Countering torque reaction with a properly designed stator in a jet drive.

Exactly what I was thinking!! GA

Wouldn't the correction vary with the vessel speed?

This could be an issue at full power acceleration, but before speed had reached steady state.

GA!

My opinion exactly to the other suggestions.

True, but given a propeller and the HP of the motor, hydrodynamics of the torpedo, etc., there will be a maximum speed. Until that speed is reached, there could be (and most likely will be) rotation of the torpedo. However, at that maximum speed, the pitch of the tail fins can be adjusted to eliminate or minimize rotation.

Adding ballast (in the form of a skeg??) to the bottom will further reduce the tendency to rotate.

I would imagine that there's a passive or semi-passive way to adjust the pitch of the tail fins as a function of speed, but I haven't conceived of one yet.

Gimme a minute or two . . .

Thanks Bill: This has been tried in the past. Unfortunately, it does not nullify all of the roll. Additionally, it would only work well at one specific speed. Remember that this torpedo will be RC and will have an ESC to vary speeds.

I feel that you are going the right way, ballasting the Torpedo low down should also help.

Do you want it to surface at the end of its run? If yes, then you might want to us some simple weights and fins to both stop it rolling and to stop it surfacing till power is removed for example......

I have never built anything like this but it could be an interesting project.....it just depends how simple you want to keep it!!

Really simple and who cares if it rolls......

Thanks for all the input everyone: However, the question was whether one cancompletely nullify the motor torque reaction with a properly designed stator just aft of the impeller in a jet drive setup. The stator is located inside the duct and has nothing to do with the external fins. Unfortunately, because of the small size (1.05-1.1" x 14.5-15.5" and APR. 175g displacement) and the complexity of the intended setup (motor, 350 mAh LiPos, ESC, 4 ch micro receiver, 2 nano servos and micro antenna). I have very little latitude in terms of ballasting. I have to eliminate the rotation because a) the antenna must remain on top and b) I have rudder and stern plane controls to vary direction and depth. If the torpedo rolls, the controls will switch around with the rudders acting like planes and vice versa.

Its nice to get a little bit more info!

You did not mention RC or antennas in the original post..........

Remember, answering half (quarter?) of a question means that the answer will probably only be a quarter right!!!...or less......

If there are any other valid points that you have not up to now mentioned, now would be an excellent time!!!

What do you want to finally "do" with this torpedo? How long must the motor run for? Must it surface if battery power fails? Will it be fired from a tube? Above or below the waterline? and and and and........!

I think a complete statement of intention is needed, right now please?

" . . . The question was whether one cancompletely nullify the motor torque reaction with a properly designed stator just aft of the impeller in a jet drive setup."

I don't see why a stator couldn't nullify the rotation, but you'll have the same problem with it as you would with fins if the vanes are not adjustable. At some pitch and speed it should remain fairly stable, but I can only imagine that to eliminate roll altogether, you would need a closed-loop feedback system to constantly monitor and adjust vane angle. Given the envelope of the device, you've got a pretty nice problem on your hands.

I believe that your stator can minimise roll; probably will need to test several iterations in a tank.

My personnel opinion would be that a variable powered motor would need a variable device to counteract the torque from it. Can the pitch in the stator be varied with the power applied to the propulsion engine? It should only require small changes to counter the torque. Any mis-calculations on the stator pitch to power ratio could be corrected by using paint markings on the torpedo to allow you to see the inversion. If you are aware of the rotation from perfect orientation, you will be able to add or subtract power causing it to re align itself.

If you can not vary the stator pitch, you will have to set a fixed pitch, and vary power to control the rotation to keep it properly orientated. This will result in only a single speed for the torpedo. Good luck, send pictures.

Could the fins be spring loaded so that as the speed increases the fins line up closer to the forward direction, so reducing the twisting force??

Or what about using two antennae that are bent backwards, so if the torpedo rotates there will always be one antenna to pick up signals...?

John.

Thanks again everyone: Sorry about not mentioning that the torpedo is going to be RC in the original post. I'll get down to specifics.

1) The torpedo is meant to be forcefully expelled from a submerged model submarine by compressed gas (most likely CO2). I intend to use an inertia switch to complete the circuit between the power pack and the rest of the system to arm the unit. I am aiming for a max speed of 10mph. This should be possible with up to 57W of propulsive power available.

2) I intend that the torpedo to be just barely positively buoyant so that it will automatically come to the surface and be recoverable.

3) With only 350mAh available, I don't expect the run time to exceed 5-7 minutes overall. Full power runs will be only 10 sec at most. No point trying for more as I have to be able to see the torpedo in order to control it. At 10mph, 10 seconds translates into a distance of close to 150ft!! I want enough power left to be able to drive it back to shore for recovery after a couple of high speed runs.

It occurs to me that at low power, there will, of course, be less torque reaction. The velocity of the water impinging the stator will also be reduced thus producing less counter torque so things should blance. As power is increased, the torque reaction would also increase but so would the counter torque generated by the stators. I think that with a properly matched impeller and stator, it might be possible for the system to remain balanced over a fairly wide speed range.

WHAT. Not exploding. At least send bottle rockets and get some bang.

Yes.... let me and Vermin design a war head for you

Can you imagine it down on the boating lake KERRRR BUUUMMMM!!!!!

John

In the 60's, there was a guy who made a model battleship and fired .22 bullets from the guns and min torpedoes as well that exploded. The magazine called RCM & E of those early years showed it in some detail I remember.....

I also saw a more recent Sky program with exploding Torpedoes from a small Submarine....so the idea is not that new really......