Questions regarding equations for calculating the force of a parachute opening.

[Hammertime1041]

Hello everyone.

I am currently working with a collegiate rocketry team to develop and fly a flight vehicle that is going to test a student designed roll-control system. Currently, I am performing an analysis of the rockets recovery system, to ensure that all components are strong enough to reliably withstand the forces they will experience during the flight. Recently, I have been trying to determine the forces applied to the recovery harness when the drogue and main parachutes open, but have been getting stumped by my calculations regarding the drogue parachute. I am currently using two different equations to calculate this force, in order to verify that I am calculating this properly. The first method (and simplest method) is to use our OpenRocket simulations of the rocket to determine the acceleration it will experience during the recovery events and plugging that and the mass of the rocket into Newton's Second Law (Force = mass * acceleration) to determine a force. The second method I am using is the drag equation, Drag Force = (1/2) * (air density) * (velocity)^2 * (drag coefficient) * (reference area). I am also determining the air pressure at drogue and main deployment based on equations found in the official document regarding International Standard Atmosphere from 1976 in an effort to increase accuracy. When using these two methods to calculate the force at main parachute deployment, the second method is showing a force approximately 30 pounds-force lower than the first method, calculating 185 lbf and 154 lbf respectively. While I could believe that difference is just due to the different levels of accuracy of the two equations, the drogue deployment for has me scratching my head. When using the first method, I am calculating approximately 125 lbf while the second method is showing about 33 lbf. The accelerations and velocities being used are the total acceleration and velocities at parachute deployments being shown by the OpenRocket simulations, and we are using parachutes from Rocketman Parachutes and therefore are using the advertised drag coefficient of 0.97.

These are the specific calculations being done, method one on the left and method two on the right:


Overall, I haven't been able to figure out why this difference in drogue deployment force is appearing, and was hoping someone here would have more insight or know where to look regarding this.

 

[Spacedog49Krell]

Why are you using acceleration values of 47.13m/s^2 (4.8 g's) and 70.01 m/s^2 (7.1 g's) at drogue and main deployment in F=ma equation and using velocity values of 33.9 m/s and 15.95 m/s in the drag equation?

A velocity of 33.9 m/s is, for me, very high for drogue deployment.

 

[Hammertime1041]

Why are you using acceleration values of 47.13m/s^2 (4.8 g's) and 70.01 m/s^2 (7.1 g's) at drogue and main deployment in F=ma equation and using velocity values of 33.9 m/s and 15.95 m/s in the drag equation?

A velocity of 33.9 m/s is, for me, very high for drogue deployment.

In OpenRocket, we are simulating flights in 0, 5, 10, 15, and 20 mph winds at both 5 and 10 degree launch angles. I took the peak velocities and acceleration at deployment for each parachute and used the highest possible values under normal flight conditions. Those values were the maximums I observed in the simulations, so I am using them to ensure the recovery hardware can survive parachute deployment under the most intense conditions where the rocket will actually fly safely.

 

[drewnickel]

My assumption for drogue is to estimate drag based on velocity at apogee and for the main is to estimate drag at the rocket's terminal velocity under drogue. In reality the parachutes don't instantly open and so the peak loading is somewhat lower, but assuming they are opening instantly builds in a safety factor. I also assume the maximum force on the shock cord for the drogue will be the same as for the main, as the drogue line will probably pull taught when the main deploys. Even with those very conservative estimates I'd recommend a safety factor of two over opening forces, recovery is one of those things that doesn't hurt to over-build but can be catastrophic if under-built.

 

[Blast it Tom!]

I'm kinda out of my league here, so someone correct me if I'm too far off-base. I'm just thinking off the cuff... Acceleration is a change in velocity ove a period of time; and one would think you'd try to pop your drogue near apogee when velocity would be small, and thus the change in velocity not so great as to exceed 1 g. So are you assuming the chute goes full open instantaneously? Certainly that would be conservative. But just thinking through it, then, I'd say to myself, "okay we were traveling at V1, chute comes open and exerts it's full force, that will slow us to down to V2 (drogue velocity) in x-ty seconds... I just don't know where the acceleration is coming from in the simulation, then you pick it up and use it.

But again, I'm answering kinda off-handedly in the garage on my phone... I might be way out in left field...

 

[Handeman]

You may be barking up the wrong tree here. I'm not sure the opening force of the chute is going to be the largest loads on the recovery system.

The largest loads are usually when the two halves hit the end of the shock cord at apogee when the charge goes off. The drogue opening, if it pops open before the two halves hit the ends of the cord, will usually reduce the shock some because the opening and drag reduces the speed the two pieces are moving apart. The larger your apogee charge is and the number of shear pins, the higher those shock loads are going to be.

A high speed video with a yard/meter stick at the opening point will let you measure the actual speeds when ground testing. If you block one end so it can't move and use the mass and speed of the other half, you can calculate the full energy in the system at deployment. The halves will slow slightly in actual flight, but I would use the full value at opening and add about 50% to the energy to determine what the components need to be able to withstand.

For a main chute opening, worst case would be the rocket separating at apogee and coming down ballistic with just the two halves separated by the cord to provide drag to slow it down. The main will almost certainly open below the rocket and before any of the rocket loads the chute. Assume the chute is stationary, and assume the payload section is moving at about 150 ft/sec and deaccelerates within 2 or 3 inches. Then the booster section will do about the same thing when it his the end of the apogee cord.

I think you will find that those shock loads on the recovery cords and anchor points are going to much higher that what your chute opening loads will be.

You might want to look through the Parachute Recovery Systems Design Manual also. Lots of great info there.

 

[Blast it Tom!]

You may be barking up the wrong tree here. I'm not sure the opening force of the chute is going to be the largest loads on the recovery system.

The largest loads are usually when the two halves hit the end of the shock cord at apogee when the charge goes off. The drogue opening, if it pops open before the two halves hit the ends of the cord, will usually reduce the shock some because the opening and drag reduces the speed the two pieces are moving apart. The larger your apogee charge is and the number of shear pins, the higher those shock loads are going to be.

A high speed video with a yard/meter stick at the opening point will let you measure the actual speeds when ground testing. If you block one end so it can't move and use the mass and speed of the other half, you can calculate the full energy in the system at deployment. The halves will slow slightly in actual flight, but I would use the full value at opening and add about 50% to the energy to determine what the components need to be able to withstand.

For a main chute opening, worst case would be the rocket separating at apogee and coming down ballistic with just the two halves separated by the cord to provide drag to slow it down. The main will almost certainly open below the rocket and before any of the rocket loads the chute. Assume the chute is stationary, and assume the payload section is moving at about 150 ft/sec and deaccelerates within 2 or 3 inches. Then the booster section will do about the same thing when it his the end of the apogee cord.

I think you will find that those shock loads on the recovery cords and anchor points are going to much higher that what your chute opening loads will be.

I may subscribe to your newsletter. Well put! That was more or less my point, that energy and momentum methods are more suitable.

 

[Spacedog49Krell]

In free fall, acceleration is a maximum of 9.8067 m/s^2.

F= (11.8 kg) (9.8067 m/s^2) = 115.719 N = 26.0146 lbf
Velocity will increase over time until terminal velocity is achieved.

Using your drogue velocity deployment value of 33.93 m/s, your rocket has been in free fall for 3.46 seconds and has dropped 58.7 meters. My DIY flight computers detect apogee <1 sec with vertical velocities <10m/s before deployment.

I'm assuming that the 15.95 m/s main velocity is the drogue terminal velocity.

 

[JoePfeiffer]

OR uses the drag equation to compute the parachute's drag, and reports that. It assumes instantaneous opening. Its reported acceleration on the time step when the chute opens comes from the drag force, gravity, and mass (and the coriolis acceleration, though I can't imagine that's significant).

 

[Spacedog49Krell]

Parachute deployment loads are a critical parameter for a successful vehicle recovery. The university projects that I advise on spend significant time testing recovery systems. One university project is flying two full scale test vehicles devoted to recovery systems testing and collecting data on deployment loads that are 8X this project's loads.

 

[Spacedog49Krell]

OR uses the drag equation to compute the parachute's drag, and reports that. It assumes instantaneous opening. Its reported acceleration on the time step when the chute opens comes from the drag force, gravity, and mass (and the coriolis acceleration, though I can't imagine that's significant).

The assumption of instantaneous parachute opening and deceleration is a minor issue I have with OR simulations. I've been flying 500Hz flight computers for the past 5 years. The data I have collected shows the different phases of a parachute's deployment. I find it interesting that it takes 40-60 ms for a 15" parachute to inflate. Another 160 - 200 ms of deceleration to the final decent velocity. It makes for a great science fair project.

OR does simulate launch rail velocity and initial flight stabilization oscillations with great accuracy. I wish they had better simulation of parachute shock loads.

 

[Tractionengines]

OR does simulate launch rail velocity and initial flight stabilization oscillations with great accuracy. I wish they had better simulation of parachute shock loads.

TOO Many variables in personal options. The same parachute with different packing will have greatly different deployment. Going from "most aggressive" to "least aggressive"

* Wadding only. Parachute in the open, lines folded inside. "pops" quick.

* wadding only. Parachute with lines wrapped "estes style" around the parachute. Needs to (hopefully) unwrap lines, then chute "pops" open.

* burrito wrap will have a slight slowing of both of the above.

* deployment bag is significantly slower. As the lines need to all release and stretch to full extension before the chute comes out. Then the Canopy is restricted as it is coming out. It can only reach full open after the bag is off.

*Adding a slider ring. To the lines, will slow the opening time.

LOTS more options. (Should be a NARCON presentation some year by a parachute manufacturer, or deployment specialist...) The issue is most of us experiment a little find something that "works for me" then just adapt/refine that slightly. (Which is great to develop consistency, but limits broader experience.)

 

[JoePfeiffer]

The assumption of instantaneous parachute opening and deceleration is a minor issue I have with OR simulations. I've been flying 500Hz flight computers for the past 5 years. The data I have collected shows the different phases of a parachute's deployment. I find it interesting that it takes 40-60 ms for a 15" parachute to inflate. Another 160 - 200 ms of deceleration to the final decent velocity. It makes for a great science fair project.

OR does simulate launch rail velocity and initial flight stabilization oscillations with great accuracy. I wish they had better simulation of parachute shock loads.

There's a part of me that would like to see more accurate chute opening, but (1) I haven't run across any really believable models, and (2) @Tractionengines points out just how many variables you need to account for (and, as he points out, I'm sure a little thought would turn up many, many more). Meanwhile, assuming instantaneous gives you a worst case you can design your hardware around and the try to reduce. I don't really see this one changing any time soon (as usual, if you see a good way to improve the model that we don't, start coding!).

 

[Handeman]

I like the idea of getting some firm number for chute opening loads, but to my way of thinking, when it comes to DD rockets, that's just an interesting rabbit hole to go down that provides no practical help when when trying to size recovery cords and anchor points to the shock loads the recovery components must hold up to.

Unless you are using a free bag with pilot chute, you don't usually get close to seeing chute opening loads on the whole recovery system. I use that kind of system on my first L3 rocket and even with the time it takes to pull all the shroud lines out and then the chute out of the bag, the fin can is just leaving the inverted V and is seldom at the end if it's cord when the chute opens. It hits that after the main is already open, causing a second shock to the recovery system that is unrelated to chute opening loads.

How many flights have you seen where the fin can hits or nearly hits the open chute as it falls past. This seem to happen to a DD flight at every launch. That chute opening is only going to affect the upper cord and the anchor point in the nose cone and payload. The payload to fin can cords and anchor points will be stressed when that fin can hits the bottom of the apogee cord and nothing about chute opening loads comes into affect.

The same can be said for a standard DD flight with a right sized drogue where the two halves fall in a nice controlled inverted V. The nosecone comes off at about a 45° angle to the ground and the chute is usually completely open before the rest of the rocket finally falls in line under the already open chute. The chute opening forces will have no affect on the shock loads felt on the cords and anchor points as the parts of the rockets fall and hit the ends of the cords below the already open chute.

I think the OP asked about chute opening forces because, like almost all new college teams, they have no practical knowledge of flying large DD type rockets and he assumed the opening shock loads of the chute would be what he needs to design for. That is where their mentor can provide practical knowledge about recovery system shock loads and what causes those loads and help them not waste time going down the chute opening load rabbit hole.

 

[Spacedog49Krell]

As more of us start flying 500Hz, like the Blue Raven, or faster flight computers, simulator developers will soon have sufficient high resolution data for modeling. Building to the worst case scenario, is fine for us casual fliers. The university projects, especially liquid projects, have weight constraints for maximum performance. Simple things like quick links are a weight penalty compared to their replacement.

Jeff, I agree with you that parachute loads for HPR vehicles is a rabbit hole. An interesting rabbit hole at high speed, but one that I don't spend much time on. The liquid university projects I've advised on are very different. Once depleted of propellants and pressurant gas they become very flexible and easily bend from deployment shock and landing impacts.

 

[Handeman]

As more of us start flying 500Hz, like the Blue Raven, or faster flight computers, simulator developers will soon have sufficient high resolution data for modeling. Building to the worst case scenario, is fine for us casual fliers. The university projects, especially liquid projects, have weight constraints for maximum performance. Simple things like quick links are a weight penalty compared to their replacement.

Jeff, I agree with you that parachute loads for HPR vehicles is a rabbit hole. An interesting rabbit hole at high speed, but one that I don't spend much time on. The liquid university projects I've advised on are very different. Once depleted of propellants and pressurant gas they become very flexible and easily bend from deployment shock and landing impacts.

I am not familiar with liquid projects, but unless they are able to ensure a recovery profile that is significantly different than most large solid rocket projects, I think the recovery forces and shock loads are going to be similar. Chute opening loads are well defined with man rated chutes and how they operate, but our rockets don't operate the same way so the loads during chute openings and deployments events are much different.

Kind of what makes the college project so interesting on how they solve those problems. It's just better in my opinion if their mentors can give them a heads up on how that all actually works so they don't have to re-invent the wheel every time. Keep advising and good luck!

 

[Hammertime1041]

I think the OP asked about chute opening forces because, like almost all new college teams, they have no practical knowledge of flying large DD type rockets and he assumed the opening shock loads of the chute would be what he needs to design for. That is where their mentor can provide practical knowledge about recovery system shock loads and what causes those loads and help them not waste time going down the chute opening load rabbit hole.

You hit the nail right on the head with that one. Having only been introduced to rocketry last year at the beginning of the pursuit of an aerospace engineering degree, I am very inexperienced regarding DD systems having only flown a single rocket with a DD system. I was fully convinced that the forces I needed to worry about were the shock from the parachute opening. Sadly, my club doesn't have a mentor, so I've generally been on my own for figuring this out. Thankfully though, your other post as well as others have been very insightful. I'll have to reevaluate my approach and instead try taking a deeper look into the shock cords for the loads applied to the hardpoints rather than parachute deployment forces. Thank you for the input.

 

[Handeman]

You hit the nail right on the head with that one. Having only been introduced to rocketry last year at the beginning of the pursuit of an aerospace engineering degree, I am very inexperienced regarding DD systems having only flown a single rocket with a DD system. I was fully convinced that the forces I needed to worry about were the shock from the parachute opening. Sadly, my club doesn't have a mentor, so I've generally been on my own for figuring this out. Thankfully though, your other post as well as others have been very insightful. I'll have to reevaluate my approach and instead try taking a deeper look into the shock cords for the loads applied to the hardpoints rather than parachute deployment forces. Thank you for the input.

Glad I could help. My advice is to find a NRA/TRA L3 mentor! Even if it's just someone remote that can sit in zoom meeting and bounce ideas off of in emails. From the multiple college teams that have come to our site for test launches, I've found that most professors don't know the practical issues involved with launching large projects. A mentor can help you get past all the early issues and problems that will come up, and there are many, until your professors learn enough to be a qualified mentor themselves.

Good luck with your project.

 

[Buckeye]

The assumption of instantaneous parachute opening and deceleration is a minor issue I have with OR simulations. I've been flying 500Hz flight computers for the past 5 years. The data I have collected shows the different phases of a parachute's deployment. I find it interesting that it takes 40-60 ms for a 15" parachute to inflate. Another 160 - 200 ms of deceleration to the final decent velocity. It makes for a great science fair project.

OR does simulate launch rail velocity and initial flight stabilization oscillations with great accuracy. I wish they had better simulation of parachute shock loads.

Your data says it takes a mere 0.26 seconds to inflate a chute and reach terminal velocity? Most hobbyists would consider that instantaneous.

Looks like there is 1.0 s of deceleration from deployment to terminal velocity harcoded in the simulation. Not sure what that is all about.

 

[JoePfeiffer]

Looks like there is 1.0 s of deceleration from deployment to terminal velocity harcoded in the simulation. Not sure what that is all about.

It's not hardcoded. The program calculates the force on the parachute on every time step, and calculates the acceleration. How long it takes to come to terminal velocity is just the result of that.

 

[Spacedog49Krell]

Your data says it takes a mere 0.26 seconds to inflate a chute and reach terminal velocity? Most hobbyists would consider that instantaneous.

Looks like there is 1.0 s of deceleration from deployment to terminal velocity harcoded in the simulation. Not sure what that is all about.

View attachment 626605

Here are five examples of what OR misses during the 1 second after parachute deployment. I find that I can distinguish my rockets by their parachute deployment signature better than their powered flight profile.
The MiniMean rockets are identical except for the motor mounts of 24mm & 29mm. The Bluebird is the same rocket powered by different AT G motors; G74-8, G40-10, & G40-10 that went 17 second delay. That 17 second delay was 6 seconds into a ballistic freefall when the ejection charge fired, and the opening parachute zippered the body 19.77 seconds into the flight.

 

[kjhambrick]

Piling on ...

These are Drogue and Main Deployment acceleration for two flights where I flew to 4000 ft or so where the drogue was deployed by my Blue Raven at apogee followed by main at 750 ft.

This is my level 2 flight on a J350W in "Nocturnal Missions" -- a Glass upscale of a LOC Vulcanite and is 2819 grams dry mass.


This is an I225FJ in "Spock's Johnson" an ancient, many times repaired LOC Vulcanite that is 1216 grams dry mass:

Note that most of the acceleration is due to the ejection charges in all four plots.

And this is my level 1 flight on a 25-year old H128W that smoldered on the pad before lighting and which only sent the rocket to 850 ft or so instead of 1650 ft.

It is interesting because drogue deployment was followed almost immediately by the main.

The negative shock at 11.7 seconds is from the drogue shock cord pulling backwards on the AV-Bay.

The main ejection charge was at 13 seconds and the noise from 13 -to- 15 sec is the main opening.

Both of these rockets are set up for 'classic' dual deployment ( drogue in the fin can, main is in a forward payload tube by the nose ).

In every case the drogue ejection charge kicks the AV-Bay forward ( same direction as motor thrust ) and the main ejection charge kicks the AV-Bay backwards.

Also in every case, the acceleration due to the ejection charge exceeds the acceleration due to the chute opening.

Whee ! Fun Stuff !

-- kjh

 

[kjhambrick]

Part 2 ...

Back in May 2023, when I got back into rocketry and started using OpenRocket, I asked about the instantaneous opening on the main chute thinking that there might be a parameter to set the time to open a chute OpenRocket - Chute Opening Time

As @Buckeye noted above, the simulated acceleration due to the chute opening is not necessarily usable for determining the REAL forces on the recovery equipment.

I am not complaining, I can't think of a better way to do it unless there was maybe a delta-t parameter to relate to OR that 'it takes n-seconds for my chute to open and to slow the rocket to terminal velocity' ...

The way it works now is good for worst-case -- if your chute did open instantaneously then that would be the acceleration that the system would feel.

I pack my chutes wrong -- I always have -- I lay most of the shroud lines inside the flattened chute, roll it up, top to bottom into a burrito and then wrap it a few times with the remaining shroud lines.

I AM NOT RECOMMENDING MY METHOD FOR ANYONE ELSE

But my main seems to open consistently this way, even my old AltAcc accelration data looked about the same as my new Blue Raven acceleration data.

It takes a second or two for my main to unroll and open and for the rocket to settle into terminal velocity.

Finally to the point ...

As @Handeman said, in the real world, I don't think the greatest force is due to the chute opening.

In my rockets, the largest magnitude acceleration is ALWAYS due to the ejection charge.

And if you do it right, most of that force can be absorbed a little at a time if your shock cord is 'long enough' and if you Z-Fold the shock cord into several little bundles and tape the little bundles with masking tape.

Note the large positive accelerations in my plots above when the drogue ejection charge fires which is followed by a smaller series of negative accelerations as the Z-Folds break the tape and the shock cord extends to full length.

Then when the main is deployed there is a large negative acceleration followed by a smaller series of positive accelerations.

Anyhow, don't let the huge acceleration in OpenRocket scare you, if you set up your hard-points and shock cords for the worst case, I imagine your chute will be fine.

Finally, back to your oiginal Question: Why does the drag equation for the drogue diverge so greatly from the results when you apply the OpenRocket acceleration and the rocket mass to Newton's Third Law ?

The drag equation will tell you how much force is on a chute when it hits terminal velicity.

But I would be suspicious of the magnitude of the acceleration value extracted from OR when the chutes open because it is reported as instantaneous.

Maybe if you calculate acceleration for yourself as dv/dt = ( v2 - v1 ) / ( t2 - t1 ) where ( t2 - t1 ) is in the range of 1 -to- 3 seconds you might get a number that makes a little more sense ?

-- kjh

 

[Last Ox]

The primary driver of both acceleration and peak tensile load is the elasticity of the tether (combined with, for chute loads, the that of the shrouds and canopy geometry under load). Zero elasticity would mean infinite acceleration and tension. Real tethers are elastic, but (for aramid) not very - thus rockets typically see large forces.

Mountaineers use low stretch polyester or ultra strong aramid/UHMW poly only for fixed lines - belays or anything you might fall against is relatively stretchy nylon, to mitigate shock.

You can't just put real shock cord in the tether - the rebound would wreck things. You can include energy absorbing elements - braiding, sliding knots, tearable/breakable elements, etc. to greatly reduce shock and tether strain. For years life-line tethers have included a friction pack or stitched z-fold for this purpose.

The little rubber bands or blue tape help absorb energy (but not much).

None of this is very amenable to calculation or simple modeling.

 

[Spacedog49Krell]

Part 2 ...

Back in May 2023, when I got back into rocketry and started using OpenRocket, I asked about the instantaneous opening on the main chute thinking that there might be a parameter to set the time to open a chute OpenRocket - Chute Opening Time

As @Buckeye noted above, the simulated acceleration due to the chute opening is not necessarily usable for determining the REAL forces on the recovery equipment.

I am not complaining, I can't think of a better way to do it unless there was maybe a delta-t parameter to relate to OR that 'it takes n-seconds for my chute to open and to slow the rocket to terminal velocity' ...

The way it works now is good for worst-case -- if your chute did open instantaneously then that would be the acceleration that the system would feel.

I pack my chutes wrong -- I always have -- I lay most of the shroud lines inside the flattened chute, roll it up, top to bottom into a burrito and then wrap it a few times with the remaining shroud lines.

I AM NOT RECOMMENDING MY METHOD FOR ANYONE ELSE

But my main seems to open consistently this way, even my old AltAcc accelration data looked about the same as my new Blue Raven acceleration data.

It takes a second or two for my main to unroll and open and for the rocket to settle into terminal velocity.

Finally to the point ...

As @Handeman said, in the real world, I don't think the greatest force is due to the chute opening.

In my rockets, the largest magnitude acceleration is ALWAYS due to the ejection charge.

And if you do it right, most of that force can be absorbed a little at a time if your shock cord is 'long enough' and if you Z-Fold the shock cord into several little bundles and tape the little bundles with masking tape.

Note the large positive accelerations in my plots above when the drogue ejection charge fires which is followed by a smaller series of negative accelerations as the Z-Folds break the tape and the shock cord extends to full length.

Then when the main is deployed there is a large negative acceleration followed by a smaller series of positive accelerations.

Anyhow, don't let the huge acceleration in OpenRocket scare you, if you set up your hard-points and shock cords for the worst case, I imagine your chute will be fine.

Finally, back to your oiginal Question: Why does the drag equation for the drogue diverge so greatly from the results when you apply the OpenRocket acceleration and the rocket mass to Newton's Third Law ?

The drag equation will tell you how much force is on a chute when it hits terminal velicity.

But I would be suspicious of the magnitude of the acceleration value extracted from OR when the chutes open because it is reported as instantaneous.

Maybe if you calculate acceleration for yourself as dv/dt = ( v2 - v1 ) / ( t2 - t1 ) where ( t2 - t1 ) is in the range of 1 -to- 3 seconds you might get a number that makes a little more sense ?

-- kjh

Thanks for posting your DD shock data. I found it informative. Most of my rockets are too small and light to incorporate DD. My main chute is a small drogue for most DD systems. All of my DD experience is with very large university rockets.

I fold my parachutes with the shroud lines wound on the outside to delay inflation and reduce entanglement with fins. I'm hoping that the data will indicate which packing method is best for specific applications.

For us LPR to HPR fliers, the ejection charge delivers the highest shock reading but not necessarily the highest load on components. I've witnessed several non-welded eyebolts straightened from parachute inflation shock loads. Most of the universities use CO2 pressurant for a softer parachute deployment of both the drogue and main w/tender simultaneously.

Newton's Third Law does apply if your parachute deploys during the motor burn acceleration.