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BMAC615

Glide ratio and airspeed information

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Does a comprehensive table of glide ratios exist for a wide spectrum of canopies? I recognize the typical glide ratio is ~ 3:1 in no wind conditions, but, I’m curious to see how much the glide ratio differs on various aspect ratios and canopy designs. For example, people talk about the Storm being ground hungry compared to the Spectre and the Stiletto being flat compared to the Katana. I can’t find any numbers that show how much the glide ratio differs between them.

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1 hour ago, BMAC615 said:

Does a comprehensive table of glide ratios exist for a wide spectrum of canopies? I recognize the typical glide ratio is ~ 3:1 in no wind conditions, but, I’m curious to see how much the glide ratio differs on various aspect ratios and canopy designs. For example, people talk about the Storm being ground hungry compared to the Spectre and the Stiletto being flat compared to the Katana. I can’t find any numbers that show how much the glide ratio differs between them.

I'm not aware of any canopy companies publishing figures on glide ratios. Whenever I have seen the subject discussed the consensus seems to be that there are to many variable to make valid measurements. In general PD will make vague statements like you are mentioning as comparisons. FWIW, my belief is that the biggest factors are first line trims and secondly aspect ratios. 

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2 hours ago, gowlerk said:

I'm not aware of any canopy companies publishing figures on glide ratios. Whenever I have seen the subject discussed the consensus seems to be that there are to many variable to make valid measurements. In general PD will make vague statements like you are mentioning as comparisons. FWIW, my belief is that the biggest factors are first line trims and secondly aspect ratios. 

I agree. The only online data I’ve found is in this video around the 36 minute mark where John talks about the differences between a Pulse and Katana.

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I think the quickest way PD could do it would be to get four groups of five test jumpers (20 total) w/ FlySight and do one load for each canopy type of various sizes with test jumpers within the weight range aligned in their WL recommendations.

Edited by BMAC615

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Tests have been done over the years but little by individual jumpers as opposed to companies.

Just whipping this post off:
While GPS data is easy to get these days, you would still need to do some analysis to get good data out of it. It is hard to find "no wind" conditions all the way up to altitude, so you are going to have to take data acquisition runs in different directions, ideally up and down wind, to help calculate out the wind's effect.

Plus, for any observed rates of descents and airspeeds,  you'll want to do all your tests in similar conditions to avoid density altitude effects messing up your numbers. At least if you measure on a similar temperature day (across the air mass and not just on the ground), and at similar altitudes, you could compare canopies, even if they are not the 'proper' numbers as one would have for an airplane. That is, airplane flight data is always adjusted to be what it would be at sea level, International Standard Atmosphere conditions (29.92"Hg, 15 deg C), that sort of thing.  So if measuring canopy speed and rate of descent at 6000' on a hot summer's day, it'll be faster than if measured at 3000' on a cooler day, in a predictable way.

If all this goes over one's head, then one isn't ready to do accurate comparisons of flight characteristics of different canopies.

... Still, it can be fun to go up and get a little data just for fun, comparing different canopies for some rough numbers.

Back 15-25 years ago I did a bit  of data collection on a few canopies of the era, using a calibrated anemometer, electronic variometer, and a whole bunch of data reduction (analysis) to take into account density altitude effects. So the canopy types are a bit old now! -- and I'm not including modern competition style swooping canopies like a Leia or Valkyrie.

This is a very quick summary that I used in a canopy flight course I have sometimes given, to give people some "rough numbers":

From my testing.

(These numbers have been adjusted to sea level standard conditions... because that's how it is done in aerospace engineering for comparing airplanes in a standardized way. On a typical summer day at a typical dropzone, at a typical height above sea level when flying one's canopy,  the air density will be somewhat less. The Glide Ratio won't really change, but the Airspeed and Rate of Descent will be a little higher.)

- Glide ratio typically:    (brakes off)

            3  student canopy

            2.5 medium modern ZP canopy

            2.1 small canopy

                        In partial brakes, my Icarus FX 88 at 1.9 loading went 2.1 to 2.8! (lowered the rate of descent a lot, while only moderately reducing the speed)

 (While big F-111 canopies might just get less glide angle with brakes, with less effect on their already slow descent rate)

(Sabre 1  135 when adding brake: got only bit better glide ratio with a bit of brake, then a lot worse as one got into heavy brake).

Different designs could be more efficient…   e.g. a special experimental high glide ratio 11 cell 170 from PD over 20 years ago that I jumped = 4.5 glide ratio in slight brakes

- Airspeed: (Bit more than Forward speed horizontally)

            25 mph student canopy

            46 mph small crossbrace  @ 1.9 loading (Icarus FX)

                        But: Deep brakes only 25 mph

- Sink rate:   

            800-1000 fpm big canopy  (13-17 fps) for students or novices

                        (On the lower side of that for modern ZP student canopies compared to ones like F-111 Mantas)

            1300 fpm Sabre 1  135 @ 1.25

loading

            1750 fpm (29 fps) small crossbrace @ 1.9 loading (Icarus FX)

In brakes any of those down to only 750 fpm

(So one can have the case of an instructor under a crossbraced canopy, maybe not a modern competition style one, being able to almost stay with a student or novice flying full speed under their rental canopy.) 

 


Note that glide ratios are only partially affected by the design of the canopy itself. Certainly a fat Parafoil with giant nose openings will be draggier than a modern highly elliptical swooping canopy with small nose opening and crossbraces for holding the shape well.

Much depends on the trim the designers have chosen, nose up or nose down. That's why many swoop canopies are so 'ground hungry', trimmed nose down for more speed to use for a long swoop & flare, not just floating around in the sky.

Another big factor is jumper size relative to the canopy. Scale the same parachute design down, and keep the same sized jumper under it, and now that jumper is in effect a larger draggy object below the canopy, dragging back from under the canopy even more as the speed increases with a smaller canopy. I saw some manufacturer test data way back that certainly showed the effect: Same canopy design at the same weight had a much worse glide ratio as it scaled to smaller and smaller sizes.

- The PD info in a youtube video that BMAC posted is good, comparing a Pulse and Katana 150 at the same loading. 
Note that it looks like the data hasn't been adjusted to sea level standard conditions -- it is just the data they got that particular day and speeds would be slightly faster than in my type of data.  Still a great comparison -- You can see how with brakes set, the Katana and Pulse are only somewhat different. Pop the brakes and now the Katana is super ground hungry in comparison. 

 

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4 hours ago, BMAC615 said:

I think the quickest way PD could do it would be to get four groups of five test jumpers (20 total) w/ FlySight and do one load for each canopy type of various sizes with test jumpers within the weight range aligned in their WL recommendations.

I'm sure PD has a wealth of this data, they just aren't sharing it. They do tons and tons of test jumps.

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