TAO Finless Sustainer Build Thread

[jlabrasca]

Too sick to do much in the shop today -- but a little progress nevertheless.


The taller hatch broke away from the bed about 20 minutes after I posted the picture last night. I cut the model into two pieces and -- becuase I knew I was going to have to do some drilling and sanding to assemble the hatch -- I switched to carbon-fiber infused PETG.

Then I did this


I installed the rigid rotator/fly-wheel/bearingless disappointment in the nose cone. I put in a plug cut from a scrap of packing foam, and poured in a few ccs of Gorilla Glue. I painted BSI 15 minute epoxy on the inside surface of the cone, installed the flywheel, and then sealed the gaps with thick CA+kicker (my next HPR is going to be assembled without adhesives)


This is easily my most stupidly over-engineered/over-thought rocket project to date. It is taking WAY longer than I'd budgeted. As I type this, I can see my dusty soldering station and the boxes of parts I've been collecting for a non-pyro dual deployment mechanism, and the multi-materials upgrade for the Prusa (still in the box), and the partially assembled low-vacuum chamber, and the parts for a catadioptric telescope, and the projection lens I was going to convert into an anamorphic camera lens adapter, and the parts for a heliospectrometer...and...and... >sigh<

 

[Alan15578]

Well, did you get if finished? Flight report?

Just a few obvious comments:
you actually want a linear twist to the fins, like a propeller. The original design gave a reasonable approximation to that using just two flat fin segments. Since you are printing the part, you could print the fins with the proper twist.

In the old days Estes used to cant the booster fins and leave them straight on the upper stage, e.g. on the Delta (Camroc Carrier). Since Estes has mostly gone to injected molded fin cans for boosters, they omit the fin cant. Rolling is still a good idea, especially if the thrust is not perfectly aligned.

I don't trust OR to sim and pass stability judgement on spin stabilized or rapidly spinning rockets, if only because I have not written OR myself. Does it even include the Magnus forces?

Objects spun up around the minor axis are never really stable. In the real world they will eventually transition to a "flat spin". However, if the the object is well designed and balanced, that transition time can be put off until after the mission is completed. For rockets, you need to align the minor axis to the aerodynamic centerline. This process is called spin balancing. We need a low cost effective DIY spin balancing rig, and I think you have the skills to design and develop it for us.

Spinning around the major axis is stable. I had dreams of spinning up a PMC Cylon Basestar. I even had an old automotive starter motor to spin it up with. Unfortunately, I could not figure out a way to safely recover it, and it would take too much time and effort to get the GLM down to 16 Oz. Of course today we can go up to 1500 grams GLM and still be a competition legal model rocket.

I have always considered the concept of stability testing by using a stable booster stage. A rocket going unstable 100+ feet overhead is observable and safer that one going unstable 20 feet away at launch! I have just never needed to fly a rocket of such indeterminate stability. I have launched rockets that went unstable because, s*^% happens. On the mundane practical side. I once launched a contest rocket that went unstable, and I traced it back to an error I made in the CP calculation. I launched an unstable rocket in PD once. On a windy day I took out the big chute and replaced with a very small chute, and I forgot to check the CG. These were simple mistakes that I learned from and never repeated.

 

[jlabrasca]

Well, did you get if finished? Flight report?

Not yet. It was officially put aside so that I could work on rockets for yesterday's low power launch, but mostly I am just sick and easily fatigued. I will try to get it finished for the high power launch next weekend -- but I need to get ready for the Fall term and this week's schedule is crowded with appointments that have nothing to do with either my job or building rockets.

Watch this space, I will post when I have it back on my bench.

 

[jlabrasca]

First dry fit. All of the outside parts are cut and ready. The hatch is actually a LOT easier to put into place with coupler in the fin can. I am bound to say that trying precisely cut segments out of paper cylinders is less fun than I'd imagined.

I had to fiddle with the edges of the cut-out from the coupler for a while, before I could get the hatch to fit. When I started on the airframe it occurred to me to stop my through cuts just short of the ends. The piece still sagged away from the knife, but it was easier to keep the tube against the straight edge as I cut.

 

[jlabrasca]

None of the redesigns on the hatch comprehended a redesign of the forward centering ring in the booster. I did some surgery, but couldn't quite manage a clean fit. Going back to the drawings, it should work if the OD of the centering ring is reduced by about 1 mm -- which precision my eyes and hands will not deliver. I am going to have to make a new one.

Only about 20 more shop hours between now and the launch this weekend -- I am going to have to strategize the crap out of this week.

 

[jlabrasca]

New booster CR





It works, but there isn't a whole lot of room in there



For the chute, I pulled some grocery store produce bags out of the recycling -- very thin polyethylene that will probably pack tightly enough to fit behind the hatch. The worry is that the heat of the motor will cook it, or that it just won't unfold itself when it hits the air (if you've ever tried to get the mouth of one of these bags open with dry fingers, you will understand the problem).

I also have some emergency blanket mylar, very thin stuff. By the time I adhere the shroud lines, though, it'll be as bulky as anything else.

Piston next.

 

[OverTheTop]

Interesting rocket. Keen to see how this one goes!

 

[jlabrasca]

Interesting rocket. Keen to see how this one goes!

Thanks. Me too. >smile<

I worked on the piston and the parachute for the booster this morning (nothing worth a picture, just a lot of spilled CA, some rings that will need to be re-cut, and bits of mylar stuck the bottom of a clothes iron) but I have more problems to solve than I have time to work on them.

It occurs to me that EVERY high power launch I have attended has been preceded by a last-minute scramble to finish some challenging (for me) project. I think this time I will just go down and launch rockets. If the weather and the rest of my life cooperate, I will take the TAO* to the October launch in Brothers, Oregon.

* edit: trying to decide if the redesigns and modifications are sufficient to warrant renaming this project. For various reasons Roll for Initiative appeals to me. Maybe the Tao RFI?

 

[neil_w]

For various reasons Roll for Initiative appeals to me.

If you're trying to win some sort of geek award for rocket names, I think you've got it there.

(and this after the potato rocket...)