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speedy

Glide ratio for different canopies

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I know I could probaly find this stuff with lots of searching, but maybe someone with knowledge can gives me estimates to work with. I just want to get an idea of differences (if any).
So what is that glide ratio for :-
a) a pocket rocket like Velocity
b) sabre 2
c) a typical student canopy
d) a tandem canopy

all assuming full flight with no riser/toggle input.
Dave

Fallschirmsport Marl

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Wow, 162 views and no one has any input? :S

Ok, I'll work with 3:1 and assume they all fly the same.



Maybe no-one knows? I'd expect that if anyone has that data it would be the manufacturers.

PG manufacturers always publish the L/D, min sink, max trim speed etc, so it must be measurable. I guess in skydiving no-one sees it as important enough to test.
Do you want to have an ideagasm?

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Wow, 162 views and no one has any input? :S

Ok, I'll work with 3:1 and assume they all fly the same.



A while back, I searched looking for this information. I didn't find much of anything useful.

I did make a half ass comparison between my Tri 190, and my Sabre2 150 by jumping them
consecutively the same day. The spot was not exact from jump to jump, but it was within reason, and I pitched at about the same altitude. The altitude when I flew over the parking lot next to the LZ was about the same. I just made it there a lot faster under the 150...

When you sit down and write all of the X factors that influence flight, it becomes pretty complicated.

You can come close by calculating your horizontal progress compared to your vertical descent under your own canopy.

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Ok, ok, I'll try to throw some data in here, although it isn't exactly answering your question in a clear fashion:

FX 88 = 2.1 glide ratio brakes free, 2.3 at quarter brakes, 2.8 in deep brakes (Goes way up in deep brakes, unlike old F-111 canopies where the glide ratio would go down.)
(All tests at 165-170 lbs suspended)

Sabre 135 = 2.1 free

Stiletto 120 = 2.4 free (Stilettos were always good at gliding.)

a 265 ft sq F-111 7 cell canopy = 2.2 free, 1.7 brakes set

an experimental high-glide 11 cell 170 elliptical = 3.2 brakes free, over 4 in quarter brakes (Just to show what can be done largely with different trim.)

I haven't confirmed it but figure something like a Manta, although bulky, is a high aspect ratio canopy with a decent glide, so it could be in the 2.75 range.

In another earlier thread I wrote about 2.25 to 3.0 glide ratios for skydiving canopies in general, but now I'd revise that down to "2.0 to 2.75". (I've gained a better understanding of the characteristics of my variometer and anemometer instrumentation and thus fixed how I adjusted for density altitude.)

Other reminders from an earlier post of mine:
========
Remember that skydiving canopies are often built nose low for speed, rather than trimmed nose up for efficient glide (more like paragliders). So a skydiving canopy's airfoil usually has potential for a higher glide than it actually achieves.

Also, for small canopies, the pilot size may not change, so the "payload" gives proportionately more drag. A smaller version of the same canopy, with the same pilot, will therefore glide more steeply.
==========
As an example of the above, Paraflite used to publish some detailed flight test results on their canopies. One high aspect ratio zero-p topskin canopy showed a brakes free glide ratio varying between 2.2 for the 154 size, and 2.8 for the 240 size.

With all of this, remember that the numbers could easily be off by + or - 0.2. It's hard to get really good data without a lot of test jumps in still air, and well calibrated instruments. So use this as a general guide only.

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Ok, ok, I'll try to throw some data in here, although it isn't exactly answering your question in a clear fashion:



I think you just posted the most detailed statistics in skydiving canopies... I have asked for this data before from manufactures, and they did not have data to give.

How did you measure. GPS? How did you account for airspeed vs groundspeed?

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>(I've gained a better understanding of the characteristics of my
>variometer and anemometer instrumentation and thus fixed how I
>adjusted for density altitude.)

I'm starting to think that a vane and a tilt sensor would be a better way to measure all this. No densities to calculate out.

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As for the issue of the instrumentation I used, for those wanting the details:

THE SHORT ANSWER
Electronic vario and anemometer. Decent, but not professional quality. No need to deal with groundspeed vs airspeed issues.

THE LONG ANSWER

1) For rate of descent it was an electronic variometer (rate of descent meter) as used by paraglider pilots.

2) For speed, it was a hand held electronic ducted propeller style anemometer, that is supposed to be accurate within a few percent. (Some cheap ones are shown in the manual to be much less accurate.)
The anemometer was held out away from myself, risers, etc. to avoid either blockage or venturi effects. It was simply pointed in the direction of the apparent wind, and rotated up or down a bit to see a maximum value. Also, ducted props show insensitivity to errors due to not aligning them perfectly with the airflow. I once calibrated the anemometer in a university wind tunnel to remove what seemed to be small errors at the high end of the speed range.

3) Altitude corrections. The rate of descent changes with altitude, so I had to correct data from different altitudes to a sea level equivalent. I would get a pressure altitude on the ground using the plane's altimeter, and get a rough temperature reading on the ground and at jump altitude, to work out average air mass temps. Formulas are available to do density altitude calculations, or one can plug the numbers into a pilot's old circular slide rule.
Initially I did altitude corrections on the speed data but then realized I didn't need them, as the propeller style anemometer reads True Airspeed, rather than Indicated Airspeed as an airplane pitot system would do. This seemed to be confirmed by comparing results for data collected both up high and down low. This made for small corrections in my original glide ratios, bringing them down a bit.

Some day I'd like to put all my data together, double check the calculations, and do a clear writeup on it all. The results won't be perfect, but will be better nothing, which is usually what is available!

As for a vane and a tilt sensor, sure, that could work, if the difference between the vane and level measurements could easily be recorded.

In some ways it could be better because it would be a more direct measurement, rather than relying on calculating descent rate and speed along the flight path, and then doing the trigonometry.

For me, I wanted to get speed information as well as glide angle. Paragliding companies use instruments similar to mine, but I have heard that to get really clean speed data with little effort, they use a 'trailing bomb' system with a vane-pointed ducted prop sensor hanging down below the pilot, well away from the interference of the pilot & harness.

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Can you share the speed information too, for the canopies you mentioned above?



Too much time on dz.com today already, but I'll bite.
Just briefly:

My FX88 was flying roughly 46 mph brakes free, and 1750 fpm descent rate (29 fps!). That's at standard temp & pressure conditions, basically sea level. So the actual speed through the air will be higher in summer and higher altitudes. Getting consistent speed data is tougher with the FX, as even a little movement in the harness, or the tiniest harness turn, would increase the speed a couple mph as it tried to dive off to the side.

In very deep brakes I was down to 25 mph and 730 fpm.

With a Sabre 120 I was getting about 35-36 mph & 1350 fpm. The Stiletto 120 was the same or marginally faster, but descending slightly slower.

Under a Manta I was doing 25 mph or just under.

Note that these are flight speeds, so the horizontal speeds will be somewhat less.

In a previous post in the thread I wrote:

Quote

Initially I did altitude corrections on the speed data but then realized I didn't need them, as the propeller style anemometer reads True Airspeed, rather than Indicated Airspeed as an airplane pitot system would do.



Oops, I misspoke. I actually did things the other way around. Since the anemometer is supposed to show true airspeed, therefore if testing up high, the speeds have to be reduced for density altitude effects, so that one can compare all numbers at sea level conditions.

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Thanks everyone for your input. B|

I think my original estimate of 3 is somewhat high. The stuff from pchapman seems to match some other stuff I got via PM quite well.

It seems that the type of canopy ( by that I mean student, tandem or HP) is not the main factor in glide ratio, therefore, when estimating how far someone can fly from a given altitude, larger canopies may not have an advantage.
Dave

Fallschirmsport Marl

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My FX88 was flying roughly 46 mph brakes free, and 1750 fpm descent rate (29 fps!). That's at standard temp & pressure conditions, basically sea level. So the actual speed through the air will be higher in summer and higher altitudes.



My FX 93 loaded to 2.1 had a descent rate of 36fps (2160fpm) on full drive last weekend at 3000ft AGL. (8000ft AMSL) It's cooler here now, heading into winter, so I imagine it would be even higher in the summer.

t
It's the year of the Pig.

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which garmin do you have?



It is either the vista or the legend, I forget as I have both. It has two features useful under canopy, but I have yet to try them.

One displays glide, the other displays glide needed to get to a certain way point.

Of course it fails to take into account the extra 1000 feet needed to setup your pattern in order to behave in traffic and land safely into the wind. I might be able to offset a way point upwards by 1000 feet, but I haven't tried yet,
"The restraining order says you're only allowed to touch me in freefall"
=P

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Lots of useful info, thanks for sharing!

A simple calculation can explain why fast canopies glide better in deep brakes, and how we can estimate "raw" L/D of the canopy (without the pilot ;)).

Quote

FX 88 = 2.1 glide ratio brakes free, 2.3 at quarter brakes, 2.8 in deep brakes (Goes way up in deep brakes, unlike old F-111 canopies where the glide ratio would go down.)
...
My FX88 was flying roughly 46 mph brakes free
...
In very deep brakes I was down to 25 mph



In belly freefall at 120mph, the drag is equal to 100% of your weight. At 46mph under canopy, with almost the same body position presented to relative wind, the drag will be (46/120)^2, or 15% of your weight (since drag is proportional to the square of speed).

At 2.1 glide ratio, corresponding to glide angle of atan(1/2.1) = 25 degrees, the total drag of your body and canopy is equal to your weight times sine of the glide angle: 100% * sin(25) = 43% of your weight. Since your body contributes 15%, the drag of the canopy (with lines and PC) is 43-15=28% of your weight, or 43/28=1.5 times lower than the total. So the canopy's true L/D is 2.1 * 1.5 = 3.2.

In deep brakes, your speed was down to 25mph, so the drag created by your body was only (25/120)^2 = 4% of your weight, the total drag of canopy+you was 28+4=32%, or 32/28=1.14 times higher than that of the canopy alone, so the glide ratio was 3.2/1.14 = 2.8.

Pure fucking magic at work! ;)

So when comparing glide ratios of different canopies, the speed and corresponding drag of the body should be taken into account, at high speeds body generates a major chunk of total drag!

Yuri
Android+Wear/iOS/Windows apps:
L/D Vario, Smart Altimeter, Rockdrop Pro, Wingsuit FAP
iOS only: L/D Magic
Windows only: WS Studio

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Yuri,

That is some nice math. Thank you for sharing.

A good mathmatical reminder to pick up my legs when trying to get back, esp when flying into the wind when I need both max glide ratio and max airspeed.

Seth
It's flare not flair, brakes not breaks, bridle not bridal, "could NOT care less" not "could care less".

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so in non-math terms...

At full speed, the drag of the human is more. The drag "moves" the human back in the "window", changing the angle of attack of the canopy to be more "divey". With the "divey angle of attack", the speed of the canopy increases, causing even more drag, causing even more shift of the window, changing the angle of attack even more - until a fast divey equilibrium is found...

In deep brakes, the drag of the human is less. The lack of drag "moves" the human forward in the "window", changing the angle of attack of the canopy to be "flat". With the "flat angle of attack", the speed of the canopy decreases, causing even less drag, causing even more shift of the window, changing the angle of attack even more - until a slow flat equilibrium is found.

Is this accurate in your opinion?

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