Sinking: Z-Po vs. Lo-Po (F-111)

[stitch 0]

Can someone with some background please explain the differences in the fabrics, their flight characteristics and what each type of fabric is or is not capable of ??

That way there will be a thread that is easy to find everytime this ZP vs. Lo-Po (F-111) arguement comes up.

I personally have never been able to get a ZP canopy to do a traditional sink like a F-111 type canopy. Maybe that is due to low jump numbers. Although I've always thought it was because ZP is, well ZP. Maybe there is a new variable ZP I haven't heard of. I do know if you sink a F-111 type canopy all the way to the ground, you had better be ready to PLF.

"No cookies for you"- GFD
"I don't think I like the sound of that" ~ MB65
Don't be a "Racer Hater"

[DrewEckhardt 0]

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Can someone with some background please explain the differences in the fabrics, their flight characteristics and what each type of fabric is or is not capable of ??

That way there will be a thread that is easy to find everytime this ZP vs. Lo-Po (F-111) arguement comes up.

I personally have never been able to get a ZP canopy to do a traditional sink like a F-111 type canopy. Maybe that is due to low jump numbers. Although I've always thought it was because ZP is, well ZP. Maybe there is a new variable ZP I haven't heard of.

ZP lasts for more pack jobs, has different failure modes, and takes more packing skill to get in the bag especially with tight containers. Otherwise there isn't a difference. George Galloway of Precision talked about this when he had an internet presence (rec.skydiving? dz.com? I don't remember) and was quizzed about the -MZ Raven reserves.

Most ZP canopies have _very_ different planforms, airfoils, and/or line trim from most 0-3 CFM canopies.

Most ZP canopies are jumped at wing loadings beyond where you'd be happy starting at the stall speed, dropping to zero forward speed, and just using the aerodynamic drag to slow you down over the last X feet. Comfort calls for converting your forward speed to lift (or even brakes in the forward direction) and with a slow approach to a pure sink there isn't any.

Canopies which sink well have low aspect ratio planforms, big fat airfoils, wide open noses facing downward, and a nose-down trim. There's no intersection with typical skydiving canopies having tapered planforms with 2.5-3:1 aspect ratios, skinny low drag airfoils, closed off noses for nice openings and less drag, and flat trims to get back from long spots without using any controls. I don't know how much of that is technically relevant; some may just be correlated to sinking ability, things like wanting such canopies to recover more quickly when you do go too far with the toggles.

Try a ZP topskin BASE canopy (I really like my Fox, and the Flik should be similar), ZP Lightning, or maybe a Raven -MZ for comparison purposes at under a pound per square foot.

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I do know if you sink a F-111 type canopy all the way to the ground, you had better be ready to PLF.

At least 3/4 brakes level from any altitude followed by a small flare close to ground level works great for comfy stand-up landings at reasonable wing loadings. Full sink (zero forward airspeed) from a few feet works with any landing conditions. I haven't tried a full sink from roof-top level or beyond all the way in (maybe once when the idiot I was jumping with flew himself into a cliff and I was paying more attention to him lying on the ground than landing before the end of the 50x100' landing area with no outs and I had to get down without over-flying after loosing half it to distraction). With a canopy that will steepen into a nice classic accuracy approach you just don't need to sink from roof-top height or beyond.

This requires the F111 canopy to be fresh. A couple hundred jumps qualifies at reasonable wingloadings. 1000 jumps is dumpster or car-cover material. Old Pharts with Excalibur F111 cross-braced tri-cell experience say it was jumped out before 500 landings.

"reasonable" is defined as under a pound per square foot, with .7 being a nice number that doesn't get too mushy on the controls. That wingloading is both a speed and control sensitivity thing.

"sink" means gradually slowing down to zero forward airspeed and not going backwards. It's not good to go too far and fly backwards to an ass-first landing.

Flying small ZP canopies in where your feet would be below ground level if extended, popping up to kill your forward speed, and sinking a couple feet works really well especially at moderate to high (1.9) wing loadings and density altitudes (9000 feet plus) where your short stubby legs may have problems running as fast as the canopy stops flying when flown all the way to the ground.

This also disregards user interface issues. On canopies which sink nice adding brakes steepens your glide path (maybe 1:1 at 2/3 brakes) and past where the wing is stalled you still have control with too much brakes sending you backwards and the boundary between the two being a little like riding the clutch on a stick shift or motorcycle in traffic. Without good sinking ability the glide flattens and then remains pretty constant until it steepens around the stall point with little room before things get exciting.

[davelepka 4]

Sinking is not related to fabric type. Sinking in is simply going straight down as a result of headwinds matching the forward speed of your canopy. The end result is zero groundspeed, aka sinking it in.

The reason people think it's an F-111 thing is because accuracy canopies, which do the majority of sinking in these days, are F-111, but as already stated, they are also huge 7-cells.

Modern canopies are designed for speed, and with forward speeds pushing 20 mph, you need alot of wind to get one of them to sink straight in, but it can be done.

As also previously mentioned, the cells on accuracy canopies are huge, and even in deep braked flight, such as when sinking in, there is a good deal of airflow in to the cell. They are also cut with the top skin hanging way over the bottom skin on the leading edge, so airflow into the canopy is provided by the vertical motion as well as the forawrd motion.

If you sink any canopy all the way to the ground you better be ready to PLF.

[stitch 0]

I have been misinformed by both Scott Miller and Brian Germain then. During both their courses we were told ZP is incapable of traditional sink characteristics because no air can flow through the fabric. Something along the lines, if I can remember correctly, that flying a ZP canopy on a deep braked approach while letting the toggles up occasionally for a "surge" was referred to as a "false sink".

"No cookies for you"- GFD
"I don't think I like the sound of that" ~ MB65
Don't be a "Racer Hater"

[faulknerwn 36]

Why makes it a false sink? You can definitely sink ZP canopies straight down.

[davelepka 4]

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During both their courses we were told ZP is incapable of traditional sink characteristics because no air can flow through the fabric.

ZP canopies don't any 'sink' built in to them, but if your head wind equals your airspeed, you're going straight down.

F-111 canopies do indeed have 'sink' built in, as air moves through the fabric, with the condition of the fabric being the controlling factor. This gives the canopy a natural amount of 'sink' off of the glideslope the canopy is trimmed for.

The sink of the air moving through the fabric gives the canopy a stepper glide, and makes it easier to sink it in with deep brakes to equalize the air and wind speeds.

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if I can remember correctly, that flying a ZP canopy on a deep braked approach while letting the toggles up occasionally for a "surge" was referred to as a "false sink".

This is the same conpect as a sink, but just to a lesser degree as modern canopies don't perform well in a traditional sink.

The traditional method, used in accuracy, is to come over the target high, and once you are over top of it, brake until your ground speed is zero, and drop right down on the target.

The idea is that if you we're to come up short, there's no way to extend your glide facing into the wind. However, there is a way to shorten your glide facing in to the wind (the sink), so your safe play is to come in high and sink it down. This is where 280+ sq ft of canopy helps out when you set it down in deep brakes with no flare.

The modern version is to use brakes further up the glide slope, reducing your forward speed, and bringing your touchdown point closer to you. Before you get too low to recover, you return the canopy to full flight, and land it as normal.

You could try to ride the deep brakes all the way to the ground, but the size of most modern canopies (well under 280+ sq ft) won't set you down soft at all. In truth, the accuracy canopies dont' even set you down that soft, which is why they use a giant pad to land on (they call it a tuffet, but it's really an ass-saver).