N-Decision: 15 inch x15 foot

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SMR,
Important to note is there is no “e-bay” in the traditional sense. Instead there is a box epoxied into the upper airframe having a single breather hole. My greatest fear is coupler bulkheads ripping free and stripping the “e-box” from its mount. Safety first.

I am concerned about a single breather hole, as I think that opens you up to the possibility of getting self-sustaining pressure oscillations (just like when you open one window in your car and your eardrums want to explode). That could really confuse a barometric altimeter, I would think.

Bill _/)_
 
Jim,

That’s not a feckless idea. That’s bananas!

You’ve understood the situation exactly and I’ll take your recommendation with gratitude. Only potential setback is I had hoped to run all-thread down the center of the payload section. That would clamp the coupler bulkhead to the couplers edge. Wanted to do that because, as you recognized, I’ll need access to the “e-box.” Maybe divide the all thread into two pieces either side of the donut?

All good stuff and much appreciated.

Feckless
 
Bill,

So I’ve asked the question before and several have assured me the single side-hole works. I did equip Anima Mundi with a single side-hole but, as you know, CATO prevented my having any direct experience with the thing.

Anyone with recent experience?
 
Anyone with recent experience?
I've used single vent holes on many rockets without issues, though nothing anywhere near this large.

Modern altimeters have enough filtering that I don't think they are bothered by small oscillations very much, though I have never see anything like them in recorded data.
 
I've used single vent holes on many rockets without issues, though nothing anywhere near this large.

Modern altimeters have enough filtering that I don't think they are bothered by small oscillations very much, though I have never see anything like them in recorded data.

+1.
 
Jim,

That’s not a feckless idea. That’s bananas!

You’ve understood the situation exactly and I’ll take your recommendation with gratitude. Only potential setback is I had hoped to run all-thread down the center of the payload section. That would clamp the coupler bulkhead to the couplers edge. Wanted to do that because, as you recognized, I’ll need access to the “e-box.” Maybe divide the all thread into two pieces either side of the donut?

All good stuff and much appreciated.

Feckless

If you incorporate this idea, it also solves the av-bay problem. The entire volume of the doughnut is sealed. Use your threaded rod going between the BP/CR's to hold one plate on. Permanently fix one end of rods and plates to coupler & make the other removable.....

Ta...da now you have the perfect place for altimeters, inside the doughnut on sleds ....on threaded rods [4 maybe] add 1-1/4 threaded for the sleds only [simplicity & moving to other rockets]. Now you can have the needed vents spread around the outside of coupler as in a normal situation.

Drogue goes in back around motor...I think you have plenty room. Main out the front of coupler. If there is too much volume in payload or you want to cut it down to minimum for a safer lower BP charge.....install a bulk plate as far forward in payload as possible, leaving you just enough room for chute, cords etc. Small hole in that BP is all that's needed for Matches & charges.

This also keeps your CG as far forward as possible & keeps recovery gear from shifting around inside the "cavern".

Yes I have done this [all the above] on various projects, so it is tested, valid and NOT feckless.........:smile:

PS used 3/8 bolts and well nuts to install coupler/av-bay into payload. The well nuts give you a bit more "wiggle" room when doing field assembly than just bolts and threaded inserts. Much easier to assemble on field [experience taught us this one] & the rubber well nut keeps the paint job intact. Wet the well nut goes in better than dry.

If you wish to discuss details, PM me & I'll give you my ph# .


Added pics of a smaller version of this design I came up with. I used aluminum stepped BP's . Notice the Y-harness for recovery gear.

DSCN3001.jpg

DSCN3003.jpg
 
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Jim,

Those pictures are much appreciated especially as they illustrate the displacement of avionics bay airspace by the “donut hole.” At 15-inch diameter the sizing of “traditional” static port arrangements is a concern. I want a reasonable time constant but also don’t want to perforate the airframe. Your illustration presents a solution to both the long motor and the avionics bay problem. Good stuff!

Let me feck with the numbers and see if there is a convergent solution?
 
TRF,

So I have the booster marked for fin slots. I’m ready to cut but have realized a shortcoming of my overhead router set up. There is no absolute or square datum. That is to say I will cut along the lines marked on the tube.

The lines I have marked are parallel. They are also equidistant about the circumference. I have measured in multiple places. But that gives me no assurance against “rotation.”
Rotation is illustrated in the attached drawing of a flattened airframe. The lines L are equidistant about the circumference and slot lines are parallel as measured by S. But the entire layout is wrapped around the airframe as would produce spin.

Anyone encounter this layout issue before?

Feckless Again

Rotation of slots.jpg
 
You can also lay a piece of 90 degree angle iron upside down on the tube. It will self-orient square and you can check your lines.

+1

I think this is probably the most reliable way to do it.

I saw one of the fins for this project Thursday night. Nothing feckless about this: it is a work of art. Very nicely done.


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Todd,

Very nice to hear from you and thanks for your reply. I did use aluminum angle to strike lines. I just wanted to double check everything before committing. Slots can be tweaked with a mill bastard. But if they’re way off it’s going to end up a hard drunk followed by lost enthusiasm.

I think the cuts are clean and straight. I’ve dry fitted the fins and the tip-to-tip distances measure to 1/16-inch. Photo is attached.

Bill,

Thanks for your advice towards that fin stock. It is indeed stiffer than a board. But, as shown in the attached photo, cutting that laminate totally smoked my $130 router bit. Awesome!

One concern for the H80 core remains. As shown in the attached photo it is exposed and in close proximity to the motor. Deflection temperature is less than 200’C, the maximum allowable case temperature under NFPA rules. I’m compelled to cover that edge with something.

Feckless

Booster dry fit.jpg

Exposed foam core.jpg

Smoked router bit.jpg
 
One concern for the H80 core remains. As shown in the attached photo it is exposed and in close proximity to the motor. Deflection temperature is less than 200’C, the maximum allowable case temperature under NFPA rules. I’m compelled to cover that edge with something.

Feckless

Something as simple as thin EPDM rubber sheeting could be laid on that edge, adhered with an appropriate glue. If this will cause too much friction when inserting motors, maybe use your table saw to cut some thin furring strips.
 
Something as simple as thin EPDM rubber sheeting could be laid on that edge, adhered with an appropriate glue. If this will cause too much friction when inserting motors, maybe use your table saw to cut some thin furring strips.

As long as surface temps don't exceed 150 degrees C the EPDM rubber would do just fine with a liberal coating of talc. Temps any higher would cause the rubber to break down and need replacement.

I would suggest using a thin aluminum strap like material.


Sent from my iPhone using Rocketry Forum
 
TRF,

For those interested recent progress on this project includes the edging of rectangular fin sections (picture 1). Edging was prepared using a “thumbnail” bit to route profile in ¾ -inch poplar board. Edged board was then ripped to height on a table saw. This bit is available from Yonico in three stock thicknesses (picture 2). Cost is $20.

Profiled edging is cut to mitered length using a table saw. Miter angle measurement is taken directly from the fin cutting template. Half angles, bisected by compass, are transferred directly to the saw’s miter gauge (picture 3). Start by cutting the leading edge to airframe angle. Then each stick is directly marked and cut, one at a time, for both length and angle (picture 4). Note this process is “measureless” in that no ruler or protractor is ever used.

Clamping edge stock is achieved using standard clamps coupled with block and wedge. Note the orientation of the wedge (picture 5). The method is quite secure and does not mark the wood.

I’m using US Composites 625 resin with fast hardener for this process as garage temperatures are average 65’F.

A friendly note for those recent to table saws. Leading edge here is ¾-inch height. I elected to rip those by setting the fence ¾-inch from the blade. But you should be aware that presents a projectile hazard. End of rip the narrow piece will bind and shoot towards the operator. Those ¾-inch strips could surely impale an operator or bystander. If you also elect to rip close to the fence then please do stop your rip about 5-inches from finished. Flip the board over and finish the rip. The chances of dangerous projection are greatly reduced.

Feckless

Edging fins.jpg

Thumbnail profile.jpg

Half angle direct.jpg

Mitre on table.jpg

Clamping block.jpg
 
Complete and flown at Red Glare 17 this Sunday, 12 April. Dry weight an astonishing 91 pounds. Pad weight 151 pounds. Propulsion by a white O-4000. Perfect recovery.

N-Decision Red Glare 17 Sunday.jpg
 
How did you end up doing the av-bay/seperation joint....as discussed? Any pics.

Congratulations on the successful flight.
 
Complete and flown at Red Glare 17 this Sunday, 12 April. Dry weight an astonishing 91 pounds. Pad weight 151 pounds. Propulsion by a white O-4000. Perfect recovery.

View attachment 260847

WoooooooHooooooooo! Beautiful launch shot, and it sounds like a flawless flight. Awesome. Did you get video and can you add some flight details? i.e. How high did it go, did you stick the landing, etc. I know you are probably busy with post-flight unpacking and cleanup, so no hurry. Great build and again, congratulations!

Sather
 
Great Job! And Congrats on a Great flight! Wish I had been able to get down there to see it. I was instead subjected to watching the Orioles pitching get their A$$es handed to them!
 
I missed the flight by 10 minutes, which means you have to do it again :)
 
I have always enjoyed Feckless Council's build threads. This flight was FANTASTIC to witness.

Truly impressive. Great job!


Later!

--Coop
 
WoooooooHooooooooo! Beautiful launch shot, and it sounds like a flawless flight. Awesome. Did you get video and can you add some flight details? i.e. How high did it go, did you stick the landing, etc. I know you are probably busy with post-flight unpacking and cleanup, so no hurry. Great build and again, congratulations!

Sather

Here's the video from MDRA's YouTube page:

[video=youtube;WqtGd6IcMPw]https://www.youtube.com/watch?v=WqtGd6IcMPw&list=PL2LMq2TTPTZoKqDt-NnNpx9JFVsRuO-S4&index=1[/video]


All the flights can be seen here:
https://www.youtube.com/playlist?list=PL2LMq2TTPTZoKqDt-NnNpx9JFVsRuO-S4
 
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