Swooping perception?

[RichM 0]

I spent yesterday at Langar, UK on a stinking hot day with nil winds and found that my normal swoop initiation height was a shade too low and I'd be interested in understanding why. My normal DZ is Headcorn, UK.

This DZ is about the same altitude as my home DZ. The grass landing area though is in the centre of a triangular triple runway setup with large cornfields all around. There were powerful thermals from the runways.

I can think of 3 possibilities:

1) Perception. I judge initiation height by eyeball only so the slightly smaller landing area may have fooled my depth perception. I have virtually discarded this as I was definitely going much faster than normal at ground level and slotted a significantly longer surf than I normally do.

2) Thermal lift from the surrounding areas and runways may have made a large and steady downward airstream above and onto the landing area. I'm tending toward this one.

3) Density altitude giving a much thinner and dryer atmosphere. It was about 10C hotter on this day than is normal. Barometric pressure unknown I'm afraid. I kinda grasp the d.a. theory but don't understand how it affects canopy flight.

Any suggestions on why would be greatly appreciated as I found on my screaming swoop I had to just dab the brakes at about 10 feet to dig it out of the corner whereas I normally square the canopy with double fronts and ride them down for the last 5-10 feet.

But that was a damn fast and long swoop and I loved it apart from the dig :-D

Cheers, Rich

Rich M

[freeflir29 0]

If you are used to a more windy DZ I think this is pretty normal. I find that I hold my front riser longer on a windy day. My perception is that my canopy dives more on a no wind day. Tepmerature also plays a part. I had an experience in the spring where the temp had gone from about 50F one weekend to 80F the next. HUGE difference in recovery arc. I had to dig really hard!!! I think your on with all your observations. On hot no wind days everything happens a little faster and with more altitude loss.

[quade 4]

Quote

My perception is that my canopy dives more on a no wind day.

How would it know?

Unless there is significant wind-shear or turbulence, winds should play little if any role other than for speed and distance over ground. Your perceptions may be different, but the altitudes and rates of decent should not.

Density-altitude plays an important role.

quade -
The World's Most Boring Skydiver

[freeflir29 0]

Quote

My perception is that my canopy dives more on a no wind day.

OK....I'll put it in bold print......

[Samurai136 0]

Temp. measures the average speed of the surrounding molecules. As it gets hotter, the molecules of air are not as dense because they moving faster. So the canopy will fly like you are at a higher altitude where the air is thinner. That is to say, faster.

Additionally, as relative humidity increases molecules of air are being replaced with molecules of water. So the air becomes even less dense on a hot and humid day.

The lift off the runways probably changed your perception of your glide path as opposed to your theory of 'sinking air'. I'd think of it as 'floating canopy' retuning to it's standard glide path.


A Crossfire has a negative recovery arc so it will stay diving after you let the risers up. You should be able to avoid digging out of the corner if you let up on the risers a bit higher. let the canopy fly to the surf window instead of driving it there. If that makes any sense.





Ken

"Buttons aren't toys." - Trillian
Ken

[quade 4]

Clay --

Didn't mean to offend, I was just confirming the subject line of the thread.

quade -
The World's Most Boring Skydiver

[freeflir29 0]

Quote

Didn't mean to offend

If anyone is trying to offend me....they'll have to try much harder. None taken....

[VectorBoy 0]

Quote

Clay --

Didn't mean to offend, I was just confirming the subject line of the thread.

Hey Quade, Just curious, You are not currently a fan of high speed landings But were you in the past a fan or practitioner of hooks or carving approaches? Again just being curious. Glen.

[quade 4]

I've done a few, but certainly nothing most people would consider all that radical. I'm getting to an age where bones don't heal quite as well, so I've decided that my focus will be the opposite end of the scale with PRO-Rating style landings. Kind of boring, it's not the kind of stuff that makes the papers (note: see sig).

Most of my negative thoughts on high-speed landings come from the over glorification of them and the intense interest I see in newbies to perform them. As much as I like the Team Extreme guys, I think the emphasis on their exploits is far too overblown. For instance, has an issue of Parachutist or Skydiving Magazine in the last year -not- contained a story about them? Maybe, but I don't think so. So, obviously this sends a huge message to the newbies.

I just wish there was equal time for the slow-speed end of the scale.

Oh, all the way-too-over-the-top geek aerodynamics you'll see me sometimes spout when talking about canopy control comes from my previous preoccupation with Flight Instructing. I've taught a few folks how to land in airplanes and a lot of that transfers readily to parachute skills as well.

Hell, I even taught Michele how to do a stand-up landing -- that ought to tell you something! (No offence Michele!)

quade -
The World's Most Boring Skydiver

[VectorBoy 0]

Oh, all the way-too-over-the-top geek aerodynamics you'll see me sometimes spout when talking about canopy control comes from my previous preoccupation with Flight Instructing. I've taught a few folks how to land in airplanes and a lot of that transfers readily to parachute skills as well.

Ya I thought I smelled " Aerodynamics for naval aviators" in a few of your posts about a year ago. Do you still actively instruct?
And I know what you mean about the overglorification. If its not buffered with the respect for the skills required and the long road to get that level of experience then that attitude is a recipe for disaster.
I love the short field, Bush pilot, stol approach of a Porter. But there is something beautiful, almost ufo like, in the flat no flap, 90 knot over the threshold landing of a fast glass homebuilt like a Lancair or EZ. I want to be proficient at both.
I guess I'll never be happy with just one canopy, or happy with just one airplane for that matter.

[PhreeZone 20]

>Kind of boring, it's not the kind of stuff that makes the papers

And then

>has an issue of Parachutist or Skydiving Magazine in the last year -not- contained a story about them?

I think that you just figured out why they get so much coverage... no one wants to write articles on how to do a normal landing... but when asked on how to do HP landings everyone wants to have their turn. Also doing a normal or even an accuracy approach is something that really does'nt impress the normal skydiving crowd but seeing some one go across the pond with a toe dragging... thats different and gets skydivers attention. Until it reaches the point that skydivers are turning their backs and not watching swoops anymore I think you will always have the swoopers being high profile.


On the original question.. my first guess would be DA had a big part to play in it. The Recovery arc would be the same reguardless of what the weather was like (minus turbulence) but the flair is different with different DA's.

Yesterday is history
And tomorrow is a mystery

Parachutemanuals.com

[quade 4]

Quote

But there is something beautiful, almost ufo like, in the flat no flap, 90 knot over the threshold landing of a fast glass homebuilt like a Lancair or EZ.

Yes, but that's a somewhat misleading analogy because you certainly aren't performing a split-s to landing. Not twice anyway.

Also, most of the really smart pilots that fly aerodynamically slick aircraft know the value of touching down at the recommended airspeed and right on the numbers. Carrying extra airspeed in a slick airplane generally isn't very healthy unless you have lots of extra runway to play with.

As for me, no, I haven't sat in the right seat for awhile. I keep my CFI status current just because it was such a pain in the ass to get, but other than that it's pretty rare to see me near an airplane these days without me wanting to jump out of it.

quade -
The World's Most Boring Skydiver

[RichM 0]

Quote

Temp. measures the average speed of the surrounding molecules. As it gets hotter, the molecules of air are not as dense because they moving faster. So the canopy will fly like you are at a higher altitude where the air is thinner. That is to say, faster.

Thanks for the explanation that even I can understand

Quote

Additionally, as relative humidity increases molecules of air are being replaced with molecules of water. So the air becomes even less dense on a hot and humid day.

Can I just confirm you do mean relative humidity?

Quote

A Crossfire has a negative recovery arc so it will stay diving after you let the risers up.

My Crossfire 119 loaded at 1.5 (recalled and line trim done) has a positive recovery arc, and I sometimes can't hold double fronts down to surf height as they have loaded too much for my skinny arms. Hehe

Quote

You should be able to avoid digging out of the corner if you let up on the risers a bit higher. let the canopy fly to the surf window instead of driving it there. If that makes any sense.

Thanks, it does makes sense and my aim is to finish the natural recovery arc too high and so need double fronts to reach surf height to give me that larger margin for error.

Thanks to all who have offered advice, it seems clear that this was likely caused by density altitude. Is there any way of measuring density altitude on an absolute scale?

Rich

Rich M

[quade 4]

Quote

Is there any way of measuring density altitude on an absolute scale?

Yes, density-altitude is based upon the International Standard Atmosphere.

You might want to have a peek at this article.
http://futurecam.com/densityAltitude.html

If you need exact density-altitude calculations, then there are calculators available for that (and other) purposes, but the rule of thumb calculations given in the article will work pretty well for everything from bush flying to skydiving.

quade -
The World's Most Boring Skydiver

[quade 4]

Oh, I know -why- swoops get so much attention. That's not difficult to understand. I've even watched a few myself.

Of course, nothing gets attention like a bad landing. Lights and sirens. Personally, I'd prefer to never have that sort of attention.

I think that if you're doing your landings in order to draw attention to yourself or impress the whuffos, then you need to be careful what you wish for.

quade -
The World's Most Boring Skydiver

[RichM 0]

Quote

Yes, density-altitude is based upon the International Standard Atmosphere.

You might want to have a peek at this article.
http://futurecam.com/densityAltitude.html

If you need exact density-altitude calculations, then there are calculators available for that (and other) purposes, but the rule of thumb calculations given in the article will work pretty well for everything from bush flying to skydiving.

Thanks Quade, will absorb that this week and program my calc to carry around with me. I expect to see d.a. and perception tie up quite nicely.

Rich
Skydiving nerd ;P

Rich M

[freeflir29 0]

Quote

and program my calc to carry around with me

You really don't have to do that. If your DZ has a hand held aviation radio all you have to do is tune it to AWOS (Automated Weather Observation System) at the airport. It will tell you the DA as well as Temp, Cieling, vis, and probably one or two other things I have forgotten.

[RichM 0]

[replyYou might want to have a peek at this article.
http://futurecam.com/densityAltitude.html

[quade 4]

I'm sure there must be a rule of thumb about millibar pressure variations and kilometers of altitude change, but honestly I don't have the foggiest idea what it would be. You might try asking one of your pilots -- they might have a little rule of thumb they use.

In the U.S. we use inches of mercury and a 1 inch variation equals about a 1000 foot variance -- so it's pretty easy.

Since local barometric pressure only varies about 1 inch in total anyway (about 500 feet either side of normal), I think you can see it's not usually the most sigificant factor here -- temperature is.

Again, for exact calculations, I'd use a calculator, but that's usually not required for the types of things we're doing.

As for getting the information via radio from some automated weather service, it's going to depend (In the U.S. at least) on what specific information the automated weather service gives -- not all are created equal and some are just damn near worthless. I have no idea what kind of automated weather via radio you can get in the U.K..

quade -
The World's Most Boring Skydiver

[rhino 0]

Quote

A Crossfire has a negative recovery arc so it will stay diving after you let the risers up.

My crossfire2 will level out just fine where the recovery arc is conerned. Not being in the corner to begin with in any canopy is a great preventative measure. It is the ONLY preventative measure.

Rhino

[AndyMan 7]

I don't know about the crossfire 2, because I've never jumped it, but I do know the Samurai. If you put it into a dive, it will maintain part of that dive until you give it some toggle input.

This allows you to do your turn up even higher, ride the dive down until it's time to plane out. It gives a whole new way to setup your approach.

_Am

__

You put the fun in "funnel" - craichead.

[rhino 0]

Not directed at anyone in particular. But if one can't land "his" own canopy "one" probably shouldn't be giving advice in the swooping and canopy control forum.. For example if "one" had two broken feet for example?? Maybe that "one" should be reading instead of posting?

Again.. Not directed at anyONE in particular to avoid the personal attack issue.

Rhino

[PhreeZone 20]

Agreed.. the continuing dive of the Samauri caught me off guard at first too. It will continue to dive after a turn unlike most other canopies I've jumped that will start to level out after coming around the corner.

Yesterday is history
And tomorrow is a mystery

Parachutemanuals.com

[AndyMan 7]

It wasn't my canopy. It was phree's, and the first ankle was done running.

That said, I only made that post because I think you missed the point of the previous one.

_Am

__

You put the fun in "funnel" - craichead.

[freeflir29 0]

Quote

It will continue to dive after a turn unlike most other canopies

Hmmm...sounds like something I need to try out....The sharp recovery arc is what I hate about my Stilletto.