Thread Rating:
  • 1 Vote(s) - 5 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Three inch CTI M2245 minimum diameter build
#21
Got some sanding to do, but the fins are pretty rock solid.


Attached Files Thumbnail(s)
   
Reply
#22
Moving on up from the fin can, here are the rest of the parts.  

The long piece of BT is 48 inches.  My fin can is 16 inches, so I was looking for a 51 inch total length between the two, so I cut down the 48 inch tube.  Actually, I enlisted my Dad to cut the BT to size.  He has a diamond tip saw blade.

Nose cone has already flown on another rocket... is why it is painted.


Attached Files Thumbnail(s)
           
Reply
#23
The CTI boat tail for the 75 mm case is not very good in my opinion. Doing some research through various aero reports online,  the optimal boat tail angle seems to be somewhere in the 10-15 degree range before the performance benefit starts to diminish.   The CTI boat tail  has about a 23 deg. taper (dictated by the relatively short exposed portion of the 75 mm XL nozzle).  The CTI BT also is not concentric when screwing it down; when it is tightened, it walks about due to the course threads, and one side or the other sticks out into the airflow.  The thrust ring on the bottom of my motor case could also be off center (I believe it is just epoxied on).  Open rocket and RasAero don't seem to accurately simulate boattails at speeds much above mach 1.

So I went about to try my skillz or lackthereof at making a tailcone on a Harbor Freight mini lathe. I made mine with a larger base diameter and therefore less taper than the CTI 75 mm boattail.   Results were better than I expected for a novice.  It turned out ok, but the parting on the HF mini lathe is nearly impossible for something this size.  I plan to part the piece just before the taper. I tried to part a one inch dia. piece of bar stock and it worked but only at a snails pace.  3 inch is probably past the limit of the mini lathe, so I didn't even try to part it.   I will probably have a machinist clean this up and cut it, and maybe reduce some mass on the inside diameter.  I plan to affix the cone with JB Weld  to the standard CTI retaining ring and screw it down.  We'll see how that goes.


Attached Files Thumbnail(s)
           
Reply
#24
I made essentially the same part for a friend, but with the intention of it being used as a transition for their fin can.  The rocket will be a flying case, so the thickness of the tube that the fins are adhered to would otherwise be exposed to the airflow.

https://www.facebook.com/PatellManufacturing

[Image: 11742798_1473204916311288_57103898165772...e=561210B3]
Reply
#25
patelldp Wrote:I made essentially the same part for a friend, but with the intention of it being used as a transition for their fin can.  The rocket will be a flying case, so the thickness of the tube that the fins are adhered to would otherwise be exposed to the airflow.

https://www.facebook.com/PatellManufacturing

Nice.  What type of lathe do you have?  How do you get the polished look on your motor tubes?
Reply
#26
I have a South Bend 13" swing, 6' bed, quick change gears, 1 HP motor.

I polish the motors with varying grades of steel wool.
Dan Patell
TRA 10904 L3
Patell Manufacturing Facebook Page
Reply
#27
More lathe work.

I was going to try and make a new tip for the nose cone with an integrated shoulder. The purpose of the shoulder is to keep the tip from shifting due to aerodynamic forces at high speed.

After giving it some thought  I decided all I really needed to make was a shoulder that could be threaded to butt up against the stock Rocketrywarehouse nose cone tip.  I probably will tighten them together and use Loctite on the threads.   I may even permanently fix the tip to the nosecone and pot the whole tip internally to the nose cone with epoxy.


Attached Files Thumbnail(s)
                   
Reply
#28
Looks great! I'm amazed that those tips don't have even a short shoulder to engage the cone. My guess is that it's difficult for them to do it in their CNC process, but I'm not sure.
Dan Patell
TRA 10904 L3
Patell Manufacturing Facebook Page
Reply
#29
(07-23-2015, 09:53 AM)patelldp Wrote: Looks great!  I'm amazed that those tips don't have even a short shoulder to engage the cone.  My guess is that it's difficult for them to do it in their CNC process, but I'm not sure.



Thanks.

I believe Wildman sold some 54 mm pro fusion cones of theirs at one time with a shouldered tip.  It should be a standard feature even if it adds some cost.
Reply
#30
(07-14-2015, 09:21 AM)MarkH Wrote:
(07-13-2015, 10:22 PM)Pitter Wrote: Great work so far.  I am unclear as to what caused the ridges in the fiber glass, did you use peel-ply?  Also I see you are using a refrigeration pump to pull your vacuum, how are you regulating the vacuum and do you have an accumulator in-line?  I ended up building a vacuum press as per the following link, looking forward to seeing more as it progresses.  I really like the look of a 4 fin rocket!

Joe woodworker project EVS

The lines are from the glue on the back of  the uni-directional carbon fiber.  The carbon fiber is not woven so there are glue lines that run perpendicular to the fibers to keep it together. You can see these white lines in the picture of the cut out carbon fiber pieces.  The surface of the finished layup is actually a lot smoother than it looks in the photos. 

The vacuum pump runs continuously so there is no need to regulate vacuum.  It pulls nearly a full vacuum, 29 to 30 inches Hg,  as long as there are no noticeable leaks.  I let it run for about 4 - 5 hours until the epoxy I had left in the mixing cup started to get hard.

The peel ply is the beige material in the last picture above, after I removed the fin can from the bag.

The pump running continuously is exactly why I went down the project EVS road.  If I can get a good enough seal on the bag the pump cycles off an on only when the vacuum drops below whatever I set it to.  I believe there is about a 4-6 Hg range.  I have mine set for 24 Hg before it shuts off the pump, the reservoir provides some relief then when it drops below 20-18 the pump kicks back in.

It works well, I am not overheating my pump, likely extending the life, and it allows me to keep it under vacuum for about 12 hours, at which time I remove it from the bag, remove the peel ply and trim while the layup is not fully cured and slightly rubbery.

BTW great work on that mini lathe, I would love to pick one up at some point.  I agree on the shoulder on the nosecone tips.  They should have at least a small shoulder and maybe a convex base to keep them centered if you are worried about the additional mass.  They can be a pain to keep centered.
Reply


Forum Jump:


Users browsing this thread: 2 Guest(s)