Anima Mundi

[Feckless Counsel]

TRF,

This is Anima Mundi, that which animates everything.

It would be my privilege to share this build in fellowship with The Rocketry Forum. May I humbly request, however, your advance understanding of my feckless tendencies?

Goals:

3FNC format
22-inch diameter by 222-inch length
110-pound pad weight
Flight to one mile AGL on a single N2000W
Option to 4 motor cluster
Dual deploy recovery
Stress / strain gauge data logging
Flight cameras

[rdbones]

Looking forward to watching this one

[bradycros]

feckless[fek-lis]   Origin feck·less   /ˈfɛklɪs/ Show Spelled[fek-lis] Show IPAadjective

1.ineffective; incompetent; futile: feckless attempts to repair the plumbing.

2.having no sense of responsibility; indifferent; lazy.

Origin: 1590–1600; orig. Scots, equivalent to feck,late Middle English (Scots ) fek,aphetic form of effeck(Scots form of effect) + -less

Related forms
feck·less·ly, adverb
feck·less·ness, noun
Can be confused: feckless, reckless.



222.75 inches long and 21.75 inches wide? I don't belive that none!

[Feckless Counsel]

TRF,

A nosecone is, arguably, the most complex and expensive aspect of a large format rocket. Fortunately a 21.75-inch by 78-inch ogive nosecone is purchased from Ken Allen of Performance Hobbies. Cost is $300. Weight is 26-pounds. The nosecone is salvage from a move set. It is constructed from fiberglass matt and polyester resin. It is apparently true and airworthy with the addition of two centering rings and some surface patching.

Feckless Counsel

[Feckless Counsel]

TRF,

Airframe diameter is predefined by the nosecone and 21.75-inch airframe is strictly a custom component. It is composed of 9 turns of 6-ounce glass cloth and epoxy wound convolute to a rigid mandrel. Dunstone heatshrink tape is used to compress fibers, eliminate voids and assure proper glass-to-resin ratio. Finished wall thickness is approximately 0.055-inch.

The mandrel is built from four MDF disks chucked to black iron pipe. That assembly is wrapped in "kerf board", an architectural product used to form curved surfaces. A final surface is prepared with countertop laminate. Total cost is $100.

Release will, hopefully, be assured by lots of wax, a few turns of 5-mil polyester film and compressed air. If release fails I'll have to destroy that mandrel. But at least I'll have one of three tubes required. Back-up plan is to fabricate an inflatable mandrel from MDF end-caps and cloth reinforced rubber sheet.

Pictures of the present mandrel core, kerf board and MDF disks are attached.

Feckless Counsel

[Feckless Counsel]

TRF,

Airframe wall thickness is to be just 0.055-inch GRP. That is necessary to achieve those goals off 110-pound pad weight and one mile AGL on a single N2000W. Is the proposed airframe strong enough to support flight loads? I think it is and the reason follows.

Peak thrust of Aerotech's N2000W is 600 pounds-force. The rocket weighs 110-pounds at launch. Therefore the maximum compressive force on the airframe can not exceed 710-pounds. The annular area of airframe is 8.2 square-inch. So the compressive load to the airframe can not exceed 86.6 pound per square-inch.

Using bulk material properties of G10 is insufficient for analysis. Instead we must turn to the theory of shells. That theory is concerned with the onset of periodic buckling, a phenomenon illustrated in the attached picture. Shell buckling occurs at a load MUCH lower that would be predicted from bulk material properties.

Without detail I claim the airframe will buckle under a UNIFORM compressive load of 7,900 pound per square-inch. Design margin is 90 to 1.

Glass cloth selected for this project is electronics industry style 7628 by JPS Composite Materials of South Carolina. That is a dense plain-woven cloth with an open area of 30 percent. Thickness is nominal 0.0065-inch. Raw cloth strength is 250 pound per linear inch in the warp and 200 pound per linear inch in the weft. Cloth is finished in CS-550 Silane.

US Composites type 635 epoxy resin is selected for lamination. That is a low viscosity diglycidyl ether of bisphenol-A manufactured by Reichhold of North Carolina. Medium cured material data are substantially equivalent to those of West Systems, Raka, System Three and MAS. Note that neither phase (glass) transition temperature nor a tendency to amine blush are concerns for airframe epoxy selection.

Feckless Counsel

[mikec]

Peak thrust of Aerotech's N2000W is 600 pounds-force. The rocket weighs 110-pounds at launch. Therefore the maximum compressive force on the airframe can not exceed 710-pounds.

As a static load, I buy this, but what about vibration and shock? You will inevitably have parts of the structure that see stresses far above these values.

That said, I have very little doubt that building an airframe strong enough and light enough for your goals is possible. Less obvious is how you are going to demonstrate that your airframe does. If this isn't your L3 flight, then all you have to do is convince the RSO that it will. If I were that RSO, all I would do is jump up and down on the tube a few times

[Feckless Counsel]

Mike,

Your concern is mine as well. Shock and vibration are accelerations not included in that calculation. That is why I've noted a 90 to 1 static design margin. Agreed, static design margin.

Please also note a specific goal to prove big rockets need not weigh 300-pounds nor burn 50,000 N-s to fly. Impressive as those are I believe many are overdesigned and, perhaps as such, constitute greater dangers than what is proposed.

The answer to your specific question is I will demonstrate MY airframe in flight. The RSO and safety committee at my club have granted advance approval. Success or fail, it's going to be great day.

Have you as RSO ever stomped a fliers rocket? How was that received?

Feckless Counsel

[mikec]

Have you as RSO ever stomped a fliers rocket?

I think you missed the smiley; I would never intentionally damage someone's rocket. That said, I should certainly be able to stand and even jump on the tube (if I had an appropriate platform to do it from an end) if it can handle a 710-lbf compressive force.

I'm in complete agreement with you that many large rockets are overdesigned.
I'm just saying that if I were the RSO I would want more assurance than your calculations that the tube wasn't going to fold up or the motor fly free under thrust.

[Feckless Counsel]

TRF,

A winding station is made to assist in tube construction. The mandrel sits below a black iron pipe spindle. That spindle will hold the bolt of glass cloth and feed the wrapping process. The mandrel rotates freely on pillow bearings.

Note the application of laminate about the mandrel. More on this later as it has caused some problems at the seam.

Feckless Counsel

[rstaff3]

The answer to your specific question is I will demonstrate MY airframe in flight. The RSO and safety committee at my club have granted advance approval. Success or fail, it's going to be great day.

Feckless Counsel

As clubs go MDRA is pretty lenient, however, make sure you get the specific people who will sign off your L3 package on-board with the design. (Not that you haven't done so, just saying...) I wondered where you got that cone. I was in the wings when you were discussing this but missed a lot of the details. Hope I'm there when it flies.

[Feckless Counsel]

Mr. Stafford,

Thanks for your reply. The nosecone is movie surplus by way of Ken Allen at Performance Hobbies. It comes from the set of a Russian movie filmed in Florida. The cone was made there by a boat builder. Ken didn't know what movie. I'm a little disappointed.

Construction is fiberglass matt and polyester resin. Diameter is 21.75-inch. Weight is 26-pounds. I speculate the set dresser found some scrap 20-inch ductile iron pipe and commissioned the cone to fit.

I tested the "trueness" of the cone by eyeballing the tip's center. Then I pulled an inelastic cord from that center to the shoulder. Cord length was measured at 30-degree increments about the shoulder. All lengths are within 0.125-inch. Good for a 78-inch tall cone, don't you think?

Ken told me he has two more pieces. I paid $300.

Feckless Counsel

[Feckless Counsel]

TRF,

One of many challenges in this design is how to couple and break sections. The concept presented here is the SHEAR PLATE. Two mating annular plates are epoxied into the airframe. The plates are pinned with nylon screws. A piston drives the plates apart at deployment. Parachute is stowed in a bay separate from the deployment piston.

The concept is illustrated by drawings attached.

Feckless Counsel

[Feckless Counsel]

TRF,

How forgiving is a glassing mandrel? That is difficult for me to quantify but "not very" is surely the answer. I applied countertop laminate to have a hard, smooth surface from which to release. Seemed a smashing concept. I regret that decision now. Feckless perhaps?

Laminate countertop is rather stiff and must be forced onto the cylindrical core. That is no problem except at the seam where the material wants to stand proud. Despite my edge clamping "technique", basically a 1-inch square stock coated with flash tape, the seam presented several issues:

1. There is a slight ridge or hump along the entire seam. The height, about 0.7-millimeter, is somewhat variable along the length. Picture 1 below.

2. Seam ends are lower than the mandrel center by about 4mm. That is only at the seam. Picture 2 below with aluminum edge reference. Note opposite side of the mandrel is true end-to-end.

Feckless Counsel

[Feckless Counsel]

TRF,

I've managed to repair those ends and sand that hump a little. Now is probably a situation where more fiddling begets wider problems. Forward on.

The mandrel is wrapped in 0.005-inch thick polyester film (Mylar). The film is pulled tight as possible and secured by a few pieces of "painters" tape. In that position the polyester film does indeed slide along the length of the mandrel.

Anyone care to comment on prospects for successful release?

Feckless Counsel

[CCR]

TRF,

Anyone care to comment on prospects for successful release?

Feckless Counsel

I won't hazard a guess as to the odds of success but I will wish you the best of luck!

Subscribed and watching with interest.

[GregGleason]

TRF,

I've managed to repair those ends and sand that hump a little. Now is probably a situation where more fiddling begets wider problems. Forward on.

The mandrel is wrapped in 0.005-inch thick polyester film (Mylar). The film is pulled tight as possible and secured by a few pieces of "painters" tape. In that position the polyester film does indeed slide along the length of the mandrel.

Anyone care to comment on prospects for successful release?

Feckless Counsel

You might consider waxing it with mold release wax, then dusting it with talc (baby powder), then adding another layer of 0.005-inch thick polyester film. I have been contemplating that method on a smaller project. I think having two layers of Mylar with one surfaced waxed with the talc acting as a dry lubricant might increase your likelihood of a successful release. For something this big, I think you should go for all the help you can get for it to break free.

What is the weight of the glass and how many wraps do you plan on?

BTW, looks like you are trying to think it through, which is certainly a good thing on this mega-rocket. Are you doing this by yourself, or is this a team project.

Greg

[Feckless Counsel]

Greg,

Thanks for your reply. I had considered the double film idea. It’s a good one.

I plan 9 turns of 6-ounce industry style 7628 cloth. Thickness is nominal 0.0065-inch. Finished wall thickness will be between 0.060-inch and 0.055-inch. Each 48-inch length is estimated to weigh 17 pounds. Three lengths are required.

I’m doing this by myself with occasional help from friends, neighbors and TRF.

Feckless Counsel

[THarrison]

Interested build...

I'm puzzled at how it is only going to weigh 110lb though. Might want to revise that estimate...

[patelldp]

Interested build...

I'm puzzled at how it is only going to weigh 110lb though. Might want to revise that estimate...

He's at 77 pounds using his estimated 17# per tube (needs 3) and 26# for the cone.

An N2000W weighs 27# loaded, bringing his pad weight to 104# without parachutes, couplers, bulkheads, fins, electronics, shock cord...

My guess is closer to 175-200# loaded.

[daveyfire]

You might consider waxing it with mold release wax, then dusting it with talc (baby powder), then adding another layer of 0.005-inch thick polyester film. I have been contemplating that method on a smaller project. I think having two layers of Mylar with one surfaced waxed with the talc acting as a dry lubricant might increase your likelihood of a successful release.

I'd just stick with wax. One time, on a 6" tube, we tried doing three layers of wax and then a teflon release layer over that; the stuff turned into effectively the consistency of boogers and glued the airframe to the mandrel. We ripped out concrete anchors trying to demold that tube. Just wax, or just Teflon from now on. (I realllllly like this stuff: https://www.airtechonline.com/Airtec...1&ProductID=27)

[jsdemar]

I'd just stick with wax. One time, on a 6" tube, we tried doing three layers of wax and then a teflon release layer over that; the stuff turned into effectively the consistency of boogers and glued the airframe to the mandrel. We ripped out concrete anchors trying to demold that tube. Just wax, or just Teflon from now on. (I realllllly like this stuff: https://www.airtechonline.com/Airtec...1&ProductID=27)

Here's a source to try a quart for $33.

[daveyfire]

Here's a source to try a quart for $33.

...and they're even in Indy! Slam dunk, good find!

[dixontj93060]

...and they're even in Indy! Slam dunk, good find!

Hey, what else do they do on Gasoline Alley?

You can find some low/no cost carbon fiber scraps (well, scraps to them; nice sized pieces for most of our builds) at many places on the west side.

[Feckless Counsel]

THarrison and Dan,

110 pounds is a goal. The weight of each section is estimated at 17 pounds including reinforcements, adhesives and fasteners.

But, being feckless, I invite you to check my math:

Total area of glass cloth is:

9 x 48 x pi x 21.75 = 29, 518 square-inch = 22.8 square-yards

Cloth weight is 6-ounces per square-yard:

22.8 x 6 = 136.8 ounce = 8.6 pound.

Cloth is 30% open area. Cloth is 0.0065-inch thickness. So open volume for epoxy is approximately:

30% x 29,518 x .0065 = 57.6 cubic-inch = quart

In reality I'll use double that, about a half-gallon. Density of cured epoxy is 0.69 ounce per cubic-inch. So the weight of epoxy is:

0.69 x 115.1 = 79 ounce = 5 pound

Total weight of the fiberglass shell alone is 13.6 pound. Sanity check anyone?

Feckless Counsel

[dixontj93060]

I did it another way...

22.75" dia. / 36" per yd*pi=1.99 yds
1.99 yds * 48" length / 36" per yd=2.65 sq yds
2.65 sq yds * 12 oz (typical epoxy weight 2X cloth weight) / 16 oz per lb = 1.99 lbs per layer
1.99 lbs/layer * 9 layers = 17.9 lbs per 4' section

[Feckless Counsel]

Dixontj93060,

Thanks for the reply. Looks like our numbers agree except in resin weight. I chose a dense weave cloth hoping to defeat that two-to-one resin rule of thumb. Will let you know shortly.

Feckless Counsel

[Feckless Counsel]

David and John,

Looks like good stuff. Have any tips for application?

Feckless Counsel

[blackjack2564]

TRF,

One of many challenges in this design is how to couple and break sections. The concept presented here is the SHEAR PLATE. Two mating annular plates are epoxied into the airframe. The plates are pinned with nylon screws. A piston drives the plates apart at deployment. Parachute is stowed in a bay separate from the deployment piston.

The concept is illustrated by drawings attached.

Feckless Counsel

This is the only design gothca that would concern me. I have seen several large diameter projects with a tube in a tube coupler/shear plates.

They have a tendency to buckle at that weak point under wind shear or off vertical flights under higher thrust motors. Once it starts, ain't no going back, they break right there. The smaller inner tube cannot handle the load, even though the outer is capable. there is a leverage effect.
You might consider a rod & tube receiver set up . rods on on BP & tube receivers on the other. Double up on the bp's several inches apart with the rods mounted in both. Same for the other side with tubes. Glass, carbon fiber for rods. Aluminum for tubes or whatever you consider stress worthy.

By the way... I have stood on fin cans when RSO' ing. If the fincan cannot take me standing on it or the flier is not confident enough the building skills, I don't give it a prayer withstanding high thrust motors. Usually a minimum diam. with a M or N stuck in it.

I always bounce on mine to test, they better be able to handle more than 200lbs of shear.

[Feckless Counsel]

Jim,

Excellent reply and exactly the sort of experience I’m seeking. Thanks.

Feckless