Canting a rocket nozzle to induce a spin

[MetricRocketeer]

Hi everyone,

I think that I am posting this message in the correct forum.

Here is my question, please.

Consider a rocket with a cluster of nozzles. I have heard about canting the nozzles so as to induce a spin. Now I will break up my question into two parts:

1) Does canting the nozzles indeed induce spin into the rocket's flight? I guess that seems intuitively obvious, but I wouldn't mind getting confirmation.

2) Here is my main question. What does it mean to cant the nozzles? You are not splaying them out -- am I right -- so that the aft end of the nozzle is farther away from the longitudinal axis than is the forward end of the nozzle? The caning takes place so that the forward end and the aft ends both continue to be equidistant from the longitudinal axis.

Actually, could someone produce a drawing of what canted nozzles would look like.

Thank you for your assistance.

Stanley

 

[Reinhard]

1) Yes. The ROS-40-5 rocket motor is doing that for example. See here for pictures:
http://www.airsofthouse.cz/Raketovy-motor-ROS-40-detail-zbozi-7819.htmlThe smaller outer three nozzles impart the spin. When it is used for model rocketry, for which it wasn't originally designed, folks tend to plug those extra nozzles with screws (Not a certified motor, not available in the US).

2) I haven't found a good picture of an actual rocketry motor, but think about the teeth on those helical gears to get an idea how those nozzles are oriented.

(Source: Wikipedia)

Reinhard

 

[Steve Shannon]

I’m not going to make a drawing for you, but if I wanted to have a canted nozzle to induce spin I would start with an Aerotech Medusa nozzle and I would use a milling machine to redrill the outer holes, making sure they all have the same angle.

 

[shockie]

Google is evil
https://www.google.com/search?q=can...zRjABHU4-AiQQ9QF6BAgREAE#imgrc=SsLjNhVRGpenMM

 

[boatgeek]

There's two ways to approach this. The first (harder and making it a research motor) is what Steve said above, where you have a single motor with multiple nozzles, some of which are canted. If the motor has a single expansion cone, I'm not 100% sure that would even work. It would definitely make for a messy exhaust plume.

The second and far easier way would be to cluster two or more motors and cant them. You'd do that by rotating the centering rings slightly relative to each other as you glue in the motor mount.

 

[CoyoteNumber2]

Canted nozzle


Canted motors

Photo cred: NGIS; Apogee.

 

[G_T]

That's canted for thrust alignment to be more forgiving of unequal thrust. That does not induce spin. To induce spin, the thrust axis needs to be non-parallel with the rocket's major axis and needs to not intersect the rocket's major axis.

If you do cant the nozzles to induce spin, your spin is going to decay quite quickly once thrust stops.

Gerald

 

[neil_w]

This is not geometrically correct (proved harder to do in TinkerCad than I expected) but maybe conveys the idea (or maybe not, but this is the best I can do quickly.)

 

[MetricRocketeer]

Hi neil_w,

Good. That was really helpful. Thank you.

And thanks to everyone who sent me images or links. But neil_w's drawing really clarified it for me. Actually, Reinhard's image in Post #2 also explained the issue, but I understood it only after seeing neil_w's drawing. Maybe I should have understood it right from the beginning and I am just dense.

Again, I thank all of you.

Stanley

 

[Kelly]

Laurel: How do you get a rocket to spin, using the nozzles?
Hardy: You cant.
Laurel: Why not?
Hardy: Why not what?
Laurel: Why can't you get the rocket to spin?
Hardy: Oh, you can!
Laurel: OK, how?
Hardy: You just cant!

 

[DrewW]

Hi everyone,

I think that I am posting this message in the correct forum.

Here is my question, please.

Consider a rocket with a cluster of nozzles. I have heard about canting the nozzles so as to induce a spin. Now I will break up my question into two parts:

1) Does canting the nozzles indeed induce spin into the rocket's flight? I guess that seems intuitively obvious, but I wouldn't mind getting confirmation.

2) Here is my main question. What does it mean to cant the nozzles? You are not splaying them out -- am I right -- so that the aft end of the nozzle is farther away from the longitudinal axis than is the forward end of the nozzle? The caning takes place so that the forward end and the aft ends both continue to be equidistant from the longitudinal axis.

Actually, could someone produce a drawing of what canted nozzles would look like.

Thank you for your assistance.

Stanley

Side note: you can induce corkscrew (precessional spin) by keeping a motor parallel to the rockets primary axis but offsetting (radial shift) from that line (towards the rocket sidewall)

 

[Arpak]

This idea is extremely easily demonstrated in Kerbal Space Program, I used to love launched spinny boys by slapping 8 off angled SRBs to the side.

 

[MetricRocketeer]

Laurel: How do you get a rocket to spin, using the nozzles?
Hardy: You cant.
Laurel: Why not?
Hardy: Why not what?
Laurel: Why can't you get the rocket to spin?
Hardy: Oh, you can!
Laurel: OK, how?
Hardy: You just cant!

Hi Kelly,

Thank you! That is really funny.

Stanley

 

[MetricRocketeer]

This idea is extremely easily demonstrated in Kerbal Space Program, I used to love launched spinny boys by slapping 8 off angled SRBs to the side.

Hi Arpak,

I keep thinking that I should learn Kerbal Space Program, that perhaps it would teach me more about rocketry. What you said gives me further impetus to learn KSP.

Stanley

 

[Steve Shannon]

Easiest is to cant the fins slightly. As long as the rocket is in air it’ll spin. It’s important not to cant them too much because spinning a rocket flexes the body tube. I did that with a polycarbonate body and it folded in half on the way up. I keep it around as a reminder.

 

[prfesser]

The old Estes TR6 report on clustering shows three methods for inducing slight spin. I guess it evens out slightly uneven thrust.

As was pointed out, tilting the MMTs so that their axes point (roughly) thru the CG doesn't induce spin, but it is said to reduce the hazard when a motor fails to ignite.

Best -- Terry

 

[Kelly]

Laurel: How do you get a rocket to spin, using the nozzles?

Yeesh, I meant Abbott and Costello, not Laurel and Hardy.

 

[prfesser]

Yeesh, I meant Abbott and Costello, not Laurel and Hardy.

'T'was funny either way!

 

[Brad_G]

Honest John Field Artillery Missile Components
The Honest John rocket consists of four major components; the warhead, pedestal, rocket motor, and fin assembly. Each component has a specific function in the overall operation of the rocket.

Honest John missile on display, Texas Military Forces Museum, Camp Mabry, TX, 30 January 2006. Photo: Courtesy of Bob Pettit.

The pedestal section of the rocket houses eight spin rockets. These small rockets are mounted in pairs in the four quadrants of the pedestal. They are positioned so their thrust is delivered perpendicular to the Honest John's longitudinal axis. The spin rockets are fired immediately after the Honest John clears its launching rail, giving the weapon a two revolution per second spin. Spinning the rocket in this manner distributes errors caused by uneven propellant burning.

 

[MetricRocketeer]

The pedestal section of the rocket houses eight spin rockets. These small rockets are mounted in pairs in the four quadrants of the pedestal. They are positioned so their thrust is delivered perpendicular to the Honest John's longitudinal axis. The spin rockets are fired immediately after the Honest John clears its launching rail, giving the weapon a two revolution per second spin. Spinning the rocket in this manner distributes errors caused by uneven propellant burning.

Hi Brad_G,

What you wrote is interesting. But I cannot picture the process in my mind, in particular how the "thrust is delivered perpendicular to the Honest John's longitudinal axis."

Could you explain that a bit more, please?

Thank you.

Stanley

 

[Brad_G]

Hi Brad_G,

What you wrote is interesting. But I cannot picture the process in my mind, in particular how the "thrust is delivered perpendicular to the Honest John's longitudinal axis."

Could you explain that a bit more, please?

Thank you.

Stanley

http://designation-systems.net/dusrm/r-1.html

 

[MetricRocketeer]

OK, Brad_G, that reference explains everything. And it is most interesting. Thank you.

 

[Ronz Rocketz]

Unfortunately that’s what Rocket Labs did this morning.