How would you build this?

[MaxQ]

I've been pondering this one for quite awhile...

If you wanted to make several of these grid fins at small scale (checking into the size of the squares now)...
what would you do?

I have checked plastruct and model railroad catalogues and all manner of stuff online.....no luck.

Building one of these units from scratch, let alone making four of the same is daunting...

http://upload.wikimedia.org/wikipedia/en/thumb/6/6c/MOAB_grid_fins.jpg/800px-MOAB_grid_fins.jpg

[kramer714]

I know how to make the full size ones, (we do have some fun at work)

My guess is you plan to go a little smaller...

Ever look at light filters? They put them under lights in suspended celings.

[MaxQ]

I know how to make the full size ones, (we do have some fun at work)

My guess is you plan to go a little smaller...

Ever look at light filters? They put them under lights in suspended celings.

Yep...light filters did cross my mind, but they don't appear to me to be available in a modeler scale.....

[georgegassaway]

It might be too costly, but one way would be this:

Have long rectangular strips of the fin material (say 1/16" plywood) laser-cut with notches cut exactly half-way thru them (and the notches the width of the fin material). The notches spaced the same as each intersection of the grid. you'd need a LOT of these to be laser-cut.

The reason for the half notches would be so that the diagonal fin strips running upper left to lower right would be face-up, and the intersecting fin strips running upper right to lower left would be face-down, fitting together as a unit very well.

Indeed, I would think it is likely that is how the real ones are made. Long strips with half-notches (not necessarily laser-cut, but the design approach). It would be nuts if they fabricated the real ones out of solid aluminum billets and machined them to cut out all of the squares, but I have to admit that is possible.

If you do not value your sanity, then change "laser-cut" above to "cut by hand". Unless you happened to have a table saw and a blade with juuuust the right Kerf to match the material thickness.

BTW - this half-notch idea came to mind pretty easily. Seen it done with cardboard dividers inside of cardboard boxes.

No matter what you do, they will be fragile and at risk of breaking on landing, if these are to be used for fins at the back (The Soyuz spacecraft shroud has deployable stabilizing grids, which are folded up flush with the body)

- George Gassaway

[AKPilot]

Well, I may know a few people who know how to make one of these for you in 1:1 scale. ;)

[stantonjtroy]

Might try looking into composite core material. It's a honycomb material and comes in different thicknesses. http://www.acp-composites.com/home.php?cat=256

[MaxQ]

It might be too costly, but one way would be this:

Have long rectangular strips of the fin material (say 1/16" plywood) laser-cut with notches cut exactly half-way thru them (and the notches the width of the fin material). The notches spaced the same as each intersection of the grid. you'd need a LOT of these to be laser-cut.

The reason for the half notches would be so that the diagonal fin strips running upper left to lower right would be face-up, and the intersecting fin strips running upper right to lower left would be face-down, fitting together as a unit very well.

Indeed, I would think it is likely that is how the real ones are made. Long strips with half-notches (not necessarily laser-cut, but the design approach). It would be nuts if they fabricated the real ones out of solid aluminum billets and machined them to cut out all of the squares, but I have to admit that is possible.

If you do not value your sanity, then change "laser-cut" above to "cut by hand". Unless you happened to have a table saw and a blade with juuuust the right Kerf to match the material thickness.

BTW - this half-notch idea came to mind pretty easily. Seen it done with cardboard dividers inside of cardboard boxes.

No matter what you do, they will be fragile and at risk of breaking on landing, if these are to be used for fins at the back (The Soyuz spacecraft shroud has deployable stabilizing grids, which are folded up flush with the body)

- George Gassaway

<BTW - this half-notch idea came to mind pretty easily. Seen it done with cardboard dividers inside of cardboard boxes.>

That very same idea crossed my mind early on, but only for a brief moment, as I shuddered at the thought of trying to make a consistent cut at each location, on each strip and each corresponding side....and then not having them seat properly when combined into one unit.
It's giving me the shudders just thinking about it right now...

(The Soyuz spacecraft shroud has deployable stabilizing grids, which are folded up flush with the body)
You read my mind.
I'm converting a Cosmodrome Vostok.

Funny lookin with the stars and stripes on it ain't it?


http://farm4.static.flickr.com/3419/3398453337_cb80ef9b04_b.jpg

[brianc]

I thought we had already covered this one...

http://www.rocketryforumarchive.com/showthread.php?t=41882


Good to know I'm not losin' my mind. Yet.

[MaxQ]

Well, we're in fall reruns...

Thanks for resurecting the thread...I thought there was some discussion before.

Don't think anyone had an answer then either.

[MaxQ]

Might try looking into composite core material. It's a honycomb material and comes in different thicknesses. http://www.acp-composites.com/home.php?cat=256

There may be something to that...thanks.
Anyone have this stuff that could give me some more details...?

[georgegassaway]

Well, since you indeed want them for use as folded up detail parts on a Soyuz, and not working fins, that opens up more possibilities.

Window Screen material. Do not know if it might be close enough to ballpark size to work at the scale of your model, or not. I used Window Screening for walkway grid flooring on my Little Joe-II Scale Pad (the real thing had Chicken Wire-ish compressed Hexagonal type patterns, not squares, but it was OK visually since it was so small).

Of course the window screening would be too flexible to hold up by itself, but the outer frame should do it, if you can find screening to the close enough scale.

I suggest you jump over to the SpaceModelers YahooGroup and ask there. Most there make Static (non-flying) scale models of various rockets and spacecraft. Some from kits, some totally from scratch. Maybe someone there has done those types of grids before.

And I would not be surprised if one answer you’d get over there would be photo-etched brass. There might be some pre-existing photo etched brass patterns like that. Then of course there would also be custom photo etching that would solve the problem of getting it dead-on-scale.

OK, I also thought of Plastruct, who makes various interesting plastic shapes. Did a Google for Plastruct and fence and this was one of the hits:

http://www.hobbylinc.com/htm/pls/pls90451.htm

Railroad HO Scale Chain link fencing. You might try other suppliers of model railroad details/accessories.

If $ was no object at all, Rapid Prototyping.

- George

[powderburner]

How would I do it?

Probably the most difficult way possible. Paper or cardstock, maybe with a very thin plywood outer frame (if the scale was large enough that 1/64th plywood was the right "scale" thickness).

I would have to really really want to get a super-scale appearance before I would be willing to mess with this much tedium.

You're going to want to make a tool to keep all the fins a consistent size, right? So I would place the fin outer perimeter pieces into the fin tool/frame and tack them together (from the inside surface) with some very small drops of glue, applied with the point of a pin. The tool could also serve as an alignment guide for me to accurately align and drill a hole in the base plate so I could eventually mount the finished fin to the model rocket on a dowel pin.

Then I would cut strips of paper or cardstock wide enough to model the chord and long enough to make all four sides of each grid cell. I would suggest using an overall piece of "cell stock" that is wide enough that I could cut N strips of individual cells, and I would pre-fold that one overall piece (it's easier than fumbling with N little separate strips of paper). Once I had all the cells I would dry-fit them inside the fin tool/frame and stack all the cells in place. Work the cells with a pin or something pointy to wiggle them into alignment. You could also use some straight (unfolded) strips of paper placed between cells to help get them aligned in at lease one direction? Using a pre-folded piece of paper or cardstock (to help with consistency in cell size) and a tool (a precision straightedge) to help get the folds really sharp and clean, I would expect to be able to make individual cells down to a few millimeters in size.

At this point in the process I will point out that if you don't like what you see, toss the cells and start over with another piece of pre-folded material. It's not like a sheet of paper is expensive or anything--

Once I have what I think I want, still in dry form, I would gently remove the dry assembly from the fin tool and drip in a small amount of CA at each cell corner. Once that batch is set, I would soak the fin thoroughly with CA and let it cure. From here, some touch-up sanding and tweaking would probably be needed.

Definitely lots of tedious work, but if you want true scale grid fins, I can't imagine how else you would tackle this. I'm not going to micro-machine something like this fin out of a blank plate of steel...

One last thing: I would make about ten of the individual fins, and select the best four to use. Paper is cheap.

[stantonjtroy]

Following on what George said; photoetching is a viable option if you're looking for form over function. Micro Mark has a complete do-it-yourself kit. It's a little pricey at $125 but once you have the kit you can make whatever you want, as much as you want, as many as you want. I'm looking to get this set myself as I've used etched details on static models for years and my rocketry intrests lean mostly toward scale. As for the composite core, I'll grab some scraps from work on Monday and post some info shots, Grid scale, thicknesses and the like.

http://www.micromark.com/MICRO-MARK-PRO-ETCH-PHOTO-ETCH-SYSTEM,8346.html

A brief description of the photoetch process;
https://www.micromark.com/html_pages/instructions/83123i/83123proetch.htm

[Verna]

Yep...light filters did cross my mind, but they don't appear to me to be available in a modeler scale.....

First off, that's one neat rocket. I haven't seen it before.

Other than the obvious thing of rummaging through a Michael's or HL, if you are looking for a much smaller scale I am positive my kids had a building piece that was very similar from a Legos set, that would be ideal for the fins.

Verna
www.vernarockets.com

[MaxQ]

Thanks everyone, gave me some things to think about.

First, I need to protype the dimensions of the individual grid itself so I can estimate the number/size of the grid cells in each unit.

That would go a long way in determining if commercially availble grid, honeycombs or other found objects would portray the size grid acceptably.


As far as deciding how to portray them...whether with a real box grid, or just a surface treatment....this exercise might indicate that as well.

The World Space modeling guys have done it..to varying degrees.

I'm not in their league, but I like some of what I've seen.

[Rocket Al]

First off, that's one neat rocket. I haven't seen it before.

Other than the obvious thing of rummaging through a Michael's or HL, if you are looking for a much smaller scale I am positive my kids had a building piece that was very similar from a Legos set, that would be ideal for the fins.

Verna
www.vernarockets.com

It ought to be clarified i guess. This isn't a missile (notice the lack of a nozzle) Based on the letters on the side, MOAB, it would be the smart bomb called the GBU-43/B Massive Ordnance Air Blast Bomb a.k.a. Mother of All Bombs. So it really isn't propelled as much as dropped....


Alan

[roadkill]

Being the nutcase that I am,
I'd prolly scale it big enough to use
the bottoms from milk crates....
:o

[rockets2000]

Today I saw the perfect material for your fins. I went to an antique store (junkyard) who specializes in old signs and ornamental metal stuff. He had some fairly new-ish crosswalk signs. They have this plastic diffuser material that has a "mesh" of about 1 sq. in. diamond shapes. It's an inch thick, and the whole piece was a 18" square. Like this:

http://i388.photobucket.com/albums/oo325/Rockets2000/Countdownpedestriansignal.jpg

You could easily bisect the cells with cardstock to make them continually smaller until you get the size you want.

[wilsotr]

We were looking at grid fins for MLAS at one point, and I poked around here for ideas how to model them (thus the TRF archive post someone linked). Best I could do was a flourescent light grid, one of which is sitting in my garage -- unused, because we ended up doing MLAS with conventional fins and the immediate need went away. Good luck with this one Max ... if you find a good grid source, let us know!

[MaxQ]

We were looking at grid fins for MLAS at one point, and I poked around here for ideas how to model them (thus the TRF archive post someone linked). Best I could do was a flourescent light grid, one of which is sitting in my garage -- unused, because we ended up doing MLAS with conventional fins and the immediate need went away. Good luck with this one Max ... if you find a good grid source, let us know!


Well, it may be difficult as I'm in need of something kinda small (1/33 scale see pic for reference) ...which I think makes the light filters and other premade grid structures too large for my need.
https://www.discountrocketry.com/images/big_images/big_vostok.jpg
I was thinking of scratch building a grid assembly using Plastruct angle "L" beams - put together to form the grid...one angle attached to another to make a box...and keep repeating the boxes until a grid is made.

I would make one frame and then pull an RTV mold and make three more in resin.
Since it is basically decorative and not functional, it is a bit easier to pull off...
(MLAS - you haven't flown that thing yet? Bring it to Culpeper this month....I'd like to see it close up)

[Verna]

It ought to be clarified i guess. This isn't a missile (notice the lack of a nozzle) Based on the letters on the side, MOAB, it would be the smart bomb called the GBU-43/B Massive Ordnance Air Blast Bomb a.k.a. Mother of All Bombs. So it really isn't propelled as much as dropped....


Alan

Oh, I see. Duh! No nozzle. :blush: I was thinking so much about where to get the grid I didn't even notice. Thanks for pointing it out.

I should spend more time with my kids who are in the military learning about different kinds of ordinance.

Oh well, Randy got a good laugh from it. :rolleyes:

Verna
www.vernarockets.com

[wilsotr]

Well, it may be difficult as I'm in need of something kinda small (1/33 scale see pic for reference)

Poke around here a bit ...

http://www.mcmaster.com/#brass-screens/=3x57iw

... you might find a screen with a mesh suitable for simulating the fins.

[wilsotr]

The Russians are heavy into grid fins ... here are the ones on the SS20 at the NASM.

[luke strawwalker]

Here's something that might work...

In Walmart, over in the school/office supplies section, they usually have these black miniature expanded metal "inbox" trays and other things made from the same material-- card holders, even wastepaper baskets. I've picked up a few to use for expanded metal (diamond shaped holes) commonly used on farm equipment for a scratchbuilt 1/8 scale cotton picker I've been planning and gathering materials for. It looks identical to the expanded metal you see used on equipment and sold at steel suppliers, TSC, etc., only smaller...

Later and good luck! OL JR :)

[brianc]

Disclaimer- while this company is also located in Orlando,
that's the extent of any link I have with them... ;)

Don't know if this is feasible from a cost stand-point, but
sounds interesting!

http://www.mydeatechnologies.com/index.php

[mjennings]

I just looked up, in the buildings I'm in at work all the air vents have grates that look to be made up of about 1/2" squares. Should be able to track that down at graingers, mcmaster-carr etc

[SteelyEyed]

I stumbled across this thread today... I too have been thinking about building a grid fin rocket for a few years now and this thread is making me re-consider it. I had also thought about using the 1/2" grid, lighting fixture filters (that I sit under every day at work) that were mentioned above. I had mentally ruled them out as a solution because they look too flimsy to survive HPR thrust profiles (don't know it for sure, that was just an engineering judgement call without the benefit of testing or calculations). Giving it a little more thought today, maybe it would be worth a try if one could build a robust frame in which to in lay the plastic grid material.

I have also collected a number of photos of grid fin designs, see below...

http://i138.photobucket.com/albums/q273/steelyeyed/aa12-grid-fin.jpg

http://i138.photobucket.com/albums/q273/steelyeyed/aa12.jpg

http://i138.photobucket.com/albums/q273/steelyeyed/ORD_Affordable_Weapon_Missile_Boost.jpg

http://i138.photobucket.com/albums/q273/steelyeyed/ss21-missile.gif

[SteelyEyed]

Hey, now that I think about it a bit more. I have seen some automotive grills that look like they are made of a grid material that might work for a rocket build. Maybe I need to visit a junk yard or an auto parts store...

Bret

[foose4string]

Well, it may be difficult as I'm in need of something kinda small (1/33 scale see pic for reference) ...which I think makes the light filters and other premade grid structures too large for my need.
https://www.discountrocketry.com/images/big_images/big_vostok.jpg
I was thinking of scratch building a grid assembly using Plastruct angle "L" beams - put together to form the grid...one angle attached to another to make a box...and keep repeating the boxes until a grid is made.

I would make one frame and then pull an RTV mold and make three more in resin.
Since it is basically decorative and not functional, it is a bit easier to pull off...
(MLAS - you haven't flown that thing yet? Bring it to Culpeper this month....I'd like to see it close up)

Check out Star Hobby on Rt.50 next time you are heading over the Bay Bridge(MDRA?). It's in a little shopping center about a mile or two from the bridge on the right side(might be last exit before toll). It's one of the few stores left in the complex. I was in there last week and saw some photo etched brass in a perfect grid pattern. I think there were a couple different sizes, and might be close enough for this scale. The thin brass might not give you the depth and actual detail you are striving for, but it sure would make this easy enough, while still giving it some realism.

Edit: I just called Star Hobby and he gave me the manufacturers name. It's made by K&S engineering. Here it is on Hobbylinc:

http://www.hobbylinc.com/htm/k+s/k+s02712.htm
and
http://www.hobbylinc.com/htm/k+s/k+s02706.htm

Looks like it also comes in 1/16" , 3/64" , and 1/32" mesh, but that might be too small.

[Micromeister]

A couple of folks I know have modeled these drag fins with 1/2" opening Plastic "eggcrate" drop in fixture lens. I seem to recall they come in 24"x 48" lens size in white and chrome plastic, are 1/2" thick and have either 1/2" or 3/4" open cells. A bit on the heavy size but for larger models seemed to work very well.

If I were modeling it in micro size i'd use 1/64th ply with the half split slat method someone discribed earlier. it's a pain but it works.

[luke strawwalker]

http://www.hobbylinc.com/htm/k+s/k+s02712.htm
.


That's the same stuff that the Walmart office supplies are made from, only the WM stuff is steel I think. You can get a wastepaper basket made of that stuff gently rolled into a cylindrical cone (probably about 2 square feet; enough for a dozen grid-finned rockets!) for about half what they're charging for that little piece.

You can also get some smaller 'inbox trays' and cylindrical pencil holders made of the same stuff if you want to keep your costs down to a few bucks!

I'd post a link but I can't find one on walmart.com... :rolleyes:

Good luck! OL JR :)

PS... here's a couple pics of the WM stuff... I THINK it's the Homedics brand IIRC-- It's in the office/school supply section at WM... This is an 'inbox'...
Later! OL JR :)

[El Cheapo]

If it hasn't been mentioned, what about a milk crate?

[rocketsmith]

Outwater Plastics sells 5/8" x 5/8" x 3/8" thick white or black plastic egg crate louver. Product # L2-wh for white. outwater.com

[Bernard de Go Mars]

Hello guys !

This old thread is interesting, but it would be useful to know if you want (wanted ?) to do a static rocket with grid fins or a realy flying rocket .
In the later case, it must be said that grid fins does not stabilize the rocket with their drag but with their lift.

I worked (hard) some years ago to calculate the lift of grid fins, so that I can tell you the equivalent lift area of a grid fin is somewhat 2,5 its frontal area (the area of its frame).

In the other side, you can stabilize a rocket by installation of grid fins that works really by their drag.
In such a case, the moment of stabilisation will be twenty time lower...

Friendly yours,

Bernard de Go Mars

[cruiten]

Hello guys !

This old thread is interesting, but it would be useful to know if you want (wanted ?) to do a static rocket with grid fins or a realy flying rocket .
In the later case, it must be said that grid fins does not stabilize the rocket with their drag but with their lift.

I worked (hard) some years ago to calculate the lift of grid fins, so that I can tell you the equivalent lift area of a grid fin is somewhat 2,5 its frontal area (the area of its frame).

In the other side, you can stabilize a rocket by installation of grid fins that works really by their drag.
In such a case, the moment of stabilisation will be twenty time lower...

Friendly yours,

Bernard de Go Mars

Check out the Project Platypus rocket from the Cal Poly Pomona University USLI team for the 2013 NASA University Student Launch Initiative competition.

The Platypus is a 4" diameter grid fin stabilized rocket that is about 12 feet long, you can find out more here: http://www.cppusli.com/

Cor

[Bernard de Go Mars]

Hello!
And thank you very much for your answer, Cruiten.

The explanations I've read about the PLATYPUS project shows that the braking created by the grid fins was really used to reach a specific altitude by braking with the grid fins at a certain time.
This is a very special case.

I wrote some years ago a long text on the problem of the lift to be expected for Grid so that I know that, in the general case, engineers rather try to minimize drag of the grid fins.

I will answer you as long tomorrow.

Friendly,

Bernard

[cruiten]

Bernard,

It is my understanding that the Platypus is supposed to fly this weekend as part of the University Student Launch Initiative (USLI) competition in Alabama.

It is definitely a neat rocket...

Cor

[Bernard de Go Mars]

Hello Cruiten,

Yes it is an neat rocket.
To my knowledge, this rocket is the first amateur rocket (non professional) using grid fins ! This is a nice performance !

I made some calculus about the grid fins of Platypus.

The Cx of these grid fins seems to be rather bad (due to the manufacturing difficulties : all the members that compose them are very thick).

I am very disturbed by the choice of unities in the texts describing the rocket (inches, lbs, fps, etc.) : very unusual choice, not really international, neither even less scientific. It would have been better to choose adimensional coefficients (Cx and Cn) these adimensional coefficients being used everywhere in the Universe (and therefore by the extraterrestrials).

Nevertheless, concerning what I meant previously, in normal flying (with the fin at right angle) :

At 2° incidence, the drag produces a stabilizing force of 0,24 lbs when the lift gives 3 lbs (i.e. the eighth).

I'm sure that the Cx can be lessened to half with another producing mode.


As regards the lift of the grid fin, I will also try to make calculus.

Some years ago, comparing all the grid fins I founded (but not the ones of Platypus), I made the proposal of a simple formula to find out (in subsonic) this lift in my (too long) text :

http://perso.numericable.fr/gomars/port_pan_cell.doc


...text in which the Drag is also approached.

I think this is the only text of this kind on this issue, on the Web.

Friendly yours,

Bernard

[Bernard de Go Mars]

Hello Cruiten !

I made some calculation about the lift of the grid fins of Platypus.

From the position of the center of pressure as it is drawn by the project members, it can be concluded that the whole grid fins develop a Cnalpha of 13,5 (in reference to the nosecone area ), but in reference to their own passing area, of only 2,21.

I find this Cnalpha a bit weak though it was deduced of the wind-tunnel tests (without influence of the cylindrical body, I guess) : in fact, the internal Lift (due to the deflection of the air passing inside the cells of the grid fins) may be thought to be 2 (in reference to the passing area of the grid fins) as it is easy to demonstrate.

Friendly yours,

Bernard