBCOOPER 5]

A typical certified GA airplane will stall from the wing root out to the wing tip. The buffeting you feel is the disrupted airflow from the part of the wing near the root that is stalled flowing over the rear stabilizer/ rudder. This is accomplished by the wing having a twist in it so the angle of attack varies along the wing. The root reaches the critical angle first and as you hold it there more of the wing stalls until it "breaks".

Replying to: Re: Stall On Jump Run Emergency Procedure? by billvon

If the plane is unrecoverable then exiting is a very very good idea.

[chuckakers 426]

Quote

Quote

And again I ask - does it make sense to practice something that might hurt you just so you don't get hurt when you do it later?

You mean like PLFs? Or skydiving?

Quote

No, I meant more like practicing getting out of the plane safely after your pilot chute goes out the door without you, practicing getting out of a canopy wrap seconds after deployment, or any number of things that we may have to actually do someday that we don't practice.

It is perfectly possible to practice landing on rears without getting hurt.

Quote

Of course it is. It's also possible to get hurt and completely unnecessary.

Would you not agree that someone should fully explore the performance envelope of their canopy before downsizing? Landing on rears is part of that exploration, in my opinion.

Quote

No I wouldn't. The vast majority of jumpers will NEVER fully explore the performance capabilities of any canopy they jump, nor should they unless by choice. What jumpers should do is become competent in the use of a canopy before downsizing, but more importantly they should understand that in most cases there is NO REASON TO DOWNSIZE.

The suggestion that a jumper isn't safe unless he/she is competent to fly their canopy like a bat outta hell (full performance envelope) is absurd.

Chuck Akers
D-10855
Houston, TX

• Quote

[jacketsdb23 49]

there is a difference between being safe, and having the full range of tools to work with when shit hits the fan.

Flying on and landing on rears is a skill that everyone should practice and feel comfortable with, by the time they have the skill set to receive a C license...IMHO (i'm not suggesting that you should have to do this for a C, i'm just saying that by the time you get a C, you should be pretty comfortable with all aspects of canopy flight)

Losers make excuses, Winners make it happen
God is Good
Beer is Great
Swoopers are crazy.