How much difference in loadings?

[Jessica 0]

How much speed do you gain with a downsize?

I'm just trying to wrap my mind around this. I jump a Hornet 150. When I bought it, I meant to be loading it at 1:1, but I gained enough weight to load it at almost 1.2:1. This isn't a dangerous loading for me, but how much of an actual difference is there between my intended loading and my actual one?

Someone with 50ish jumps should probably look at a 1:1 loaded canopy, most people agree. But if he buys a 1.3:1 loaded canopy, the canopy nazis feign heart attacks. Is there any way to represent the difference in speed with a percentage, or some kind of number?

I guess it's hard for people to really understand why 1.3 is so much more dangerous than 1.0, and why 1.8 is so different from 1.5. If we had a better way to quantify it, maybe it would be easier to explain.

Skydiving is for cool people only

[Watcher 0]

I don't notice much difference in .1 on the same model. I would notice more on different canopies. Course a 135 is not always a 135 so the wing loading could easily be different by .1-.2. I flucuate weight by about +- 7 lbs off my base weight of 162 So I see that .1 change in either direction on a given weekend.



--

Jonathan Bartlett
D-24876
AFF-I

[quade 4]

Because things like drag don't scale on a straight line, it's impossible to give a precise number.

quade -
The World's Most Boring Skydiver

[relyon 0]

With the same canopy and jumper, the ratio of freestream flight velocity will be proportional to the square root of the ratio of wing loadings. Compared to a wingloading of 1.0, a canopy loaded at 1.3 (NOT 1.3:1 as is so often incorrectly notated) will be (1.3/1.0)**0.5 = 1.14 times faster. That means if a Hornet 150 @ 1.0 flies at 40 kts, the same canopy will fly at 45.6 kts @ 1.3.

Bob

[rigging65 0]

You've got to remember a few things when it comes to wing loading:

First: Wingloading is a guide that tells you how fast you'll come down the glide slope for a given canopy model. If you change models (even if the sq. footage is the same) it may have a different glide slope, and therefore all your numbers are off. Also, wingloading doesn't really tell you what a canopy will do in turns or about it's recovery arc.

Second: The sq. footage that a given mfg. gives for their canopy is probably not the same as what another mfg. would size it at. What that means is that you can't get a good comparison between mfgs. unless you actually measure the canopy yourself (in some method) then compare two like sizes (which you'll never find) to get comparable results. You've got to love marketing!

Last: Wing loading is only a rough guide to give you some idea of how you're loading compares to another person's and (because there are very general characteristics associated with higher or lower wing loadings) some way to guess what going up (or down) in wingloading might produce on a given canopy. There are simply way too many other variables involved to use any one as a guide for canopy flight.

So, what this tells you, is that wingloading is a very basic method for telling you something about speed in canopies. Kind of like comparing a 4-cylinder, 6-cylinder, 8-cylinder, and 12-cylinder automobile. It'll let you know something about it, but only in one area, and not all that much.

"...and once you had tasted flight, you will walk the earth with your eyes turned skyward.
For there you have been, and there you long to return..."

[quade 4]

Quote

With the same canopy and jumper, the ratio of freestream flight velocity will be proportional to the square root of the ratio of wing loadings. Compared to a wingloading of 1.0, a canopy loaded at 1.3 (NOT 1.3:1 as is so often incorrectly notated) will be (1.3/1.0)**0.5 = 1.14 times faster. That means if a Hornet 150 @ 1.0 flies at 40 kts, the same canopy will fly at 45.6 kts @ 1.3.

I'll agree with everything except the note regarding the proper notation regarding wingloading.

Correctly stated, wingloading is the ratio of weight to surface area. In the US, that would be pounds per square foot. Ratios are written in the form of x:y and since in our case the y is always assumed to be 1, it -could- be written either way and -should- be understood as being the same thing unless otherwise noted.

For instance, if we were talking kilograms per square meter, I think you'll find that 1.3 pounds per square foot is vastly different than 1.3 kilograms per square meter!

Now, on to the topic of F=ma!

quade -
The World's Most Boring Skydiver

[relyon 0]

Quote

Correctly stated, wingloading is the ratio of weight to surface area. In the US, that would be pounds per square foot. Ratios are written in the form of x:y and since in our case the y is always assumed to be 1, it -could- be written either way and -should- be understood as being the same thing unless otherwise noted.

It can be looked at the same, but that doesn't mean it is standard practice (it's not). I read engineering texts and periodicals all the time. Nowhere that I'm aware of in standard aerospace industry practice is wing loading ever referred to using x:y format where y is always 1. The same material usually leaves out the x (times) in F=ma, even though that is technically correct too.

By the same token, speed limits (or airspeeds, for that matter) are a ratio. Yet no one sez "Damn. I got pulled over this morning for doing 73:1 in 60:1 zone!" or "the power off stall speed of this aircraft is 43:1". Again, a matter of accepted convention.

Bob (who sometimes jumps a Lightning 126 loaded at 31:20 aka 1.55)

[quade 4]

Really? 'Cause, like, I've read maybe one or two books on the subject of aerodynamics and I see it all the time.

(At this point quade glances over at the private and commercial pilot syllabi he's written . . . )

Yep, I think I've seen one or two books express it that way.

quade -
The World's Most Boring Skydiver

[nacmacfeegle 0]

"I jump a Hornet 150. When I bought it, I meant to be loading it at 1:1, but I gained enough weight to load it at almost 1.2:1. "

I know how you feel Jess,, but I'm guessing you didn't expand overnight, and the weight gain might have been over a period of time while you were jumping....
So its a gradual thing, and not a step change, so its prgression in a round about way..
I can't help you with the actual percentage increase, sorry.

As for Quade and Relyon.
As far as I'm concerned, the accpeted norm for describing wingloading is 1.6:1 format, or even just 1.6
Regardless of whether thats actually technically specific or not, its the accepted norm. As for describing a wing loading beyond 1 decimal number, well I believe thats kinda pointless as the parachute industry haven't agreed on how they measure surface areas.
And don't get me started on lbs/sqft versus kg/sqm.
Sheesh guys the rest of the world works with a decimal metric system, get with the programme.....
But again as the accepted norm is lbs/sqft, I guess the rest of the civilised world will just have to get dragged along with it.
Just my 0.0178964 EUR worth.

--------------------

He who receives an idea from me, receives instruction himself without lessening mine; as he who lights his taper at mine, receives light without darkening me. Thomas Jefferson

[apoil 0]

Quote

So, what this tells you, is that wingloading is a very basic method for telling you something about speed in canopies. Kind of like comparing a 4-cylinder, 6-cylinder, 8-cylinder, and 12-cylinder automobile. It'll let you know something about it, but only in one area, and not all that much.

Actually, wingloading is more analogous to total displacement in an engine.

The number of cylinders is more like the shape of the canopy, 7cell/9cell/square/elliptical, etc.

Displacement relates fairly directly to horsepower, but not entirely, and horesepower doesn't completely answer the question of 'how fast will I go'. Consider a 5litre V8 in an SUV full of people versus the same engine in a Corvette.

Obviously the analogy breaks down because there are more different options for an automobile configuration.

[Steel 0]

wow that is some good stuff. you seem to have answers I have seeked. However lets just look at the theory because something is obviously missing here. It reminds me of standard temperature you know the temperature cools 2 degrees celcius for every thousand feet but hey the space shuttle that recently exploded was last contacted at 208 thousand feet could they have been about 400 degrees celcius below zero. (obviously not since that is below absolute zero) Now back to your formula. According to your formula as the square footage of a canopy approaches zero the speed goes to infinity. Now we know that is not true either. So where do you draw the line. At which point is the asymtope on your graph. Does you theory hold true between 3.0 and 5.0 wingloadings? One might think it holds true as long as the canopy is generating enough lift to sustain flight but I don't think that is true either because canopies are not really proportional. if you take a 210 square foot canopy and a 70 square foot canopy you will see that the 210 has no where near 3 times the wing span, and now where near three times the line length. For that reason, I don't see this equation as able to be linear. But I do believe you can have a linear approximation for a certain interval. That is what I think you have here and I am just trying to find out what the interval is.

If I could make a wish, I think I'd pass.
Can't think of anything I need
No cigarettes, no sleep, no light, no sound.
Nothing to eat, no books to read.

[relyon 0]

The formula I referenced is not linear w/respect to canopy size. It's linear to the square root of the ratio of wing loadings. My example was for the same person under the same canopy at different loadings. The only assumption was that the drag coefficient of the jumper's body is constant as their weight (and therefore wing loading) changes. That's a reasonable assumption over the range of loadings discussed.

If the jumper is Harry Steel and varying amounts ballast are used to adjust loading, the drag actually will be constant. In that case the velocity/loading relationship will hold up to the point the load (low or high) deforms the canopy such that it's aerodynamic characteristics change. For 7-cells, I'll guess that's somewhere between .6 and 2.2. At loadings of 3.0 - 5.0, a non-crossbraced canopy is probably going to collapse; there's simply not enough spreading force to keep it open.

Having 3 times the area means having the dimensions (span/chord/etc) proportional to the sq root of 3, so the 210 sq ft canopy will be a little over 1.7 times as big as a 70 sq ft canopy of the same design.

Bob

[rigging65 0]

Quote

--------------------------------------------------------------------------------
In Reply To
--------------------------------------------------------------------------------


So, what this tells you, is that wingloading is a very basic method for telling you something about speed in canopies. Kind of like comparing a 4-cylinder, 6-cylinder, 8-cylinder, and 12-cylinder automobile. It'll let you know something about it, but only in one area, and not all that much.

--------------------------------------------------------------------------------


Actually, wingloading is more analogous to total displacement in an engine.

The number of cylinders is more like the shape of the canopy, 7cell/9cell/square/elliptical, etc.

Displacement relates fairly directly to horsepower, but not entirely, and horesepower doesn't completely answer the question of 'how fast will I go'. Consider a 5litre V8 in an SUV full of people versus the same engine in a Corvette.

Obviously the analogy breaks down because there are more different options for an automobile configuration.

Ok, I suppose you're right with that, but without getting too technical, I think my point was that within a common model, changing the wingloading speeds up (or down) your rate of descent down the glide slope...providing everything else is the same.

Thanks for the lesson on engines though

"...and once you had tasted flight, you will walk the earth with your eyes turned skyward.
For there you have been, and there you long to return..."

[raymod2 1]

> Displacement relates fairly directly to horsepower,
> but not entirely, and horesepower doesn't
> completely answer the question of 'how fast will
> I go'.

Not to get too far off topic but this statement is completely untrue. Consider a Honda VTX 1800 which has a displacement of 1795cc compared to a Honda CBR600RR which has a displacement of 599cc. Despite having 1/3 the displacement of the VTX the CBR600RR produces more horsepower (105.4 versus 94.6).

[bobsled92 0]

Agreed:
My RF900R tops@164mph
GSX-R750R Tops@181mph
I SAME am 205lbs whan sitting on both bikes
p.s. with the canopies :Cobalt 170
Sabre2 190
speed felt no different with same wind(0mph)
same tested maneuvers & identical Silly ass grin

_______________________________
If I could be a Super Hero,
I chose to be: "GRANT-A-CLAUS". and work 365 days a Year.
http://www.hangout.no/speednews/

[GroundZero 0]

uh-oh... here comes politically incorrect...

Guys we're talking to a chick here, drop the motorcycles... use something she's familiar with...

oh no... don't go here!

don't do this...

Jessica,

nevermind...

[skycat 0]

Quote

uh-oh... here comes politically incorrect...

Guys we're talking to a chick here, drop the motorcycles... use something she's familiar with...

oh no... don't go here!

don't do this...

Jessica,

nevermind...

no no no...please continue with the bikes, I used to have an FZR600

Fly it like you stole it!

[GroundZero 0]

well i'll be damned...
and now i find out you have an fzr-600... What year?

Mine's a '93

Chris

I suspect you're lighter than me... but I've still seen mine over 150mph!

[skycat 0]

Quote

well i'll be damned...
and now i find out you have an fzr-600... What year?

Mine's a '93

Chris

I suspect you're lighter than me... but I've still seen mine over 150mph!

Had. Had to sell it when I moved to Houston, and haven't gotten around to getting a new one (probably an R6) my old one was an 89.

Oh and I'm a wuss, highest I went to was 100mph.

Back on the subject of wingloading. With and exit weight of 120, the biggest change I felt in WL was from 1.2 to 1.3 (5000 ft msl) which right now is when I add 10 lbs of lead for belly flying. From 1.1 to 1.2 (sea level) I couldn't tell a difference at all. This was all on crossfires, btw..

Fly it like you stole it!

[Steel 0]

> I've still seen mine over 150mph!

[Hooknswoop 19]

Quote

Maybe these people are just making themselves feel better by saying their bike actually goes faster than it really does. Aha I think that is it.

Also could be you weigh more than these other people, decreasing the power to weight ratio, and increasing wind resistance. Skycat weighs 110-ish and doesn't present a whole lot of drag.

Hook

[GroundZero 0]

I find that at top speeds it's a little about weight and mostly about drag...

I'm in the mid 150's weight wise... (compare horsepower to weight loadings here)...

The biggest difference is drag... on first few runs i too was finding mid 140's, then by burrying my chin itn the tank bag I was upper 140's, by squeezing my knees tighter into the tank, another few mph, then point toes aft another mph, then flattening back and pushing ass more rearward another mph.

Look at parasitic drag on an airplane... I could not believe the little 108 hp veri-easy outclimbing and passing me in my 230 hp 182... let's see, i forget how it goes... (in overcoming existing drag) to double speed, you need to square the horsepower... something like that.

Same reason Rutan doesn't add hp, he simply cleans up the drag.

Chris

I love to drag race the 250 lb guys on 900's!! Smoke em all day long on my little 600... (but i also cheat a bit, the bike's been tricked too.)

[GroundZero 0]

Bruno,

Haven't you todl me you're 200+ lbs... that'll make a difference (in addition to additional drag if you're taller and a bit more exposed...)

Chris

[Steel 0]

my weight can actually vary between 180-200 ( your probably confusing exit weight with actual weight) I have never weighed more than 205. As for drag I am not extremely tall a little over 5'9". Considering that most people fudge their height a bit if I say 5'10" you will have an accurate picture. But since I am putting this information online its important that I clear up that I am not fat. 8% bodyfat, 17 inch arms, 44 inch chest. I do agree that drag is the most significant factor in slowing the bike's top speed. I have done 140 with a chick in the back and it did not seem to take significantly any longer to get to that speed than it does when I am alone and not tucked down.

If I could make a wish, I think I'd pass.
Can't think of anything I need
No cigarettes, no sleep, no light, no sound.
Nothing to eat, no books to read.

[Steel 0]

>I love to drag race the 250 lb guys on 900's!! >Smoke em all day long on my little 600... (but i >also cheat a bit, the bike's been tricked too.)
I must say I have never drag raced on a motorcycle before. It kind of doesn't make any sense to me. See I know my bike does a quarter mile in just under 10 seconds (by professionals who have been racing for more than 10 years and who are damn good at it). I also know that the overwelming majority of riders would be flipped on their ass if they tried to take off that fast. But anyway the ability to take off fast on a bike is just something that comes with time, while working on what really matters. I.E. how fast can you take that swooping turn. And when your looking to see who is the fastest taking turns the power of the bike is pretty close to meaningless. Its all about the rider and almost nothing about the bike. Here the bike can always go faster its the rider with limited ability. Which is why I have a zx-9 R and not a zx-12R.

If I could make a wish, I think I'd pass.
Can't think of anything I need
No cigarettes, no sleep, no light, no sound.
Nothing to eat, no books to read.