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https://vimeo.com/303395697

It seems the technology to fly backwards is available.

It depends on how you define "flying" doesn't it?

I have clear video of Vision and Outlaw (as well as Hayduke) canopies in a similar mode, as I said early on in that other thread.

Are they actually generating lift? Is the generation of lift your definition of "flying"? Or is your generation of "flying" that the parachute retains internal pressure?

I think we need to establish some general definitions, then find a way to measure the actual lift generation. I'd love to see (just for starters) some streamers on the surface of a canopy in that mode, so we can see where the airflow is going. Then I'd like to see some data on the motion of the canopy in various flight modes (full flight and steep sink at a minimum) and compare the descent rates to the descent rate in the mode shown in the photo.

In general, promotional materials created to sell an item are a poor place to get unbiased technical data about that item.

In reply to:

I have clear video of Vision and Outlaw (as well as Hayduke) canopies in a similar mode

Squirrel seem to state (I think) that this mode is specifically due to float flaps which I don't think the Vision has.

They have severally stated it is flying backwards and when I watched the video it really looks like it is. It looks like it's generating lift as it does so.

I understand what you are saying but it seems to be far more pronounced than I had imagined.

See my previous comment about promotional materials.

In our use, the Vision, Outlaw, Hayduke and OSP all seem to perform quite similarly in this mode. The Vision was the first canopy that we saw doing this, and we went back and tried them all, with very similar results in each case.

In theory, I do believe that the slat placed near the rear (the "float valve") should be more efficient than the slat placed near the front, but in actual practice, the flight characteristics seem very similar.

Note that I'm using "float valve" in quotes because the term slat is commonly used and accepted in the wing design literature, but the term "float valve" is not. I believe that Simon (the designer of the Outlaw) may have coined the term to describe his use of a slat placed further back, in an effort to differentiate it from the rear located "slot" (which is not quite a slot as generally accepted in wing design) on the PD Zero accuracy canopy.

Tom,

The Squirrel canopies seem to have both.

The Vision only has Slats.

I'm not meaning to contest anything, I'm trying to get my head round this new technology.

Your photos show how Squirrel uses them.

Where did you find those labels? I honestly haven't seen them used that way in any wing design materials. The only terms that seem to be widely agreed on in the aero text books (for these kind of devices) are slot and slat (which are two different features).

I've also never seen a photo of a parachute used to illustrate those points in any aero text, so I'm a little skeptical that they come from the general literature.

The pictures plus labels plus descriptions are on the Outlaw sections of the Squirrel Web site.

Please rewatch the video mentioned above. I find the backward flying section quite dramatic and convincing.

"New" may be relative. The origins of the technology are in 1930's aircraft (I believe they first appeared on German reconnaissance aircraft to aid in low speed flight necessary for observing ground troops), and this class of technology has been present in BASE canopies for 10 years or so (since the OSP was released).

I tend to be hesitant to adopt the terminology of one company, when it's not in use more generally. Your original response to my note about why I was quoting a term (to simply post photos which were apparently drawn from marketing materials) with no explanation, seemed a little odd to me. I apologize if I misinterpreted your original meaning.

I've shot several pieces of video that look pretty much exactly like that, before that particular video was released on the internet. I mentioned them several days ago in your other thread.

I don't really need to re-watch them. I've watched them backward, forward and in slow motion, many times.

We're still basically just discussing;

(a) How to define "flight", and;
(b) Whether actual lift generation is occurring in this negative airspeed mode.

Those videos (which I am extremely familiar with--remember that we were the first people to start looking at them) don't give me a lot of insight into either of those questions.

If we re-define the term "flight" to mean something like "with a descent rate that gives a survivable landing for an average human" we can say for certain that there is "flight" occurring. But it might be more useful to describe what is actually happening in more precise language, rather than trying to change the commonly accepted meaning of widely used terms to make up for the fact that we (in which I include myself) simply haven't done sufficient research to give a better answer. That approach seems to me to involve some serious intellectual laziness, though.

Video can be dramatic and visually interesting, but in general it does not provide hard data.


I think we can all agree that slat (and slat-like) technologies improve BASE parachutes.

At this point it seems like you're arguing over semantics, and trying to re-define commonly used aerodynamics terms to bring them in line with either what you are hoping to be the case, or what you are implying from promotional materials. What's the point of that argument?

I saw a lot of people going backward this summer (Hayduke, Outlaw, Vision).
I never saw a really inflated canopy during this maneuver. I still think it is mostly a stall moving backward as the paragliders are doing with their gliders or like a round canopy with controls.

Ok

We've been able to get them to hold pressure while moving backward. They have a higher descent rate than a canopy that is in forward flight (generating lift) but it seems to be a state they can maintain--they are not in the process of depressurizing.

In functional terms, I guess the question is what descent rate is acceptable in various situations, and which situations the descent rate in this (negative airspeed) state is low enough to be useful. Is it slow enough that it's useful in an object avoidance situation? I'd say it definitely is--it gives the jumper a much better chance to turn the canopy around without striking the ground. Is it slow enough to land? That's an interesting question, and one I'm personally not willing to investigate without a lot of water landing rehearsal to gather more information.

For me when you are facing the wall it is better to go backward than forward, specially when you are too close to turn :D

You really have pressure like when going forward or even stalling ?
All the backward I saw the canopy was inflated but not pressurized.

I think I'm confused on the difference between inflated and pressurized, as you are using them.

Can you tell me what the difference is between an inflated canopy and a pressurized one? Are you talking about pressure inside the parachute? Or a parachute that has full expansion of the bottom skin but has lost pressure within the cells?

Pressurized means the fabric is tight by the pressure.
Inflated means it has its global shape, but it can not have pressure inside, like a canopy after landing when it has no more forward speed.

Ok. Understood.

Then yes, we've gotten the canopy to hold internal pressure simultaneous to negative airspeed (PC forward over nose).

I'm tempted to go skydive some canopies and play around with them in this mode. I'd be especially interested to see the difference between achieving and maintaining this mode in comparisons between slatted and non-slatted canopies. Using instruments to measure descent rate would be pretty cool, too.

Slat: a deployable/retractable feature of the wing leading edge that temporarily increases a wing's stall AOA (Often found on large, swept-wing turbofan aircraft)

Slot: a fixed feature of the wing leading edge that permanently increases a wing's stall AOA. Usually found on STOL aircraft

Slat: a term borrowed by base jumpers to describe a piece of ZP sewn over the upper nose leading edge, which is not exactly either of the above definitions, but may be closer to a slot than anything else.

Float valves: Sounds like they use the tangential blowing effect, or are akin to blown flaps, but I haven't studied the Hayduke so I'm just guessing. Float valves definitely aren't slots or slats in any conventional sense.

But BASE is unconventional. What's in a name...

This guy flew backwards better than all these previous videos shown...And he did it way back in the day from the looks of the video . ;)

https://www.youtube.com/watch?v=7UOMALNaZlA

It is understood that these slots or slats (whatever they are called) in the top skin of the canopy seem to offer some advantages which were not available previously on canopies such as my BJ etc. They seem to offer greater stability in deep brakes, more flare power from deep brake approaches and a bunch more.

One manufacturer (Squirrel) advertises their canopy's ability to fly backwards as a function of these slots/slats and although the canopy may not be flying in the true sense, does seem to Reverse in a stable controllable condition rather than stalling and collapsing. As mentioned by Antoine, the ability to Reverse away from an object is interesting and if a minimum loss of altitude can be achieved, makes it highly desirable. Reversing might also be used in setting up the landing pattern, object avoidance etc.

This technology might well be the future of canopy design considering all of the advantages that it offers so it seems worthy of further investigation and understanding.

Squirrel has two lots of slots/slats located in completely different parts of the canopy whereas Atair only has one lot. Both Squirrel and Atair have what they call Slats located at the front of the canopy whereas Squirrel has another set which they call Float Flaps located at the rear of the canopy. As Tom mentioned the nomenclature is not important however the concepts are.

Squirrel state that these rear positioned Float Flaps give rise to flying backwards but Tom has witnessed the same ability from the Atair canopy which doesn’t have them so clearly the rear mounted Float Flaps are not the sole reason for flying backwards. So what do they do? Squirrel, on their web site state:

* FLOAT FLAPS at rear-chord for sink performance
(and Reverse flight as per video commentary)

* Expanded SLAT System at centre span for deep brake flight

Q1 - Sink performance and deep brake flight seems almost like the same thing to me?

Q2 - Is the sink performance and deep brake flight of the Squirrel product which has two sets of slot/slats/flaps better than the Atair product (which only has one set)?

Q3 - If the Squirell product really is better at sink performance and deep brake flight then that might imply that more is better so why not have three lots of slot/slats/flaps? Add another set in the middle


A jumping buddy said to me a year or so ago that seven cell canopy design is straightforward, nothing to it.
I tend to disagree.

IMO an advantage of the float flaps is that is allows in deep brake to keep the top skin of the canopy in its place instead of pulling it back with the trailing edge.

That said when you are saying why not put more and more ?
All this stuff is fun but useless in most (all ?) situations.
More stuff = more work = higher price and fabric

About the "flying" backward I have a beginner (not very experienced skydiver and not paraglider) who on his 30th jump try to do it with his Vision, and was able to go back for seconds and do turns 2 jumps later.
Hayduke looks and is very probably cool, but I don't know if it is easier, it has been promoted so more people tried it and I think this is why more people think it is easier.

As Tom noted, this would depend on what you define as "flight". I would say they are not flying but maintaining a somewhat pressurized deceleration device. Yes maneuvering in this configuration is an awesome ability to have available in a BASE parachute but lets not pretend it is actually flying.

I am skeptical that they coined anything because the concept was lifted from paragliding to which we know the Squirrel factory has close ties with. And for the record paragliders simply lifted the concept from general aviation. As with everything we have, while new and exciting to us, it is all mostly just re-purposed technology.
Read: Blow Flaps/Jet Flaps, and to some extent Slotted Flaps.
Edit: Slottted Flaps.

A FlySight would be handy to determine if:
a) the canopy reaches a standard descent rate in reverse mode ie. not continue to accelerate vertically while in reverse mode,
and b) if it does achieve a standardized decent rate in reverse, just how fast a vertical descent it is and whether it is worth the risk to land in that configuration.
Should be easy enough to determine if somebody wanted to do the leg work.
Edit: spelling.

Just for the sake of history here. We know that the vast majority of lift is generated at the leading edge of an airfoil, especially in regards to speed of airflow. The new designs do this by what we have termed "Slat" technology and is most noticed in slow flight/higher AOA flight modes. My point is that the BlackJack with a ZP leading edge was the 1st step in this progression we have of cleaning up the nose profile and speeding up airflow through reduced skin friction generating better lift at slower airspeeds. You can also see this concept on the Peregrine/Petra class canopies.

I'm doubtful this tech would be useful at pattern altitudes unless it was for the purpose of impact avoidance.

So here is my understanding of things based on my own history and research (not from any formal study as I mentioned in your other post).
Slats at the leading edge: Again we know that the vast majority of our lift is created by the profile of the leading edge and the speed of the airflow over it. The ZP will serve to reduce skin friction and give a better leading edge profile increasing the wings lifting ability. When in slow flight/high AOA the slat then sends air out into the boundary layer to help increase/maintain airflow at slower airspeeds. I personally believe that their location is chosen to influence the boundary layer in specific relation to airflow over the leading edge. (Read "Slotted Leading Edge"). An added benefit of increased airflow or speed of airflow over the leading edge is that the laminar airflow will travel further back along the wing before it starts to de-laminate.
Squirrels "Float Valves" are more akin to Blown/Jet Flaps and Slotted Flaps. They serve a different purpose that essentially benefits us the same in the end. Again 101 aerodynamics tells us that the laminar airflow we rely on to produce lift will separate from the trailing edge first. This is the reason that we feel we fall over backwards when we stall our canopies. The purpose of having some form of valves way back there is to help encourage laminar airflow at the trailing edge for as long as possible. My understanding of it is that it doesn't generate anymore lift here because that isn't even where a wing creates its lift, what it does do is help delay de-lamination of the laminar airflow which enables the wing to maintain its lift at slower airspeeds.

If I am correct in my last 2 points then a 3rd set of valves would be pointless because at that point in the middle of the wing they wouldn't really be of benefit to the leading edge airflow and probably use less at the trailing edge if "Float Flaps" were already installed. And that doesn't even take into account the inefficiencies it may create in the wing profile. And lets not forget we are actually just throwing nylon into the sky. I bet if you researched jet flaps you would find they have tried all sorts of configurations we have never thought of.

Very interesting

Just want to leave this here for anyone who don't understand the fluid mechanics around this.
Its a rc plane with an "unstallable" wing but it think he explains both stalling and the slat system good and consist.

https://youtu.be/WH8kCTzy91A

To quote the squirrel video: "The float flaps open as you apply brake input" (1:56). An additional set of valves in the middle would not work in this fashion, since that surface isn't deformed by brake input.

I think Fledgling expressed the counter-arguments nicely, plus AntoineLaport: "More stuff = more work = higher price and fabric" for probably no real benefit

In a very steep approach, I think Fledgling's term "a somewhat pressurized deceleration device" is apt. The aerodynamic term is a "bluff body." Let's dispense with the notion that, in a true deep brake accuracy-style approach, you aren't stalled. You are steering thanks to newtonian effects (slipping and displacing air), less so bernoulli effects (lift generation) In the real world, it's really, really hard to get your critical AOA greater than ~30°. But also in the real world, we'd rarely come in truly this steep because it usually hurts.

Given all that, maybe what a float flap allows, is to create a local laminar flow over the control surface only, and that might augment steerability long after most your canopy as a whole went from "flying" to "falling." (Similarly, an ideal airplane wing stalls at the roots first, and tips last, to preserve usefulness of the ailerons) A stall isn't an "all or nothing" thing for a wing, and even, some lift can be generated in a stall.

Other canopies out there prove you don't need float flaps to fly or steer backwards. I would want to test fly a Hayduke with and without the float flaps and see if it made a difference. Presumably Squirrel has done this, and they felt strongly enough about the results to justify the effort.

Here's a thought question for anyone.

In the video they talk about "rearward stall flight" (0:49) on toggles. So which way is air moving through the float flaps, in this scenario? I initially just assumed it was moving from inside to outside the canopy. But the more I think about it, the more I question this, because:
-the outside opening of the float flap is now moving backwards, directly into the relative airstream, instead of away from it (like in normal flight).
-In the video, there is clearly negative pressure at the nose, air is moving out of the nose as you'd expect
-The vents are a much smaller surface area than the nose, and they would have to supply a lot of pressure to push air out the nose AND to overcome the outside pressure at the float flaps to push air out of there, too.

Counterargumens: The float flap openings aren't positioned to act as a "rear-facing nose" opening. Also, the tail of the canopy isn't collapsing so there must be positive relative pressure inside.

I'm not saying air is or isn't moving one way or the other, I'm just saying I question my assumptions. Can someone tack a piece of yarn to their float flap, and get some video in rearward flight, pretty please?

That's a really good video for explaining some of these concepts.

If speaking of nil wind conditions of course. Because we all know nil airspeed and nil ground speed are 2 different things.
P.S. Not directed at you.