14 replies to this topic

[Sparky]

Apologies if this is a bit of a newbie question but has anyone tried using more than one rocket to lift a single header?


E.g. 2 x 1lb core burners for a 4inch header?

Obviously would need to be quick match all the way but it should be reliable?

[barnsley-mark]

Unequal thrust would give a turning moment - boomerang springs to mind!

[digger]

caduceus rocket

[pyrothrust]

Dual or Tri motors work extreamly well, never experienced anything other than straight flight. and that is using Red line motors. If you build your motors correctly their will be no difference in thrust. and if their are differences in thrust. , they are minimal.
(As to Red line motors ,I.m talking motors that produce maximum power with the best fuel. not hand rolled tubes etc.)
No apologies if I know what I'm, talking about.

Putting a stick on the side of a motor produces an uneven thrust line let alone adding Two which can also balance out the dynamics of a single stick / motor configuration,

In reality Tri core motors with 3 sticks go where you point them. irrelevant of wind .

Edited by pyrothrust, 15 August 2012 - 12:23 PM.

[pyrotrev]

As Digger said, caduceus rocket, though those tend to have an exaggerated tilt on the motors to give a very distinct spiral tail. I wonder has anyone made one with just a slight tilt on the motors??? The spin should add extra stability and maybe allow the use of a smaller stick?

[Sparky]

OK so not much experience of trying it here it seems.

I have a lot of experience with hobby rockets and I actually do not think the thrust differential is going to cause too much of a problem with a good length stick on it. I've launched a few clustered Estes model rockets before and the main problem there was getting them to ignite simultaneously using the provided igniter's. Admittedly the build quality of their motors is probably beyond my meagre means bashing away on my ramming post :-)

I'm going to ram a couple of 1lb motors today and I'll video the results if I can. No header for testing purposes of course!

Just out of interest why the difference in name between a caduceus rocket and a Girondola where they appear to be almost the same thing.

[dr thrust]

Made a few caduceus rockets myself here's a link, didn't have much success as I was using core burners, instead of end burners and at the time there wasn't much experimentation on them but they seem quite popular now lol ,a girandola is a more complicated Affair utilising a wooden ring, sometimes a embroidery ring with multiple motors attached horizontally and vertically timed for spin then lift Caduceus

Edited by dr thrust, 15 August 2012 - 07:40 PM.

[whoof]

As Digger said, caduceus rocket, though those tend to have an exaggerated tilt on the motors to give a very distinct spiral tail. I wonder has anyone made one with just a slight tilt on the motors??? The spin should add extra stability and maybe allow the use of a smaller stick?

I have tried clustering small estes motors before but with a short burn time , as mentioned elswhere it is important to get simultaneous ignition.
Some spin is needed to take account of differential thrust although i never did enough to quantify what was the required minimum angle.

[pyrothrust]

weird comment to make saying "not much experience here". how much would you like.3rd at a PGI Comp not enough????????.

Back to Passfire.

[graumann]

I made several tri motor units, clustered around a single relatively heavy flight stick, most ended in cato, the tight cluster of the motors usually caused too much heat resulting in burn throughs. The odd one that flew went surprisingly true.

[pyrothrust]

If you NEPT, then the likelyhood of a burn through is basically non existant. I mainly use Core burners and sometimes End burners as well and never had a burn through . Once you use NEPT you will never go back to anything else. some of the cheap tubes you buy in the uk are ok for low end power, but they are all made the same with cheap recycled non directional card which are fine for low end power use but burn thoughs will occur if you try to extract too much power or the duration is too long..

Edited by pyrothrust, 16 August 2012 - 10:31 AM.

[Sparky]

Hi Pyrothrust

I meant that there didn't seem to be a lot of experience clustering more than one motor not with pyro in general lol. I wasn't really looking for advice on Girondola's or Cadaceous rockets specifically although they are both very interesting and I have in fact already tried one but it flew apart :-)

I have plenty of experience in clustering Estes rocket motors and have seen models fly with even 5 x C class/size motors clustered. I am currently using 3/4 inch core burner tooling and my motors reliable lift about 150g headers (usually 3 inch shells).

I'm going to try using a slightly longer stick and with no deliberate effort to create a rotation. Assuming you ensure the two rockets are well aligned and built using the same methods, fuel and tooling I can't see how a differential in thrust could be a problem. I think the bigger problem is simultaneous ignition. I'm going to split from a single quick match into my usual black-match right inside the core.

[Sparky]

OK I didn't manage to video the launch but this is how it went.

I rammed 2 x 1lb core burners using the tooling I got from Oliver Brown hobby supplies taking particular care to ram them in the same style etc. Using a door frame I marked the vertical line on each where they would be joined. I used wood glue and a very flat surface to ensure they were joined accurately. Once the glue was dry I also taped them for additional strength.

I didn't add a header and I used a stick 120cm long which was far more than needed to balance the rockets. I used quick-match to light both motors simultaneously and I always use the black-match I take from quick (a couple of strands) to light the core all the way up.

Launch was so fast I can only assume both rockets ignited almost simultaneously. There was a very slight jink to the left at launch which could have been the left motor not kicking in quite as quick. The flight was arrow straight but with a slow rotation and certainly nothing much more than I've seen with single rockets. You could clearly see the dual tail effects which was pretty nice too.

I was actually surprised there was any rotation at all since I'd gone to a lot of effort to ensure the motors were aligned perfectly so I presume this could be due to inaccuracies in the build of the motors. I suspect that the nozzles are not perfectly aligned so you probably get a very small off centre component to the thrust they deliver. It wasn't enough to worry about though.

I'd like to see how much these can lift but a 4 inch header is not impossible.

[pyrothrust]

Should be able to lift a 4" with ease.

My 3# lift a 6"Shell to around 900 feet. with ease. Quite easy to know the height if you get a vertical launch and use the speed of sound between the burst and you hearing it, Witha 4" shell I peaked at 1.7 seconds which is way to high.

Cluster wise. I have no problems using Two 3# motors to lift 8" shells..The only issue is the black match in BP motors is left exposed just past the chock.On the whistles , only ever light the edge or they will cato with the excessive power build up of internal pressure if they are powerful motors.

Edited by pyrothrust, 18 August 2012 - 11:55 AM.

[dr thrust]

please tell us more about your rockets pyro, how do you attach the header to a double motor? and any pics?.
i can say hand on heart ive made a few myself, twin 1lbers ignited with fast visco of all things..there ok as a novelty but the extra work,weight and reliability issues, make the next size up or higher powered hybrid motors a better prospect

Edited by dr thrust, 18 August 2012 - 09:42 PM.