Streamer Descent Rate ?

Does anyone know? What is an acceptable descent rate for a 18 oz rocket with a streamer?

My daughter got a Yank Enterprises Wraith for Christmas. It's 37 inches long and 54mm in diameter. It uses a 29mm MMT and has a 20 ft nylon streamer. I entered all of the dimensions into Rocksim and it said that the descent rate at landing was about 67 ft/sec. That seems a bit too fast to me. I'm afraid that the rocket will be damaged if we let it fall that fast. Anyone out there fly streamers and can give me some insight?

Jumping from the roof of a single story building your velocity would be about 11 feet/sec. -just food for thought-

If the rocket falls in a flat spin and lands on soft ground the likelyhood of any real damage is lessened. More often than not though, they land on their tail. Sometimes they survive for many flights and sometimes they don't.

67 ft/sec is fast. See what happens to the decent rate in simulation if you increase the length and width of the streamer.

A small correction. It is about 65 ft/sec. Still very fast. The streamer is 1 5/8 in wide and 20 ft long made of rip-stop nylon. Rocksim calculated the CD is 0.084. I'm sure that I could reduce the descent rate by getting a wider streamer. Actually, Rocksim recommends a 7 in wide by 6 ft long streamer. Better yet, I could replace the streamer with a parachute. However, I would like to know how fast is too fast?

Well, a well-built rocket of good materials (e.g. PML QT, TTW G10 fins - don't you love abbreviations) will probably survive a 10 m/s crash without damage. But that's only two times the recommended landing speed. And 10 m/s is only about 32 ft/s, not 65... I would give it a 18 in-chute.

But to get back on topic: Daughter, rockets, medium power? How old?

Oliver

My daughter just turned 10 in November. My son, age 12, has no interest in rockets whatsoever. Oh well, at least I have someone to pass the torch on to.

Just some thoughts/notes:

1.If I remember right, I've seen a 'rule of thumb' of 15 ft/sec.
2.I have gone to 20-25 with sturdy rockets.
3.The decent rate for the PML Small Endeavour's Rsim file says 24 ft/sec.
4.I've had several rockets come down without a chute and survive. My PML Small Endeavour and Public Enemy 3" Ultra Fatboy are two. Both basically landed on their ends.
5.I think it would pay to use a chute.

Good luck!

Check the calculated rate of decent based on rocksim's recommendation for a 7 inch by 6 foot streamer! Also check the settings for simulation pertaining to launch conditions in your area . . . namely latitude & longitude, altitude above sea level, etc.

Referring to rstaff3, what he has stated in his post is right on the money.

About the children:
Congratulations, Daddy O. Better one than none. But perhaps the boy's interest in rocketry is yet to come.

With the Rocksim recommended streamer, a 73 in long, 7 in wide one with a CD of 0.145 the descent rate at landing is a whopping 42.5 ft/sec. Either Rocksim's calcs are way off or I'm gonna have to put a parachute on this thing. I can't risk destroying my daughter's first "big" rocket. She'd be devastated.

Yeah, put a chute on it (we told you).

And 10 years, well, never mind...

Oliver

Just a follow up. The CD calculations in Rocksim for streamers appear to be WAY off! I tried some other programs to calculate what would be the optimum streamer size for this rocket and I came up with values that weren't that far off. Granted that the streamer that I have is still a bit too small, the descent rate shouldn't be anywhere near 65 ft/sec.

After a bit of detective work, I believe that the CD for the streamer for my daughter's rocket should be about 0.9. With a CD of 0.9, the descent rate for a 16 - 19 oz rocket should be under 20 ft/sec. That should be an acceptable rate.

I assume you mean the 20ft streamer. What detective work did you do? Did you find a program to determine CD?

No, I found a program that would recommend a streamer length given a width and rocket weight. I then assumed that it is calculating an optimal descent rate at 15 ft/sec. I then went to Rocksim and entered in the given streamer width and rocket weight and the calculated streamer length. Then I edited the streamer in the design to override the calculated CD. I started at 0.1 for the CD and reran the simulation to check the descent rate. Each time I would increase the CD until I got a descent rate of 15 ft/sec. Then I noted the CD of 0.9 and changed the streamer length back to 240 inches and reran the simulation to get the projected descent rate.

Great... You so technical...

now it says use the streamer or is this youre idead. i would go with the chut cause i think smoe estes rockets are to big for streamers

Well, we flew my daughter's Wraith this past weekend. See the High Point, NC Launch thread in the Events forum.

We chose to use the chute for recovery over the streamer because the field is small and we wouldn't be able to get sufficient altitude to let the streamer do its thing.

Streamer Size Calculator: According to "Model Rocket Design and Construction" by Timothy S. Van Milligan, a streamer should have at least 8.5 cm2 of single side surface area per gram of returned model mass (the mass of the rocket plus the mass of the expended rocket engine case.)

WIDTH: if filled with a number, the calculation will be done with a fixed width otherwise the calculation will default to a 10:1 length to width ratio

This is how we build our Streamer Size Calculator at EMRR under the Tools and Calculator tab.

Nick,
It was your streamer size calculator that I used to come up with the CD of the streamer in question.

EMRR said:

Streamer Size Calculator: According to "Model Rocket Design and Construction" by Timothy S. Van Milligan, a streamer should have at least 8.5 cm2 of single side surface area per gram of returned model mass (the mass of the rocket plus the mass of the expended rocket engine case.)

WIDTH: if filled with a number, the calculation will be done with a fixed width otherwise the calculation will default to a 10:1 length to width ratio

This is how we build our Streamer Size Calculator at EMRR under the Tools and Calculator tab.

Click to expand...

What descent rate is assumed for these calculations? I don't see it noted on the calculator. Thanks!

18 1/2 year thread necro, maybe a record?

@jadebox owns the site now, suggest contacting him directly.

neil_w said:

18 1/2 year thread necro, maybe a record?

@jadebox owns the site now, suggest contacting him directly.

Click to expand...

I don't mind setting records, accidental tho it may be. Didn't even look at dates when I was looking for streamer info. Thanks for the contact.

That was Nick responding. I am not sure what descent rate is used with those calculations.

Thank you for the response.

AFAIK, the calculator is still there on Apogee.

I must admit that I searched for it recently.

It can be found in a document entitled "The Science and Beauty of Streamer Recovery" in Technical Publication #4.

It will cost you a whole $2.52 to download the PDF.

Here's the link...

https://www.apogeerockets.com/Rocke...s/The_Science_and_Beauty_of_Streamer_Recovery