Aerodynamics 101 - A New Understanding With Chris Santacroce!

Today Chris Santacroce goes through the basics of understanding aerodynamics and how you can take advantage to better your flying experience.
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[@MitchG]

Angle of incidence is the difference between chord line and horizon. Angle of attack is chord line and relative wind. Just because the wing is diving doesn't mean the angle of attack is negative because the relative wind can still create a positive angle of attack. Brakes prevent deflations by increasing angle of attack. Even though angle of incidence stays the same (wing over head), brakes decrease airspeed which increases angle of attack so the wing can fly through sink while still maintaining positive angle of attack.

[@spartafly3014]

And relatedly, if you pull the brakes you change the L/D ratio via deformation, decrease speed and cause airflow separation. And that is what we call stall, separated airflow. The glider might stay over the head but Vsink versus TAS becomes large and you have a high angle of attack as consequence.

[@mathieuc8770]

I agree :)

[@samroyds6313]

Spot on. Pumping the brakes slows the glider and increases rate of descent, therefore the relative airflow has now changed and had a slight increase in angle of attack. Also at the point when the brakes are pulled the camber of the wing is at its maximum relative to hands up. Angle of attack is angle between the relative airflow ( the reverse of the flight path) and a line from the leading edge to the trailing edge. Deflation’s are prevented from always trying to maintain a positive angle of attack even sink, down draughts and turbulence. With speed bar on the angle of incidence decreases and therefore you are flying at a lower angle of attack reducing the margin for error and increasing the chance of a collapse. A stall is the opposite. The trick here is to not have to high an angle of attack. But due to the glider design of a fixed angle of incidence with a pilot Hanging below its very hard to increase the angle of attack for more than a few seconds other than to apply and hold large amount of brakes. In summary don’t allow the angle of attack to get too low or you may get a collapse (pump the brakes to increase the angle of attack) be cautious when speed bar is applied and also don’t allow the angle of attack to get to high ( by holding to much brake for too long) so you don’t stall.

[@TheMatgaw]

It is important to note that in order to figure out the AoA, you have to look at the glide path through the airmass (which is moving relative to the ground - we call that "wind"), and not relative to the ground. This creates all the confusion. And I'd be hesitant to use the word "wind" when we're referring to a flying glider. For a glider there's no such thing as wind (except for gusts) - it always flies at defined L/D and speed through the airmass, and these characteristics are defined by wing profile and AoA. You can modify AoA by modifying wing profile - using brakes or speedbar

[@ronnieaarav7858]

I realize it's kinda off topic but does anybody know a good place to watch newly released tv shows online ?

[@harry-knight]

Hey Chris, Thanks for making this video, it's great to have access to some of your training. I'm not sure I fully understand/agree with a few of your points, but I’m a big geek so if I’m wrong with any of my thoughts I’d love to understand where I’ve gone wrong. My understanding is this: 

There are 2 ways that an aerofoil creates lift, bernoullian lift, created by pressure differences between the top and bottom surfaces, and Newtonian Lift, created by deflecting the airflow downwards. However both methods require an angle of attack that falls within a specific range. There are 2 airflows that act on the wing, the “True Airflow” (created by wind and thermal activity) and the “Induced Airflow” (created by the wing’s forward motion) The vector of these 2 is called the “Apparent Airflow” and is what we actually feel on our face. The angle of attack is also relative to the Apparent Airflow, but since in most forms of aviation the Induced airflow is so much stronger than the True Airflow, we normally think about AoA relative to the direction of travel. This is why we have the problem you speak of at 8:55 since the strong True Airflow may become dominate over our Induced Airflow which is limited to around 25-35mph. Angle of Attack can be altered without any change to the Angle of Incidence through variations in the True Airflow such as turbulence. This is especially true for slow flying paragliders where the True Airflow is often relatively strong compared to the Induced Airflow (See Above). Angle of Incidence can be altered without any change to the Angle of Attack as long and the wing continues to move through the air in just the right way. In the example at 3:15, the paramotor flying in calm air can porpoise up and down without stalling or taking a frontal collapse because the relative motions of the wing and pilot works to maintain a positive AoA throughout the sequence. In the he scenario you describe at 3:50, since applying brake pressure will slow the wing down but not the pilot, any rapid application of the brake will cause the pilot to pendulum out in front of the wing. Therefore the only ways to achieve the scenario would be to slowly and steadily apply brake pressure, so that the wing and pilot slow down at the same rate, or fly into a rapidly rising True Airflow. Either way this stall is still caused by AoA, as the Apparent Airflow is no longer at the correct angle. In your example at 7:17, you change from talking about your hand being the wing, to your whole arm being the wing. With you arm maintaining a positive AoA, the angle of your hand becomes less relevant, as it only represents 15% of the total wing area. All that said, I don't think anything I've said changes the application of your mantra "brakes prevent collapse", and as I said at the start, I'm writing this wanting to understand better if any of my assumptions above are incorrect.

[@MitchG]

Negative angle of attack is the cause of deflation. Brakes do not always prevent deflations. Stalls can occur with little or even no brake pressure because its all about angle of attack. The air that we fly in constantly changes angle of attack, its the pilots job to maintain that angle of attack in the flyable range of their specific glider

[@ChrisSantacroce]

Thanks for chiming in Mitch - that hasn’t been my experience but that’s what this is all about - sharing our experiences - thank you so much!

[@jaredyatesdotcom]

I can see that the root of this difference of opinion is that Chris provides his own definition of AOA in the video. More broadly at least in my experience, AOA is the difference between the direction the airfoil is pointed and the direction it is going. Chris refers to AOA as the position of the glider relative to the pilot. We wouldn't expect to be able to talk in depth about AOA without an agreement of what AOA is.

[@smokinonindo]

Thank you and please more of this content! Absolutely fantastic!

[@MikeFlyItAll]

Great video and explanation...Thanks for the info Chris... Keep em coming please...

[@PPGExplorer]

Great information......thank you very much for this series... keep em coming!

[@peterbrix8077]

Thanks for the great info.

[@idanghelber8282]

Interesting point not to directly link a stall just to increased angle of attack. However, I don't believe that (it is complete to say) at least keeping a glider in stall can only be linked to trailing edge deformation. If you are a good enough pilot you can maintain parachutal which is a stall with having no trailing edge deformation, at the same time your angle of attack is neutral. Negatives are pretty interesting on a paraglider, theres way more nuance than on any fixed wings.

[@ChrisSantacroce]

Thanks for your message. It is true that we can knock the glider into deep stall without gross trailing edge deformation. Still - it is often times due to some trailing edge deformation applied in some combination. It is also true that a glider that is out of trim, full of sand, full of snow, wet or a glider that has just suffered a malfunction can slip into deep stall. I put stall and deep style in different categories and while I do address deep stall in some other videos - it’s not the focus of this video. Again thanks for chiming in.

[@David65702]

Thanks man I'm learning.

[@Plastpackad]

Old free flying paragliding pilot saw deflation as a result of negative g force on parts of the glider. As long as the entire wing is under positive G it will keep its shape. To keep it this way one need both active breaks and wight shifting (letting your body roll with the glider, adding pressure to the side going light). Very good point in making a difference between AoA and AoI.

[@keithsmith-aka-scottsummer8926]

Great lesson!

[@YankeeinSC1]

How did I not see this when you published it?! Since it's 101, I think it is important to emphasize that a stall is not a collapse. 2 different events, that I often hear new pilots confused about. I'd much rather stall, which is typically pilot induced, as opposed to a collapse that is most often dynamically induced from thermal or rotor. Great stuff for discussion.

[@ripmanridin7092]

Great info CS.........thanks for continually putting this stuff out there!

[@susannewilliams]

The Magic Words that set me free to confidently and safely fly my dynamic mountain sky here in the Alps? “Brakes Prevent Deflation.” That is all you gotta know. Then do it. ASB is like ABS braking for the sky. It’s now my calm and solid reflex to any alertness trigger. Bye bye hypervigilance, hellloooo genki flying. That you eternally man. You just unlocked the sky for me. So obvious.

[@chumpp12]

Great video I would say I agree about the brakes. My dudek warp manual recommends the opposite. It’s frustrating... obviously coming in for a landing in rotor you need brakes because you’ll be slowing down to a running speed but it just doesn’t feel right to dump trims and let go of brakes in turbulence when at altitude. Where do you recommend trimmers he set?Everyone even the manuals are saying reflex wings don’t react like classic gliders and should be treated different in turbulence. What are your thoughts on these reflex wings and how we should keep them inflated in turbulence?

[@ChrisSantacroce]

No doubt that you should honor the manual and I’m not going to pretend that I am an expert about your glider. I think you hit the nail on the head when you pointed out that it doesn’t do the average pilot much good to know that the fast trim setting with zero brake is the safest place to be on a given reflex glide. This - for the exact reason that you mentioned… Many times we are low and many times we don’t want to be flying with that much throttle so as a practical matter - we can’t fly fast all the time. We have to reconfigure the glider to slower settings for approach and landing and takeoff and fuel burn etc. Finally - it is unfortunate but true that the record shows that as much as certain configurations might yield better stability in theory - all gliders can and will deflate and it is the highly loaded gliders with the trim set fast that are usually uncertified which dive the hardest when they do deflate.

[@RonaldDump_real]

You making this is helping me make a laser guided bomb

[@frankzj]

Relative newbie here. I'm somewhat skeptical of 7:20 ("all you ever feel here is a lifting sensation"). I'm sure this applies to a rigid object, such as one's hand, but a canopy in that situation? If rather than your hand, you used a piece of paper, would this still hold true? Or would the front be forced down, propagating down the rest of the surface? That seems to be what a frontal collapse basically is.

[@paraglidingflyer]

Adding, subtracting brake...is this idea different then active piloting. Keeping consistent pressure on the brakes? Or is it a slight pumping of the brake with continued active piloting?

[@ChrisSantacroce]

If we are savvy then we add and subtract brake in a precise way but some of us aren’t always able to be savvy so adding in subtracting brake arbitrarily is much better than the alternative of no brake being added or subtracted.

[@RussellWHanson]

Brakes prevent deflation, but also hands up!!

[@renhuschle6586]

Not a single aerodynamic term is used correctly, or only partially correct in the entire video. These terms have scientific definitions, not versions. Chris, from your other replies I doubt you will listen to me so I challenge you to show this to any designer at a major pg manufacturer and further your education. If you are watching this video, look up the definitions of Angle of Attack, aircraft Attitude, Airspeed, and Stall. Watch other videos to compare.

[@SuperFlyParaglidingSchool]

Thanks for the message Ren. I am perfectly ready to be wrong about all of this. I’d even love it if somebody pitched me a refreshing spin on this that could help my students to understand deflation and stall and deep stall and apply it in the real world in a way that would keep them out of trouble over the years. Thing is - I’ve been pitching this earful for a long time and Super Fly students have way above average numbers in terms of staying out of trouble. I also acknowledge that I must come off as a clown to gentlemen aviators of all kinds. Still - I have to I believe that we are dealing with an unusual animal here. For example - very few books videos etc. that are going to speak to an aircraft in which the pilot is hanging below the airfoil and very few aircraft which deflate - very few aircraft which are capable of such dramatic flap being exercised. I literally thought about deleting this video because your words are so strong and I really don’t enjoy being in the hot seat. I’d much rather pitch information that’s not so controversial that all people would agree with - believe me. So - here we are. You are doing a great thing by encouraging people to do their own research. I’d love to see somebody smarter than me throw down with a video that explains these dynamics in a way that will appeal to new students and work for them over the long term. Am I taking liberties by suggesting that there are versions associated with these aerodynamic terms? Absolutely and I think you are right to call me out. Just trying to think solutions here - I love it when I’ve been teaching something one-way for years and I figure out that I had it all wrong. It happens. Just looking for the next level.

[@renhuschle6586]

Chris, was just talking about this video with another long time aviator and wanted to follow up. The first thing that really stands out is the difference between Pitch and Angle of Attack. Pitch is the the relative angle between the horizon or ground, which is fixed. Angle of Attack is the angle of the airflow relative to the wing itself, and is not a fixed angle relative to the ground. This is related to pitch, but not the same. A wing can be pointing any direction relative to the ground and still have a low Angle of Attack. High or low pitch angles require Airspeed (energy) to keep air flowing over the wing and an Angle of Attack that the wing won't stall at. The first example of the paramotor porpoising you use as a demonstration. What you are describing is high pitch angle, but you're carrying speed and power so the Angle of Attack remains lower than stall angle. You allow the wing to level off and dive before the Angle of the wing to the air hitting it moves from the leading edge to the bottom surface. The conclusion that you make, paragliders won't collapse at high Angles of Attack, is based on using Pitch in place of Angle of Attack. What you are really demonstrating is that a paraglider won't stall at higher Pitch angles as long as it has Airspeed (energy). The same is true for the infinite tumble. In this case, the pendulum that you mention, is what keeps the energy high and air flowing over the wing at an Angle of Attack that doesn't allow the wing to Stall. This is a great example that wing can be in any Pitch angle relative to the ground and with enough Airspeed and energy to maintain an Angle of Attack that keeps the wing flying. I think I will try and take you up on that and make a video that can explain this better.

[@theq5762]

The level to which you dumb down aerodynamics in this explanation is not only wrong but also dangerous. You can totally stall a wing with minimal break input. You are also getting the nomenclature wrong, (as explained in the comment by @MitchG) which creates more questions for pilots down the line rather than (what you claim to be doing) keeping people from having questions. Accident analysis in the past years has shown that different types of stall are the most common cause of accident, whether during take-off, flight, or landing. It might be true that in turbulence, one can prevent collapse of the wing by adding break in certain situations. But really what you are doing when adding breaks is increasing the angle of attack (AoA), when oncoming turbulence is reducing the AoA, and therefore one might be preventing a collapse. Teaching new pilots & students to pump the breaks during landing as a way to mitigate the effects of turbulence most probably does more harm than good. People who have not experienced a controlled stall themselves and have not mastered the skill of stalling a paraglider should not live under the impression that "pumping" the breaks, or applying breaks in general, would keep them safe. Stalling a wing is not a direct effect of break input, but rather of glider speed. A glider that is already slow requires barely any break input to stall and a glider that is shooting in front of you with lots of energy and speed is very hard to stall in the very moment it is in front of you and traveling fast, even with lots of break input (to catch the surge for example).

[@mamatuja]

I don't want to be too rude but you need to research some more before you give lessons to other people. There's a bunch of missing and confusing information.

[@ChrisSantacroce]

Thanks for your message - I have been teaching for 30 years - every flyable day. I have thousands of students and I continually check to see how their training serves them. Many become instructors, they go to Red Bull X Alps, they fly in the World Cup. Good pedigree. If you look at this from a traditional airplane perspective there will be tons of missing and conflicting information. That’s because airplanes and paragliders are so different. We constantly parse the information to figure out what info will work for newer pilots with no confusion and for clarity when they are flying in their first few years and beyond. I am happy to chat about any one of these dynamics if you are interested.

[@susannewilliams]

mamatuja - how many flying hours do you have on paragliders in dynamic conditions? Y

[@susannewilliams]

@mamatuja. I think you have not yet grasped the fundamental nature of this lesson. The whole point is to reduce the amount of information that the pilot needs to know or think about. We want the maximum percentage of mind resources focused on situational awareness. It is like with technical diving. Mixed gas. Caves. We could do zillions of hours of theory and all sorts of maths. But we don’t. We find the few empirically proven MOST relevant factors for safe enjoyable flying and only focus on those. So yeah if you wanted a theory text on aircraft aerodynamics I am sure you found it very confusing. That is because that is not what this is. As for the missing info, YES, we do that on purpose. It is called Human Factors. Gareth Lock has a good book about it called Under Pressure.

[@mamatuja]

@@susannewilliams Hey dude, this was a year ago. Are you smoking something?

[@Sampsonoff]

@@mamatuja can you explain what Chris got wrong? It made sense to me