3/4 Mercury Redstone

John,

Was made aware of the flight today. Just now I understand your connection. Context is those guys are brothers. They built big and light weight. They accepted every risk. They pushed materials and design to the limit.

Peace brother. We love it.

Please pass along details of our project and a standing invitation for VIP status at our attempt.

Feckless

Yes John, peace brother... [emoji4]



From the Ether...

TRF,

We revisited stress at the airframe parachute attachment. We agree some reinforcement is necessary as the 12mm thick center is stressed right to yield.

As speculated by AdAstraPerAspera joined diaphragms in unequal thickness simulate unequal stress. Deflections are identical. Thinner pieces at same deflection are less stressed. The 12mm center diaphragm is disproportionately at risk.

Pictured below are CAE results.

First is a 2D simulation illustrating the eye nut anchored and the 300 pound airframe accelerated at 4G. Result is 60MPa about the 51mm washer assuming 4.5GPa stiffness in the cardboard parachute canister. That stress is about double “characteristic” strength and likely equal to mean strength.

Maybe survivable. We can do better.

Next is 3D simulation illustrating addition of an 18-inch diameter aluminum washer 1/8-inch thick. Result is 66% reduction of load totaling 10MPa in plywood. That is about 1/3 yield. Washer’s weight is 3 pounds. We accept that as a positive improvement to be included in construction.

Note we will bond the washer to plywood using US Composites 635 and fast hardener.

Finally some red is seen in fiberglass and metallic components of these illustrations. Please note threshold of red is 30MPa, the yield of plywood and not that of fiberglass, aluminum or steel.

Feckless Counsel,

dixontj93060 said:

There are a few people "down under" that would dispute the "largest model rocket" claim:

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I 'spect so especially since theirs performed pretty much as planned. Kurt

Feckless Counsel said:

First is a 2D simulation illustrating the eye nut anchored and the 300 pound airframe accelerated at 4G.

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Again, where did you come up with 4-G's for the shock on the attachment point? That is way too small in my experience. I have measured a 30-G shock on a 140# rocket (the largest I've design, built, and flown). It took 3 flights before I staged the deployment in multiple rigging steps and pilot chute before I got the shock down to 8-G's.

If this were my 400# rocket, i would have 3 anchor points and a 3:1 bridle to the main shock cord, long enough to limit side-forces at the anchor points. I would move the anchor points close to (or at) the main vertical structural elements to limit the worry of stress failure in the ply (or adding heaving load-distributing plates).

I know you are relying on your FEA runs, but they are only as good as your assumptions.

jsdemar said:

Again, where did you come up with 4-G's for the shock on the attachment point? That is way too small in my experience. I have measured a 30-G shock on a 140# rocket (the largest I've design, built, and flown). It took 3 flights before I staged the deployment in multiple rigging steps and pilot chute before I got the shock down to 8-G's.

If this were my 400# rocket, i would have 3 anchor points and a 3:1 bridle to the main shock cord, long enough to limit side-forces at the anchor points. I would move the anchor points close to (or at) the main vertical structural elements to limit the worry of stress failure in the ply (or adding heaving load-distributing plates).

I know you are relying on your FEA runs, but they are only as good as your assumptions.

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John, Out of curiosity how did you do that? Did you do live testing with a strain device on a flight?
I had a friend who flew an O powered large rocket and the main deployment ripped the attachment point right out of the ebay. I didn't witness the event but said something like "I should'a used four all-thread and not two".
I think this can be a serious problem if not well thought out. The deployment sequence timing would have to be absolutely perfect for the least stress on the airframe.

We get away with a lot of this because for the average "Joe" with super strong stuff relative to size, our recovery harnesses and structure are overkill on the small scale. Kurt

If you ask me (which you aren't), the naked ply is weak as heck. I use a 10oz Kevlar laminate on the ply to reinforce the stress points.

From the Ether...

John,

Thank you for your comments. They are respected and appreciated. Two questions please?

1. What is the bandwidth of acquisition system used to record 30G? Are you able to post process or otherwise see the acceleration spectra? Can you please share that spectra?
2. What compels a 3 point bridle to load share in all circumstances? Can you picture any scenario where one leg is taught and the other two are slack?

Feckless Counsel

Your diagram indicates a straight-out load. What about side loading. If your eyebolt is on an exposed bulkhead (I.E. the end of a coupler/bulkhead that is in free air), you will have up to 90 degrees, maybe even 95 degrees of side loading. Your payload WILL separate from your eyebolt... Especially if you are already near the loading limit.

Mike,

Excellent point and one not considered. We will discuss that torque in team meeting.
The bulkhead is not exposed. Instead it is inside a substantial tube 17 inches inside diameter and 36 inches deep. Maximum angle should be constrained to about 12 degrees or, equivalently, 20% of total as side load.

Feckless Counsel

For side loading, you may want to go to a swivel hoist ring. They are expensive, but designed for this sort of thing.

TRF,

In yet another 16 hour session our team has advanced the construction.

We decided to reinforce airframe’s recovery attachment. That reinforcement is a 23-in diameter aluminum plate 1/8-inch thick. Plate is epoxied to the central 12mm former by US Composites 635 medium. We consider that arrangement an extension of John’s three point harness as we now have a continuum of attachments out from the center. The former is equivalently laminated as suggested by Tim. We appreciate Mike’s observation but did not calculate side load a factor in plate buckling. Thanks to all who contributed to this aspect.

Both the shorter recovery sections are completely skinned and trimmed. Just before dark I captured one recovery section alongside three airframe sections. Note the stock piece of PML 11.5-inch tubing for reference.

Capsule is planed, sanded and inspected. It’s run through with threaded rod and clenched both ends with eye nuts. A recessed piston 2.5 inches high is mounted to float on capsule’s bottom. Capsule is now ready to skin.

Leading edge for the booster and for the rudders are made from two pieces of 12mm plywood glued to 24mm thickness. Unfortunately the majority of our glue-ups warped. So we’ll be remaking several of those. Otherwise one of our successful pieces is pictured below. They have the look and strength of Damascus steel.

Finally we have received motor tubing. That is 8 inch seamless schedule 40 aluminum pipe. We’ve purchased two lengths; one for test and one for flight.

In January look for reports on capsule and booster completion. We will test fit parachutes. We will install electronics and ground test pyrotechnics. There will be dry assembly of the entire rocket and CG tests. By January end we hope to be at paint and decoration.

Thanks to all for your interest. Best wishes and a happy holiday.

Feckless Counsel

I was on the UNM Redstone team. We were about 6 inches bigger, err, taller, than the Aussies....

dixontj93060 said:

There are a few people "down under" that would dispute the "largest model rocket" claim:

[YOUTUBE]xzcxEXHdHx0[/YOUTUBE]

From the Ether...

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BABAR said:

Something tells me they will not use this is their resume folders.

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I would venture to say you don't know much about engineering school projects.... Odd comment to make considering your signature...
We designed and built this rocket in about 6 months. About 46.5 feet tall and about 300lbs at liftoff. Half the weight of the V2 or the Feckless Redstone. Largely made out of foam, plywood, and aircraft cloth. Only one member of the team had ever had any high power rocketry experience. Most of the team had to be taught how to use glue and use basic hand tools. All things considered we did pretty good. I have detailed more of the project, issues, and results in this thread:
https://www.rocketryforum.com/showthread.php?140756-3-4ish-semi-scale-Redstone-Missile

I hear they are retrying the same build again, so Feckless has until about May to get his in the air ;-)

kclo4 said:

I was on the UNM Redstone team. We were about 6 inches bigger, err, taller, than the Aussies....

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Yeah but I think they can lay claim to the "biggest" that flew and recovered as planned. Let's just say UNM flew. [video=youtube;Wv5xXMLGs8U]https://www.youtube.com/watch?v=Wv5xXMLGs8U[/video]
Kurt

I am surprised you missed the threads here and on reddit from our flight, I was certainly watching yours. We do have a fairly similar build to yours, but ours is even more bare bones. Our bulkheads are gatorboard foam where yours are wood, and our skin was Dacron cloth instead of fiberglass. Only fiberglass on ours was the motor tube. Our stringers were smaller but higher density. Our fins were the same foam, which was our ultimate failure point. I suggested they be more securely mounted and laminated with carbon fiber, but they left them bare and had weak mounting. The weak mounting was so that they would break free on landing, but it was not sufficient for flight.

I am pretty confident with the laminated fins and about 10 more lbs of reinforcement in key places we would have resulted in a successful flight.

Yours looks good, glad you guys are spending more time than we had on design, and your workers are likely more skilled. Since your motor is going to be quite a bit larger the extra strength will come in handy.

Feckless Counsel said:

John,

Was made aware of the flight today. Just now I understand your connection. Context is those guys are brothers. They built big and light weight. They accepted every risk. They pushed materials and design to the limit.

Peace brother. We love it.

Please pass along details of our project and a standing invitation for VIP status at our attempt.

Feckless

Click to expand...

What? You don't think confetti recovery and motor acrobatics was not by design?


(BTW, I didn't title the youtube video, haha)

ksaves2 said:

Yeah but I think they can lay claim to the "biggest" that flew and recovered as planned. Let's just say UNM flew. [video=youtube;Wv5xXMLGs8U]https://www.youtube.com/watch?v=Wv5xXMLGs8U[/video]
Kurt

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Anybody can build relatively tall skinny rockets and some can even make them fly and recover. The V2 still wins on sheer volume. Maybe I am a little biased though.

In Melbourne (Oz) there are quite a few buildings that were built and then they added tall skinny communication towers just to say they were taller than the other buildings. I don't get it myself.

Show me a twice-scale V2 and I will applaud you. Not that I'm trying to stir anyone up here with this post :wink:

kclo4 said:

Our fins were the same foam, which was our ultimate failure point. I suggested they be more securely mounted and laminated with carbon fiber, but they left them bare and had weak mounting. The weak mounting was so that they would break free on landing, but it was not sufficient for flight.

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The UNM fins were also a poorly-chosen shape, considering the material and mounting. You need a simple planform with sufficient root attachment length. I helped with Robert DeHate's full-scale Patriot which had CF-covered plates mounted with bolts in U-slot hard-points in the body. Recovery failure was due to drag separation (with early deployment of the payload - Paul Robinson's ashes).
https://goo.gl/photos/ZCV5gS1Dqc9EiPtQ7

TRF,

Yesterday we enjoyed a visit from Mr. Tom Cohen. Many of you are familiar with his collection of “Big Freaking Rockets” from Higgs Farm, Potter and other East Coast launches. Tom is a respected expert at heavyweight recovery. We are delighted to have his experience inform our recovery design.

Tom brought a large selection of parachutes, deployment bags and other recovery gear. Our generous 17 x 36 inch parachute canisters easily fit all of Tom’s gear including one massive 60-foot chute capable to land 600 pounds at 15 feet per-second.

Perhaps the most important part of Tom’s consult was planning “who pulls what.” His concern is that, when chutes are pulled out by the bag, there is a chance the chute just says in the canister while bag pulls free. That is different from when the chute is pulled from bag and the bag is attached inside the canister. We never thought of that. The potential exists in two of our 4 deployments: airframe and capsule.

Another concern is for deployment bag’s loop. Tom suggested we might add a dowel or similar reinforcement to prevent the loop bursting.

Finally we agreed to very short “shock cords.” We are apogee deploy specifically to minimize shock load. No need for long cords that allow excessive free fall under the canopy.

Feckless Counsel

There was quite a bit of talk about you guys at the MDRA holiday party last night. :wink:

Tom Cohen is a great addition to your team of wizards.

What is the expected altitude? The time you have to deploy will limit your options, as you know. The main trade off for fast parachute deployment and inflation is high shock load to the attachment point(s).

Expected altitude is about a mile, give or take.

Out of curiosity, what do you consider a short shock cord?

Feckless Counsel said:

TRF,

Yesterday we enjoyed a visit from Mr. Tom Cohen. Many of you are familiar with his collection of “Big Freaking Rockets” from Higgs Farm, Potter and other East Coast launches. Tom is a respected expert at heavyweight recovery. We are delighted to have his experience inform our recovery design.

Tom brought a large selection of parachutes, deployment bags and other recovery gear. Our generous 17 x 36 inch parachute canisters easily fit all of Tom’s gear including one massive 60-foot chute capable to land 600 pounds at 15 feet per-second.

Perhaps the most important part of Tom’s consult was planning “who pulls what.” His concern is that, when chutes are pulled out by the bag, there is a chance the chute just says in the canister while bag pulls free. That is different from when the chute is pulled from bag and the bag is attached inside the canister. We never thought of that. The potential exists in two of our 4 deployments: airframe and capsule.

Another concern is for deployment bag’s loop. Tom suggested we might add a dowel or similar reinforcement to prevent the loop bursting.

Finally we agreed to very short “shock cords.” We are apogee deploy specifically to minimize shock load. No need for long cords that allow excessive free fall under the canopy.

Feckless Counsel

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I had a chute hang up in a D-bag one time. Had a 36inch pilot chute on the bag and the chute didn't come out. D-bag I believe now was poorly designed. Long and narrow tube. Kurt

Any updates on when this beast will fly? I want to plan a trip to MDRA in the spring of 2018. I’d love for it to coincide with this launch.

BDB said:

Any updates on when this beast will fly? I want to plan a trip to MDRA in the spring of 2018. I’d love for it to coincide with this launch.

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i know the original plan was for Red Glare in early April. If that slips, then it has to move to November or December, since we move to the sod farm for the summer and the recovery area is much smaller, not to mention millions of trees. Well, it feels like millions. :rant:

It won't be at a Red Glare as the logistics for both are simply too great. It will have a dedicated launch like the Saturn 1Bs and the Saturn V before them.
The BOD is working with Jeff and Tommy to provide the best launch window possible.

stantonjtroy said:

It won't be at a Red Glare as the logistics for both are simply too great. It will have a dedicated launch like the Saturn 1Bs and the Saturn V before them.
The BOD is working with Jeff and Tommy to provide the best launch window possible.

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I like that idea. That gives people a chance to observe the whole thing without being involved in prepping or launching their own rockets. Safer, too.

Bat-mite said:

I like that idea. That gives people a chance to observe the whole thing without being involved in prepping or launching their own rockets. Safer, too.

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If like the SatV, the crowd will be huge and the powers that be will want more separation from said crowd. This means different planning/prep than our normal launches.