# How to determine range dimensions for safe recovery?

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#### DarkStar

##### New Member
I flew some Estes rockets in a park in Riverwood a while back, and nearly lost the smaller rocket to the M5 when fitted with the largest recommended engine. I had cut out the apex of the canopy (as recommended in the instructions), which helped it to come down faster, but it was pretty close. (I had made an alignment jig to get the fins straight, filed the leading edges, and used the bare minimum of paint, so she climbed pretty high; we lost sight of her for over 30 sec.)

It would be good to know how to estimate how big the rocket range needs to be based on wind speed and glide ratio for the rocket. Are there any available data on glide ratios for parachute-recovery rockets? For that matter, is there any public source of timely data on wind speed versus altitude (e.g. from Bankstown Airport)?

I just found a nice big space in Heathcote, but it's only 350 m long (including the Oval), so it would need a dead calm day, I think.

#### Tonimus

##### Well-Known Member
Minimum on a perfectly calm day, I still figure at least 5 mph wind speed for small rockets. 1 mph is about 1.5 feet per second. If I send something up 1000 feet, with a descent rate of 10 feet per second, it'll take 100 seconds to come down. 5 (wind speed in mph) x 1.5 (mph to fps) x 100 (descent time) = 750 feet of drift.

Metric, 8 (kph wind) x .3 (kph to mps) x 100 (descent time) = 240 meters

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#### neil_w

##### Tenet Rocketworks
TRF Supporter
And of course, the empirical approach would be to start with small motors and get a feel for how things are behaving, and only move up to bigger stuff as it seems prudent (aka, "fly the field"). The calculations are definitely helpful but I wouldn't really trust them completely given all the variables that are in play with each launch.

#### blackjack2564

##### Crazy Jim's Gone Banana's
TRF Supporter
It would be good to know how to estimate how big the rocket range needs to be based on wind speed and glide ratio for the rocket. Are there any available data on glide ratios for parachute-recovery rockets? For that matter, is there any public source of timely data on wind speed versus altitude (e.g. from Bankstown Airport)?

I just found a nice big space in Heathcote, but it's only 350 m long (including the Oval), so it would need a dead calm day, I think.
Here is basic field dimensions from Estes:

What is does NOT take into account is wind drift. Example:
Light breeze of 5mph = 7.33 ft/per/sec.

If you rocket descends at a rate of 10fps it also is drifting sideways at 7.33 fps.

If your field is 500 ft of recovery area & you hit 1000ft altitude it will take 100 seconds to land. During this the rocket has drifted downwind 733 ft. you will land off field by 233ft.

There is a program called Open Rocket [free download] that simulate/plot all this, along with giving you simulated flights [altitudes for all your rockets]

Files for all Estes rockets here for use in Open Rocket:

https://www.rocketreviews.com/rocksim-library.html

My personal experience would say for most flying conditions, you would want a field at minimum of 1500 x1500 ft for standard low wind flying up to 1000 ft. It won't take much breeze to blow you off field.

Edit: looks like others were thinking just like me!!:wink:

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#### blackjack2564

##### Crazy Jim's Gone Banana's
TRF Supporter
Just to show how well the Open Rocket works for predicting wind drift.

I entered Estes Alpha using A-8-3 motor. Altitude show 396 ft.

Entered my wind data 6.93 meter/per/sec launch rod length & temp into launch sims.

Then picked type of plot I wanted.... Altitude and drift down range.

Hit plot button, results are altitude of 396 ft and rocket lands east of pad 1050ft!

#### Bat-mite

##### Rocketeer in MD
Here is a nice online calculator for descent rates. As everyone else wrote, descent time is what you need, then just do the drift math. Of course, none of this is perfect. The rocket will weather cock a bit, and the point of apogee will normally not be directly overhead. Delay times are never perfect, and sometimes you'll get some stable, post-apogee descent prior to chute deployment, etc.

To account for weathercocking, make sure you angle your launch rod slightly with the wind. This seems counter-intuitive, but what happens is that the wind blows against the fins, which causes the rocket to weathercock into the wind. If the angle with the wind is correct, you'll get a closer-to-straight-up launch, and then descent calcs will be closer to true.

#### blackjack2564

##### Crazy Jim's Gone Banana's
TRF Supporter
Here is a great site for wind speed & direction at many altitudes. Note tabs on right to pick elevation. I put Sydney in location

https://www.windyty.com/-33.855/151.216?200h,-33.854,150.639,10

You must click setting lower right to expand all:

With a bit of looking around, you can click settings for Google earth & when you enlarge to your launch site, find winds at every level... here's our sod farm launch site and all wind directions at various altitudes!

https://www.windyty.com/RU-0196?200h,-33.924,150.986,15

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#### dhkaiser

##### Well-Known Member
Here is a great site for wind speed & direction at many altitudes. Note tabs on right to pick elevation. I put Sydney in location

https://www.windyty.com/-33.855/151.216?200h,-33.854,150.639,10

You must click setting lower right to expand all:

View attachment 296317 View attachment 296318

With a bit of looking around, you can click settings for Google earth & when you enlarge to your launch site, find winds at every level... here's our sod farm launch site and all wind directions at various altitudes!

View attachment 296319

https://www.windyty.com/RU-0196?200h,-33.924,150.986,15
Very cool. And there is an app!

Edit: This gives a forecast not real time readings. Checked against my wx station and does not agree on surface winds. :-(

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#### bobkrech

##### Well-Known Member
Visual Drift is an equivalent app for an I-phone.

The Estes recommendations are for very low winds (below 5 mph). The fact is your rocket will drift 1' downwind from apogee for every foot of altitude in a 10 mph wind. It will drift half that distance in a 5 mph wind, and twice that distance in a 20 mph wind.

#### Handeman

##### Well-Known Member
TRF Supporter
And of course, the empirical approach would be to start with small motors and get a feel for how things are behaving, and only move up to bigger stuff as it seems prudent (aka, "fly the field"). The calculations are definitely helpful but I wouldn't really trust them completely given all the variables that are in play with each launch.
I think this is the best advice you can get. You learn to "fly the field" with every level of rocketry. If you are flying small rockets on A motors and move up to larger rockets on C or D motors, you have to relearn how to "fly the field" As you move up through MPR into HPR, you are learning how to "fly the field" at every level. It is something that never really ends. The sooner you start doing that, the easier it will be as you move up to larger and larger rockets. Calculations and simulations are great and give you another data point, but they are just inputs into that knowledge and feel you get when you really learn to "fly the field".

The more you fly the more you learn, so get out there and fly a lot! Have fun!

#### SaturnV

##### Well-Known Member
you move up to larger and larger rockets
Everything is very personal. I started with small rockets went bigger to about 10 pounds and then back again to the small but already flying higher . For my main goal is not rocket itself, but &#1086;nboard video. The basic rule is to wait a day with very little wind. Second rule rocket to be as strong to benefit maximum small parachute.Or parachute system with two parachuts ,one small and one large that opens 200 meters from the ground.But it is complicated and not my deal.
There must be a clear boundary between pleasure rockets and large and potentially dangerous rockets. Moreover example rocket 50 kg without management system is something fundamentally dumb, it's like having a Ferrari without a steering wheel.To be 100% safe to be fired from a concrete bunker in the area of horizontal flight no people. Something very difficult if you live in a densely populated country like me with towns of 3-5 km apart. Otherwise cardinal question of finding the Rocket is solved by GPS system. But it makes sense to put a rocket least expensive as herself. Rocket for $30 to put your system for$ 100, not to open the parachute as it happens to the best and expensive system there is no.

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