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Formula 200 L3 Build Thread
#11

(12-08-2015, 10:25 PM)Tom C Wrote:
(12-08-2015, 10:22 AM)Bat-mite Wrote: I never drill my vent holes or static ports until after I paint.  Do others drill before paint?  Is there an advantage?

This is a fiberglass rocket.
SONOTUBE pushes out when drilled so it needs to be pilot drilled then full size drilled..sanded both sides of the hole..CA into the hole..drilled again and then sanded and repeated till the hole is clean. Drill again after painting and after the rocket is flown you may need to drill out dirt and mud if any from the holes.
Tom Cohen

MDRA...Maryland
MARS...Geneseo N.Y.
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#12
More drilling today.  Not that interesting but here goes.

Vent Holes and Witness Marks. Each body cavity gets two vent holes just in case one gets blocked.

       

Nose cone coupler retaining bolts and shear pins.  The nose cone gets 6 shear pins to give it a little more holding power against the drogue shock cord opening:

   

Just for fun this is the nose cone compared to our Estes Mega Der Red Max:

   

Rail button holes will wait until I'm sure where the centering rings will go.

I always drill first too.  The thought of the drill skating across a fresh paint job, not nice.  I usually run a metal machine screw through the shear pin holes after painting just to make sure the threads are clean.
NAR 98479 L3
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#13
Prepping the centering rings and thrust plate today.  I needed to drill the CRs for the 1/4-20 threaded rod and the two 5/16" u-bolts.  Normally, I would make them from G10 stock but since they came in the kit, I'm just drilling them according to the hole pattern on the thrust plate.

Machining the drill guide from 1/8" ply:

       

Fits nice with the thrust plate:

   

Drilling the pilot holes in the three CRs.  I used a coupler scrap wrapped in some masking tape to wedge the guide and the CR together:

   

The 1/4" and 5/16" holes just track the 1/8" pilot bit hole:

   

Drilling out the thrust plate to accept the 1/4-20 rod:

   

All done and ready for the motor mount:

   
NAR 98479 L3
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#14
Very nice so far!

A couple of questions, though:

1) I think the thrust plate is cool--but I'm curious: what made you go with this over a more standard option, such as a retainer bolted on to the rear CR? Were/are you concerned of splitting the CR under thrust, or dislodging the MMT? Or does this permit you to do something else?

2) You mentioned two vent holes per compartment, in case one becomes blocked. That certainly makes sense, but am curious, again: have you experienced a blocked vent hole before that has led to problems? Is this because of the FWFG airframe?

I admit: I haven't used the material much. Whenever I've considered using it... I just wind up laying up some FG over a LOC tube. As such, I suspect my birds may be a bit more... leaky. I've used vent holes on some of my builds, but never considered using two.

I'm not criticizing--merely curious.


Later!

--Coop
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#15
(12-10-2015, 10:47 AM)Coop Wrote: Very nice so far!

A couple of questions, though:

1) I think the thrust plate is cool--but I'm curious: what made you go with this over a more standard option, such as a retainer bolted on to the rear CR?  Were/are you concerned of splitting the CR under thrust, or dislodging the MMT?  Or does this permit you to do something else?

2)  You mentioned two vent holes per compartment, in case one becomes blocked.  That certainly makes sense, but am curious, again: have you experienced a blocked vent hole before that has led to problems?  Is this because of the FWFG airframe?

I admit: I haven't used the material much.  Whenever I've considered using it... I just wind up laying up some FG over a LOC tube.  As such, I suspect my birds may be a bit more... leaky.  I've used vent holes on some of my builds, but never considered using two.

I'm not criticizing--merely curious.


Later!

--Coop
Appreciate the comments and questions.

(1)  I know the thrust plate isn't necessary, but I thought it was a cool idea.  Besides putting the motor loads straight on the FWFG tube, I see are couple other plusses.  First, the fin glue joints are now only carrying their own load under acceleration and from a knock on landing, and I feel comfortable leaving the rear centering ring removable to inspect the fillets for damage.  Second, I can run threaded rod right to the front CR so I've got a continuous path of metal (plate, rod, u-bolts) and Kevlar in the recovery system.  Not relying on any adhesive to keep things together in the recovery chain.  I've never been comfortable epoxying the shock cord to the motor tube, for example, even though I've done it several times and I know it's common practice for rockets up to 6" diameter.  The plate and rods add a couple pounds, but they don't hurt the stability or power margin of this particular rocket and I'm not interested in optimizing for altitude.

(2) I'm sure two holes are unnecessary.  I've always drilled one 1/8" hole in each cavity and never had a premature separation due to pressure differential.  Also I don't tightly friction fit any joints so there's probably more margin there.  When planning, I did run someone else's calculations from TRF for the size of the vent hole.  1/8" seemed marginal but still safe so I just went ahead and made two 5/32" holes.  Compared to the airframe they are tiny.

I think we met at MDRA last month.  Your L3 rocket was beautiful and I hope to duplicate your success.
NAR 98479 L3
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#16
Thinking it's cool and wanting to use it is more than sufficient reason--after all, how many L3 cert attempt projects does one get to make?  Do it as you like--that's the important thing.

I like the idea of being able to inspect internal fillets afterward.  That is a nice benefit--one I'd not considered.

I think I know the thread you mentioned while calculating the vent holes--Bob's posts were always good for some hard math.  If 1/8" seemed marginal, then going with two might be a good course of action--particularly if planning on future, faster ascents.

Thanks for the kind words on Hellraiser--I'm sure this is going to be a successful flight.  I'm very much digging the build so far.


Later!

--Coop
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#17
Motor Mount Construction and Installation.  After sanding everything, dry fitting centering rigs, and then tack them in place with just a little 30 minute epoxy.  The threaded rods help keep the CRs square, but unthreading all the nuts is kind of a pain:

           

The CRs are filleted to the Motor Mount with West, High Density Filler and Chopped CF:

   

Epoxying the back of the 5/16" U-Bolts:

   

MM Installation into Body:

Using Rocketpoxy to glue the MM into the body tube:
 
   
 
I smear a ring of epoxy around the location of the middle CR with a long stick, push the MM in from the top a little extra deep, smear another epoxy band in the front, and slide the MM forward to its final location.  So both forward CRs are glued in:
 
             

Finally, friction fit the rear CR until everything sets:
 
     
NAR 98479 L3
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#18
      Dremel 511E EZ Lock Coarse Grit and Medium Grit Finishing Abrasive Buffing wheel.

------------------------------------------------------------------------------------------------------------------------------------------------------------------
DREAGO
The threaded rods help keep the CRs square, but unthreading all the nuts is kind of a pain:
-------------------------------------------------------------------------------------------------------------------------------------------------------------------

Use this Dremel attachment..or another similar... to spin nuts on long lengths of allthread.
WEAR SAFETY GLASSES as the buffing wheels spit out material.
Try the dremel on medium-high speed...touching the buffing wheel to the side of the nut. If the allthread is clean and epoxy free the nuts spin + move very easily...and fast.

I use washers and lockwashers on both sides of the CR's and bulkheads when I want to tie all together.
On some applications I have wanted to connect only the aft thrust plate to the forward bulkhead and used no nuts on the CR's.

--------------------------------------------------------------------------------------------------------------------------------------------------------------------
DREAGO
 I can run threaded rod right to the front CR so I've got a continuous path of metal (plate, rod, u-bolts) and Kevlar in the recovery system.  Not relying on any adhesive to keep things together in the recovery chain.
---------------------------------------------------------------------------------------------------------------------------------------------------------------------
Yes...your continuous path of metal will help assure that when your chutes open the rocket stays together. Well done.
Tom Cohen

MDRA...Maryland
MARS...Geneseo N.Y.
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#19
(12-12-2015, 10:02 PM)Tom C Wrote:   Dremel 511E EZ Lock Coarse Grit and Medium Grit Finishing Abrasive Buffing wheel.

------------------------------------------------------------------------------------------------------------------------------------------------------------------
DREAGO
The threaded rods help keep the CRs square, but unthreading all the nuts is kind of a pain:
-------------------------------------------------------------------------------------------------------------------------------------------------------------------

Use this Dremel attachment..or another similar... to spin nuts on long lengths of allthread.
WEAR SAFETY GLASSES as the buffing wheels spit out material.
Try the dremel on medium-high speed...touching the buffing wheel to the side of the nut. If the allthread is clean and epoxy free the nuts spin + move very easily...and fast.

I use washers and lockwashers on both sides of the CR's and bulkheads when I want to tie all together.
On some applications I have wanted to connect only the aft thrust plate to the forward bulkhead and used no nuts on the CR's.

--------------------------------------------------------------------------------------------------------------------------------------------------------------------
DREAGO
 I can run threaded rod right to the front CR so I've got a continuous path of metal (plate, rod, u-bolts) and Kevlar in the recovery system.  Not relying on any adhesive to keep things together in the recovery chain.
---------------------------------------------------------------------------------------------------------------------------------------------------------------------
Yes...your continuous path of metal will help assure that when your chutes open the rocket stays together. Well done.

Tom:
That's a cool idea to use the little buffing wheel.  On our 6" Der Red Max, I did as you suggest--the threaded rod is only bolted at the front CR (with a nylock nut) and at the thrust plate (with washer and lock washer).  The threaded rods essentially serve as long bolts to hold the front CR and thrust plate in place.  In the picture above I used all those nuts to keep the CRs square to the motor tube while I glued them in.  I always seem to have problems getting the CRs really square when I glue them, so this helps me out.  It took way longer to thread and unthread the nuts than to actually glue the CRs in place so your idea would really speed things up. 
Don
NAR 98479 L3
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#20
DREAGO, looks like you did the same thing I had to do. In running the threaded rod to the top CR having to drill one of the holes between the holes for the U-bolt. I messed with it for about ten minutes before deciding to do it that way!
Dave Greger L3
NAR# 95846
MDRA #65

Hollie L1
NAR# 99687
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