Are all motor adapters like this?

dhkaiser

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I have a AERO PACK 29/38, that is it adapts a 38mm motor mount to a 29mm. I have flown it multiple times, each flight the rocket corkscrews up while under burn then is ok after burnout. Flying 38mm motors the flights are straight. Is this normal or do I have a defective adapter?
 

3stoogesrocketry

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I have a AERO PACK 29/38, that is it adapts a 38mm motor mount to a 29mm. I have flown it multiple times, each flight the rocket corkscrews up while under burn then is ok after burnout. Flying 38mm motors the flights are straight. Is this normal or do I have a defective adapter?

It sure seems like your adapter is not consentric to the motor tube. Can you provide any pictures.
 

Crumb fire

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When the motor stop, the rocket fly straight. Looks like the adaptor, or the motor mount. But if it doesn't do that on a 38mm, I would suspect the adaptor.
 

dhkaiser

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When the motor stop, the rocket fly straight. Looks like the adaptor, or the motor mount. But if it doesn't do that on a 38mm, I would suspect the adaptor.

Yes I agree, my question is this common to adapters or is it not?
 

rharshberger

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I to am going with the rocket issue not the adapter, rockets can do all kinds of things under thrust.

Does the rocket have noseweight and if so how much?

What you are describing may be coning.

Is this a kit?

Can you post a accurate .rkt or .ork file for the rocket?

Adapters dont usually do anything except add weight to the wrong end of the rocket.
 
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Crumb fire

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No. What are the motors used? Some motors, (long burns) avec a slot for the igniter that is excentric to the reload. I have this adaptor and use it whitout problems.
 

jimzcatz

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Not an adapter issue. Adapters are a no brainer device. Either its installed right or not. No in-between. Do you really think if this was a common issue with adapters they would be so widely used? You have other issues going on.
 
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dhkaiser

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I to am going with the rocket issue not the adapter, rockets can do all kinds of things under thrust.

Does the rocket have noseweight and if so how much?

What you are describing may be coning.

Is this a kit?

Can you post a accurate .rkt or .ork file for the rocket?

Adapters dont usually do anything except add weight to the wrong end of the rocket.

How can it be the rocket if it flies straight on 38mm motor? See post #6.
 

dhkaiser

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No. What are the motors used? Some motors, (long burns) avec a slot for the igniter that is excentric to the reload. I have this adaptor and use it whitout problems.

Not reloads, Aerotech DMS motors. 29mm H115, 38mm I140.
 

rharshberger

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How can it be the rocket if it flies straight on 38mm motor? See post #6.
My guess is the rocket wants to cone under lower thrust profiles and with harder hitting motors its probably more stable off the rail resulting in less "corkscrew" aka coning. An adapter plus 29mm motor may weigh more than a 38mm motor ( sometimes).
We need more data to make better guesses at the issue, things like motors used, rocket sim file, pictures of rocket, rocket weight and nose weight mass. Scale V2's are well known for "coning", "tail walking", "corkscrewing" due to relatively small fin area and the heavy noseweights necessary to make them stable, motor thrust profile can have a lot to do with how severe the coning is. Think trying to balance a sledgehammer vertically on your hand with the head being the nose, you have to use motion at the bottom to keep it balanced, its almost like coning, and the movement of air over the fins provides the corrective movement.
 

les

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If you are adapting to a smaller size there are 2 potential issues
1) the adapter is adding weight on the wrong end (moving the cg rearward)
2) the smaller motor may have less thrust than the bigger motor so it is slower off the rod/rail

According to Thrustcurve, the H115 goes to about 125N of thrust, while the I140 goes to 175N
 

dhkaiser

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My guess is the rocket wants to cone under lower thrust profiles and with harder hitting motors its probably more stable off the rail resulting in less "corkscrew" aka coning. An adapter plus 29mm motor may weigh more than a 38mm motor ( sometimes).
We need more data to make better guesses at the issue, things like motors used, rocket sim file, pictures of rocket, rocket weight and nose weight mass. Scale V2's are well known for "coning", "tail walking", "corkscrewing" due to relatively small fin area and the heavy noseweights necessary to make them stable, motor thrust profile can have a lot to do with how severe the coning is. Think trying to balance a sledgehammer vertically on your hand with the head being the nose, you have to use motion at the bottom to keep it balanced, its almost like coning, and the movement of air over the fins provides the corrective movement.

DX3 single deploy. 29mm motor H115 = 53.2oz, stability with motor = 1.56. 38mm motor I140 = 57.2oz stability with motor = 1.06.
 

dhkaiser

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If you are adapting to a smaller size there are 2 potential issues
1) the adapter is adding weight on the wrong end (moving the cg rearward)
2) the smaller motor may have less thrust than the bigger motor so it is slower off the rod/rail

According to Thrustcurve, the H115 goes to about 125N of thrust, while the I140 goes to 175N

If it is a thrust issue why would it become stable after thrust?
 

BradMilkomeda

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Perhaps just the aero pack retainer is not squarly on the motor tube, so it’s not orthogonal to the motor tube.

The direction of the adaptor and the motor inside could be determined by the flang on the retainer when the adaptor is used. While if the full sized 38mm is used the direction is determined by the motor tube and the aft thrust ring may not be squarely against the retainer.

Just my theory...
 

mccordmw

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I've got many many flights with Aeropack adapters:

98 > 75
54 > 38
38 > 29

None of them corkscrew. The adapters should be machined to pretty tight tolerances.

Since you fly straight after burnout, it doesn't seem like a bent airframe.

Really seems like a rare bum adapter. Try another one. Many people (myself included) will loan out an adapter at a launch.
 

Steve Shannon

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Corkscrewing is not the same as instability.
If corkscrewing happens during thrust and stops when thrust stops it’s related to thrust. Perhaps thrust is off center somehow. That can happen with certain motor types such as c-slots or moonburners.
If it only happens when using 29mm motors in an adapter it’s either the adapter (or how you’re using it) or the 29mm motors. Is it a variety of 29mm motors or all the same type?
People have suggested how to visually check the adapter for concentricity.
Also inspect the nozzles on the spent 29mm motors for anything unusual.
Is anything else different between the 29mm and 38mm flights?
 

grouch

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He's just going to refer you to post 16. He's not getting what people are trying to explain.


Sent from my iPad using Rocketry Forum
 

blackjack2564

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H115 is Drkmatter
I-140 white lightening.

I have flown & seen many Darkmatter motors with vectored thrust,creating the problem you describe.
If you have flown other 29 propellant & rocket didn't cone/spin. rule this out.

If not try another 29 propellent.

If adapter is not seating correctly, [ring on top of motor not centered or upside down, adaptor will be off kilt when cp screwed on.] it can vector thrust. No pics can't tell. Have you asked any witnesses to your flights...what they thought.

On same topic [kinda] , Fins beveled heavier on one side, will cause spin. [just 1 is all it takes] This can also be velocity dependent. Only spins high velocity, stops right after motor burnout, not enough off-set bevel to keep it spinning.
Not your issue,I checked thrust curves on those motors.
Your spinning with less thrust......not more, why I think it's the DM vector thing.
 
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Nathan

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How long is your motor tube? If the motor tube is shorter than the 38-29 adapter then the adapter would wobble.
 

BigDuphis

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Did you check the fitment on the spacer ring? It goes different directions based on what motor casing you're putting in. Are you using it with an aeropac retainer? I use the same adapter with the matching retainer. If I put it in with the spacer on way, there's some slack and flop, if I flip the spacer over, it's a nice tight secure fit.
 

dhkaiser

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Did you check the fitment on the spacer ring? It goes different directions based on what motor casing you're putting in. Are you using it with an aeropac retainer? I use the same adapter with the matching retainer. If I put it in with the spacer on way, there's some slack and flop, if I flip the spacer over, it's a nice tight secure fit.

You may have something here. Not sure I checked the spacer fitting. Will check that out.
 
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