3/4 Mercury Redstone

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TRF,

One issue discussed at our final design review is altimeter coordination.

This rocket is recovered in four chunks to reduce recovery stress and to limit parachute size. Independent altimeters will be required to operate in sequence and as if a single coordinated system. The question at review is can several RRC-3 altimeters achieve that coordination.

It was decided to test a sample system we named “The Gadget.” Pictured below The Gadget is built from 4-inch LOC paper tube. Each section is separated by an altimeter bay with switch band colored grey. Three altimeters recover The Gadget in 5 pieces sequentially from bottom to top. The first event is booster at apogee. Each subsequent section is deployed 1 second after the previous.

The 84 cubic-inch altimeter canisters are ported through a single ¼-inch hole. The lowest altimeter is programmed mode 3. The middle altimeter is programmed mode 2 and two seconds delay. The upper altimeter is programmed mode 2 and three seconds delay.

Results are favorable EXCEPT that one parachute failed to exit the uppermost white section. In Redstone we plan to use tethered deployment bags.

Feckless Councel

[video=youtube;x2jjxWq0Jqw]https://www.youtube.com/watch?v=x2jjxWq0Jqw&index=4&list=PL2LMq2TTPTZoZqDzecaoEbxW9Sv0fU3Rb[/video]
 
TRF,

The longerons in this design are 1-inch pultruded fiberglass tube. Those stiffen the overall structure and provide for attachment among sections. A dowel is pinned through the tube where sections adjoin. We are aware that pultruded shapes can split, crack and fray across the grain. This is a particular concern for us as the pin’s force will be along the grain.

To understand the limits of our material we pull tested a representative sample. As pictured below the tubing began to tear at 4100 Newtons or about 920 pounds. Note the tubing is 1-inch OD and 1/8-inch wall. Pin is ¼-inch alloy steel.

Feckless Counsel

Pulltrusion test.jpg
 
If you plan on doing a lot of this type of testing, having the data archived and organized somewhere we can all reference after the fact would be very helpful.
 
If you plan on doing a lot of this type of testing, having the data archived and organized somewhere we can all reference after the fact would be very helpful.
Particularly if it would be possible to mention the specific manufacturer details and/or where obtained. That kind of data is pretty rare.
 
Gents,

Thanks for following this project and for all your recommendations. We plan to publish a final report including complete 3D data, 2D drawings, bill of materials, supplier list and test data.

Feckless
 
TRF,

Below is an update on this project for those still interested.

Our team suffered delays at construction given substandard materials especially plywood.

We received a 52 sheet pallet of 5x5 Baltic birch delivered from supplier CP. Entire lot was junk. Every sheet presented excessive surface patching and central voids. After 10 days of negotiation we returned that and repurchased absolutely outstanding material from supplier IP. Total time lost in the exchange is one month.

We could not find a stock supplier of 3mm thick multi-ply at 48x96 sheet size. That was true of import and domestic birch. Finally we opted for 3mm Okume plywood in 49x98 sheet size. That material is both strong and beautiful. It also carries a Lloyds approved mark for yacht construction. Pictures are attached.

Having collected proper materials first task was to cut 19 rings for the airframe. Those are cut from 6mm birch plywood. Diameter is 52.50. Total processing time for 19 rings is approximately 10 hours.

Next task was to cut 36 stringers from 3mm Okume. The 3mm material was challenging because it is thin. Plywood had a tendency to lift from the table and cut through the separation tabs. Those tabs are essential for straight cuts across the sheet’s length. Otherwise the piece is loose a floating about the cut. Total processing time for 36 stringers is approximately 6 hours.

Feckless Counsel

Redstone rings against person (faceless).jpg

Redstone rings against ruler N486648.jpg

Okume plywood 3mm.jpg

Lloyds stamp Okume plywood.jpg

Okume stringers.jpg

Redstone rings against soda can.jpg
 
TRF,

Next step is fabrication of a sample thrustplate. We will test that piece by compressing it with a backhoe. Our goal is to support 6,000 pounds force center load.

Pictured below is construction of the sample. Two pieces 12mm plywood sandwich 8 pieces 2-1/2 x 3-1/4 inch pine board thickness planned from 2x4 stud. Short stringers are manufactured from 3mm Okume plywood. Longerons are 1-inch OD fiberglass tube. The wooden assembly is glued using Titebond aliphatic resin and screwed with 1-1/2 inch fasteners. Fiberglass longerons are epoxied using US Composites 635, milled fiberglass thickener and medium hardener.

Hopefully crush test data and video are available the next two weeks.

Feckless Counsel

Thrustplate construction.jpg

Thrustplate sample view A (faceless).jpg

Thrustplate standing.jpg
 
That's great, I did something similar with my smaller foam built up structures, doing crush and load tests. The stringers are pretty thin, do you actually intend to tie into the stringers with adhesive to the skin, I found that adds a lot of stiffness and strength. Or are you relying pimarily on the fiberglass tubes? What is your centering ring spacing distance, just curious...

Frank
 
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Cool! Thanks for.sharing; looking forward to the test results!

From the Ether...
 
Next step is fabrication of a sample thrustplate. We will test that piece by compressing it with a backhoe. Our goal is to support 6,000 pounds force center load.

Out of curiosity, how does the connection between the motor itself and the thrust plate occur? Is the motor bolted to the thrust plate in some way, or is there a thrust ring on the motor?

Very interested in this project.. looking forward to seeing the progress.
 
Frank and DJS,

Thank you for your interest and for your replies. Please see the attached CAD.

The motor is retained by a 36-inch diameter aluminum ring 1/4-inch thick. That ring is bolted through the thrustplate by 4 each 1/4-20 grade 8 fasteners. Those fasteners are also through the 2x4 material.

An equivalent ring will be used during the backhoe test.

Stringers are indeed thin at 3mm or about 1/8-inch thick. We do plan bonding formers and stringers to fiberglass skin using methyl-methacrylate construction adhesive. Fiberglass longeron tubes back-up the entire structure’s compressive strength and provide a means to pin adjoining segments.

Centering rings land about every 24-inches depending.

Feckless

Motor retainer ring.PNG
 
TRF,

Today we cut load bearing pieces of the airframe and the final lot of airframe stringers. Airframe pieces are now complete. We are ready to assemble the largest portion of the rocket.

Pictured below is the forward end of the airframe: CAD and cut pieces. There is a 17-inch ID parachute tube at 36-inches length. That tube bottoms out on a 12mm thick full diameter diaphragm. Parachute attachment goes through that diaphragm and intersects two 6mm thick members spoked to reduce weight.

The spoked pieces presented a fair amount of warp after cutting. We hope that will pull straight when constrained by the assembly. We also found one piece of 6mm plywood out of tolerance thick. We marked the cut piece as thick and may have to open stringer slots to accommodate.

Feckless Counsel

Redstone Upper Airframe.PNG

Diaphragm former 12mm.jpg

Chute tube former 12mm.jpg

Spoked former 6mm.jpg

Warped former - 6mm spoked.jpg
 
TRF,

We are making best attempts at safe design. Nothing concerns us more than unstable flight. It is well known CP behind CG is a negative feedback system favoring straight flight.

Center of pressure can be complex. Barrowman’s method and RockSim all provide CP guidance. Since we are scale we have original program data too. Note CP is strictly a function of geometry.

Center of gravity is how we have geometrically distributed mass. We can calculate that using CAD. We believe, however, anything directly and easily measurable should be measured.

We might find CG by hanging the entire assembly. Consider the practical obstacles to hanging a 63 foot 1,000 pound object in a balance study. Instead we are considering the “direct” measurement process of combining segments as illustrated below. Specifically we are interested in the net torque center of mass.

In theory the method is flawless. Anyone have direct experience with the process and specifically any limits to applicability?

Feckless Counsel

CG graphic.png

CG Calculation.png
 
As long as you have precise locations for each segment, it should be straightforward. Just try and install fasteners in their position so they don't get inadvertantly left out.

Biggest danger for that is forgetting to account for some mass.

Although I'll still vote for suspending the whole rocket from a ceiling crane lol
 
Or just set it on it's side, one large pipe in the middle and furniture dollies at each end. Roll on the big 'un until you find it, no scrapes or crashes.
 
The calc you show is standard in a variety of industries, and works as well as your input values. But be careful, it's garbage in, garbage out. Don't neglect anything, and get accurate weights and locations. You should be good the go. Remember that you need the location to be the CG of the item, not the end, or even the geometric center. You'll want to balance the individual pieces to find their CGs.
 
This is a really cool project and reminds me a lot of the way we've build our bigger projects.

The one thing I'd like to comment on is motor retention. On our big projects, we chose to use forward retention for the motor and rear retention for the recovery system.

The reason for this is that we weren't comfortable with the motor retention being attached to a thrust plate where the thrust plate is held in by fasteners in tension which could rip out of end grain. Instead, we had a thrust ring at the rear of the motor but forward retention of the motor through a plate at the top. Because that plate was notched into our stringers, it was held in place by compression.

Our recovery system was attached to cables that ran down to the bottom plate of each section. That way, once again, the entire stack is in compression for the recovery load.

-Kevin
 
Glad this is progressing.

The V2 came down in three pieces - each piece had it's own man rated chute... no worries... everything out at the top, no drogues etc KISS...

We did build it light, but it was still around 600kg+ I would have liked another chute on the fin can, it did ding up a little bit on landing (currently being repaired ;-) but yeah, it was only a tiny little ding...

I can't recall how we retained the motor LOL - IIRC it was aft retention...(but I did have a CJ induced rum headache at the time) I know it did vaporize at least one slice of tomato at lift off...

There was a light breeze on landing, which dragged the middle section a tad - makes sense to break the thing into maybe 3 or 4 pieces for recovery, less landing stresses/forces obviously... Tether the whole lot if you are worried?

Love a big build thanks a bunch for sharing it in so much detail!
 
TRF,

We have been experimenting with our 10,000 pound scale. It was purchased for $399 from Selleton, an E-bay retailer. It is advertised as NTEP legal for trade, 24-inches on square, 10k capacity at 2 pounds resolution. It is apparently an Optima Scales model OP-916N. We were able to confirm the OP-916 has an active certificate of conformance using the NETP online database.

The scale is a monster weighing almost 60 pounds. Construction is welded steel plate with 2.5k load cells at each of 4 feet. Load cells are shear beams marked Optima part number OP-310.

When we tested the scale it read overload above 5,000 pounds display. That load, pictured below, was applied with backhoe buffered by board. We called the supplier to learn why our 10k scale rolled over at 5k. Turned out the very same scale is sold as a 5k version at 1 pound resolution. With instruction we were able to reconfigure the scale to display 10k at 2 pound resolution.

Now to test its accuracy.

Feckless Counsel

Scale - 5k - bucket.jpg

Scale bottom.jpg

Scales load cell.jpg
 
When we tested the scale it read overload above 5,000 pounds display. That load, pictured below, was applied with backhoe buffered by board. We called the supplier to learn why our 10k scale rolled over at 5k. Turned out the very same scale is sold as a 5k version at 1 pound resolution. With instruction we were able to reconfigure the scale to display 10k at 2 pound resolution.

Now to test its accuracy.

I can't decide which is more awesome... the attention to detail in your construction plans or the rigorous testing literally EVERYTHING involved gets. A truly impressive build, thank you for taking the additional time from your busy schedule to document and share.

Sather
 
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