Rapidly deployable personal aerodynamic decelerator

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Main Question or Discussion Point

I have done a large amount of searching and have not come across anything substantial for a personal alternative to a parachute in the form of a glider. I started by looking at Batman (don't stop reading just because I mentioned a movie) and trying to think of anything even remotely practical that could do what his cape could. Completely aside from the electronic morphing aspect, does anyone have any thoughts on the possibility of the following aerodynamic decelerator:

-instantaneously deployable
-reduce to 10-15mph horizontal velocity in a full flare
-can carry/run with on one's back

I am not looking for anything supernatural, just something that one could jump out of a truck moving say 40mph, or off the top of a 20 ft building, and land safely with. I had some sort of glider in my mind, much smaller than a hang glider, but nothing like a wingsuit either. Again, something close to the size of batman's cape would seem reasonable, but to carry and deploy it seems like the challenge. One possibility was modified tent poles, but I haven't thought of any real specific details.

I would love to build and test this for a project have in fluid mechanics. I also have my own hang glider, which I can easily come to a full stop with a well timed flare. I imagine a good flare should leave one running or doing a well timed tumble for a glider the size of batman's cape.

I don't know if I'm just missing something major, or if no one has had any motive to develop this area better, but I have not seen anything one way or the other why this is or isn't possible.

Please let me know your thoughts,
-Josh
 

Answers and Replies

  • #2
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Deployment time is always the problem. It's why there's a minimum height for base jumping - and subsequently why it's so dangerous.

There simply isn't enough time for a device to deploy, let alone provide you with enough deceleration to allow you to perform a safe landing.

The moment you are out of the truck, you will have a matter of feet to deploy the device, slow down and land. You can calculate how roughly how much time you will have based on gravitational acceleration.

If you want the device to give you the 'flare', this will increase the time for deceleration to occur. However, you then need to factor in deployment time and specifically how long before it can produce enough lift to increase your vertical height.
 
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  • #3
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Well that's what I would say is the biggest drawback with base jumpers using parachutes, and why an alternative would be great (not for basejumping in this case). In the extreme case of batman, his deployment was essentially instantaneous, and heavily integrated into his body movements, which allowed for much faster reacting. In this case, one could begin deployment before leaving the roof or truck bed if deployment were mechanical, using some sort of spring potential energy or body motion. Parachutes rely on high relative wind speed to deploy, which is the opposite of what I am going for.

Essentially, what I have in my mind is something that will work essentially the same from 1 foot of the ground, to 10 feet, to 100 feet, to 1000 feet (assuming it is deployed as the user jumps or begins falling)
 
  • #4
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In the extreme case of batman, his deployment was essentially instantaneous, and heavily integrated into his body movements, which allowed for much faster reacting.
It was also completely fictional.

He had a material that reacted to electric and reacted almost instantaneously. More importantly, I'd also add that you may want to check the required size of parachute device in order to do what you ask.
In this case, one could begin deployment before leaving the roof or truck bed if deployment were mechanical, using some sort of spring potential energy or body motion.
Again, work out the required size for someone of average body weight.

Remember, you also need to have an amount of control. Otherwise you'd be thrown about like a rag doll.
Parachutes rely on high relative wind speed to deploy, which is the opposite of what I am going for.
Not necessarily. I always remember we had a rep from a parachute company come to my primary school. He had a parachute demo that he strapped to "the tuffest rugby player in the room". Instructed said child to pull the rip cord and the parachute exploded out of the pack across the room.
 
  • #5
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You're looking for a one-time-use jet pack with a radar altimeter for automatic ignition. It only has to have enough thrust to decelerate you from terminal velocity (about 85 MPH) in some given time, say 5 seconds.

This should be quite doable if you can somehow orient the falling body into a prone position prior to ignition. Maybe some kind of gyro flywheel?

Cool problem.
 
  • #6
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You're looking for a one-time-use jet pack with a radar altimeter for automatic ignition. It only has to have enough thrust to decorate you from terminal velocity (about 85 MPH) in some given time, say 5 seconds.

This should be quite doable if you can somehow orient the falling body into a prone position prior to ignition. Maybe some kind of gyro flywheel?

Cool problem.
Orient the body? In the time it takes to fall from the truck to the road surface?

He wants to be able to jump off a truck and land safely.

I suppose if you used a jet pack to get some altitude first and then to slow you down a bit, maybe it's possible. But given the current state of jet packs I'd say it's unlikely to be viable.

You wouldn't need an altimeter on it. Hit the power, shoots you up in the air, control yourself to a safe landing speed, descend to ground - like I said, a bit unrealistic.
 
  • #7
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thanks for the good pointers. I would definitely like to see what you're talking about with the instantaneous parachute deployment. I've never seen anything like that with base jumpers or anyone for that matter. Are you talking about the pilot chute, or the parachute as a whole?

Also, I had more of a glider in my mind. An initial idea for deployment (and I really hate to bring up another movie), is the wing used in avatar the last airbender. Nothing at all related to the wing itself. Just using some sort of cylindrical tube/frame, which has two arms that spring outwards say 100 degrees, and then telescope, forming the two wings. Possibly some additional arms for support. I imagine all of this could happen in several seconds, also, why the user is running/jumping.
My hang glider has upwards of a 30 foot wing span. Initially, I would think 1/4 to 1/3 of the surface area would be enough, maybe around a 15 foot wingspan, 7-8 on each side. Pitch control by pushing the frame forwards and backwards on one's back, and roll control using one's legs.

I'm not at the point to do any calculations (maybe sketches though). Just looking at the feasibility for someone who is physically fit and has some hang gliding experience.
 
  • #8
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And please let's not stray off towards jet packs. I guess it answers the question, but I intended for the system to rely on some sort of aerodynamic based surface. Also, I wanted something financially plausible for a college student.
 
  • #9
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thanks for the good pointers. I would definitely like to see what you're talking about with the instantaneous parachute deployment. I've never seen anything like that with base jumpers or anyone for that matter. Are you talking about the pilot chute, or the parachute as a whole?
It was 11 years ago, I was 10 at the time. I don't remember everything about it. All I know is it was GQ Parachutes - I still have the pin badge they gave us all.
Also, I had more of a glider in my mind. An initial idea for deployment (and I really hate to bring up another movie), is the wing used in avatar the last airbender.
Again, let's not get too excited by movie physics.
Just using some sort of cylindrical tube/frame, which has two arms that spring outwards say 100 degrees, and then telescope, forming the two wings. Possibly some additional arms for support. I imagine all of this could happen in several seconds, also, why the user is running/jumping.
As simple a concept as that may be / sound, it is a technical nightmare. First, you might want to check the strength to weight ratio of various materials. This would tell you a rough weight of the frame you would have to carry.

I'd also point out that the moment you increase the surface area of the person, you increase the drag. At some point during deployment (long before you get to fully deployed and ready to go), you will be lifted/dragged off the vehicle due to this fact. Hence the need for you to get it deployed and ready in as quick a time as possible.
My hang glider has upwards of a 30 foot wing span. Initially, I would think 1/4 to 1/3 of the surface area would be enough, maybe around a 15 foot wingspan, 7-8 on each side.
What you think and what the facts are may not coexist nicely. Do the maths.
Pitch control by pushing the frame forwards and backwards on one's back, and roll control using one's legs.
Are you an aerospace engineer / student? You're over simplifying both the device and the control aspects.
I'm not at the point to do any calculations (maybe sketches though). Just looking at the feasibility for someone who is physically fit and has some hang gliding experience.
Sketches are a bit pointless without a basic knowledge of the underlying mechanics. I can draw a warp engine, don't make it workable.

Start by doing some rough calcs. Get a basic system weight (including deployment mechanism).
And please let's not stray off towards jet packs. I guess it answers the question, but I intended for the system to rely on some sort of aerodynamic based surface. Also, I wanted something financially plausible for a college student.
Regardless of chosen solution, "financially plausible" isn't going to apply here.
 
  • #10
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hmm, you really seem to have it in for me. Again, this is just the drawing board. Please don't jump two steps ahead in the process and tear apart initial thoughts. I really don't think calculations are a good idea yet, especially with the amount of time they would take up. There's still too many ideas floating around. In place of calculations, I'm just using existing frames of reference. One I forgot to mention was the kitewing:

http://www.youtube.com/watch?v=Z1uvW-1-R5o&feature=related

I really wish there was a way to tell the relative wind speed, because even the times when they land on the ground with almost no ground velocity, there is probably a decent wind speed helping them out. Still, though, that is an extremely small wing surface compared to a hang glider, and even what I am thinking of.

Also, I am not an aeronautical engineer. I'm pursuing my BS in mechanical engineering. Year 3/5.

In regards to the equations, though, if you know of a good way to easily estimate the amount of wing area for say 200 lbs, let me know. Keep in mind it is not the wing area needed to fly level with X pounds of thrust, or to attain a glide ratio of X. It is the amount of wing area needed to decelerate a 200 lb object below 15 mph in a full flare. I don't know if there are simple equations to model that.
 
  • #11
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hmm, you really seem to have it in for me.
I consider myself a realist. Part of being an engineer.
Again, this is just the drawing board. Please don't jump two steps ahead in the process and tear apart initial thoughts. I really don't think calculations are a good idea yet, especially with the amount of time they would take up. There's still too many ideas floating around. In place of calculations, I'm just using existing frames of reference.
Why would the calcs take that much time? A quick run on numbers regarding wind surface area required and materials weight would take minutes.

I'm not jumping two steps ahead, I'm explaining to you what you need to consider. Failure to prepare for what is required will almost certainly complicate things in the latter stages.

First you need a rough wing area in relation to mass of person + system. Once you have that, you know what you're working to create. Then you can brainstorm how to achieve it. Otherwise all the sketches in the world aren't going to mean anything if they don't relate to the reality of the situation.

You need to note that getting initial lift to get you off the ground isn't the same as being able to land it safely. Once you are in the air (and have climbed enough / controlled the vehicle enough to give time to slow down) you will start to drop, at which point you need to ensure you don't gain too much speed and injure yourself due to that.

Also, in flight control, given the requirements of your design, is something you need to consider now not later.
In regards to the equations, though, if you know of a good way to easily estimate the amount of wing area for say 200 lbs, let me know. Keep in mind it is not the wing area needed to fly level with X pounds of thrust, or to attain a glide ratio of X. It is the amount of wing area needed to decelerate a 200 lb object below 15 mph in a full flare. I don't know if there are simple equations to model that.
Just so you're aware, I'm an aerospace engineer.
 
  • #12
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OK, so before this turns into another one of your typical back and forth threads, let's both take a step back and listen to each other a little more. Because you're an aeronautical engineer (or aspiring I would assume if you're 21), why don't you point me in the right direction for some equations. Like I said, though, I don't imagine this is a typical situation because it is the flare I am focusing on, not the gliding itself.

Also, materials could be anything from aluminum rods to fiberglass tent poles, and anything in between, so I figured 50 lbs total "contraption" weight would be more than enough, totaling 200 lbs.

I'm heading to bed now, so I won't get back to you until tomorrow (unless you post before I finish researching "flaring aerodynamics"), but thanks for your help jared, james, or whatever your name may be.

-Josh
 
  • #13
Ok sure.....a telescoping pair of plane wings....with gossamer skin skin and deployable with a compressed gas cylinder ..to shouldnt be any larger than a parachute.. even lighter.. I can even picture how to build it.....
Im a 4 x TBI survivor and if you think of the film "rain man" he saw pictures like playing cards.
I see mechanical moment and dissection like and expanded view of how things work.. this concept only took a few seconds..... anything three dimensional...My world..Ill draw it out for you if you like...
peterjohn
 
  • #14
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Ok sure.....a telescoping pair of plane wings....with gossamer skin skin and deployable with a compressed gas cylinder ..to shouldnt be any larger than a parachute.. even lighter.. I can even picture how to build it.....
Im a 4 x TBI survivor and if you think of the film "rain man" he saw pictures like playing cards.
I see mechanical moment and dissection like and expanded view of how things work.. this concept only took a few seconds..... anything three dimensional...My world..Ill draw it out for you if you like...
peterjohn
The ability to picture it doesn't mean it's easy to build and certainly doesn't make it a viable device.

I've been thinking about this one, trying to come up with a somewhat viable design.

So far, I keep getting stuck on the mechanics of it. To have something that can rapidly deploy as the OP requires would need to be quite sturdy and have good aerodynamics to allow you to take off and land.

Ignoring deployment, everything I've thought of so far gives you a good wing area but you would end up being thrown off the lorry due to the massive drag it induces.
 
  • #15
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So we've made slight progress in the design stage and have tried to narrow the project down to several key areas. Mainly wing shape, wing size, and wing airfoil. For now, we are only looking at the aerodynamic feasibility and ignoring the mechanical deployability until we can determine if this idea is even plausible. Keep in mind that a normal hang glider has around twice as much wing surface area as we're hoping to use, and they barely have the ability to bring someone to a full stop in a flare. The four factors we are hoping can make the difference are:

1. Airfoil: We plan on using an Eppler airfoil, which has a much greater lift and drag per unit area, reducing the glide ratio, but increasing the amount of lift and lowering the stall speed.

2. Wing shape: In jets, forward swept wings decrease stall speed. They are also used on fixed wing gliders for other reasons. I haven't found much anything in regards to their effects at very slow speeds. If anyone has any resources, please point me to them.

3. Control: We haven't decided any of the exact mechanics of the wing, but by being more closely attached to the body, we believe it will allow better control, and therefore more efficient flaring/landing.

4. Landing criteria: Unlike a hang glider, our landing criteria is <12 mph horizontal groundspeed. Hang gliders are able to land at a complete standstill, but we are hoping to make <12mph our average landing speed.

We are hoping to model an eppler airfoil and test in a small (~2ft*2ft) wind tunnel. If anyone has any ideas how to make it correctly, please reply. We need to decide on (1), how to make a desirable/customizable airfoil out of fabric/aluminum/string (2) What to use as fabric (3) Just learned dimensional analysis in fluid mechanics. Will that work to account for scaling?

Thanks,
-Josh
 
  • #16
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1. Airfoil: We plan on using an Eppler airfoil, which has a much greater lift and drag per unit area, reducing the glide ratio, but increasing the amount of lift and lowering the stall speed.
Given what you're trying to do and the low speeds involved an aerofoil isn't going to be as important as angle of attack, more on this in a second.
2. Wing shape: In jets, forward swept wings decrease stall speed. They are also used on fixed wing gliders for other reasons. I haven't found much anything in regards to their effects at very slow speeds. If anyone has any resources, please point me to them.
At such low speeds I don't think the wing shape is going to be much of an issue. I would say you're better off going for a design similar to the F22 wing shape. This will give you a good area and angle of attack within a smaller (and easier to deploy) shape. I think you'd be better off focusing on making something like this (especially when it comes to deployability) over trying to replicate a Buzz Lightyear style wing.
3. Control: We haven't decided any of the exact mechanics of the wing, but by being more closely attached to the body, we believe it will allow better control, and therefore more efficient flaring/landing.
Again, you need to consider time frames. At the low airspeed and with no thrust it is only going to be a very short flight - so you need to consider this when you input any form of control.
4. Landing criteria: Unlike a hang glider, our landing criteria is <12 mph horizontal groundspeed. Hang gliders are able to land at a complete standstill, but we are hoping to make <12mph our average landing speed.
Any aircraft can land at a complete standstill. However what matters is the airspeed over the wings. Without airspeed, you can bring the hang glider to a stop - at which point it stalls - but you should be just above the ground to make a 'comfy' landing.

Remember, airspeed is more important than ground speed.
 
  • #17
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On really don't think you are understanding our methodology in designing this. Please just take a step back before tearing everything apart, and I think you will see our logic. Don't just attack the ideas, because just about everything you've said thus far we've already considered, and are looking for improvement ideas.

Obviously angle of attack is very important, and that is exactly why we're choosing an appropriate airfoil. Our angle of attack will continually increase throughout the landing process until a full flare. We are trying to choose an airfoil that will allow or angle of attack to remain low while velocity decreases. So yes, angle of attack is important, but the way the wing reacts to AOA is a built in function of the airfoil for our landing strategy. Therefore, we saw it logical to choose an appropriate airfoil because the function of our AOA over time is known.

Another reason we chose forward swept wings is because there needs to be room for at least 75-100 square feet of wing area once deployed. Any sort of backward swept wing will not have nearly enough room to fit in the required wing area. Also keep in mind that the aerodynamic center of the wing needs to be on top of the center of gravity for stability (the pilot flies prone). I will upload a picture to better visualize why it is necessary. It also includes some pics of the landing path.

During landing, both the airspeed and ground speed are very important. We are assuming no wind or head wind for now. Also, the pilot's velocity will be completely horizontal upon impact, so airspeed is essentially the same speed as ground speed in no wind. However, this is not the point I was trying to get across. I was trying to say that with an easier landing velocity requirement, our stall speed can be slightly higher than it would have to be to land at a full stop, thus allowing for a smaller wing area.
 
  • #18
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I know what you're trying to do, but you are missing important issues. So far I've seen nothing that indicates you've done serious analysis with actual numbers.

It's not good for someone to simply sit here and tell you it's great - having someone tearing every little thing apart is good. If you can answer this adequately then you know your design is going well.

I would appreciate some pics as it may clear the issues I have with it up.
 
  • #19
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It's not that I don't mind having it torn apart. That's what I want. However, I think we're thinking on different tracks because nothing you've said has really helped out so far. Attached is a pic of our thinking so far. Sorry about the bad quality. The top left is an image of the wing shape, which totals 80 ft squared. Assuming 200lb total weight, that is a wing loading of 2.5. In terms of numerical analysis, I'll admit that's the extent of what we've done. However, based on the work over the past half a century with hang gliders, I'd say we are tapping into that. The top right shows a line indicating the four stages of landing:

1. terminal velocity/glide
>y component of lift=mg, no vertical acceleration
>x component of lift=drag, no horizontal acceleration
>Move to stage 2 upon pilot input
2. increase angle of attack
>y component of lift>mg, positive vertical acceleration
>x component of lift is negative (to the right), so is drag, so deceleration occurs horizontally
>Move to stage 3 when vertical velocity and acceleration are 0, pilot is 0-4 feet above the ground
3. control angle of attack until stall
>y component of lift=mg, no vertical acceleration, vertical velocity is close to 0, possibly even slightly positive to perform a small "swooping" motion
>x component of lift is largely to the right, as well as drag, horizontal deceleration is high
>Move to stage 4 upon stall, preferably with a slightly positive vertical velocity (upwards), allowable due to the difference in height between prone and standing
4. Full flare/run
>Use wing as a parachute, waiting until last moment possible to begin running

To do our experiment, there are no other numerical calculations we need. All we need to know is how to make an airfoil using fabric, and which fabric is advisable. Any advice in this area would be greatly appreciated. From the experiment, we will have data to start doing some calculations. We will be able to find the lift and drag values at numerous angles of attack. From that, we can begin to make rough estimations.

-Josh
 

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  • #20
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The picture is too poor to be of any use. I'll try though. However, can you correct you below post as it is wrong (not just me being picky, actual wrong terminology and description of flight).
1. terminal velocity/glide
>y component of lift=mg, no vertical acceleration
>x component of lift=drag, no horizontal acceleration
>Move to stage 2 upon pilot input
2. increase angle of attack
>y component of lift>mg, positive vertical acceleration
>x component of lift is negative (to the right), so is drag, so deceleration occurs horizontally
>Move to stage 3 when vertical velocity and acceleration are 0, pilot is 0-4 feet above the ground
3. control angle of attack until stall
>y component of lift=mg, no vertical acceleration, vertical velocity is close to 0, possibly even slightly positive to perform a small "swooping" motion
>x component of lift is largely to the right, as well as drag, horizontal deceleration is high
>Move to stage 4 upon stall, preferably with a slightly positive vertical velocity (upwards), allowable due to the difference in height between prone and standing
4. Full flare/run
>Use wing as a parachute, waiting until last moment possible to begin running
There is no "x component" of lift. It is thrust and you have none. You can only increase / decrease speed based on angle of attack. This is important.

Lift equalling drag does not give you zero horizontal acceleration.

If lift is equal to weight on a glider (ignoring thermal updraft and any wind) then you are flying in a straight line, which means you aren't generating any forward acceleration and as such have nothing to compensate for drag, so you decelerate horizontally. Lift can equal drag all you like but it doesn't mean anything so far as forward motion is concerned.

If your lift is negative, you accelerate horizontally downwards and depending on your angle of attack you will accelerate horizontally.

Drag acts against motion of travel at all times, not with it.

Drag is perpendicular to lift (or there about).

There are some bad assumptions here, I don't know whether it's your poor terminology or your understanding, but either way it needs to be cleared before we go any further.

If it's your terminology, you're going to need to correct it before we continue.

If it's your understanding then we're in trouble.

The way you've described the flight path would indicate to me you don't understand the basics of flight. Although I can kind of see what you're going for, these are some major issues that need clearing.

If you wish I can give you an approximate description of how the flight path would look with correct terminology.
 
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  • #21
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Sorry about the pic, all I had at the time was my webcam. I will scan a better copy of a new diagram I am drawing now when I get the chance.

By lift I am referring to the force generated by the pressure differences along the airfoil, which always acts perpendicular to relative wind flow. Therefore, depending on the orientation of the wing, there can be x (horizontal in relation to the ground) and y(vertical in relation to the ground) components of lift. The drawings were relative to the ground, not to the air. Assuming absolute wind speed is zero, the relative velocity would be in the opposite direction of each part of the flight path pictured in the top right.
I am keeping my coordinate system relative to the ground plane because we are analyzing landing where the ground location and speed are critical.

By drag I am referring to the force generated by air particles hitting the body and wing at a given velocity. In this case, I should have included a y component of drag as well (again, relative to the ground).

So yes, my terminology was incorrect, but the sum of all forces would still sum to be the same amount at each frame. Lift can still propel someone forward relative to the ground, and drag can still decelerate someone's downward acceleration depending on relative wind speed.

Also to clear up for my post,
x=horizontal
y=vertical
 
  • #22
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So yes, my terminology was incorrect, but the sum of all forces would still sum to be the same amount at each frame. Lift can still propel someone forward relative to the ground, and drag can still decelerate someone's downward acceleration depending on relative wind speed.

Also to clear up for my post,
x=horizontal
y=vertical
No, the sum of the forces is not correct. You have ignored the "thrust factor". When you pitch down, acceleration due to gravity gives you forward motion - nothing at all to do with the lift produced by the wings.

There is a reason why aircraft manufacturers don't include your "x component" of lift in their calculations.

When the airfoil is pitched nose down (negative AoA) the lift generated that goes towards forward motion is negligible to the point of being worthless.

If you are talking about an aircraft wing, the lift can never propel you forward - unless you stand with your back to the wind and the lift is from the wind pushing upwards on the wing (reverse parachute).

Aerodynamics 101: Lift, Weight, Thrust and Drag. Lift needs to compensate Weight, Thrust needs to compensate for Drag. You have a Lift / Drag ratio which is used to decide on various phases of the flight, but it isn't useful in the calculations you are doing at this stage.
 
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  • #23
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OK, good clarification. There is still something missing then. If the "thrust factor", which I thought was coming from lift, is not, then it must be coming from drag. See the attached picture. In part one, what force am I missing that causes forward acceleration, if it's not lift. Also, do you have gmail to chat, it would be much faster.
 

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  • #24
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OK, good clarification. There is still something missing then. If the "thrust factor", which I thought was coming from lift, is not, then it must be coming from drag. See the attached picture. In part one, what force am I missing that causes forward acceleration, if it's not lift.
Please re-read my last post, pay attention to:

"When you pitch down, acceleration due to gravity gives you forward motion."

Gravity, the thing ya just can't get away from.

Your forward motion on a hang glider is provided by pitching down and accelerating - the key is to pitch down enough to get you going forward whilst maintaining height as long as possible.

Note, in the flight path of you glider you are already travelling forward with the velocity of the truck. Once detached from the truck you will constantly slow down whilst gaining height. It is only when you begin to descend that you can regain some speed and it is only by pitching down can you ensure you don't stall too soon once you reache the minimum glide speed.
 
  • #25
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yeah, I saw that, but gravity always points downwards. there is no horizontal component. The way I understand it, gravity causes downwards acceleration, which causes downwards velocity, which causes relative wind to hit the airfoil at an angle of attack that either produces lift or drag, pushing the wing forward. I'm not sure which though. And if you have gmail, please private msg me it to talk faster.
 

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