Help needed
Moderators: richardh08, Boophoenix, Lloyd
Help needed
Hi can anyone suggest the dimensions needed for a one pound or 3/4" rocket tool with a parallel spindle using whistle as fuel,I have the use of a lathe at present and would like to knock one up.many thanks Biffo
Re: Help needed
I'm not certain what you mean by "parallel spindle". All 'full-length' spindles should have at least a half-degree taper, in order for them to be extracted with reasonable ease.
Typical spindles run in the range of 33% to 50% in diameter of the tube i.d. at the exhaust end, and taper slightly toward the forward end.
Lloyd
Typical spindles run in the range of 33% to 50% in diameter of the tube i.d. at the exhaust end, and taper slightly toward the forward end.
Lloyd
"Pyro for Fun and Profit for More Than Sixty Years"
Re: Help needed
Thanks Lloyd that's what I was after. Regards B
Re: Help needed
Lloyd my bp one pound tubes are 7and 1/2" long could you suggest a typical length for spindle and tube using whistle fuel ie is the delay the same as for bp or does it differ .many thanks B
Re: Help needed
I've never built whistle rockets except in 1/2" tubes for line rockets, so I can't help you with that one.
Lloyd
Lloyd
"Pyro for Fun and Profit for More Than Sixty Years"
Re: Help needed
It depends on what whistle motor you want to build IE: long winded screamer/ standard/ or pusher, you will indeed need a taper on the spindle in my opinion at least 2 degrees.
- richardh08
- Site Admin
- Posts: 2226
- Joined: Wed Aug 07, 2013 1:54 pm
- Location: Bedfordshire
Re: Help needed
I don’t have much experience with whistle rockets; the only tooling I have is Ken’s 10mm set, which works well with either fast BP or whistle mix.
Not being able to resist, I just had to run a few sums on how it might be scaled up. Assuming a proportionally increased burning surface suggests that, for a ¾ inch (19mm) tube, a cylindrical spindle should be about 9mm in diameter and about 20mm long. As Lloyd mentioned, a tapering spindle makes it easier to extract, and such a spindle should be a bit longer – say, 25mm.
However, that doesn’t take into account that when you double the dimensions, areas go up by a factor of 4, but volumes (and hence weights) increase by a factor of 8. That would suggest that a modestly tapering spindle should be twice as long, or around 50mm in length.
Bear in mind that these arguments might be pure fantasy on my part. However, a brief search of FW.com revealed a description of a couple of spindles that someone used on whistle rockets of this size. The first - said to be for a 'slow screamer' - with a diameter of 6mm and a length of 28mm, is somewhat smaller than my rough calculations would suggest. But the second, described as giving ‘more power’, has a diameter of 8mm and a length of 67mm, which makes it a bit larger than my result.
So, no guarantees, but it looks as though these dimensions are not too far away from what is needed. I hope that helps.
Not being able to resist, I just had to run a few sums on how it might be scaled up. Assuming a proportionally increased burning surface suggests that, for a ¾ inch (19mm) tube, a cylindrical spindle should be about 9mm in diameter and about 20mm long. As Lloyd mentioned, a tapering spindle makes it easier to extract, and such a spindle should be a bit longer – say, 25mm.
However, that doesn’t take into account that when you double the dimensions, areas go up by a factor of 4, but volumes (and hence weights) increase by a factor of 8. That would suggest that a modestly tapering spindle should be twice as long, or around 50mm in length.
Bear in mind that these arguments might be pure fantasy on my part. However, a brief search of FW.com revealed a description of a couple of spindles that someone used on whistle rockets of this size. The first - said to be for a 'slow screamer' - with a diameter of 6mm and a length of 28mm, is somewhat smaller than my rough calculations would suggest. But the second, described as giving ‘more power’, has a diameter of 8mm and a length of 67mm, which makes it a bit larger than my result.
So, no guarantees, but it looks as though these dimensions are not too far away from what is needed. I hope that helps.
Even when I'm wrong, I'm convincing.
Re: Help needed
I have a Firesmith 3/4 inch long-winded screamer set I could potentially take measurements from.
Re: Help needed
You do not have the required permissions to view the files attached to this post.
Re: Help needed
Thank you gentleman for all your help,and yes Sam the measurements would be useful for comparison .Regards B