Construction of Single Sheet Steerable Airfoil

My most recent rocketry project includes a steerable parachute for guided recovery. My first plan was a commercial parafoil for Hobby King, but I was not impressed with its build quality. After reviewing kite designs I felt comfortable with designing a stable steerable platform with sufficient forward speed. It consists of nine 7" stripes with diagonal cutouts and four ribs. The ribs create 3 main wind cells with the outer two having brake lines on the rear for steering and braking.

Parachute, still missing ribs and bridle:


Bridle preliminary layout:

Interesting. What are the lengths of each section of shroud lines?

If you are using a single sheet, how do you get forward movement without collapsing the chute? If you rig it with the forward edge down, wouldn't it collapse when the forward edge gets pushed under the trailing edge? If you rig it with the forward edge above the trailing, wouldn't that prevent forward movement?

I understand how a single sheet would work for a kite since the anchor point if fixed and the upper edge would be further from the anchor than the trailing edge and wind keeps it up, but how does it work for a chute?

With a cell type parasail, the leading edge can be lower then the trailing so a forward speed is induced. This forward speed is what fills the cells with air and keeps the foil inflated and shaped right.

Maybe I'm missing something, but I don't understand how a single sheet can accomplish the same thing as a chute without having spars to stiffen the panels and keep them from folding up.

Shroud line lengths still need to be calculated, and will be more of a manual painful process. The design is similar to a Rogallo wing which was briefly entertained by NASA as a recovery method for Apollo and Gemini missions.

Leading edge rigidity on my design is supplemented by the ribs and bridle which prevent over expansion of the leading edge, at the same time air from below being caught by the parachute provides the force to keep it inflated.

https://www.kiteplans.org/cat_3/sub_34/ might give some ideas

To go into more detail, just like a kite the angle of attack induces forward motion. If a normal spherical parachute's shroud lines were arranged to change the angle of attack forward motion would be gained. Too much angle imparts too much motion and collapse of the shape, there definitely needs to be a balance between forward air speed and wing loading to provide enough air underneath to keep the structure inflated.

On kites the angle of attack is set (on two line kites) and forward speed can be seen as a vector angle from the wind direction, The person holding the reel becomes the mooring for the kite, with a parachute you also have a mooring, just a mobile one. The connection between the mooring and parachute determine the angle of attack. So basically, it's operating just like a kite

Here's an image of a similar design:

Jeffmhopkins said:

On kites the angle of attack is set (on two line kites) and forward speed can be seen as a vector angle from the wind direction, The person holding the reel becomes the mooring for the kite, with a parachute you also have a mooring, just a mobile one. The connection between the mooring and parachute determine the angle of attack. So basically, it's operating just like a kite

Click to expand...

I guess that is where I'm having a problem. How can you expect a parachute to act like a kite? They are two different devices operating in completely different environments.

The kite is anchored to a single point, the flyer, and the wind flows in one direction relative to the anchor. The kite can be made to fly in different directions on the wind because the anchor doesn't change and the angle of attach relative to the wind can be changed by the flyer.

A parachute and it's anchor has NO relative wind. Both are moving with the air mass at the same speed as the air. The only air movement relative to the chute and it's anchor is in a vertical direction from the anchor directly toward the chute. I can see how a kite like device with solid spars can be made to create forward motion by causing the air to flow off one side of the device while the spars keep it open and inflated. Without the spars to keep things stiff, what keeps the single sheet inflated if air is allowed to escape off one side?

You can get forward motion from a hemi chute by allowing air flow out one side, but the motion is not a lot because if you open up one side too much, the hemi structure would collapse because the air needed to keep it inflated is flowing out instead. The multi-cell parachutes used by today's skydivers stay inflated because the forward motion create by their downward angle causes horizontal air flow into the cells and inflate the cells. That is what keeps them inflated, not the air flow in a vertical direction. With a single sheet you only have the vertical air flow to keep it inflated and if you let too much of that slide of one edge, there won't be enough to keep it inflated.

I'm no expert and could easily be looking at this completely wrong. If I am, please let me know, I always want to learn more. Subscribed!

As you stated air from below inflates a spherical chute, and if you open one side too much it will lose shape. But if the shape is slight and you have high wing loading you can achieve the necessary inflation as long add the pressure under the canopy is higher than the oncoming pressure from forward movement.

These Rogallo wings basically create a cone, where the rear is opened and the front is closed, but because there is enough air captured under the canopy it is able to retain shape.

4 string kites are able to change angle of attack and drag characteristics, which is independent from wind direction. You can literally make them fly sideways in the wind.



You can see on this picture the ribbing is slight, most air is still caught in the shape between the three large cells, not by the front lip. I won't achieve great glide characteristics, but a 1:1 glide radio still achieves 10-20mph forward velocity.

I dunno, make more sense?

Jeffmhopkins said:

As you stated air from below inflates a spherical chute, and if you open one side too much it will lose shape. But if the shape is slight and you have high wing loading you can achieve the necessary inflation as long add the pressure under the canopy is higher than the oncoming pressure from forward movement.

These Rogallo wings basically create a cone, where the rear is opened and the front is closed, but because there is enough air captured under the canopy it is able to retain shape.

4 string kites are able to change angle of attack and drag characteristics, which is independent from wind direction. You can literally make them fly sideways in the wind.

View attachment 271182

You can see on this picture the ribbing is slight, most air is still caught in the shape between the three large cells, not by the front lip. I won't achieve great glide characteristics, but a 1:1 glide radio still achieves 10-20mph forward velocity.

I dunno, make more sense?

Click to expand...

Not yet, but I'm trying. When you say wing loading, does that mean the vertical speed? That is the only speed you have in a chute until you induce a forward speed somehow. If you can get a 1:1 glide, that means you can get and maintain a forward speed equal to your vertical drop? In a kite it would be vertical assent equal to the horizontal wind speed. The problem with comparing a kite to a chute is that as soon as the kite changes it's vertical angle to the anchor, it's changed the angle of attack to the wind.

It sounds like you may have it worked out. I just tend to question the design because it took me a long time to get it through my head how parachutes work in an air mass and most times others are where I was and don't have it worked out yet. We are creatures of the ground and any air movement we tend to measure relative to the ground and we call it wind. We naturally see wind affecting things and reference that wind from a ground perspective. That doesn't happen with parachutes. The chute and the rocket are only dropping vertically from their point of reference, there is no horizontal wind speed, only vertical speed. If you want a design that induces a horizontal speed, it has to do that based only on the existing vertical drop and movement.

You may have the whole "no relative wind, only a vertical drop" part worked out, I just don't see it yet. Sorry.

Ragollo wings were popular as skydiving chutes for a long time and are definitely up to the task

old NASA footage of the parawing
[video=youtube;WiF0KPqnbic]https://www.youtube.com/watch?v=WiF0KPqnbic[/video]
air drop starts at 2:10 or so

That's an awesome old NASA video! Thanks for the link.

Forward velocity in this case is relative to the air column, and is represented by a stronger vector that is no longer directly from below. A kite might be changing its AOA based on elevation, but this actually represents the same as the wing with forward movement in the air column.

If a horizontal speed is faster than air column speed relative to ground, all is good.

Do you plan to fly back under RC ground control, or maybe go for something autonomous? A GPS multi-copter controller should be capable of autonomy but I'd be curious to see how the programming would go because the vehicle has differing ground speeds depending on direction of flight.

N

Handeman said:

I guess that is where I'm having a problem. How can you expect a parachute to act like a kite?

Click to expand...

While the environments are different, these devices are closer than may appear. Indeed some designs converge almost entirely:

https://www.google.com/search?q=kite+parafoil&tbm=isch
https://www.google.com/search?q=paraglider&tbm=isch

Ari.

This project will have options for both GPS autonomous flight and manual flight control. Onboard sensors include GPS, barometer (and thermometer), magnetometer, gyroscope, accelerometer and onboard video capture. Information is relayed down to the base station via a 70cm transceiver operating at 4800. The onboard processor is a Cortex M4 running at 94MHz.

Programming wise the auto pilot will use the magneometer/gyro/gps heading to account for wind and fly to a preset location and then spiral down to 300 feet where the backup 45" hemispherical parachute still deploy for a nice soft landing. Also, if the main parachute gets tangled the computer can deploy the backup, or remotely I can deploy it as well.

It's all custom, and detailed in a couple of posts:

https://hackaday.io/project/6381-high-power-experimental-rocket-platform

https://www.rocketryforum.com/showt...e-Google-Earth-Tracking&p=1495026#post1495026

https://www.rocketryforum.com/showthread.php?127775-The-EX-CATO

Handeman said:

You may have the whole "no relative wind, only a vertical drop" part worked out, I just don't see it yet. Sorry.

Click to expand...

If it helps, a parachute that generates lift is like a glider. It generates its own relative wind.

-- Roger

iter said:

While the environments are different, these devices are closer than may appear. Indeed some designs converge almost entirely:

https://www.google.com/search?q=kite+parafoil&tbm=isch
https://www.google.com/search?q=paraglider&tbm=isch

Ari.

Click to expand...

I like all of those, but I didn't see any of those that were single sheet. They are all "cell" type parasails unless I missed one. I guess that is what I was looking at. Forward speed will fill the cells and stiffen the chute. I don't know how you do that without the cells or stiffeners.

jadebox said:

If it helps, a parachute that generates lift is like a glider. It generates its own relative wind.

-- Roger

Click to expand...

I completely agree. I just don't see how you can design a single sheet chute that will stay open and create any appreciable forward speed. If you use stiffeners or air filled cells to keep the chute inflated, there are lots of ways to do it, but a single sheet without the stiffeners.... it seems like you're limited to a hemi type, or something similar, with vents to get some forward movement.

I'm looking forward to seeing something. I don't know exactly what a Ragollo wing is and haven't had time to look it up yet.

Handeman said:

I completely agree. I just don't see how you can design a single sheet chute that will stay open and create any appreciable forward speed. If you use stiffeners or air filled cells to keep the chute inflated, there are lots of ways to do it, but a single sheet without the stiffeners.... it seems like you're limited to a hemi type, or something similar, with vents to get some forward movement.

I'm looking forward to seeing something. I don't know exactly what a Ragollo wing is and haven't had time to look it up yet.

Click to expand...

Oh, I see. I think your concerns are that without a relative wind, the single-sheet 'chute won't be able to open and support itself. And that it wouldn't form a rigid-enough shape to stay open and glide.

But, a falling parachute does feel a relative wind until it opens and reaches it's terminal speed. So, that would provide the "wind" to open the 'chute. And, once it starts glide, the relative wind is at an angle based on the descent rate and forward speed, not straight up as with a non-gliding 'chute.

In the design that Jeff is considering, it appears like the attachment of the shroud lines and the weight of the rocket hanging from them (balanced right) provides the anchor that allows the parachute to act like a kite. They also cause the 'chute to assume a shape that would stay open and "rigid" as the air flows past it.

If the above sounds like rambling it is because I am trying to understand it myself.

I used to have a kite (probably still do) that looked a lot like what Jeff is working on. I carried it with me because it could be folded up and stored in a small pouch along with the line and handle for it. I used to live near the beach in Northwest Florida and it was fun to have a kite handy.

-- Roger

Vowels are transposed: Rogallo Wing.

Finalized ribbing and darts:








Next comes the laborious task of shroud line attachments...

That is looking like an outstanding job of construction! I really hope you can get it to work the way you want.

I built a seven cell parasail chute that has a 15 deg downward angle. It works great. I also have a control unit in a 4" coupler that works great. The intention was to be able to put the chute and the control unit in any 4" dia. rocket. Unfortunately that hasn't worked out. The chute works and the control unit works. It's the deployment I've had problems with.

Definitely looking forward to anything you can show me that would help me get that deployment to work right.

I'm worried about deployment as well. I'll be creating a pilot chute and deployment bag to help ease the process. And if all else fails my rocket is setup with a backup 44" 14 gore semi hemispherical parachute with intent of high speed deployment.

When I get the chance I'll post my ideas for the control tube. It's kind of unique as it is pulled out of the upper section after deployment and then lays sideways to increase distance between control lines.

I'll be away on business for the next month or so regrettably, but I have finished the shroud line attachment loops, so next is just bridling it...

Jeffmhopkins said:

IWhen I get the chance I'll post my ideas for the control tube. It's kind of unique as it is pulled out of the upper section after deployment and then lays sideways to increase distance between control lines.

Click to expand...

This is what I did for my steerable chute project, I have used it to successfully deploy a spherical chute with two sets of lines and control lines for reefing. Getting the setup right took some work. My nasa wing kite is on its way and will fly at MWP. Eventually I hope to commercialize it as a kit.

I'll be using two continuous rotation servos as well in the brake lines to get more throw and really be able to stop the chute and land safely. At least that's the plan. If not I'll get down to 300 or so feet and pop the backup parachute for a slow landing.

Continuous servos will cause you a problem because they don't remember 0 so your steering won't stay trimmed, also they won't be exactly the same speed and will get it out of sync. I use 6 turn sail winch servos and get 16"of travel.

I was going to implement a pattern wheel on the servos to track them , but I wasn't aware of sail winch servos, those sound prefect.

The only problem with winch servos if you use the included drum they can bind. I think I have a solution to this, we will see in October.

First bridle test! I look a little goofy, but no wind right now

[video=youtube;cwzfTMIDBSw]Http://www.youtube.com/watch?v=cwzfTMIDBSw[/video]

[video=youtube;0PywmxXToD4]https://www.youtube.com/watch?v=0PywmxXToD4[/video]

At BALLS there was a GPS guided ram air chute.
8" diameter airframe, controls all custom, not made from hobby components.
It worked.

M

I liked the idea of a full ram air parachute or parafoil, but size restriction in my 3" rocket brought me to this custom design that I'm feeling quite good about.