Recovery Principle

[PWALPOCO]

Hi there,

Just a quick quesiton about "recovery".

Theres an interesting thread going on in ;

https://www.rocketryforum.com/showthread.php?s=&postid=72924#post72924

basically WiK wants to simulate a "bomb" with a scaled bomb/rocket. In my mind its raised a question about "recovery".

You see , I often see it mentioned that rockets are recovered on streamers , or glide back in , or on a chute , but a rocket landing back in on nothing is a "bad thing".

What I dont understand is , how much better is a streamer recovery over no recovery at all ? Surely a rocket coming back in on a streamer would more or less have the same effect as falling without anything , when considering safety at any rate.

Is it just the "principle" of the thing , youve managed to get some sort of device to come out of the rocket? The fact you chose a streamer over a chute means you COULD have deployed a chute if you wanted to, when in fact a streamer actually came out ?

This is just a curiousity of the hobby , I dont advocate not using a chute or streamer etc , just wanted to know what the logic is behind the streamer/chute/nothing at all safety thing.

Paul

 

[wwattles]

Principle #1:
Streamers are generally used for smaller, lighter-weight rockets, and actually do provide a fair amount of wind-resistance in their descent.

Principle #2:
For anything falling from the sky, it's best to at least have made some attempt to slow it down. Some models use tumble recovery to utilize the aerodynamics of an unstable rocket to slow themselves down, whereas some use a glide, others a chute or streamer. This is why both NAR and TRA here in the US have rules regarding recovery devices being required. Itty-bitty rockets like Mosquito's still use a tumble-recovery to keep from hurting anybody on the ground. Launching rockets that have no means of slowing themselves is pretty highly taboo.

Hope this helps clarify things a bit.

WW

 

[PWALPOCO]

Okeis , that helps ......

The logical progression of my query is to ask if there is written guidance about what rocket sizes/types/weights should be recovered by a particular means , and where can I lay my hands on it ?

I often read comments like " gee , got so much drift with that (insert drift mad rocket name of choice) , Im going to streamer it next time ..... " etc , apart from peoples experience Im wondering if theres a table to help out choosing their recovery systems.

Paul

 

[wwattles]

There are tables available to help you decide what size of chute to use, but beyond that, I haven't heard of anything. This is part of the fun, and the "art" of rocketry! I'm sure that someone with a massive slide rule who was more interested in mathematics than rocketry would be able to figure it out, but there's no fun in that!

WW

 

[shockwaveriderz]

Not sure if there is a table anywhere to tell you this stuff it mostly comes from flying experience.

Only You know your flying field better than anybody. You should have an idea from prior experience with various rockets and recovery systems work best with what wind conditions.....

You basically have 4 choices:

1. Tumble recovery(preferably a model that "breaks apart" but
stays together by a shock cord)
2. Streamer recovery
3. Parachute recovery(with large spill hole)
4. Parachute recovery(without spill hole)

Now obvious from looking at the above table, for a rocket of any given weight, it will fall faster(AND HARDER) with 1 while it will fall slower(and softer) with 4.....

Also obvious lets say you have a wind speed of 10mph at the ground.....the wind at higher altitudes(say 3-6K ft) could be much faster...so obviously with 1-2-3 the model for any given weight and size might land within youe flying field, while using 4 it might not....

This obviously also depends on how large your flying field rcovery area is.....if you have a filed where you have 1 mile downwind then take your pick...on the other hand if you have maybe 500 ft.....you might pick 1-2-3....instead of 4...

When it comes to streamers you might have a number of different sizes and the same for parachutes with and without spill holes.....mix and match as you deem necessary...

I build all my model rockets and large model rockets with the ability to use whatever recovery technique I might need to change to depending on the wwind speed and direction, and the size of the field that I am launching from.


I ususally will throw up an alpha on a C6-7 with a streamer at my flying field to see whats happening.....and launching one periodically thru out the day wouldn't hurt...as winds can pick up through out the day..
You also need to learn how to launch a rocket with the wind or against the wind to get weathercocking.....on purpose....

You can also get the wind speeds at altitude from here:

https://aviationweather.gov/products/nws/fdwinds/

click on your state and you will get a table that looks like this:

000
FDUM01 KWBC 131415
DATA BASED ON 131200Z
VALID 131800Z FOR USE 1700-2100Z. TEMPS NEG ABV 24000

FT 3000 6000 9000 12000 18000 24000 30000 34000

These are the altitudes

then look and select the line with the airport nearest you, and you will see this:

LOU 0911 9900+02 2609+00 2521-06 2738-19 2746-29 275646 286455

0911 means the wind is coming from 09 degrees at 11 knots

9900+02 means the wind is coming from 99 degrees at 00 knots and the air temp is 02 C

Usually knowing the 3 and 6 K winds aloft will suffice for most models that you will be launching

where 0 degrees is Due North 90 is Due East 180 is Due South 270 is Due West.....


Have you ever had a say an estes A3-4T hit you in the top of the head from say 1000 ft? how about an C6-5? Ok how about a E9-8?

The purpose of a recovery device like a streamer or parachute is to also allow the person lauching the model to track and see it...along with any spectators...... so its a safety issue too

As you can well imagine this is why models engine ejection is frowned upon.......


HTH

 

[Johnnie]

Our group has gone with no parachute in 1st stage recovery in a dual stage deployment set-up. Going drogueless lets our rockets come within the limits of the fields we fly in, when we fly extreme altitudes. Our main chutes will usually deploy at 500'

If you can break up the aerodynamics of recovery there-by creating drag, sometimes you can get away with little or no chute. This is were streamers are optimized for small light airframes...otherwise start walking.

 

[Dr. Don]

Hey!!
Thanks for the wind speed link!
I will keep it in my favorites for launch days!!
Just an interesting tidbit: The Estes Mongoose is a 2 stager that goes outta site! The booster comes down close by while the upper stage can really go a long way on only a streamer !!
Estes aparently feels confident that the rocket is lite enough to safely recover in that manor. I have had many happy returns with the Mongoose! Dr Don

 

[Stymye]

actually there are two slightly different techniques for #1

tumble recovery can simply be achieved by a change in the cg(example,spitting the motor at ejection)
causing the rocket to decend unstable..
or as in a booster stage,made to tumble,rather than glide

annother option ,nose blow recovery ,was accidentally discovered to work,when the military was firing V2's in the 1940's..most of the onboard experiments were recovered intact...the breakup caused the seperate parts to tumble and slow their decent
the mini mars lander is basically the same idea as nose blow
although the 2 halves remain connected
( the tiny streamer seems to have little effect )

 

[Dr. Don]

And just for the fun of it.........
The funny looking thing in the right corner is a minimum diameter 'D' I built from stuff laying around. The sucker VANISHES!! It is so lightweight, I use only a small streamer.
After many flights, there has been no damage. and the streamer helps to spot it during descent!

 

[Ryan S.]

styme is right, I forgot about that, but the V2 would come in so fast everything would be destroyed, so they started popping the nose off which slowed it down.

I think a streamer does provide some drag, I mean let a big peice of cloth out your car window while driving down the highway, a bit of an exaggeration, but still.

Also, the streamer makes the rocket tumble a bit more and that would slow it down.....just my thoughts

 

[Stymye]

no doubt streamers work .
I just meant the one on the mini mars lander..its pretty small... lol

I remember someone posting the ideal ratio is 10 times the width of the streamer

as in a 1" wide streamer should be 10" long..or is it more than that?

 

[Ryan S.]

I agree, they dont do much.

Im not sure the ratio, but now that I think of it I once saw a HP rocket recovered on a streamer, it flew on an I or something, and it must of worked because the rocket was fine

 

[wwattles]

A buddy of mine (actually the guy who got me into rocketry in the first place!) flew a J-motor with a streamer recovery a couple months ago. He used about 100 feet of caution tape to make 2 giant yellow streamers... sure made it easy to spot coming down!

WW

 

[Dr. Don]

I flew my EZI last 4th of July on an I motor and stuck in about 50'
of red "danger do not cross" ribbon just for fun. The main parachute tangeled (possibly BECAUSE of the streamer) and
the EZI came down hard enough to snap a fin. but even with a 5lb rocket, the streamer saved it from total destruction. With a little epoxy and an internal ZIPPY for insurance, she was flying again at the October launch. Dr Don

 

[BlueNinja]

Yep, Dr Don is right the Mongoose goes out of sight. Lost mine to a cloud. I think the ratio is for competition. The Quark I built was supposed to tumble without a motor, but it would just come straight down.

 

[Missileman]

I have seen streamers used on fairly heavy rockets.
I launched an Estes clone Maxi Streak. D engine with streamer recovery a couple of weeks ago and had to walk darn close to half a mile through a muddy field to recover. It actually drifted past the launch pad and kept going.
I don't remember the ratio 1:10 or 1:20 but it is important.
A streamer in proper ratio flaps like a flag on a windy day. This causes wind resistance and slow descent considerably.
If the streamer is too long it dampens this effect and will not generate as much resistance as a shorter streamer would.
Seems funny but thats the physics of it.

 

[Neil]

Dang! Thats a good idea! I never thought of caution tape... I have always used long strips of flagging tape on my Estes models! I feel Estes models (BT55 and smaller) are light enough to use streamers in, at least when you are on your own with no spectators. If it were at a crowded launch and there was any doubt about safety, yes, I would put a chute in, but the rockets recover every time for me, but it would still hurt to get knocked on the cranium with one.... Streamers really do help visually if you ask me. I think I will buy some caution tape and stick in in my MB1 for my I161 flight... Thats a durn good idea! Just to give it a LITTLE drag and a visual aide.

I once had a D powerd bird that I thought I had a chute in come down with no recovery at all, just the nose tied to the tube by 10 feet of nylon. It came down in the woods, and I got it back, no damage. Go figure On the other hand, I have lost B powerd rockets on tiny flagging tape streamers to the woods.... It was a windy day, but still!

So I would say they definetly do give you some drag.