Your Opinion Matters.

[John Galt]

My scratch built "E" motor mount is off center by 5mm.
How will this affect the flight of the rocket?
I have not mounted it in the body tube yet. Should I do it over?


Thanks for the help.

 

[Cl(VII)]

I would redo it, but I have no data to support why other than it just looks like it could be a problem. My OCD alone would drive the decision though.

 

[dixontj93060]

Looks as if the 5mm deviation is a high percentage of the body radius. I would redo it.

 

[rocketgeek101]

I would definitely redo it.

 

[cvanc]

Redo it for sure.

 

[jpummil]

Yeah, I'd redo. I think a Mean Machine is too big to make an Estes Corkscrew out of :grin:

 

[John Galt]

Redone.
I was more patient second time around and the result looked more professional.
I've always had to do everything TWICE in my life, professional promotions, educational degrees, marriage... and rocketry. It just frustrates the hell out of me to do something a second time when all I really have to do is take my time and double check my work.

 

[powderburner]

I would leave it alone.

Yes, your MMT puts the thrust line off of the centerline of the model (and presumably the c.g./c.m. of the rocket). However, if it's only about 5mm----less than a 1/4 inch----this is not going to produce much of an upsetting moment that would try to turn the rocket. Especially for a Mean Machine configuration (if that is the rocket we are talking about) that is long and has relatively high pitch/yaw inertia, it will take quite a bit of something to get that rocket to turn. And any off-center thrust effects will last only as long as the motor burn; the coasting rocket will not be affected. I think you might be perfectly fine with your MMT as is.

Given the first problem, though, you should take extra efforts to BE SURE the fins are all aligned properly. You want to avoid adding any further pitch-inducing problems like canted fins.

If absolutely nothing else this should make for an interesting experiment, generating some actual experience with off-center thrust. Please report back with flight results?

 

[BABAR]

Depends on the rest of the rocket AND whether this is canted of just off center. Canted would be if one centering ring is off center AND other IS centered. Then your axis of thrust is non parallel with the long axis of the rocket. "just off center" is if BOTH centering rings are equally and "appropriately" off the center line. Axis of thrust is not colocated with but PARALLEL to long axis of the rocket. I THINK canted can be okay IF the Centerline of thrust still goes through CG of Rocket (I am guessing some have experience with canted motors like Fliskits Deuces Wild and occasionally.one engine doesn't light, still should fly safely otherwise Jim wouldn't sell it! But if it is significantly non parallel and axis OFF CG would be a problem, especially if your stability is marginal to begin with.

If your engine axis is PARALLEL to long axis off rocket and just off center a bit, I think the effect on stability would more forgiving. Having flown a lot of experimental designs with markedly asymmetric fins

https://www.rocketryforum.com/showt...ymmetric-Fin-Designs&highlight=Asymmetric+fin

https://www.rocketryforum.com/showt...ven-Glider-and-New-Gyskelion&highlight=Scoupe

Some go arrow straight, some corkscrew a bit, but they all had acceptable and safe flights.

Just my opinion and experience.

 

[scsager]

If it were me - I would see this as an opportunity to build two rockets. One with perfect centering rings, and one as shown in your photo. Using the scientific method, you could fly them both and find out what really happens.

 

[cvanc]

If it were me - I would see this as an opportunity to build two rockets. One with perfect centering rings, and one as shown in your photo. Using the scientific method, you could fly them both and find out what really happens.

LOL all us 'rocket scientists' probably should have thought of this approach! Fun and clever.

 

[AfterBurners]

Redone.
I was more patient second time around and the result looked more professional.
I've always had to do everything TWICE in my life, professional promotions, educational degrees, marriage... and rocketry. It just frustrates the hell out of me to do something a second time when all I really have to do is take my time and double check my work.

Welcome to my world. I threw out many a rockets because of my gooberness

 

[Winston]

My scratch built "E" motor mount is off center by 5mm.
How will this affect the flight of the rocket?
I have not mounted it in the body tube yet. Should I do it over?
Thanks for the help.

When I make custom centering rings for anything up to a black powder Es, now Fs, usually because I'm out of the needed centering ring size in my stock of the excellent lite ply ones made by Balsa Machining Works, I use a circle cutter:

https://www.amazon.com/dp/B000KNNJ2I/?tag=skimlinks_replacement-20

to cut "cold pressed illustration board" I buy at Hobby Lobby:

https://shop.hobbylobby.com/products/crescent-15-x-20-cold-press-illustration-board-150367/

Tough stuff to cut, but very strong. The circle cutter wants to flex unless the cut is done gradually, so I might buy a different cutter if I ever need to replace the X-Acto.

 

[powderburner]

When I make custom centering rings ....[snip].... I use a circle cutter to cut "cold pressed illustration board" I buy at Hobby Lobby.

I buy their picture-frame matte boards when they are on sale. One huge sheet (like 2 ft x 3 ft?) goes a long way. One side is finished smooth and flat, and makes for easy pattern drawing. If you handle this cardboard with a little care it works fine, but if you abuse it very much it starts peeling apart around the edges.

Have you tried the matte board stuff? Is it about the same to work with as your illustration board?

 

[AfterBurners]

I use the card stock from, Apogee. Seems to work well. It seems the last few scratch builds I cut my own rings. For me it makes sense to do it that way.