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Forward Speed at Opening
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John_Scher

Jan 12, 2019, 9:50 PM
Post #1 of 32 (2245 views)
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Forward Speed at Opening Can't Post

 
I am trying to determine if all canopies can be made to open with zero forward speed without seriously impairing the efficiency or effectiveness of that wing especially if that wing is designed for high forward speeds.

Scenario:
Let’s say the deep brakes have undergone appropriate adjustment and all other things are constant except for the wing design.


Atair OSP loaded at 0.65ibs/ft
(note: OSP is designed to have a slow forward speed at opening)

vs

Atair Vision loaded at 0.65ibs/ft
(note: Vision is a high glide, high forward speed canopy)


The genesis of this query is as a result of back reading thru a comment made by JasonF in 2004 where he mentioned:

"I do not believe it is possible to fly and land a Black Jack at the same speed as a FOX and if it were I believe it would take a lot of practice. Flying in brakes is necessary sometimes but it means you are deforming the wing and hence the more brake you have to use the less efficient your wing is going to be."

Now the BJ is similar to a Vision in that they are both high glide canopies and a Fox might be considered relatively similar in some respects to the OSP as it was a very docile canopy with a slow forward speed.

Thus I'm thinking that setting extra deep brakes on a Vision to offset its tendency to race forward at opening might well mean a deformed wing making it less than ideal especially at such a crucial moment i.e. next to a solid object.

So to be more specific I'm asking if now that we have access to specialised, dedicated canopies are high glide high speed canopies still ok for slider down, solid object jumps?

(This post was edited by John_Scher on Jan 13, 2019, 7:21 AM)

Fledgling

Jan 13, 2019, 1:51 AM
Post #2 of 32 (2205 views)
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Re: [John_Scher] Forward Speed at Opening [In reply to] Can't Post

John_Scher wrote:
I am trying to determine if all canopies can be made to open with zero forward speed without seriously impairing the efficiency or effectiveness of that wing especially if that wing is designed for high forward speeds.
Short answer... no. No forward speed equals falling not flying.

John_Scher wrote:
So to be more specific I'm asking if now that we have access to specialised, dedicated canopies are high glide high speed canopies still ok for slider down, solid object jumps?
I don't think this is a new argument at all. There have always been faster and slower canopies. There have always been higher glide or better sinking canopies. There have always been canopies that are best handled differently from other canopies on the market.
The real choice is what are you willing to jump, what is the best way for you to operate given your canopy choice, and do you actually have the skills necessary to jump your chosen configuration.
None of these choices are new, just the names on the side of the canopies has changed.

John_Scher

Jan 13, 2019, 6:20 AM
Post #3 of 32 (2150 views)
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Re: [Fledgling] Forward Speed at Opening [In reply to] Can't Post

Short answer... no. No forward speed equals falling not flying.
The real choice is what are you willing to jump, what is the best way for you to operate given your canopy choice, and do you actually have the skills necessary to jump your chosen configuration.
None of these choices are new, just the names on the side of the canopies has changed.



All canopies irrespective of wing design and trim can be made to stall. This stall point is the basis of how we set our deep brakes

Thicker profiled, slow forward speed canopies are designed to be efficient (generate lift) at and around this point whereas thinner faster canopies begin to lose efficiency due to the excessive amount of wing distortion as a function of a much deeper brake setting. This was the point of JasonF in 2004 however times and technology have changed. Modern canopy designers might utilise Top Skin Slats on both their fast and slow canopies. The Outlaw and OSP are relatively slow canopies and they utilise Top Skin Slats. The Heyduke and Vison are high speed canopies and they too utilise Top Skin Slats. I believe these slats are specifically designed to enhance slow speed performance (shift the stall point) which therefore might make a modern high speed canopy just as safe to open next to a solid object as a modern slow speed canopy. Perhaps with this technology the forward speeds and the wing efficiency at opening time are comparable?

(This post was edited by John_Scher on Jan 13, 2019, 7:23 AM)

TomAiello

Jan 13, 2019, 11:25 AM
Post #4 of 32 (2080 views)
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Re: [John_Scher] Forward Speed at Opening [In reply to] Can't Post

I think maybe we need some instrumentation and real numbers to really answer that question.

My personal experience has been that the high speed (Vision, Hayduke) slatted canopies shut down _almost_ (but not quite) as well as the low speed (OSP, Outlaw) slatted canopies.

We have clear video of these canopies achieving negative airspeed (PC in front of the leading edge) while maintaining pressure, which ought (with traditional aerodynamics) to be impossible. And that's even with the high speed airfoils.

My gut says that there are still differences in how far you can shut them down (with deep brake settings) at opening, with the Outlaw shutting down furthest and the Vision retaining the most speed (basically in reverse order of their top speed), but the differences are very small, such that personally I'm happy to make that trade off. If I lived in Moab and jumped slider down cliffs every day I'd probably still opt for the slower canopies (OSP, Outlaw) but for my actual uses (mostly bridges and slider up stuff, with occasional antennas and turbines, but almost no solid, slider down objects) I definitely prefer the faster (Hayduke, Vision) slatted canopies.

John_Scher

Jan 14, 2019, 4:36 AM
Post #5 of 32 (1934 views)
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Re: [TomAiello] Forward Speed at Opening [In reply to] Can't Post

 


Tom,

I think what you've said is pretty much how it is. Slatted technology is all still a bit new. Aerodynamic logic says one thing and yet actual experience ie negative airspeed with a pressurised canopy says another.

As of now It's down to "Gut Feelings" rather than science. Wait and see I suppose. Get more feedback from actual jumpers as time goes on.

Wouldn't it be fantastic if we really are seeing the convergence of high glide characteristic's with slow speed benefits.

TomAiello

Jan 14, 2019, 6:04 AM
Post #6 of 32 (1906 views)
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Re: [John_Scher] Forward Speed at Opening [In reply to] Can't Post

When selecting a canopy, there is still the question of full flight speed and flare power to consider as well.

Will a fast canopy flown slower (to match the speed of a slower canopy) flare as well, better or worse than a slow canopy flown at it's top speed? Which is going to flare better on a steep accuracy approach?

BASE canopies continue to develop. I'll be interested to see where they go in the next ten years.

Fledgling

Jan 14, 2019, 9:10 PM
Post #7 of 32 (1790 views)
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Re: [John_Scher] Forward Speed at Opening [In reply to] Can't Post

John_Scher wrote:
All canopies irrespective of wing design and trim can be made to stall. This stall point is the basis of how we set our deep brakes

Thicker profiled, slow forward speed canopies are designed to be efficient (generate lift) at and around this point whereas thinner faster canopies begin to lose efficiency due to the excessive amount of wing distortion as a function of a much deeper brake setting.

Yes yes. All basic 101 stuff. Stating the obvious doesn't change the fact that not flying equals no more lift.
Your question was: "I am trying to determine if all canopies can be made to open with zero forward speed without seriously impairing the efficiency or effectiveness of that wing especially if that wing is designed for high forward speeds." The only answer to this is "No" because as we know, No airspeed means you are not flying and therefore your parachute is no longer acting like an airfoil. Just because we have canopies that can sustain a stalled configuration without collapsing it does not mean they are "flying". Yes we can use techniques to maneuver our canopy in this state but it's effectiveness is greatly reduced and by the criteria of your question it would be considered seriously impaired.

I also have an issue specifically with the following 2 points you are trying to make (I am unsure if you actually understand the concepts and it's lost in translation or you actually don't understand airfoils)

1)
John_Scher wrote:
This stall point is the basis of how we set our deep brakes
Thicker profiled, slow forward speed canopies are designed to be efficient (generate lift) at and around this point
This is an incorrect statement. Thicker airfoils are no more efficient at their stall point than any other canopy ever created. They will be most efficient in generating lift at full flight because that's how airfoils work (increased airspeed equals increased lift). However, Thicker airfoils are better able to provide lift at slower air speeds than thinner wings. Thicker/lightly loaded airfoils also have a less dramatic stall response too. For this reason we use them in BASE because they perform better in the realm that we are using them.

2)
John_Scher wrote:
whereas thinner faster canopies begin to lose efficiency due to the excessive amount of wing distortion as a function of a much deeper brake setting.
Again, an incorrect statement. Thinner airfoils need to maintain a higher minimum airspeed to create the pressure difference necessary to generate lift. It is for this reason that they can't be flown as slowly as thicker airfoils, not because any "Wing Distortion" (even though you are correct that the wing does distort when in deep brakes).

Fledgling

Jan 14, 2019, 9:14 PM
Post #8 of 32 (1789 views)
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Re: [TomAiello] Forward Speed at Opening [In reply to] Can't Post

TomAiello wrote:
We have clear video of these canopies achieving negative airspeed (PC in front of the leading edge) while maintaining pressure, which ought (with traditional aerodynamics) to be impossible.

I think it is important here for you to ensure that people reading this statement understand that when you say "negative airspeed" you do not mean to say the parachute is "flying" backwards.
Moving backwards and not collapsing due to venting is still falling and not flying ie. it is not a lift generating mode.

Colm

Jan 14, 2019, 11:03 PM
Post #9 of 32 (1775 views)
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Re: [John_Scher] Forward Speed at Opening [In reply to] Can't Post

Just curious. When you say "efficiency," do you specifically mean L/D ratio? Or are you using it more colloquially? (and if so can you clarify)

In general I agree with Fledgling, the answer to your original question is "no." But maybe a better way to ask it is, what makes some canopies great, and others, pieces of shit, at slow speeds?

Slats (in theory) encourage topskin surface laminar air flow at high AOA, but if forward airspeed is zero, there is no laminar topskin flow no matter what you do.* If it still stays inflated, thank the vents. If you can still steer, it's because you're spilling air differentially.

I think it's a great question you ask because everybody has a different impression of what slats do.

(*The slat will catch a miniscule portion of air that spills out from in front of the leading edge, and redirect it backwards a foot or so, but I doubt that counts for anything. I'd love to be corrected if I'm wrong tho)

TomAiello

Jan 15, 2019, 8:31 AM
Post #10 of 32 (1708 views)
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Re: [Fledgling] Forward Speed at Opening [In reply to] Can't Post

Fledgling wrote:
TomAiello wrote:
We have clear video of these canopies achieving negative airspeed (PC in front of the leading edge) while maintaining pressure, which ought (with traditional aerodynamics) to be impossible.

I think it is important here for you to ensure that people reading this statement understand that when you say "negative airspeed" you do not mean to say the parachute is "flying" backwards.
Moving backwards and not collapsing due to venting is still falling and not flying ie. it is not a lift generating mode.

Yes. I guess I thought that would be obvious. Positive airspeed over the wing surface is a requirement for lift generation.

Creating a separate airflow at the actual surface of the wing is the basis of how the slat systems work, though. They are an effort to keep airflow moving faster than the overall airspeed, to maintain lift at speeds below the point where airflow would naturally separate from the airfoil. I believe that's what John's initial point was--that slat systems help the thinner (relative to BASE canopies) airfoils fly "more like" the thicker airfoils with regards to low airspeeds.

In highly speculative theory it might be possible to create a slat system on both top and bottom surfaces that would create an airflow along the wing surfaces that would move in the direction opposite the overall airspeed of the canopy. It would be something like putting high pressure air nozzles on the surface to push air in the "lift creating" direction even though the aircraft was flying backward. You would still need to find a way to create inflow to redirect, though (maybe some kind of airlock arrangement near the tail?). At any rate, I'm not aware of anyone actually trying to create such a system, even experimentally, and it would take a lot of lab and wind tunnel time to even begin to investigate the idea.


(This post was edited by TomAiello on Jan 15, 2019, 10:57 AM)

John_Scher

Jan 15, 2019, 9:15 AM
Post #11 of 32 (1693 views)
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Re: [Fledgling] Forward Speed at Opening [In reply to] Can't Post

“Yes yes. All basic 101 stuff. Stating the obvious doesn't change the fact that not flying equals no more lift.”

“(I am unsure if you actually understand the concepts and it's lost in translation or you actually don't understand airfoils)”



Let me start by stating that I’m not an expert in anything. I studied electrical engineering not aerodynamic engineering. I most certainly don’t profess to be an expert in air-foils and equally I’m not an expert in combustion engines but I drive cars every day. I have made many jumps over the years and have jumped numerous different wings including Para Commanders, 5cell Stratostars, 7cell Clouds, 21 cell Velocities and currently jump a BJ280. So as much as I’m not an expert in aerodynamics I do have some idea of various wings and concepts. I’m British so I don’t think I’m lost in translation and finally I apologise if I’ve offended you in some way as you sound bitter.

If you are an expert in this field, really did study aerodynamics and do have a solid understanding of this subject it might be helpful to this debate if you offered your expertise in a way so that we can all learn from you.

You have raised some good points i.e. not moving forward = not flying and I will remember this next time I open next to a solid object, slider down with my brakes set near to the stall point.

John_Scher

Jan 15, 2019, 9:28 AM
Post #12 of 32 (1688 views)
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Re: [Colm] Forward Speed at Opening [In reply to] Can't Post

Just curious. When you say "efficiency," do you specifically mean L/D ratio? Or are you using it more colloquially? (and if so can you clarify)

I believe that when Jasonf made the statement mentioning reduced efficiency he was referring to its ability to produce lift due to two factors;

1 - the distortion of the wing due to applied brakes in an effort to slow it down
2 – the reduction of forward speed again in an effort to slow it down

I don’t really know if that can be termed as Lift to Drag ratio or what it is only that if one slows down a high speed canopy by applying brakes then that canopy is not flying optimally as it was designed and is actually less “efficient” which I interpret to mean providing less lift.

TomAiello

Jan 15, 2019, 11:03 AM
Post #13 of 32 (1665 views)
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Re: [Colm] Forward Speed at Opening [In reply to] Can't Post

Colm wrote:
*The slat will catch a miniscule portion of air that spills out from in front of the leading edge, and redirect it backwards a foot or so, but I doubt that counts for anything. I'd love to be corrected if I'm wrong tho

It should be possible to test that by sewing extra tabs along the top surface of a test canopy and stalling it, to see how far back the airflow from the slat reaches.

In theory the "float valve" location used by squirrel, would be more likely than the front mounted slats (used by both Atair and Squirrel) to direct airflow all the way back to the tail. In theory, if that airflow reached the tail seam, and if there was a corresponding bottom skin airflow, you could still create some lift there. I'd expect it to be very little lift, but there are so many speculations in that chain that the only real way to find out would be to start hacking up canopies and testing it.

Fledgling

Jan 15, 2019, 5:02 PM
Post #14 of 32 (1611 views)
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Re: [John_Scher] Forward Speed at Opening [In reply to] Can't Post

John_Scher wrote:
I’m British so I don’t think I’m lost in translation
I guess I meant that sometimes you can miss the point you are trying to convey when you write something vs face to face conversation. Not necessarily an English non English thing. Aerodynamics can be very confusing to parachutists (do they actually understand the info but struggle to express their knowledge? do they have no idea at all? or do the think they know but are really just perpetuating common mis-conceptions?) and without actually knowing the level of someones knowledge it's hard to know where to start a conversation.


John_Scher wrote:
and finally I apologise if I’ve offended you in some way as you sound bitter.
Not sure what gave you that impression. Again sometimes things are mis-interpreted in writing.


John_Scher wrote:
If you are an expert in this field, really did study aerodynamics and do have a solid understanding of this subject
Parachutes have been my entire life for the last 18 years. I am a career Instructor and Master Rigger. I work with this equipment daily. I repair and maintain this equipment daily. I have designed, test jumped, and manufactured various forms of this equipment. I am a total nerd when it comes to the history of parachute design,construction and evolution. I have spent countless hours teaching people about their equipment and how to better understand and use their equipment and you would be surprised by just how little people actually know and understand their gear and its functions. Between Skydives and BASE jumps I have made over 14,000 parachute descents as well as numerous hours of paraglider flights as well as more recent forays into sail plane flying. I have jumped more types of wings than I would bother listing here, but for the sake of metrics I have jumped canopies from 69ft to 500ft at wingloadings of 0.5 up to 3.5lbs/ft. So while I have never been to school to study aerodynamics I would claim that I have as you put it "a solid understanding of this subject".
(Enough of that though please. I'm not a narcissist and it actually grosses me out to write in such a self aggrandizing manner).

John_Scher wrote:
it might be helpful to this debate if you offered your expertise in a way so that we can all learn from you.
I thought my point by point rebuttal of your post including the issues with your comments as well as the correct reasoning was doing exactly that.

Fledgling

Jan 15, 2019, 5:07 PM
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Re: [TomAiello] Forward Speed at Opening [In reply to] Can't Post

TomAiello wrote:
Yes. I guess I thought that would be obvious. Positive airspeed over the wing surface is a requirement for lift generation.

You teach enough students to know better :-)

Colm

Jan 15, 2019, 9:05 PM
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Re: [John_Scher] Forward Speed at Opening [In reply to] Can't Post

OK i think i'm with ya. Well, I think it may come down to the difference between how canopies behave when sinking in, versus flaring from full flight.

Here's the flare-from-full-flight sequence: apply the brakes relatively swift & smoothly. This does 2 things. One, it directly changes the chord line of the wing in a way that increases AOA and (I assume) the coefficient of lift. This increases lift but also drag. Two, by increasing drag, the parachute decelerates horizontally, but the suspended jumper still has momentum, so the jumper swings forward. This further increases the AOA, and yields even more drag. More AOA means more lift (up to a point), and because one is well practiced in flaring parachutes, one coordinates the flare perfectly so the lift is constant (you are "planing out") despite airspeed decaying. With lots of forward airspeed to begin with, you have intact laminar airflow over the topskin, until you slow down enough that you would stall if you didn't put your feet down on the ground. The key here is, you start with a good attached upper boundary layer of airflow, and the "low-speed lift devices" (i.e. slats, float valves) can help you preserve that laminar flow as you decelerate.

Now comparing that to "sinking it in". You have very slow airspeed to begin with (let's assume it's not zero, though it could be). When you add additional brake input, your wing deforms again, but without a lot of forward motion the effect of drag is going to be much less. You aren't going to have any dramatic pendulum effect of the jumper swinging forward, so the additional AOA never occurs. Instead you just lose whatever last few knots of forward airspeed you may have had, and maybe your sink rate slows a bit because you are trapping more air under your canopy now. It's primarily a drag device slowing your descent, not anymore a lift device (as Fledgling pointed out). Unlike the first scenario, you don't really have a coherent upper boundary layer (it's all turbulence) so I'm skeptical that float valves and slats would be as impactful.

So to re-hash. In the first scenario, I can envision low-speed lift devices helping a lot. In the second scenario, I think slats are probably, if anything, only good for being a ZP upper leading edge that keeps the nose inflated but not really adding anything to lift. In that scenario, vents save the day.

Tom's comment about sewing tabs (or yarn) to the topskin to test this would be a really awesome experiment.

As for float valves. If they help keep the canopy inflated at near-zero airspeed, then the overall benefit to drag might outweigh the fact you are leaking air out the top. I wonder if they don't function more like "slotted flaps" in reality though-- again, nice for preserving your upper boundary layer as you decelerate. But if you are sinking it in there's no upper boundary layer to preserve, because you already caused it to separate by sinking in.

In reply to:
So to be more specific I'm asking if now that we have access to specialised, dedicated canopies are high glide high speed canopies still ok for slider down, solid object jumps?
I don't know, but I do know that some canopies are a lot better suited than others, to open with near-zero airspeed (similar to second scenario), and I want the one that is best-tuned to that environment. If you can get your high performance canopy to be stable, controllable, and have near-zero airspeed upon opening, sure have at it! But based on my experience designing exactly zero parachutes, I suspect the tradeoffs in design will probably make those canopies always a little less effective than the OSPs and Outlaws of the world.

I dunno. Thoughts?

Fledgling

Jan 16, 2019, 5:48 AM
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Re: [Colm] Forward Speed at Opening [In reply to] Can't Post

Colm wrote:
So to re-hash. In the first scenario, I can envision low-speed lift devices helping a lot.
It sounds like you are trying to suggest that when flaring from full flight you would see a benefit and increased lift from the slats on a canopy. If so I would have to dis-agree with you on the basis that if you are already at full flight you probably aren't going to be concerned about delamination of the airflow.

Colm wrote:
But if you are sinking it in there's no upper boundary layer to preserve, because you already caused it to separate by sinking in.
I would have to say this is also incorrect. "Sinking it in" is still flying. Just really really slow flying, usually in reference to ground speed not airspeed and much easier to achieve on a windy day. If the airflow was zero and already truly separated from the top skin as you suggested then you would be stalled and begin falling. We may get away with this from time to time but your vertical descent will rapidly build once the canopy goes from being a lift device to a drag device. This is where slatted canopies truly shine as the slats prolong delamination of the airflow in slow speeds allowing a canopy to fly slower for longer before stall onset occurs.
So in both of your 2 points it sounds like you are trying to discuss what slats can do for flare power which was not their function. Their function was always to maintain lift (or a flying wing) at slower air speeds by encouraging laminar airflow as you already noted.

Fledgling

Jan 16, 2019, 6:02 AM
Post #18 of 32 (1523 views)
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Re: [John_Scher] Forward Speed at Opening [In reply to] Can't Post

John_Scher wrote:
a comment made by JasonF

So after re-reading your original post it sounds like you are taking his post (that really sounds like it is more related to AOA change during flaring) and trying to apply it to canopy control immediately after opening in a deep brake configuration? Based on the words deep brakes, canopy distortion and less efficiency.
Is this correct before I bother writing more?

John_Scher

Jan 16, 2019, 7:14 AM
Post #19 of 32 (1507 views)
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Re: [Fledgling] Forward Speed at Opening [In reply to] Can't Post

Fledgling wrote:
John_Scher wrote:
a comment made by JasonF

So after re-reading your original post it sounds like you are taking his post (that really sounds like it is more related to AOA change during flaring) and trying to apply it to canopy control immediately after opening in a deep brake configuration? Based on the words deep brakes, canopy distortion and less efficiency.
Is this correct before I bother writing more?


jasonf Apr 16, 2004, 12:58 AM
As an experienced Australian jumper I would recommend a canopy that is best suited to classic accuracy style landings. The following characteristics would be highly desirable:
• Able to sink with little forward speed in nil wind conditions
• Forgiving flare
• Easy to fly
• Consistently land with little forward speed in nil wind conditions

I have not jumped a Blackjack but I have seen them jumped and consider their forward speed excessive, unfortunately this applies to most BASE canopies with respect to jumping in Australia. I don't believe the sites we jump in Australia are any harder that those jumped in other countries. We just jump hard sites on a regular basis due to a lack of objects at the easier end of the spectrum. The height of the objects is not the big issue; however the nature of the landing areas we regularly use is. Not to many of the landing areas are flat or have grass. Jason Fitz-Herbert


TomAiello Apr 16, 2004, 6:54 AM
In reply to: ...forward speed excessive...
Can you elaborate on this? I'm generally of the opinion that forward speed can always be eliminated by flying in deeper brakes. For this reason, I've always seen more available forward speed as always positive, since it just means a wider performance range that I can choose not to use. So long as the canopy flies well slowly (i.e. in deep brakes) I haven't seen a situation where I thought having forward speed available if I chose to use it was a bad thing.


jasonf Apr 22, 2004, 3:34 PM
In reply to: "I've always seen more available forward speed as always positive".
You definitely have a valid point, a faster canopy has a wider range of possible speeds. It also enables better penetration into strong winds and has potential to generate more lift during flare. If two canopies were identical in every aspect of their performance only one had more available forward speed - then I would choose it. However, in reality if two canopies have different forward speeds then they will also behave differently in other ways. There are many different factors that need to be considered when selecting a canopy such as - nature of landing areas primarily being used, types of approaches needed for landing areas, available height/time to set up for landing, type of jumps being performed, jumper's background and personal preference etc. and how the canopy performs in these areas. I do not believe it is possible to fly and land a Black Jack at the same speed as a FOX and if it were I believe it would take a lot of practice. Flying in brakes is necessary sometimes but it means you are deforming the wing and hence the more brake you have to use the less efficient your wing is going to be. In my opinion a faster canopy has the potential to result in the following disadvantages:

• Harder to sink at steep angles for extended lengths of time (as required when sinking into a small landing area surrounded by 20ft trees)

• Landings with little forward momentum tend to be harder to achieve

• Landings with forward momentum require several steps to be taken when touching down (more suited to landing areas without large rocks & not on steep slopes)

• Object strikes when landing have the potential to be harder

• Has potential to generate more speed in turns

• Potential to surge more erratically when transitioning from a deep sink to drive

• More difficult to establish ideal brake settings for various openings (slider down, sub-terminal slider up etc.) due to increased sensitivity

• Less time to make decisions while under canopy

In Oz the landing areas are primarily steep slopes or covered in large rocks and sometimes both. When your feet touch the ground you want as little
forward speed as possible. The landings I have seen in nil wind with the Ace/BJ indicated that the canopy planes out in the flare. I have not been in a position to measure the speed but when you hear the suspension lines whistle through the air, the thought of jumping one is Oz scares me. Jumpers do own Black Jacks in Oz and maybe one of them will post how they feel. I suspect they would rather have a slower canopy.

(This post was edited by John_Scher on Jan 16, 2019, 7:21 AM)

TomAiello

Jan 16, 2019, 7:26 AM
Post #20 of 32 (1501 views)
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Re: [Colm] Forward Speed at Opening [In reply to] Can't Post

Colm wrote:
So to re-hash. In the first scenario, I can envision low-speed lift devices helping a lot. In the second scenario, I think slats are probably, if anything, only good for being a ZP upper leading edge that keeps the nose inflated but not really adding anything to lift. In that scenario, vents save the day.

Although the theory seems sound, my experience in the real world is that slats (or float valves) do help the canopy in a "sink in" scenario, both by reducing the minimum attainable forward speed (before stall) and by improving flare from deep brakes. One of my friends actually retrofitted slats onto a Raven to test the "before and after" of slats on exactly the same canopy. I don't have any actual measured data, but my subjective impression that the flare from deep brakes was improved was very strong.

It's also worth noting that while I agree with you on the value of bottom skin inlets in this ("sink in") scenario, the designer of the first commercially available canopy with valves on the bottom skin told me that he did not believe they had any effect on steep approaches--only on opening pressurization. Personally, I disagree with him, but that opinion is definitely worth considering, given the source.

TomAiello

Jan 16, 2019, 7:33 AM
Post #21 of 32 (1496 views)
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Re: [John_Scher] Forward Speed at Opening [In reply to] Can't Post

It sounds like you are asking;

"would Jason have had a different opinion if he had a slatted canopy option available?"

Am I reading you correctly?



As an aside; Jason was a good friend of mine, and I had a lot of respect for his technical expertise, but remember that he was sponsored by the company that made the FOX, and the brand wars were in full force then, as now, but were primarily CR v. BR (i.e. FOX v. Blackjack, at that moment in time). It's possible that the market context might have had some impact on the opinions he presented in that post.

Colm

Jan 16, 2019, 10:46 AM
Post #22 of 32 (1474 views)
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Re: [Fledgling and Tom] Forward Speed at Opening [In reply to] Can't Post

I'll start by admitting that "sinking it in" is not the same as "pounding it in under a pressurized canopy", and while I was describing more of the latter purely for theoretical discussion, I'm not saying its a sound practice :) I was not at all trying to discount the benefit of slats at slow airspeed, that's obviously why they even exist in the first place.

Fledgling wrote:
It sounds like you are trying to suggest that when flaring from full flight you would see a benefit and increased lift from the slats on a canopy. If so I would have to dis-agree with you on the basis that if you are already at full flight you probably aren't going to be concerned about delamination of the airflow.
Not what I meant to say. To clarify, I'd expect the maximum benefit from the final stages of the flare when AOA has become very high and you are hoping to avoid boundary layer separation as long as possible. I agree with you that it wouldn't make sense at full flight or in the early flare. Slats should also help you regain laminar flow sooner when recovering from stall, too. Sorry for the poor description.

Fledgling wrote:
I would have to say this is also incorrect. "Sinking it in" is still flying. Just really really slow flying, usually in reference to ground speed not airspeed and much easier to achieve on a windy day. ... it sounds like you are trying to discuss what slats can do for flare power which was not their function.
See my top sentence. How you said it makes a lot more practical sense than me. (Though see my last paragraph, I brought up "stalling it in" instead of "sinking it in" for a reason)

TomAiello wrote:
Although the theory seems sound, my experience in the real world is that slats (or float valves) do help the canopy in a "sink in" scenario, both by reducing the minimum attainable forward speed (before stall)
Reducing minimum attainable forward speed before stall was exactly what I was trying to say, too. I was trying to show more extreme opposite scenarios. Obviously in practice "sinking in" is not stalling (if you are doing it right) and there may be some wind helping too. In that case yes absolutely the slats will be great because they are preserving that laminar flow, as long as possible. Once you are in a pressurized stall though, (and yeah going to pound in, at this point) I think the slats revert to the benefit of helping keep the nose open, and then if you do regain some forward speed they will immediately benefit reattachment of the boundary layer. Does that make any more sense? (It might not, again, all postulation, criticize away)

TL;DR - Agree with Fledgling, slats help in slow flight not fast flight. Agree with TomAiello, they benefit when flaring from deep brakes. When I wrote "sinking it in" I really meant on the very verge of stall, or maybe even stalled which was maybe confusing. I'm just pointing out the obvious that at a slow enough speed, even slats will stop preserving lift. But maybe will still help to keep the opening of the nose inflated and then will help you recover sooner.

So why talk about the "extreme end" which is impractical for landing? Tying it back to the OP. It's not actually about sinking it in & landing, it's about jumping "solid slider down objects"-- The OP brought up the scenario of object avoidance upon opening, Here there is a higher likelihood of truly stalling the canopy, and now you have to recover from that. I've had 180s, but I've had a lot more actual practice with very steep approaches, so it's just an alternate way for me to think about it.

Colm

Jan 16, 2019, 11:14 AM
Post #23 of 32 (1465 views)
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Re: Forward Speed at Opening [In reply to] Can't Post

I guess my prior post wasn't written too clearly. But let's identify 3 scenarios: Full flight, pressurized stall, and then somewhere in between: flying in deep brakes.

Full flight: Worst scenario when you have a 180 after opening, but best way to start your landing
Pressurized stall: Best scenario to create when you are imminently faced with object strike, so you can prevent forward movement or slide backwards. But, worst way to come in for a landing.
Deep brake flight: Akin to after opening, before you release your brakes. After a 180, you can transition to doing whatever needed to avoid an object strike. Not the optimal way to land, but often necessary depending on the LZ.

Where I most want slats or other high-lift devices, is in the latter two situations. The OP was asking if maybe such technology is unnecessary now in the age of high performance BASE canopies which seem to "do it all" quite well in some people's opinions.

Being that aerodynamic design is all about balancing tradeoffs... Personally, if I want the best tool for a job, and if my job is to avoid object strikes, I go with the specialized canopy. But others may (with excellent reasons) prefer a "one canopy to do it all" and there are certainly some decent items on the market. Personal choice ultimately, no?

TomAiello

Jan 16, 2019, 1:37 PM
Post #24 of 32 (1435 views)
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Re: [Colm] Forward Speed at Opening [In reply to] Can't Post

Colm wrote:
The OP was asking if maybe such technology is unnecessary now in the age of high performance BASE canopies which seem to "do it all" quite well in some people's opinions.

I didn't read the OP that way.

I thought he was saying that the slat/float valve technologies help the higher performance airfoil mimic the flight characteristics of the lower performance airfoil, such that higher performance airfoil+slat was approaching the performance of lower performance airfoil or even lower performance airfoil+slat.

I did not read him as saying that the slat technologies are unnecessary with higher performance airfoils, but rather that they are _more important_ with higher performance airfoils because they make the higher performance airfoils more useable for a wide range of scenarios.

Fledgling

Jan 16, 2019, 5:38 PM
Post #25 of 32 (1410 views)
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Re: [John_Scher] Forward Speed at Opening [In reply to] Can't Post

So again can you please answer this question:
In reply to:
So after re-reading your original post it sounds like you are taking his post (that really sounds like it is more related to AOA change during flaring) and trying to apply it to canopy control immediately after opening in a deep brake configuration? Based on the words deep brakes, canopy distortion and less efficiency.
Is this correct before I bother writing more?

Because your last post didn't address this in any way and reads like it is mostly referring to AOA change through jumper inertia, accidental or otherwise. Just trying to nail down what your exact point is to see if I am on track with your thinking.

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