Quantcast

"Safe Deployment Velocity"

The Rocketry Forum

Help Support The Rocketry Forum:

ScrapDaddy

Well-Known Member
Joined
Jan 26, 2010
Messages
2,083
Reaction score
1
Iv Been Told Time and time again "The deployment velocity is unsafe or is in shred territory" so now im wondering what IS the max safe deployment velocity? 15mph or 20? 10 mph? i really have no clue:blush:
 

blackjack2564

Crazy Jim's Gone Banana's
TRF Supporter
Joined
Jan 18, 2009
Messages
9,063
Reaction score
1,171
Location
Savannah Ga
Depends on size and weight of rocket. For the stuff I fly[high power] 3-6inch and 3-60lbs it would be 60-100ft per second. This is pretty much the accepted standard. You get into stripped chutes and zippered airframes by exceeded it too much.

For low power light weights some one else will have to reply. It would help if you specify what size and weight rocket you are referring to.
 

MarkII

Well-Known Member
Joined
Jan 18, 2009
Messages
8,255
Reaction score
9
Iv Been Told Time and time again "The deployment velocity is unsafe or is in shred territory" so now im wondering what IS the max safe deployment velocity? 15mph or 20? 10 mph? i really have no clue:blush:
Rule of thumb: 0-10mph is good, 11-20mph is firm, 21-29mph is harsh, and 30 mph and up is very likely to seriously damage the rocket and shred the recovery device. Much depends on the rocket design and construction, the recovery device and the method of deployment, though. The slower the rocket is moving when the recovery system comes out, the better. The speed ranges I mentioned are basically true for low power rockets; high power rockets that are equipped with very strong recovery bridles and utilize dual deployment are designed to withstand much higher deployment speeds. Also the point in the flight sequence that the high speed deployment occurs can play a role, too. If the deployment happens while the rocket is coasting upward, losing momentum and decelerating rapidly it can be more survivable than one that occurs after the rocket has gone over the top and is rapidly gaining speed and momentum as it falls back to the ground. It is best to keep the deployment speed under 10 mph; 0-5 mph is ideal, and 0 mph (just when the rocket has reached apogee and stopped) is perfect.

MarkII
 

MarkII

Well-Known Member
Joined
Jan 18, 2009
Messages
8,255
Reaction score
9
CJ's range translates to 45-68mph. But that's for high power, which uses materials, designs and deployment methods that enable the rocket and the recovery system to tolerate those speeds. With a smaller rockets that uses paper tubes and a plastic parachute, the chute is likely to strip most if not all of its shroud lines if it opens when the rocket is going at 25 mph or faster. Mylar parachutes can tolerate speeds that are a little higher, but not much. Even small nylon parachutes and streamers can tolerate much higher speeds if they are well-made, but the rocket cannot. Usually an anchor point will snap, either where the recovery device attaches to the shock cord or where the shock cord attaches to the rocket. If those points manage to hold and the device doesn't shred, the harsh snap of the shock cord will often produce serious damage to the rocket itself. In order to boost well on low impulse motors, low-power rockets are built out of thin, lightweight components that cannot tolerate such harsh forces. You can reinforce the rocket, but at the sacrifice of some performance. The better solution is to find a combination of motor and delay that avoids the issue. If no combination is available, then the only option is to redesign the rocket. It is profoundly irresponsible to disregard this issue and launch the rocket anyway.

MarkII

Shredded Nebula.jpg
 

The EGE

Well-Known Member
Joined
Sep 11, 2009
Messages
546
Reaction score
0
Assuming you can run a fairly accurate simulation of the rocket, you should be able to choose a delay that will put your rocket at a very slow velocity at ejection.

==== WARNING: MATH AHOY ====

Ignoring air drag, which has little effect at low velocities, position of a rocket near apogee = -4.9t^2. Differentiating that, the velocity at t seconds before / after apogee is 9.8t. A properly selected delay with 2-second intervals between delays (Estes C6-3,5,7, etc) thus has a maximum time between apogee and delay of +/- 1 second, which means a maximum velocity of 9.8 m/s at ejection.

2-second interval and max. 1s mismatch (Estes BP motors; CTI ProX motors): maximum of 9.8 m/s = 32 fps = 21 mph

3-second interval and max. 1.5s mismatch (AT 18mm-29mm SU and RMS): maximum of 14.7 m/s = 48 fps = 32 mph

4-second interval and max 2s mismatch (AT 29mm-54mm HPR RMS): maximum of 19.6 m/s = 64 fps = 42 mph

5-second interval and max. 2.5s mismatch (some older SU motors): maximum of 24.5 m/s = 80 fps = 53 mph

==== END MATH ====

As a general rule, if the motor's shortest delay is too long, you need a bigger motor. If the longest delay is too short, chances are you've got a slim machbuster / altitude record-setter.

ScrapDaddy, I'm guessing that a D21-7 is too short for your Machbuster. Fortunately, the Machbuster is extremely light, and as long as you use kevlar thread, it should be able to survive a deployment up to 100 mps or so.

My 29mm Machbuster, the Machnum Force, survived deployment at around 150 fps on the way up, but it got a nice chip where the heavy nose rebounded and hit the body tube. Next time, I'll use a longer delay...
 

ScrapDaddy

Well-Known Member
Joined
Jan 26, 2010
Messages
2,083
Reaction score
1
Oh great now whenever I ask somthing about rockets the EGE and MarkII wi think I'm talking about my machbuster : D Oh and The EGE And MarkII Check ur privite messages tommorrow at about 5pm eastern time I have a fin design I want to run thru you for my 2nd machbuster this one uses featherwight recovery! And can reach Mach 1.35!!!!! On a D21 assuming the fins don't shred off (that's what you and MarkII are here for right : D)
 

ScrapDaddy

Well-Known Member
Joined
Jan 26, 2010
Messages
2,083
Reaction score
1
Hmm machnum force that's a good name I wish I though of that I named mine "The All American Machbuster" and even you are doing 29mm for a machbuster is it really that hard to put a D21 in a little rocket?:neener::confused: then again you got your 29mm back, me on the other hand..........
 

MarkII

Well-Known Member
Joined
Jan 18, 2009
Messages
8,255
Reaction score
9
Oh great now whenever I ask somthing about rockets the EGE and MarkII wi think I'm talking about my machbuster : D Oh and The EGE And MarkII Check ur privite messages tommorrow at about 5pm eastern time I have a fin design I want to run thru you for my 2nd machbuster this one uses featherwight recovery! And can reach Mach 1.35!!!!! On a D21 assuming the fins don't shred off (that's what you and MarkII are here for right : D)
I don't know what you are talking about; I was making some general observations. You asked for some guidelines so that you could distinguish between high deployment velocities and low ones. I provided you with a very simplified scale (simplified because it's easier to remember that way). I also talked about appropriate deployment speeds for high power and low power rockets. At no time did I refer to any rocket designs of yours. The things that I discussed are generally applicable to all rockets. In some other threads, you and everyone who posted, including me, did talk about one of your designs, but that was not the case here.

MarkII
 

The EGE

Well-Known Member
Joined
Sep 11, 2009
Messages
546
Reaction score
0
Hmm machnum force that's a good name I wish I though of that I named mine "The All American Machbuster" and even you are doing 29mm for a machbuster is it really that hard to put a D21 in a little rocket?:neener::confused: then again you got your 29mm back, me on the other hand..........
All my Machbusters are puns off Dirty Harry. Mach My Day, Machnum Force, Sudden Mach. It remains to be seen whether the rockets or the bad puns run out first :D

18mm and 24mm Machbusters involve very small, lightweight rockets, which are too small to carry electronics or much tracking powder. The most powerful motors available in those sizes - D21 and F32 - barely get past Mach.

29mm Machbusters have a wider motor range that, in the high-power range, can get well past Mach. They can carry electronics that can reliably document the altitude and velocity, so it's possible to prove that it made it to Mach. They can also carry tracking powder - and lots of it - to make it easier to find, and dual-deployment electronics so they'll stay in the field.

You can stick a D21 in a little tiny rocket and say it'll go to Mach, but you'll never see it again.
 

The EGE

Well-Known Member
Joined
Sep 11, 2009
Messages
546
Reaction score
0
What about the g54? I know it's a reaload
There are currently 2 G54s on the Market; both are 29mm reloads.

There's the Cesaroni G54 Red Lightning; it's a 3-grain full (159 Ns) G.

Then there's the Aerotech G54 White Lightning; it's a baby (81 Ns) G.

The CTI G54 will prolly push a light rocket past Mach; the AT G54 will not.


There used to be G55 and F72 single-use motors, both 24mm, but they are not produced any more and getting one would set you back a pretty penny.
 

ScrapDaddy

Well-Known Member
Joined
Jan 26, 2010
Messages
2,083
Reaction score
1
I was indeed refering to the g55 and f72 it's a pity I know I manufacturer who based a model around these two engines
 

cjl

Well-Known Member
Joined
Jan 18, 2009
Messages
12,549
Reaction score
5
There also used to be an F101 Blue Thunder SU 24mm - I still have 4 of those, and I plan to build a machbuster based around them.
 

ScrapDaddy

Well-Known Member
Joined
Jan 26, 2010
Messages
2,083
Reaction score
1
There also used to be an F101 Blue Thunder SU 24mm - I still have 4 of those, and I plan to build a machbuster based around them.
Don't you mean machbusters as in plural iv been talking alot aboutsmall machbusters recently and people say you don't have much of a chance of getting it back..... Hmm we can go to the moon but we can't track our rockets?
 

The EGE

Well-Known Member
Joined
Sep 11, 2009
Messages
546
Reaction score
0
If you got a trillion dollars and the support of the majority of the public, and the ability to hire tens of thousands of expert engineers and scientists, you too could track tiny rockets.

Problem is, we don't have much more than visual tracking. Larger rockets can garry radio transmitters, GPS devices, and sonic locators; tiny machbusters can't. Radar tracking requires specialized, expensive equipment. You can use bright-colored paint, tracking powder, and colored parachutes / streamers, etc; but there's only so much chance of being able to recover a small, lightweught object from altitudes at which it is no longer visible.
 

Chrisn

Well-Known Member
Joined
Apr 10, 2009
Messages
1,508
Reaction score
0
You can track your rockets, but any extra weight of tracking equipment in a rocket of that size and power means it likely wont end up going mach 1. It has nothing to do with going to the moon.

Train a dog to sniff out rocket motors
 

ScrapDaddy

Well-Known Member
Joined
Jan 26, 2010
Messages
2,083
Reaction score
1
ANd yet we spend 10 billion dollars on an ineffective stimulus package:rolleyes:
 

new2hpr

Well-Known Member
Joined
Jan 23, 2009
Messages
980
Reaction score
62
Location
Colorado
A parrot will fit 24mm, I believe. If you don't fly electronics in this machbuster, how would you KNOW you actually did it? You could just go by what the sim says, but then what's the point of building it?:confused2:

Get some data from this puppy!:cool:

Now we're waiting for pix!

-Ken
 

ScrapDaddy

Well-Known Member
Joined
Jan 26, 2010
Messages
2,083
Reaction score
1
Rocketry doesn't always have to be official and rocketry is for the fun of it:cool:
 

cjl

Well-Known Member
Joined
Jan 18, 2009
Messages
12,549
Reaction score
5
Don't you mean machbusters as in plural iv been talking alot aboutsmall machbusters recently and people say you don't have much of a chance of getting it back..... Hmm we can go to the moon but we can't track our rockets?
I might lose it, yes. That's why it will be cheap, and why I'm glad that the F101 is SU :D
 

cjl

Well-Known Member
Joined
Jan 18, 2009
Messages
12,549
Reaction score
5
Yep - it's too bad it's OOP. I've only flown a couple, but they're nice motors.
 

ScrapDaddy

Well-Known Member
Joined
Jan 26, 2010
Messages
2,083
Reaction score
1
All my Machbusters are puns off Dirty Harry. Mach My Day, Machnum Force, Sudden Mach. It remains to be seen whether the rockets or the bad puns run out first :D

18mm and 24mm Machbusters involve very small, lightweight rockets, which are too small to carry electronics or much tracking powder. The most powerful motors available in those sizes - D21 and F32 - barely get past Mach.

29mm Machbusters have a wider motor range that, in the high-power range, can get well past Mach. They can carry electronics that can reliably document the altitude and velocity, so it's possible to prove that it made it to Mach. They can also carry tracking powder - and lots of it - to make it easier to find, and dual-deployment electronics so they'll stay in the field.

You can stick a D21 in a little tiny rocket and say it'll go to Mach, but you'll never see it again.
Well Assuming You use a G77 motor for the mach Attempt that will set you back about $30 dollars then Being Very Conservative ill assume you spent $30 on the rocket you may get the rocket back but you are losing $30 a flight; while i am spending $10 on the rocket and another $5 on the motor even if i lose the rocket i will still be the man with the happier wallet in the long term :D
 

cjl

Well-Known Member
Joined
Jan 18, 2009
Messages
12,549
Reaction score
5
You could build a 29mm machbuster for ~$10 (except the motor). There's no need to spend $30 on what is essentially a disposable rocket.
 

ScrapDaddy

Well-Known Member
Joined
Jan 26, 2010
Messages
2,083
Reaction score
1
And the EGE said he would get it back....... Well he did I'm still waiting to fly mine..... Waiting to join ASTRE
 

The EGE

Well-Known Member
Joined
Sep 11, 2009
Messages
546
Reaction score
0
And the EGE said he would get it back....... Well he did I'm still waiting to fly mine..... Waiting to join ASTRE
I *did* get mine back. I had absolutely optimal conditions, a huge field, a lot of tracking powder, and a lot of luck.

It cost $3.55 for the 29mm nose cone from BMS, $1.99 for a can of lead shot from wally world, and about a buck for the tubing from Apogee. The eyebolt, shock cord, fins, streamer, and launch lug were all stuff I have lying around. The Mach Goon cost only a few bucks more, except of course the reload casing which I do plan to get back, and use again.

The Sudden Mach will cost somewhat more, because I'll be using thick LOC tubing, a plastic nose cone, blue tube couplers, and dual-deploy. But I'll get it back every time, so it's worth the cost, and I can fly it off 4-dollar D12s near home.
 

uwish

Member
Joined
Feb 9, 2010
Messages
12
Reaction score
0
if you are worried your deployment velocity will be too high, use a deployment dampener. A sleeve that goes through the shroud lines, they work well and if you are in minimum diameter airframe there is no concerns over deployment bags etc.
 

dave carver

Nam Myoho Renge Kyo
Joined
Jan 18, 2009
Messages
4,972
Reaction score
4
My little hi fliers I use a chrome mylar streamer and Monocote chrome RC plane covering, the self adheasive kind. As bad as my eyes are I can follow one so equiped with no problems, no matter the altitude. Of course, finding it after landing poses another problem;)
 

Latest posts

Top