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Power of this Motor


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#1 Pretty green flames

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Posted 10 November 2004 - 03:53 PM

I've got a B6-4 rocket motor.
Now i can't find any information on how much payload it can carry.

Could it carry a 90 gram star+burst charge payload (motor incl. in weight)


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#2 StarScream

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Posted 10 November 2004 - 08:12 PM

Shouldn't be a problem. If memory serves me correctly, a rocket usually needs a motor that provides at least a 5:1 thrust to weight ratio. In other words a 1 pound rocket needs a motor that provides at least 5 pounds average thrust to be stable.

A B6-4 motor has an average thrust of 6 newtons or 1.35 pounds (612 grams). It should therefore be enough to safely lift a device weighing up to about 122 grams.

612 grams (average motor thrust) divided by 5 = 122 grams (max liftable weight)

Hope this helps!
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#3 sasman

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Posted 10 November 2004 - 09:56 PM

Err... i read this with intrest as i still havent had time to work out the max payload of my 1 lb rockets..When i saw the 5:1 rule of thumb?.thrust ratio that would be quite handy... To Fine tune my rockets.
So that means my 1lb rocket should Give 5lb thrust so its able to lift a 1 lb ? Payload(altho may not work with BP rockets?)....So i did a quick google on B6-4 motor and got the folowing Data..

Max Lift of weight 113g

Max thrust 12.1 newtons(2.7 Lbs)

Thrust Duration 0.8 secs

Total Newton impulse? 5.00..

So Starscream this motor gives double the thrust so 5:1 ratio dont work?

1224g(2.7 Lbs) thrust? max liftoff weight 113g(1/4 lb) thats nearer 10:1 ratio? ..


I would like to have data on an avg 1lb rocket should lift?..What is the nearest estes eqivalent rocket motor to a 1Lb BP rocket?

What effect does inner core diameter have on a BP rocket Motor?

If i had 2 identical rockets one had a core of 3mm the other 6mm what effect would it have?... would the 6mm core produce more thrust?

#4 Richard H

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Posted 11 November 2004 - 01:15 AM

sasman are you confusing total thrust with average thrust? The 5:1 ratio is concerned with thrust at any given moment, not the total thrust over the motors burn time.

B6-3 = average thrust of 6 newtons. Multiply by burn time to get total thrust.

Quoting Bob Arnott's handy rocketry site the following will come in handy:

You can calculate the thrust to weight ratio of a motor by this simple equation:

Thrust to weight ratio = Motors average thrust / 4.45 / ratio
Thus to get the 5:1 thrust to weight ratio of the I357 you divide 357 by 4.45, this is the number of Newton's in a pound. Then divide this number by 5 to get 16 Lbs., which is the 5:1 thrust to weight ratio. If you would prefer to find out what the 4:1 ratio is then divide by 4 instead of 5.

If you have chosen a rocket before choosing a motor you can also find out what motors will be ok to fly in your rocket by using this equation:

Motors average thrust = Rocket weight in Lbs * 4.45 * ratio
So if your rocket weights in at 16 Lbs. then multiply it by 4.45 and then again by the ratio you want and you'll get the average thrust of a motor. Any motor with an average thrust greater than the value you calculate should be suitable.



#5 Pretty green flames

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Posted 11 November 2004 - 05:23 AM

Thnx for your help guys.

Take care

#6 StarScream

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Posted 11 November 2004 - 06:17 AM

So that means my 1lb rocket should Give 5lb thrust so its able to lift  a 1 lb ? Payload(altho may not work with BP rockets?)....So i did a quick google on B6-4 motor and got the folowing Data..

Max Lift of weight 113g

Max thrust 12.1 newtons(2.7 Lbs)

Thrust Duration 0.8 secs

Total Newton impulse? 5.00..

So Starscream this motor gives double the thrust so 5:1 ratio dont work?

1224g(2.7 Lbs) thrust?  max liftoff weight 113g(1/4 lb) thats nearer 10:1 ratio? ..
  I would like to have data on an avg 1lb rocket should lift?..What is the nearest estes eqivalent rocket motor to a 1Lb BP rocket?

  What effect does inner core diameter have on a BP rocket Motor?

If i had 2 identical rockets one had a core of 3mm the other 6mm what effect would it have?... would the 6mm core produce more thrust?

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Let's try to clear things up a bit.

When I say "rocket" I mean a model rocket weighing 1 pound including the motor, not a 1 pound BP firework rocket.

Also, the motor doesn't give double the thrust. You only get 5 newtons total impulse from any "B" class motor. (max thrust of 12.1 newtons doesn't mean anything in terms of lift capability of the motor)

Core diameter affects a lot of things. Burn profile of the motor for one. The smaller the core diameter, the more progressive the burn profile usually. It affects Kn (area ratio), which affects chamber pressure, which affects thrust.

I believe a 6mm core would produce more thrust than a 3mm core, but for less time because there's less propellant.
"Life is a tragedy for those who feel and a comedy for those who think."

#7 StarScream

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Posted 11 November 2004 - 06:31 AM

B6-3 = average thrust of 6 newtons. Multiply by burn time to get total thrust.

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Almost... :)

B6-3 = average thrust of 6 newtons. Multiply by burn time to get total impulse.

Total impulse and total thrust are not the same thing. Total impulse is measured in newton-seconds. Thrust is measured in newtons or pounds.
"Life is a tragedy for those who feel and a comedy for those who think."

#8 alany

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Posted 11 November 2004 - 07:40 AM

For fireworks rockets (ie, in an atmosphere and gravity field):

The key thing is that the average thrust the motor provides is more than the gravitational force the motor and payload mass creates. If not, the rocket won't overcome gravity and take off. If it isn't significantly more than "just enough" the rocket won't accelerate rapidly enough for its stabilisation system to keep it flying roughly upwards, hence rules of thumb like the 5:1 ratio.

It has to have sufficient total impulse to carry the payload to a safe height for deployment too. If that is delivered with a short high-thrust burst the acceleration can cause structural problems, a more gentle, longer push, is easier on the payload but means the stabilizers are less effective for a significant fraction of the flight.

Doing the math isn't that hard, but a full treatment means you need to consider the changing mass as propellant is consumed and air resistance. You can get a reasonable result by assuming no air resistance and constant mass then multiplying the altitude by a fuge-factor calculated from experence. There is software available for model rocketry which can predict altitude quite accurately, the better ones compensate for air pressure drop with altitude, but that isn't a big issue for the relatively low altitudes we use for fireworks.

#9 sasman

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Posted 15 November 2004 - 09:14 PM

Well i tried to launch a 4" shell using a 1 lb rocket a few weeks ago and it barely reached 20 or 30 foot ,not very impressive..carrying small payloads of say 100grams my 1 lb BP rockets are pretty impressive...

I never thought of trying to measure the thrust...Well i bought a ORB rocket and that motor can carry payloads upto 300 to 400g to a nice height ..So i have just done some experimenting. here is 3 clips Thrust test ORB rocket standard rocket then a tuned rocket 1lb.

.The ORB produces about 9.5lbs initail thrust for 6 frames( about 1/4 second) then about 1/2 lb thrust for rest of duration..Total duration 3 secs..

My normal BP rocket gives really poor 2lbs initail thrust and about 1/3 lb thrust for rest of burn...i was not very impressed i tried various core lengths and diameters thru rest of the day to end up with the last clip much better 9 1/2 lbs thrust tho not for as long as the ORB then the rest was about 1/3 lbs thrust..Much better than my original rocket..

The only problem with all this thrust is nozzle errosion. the bentonite clay nozzle erroded to nearly 7mm from 5mm so ill need to fix that somehow...Ill do some more test tommorrow..

#10 sasman

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Posted 20 November 2004 - 01:05 PM

I'm really enjoying this Fine tuning lark...with out using some way of measuring the thrust of my BP rockets i cant see how you can fine tune them...

I have increased my initial peak thrust to over 10 lbs.. this peaks for 3 or 4 frames ( 25 frames per sec) then drops down to about a 1lb of thrust. thats a far better than my original rockets which seemed to fly pretty good.


. Havent fired any of these new powerfull motors in to the air yet...Hopefully i can get 10 lb peak thrust up to 6 frames.. then that will match the ORB rocket im trying to duplicate..Also i solved the Nozzele erosion by adding some smashed up pottery to my bentonite clay.. It also make removing the spindle easier ,before the clay would stick to the spindle but with this "grog" it just slides of easily..

Edited by sasman, 23 February 2005 - 09:12 AM.


#11 StarScream

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Posted 23 February 2005 - 01:00 AM

Also i solved the Nozzele erosion by adding some smashed up pottery to my bentonite clay.. It also make removing the spindle easier ,before the clay would stick to the spindle but with this "grog" it just slides of easily..

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This is interesting and good news. I read recently that "grog" really is the cat's meow when used in nozzles. I'm guessing because grog is ground-up pottery that has been fired at very high temperature, it can withstand the high temperature and velocity of rocket motor exhaust much better than regular clay.

Definitely going to have to try it, along with making some coloured stars, now that I finally found a local ceramic supplier who sells grog, carbonates & oxides! ;)
"Life is a tragedy for those who feel and a comedy for those who think."




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