Motor Retainers & BP Motors

I've been working on the logistics of the PSII series rockets. They come stock with 29mm motor retainers. Plastic but they're still there. They are designed originally for use with the 29mm BP motors and this have an engine block. I'd like to keep the viable for use with RMS and composite motors. This means leaving out the engine block.

Could they still be flown with BP motors if I did this? If so, would it be better to friction fit the motors or create a thrust ring using either masking tape or pre prepping the motor with a thin, glued on ring?

I've never use the newer 29mm BP motors, but I'm thinking I would probably use both. I would create a thrust ring to position the motor correctly and put some tape on the motor to friction fit it. I have never friction fit a motor for thrust, only for retention. The motors thrust ring keeps it from going through the tube during thrust. The friction fit is only there to keep the motor tube from coming out when the ejection charge fires.

If you are going to use the retainer, you should be able to only use a masking tape thrust ring to keep the motor in place during thrust and ejection.

Guess I'll find out the hard way lol. Worst case I can see is the motor blowing out the wadding/recovery gear and spinning out till burnout. I'll be sure to keep an extinguisher on hand and consult the club president prior to testing the theory. My guess is a 1-2mm thick CA wrap on the engine base should be a viable thrust ring. And probably what a 1-1.5mm width? I'm thinking that'd be 3 wraps and then allow to set solid over night.

Any better suggestions?

With a thin ring of tape, like pinstriping tape, around the base (aft) of a BP motor, you can create a thrust ring like that on an RMS casing. It works quite well. Just make it thick enough so that the motor doesn't slip into the tube, but small enough so that you can still screw on the retainer.

I'm sure someone can post pictures.

All the older PSII (not E2X) rockets are designed for composites and BP motors in them is generally not the best idea. I'd definitely go with the stock retainer and leave the motor block out.

Ok never realized that. Are the e2x composite compatible if the block is left out? My wife is doing e2x and I am going to build the others. I have 4 of 6 waiting to be built.

There are 2 kinds of PSII kits. There are the builder kits that were originally designed for composite F and G motors, but some people want to fly them on E and F black powder motors. And there are the E2X kits that were originally designed for the E and F BP motors, but some people want to fly then with composite motors.

In either case, you can make the motor mount so that it will accept both kinds of motors. There are two ways to do it.

First, you can leave the motor block out of the motor mount tube. That way the mount will accept any composite motor or reloadable casing. If you want to use a BP motor, you must make a thrust ring on the BP motor using tape or glue.

The second way is to install the motor block, but install it far enough in so that it does not interfere with the largest composite you want to use. For example, shove the motor block into place using a single-use G80 motor (or use an RMS casing). That way you know the composite will fit. If you want to use the BP motors, you can make the thrust ring as described before, OR you can use a spacer. Cut a piece of used single-use 29mm motor casing from either a spent BP motor or used composite. Load that into the MMT in front of the BP motor, and you won't need a thrust ring (like using a D motor and a spacer in an E mount).

install it far enough in so that it does not interfere with the largest composite you want to use.

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Exactly, and no reason the spacer has to be a really short either. You could put a block for 6XL cases 14" up the MMT and use a 9.5" spacer. I often put a block at around 9" allowing up to a 4G motor, or using an old 24 mm adapter as a spacer and another 24 mm adapter as an actual adapter, or the old adapter and a smaller spacer for 29 mm BP. OTOH, If I were building a PSII E2X kit, over G might be ridiculous so might just put in a G sized thrust block.

That's a very interesting idea. And I like it. So if I order a 29/40-120 I could block it at that length then still use the BP motors. Not an idea I had considered. But it's really just an expansion on the D to E spacer. Thanks for the help guys. Btw, how long is the 29/40-120? Is it the same length as the G80? Or should I wait to block it until I have the actual RMS case?

Btw, how long is the 29/40-120? Is it the same length as the G80? Or should I wait to block it until I have the actual RMS case?

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the reload case is just slightly longer than the single use motors. I'd wait.

This is what I did with my Mean Max, I placed the ring far enough in to clear a G80 single-use, then made a ring to adapt space back to a 29mm BP engine. I wanted to do that so that I could use an E16 for the first flight, since I thought something like an F27 might be overkill the first time up. I just haven't brought myself to risk trying a big BP motor in the thing. I'm worried that the BP motors might have gotten tossed about in shipping and possibly have cracked...

Looking at the E2X instructions, they come with a spacer set up so you can fly up to G80s and the Hobbyline 29/40-120. You then add an included spacer to fly the BP motors. Basically, it comes with the setup Thirsty described. I'm probably getting an ascender soon so I can check the block fit on it, but here are the instructions: https://www.estesrockets.com/media/instructions/009706_ASCENDER.pdf

bill_s said:

Exactly, and no reason the spacer has to be a really short either. You could put a block for 6XL cases 14" up the MMT and use a 9.5" spacer. I often put a block at around 9" allowing up to a 4G motor, or using an old 24 mm adapter as a spacer and another 24 mm adapter as an actual adapter, or the old adapter and a smaller spacer for 29 mm BP. OTOH, If I were building a PSII E2X kit, over G might be ridiculous so might just put in a G sized thrust block.

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That's true. And another good thing about putting the block far up in the motor mount tube and using removable spacers is that the spacer protects the MMT from the ejection gasses and the after burn that can slowly roast the tube over time.

Spent BP motors make good spacers. You can fly your first one with a tape thrust ring, then cut the nozzle end off the spent motor so that you have a spacer of the right length for your next flight.

Well the 29/40-120 only goes up to G motors right? I'm just looking to be able to expand my flight capabilities off the one case. That way I can adjust the engine grains based on each rocket's c/p value for balance and still save money over time using RMS.

I've flown a bunch of the 29mm BP motors, and in most cases, use a 1/4" masking tape thrust ring, with no motor block. Works great with or without the Estes retainers.

Just make sure that whatever BP motor you use has enough thrust for the loaded weight of the rocket.

Bat-mite said:

Just make sure that whatever BP motor you use has enough thrust for the loaded weight of the rocket.

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Almost everyone builds heavier than the manufacturers estimated weight. All of the Estes PSII builder kits are at or above the Estes 29mm BP motor maximum lift-off weights. Don't be surprised if an RSO weighs and fails to pass your rocket at a club launch.

Jerome

My Argent flew great on a 29 mm BP engine at NARAM. Even placed in the set altitude competition.

Well I may have to use the F BP motor to get them off the ground, but it's worth a try. I may have a private piece of land I can safely perform test launches on. It will fully comply with FAA regulations and will be done under full safety code.