18 to 24mm adaptors that work with screw in engine retainers

I'm considering buying one of the Vapor/Star Orbiter rockets from Estes, and using Aerotech composite engines in it (D10/21). From reading about the 18mm to 24mm adaptors that Estes sells, the won't work with the screw in engine retainers, only rockets with engine hooks.

Other than converting the rocket to use a hook, does anyone know of an adaptor that will work with screw in adaptors?

Bill S said:

I'm considering buying one of the Vapor/Star Orbiter rockets from Estes, and using Aerotech composite engines in it (D10/21). From reading about the 18mm to 24mm adaptors that Estes sells, the won't work with the screw in engine retainers, only rockets with engine hooks.

Other than converting the rocket to use a hook, does anyone know of an adaptor that will work with screw in adaptors?

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First I've heard of this. I'm pretty certain I've used the Estes adapters with the Estes screw-on retainers with no problem. Trying to think of specific instances to be 100% certain... I believe I flew my Trajector on a 24mm E15, also my upscale Quinstar using a 24mm reload, both using the Estes adapter and screw-on retainer.

Is this allegedly a problem specifically with the 18-24mm adapters? Certainly not an issue with the 24-29mm adapters.

I had been looking at them on the Estes website, and one of the reviews mentioned this:

"
Make sure your rocket uses an engine hook!
If your rocket uses an engine cap, the adapter will add a tiny bit of length that will result in the cap being unable to close! The design prevents this issue when you use an engine hook ( as intended by the product description ), so make sure you pay attention to this detail and only try to use this for rockets with engine hook mounting!"

I don't know what an "engine cap" is.

The screw-on retainers, certainly, can accommodate extra length; they just won't screw on as far. Similar situation if you use a BP motor and wrap tape around the base to create a thrust ring: that'll stick out the back a bit more than a typical composite motor. The retainers work fine.

I don't think there's any issue here, just MHO.

Cool, thanks for the reassurance. I'll go ahead with buying some then.

As long as you can get a couple threads on, you're fine for retaining an 18 or 24mm motor

(A screw needs 3 threads of full engagement for maximum strength, but I'm going to say we don't exactly push that at the 18/24 mm level)

If you set the thrust ring at just the right depth, you will have the best of both worlds as far as getting enough threads for the Estes adapter or a regular 24mm engine.

BRS Hobbies said:

If you set the thrust ring at just the right depth, you will have the best of both worlds as far as getting enough threads for the Estes adapter or a regular 24mm engine.

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That is a good idea. Would that be shallower or deeper into the body tube, and by how much? I don't have a kit that has a screw on retainer right now.

If you're putting in a motor block, just put it in the normal location. With BP motors you won't need any tape wraps; composite motors will utilize their thrust ring at the rear. Of course with a motor block you won't be able to use longer reload cases; that may or may not matter to you.

I think you're overthinking this one (take this from someone who overthinks almost everything). Build normally with the screw-on retainer and you'll be in good shape.

I wonder what model that reviewer was trying to fly using the 18/24 adapter. Yes, the adapter will add about 1/8 of an inch to the overall length of the motor assembly if you use it. And it does have cutouts for the tabs of a motor hook so that the hook's ends can engage the motor inside directly.

I'm trying to think of what models I may have with the 24mm screw-on retainer so that I can test this....but the only one I am sure about is my Estes SLV and it would be a bit of project to get down to it.

This is what a Booster-60's screw-on retainer looks like tightened against an 18/24 adapter. As you can see the cap doesn't quite bottom against the base of the booster as it does if you put the usual D12-0 in here. But it still goes on a full two turns, which is plenty for retention.

I would dry fit the parts first just to double check. With that being said, I think the thrust ring at 2 9/16" should be just right for C11 and D12 24mm engines. If you want to set it up for E engines, then 3 9/16" and you would need to use a spacer with the C11 and D12 engines.

Another option is to eliminate the thrust ring all together and just use a tape thrust ring on whatever engine or adapter that you use.

A tape thrust ring is typically thicker than the one built into composite motors, so it will again have the effect of pushing the retainer out a bit.

Okay, sounds good then, Neil. Yes, I do have this tendency to overanalyze things.

Thanks for the info, everyone.

Also: those estes adapters are good in general. You’ll use them.

I have flown many SU AeroTech 18mm & Q-jet motors in the Estes adapters. The adapters wrap completely around the smaller motor including the fwd & aft ends so it is about an 1/8” longer than a 24mm D. I have had no problem with Aeropack retainers and would imagine the Estes retainer works just as well. The 18 mm RMS case will NOT fit because of the Aft closure. You will need a “mount in mount” style or one of the aluminum versions.

I can see the extra length being a problem with a bayonet style cap. The longer motor could prevent the cap from being installed all the way to clear the tabs. I don’t know of any 24mm models that use this style but perhaps that’s what the reviewer had trouble with?

Here are a couple of ideas for you. First, is the Rocketarium 18/24 adapter. I have one and use it with the 18/20 RMS case. It works fine in Estes retainer. Just don’t forget to use the washer or your motor will spit out the back end.

https://www.rocketarium.com/Build/Motor-Adapters



If you go motor hook, you can easily build and adapter. The hook on the rocket actually engages the motor in addition to the adapter. I usually throw a wrap of masking tape just to make sure the hooks don’t open.

Estes adapters work for both the Estes plastic screw-on retainers and Aeropack.

gtg738w said:

The 18 mm RMS case will NOT fit because of the Aft closure. You will need a “mount in mount” style or one of the aluminum versions.

I can see the extra length being a problem with a bayonet style cap. The longer motor could prevent the cap from being installed all the way to clear the tabs. I don’t know of any 24mm models that use this style but perhaps that’s what the reviewer had trouble with?

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I won't be using any of the Aerotech reloadable engines, but thanks for mentioning that.

Russ' comment about a bayonet-style retainer rang a bell for me. I don't know of any current Estes models that have that kind of retainer and use a 24mm motor. But I do have one to hand, a recent eBay purchase, Super Nova Payloader. Sure enough, no way to put on the retainer with an Estes 18/24 adapter inside.

Second picture is a spent D12-5 next to a well-used Estes 18/24 adapter.

IIRC the Blue Ninja uses a bayonet style motor retainer, but that the only 24mm I can think of with one.

gtg738w said:

I have flown many SU AeroTech 18mm & Q-jet motors in the Estes adapters. The adapters wrap completely around the smaller motor including the fwd & aft ends so it is about an 1/8” longer than a 24mm D. I have had no problem with Aeropack retainers and would imagine the Estes retainer works just as well. The 18 mm RMS case will NOT fit because of the Aft closure. You will need a “mount in mount” style or one of the aluminum versions.

I can see the extra length being a problem with a bayonet style cap. The longer motor could prevent the cap from being installed all the way to clear the tabs. I don’t know of any 24mm models that use this style but perhaps that’s what the reviewer had trouble with?

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The only thing I can think of that might be an issue is if you can’t fit an18mm motor with a thrust ring into an Estes Adapter and I’m nit even sure on that

solid_fuel said:

The only thing I can think of that might be an issue is if you can’t fit an18mm motor with a thrust ring into an Estes Adapter and I’m nit even sure on that

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I haven't tried that, but the larger adapters accept thrust rings with no problem so I don't know why it wouldn't be the same with the 18mm.

What 18mm motor (other than the 18/20 reload case) has a thrust ring? The 18/20 case will NOT fit the Estes 18-24 adapter—it’s too long even with both closures all the way in, thanks to the rear closure/thrust ring.

AFAIK 18mm SU composite motors do not have thrust rings (Quest and AT).
And they fit the adapter.
The AT 18mm RMS casing does have a rear flange (closure) and it does not fit the adapter.

But oh, how I wanted it to.

EDIT: I see that Bernard beat me to the punch.