Canting a rocket nozzle to induce a spin

The Rocketry Forum

Help Support The Rocketry Forum:

MetricRocketeer

Member of the U.S. Metric Association
TRF Supporter
Joined
Jun 1, 2018
Messages
367
Reaction score
63
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

Well-Known Member
TRF Supporter
Joined
Jan 18, 2009
Messages
1,159
Reaction score
371
Location
Austria
1) Yes. The ROS-40-5 rocket motor is doing that for example. See here for pictures:
The 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.
1620911455850.png

(Source: Wikipedia)

Reinhard
 

Steve Shannon

Well-Known Member
TRF Supporter
Joined
Jul 23, 2011
Messages
6,761
Reaction score
3,669
Location
Butte, Montana
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.
 

boatgeek

Well-Known Member
Joined
Dec 27, 2014
Messages
3,472
Reaction score
2,018
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

Original San Diego High Power Rocketry
Joined
Jan 30, 2009
Messages
655
Reaction score
148
1620933647337.png

Canted nozzle

1620933737044.png

Canted motors

Photo cred: NGIS; Apogee.
 

G_T

Well-Known Member
Joined
Dec 29, 2011
Messages
2,347
Reaction score
409
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

Ennui poster child
TRF Supporter
Joined
Jul 14, 2015
Messages
11,845
Reaction score
4,653
Location
Northern NJ
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.)
1620945773617.png
 

MetricRocketeer

Member of the U.S. Metric Association
TRF Supporter
Joined
Jun 1, 2018
Messages
367
Reaction score
63
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

Usually remembers to get the pointy end up
Joined
Apr 26, 2010
Messages
514
Reaction score
383
Location
Oregon
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

Rocket Surgeon
TRF Supporter
Joined
Aug 23, 2020
Messages
258
Reaction score
167
Location
Arizona
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

Well-Known Member
Joined
Nov 23, 2020
Messages
125
Reaction score
98
Location
San Antonio, TX
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

Member of the U.S. Metric Association
TRF Supporter
Joined
Jun 1, 2018
Messages
367
Reaction score
63
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

Member of the U.S. Metric Association
TRF Supporter
Joined
Jun 1, 2018
Messages
367
Reaction score
63
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

Well-Known Member
TRF Supporter
Joined
Jul 23, 2011
Messages
6,761
Reaction score
3,669
Location
Butte, Montana
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

Lifetime Supporter
TRF Lifetime Supporter
Joined
May 7, 2017
Messages
1,968
Reaction score
2,109
Location
Murray, KY
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
 

Brad_G

Active Member
Joined
Oct 24, 2017
Messages
28
Reaction score
45
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

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

Member of the U.S. Metric Association
TRF Supporter
Joined
Jun 1, 2018
Messages
367
Reaction score
63
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
 

MetricRocketeer

Member of the U.S. Metric Association
TRF Supporter
Joined
Jun 1, 2018
Messages
367
Reaction score
63
OK, Brad_G, that reference explains everything. And it is most interesting. Thank you.
 
Top