259 replies to this topic

[digger]

Thank you all for your kind comments.

With everything to hand, the wheel took around an hour and a half to make. It was very enjoyable to make, which made time less of an issue as I was immersed in the build.

Now onto the details...

The titanium used was sponge, between 40 and 80 mesh. The choke size was a third of the diameter of the tubes, which had an internal diameter of 3/4" and 1/2".


The internal shape of the nozzle was achieved with tooling from Wolter: http://www.wolterpyr...g?1216367984453

The drivers were made using a press.

Once again, thank you all for your comments.
Regards,
Vic.

Did you get any further with this issue?

Have you tried a larger nozzle apperture? It looks as though you could slow this wheel down a bit and still get a good effect as it is possible that the rotational force of the wheel is holding the Ti in the tube (as previously mentioned)

Have a look at this slower wheel on pyrobin (not mine)

Chromatrope

Edited by digger, 27 July 2008 - 11:28 AM.

[portfire]

How hypnotic is that wheel...Fantastic!

Could it be the Ti is been rapidly cooled on exiting the nozzle?


Off topic. Digger, I've found an excellent vid of your cake, I'll post it later

[Vic]

Did you get any further with this issue?

Have you tried a larger nozzle apperture? It looks as though you could slow this wheel down a bit and still get a good effect as it is possible that the rotational force of the wheel is holding the Ti in the tube (as previously mentioned)

Have a look at this slower wheel on pyrobin (not mine)

Chromatrope

We have given the titanium issue some more thought and have come to the conclusion that the titanium is being trapped by the forces of the spinning wheel.

It was revealed that, after firing, burn through occured on the outer edge of the driver. This went on for a number of minutes after firing. The damage can be shown in the following picture...

http://i271.photobuc...un/DSC05469.jpg

We also did a static test on a driver in which the titanium sparks were flowing perfectly, which we concluded to be due to the lack of centrifugal force.

As to the solution, we have considered a larger choke size, or possibly an off centre choke which would leave less restriction for the titanium. Finer titanium may also be an option to be explored. We have also considered increasing the diameter of the wheel, which would lower the spinning speeds and as such also lower centrifugal forces.

I have previously seen the chromatrope, and it is very impressive. I think one of the most amazing feats is how slow that wheel manages to turn: Fast is easy!

Regards,
Vic.

[digger]

We have given the titanium issue some more thought and have come to the conclusion that the titanium is being trapped by the forces of the spinning wheel.

It was revealed that, after firing, burn through occured on the outer edge of the driver. This went on for a number of minutes after firing. The damage can be shown in the following picture...

http://i271.photobuc...un/DSC05469.jpg

We also did a static test on a driver in which the titanium sparks were flowing perfectly, which we concluded to be due to the lack of centrifugal force.

As to the solution, we have considered a larger choke size, or possibly an off centre choke which would leave less restriction for the titanium. Finer titanium may also be an option to be explored. We have also considered increasing the diameter of the wheel, which would lower the spinning speeds and as such also lower centrifugal forces.

I have previously seen the chromatrope, and it is very impressive. I think one of the most amazing feats is how slow that wheel manages to turn: Fast is easy!

Regards,
Vic.

Just one thing to remember, the centripetal acceleration at the driver is omega squared multiplied by the radius so a larger slower wheel may not reduce the force that the titanium particles experience. The relative force on smaller particles will be no different so the mesh size will have little bearing on whether it will exit the nozzle unless the mesh size is so small that the settling velocity as defined by stokes law prevents them reaching the wall before they escape with the gas stream.

Takes a breath, how does that sound?

[Vic]

Thanks for clearing up the effects of the radius on centrifugal force- that is one less thing to have to experiment with before getting this to work

Now, please bear in mind you are not speaking to an academic, but could you please explain (Or link to an explanation of) "Stokes law"? It would be most helpful, as at the moment I'm left feeling a little bit ignorant

[portfire]

This may help....It makes my head hurt abit

http://en.wikipedia.org/wiki/Stokes'_law

[cooperman435]

If the Ti is basically being "flung" to the side wall of the tube and is unable to flow with the gas stream through the nozzle an idea would also be to angle the driver outwards.

This will have a double effect of slowing the wheel slightly as thrust will be "wasted" pushing inwards slightly and it will aid the Ti flowing through the nozzle as the angle of centrifugal force will be more in line with the gas flow.

[digger]

This may help....It makes my head hurt abit

http://en.wikipedia.org/wiki/Stokes'_law

Yep thats about it, however replace g in the formula with a (it is a bit more complicated than that, but if you assume a is high compared with g then it is a good approximation) from the formula a=ω²r. For the correct analysis you would also need to consider gas velocity.

Although non of that is really needed, just slow it down a bit, that should do the trick.

If the Ti is basically being "flung" to the side wall of the tube and is unable to flow with the gas stream through the nozzle an idea would also be to angle the driver outwards.

This will have a double effect of slowing the wheel slightly as thrust will be "wasted" pushing inwards slightly and it will aid the Ti flowing through the nozzle as the angle of centrifugal force will be more in line with the gas flow.

Yep I agree that will help to reduce the rotational speed and help the Ti out of the nozzle.

Sorry in advance. Nerdy voice engaged.

No such thing as centrifugal force. Centripetal force is the acceleration due to the change in direction of the tube as it rotates so the tube crashes into the Ti not the Ti flung to the tube.

Edited by digger, 27 July 2008 - 07:39 PM.

[Vic]

Things are beginning to make sense at this point.

I think the next step will be to try out Cooperman435's idea of angling the drivers, and see how it goes. I will post video and picture updates of this when it is carried out.

Thanks for all the help.
Regards,
Vic.

[digger]

Things are beginning to make sense at this point.

I think the next step will be to try out Cooperman435's idea of angling the drivers, and see how it goes. I will post video and picture updates of this when it is carried out.

Thanks for all the help.
Regards,
Vic.

or you could slow the formula down a little by adding more fuel, this should give a longer burn time too.

[BrightStar]

Yup, this is all starting to make sense.

The Glasswick type colour formulae are distinctive in that they burn much hotter, slower, more drossy and with less gas than typical BP mixes. It seems likely that the Ti is somehow burning up inside the driver. I've observed this even with static gerbs and rotational forces certainly won't help.

One modification might be to make the drivers 'short and fat' rather than the typical 'long and thin'. Glasswick mentions that a choke of slightly more than 1/3 id might be helpful with the dross. I'll be experimenting with some meal powder in the mix, sacrificing some of the colour saturation for more gas and hopefully more sparks.

It's notable that successful colour + spark gerbs are often based on cooler burning ammonium perc blues.

Edited by BrightStar, 27 July 2008 - 11:41 PM.

[dr thrust]

ey up! heres a vid of a "work in progress 70 perc,30 k benzoate whistle motors. i wondered why the cores on whistle rockets are wider than bp rockets so i tried a "1/3rd" id bp sized short core to see what would happen, anyway they where gutless to say the least so the tooling's "in bin" also i was fusing the rockets by just having the visco touching the fuel grain how does everybody else fuse there's? up the core yawn!!! takeoff!

[cplmac]

If the Ti is basically being "flung" to the side wall of the tube and is unable to flow with the gas stream through the nozzle an idea would also be to angle the driver outwards.

This will have a double effect of slowing the wheel slightly as thrust will be "wasted" pushing inwards slightly and it will aid the Ti flowing through the nozzle as the angle of centrifugal force will be more in line with the gas flow.

You could also try putting the nozzle along the sidewall of the tube rather than the center, or you could press/ram the inside of your clay nozzle in a conical shape, similar to how you press an end plug for a stinger or torbillion which would channel all contents from the walls to the nozzle.

[pihop]

From my last shoot:

[portfire]

Those 6" were excellent!!!. Great work pihop. How long have you been building shells?....Oh, and Details please