Siren concept: self-supercharged STH-10 (Modified 2T22)

[bigloudnoise]

This is more of a "What if" concept I thought of, as opposed to something that I think should be made. This is just a concept created out of curiosity.

Anyway, I had a thought about a possible way to create what would essentially be a supercharged STH-10. Basically, it would involve modifying a 2T22 by removing the lower rotor and stator, and replacing it with a centrifugal blower/compressor. The output from the blower would then be piped up to the intake of the upper rotor.

Here's a quick mock-up I constructed in Bryce, showing how I visualize such a setup may appear. As mentioned, the lower rotor has been replaced with a centrifugal blower, with the output piped to the intake of the upper rotor. One of the horns have been removed to provide space for the air tubing to run to the top of the siren, and a brace has been added to hold the tubing steady to the motor.


(Click for larger view)

Obviously, efficiency and effectiveness on such a setup would be questionable. As I said, this was created merely as a curiosity. Still interested to hear any input about this.

[Justin]

It would certainly assist in keeping the wind down tones loud, in comparison to say an unassisted rotor (like that of the T-128 or the 2001) where they get quieter as they spin down as less air is being sucked in; this design seems to keep the air supply up to the rotor.

If you look for my Year 12 D&T project thread on here, you might find a few ideas to improve this.

One idea I had was similar to yours: I had a way of incorporating a fan into the rotor assembly that spun in the opposite direction, as a way of acting as a blower. How effective it was, I don't know. I never got my rotor to work unfortunately.

[Jim Z]

- what you would theoretically gain by boosting the airflow to the chopper would likely be negated by the blower sapping that much power from the motor.

- in order to appreciably increase the sound output, your blower would have to be able to generate a measurable increase in air pressure over what the chopper's impeller can do itself. That would require a very large blower and its own, more powerful motor.

- along with that, you would need a blower which can push a really large volume of air at the same time as generating that pressure due to having 10 or 12 open stator ports. A "squirrel cage" type of centrifugal blower can move a lot of air but can't generate much if any pressure.

the last two are the killers. The Thunderbolt and Hurricane make this work by having a single, small stator port which lets the blower generate head pressure. You would probably need to move a couple thousand cfm of air at around a few psi in order to make an appreciable difference in sound output, and you aren't going to be able to drive that from the 7.5 or 10 hp chopper motor. You'd probably need 50 hp for the blower alone.

[JasonC]

You'd have to have a blower up around 1,000hp. Think of the tiny slit the t-bolt has just for it's opening. This theory has been discussed on here before and it would just never work.

[CJ]

It would certainly assist in keeping the wind down tones loud, in comparison to say an unassisted rotor (like that of the T-128 or the 2001) where they get quieter as they spin down as less air is being sucked in; this design seems to keep the air supply up to the rotor.

Unfortunately it wouldn't as the blower would slow down with the chopper

[Mathew Bailey]

There are such things as high pressure centrifugal blowers known as centrifugal compressors. These have impellers similar to a turbocharger inlet impeller. An example of numerous applications of centrifugal compressors is pipeline transport of natural gas.

[Jpressman8]

Get an STH-10 or 2T22 and try it. 8)

[acoustics101]

What you are proposing is essentially a two stage blower, as the first blower is already incorporated into the chopper. It would increase the output, but you would also need more HP to drive it. Probably double the HP. That would add an extra 3 dB.

Since (I am assuming) the extra blower is on a common shaft with the chopper, you would not get full output at lower RPM as in a Thunderbolt or Hurricane siren, as the pressure would drop with the RPM. However, if my assumption is wrong and you are usung a separate blower, much higher output could be obtained at lower RPM. That would make it much more effective.

From an efficiency standpoint, it would be better to put the blower inline with the siren's intake as opposed to piping it to it as shown. Also, the size of the horns should be increased to extend their cutoff to the lower frequencies. That would make it really effective.

[Justin]

Unfortunately it wouldn't as the blower would slow down with the chopper

Unless of course it was independently driven.

[CJ]

Unfortunately it wouldn't as the blower would slow down with the chopper

Unless of course it was independently driven.

Said picture appears to be using the standard XT22 series motor.