Hang Time Charts - Parachute Recovery

Are there any "hang time" charts that graph..

• rocket weight -vs-
• wind speed -vs-
• ground distance traveled

for various size parachutes?

Thanks,

John

The chute manufactures each have decent rates and recommendations, but I've never seen a chart that would compare different manufactures.

After a bit of searching here on TRF I found these helpful links..

Recovery Tools

Descent Rate Calculator
Enter the weight of your rocket and the size of the parachute to estimate the rate at which your rocket will descend.

Calculate Parachute Size
Estimate the size of the parachute to use for your rocket.

Calculate Streamer Size
Calculate the size of the streamer to use for your rocke

Open Rocket can do all of this for you, however it uses default values unless manufacturer specific values for Cd are known. Another advantage to OR is the ability to adjust the Cd to get the correct Cd if you haveva recording altimeter to get descent data.

rharshberger said:

Open Rocket can do all of this for you, however it uses default values unless manufacturer specific values for Cd are known. Another advantage to OR is the ability to adjust the Cd to get the correct Cd if you haveva recording altimeter to get descent data.

Click to expand...

Adjusting to the actual decent rates is a great idea. It seems like all the manufactures use different numbers when they calculate the Cd of their chutes. If you take the diameter and weight of a rocket and plug it into one of the calculators, it seldom matches what the manufactures claim. The question is, who's right?

Also be aware, that a 60" chute from one manufacturer can have a very different decent rate with the same weight rocket because of chute design.

lakeroadster said:

After a bit of searching here on TRF I found these helpful links..

Recovery Tools

Descent Rate Calculator
Enter the weight of your rocket and the size of the parachute to estimate the rate at which your rocket will descend.

Calculate Parachute Size
Estimate the size of the parachute to use for your rocket.

Calculate Streamer Size
Calculate the size of the streamer to use for your rocke

Click to expand...

I looked at all of the above, and would still much prefer to rely on OpenRocket.
The challenge you might face is importing the complex bird, like yours, into OR. But for the sake of descent calculations, you can just mock-up a 3FNC rocket that matches the weight of yours.

The key question you likely want to answer is - what size chute do I want to put into my rocket?
To that end, plug in different size chutes, with manufactures specified Cd's (they do vary!), and see what descent rate you get.

20 f/s is a good, conservative target.
For an architecturally complex rocket like yours, I would play it safe and stay under 20 f/s to minimize damage upon landing.

The down-side to 20 f/s is that if you loft your rocket high enough, 20 f/s will take a LONG time to come down, subject to vagaries of cross winds. That can mean a long walk, or a rocket stuck on a tree, or lost altogether (depending on how high you fly).

One solution to that is JollyLogic Chute Release device (JLCR), but you need at least 42mm body tube to accommodate:
https://www.jollylogic.com/products/chuterelease/
I don't remember your model's dimensions, but it may not have large enough airframe to JLCR.
If so, prepare for a long walk.

a

Thanks for the replies.

afadeev... The X-wing body is made from a BT-50 (0.950" i.d.) tube.

As for OpenRocket... Being a retired Mech Engr. I'd kind of like to gather data and crunch the numbers myself... using some spreadsheets for the evaluations.

lakeroadster said:

As for OpenRocket... Being a retired Mech Engr. I'd kind of like to gather data and crunch the numbers myself... using some spreadsheets for the evaluations.

Click to expand...

I can respect your desire to verify the simulations yourself. Unfortunately, the data quality available for the types of chutes out there may make your pursuit a bit frustrating since the manufacturers use different dimension nomenclature (flat to flat or tip to tip diameters?) different geometries (Iris chutes are a bugger) etc....

Highly recommend comparing your manual approach to properly defined OR simulations. It's basically doing the same calculations iteratively in the background

Handeman said:

If you take the diameter and weight of a rocket and plug it into one of the calculators, it seldom matches what the manufactures claim. The question is, who's right?

Click to expand...

Simulators like Open Rocket and RockSim are more correct than a manufacturer's simple descent tables. The main reason is that a proper simulation will account for local air density impact on the parachute drag. If you launch in Denver on a humid day, the air density is much less than the standard day sea level density probably used in the manufacturer's table. Also note that the descent rate is NOT constant, because the air density changes with altitude as the rocket falls. The non-constant rate is subtle, but it is there, especially if you launch to great heights. You can see it in your sim data and altimeter data.

Parachute makers are sometimes vague on the reference area used in their Cd estimation. When adjusting to altimeter data, it doesn't matter what Cd and A are individually, but the product CdA is what matters.

The simulators simply calculate ground distance by the hang time times the cross wind speed. Nothing fancy.

Particularly for the high altitude flights, you need to account for the multilevel wind directions, speeds and air density. Rocksim Pro, or the Cambridge Rocketry simulator with the OR GUI will provide splash pattern analysis.

BAR question: What's considered high altitude?

Here in Central Colorado I'm launching LPR's from a pad altitude of about 8,000 feet.

Once you know the descent time for your chute/rocket, then use this formula to calculate how far away it may come down. Keep in mind that it assumes a perfectly straight up flight with no arc.

Windspeed in MPH X 1.5 X descent time

The 1.5 converts from MPH to FPS.

For 10 MPH wind and a 32 second descent time:

10 X 1.5 X 32 = 480

So if apogee is directly above the pad, then expect it to come down 480 feet away.

lakeroadster said:

BAR question: What's considered high altitude?

Here in Central Colorado I'm launching LPR's from a pad altitude of about 8,000 feet.

Click to expand...

I was really referring to flight altitudes above ground level. If you’re sending a rocket up above 10,000’ AGL, then you’re likely to experience many changing wind speeds and directions on the way down.

Thanks again for your input folks.

rharshberger said:

Another advantage to OR is the ability to adjust the Cd ..

Click to expand...

Thanks for the tip. I emailed Top Flight Recovery LLC and was informed the the drag coefficient of their 12" 1.7 oz nylon parachute is 1.09. :wink: