Parachute Recovery for the sUAS Industrya Tutorial

• Why you need it – Safety, Regulatory, Insurance, Loss Mitigation

• It’s all about the Parachute – Comparing types and why it matters

• Deployment Methodology

Who is Fruity Chutes

Started for hobby rocketry recovery in 2007. Rocketry recovery is a very demanding in terms of harsh recovery situations – high speeds, altitudes, stuff goes wrong a lot!

Began to sell to emerging sUAS users around 2009.

sUAS now outpacing other industry segments for need for Parachute Recovery Systems (PRS).

Sold well over 1000 UAS systems to large range of customers. Many companies are integrating now.

Earned a place as a topic expert!

Some Marque Customers…

Why do I need a Parachute?

Some Fixed Wing systems need PRS – they are primary or backup recovery.› Examples, no landing gear, PRS is primary recovery› Limited space to land, i.e. in the jungle or rugged

terrain. Other drivers toward the need for Parachute

Recovery Systems (PRS)› Safety – Protect people and property› Regulatory – Not lost on government agencies is backup safety

systems make since for public safety. › Insurance – Insurance companies drive need via lower premium

rates or even mandate to get insurance.› Cost of Failure Mitigation – Parachute safety but a fraction of UAS

costs in case there is a failure.

UAS Systems not fool proof, they fail. And any system even with redundancy can also fail.

Can be mechanical, electrical, software, environmental – think wind, rain, etc.

Failre result usually similar, impact into the ground!

People can be hurt, and property can be damaged.

Safety – Helps protect people and property

Regulatory – Government Mandating Backup Safety

Government agencies primary driver is need to protect the public.

They recognize even the best systems can fail. Safety systems like Parachutes greatly lessen risk of

injury or property damage. But PRS are not perfect either. But UAS with PRS will have statistically much better outcome than not!

Many UE countries now mandate. Canada (?) and some South America countries do as well.

ASTM F38.02 subcommitee is working with FAA now on safety standards for commercial use over populated areas. Parachute safety is part of the standard!

Insurance – Providers want to lower their risk and underwriting cost

Insurance industry driven by risk assessment vs cost of claims settlement.

PRS in their eyes is a quick win – statistically lowers risk of personal injury, and lower property damage.

Some companies are requiring PRS in order to get business operational liability coverage. Also will lower premium fees.

Cost of Failure Mitigation – PRS stops total system loss

Why most people contact us about a PRS. A $50K system can be protected for <5% of the UAS cost!

Alternative is failure can lead to total UAS loss.

PRS makes since when the value of the UAS is 10 x the cost of the PRS. At $5K system cost or more it makes since.

It’s all about the Parachute – Comparing types and why it matters

There are many styles or parachutes. We’ll discuss the various styles, the advantages and disadvantages of most popular chutes… These include:› Flat Sheet Chutes› Multi-Panel Chute› Elliptical, or Conical Chute› Annular, Pull down Apex, Toroidal

And why it matters!

Challenge in Comparing Types

Before we start there are challenges in comparing designs:› Inconsistency in how chute size is sold to the user.

Some as canopy area Some as circumference across canopy FC measured based on projected frontal area, i.e the opening diameter Complex canopy shapes make comparison hard.

› Ultimately you want to know a chutes designs coefficient of drag, or Cd, for a given reference area.

› Knowing the Cd is essential to calculate the descent rate under any given weight, size, and base altitude.

› We feel it’s simplest to measure the chute based on the opening diameter of the skirt. The “reference area” is simply the area of the opening. This along with the Cd and you can predict the chute performance at a given size, and load weight!

Goal in design is maximize drag as least possible weight. This means a higher Cd is essential!

Sheet Chute – like Top Flight

Advantages:› Simple Design› Low Cost

Disadvantages:› Inefficient, Cd of approximately 0.7› Bulky for a given load› Poor Stability, can oscillate above the load› Lower strength – this is partly due to materials selection

Multi- Panel Chutes, like Rocket Man, TAC or Sky Angle

Advantages:› Good stability, stays above the load› Very strong, usually have over the top riser connections› Fewer risers to tangle – easier to untangle if they do› Probably most popular HP Rocketry style currently

Disadvantages:› Moderate, Cd of approximately 1, little published info on this. Type not used

outside Rocketry and racing that we can find.› Use heavier webbing for shroud lines (fewer connections to carry the load)› More complex design, two to three patterns shapes needed. Use a lot of tape

reinforcement on edged and on all seams.› Can rotate under load due to variations in symmetry. › Can sometimes breathe under slower descent (jelly fish)› Limited use in UAS as far as we can tell

Elliptical, Spherical, and Conical

Advantages:› Good stability at lower speeds, stays above the load› Good strength to weigh compromise› Better efficiency, Cd of about 1.5 – 1.6› Packs into smaller space per load rating› Simple repetitive design – only one pattern shape needed

Disadvanteges:› At high speed it can wobble› Multiple gores means more sewing and higher cost

Annular, or Pull Down Apex

Advantages:› Good stability at typical main chute descent speeds.› Good strength to weigh› Very high efficiency, Cd of about 2.2 – 2.4. Noted as the highest known Cd for

unguided chute for a given canopy area› Packs into smallest space per given load rating› Simple repetitive design – only one pattern shape needed› Fast opening good for low altitude UAS› Popular as reserve chutes for parachute jumpers, hang gliders, and ultra-lights

Disadvantages:› Not as good at high(er) speed › Very fast opening can also cause high opening shock load› More complex to make, apex pull down adds to complexity and cost

Why does all this stuff matter?

Ideal parachute has the higest load capability at least weight. This means a chute with a high Cd is better.

Different parachute designs can be boiled down to a single number called “Performance Rating” (PR) and then compared objectively.

PR is simple ratio between the parachutes load capability at a given descent speed divided by the parachute’s static weight.

Higher is better!

And now some comparisonsChute Type Chute size

determined by:

Cd Reference Area

Stability Cd Performance Rating @ 15 fps **

Use

Flat Sheet Distance across fabric

Area of fabric Ok at low speed,poor at high speed

Low – 0.7 Approx. 8:1 Main or drogue

Panel Style Distance across top panels, usually on diagonal

Area of fabric Good vertical stability, can rotate or spin

Med – 1.1 Approx. 10:1 Mostly as a Main in Rocketry

Elliptical , spherical, conical

Opening diameter, or canopy circumference

Area of opening

Medium high speed, Good low speed

Med – 1.6 13.4:1 Main or Drogue chute

Annular (Iris Ultra)

Opening diameter

Area of opening

Good medium to lower speed

Highest at 2.2

30:1 High performance main chute. Ideal for UAS recovery

Deployment Technology in BriefAlso known and getting the laundry out!

We will discuss several methods of chute deployment:› Fixed Wins UAS deployment using a

Deployment Bag and pilot chute› Compression spring based Parachute

Launchers› CO2 Ejection Systems

Fixed Wing UAS Recovery using a Deployment Bag

› Passive, requires forward flight and air movement for extraction.

› Used for Fixed Wing UAS› Small pilot chute used for extraction› Simple and low cost› Not suitable for Multicopters!

Compression Spring Parachute Launchers

Examples are Skycat Launcher, and MARS systems Active deployment does not require forward flight – use with

multicopters Relatively low cost. Limited in chute size by spring strength to around 60”D chutes. Because of this max load around 10Kg system as a safety only

device. Descent rate too high to eliminate damage. Can use with larger chutes by spring ejecting smaller chute which

acts a pilot for larger. But this delays deployment.

CO2 Deployment Systems

Examples Peregrine Sentinel, Peregrine IDS, DJI Dropsafe

Active ejection using CO2 gas, more energetic deployment, faster deployment time

Peregrine systems rated up to 100Kg loads. And also feature very high packing densities, meaning small size.

Gaps – what is missing?

While there are products to address the parachute recovery, manufactures are not necessarily thinking of failsafe deployment for the parachute built into products.

Parachute deployment needs to be standard on autopilots. Both manual, and programmatic based.

Backup failsafe devices separate from autopilot need to be developed. Algorithmic deployment based like too fast a descent speed, unsafe attitude,out of bounds, etc…

ESC need failsafe override to cut power in case autopilot fails. You can not deploy a parachute systems if rotors are active!

Airframes are not designed with parachute systems in mind. Currently they are an after thought or it’s up to the buyer to figure it out.

Further Information: Parachute Recovery Tutorial: http://

fruitychutes.com/uav_rpv_drone_recovery_parachutes/uas-parachute-recovery-tutorial.htm

More articles on recovery: http://fruitychutes.com/other_fun_stuff/genes_blog.htm

THANK YOU!