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Old 07-09-2011, 11:25 PM
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Gus Gus is offline
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Default Ultra Lightweight Construction

In light of the other thread about what type of cardstock to use, I thought I'd share this. The model below is a test model for FAI altitude contests. The upper "stage" is just Estes BT-20 and an Estes nosecone. It isn't a functional stage, just an altimeter compartment.

The booster is a single piece of BT-5 running from the top of the transition section all the way through to the bottom of the rocket, where it sits on top of a BT-5 piston tube. The aft end of this tube also serves as the motor mount.

The visible outer part of the booster is an upper transition made of 65 lb cardstock followed by a 40mm X 250 mm body made from plain old printer paper. There is a 65 lb cardstock centering ring at the bottom of the 40 mm body tube section. There are no other internal centering rings.

The transition is glued together with white glue. The body tube is taped together with Scotch Magic Transparent tape. Body tube was not strengthened in any way (no soaking in CA or spraying with anything).

The transition is CA'd at the top to a BT-20 coupler tube and at its bottom to the copier paper body tube. The bottom of the body tube is CA'd to the centering ring which is CA'd to the BT-5 internal tube.

The fins are balsa, CA'd directly to the copier paper body tube. Fillets are liquid CA which is sprayed with accelerator.

Recovery is nose-blow. There is no parachute or streamer. At ejection it simply blows the "second stage" off, which is attached to the bottom of the booster stage with an external piece of kevlar. The "second stage" with the Jolly Logic altimeter is heavy enough that it pulls the booster tube behind it like a streamer.

Of note was that I was using this to run tests with A10-0T booster engines, so "ejection" came just as the booster motor burned out, at a very high rate of speed.

I point all this out because this particular rocket has flown 9 times in the last two days. It suffered no damage. Photo, with moon just behind it, was just before the 9th flight.

Amazing what you can do with really light weight materials.
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  #2  
Old 07-10-2011, 06:26 AM
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Very nice. You could probably lighten it up another notch by rebuilding the payload compartment with 110# or even 65# card stock and losing the upper set of fins. You said the bottom "stage" is computer paper - is that 20#? How does that compare to an equivalent sized sheet of vellum?

Heh - we (Launch Crüe) have an all day launch and picnic here and It's probably a sucker's bet that Ryan and Katie will be practicing with a couple models of theirs today. I'm just looking forward to a bit of sport flying today and at NARAM - hope I finally get to meet you there (especially as one fan of Gus Grissom to another! ) I plan to be there Saturday and Sunday and I'll be hangin' with the LC crew - be sure to stop by and say hello!

Greg
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Old 07-10-2011, 08:15 AM
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Greg,

The upper stage was just a boilerplate made to simulate the weight of a fully loaded upper stage, without actually putting a motor in it.

Emma and I are really looking forward to seeing Ryan and Katie again! Give the two of them big hugs from us.

And I'm looking forward to meeting you at NARAM.

Steve
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Old 07-10-2011, 11:37 AM
AstronMike AstronMike is offline
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Quote:
Originally Posted by Gus
Amazing what you can do with really light weight materials.


Yes indeed. For many years, I have done many, many projects, mainly larger gliders, in such fashion.

Most of the postings I have made both here and TRF allude to my profligate use of cardstock, Depron, and ReadiBoard materials, all of which are very light and cheap. For instance, I have a 3" diameter gliding Bomarc (sans ramjets though) that flies well enough on a single D12, and have thermalled off 2" versions on Quest Cs.

Good timing for this thread, Gus, for right now I am hashing out a 'secret project' for the next TTRA launch......a 5.5" diameter rocket over 6 feet tall.....and decently flyable on an *Estes E9*. And reasonably sturdy too.

If you are 'only' using BP motors, and intend to construct something that is near max weight for a given intended motor, then thin C rings and a plain old paper skinned airframe will work, as I have built/flown successfully a 'dork scale' 4" Saturn V 13 years ago mainly using paper and coming in under 6z.

Now, with the advent of even thinner, lighter, and more pliable Depron, things are getting pretty interesting......
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Old 07-10-2011, 11:47 AM
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Mike,

I don't know much about Depron. Can you tell us a bit about it (sizes, various uses, where you buy it, etc.).

Steve
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Old 07-10-2011, 10:11 PM
AstronMike AstronMike is offline
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Quote:
Originally Posted by Gus
Mike,

I don't know much about Depron. Can you tell us a bit about it (sizes, various uses, where you buy it, etc.).

Steve


Sure, Steve.

Depron is much like the foam used in meat trays, but usually thinner and lighter. This stuff is typically used by small RC plane flyers, in fact, that is who ends up selling the stuff.

RCFoam.com and foamydepot.com are the main sellers. Depron comes in sheets, and typically is ordered in 10 sheet quantities or more. I use a lot of the 3mm variety, in fact, you'll see a good amount of gliders I have posted about in these Forums is made of that very stuff. Thicker Depron isnt very useful, as the excess drag and increased weight gets offset once you need more rigidity in the first place - so ReadiBoard works here.

As far as usefulness in rocketry, Depron isnt very sturdy, but is very lightweight, so even with the added minimal reinforcing results in quite a light structure. I am mainly talking glider parts here though.....

Now, I have gotten hold of the mythical 1mm thin Depron. It is exceedingly light, but also is way too flimsy for 'flat parts' such as wings or large fins. Also, this stuff comes on the sheet prewarped - it is originally made in the factory and rolled up, setting the curve in the sheet. Now, I first intended to just 'go along with the curve' and roll this up for really light body tubing, but found the stuff just too stiff to roll into anything under a 4" diameter.

I have instead rolled 4 'tubes' so far with this. Each is 5.5" diameter and 15" long, and only weighs .7z. Now *that* is light!! Also, these tubes appear pretty sturdy, not HPR or even midpower tube strong, but that is not needed here. I intend to complete the largest rocket I can easily slap together with this stuff and fly it on an E9. I will either be a genius or an idiot once the button is pressed though.....
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Old 07-11-2011, 10:06 PM
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Last time I was at John Pursley's place, he was experimenting with this stuff...

He's been working with 1/32 birch ply and rolling some REALLY lightweight and strong tubes with the stuff, down to about BT-80 size-- any smaller and the radius is so tight the plywood wants to pop. He uses bulkheads made from overlapping "moon" shaped segments matching the tube curvature on the outside and flat on the inside, usually creating a large hexagonal hole in the center of the tube. From what I saw, he's using them just in both ends of the tube, and the tubes are AMAZINGLY light!

He was "hot setting" Depron foam into tubes around 2 inches or so in diameter in his oven. Wrap the Depron around a suitably sized mandrel, pop it in the oven at the correct temp, and give it enough time, and when you pop it out it'll be perfectly "set" to the diameter you choose. He was using these techniques to make a LARGE Saturn IB model (maybe around 10 inches or so in diameter) that will fly on regular MPR motors, and not require a HPR motor. (Similar to his lightweight Saturn V's and Mercury Redstones he flew at NARAMs years ago.)

REALLY neat stuff! Later! OL JR
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Old 07-12-2011, 10:35 AM
AstronMike AstronMike is offline
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Default More on Depron

I've heard of John Pursley and some of his large/light stuff. What's really neat about his end of this is that he is also an elite *craftsmanship* guy as well!

I have also heard of heat setting Depron but havent bothered doing this yet. Anything under a 3" diameter can just be one ply 65# cardstock or even paper for tubing. Now, I'll bet that .5mm Depron is easier to roll up into a tighter tube than the 1mm stuff, but again, that would be one weak walled tube. If you ended up having to add internal structures for reinforcing, you'd also add weight, so where is the net gain? Also, there is one *HUGE* bad thing about Depron, regardless of thickness - it burns like paper (literally)! If any ejection charge residue or even stray backblast from ignition gets on this stuff, you basically recreate the Hindenberg!! Readiboard likewise, an E9 cato several years ago caused a rather large glider to just consume itself in raging goots of fire. Only a paperclip was left afterwards

My 'Depron Magnum' rocket is nearing completion partswise. It will consist of 5 15" segments of 5.5" 1mm Depron tubing, a conical paper nose with an internal wedge stiffener, and the lower 2 sections has a 34" long BT50 MMT/stuffer tube with an extra C ring. The fins will be glued/taped to the outer skin and be backed by the two C rings inside, this is strong enough. The upper section, consisting of the other 3 body segments, appears rigid enough to where I do not need any internal reinforcing (I think....). Total projected end up weight is like 7.5z, with a total length of 85".

Something like a 10" diameter rocket no more than about 9 to 10ft tall seems doable on a G motor although the drag will kill any real altitude, but who cares, we like Slow-N-Low, except GH, that is
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Old 07-12-2011, 11:00 AM
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The heat-set Depron tubes I saw at JP's were the 70 inch Redstone based outer tanks of the first stage of a Saturn IB, so no risk of ejection residue perforating it or igniting it... it's the outer tanks, just for show, and not carrying much of the vehicle thrust loads either... (just like the REAL Saturn IB!)

The birch ply tubes was the most interesting thing to me... those suckers were LIGHT and very strong! Basically the "stiffening rings" were made from lite ply "biscuits" (rounded outer edge matching the tube interior curvature) and the inside edge flat (cut from the edge of the ply sheet). The biscuits overlapped each other by about an inch at each end and were joined to the adjoining biscuits in a lap joint with wood glue. Very light and very strong.

We in rocketry often underestimate the effects of 'strength from shape' in favor of thicker and harder materials-- just the opposite of real aerospace...

Later! OL JR
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Old 07-12-2011, 09:46 PM
AstronMike AstronMike is offline
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Quote:
Originally Posted by luke strawwalker
The heat-set Depron tubes I saw at JP's were the 70 inch Redstone based outer tanks of the first stage of a Saturn IB, so no risk of ejection residue perforating it or igniting it... it's the outer tanks, just for show, and not carrying much of the vehicle thrust loads either... (just like the REAL Saturn IB!)

We in rocketry often underestimate the effects of 'strength from shape' in favor of thicker and harder materials-- just the opposite of real aerospace...

Later! OL JR


Yea, the cool thing about doing a Saturn 1B in such fashion is that you get to have those 8 outer tubes all 'pitch in' on flight loading, plus since they are smaller diameter than the core tube, they are comparatively stronger. In fact, I had strongly considered doing exactly this model for a mega project - but since my craftsmanship skills are on par with GHrocketmans diplomacy/tact level, I'd best refrain from a scale model

As for your last comment, this mirrors what I have been trying to get across for some time. Unless you are doing 'go for broke fast' HPR, then you likely do not need half the 'beef' you think you do, unless you are building a complex scale model that needs to absorb harder landings with no damage.

Come to think of it, wouldnt a Saturn 1B with a 6" core surrounded by 2.6" tank tubes be cool? Hmmm.....
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