Help me decide what to do.

So, I want to launch my first O motor. Maybe it will also be my last; I can't see past the first flight.

I don't have a big enough rocket to do this, so I will need to build something.

I was thinking about a Performance Hobbies Performer 200. It comes standard with a 98mm MMT, but can be upgraded to a 150MM MMT.

The booster is 60" long, and the coupler is 18", with a 3" switch band. When you add on U-bolts for recovery, that leaves 51" free in the booster. Need at least a few inches for recovery material, so that means that I could put at most a 46" long motor in there, and that includes the smoke grain bulkhead.

The 98mm 16,000 Ns hardware that I have access to is too long. I may also have access to a 150mm 3G case.

So, what do I do? I could ask for a custom kit with a longer booster. I could get the kit as is and extend the booster with another piece of airframe and a coupler. Or, I could get the 150mm MMT option as is.

The problem with the 150mm hole is that I won't be able to adapt down to 98mm or 75mm motors; so this thing will mostly sit in my house and take up space except for the once in awhile where I feel an O motor and get the right weather.

Thoughts? Feel free to ramble....

Just two quick thoughts...

1. Many (most actually) commercially available 6"/152mm tubes will not fit 152mm/6" hardware. They are close, but in general require significant sanding, etc. Just wanted to give a heads up that the "150mm option" may not be as friendly as it seems.

2. One can absolutely adapt down to 98/75 from a 152 host mount. Don't even need a motor tube in order to do so. Adapter plates, rings, semi-traditional motor mount adapters...many ways to accomplish this without significant difficulty. Aeropack may not make *that* adapter, but adapting "down" from 152 is not a problem.

Ok, a third thought. There's not really that much difference in construction, prep, and flying of an M/N powered bird verses and O powered bird. If you can do one consistently without dramas, you'll do just fine with the O motive power!

Enjoy!

ECayemberg said:

1. Many (most actually) commercially available 6"/152mm tubes will not fit 152mm/6" hardware. They are close, but in general require significant sanding, etc. Just wanted to give a heads up that the "150mm option" may not be as friendly as it seems.

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Did not know that. Thanks!

ECayemberg said:

2. One can absolutely adapt down to 98/75 from a 152 host mount. Don't even need a motor tube in order to do so. Adapter plates, rings, semi-traditional motor mount adapters...many ways to accomplish this without significant difficulty. Aeropack may not make *that* adapter, but adapting "down" from 152 is not a problem.

Click to expand...

Another "good to know." Thanks again.

ECayemberg said:

Ok, a third thought. There's not really that much difference in construction, prep, and flying of an M/N powered bird verses and O powered bird. If you can do one consistently without dramas, you'll do just fine with the O motive power!

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That part I am not worried about.

https://www.rocketryforum.com/attachments/gopr0249-fixed-png.106136/

Picture of an adaptor, in this case from 114mm down to probably 88mm, two custom sizes I like. The flat plate at the bottom transfers thrust to the base of the rocket and is bolted on.

Gerald

In your spot, I would probably try to get the kit extended. That seems like the least work way to get to a rocket you can (a) fly on an O and (b) fly later on your M/N 98mm hardware.

I have to concur with the above that a longer 98 is the simplest thing. On the other hand, since adapting down from 150 is not so high a hurdle, it would give you more flexibility and for my two cents is worth it. Honestly, I'd design my own bird from a blank sheet of paper. By the time you ask Performance Hobbies to give you the 150 mm option and ask for a lengthened booster section, you might as well just ask them to cut you a whole custom shipset. So start sketching.

google "jumbo darkstar" 98 mm O motor fun....

So 98mm Os are no joke. You need at least a 9 grain for it to be an O with normal propellants. And that's assuming you pack well. If you go with, say, an 8 grain with something normal like NASSA Red you need the delivered Isp to be something about 240. And let's face it, none of our propellants can get to 240 seconds of Isp in an O motor case. You may look at Imax and cite that, but Imax is pure black magic, with high-density additives and optimization, nothing that packing can achieve. I heavily advise you go with the 6" motor. Getting an O is no problem with a 4/5 grain and is less riskier in some regards, as long motors get bonkers real quick.

My motor mentor Scott has made many long motors in O, P and Q impulse. His design for the Mercury Redstone Q motor was successful, as was his P motor for Tom Cohen's Yellow Submarine. He will be engineering my HW and making the load, if I go with the 72" X 4" option.

Right now I am looking at taking 26" off the payload tube and making that a detachable fin can. That would make the booster 86" and leave 34" for the payload in a Performer 200. Glue a coupler into the aft end of the 60" booster, and bolt on the 26" fin can. Makes for easier transport, and gives me the length I need for a 72" 98mm motor. Also will attach the switch band lower on the coupler, giving me 6" exposed at the booster end, and 9" exposed at the payload end.

Assuming a 5" smoke bulkhead, that gives me a 77" motor, plus 7.5" taken up by the coupler and U-bolts. I will have 1.5" of clearance between the motor and the U-bolts. I can shove the harness down alongside the motor and compress my drogue into the 1.5"

Rough and dirty in MS Paint:

I can't make a particular recommendation, but there are a couple of things that come to mind:

1) AFAIK, most FG tubing is not available in lengths exceeding 60". You can see at the performance hobbies site, that the Performer 125 already maxes out the booster length.
2) If you want to make a detachable fin can, also consider gluing the coupler to the can instead of the booster tube. The booster is already the longest part to transport. Take care of the forward center rings when planing how to assemble an disassemble the rocket. If they are glued to the motor tube, you obviously can't push them through a coupler glued to the booster tube.
3) There are multiple ways how you can get creative with the ebay and your recovery layout, to approach your length issue. Donut ebays or head end deployment (depending on the nose cone) are two options. Single end deployment with an ARRD is another option.

Reinhard

Plans are coming together. Will share once finalized.

Bat-mite said:

Plans are coming together. Will share once finalized.

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You can do series of plywood centering rings as a tubeless motor mount. You can tie them together with all threads, coupling nuts plus you can add ribs for more strength.
Jerry O'Sullivan did ribs in locations to lock the fins in place. He did one of his where the back part of the body tube slid off to unbolt and replace fins.
You can do radial slots on some rings to also better lock in the fins.
Doing that kind of work you can use a coupler to make a longer booster section.

Here is what Ken is going to kit up for me.

This sound like a really cool project!

What altitude are you targeting and are you planning on launching it at MDRA?

Right now it exists only in the ether. Doing some guess work based on things Scott has said about the motor we think we're going to make, anticipated weight of the finished rocket, etc., I expect it to be about 120 lbs. on the pad and go to 12,000' on a baby O. The motor will be a 98mm X 72" bolted case. No discussion whatsoever about what propellant, etc.

Yes, hope to fly it at next year's Red Glare. Lots need to happen between now and then!

Design the air frame so you can remove sections and make it light enough to fly on smaller motors. That way it won't need to simply sit around the house until you have an O motor.

Is this where my 72" 98mm case is going?

H_Rocket said:

Design the air frame so you can remove sections and make it light enough to fly on smaller motors. That way it won't need to simply sit around the house until you have an O motor.

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Definitely! Would be nice to do a shakedown flight on an M. Calculating I would need about 2200 N of thrust with an M.

As designed, fin can will be 36" long, booster 60" long, coupler with switch band 18" long, payload 32" long, and nose cone with coupler 51" long. All should fit nicely in the back of the mini-van. Assembled, exactly 14' long, a hair more with the motor retainer and thrust plate.

DeeRoc29 said:

Is this where my 72" 98mm case is going?

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You have one? Hmmmm....

No, Scott is drawing one up. We are going to split the cost of manufacturing and share the casing. I will not often fly an O.

Is yours bolted or snap ring?

I'm making one for Scott

DeeRoc29 said:

I'm making one for Scott

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Ah, then YES!

Just want to make sure we know who is responsible

I am providing the turned case. I believe Scott is doing the closures/bolts.

Moving to a new thread: https://www.rocketryforum.com/threads/my-quest-for-an-o-motor-launch.152184/