3/4 Mercury Redstone

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That sounds like a very prudent plan. I'm impressed you are building your own VAB:)

Frank


Coop,

Thanks for your reply. We’ve discussed this a lot since December. Plan now is to keep it 3,300 feet (1 kilometer) altitude and spill the laundry on top. Decision is driven by the potential forces at mains deployment after free fall.

To achieve that flight we are considering a dual thrust motor. There are several reasons to favor that profile. We want 5:1 thrust to weight at lift off. We want to throttle down for altitude target. We may also operate higher pressure early in the burn where case temperatures are lower.

I visited the construction facility this afternoon. It’s looking really good. Open area is about 50 x 90 feet. Electricians are almost done. Place is freshly painted. Many machine tools have arrived awaiting installation. We should have access about 15 May.

Feckless Counsel
 
Frank,

Wish it were my own vehicle assembly building. This deal belongs to my employer who is opening a “maker space” for the rank and file. Redstone is the debut project. Sure hope it doesn’t fold or CATO. Some executive types are watching. Not sure they are entertained by failure.

Feckless Counsel
 
Frank,

Wish it were my own vehicle assembly building. This deal belongs to my employer who is opening a “maker space” for the rank and file. Redstone is the debut project. Sure hope it doesn’t fold or CATO. Some executive types are watching. Not sure they are entertained by failure.

Feckless Counsel

When your team is all on board, "failure is not an option"...
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Fred,

You are TAP for this project and attended the first design review. If you are positive on outcomes then so are we. Please look for an invitation to final design review ahead of construction start.

Feckless
 
TRF,

Just returned from the Makerspace. Construction appears on schedule for middle May availability. Given that schedule we will order long-lead materials next week. The list includes:

45 sheets of plywood
340 feet of small diameter fiberglass tubing
1300 square foot of 0.010-inch thick G10 sheet

Feckless

Maker Space Construction.jpg
 
TRF,

Some updates to this project include propulsion. Illustrated below is a motor design we call “Concept 8.” This motor promises to deliver 6,000 pounds thrust and 110,000 newton-seconds. Motor mass calculates to just under 100kg total.

The design uses tie-rods to hold closure. More traditional “Frankenstein” closure fails our objectives because of tear-out. The Frankenstein closure tears through tube’s end like ripping out a perforated page.

Feckless Counsel

Motor Assembly V1R2 up nozzle.jpg

Motor Assembly V1R2.jpg
 
TRF,

We are finalizing construction details of the recovery system.

Tom C has generously agreed to provide parachutes to this project. He has also advised us on size of recovery canisters. We believe we are in good care given Tom’s excellent reputation for recovering large rockets. Thanks Tom and we apologize in advance for trashing your chutes.

Illustrated below is the latest thinking on attachment. This shows the booster, the heaviest part, and its separation. A stubby piston protrudes from booster’s forward end. That mates to a parachute canister inside the airframe. Piston and canister are bound by shear pin through access panels.

Note an eye nut attaches to threaded rod from the forward closure. The rod's length is exaggerated and will not extend into the motor.

In this arrangement we achieve a solid parachute attachment to recover the booster. Also the arrangement unconditionally couples parachute to motor. That is a precaution against failure of the thrust ring.

Feckless Counsel

Booster assembly upaded new piston.png

Piston revised - booster airframe separation.png

Thrust ring.jpg
 
TRF,

Some updates to this project include propulsion. Illustrated below is a motor design we call “Concept 8.” This motor promises to deliver 6,000 pounds thrust and 110,000 newton-seconds. Motor mass calculates to just under 100kg total.

The design uses tie-rods to hold closure. More traditional “Frankenstein” closure fails our objectives because of tear-out. The Frankenstein closure tears through tube’s end like ripping out a perforated page.

Feckless Counsel

This is an excellent update. Good work mitigating such a disastrous failure mode.
 
TRF,

Some updates to this project include propulsion. Illustrated below is a motor design we call “Concept 8.” This motor promises to deliver 6,000 pounds thrust and 110,000 newton-seconds. Motor mass calculates to just under 100kg total.

The design uses tie-rods to hold closure. More traditional “Frankenstein” closure fails our objectives because of tear-out. The Frankenstein closure tears through tube’s end like ripping out a perforated page.

Feckless Counsel

Logical observation. Will the project do a subscale or scale test firing to prove the concept or is there sufficient certainty that won't be needed with the materials planned to be used? Just curious. Kurt
 
Kurt,

Thanks for your reply. Full scale test firing this fall. Too much time and effort are already invested. Now is not time to turn cheap.

Feckless
 
TRF,

Illustrated below are attachments for recovering the airframe. The airframe is recovered as one piece, 48 feet long and 250 pounds weight. Piston side eyebolt is attachment for deployment bag. Airframe side eyebolt is attachment for Tom C’s parachute. Cylinder size is approximately 40 x 12 inch diameter.

Concern for the airframe attachment is pull out. The ½-inch bolt links three sections of birch plywood whose combined thickness is 1-inch. Washers approximately 12-inch diameter are considered.

Feckless Counsel

Forward chute canister.jpg
 
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Labor is always appreciated especially recovery.

As always, my friend, you provide beautiful and elegant solutions to a very ambitious project. Have you considered adding secondary attachment points and tie-ins to recovery harnesses should the primary (and apparently sole) attachment point of any section fail. I may have missed it, but it appears you have just one, albeit beefy, in each section.

Best wishes for your successful flight. Will try my best to attend, and volunteer where needed.

Sather
 
TRF,

Some updates to this project include propulsion. Illustrated below is a motor design we call “Concept 8.” This motor promises to deliver 6,000 pounds thrust and 110,000 newton-seconds. Motor mass calculates to just under 100kg total.

The design uses tie-rods to hold closure. More traditional “Frankenstein” closure fails our objectives because of tear-out. The Frankenstein closure tears through tube’s end like ripping out a perforated page.

Feckless Counsel

Some thoughts...

Each of the 6 nuts has 5000 pounds shearing the threads at 600 psi (assuming 8" ID of the case). At 2.5x design margin typical for rocket motors, that's 12,500 pounds per nut. (Like hanging two F150 trucks from each rod/nut!). You'll need a minimum of grade 8, 7/16-20 rod and nuts to get this. And I have not included heating effect on the threaded rod strength.

A simple internal spiral split ring in a 7" OD with the correct groove depth is rated at 100,000 pounds. A 3.33x margin.

Ten 1/2" grade 8 bolts or pins around the case radially will provide 120,000 pounds. Sixteen will meet the shear/tear strength of 3/8th wall 6061-T6 aluminmum tube at 200C.
 
Sather,

So good to hear from you and appreciation for your kind regards.

Yes, there are many discussions on secondary means of retention. Frequently those are wires joining lower rings, joining fiberglass longerons, joining other sections and the like. Even then it is difficult to calculate adequate structure.

Hope you will be a witness to the results. Will be awesome either way.

Feckless Counsel
 
TRF,

Shopbot installation is near complete. Machine plus licensed electric cost almost $30k. We will likely spend another 25 man hours getting it up and running. This monster is become a major investment. It had better punch out plywood parts like a champion.

First parts in about three weeks.

Feckless Counsel

Shopbot assembly.jpg
 
TRF,

For those interested here is a brief update on the project.

Our first plywood piece is cut using the CNC router. That is part of the thrust plate assembly. We are building a sample of that assembly to test against calculated thrust and inertia. The sample assembly is illustrated below in whole and in section.

Absolute maximum stress is 7,000 pounds applied to the aluminum thrust ring. That assumes the sum of 6,000 pounds thrust and 1,000 pounds weight. Real stress, of course, will be less than that so we consider the balance is margin.

Testing the assembly is complicated by the requirement for a 7,000 pound anchor point. Presently the plan is to set the thrust plate assembly atop a ring of bricks. That allows deflection beneath. A portable truck scale will be centered on the assembly. The we will press down on the scale and therefore on the thrust plate using a Caterpillar backhoe.

Feckless Counsel

Thrustplate - first cut - faceless.jpg

Thrustplate testbed assembly.png

Thrustplate testbed section.png
 
Very impressive!

"Make no little plans; they have no magic to stir men's blood" -- Daniel Burnham
 
I don't mean to alarm you, but there appears to be a ghost on your head. 👻

No but seriously, that's amazing. Bricks strong enough in compression / floor strong enough?
 
The maximum load should never be more than the motors peak thrust (6000lbs). The "weight" of the rocket doesn't add in like that.
 
This is correct. However, I have no issue with testing to 7k as a margin.

The max load at a point in the stack is m * a, where 'm' is the mass of the rocket supported above that point, and 'a' is the acceleration. On the ground, 'a' is 1g. In flight, it is a positive (downward) force up to burnout of the motor, and negative (pulling upward on the part) after burnout.

There can be forces in both directions on a part, depending on how it's attached. One m*a force of the mass above and an opposite m*a force for the mass below. The +/- forces can act as a shear force on certain components. And that shear force (or separation force) is reversed at burnout.

These calculations are easily misinterpreted but many people. Draw a free-body diagram with a neutral frame of reference, then consider all the forces on the part.
 
The max load at a point in the stack is m * a, where 'm' is the mass of the rocket supported above that point, and 'a' is the acceleration. On the ground, 'a' is 1g. In flight, it is a positive (downward) force up to burnout of the motor, and negative (pulling upward on the part) after burnout.

There can be forces in both directions on a part, depending on how it's attached. One m*a force of the mass above and an opposite m*a force for the mass below. The +/- forces can act as a shear force on certain components. And that shear force (or separation force) is reversed at burnout.

These calculations are easily misinterpreted but many people. Draw a free-body diagram with a neutral frame of reference, then consider all the forces on the part.
Yes! Draw a free body diagram!

However, you just neglected to account for your aerodynamic forces. What you did is a solid (and generally conservative) estimate for many things, but nowhere near perfect. Especially after burnout.

The net compressive forces cannot exceed the max thrust, that part is true. I would still strongly advise that everything be designed and built with a factor of safety (margin). Testing a little above the expected loads is prudent, especially on a project this size when testing with less than ideal equipment.
 
Yes! Draw a free body diagram!

However, you just neglected to account for your aerodynamic forces. What you did is a solid (and generally conservative) estimate for many things, but nowhere near perfect. Especially after burnout.

The net compressive forces cannot exceed the max thrust, that part is true. I would still strongly advise that everything be designed and built with a factor of safety (margin). Testing a little above the expected loads is prudent, especially on a project this size when testing with less than ideal equipment.

No, I did not ignore aerodynamic forces. The acceleration of the rocket (as shown in a simulation or from an onboard altimeter) already takes into account the external forces on the rocket. The acceleration is the net acceleration (and deceleration) of the rocket during flight.
 
Gentlemen,

The component of concern is the thrust plate. Perhaps a free body diagram of the thrust plate is required to understand bending stress in the thrust plate? Note most of the rocket’s mass is a cylindrical shell.

Feckless Counsel
 
No, I did not ignore aerodynamic forces. The acceleration of the rocket (as shown in a simulation or from an onboard altimeter) already takes into account the external forces on the rocket. The acceleration is the net acceleration (and deceleration) of the rocket during flight.

In the more general case, the aerodynamic forces may or may not be distributed evenly. For example: If the nose has high drag and low weight, the joint behind it may remain in compression after burnout, despite deceleration.
 
In the more general case, the aerodynamic forces may or may not be distributed evenly. For example: If the nose has high drag and low weight, the joint behind it may remain in compression after burnout, despite deceleration.

Correct. The internal frame of reference only knows the acceleration and doesn't know how the forces were distributed that caused the current values of 'a'. Once you consider an external frame of reference, each component has aerodynamic forces distributed on it. A simple model also doesn't consider non-axial forces or flexible materials or vibration/resonances.

For a simple model of what an internal component will see as a stress force, the internal frame of reference works well. For examples, if you want to know the force on a bulk plate that is supporting a mass (nose weight, altimeter, etc.), it is simply the mass of those components times the peak acceleration.
 
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