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delivers1234

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Hi. I recently picked up this hobby and would like to use the knowledge for my elementary school.

so I’ve bought the rtf riptide set, wadding and some b6-4 motors. I’d like to achieve a height of less than 200ft due to the school field. Could I use an “A” motor or an “1/2A” motor instead? I think I understand that the “T” motors are minis. Would I be able to retrofit a mini into a “A” motor rocket?

I guess the Estes engine chart is a little confusing.

Thank you,

Eugene
 

GrouchoDuke

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I didn't find a recommended motor list for it, but it should fly fine on an A8-3. Estes lists 650ft on a C motor, so an A should get you somewhere in the 100-200' range.
 

delivers1234

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I didn't find a recommended motor list for it, but it should fly fine on an A8-3. Estes lists 650ft on a C motor, so an A should get you somewhere in the 100-200' range.


Thank you. I bought a B4-2 set of motors. it makes more sense now. The A is 1/2 the power so the height would change as well with a similar effect.:)
 

dhbarr

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I wouldn't mess with the minis. They have a smaller ejection charge and I've seen them fail to deploy.
 

T-Rex

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The Estes site shows the B4-4 being the smallest motor for that rocket. You say you have B4-2's which may cause damage by ejecting too early. Try a B4-4 and see how it does, you may need those extra 2 seconds.
I have to caution against using an A8-3 since it is not recommended by Estes. I ran the numbers on Thrust Curve, and it shows a launch velocity of 38ft/sec on an A8-3. Even a C6-5 only gives 46ft/sec. I would only chance an A8 on a very clam day, without spectators.
YMMV
 

samb

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I really like the Riptide because the size and finish make it easy to prep and easy to see in the air and on the ground. I've also witnessed some flights with an A8-3 motor and I wouldn't recommend that you try it. The weight and diameter of the rocket on that motor did keep the max altitude low but the 3 second delay meant the rocket was quickly coming down when the parachute deployed less than 50 feet above the ground at a speed that ripped some of the parachute shroud lines. Also the speed of the rocket off the launch rod is so low that any wind will send it sideways which has the potential for all kinds of mayhem.

Estes does sell adapters to fit 13mm motors in rockets designed for 18mm motors but I wouldn't try it in the Riptide for the same reason that the A8-3 is not recommended. I'd suggest staying with the recommended motors for this puppy.

Which engine chart are you looking at ?


The Estes Educator page has lots of background info that may be helpful: https://www2.estesrockets.com/cgi-bin/wedu001P.pgm?p=publicat

https://www.estesrockets.com/rockets/launch-sets/001403-riptidetm-launch-set
 

Zeus-cat

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Since you have B6-4 motors I would use those. They are similar enough to the B4-4 that you really won't see much difference. The B6 means that you will have 50% more average thrust than the B4, but for less burn time than the B4.
 

BDB

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Since you have B6-4 motors I would use those. They are similar enough to the B4-4 that you really won't see much difference. The B6 means that you will have 50% more average thrust than the B4, but for less burn time than the B4.

This is good advice. Just fly the B6-4’s and have fun.


Sent from my iPhone using Rocketry Forum
 

Bat-mite

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Here's a little lesson on rocket motors. There are two things to consider: how much thrust in Newtons (or, alternatively, pounds-force) do I need to actually overcome gravity and lift my rocket? And, how long do I want the motor to burn, which generally indicates how high it will go.

If you look at an A8 vs. a B6, you will see that the A8 has considerably less thrust than the B6. The A8 has 2.3 N of average thrust, and it burns for 0.7 seconds. When you multiply these together, you get the total impulse of the motor, which is 1.61 Ns (or Newton-seconds). This makes it fall into the A impulse class., which is 1.26 - 2.50 Ns.

The B6 has an average thrust of 5 N, and it burns for 0.9 seconds, giving 4.5 Ns of total impulse (Estes lists 4.3; I haven't figured that one out yet). That puts it in the B class, which is 2.51 - 5.00 Ns.

For the altitude, notice that the 4.3 Ns of impulse for the B6 is more than twice the 1.61 Ns of the A, meaning that it will go more than twice as high (for all general purposes, thought there are many other factors that affect altitude). In fact, it should go 2.67 times as high.

But we have ignored, so far, the other number, which is the average thrust. Notice that the A8 has an average thrust of 2.3 N. Estes recommends a thrust:weight ratio of 3:1 for a safe launch, but most clubs will require at least a 5:1 ratio.

There is a formula to calculate whether or not your motor has enough thrust to safely overcome gravity and lift your rocket off the pad. 1 ounce-force is equal to 0.28 N. So multiply your rocket's total, loaded, flight-ready weight times 0.28, then again by 5 to get the 5:1 ratio.

I looked at the estimate weight of the Riptide, which is 2.7 oz. That probably does not include wadding or the motor. If the weight of your rocket is, say, 3 oz., then: 3 * 0.28 * 5 = 4.2 N. Thus the A8 would not meet the required average thrust to safely lift this rocket. However, the 5 N of the B6 would.

I'm sure the Estes 1/2A motors have even less average thrust, which means they are, as Monty Python would say, right out!
 
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