anyone done grid fins?

Hello fellow rocketeers,
Have any of you used or have seen someone else use grid fins on a rocket? And if so, what was it made out of and did it work well? In case you don't know what I am reffering to, there is a picture below.

They work basically by drag... using drag effects to shift the CP rearward, specifically. So if you're looking for performance, you'd do FAR better with standard type fins.

They're certainly doable, but as to the "how", "what materials", or "how well did it work or hold up" I can't speak to that...

If you're doing a particular scale subject that needs them, go for it. Otherwise, you'd do better performance-wise with regular fins.

Good luck! OL JR

Do a search for NASA University Student Launch Initiative -- there have been some teams using grid fins. If their documents are still online (they're required to post them, but you're looking for a year or two ago, I don't remember which), you should be able to find some information.

Unfortunately, I don't recall which teams it was that used them. If Ted Cochran sees this, he may remember.

-Kevin

It's doable and they would work. They are effectively like very short tube fins. The correcting moment that they apply are very small at slower speeds. My guess is that at faster speeds the air will "pile up" at the front of the plates and the drag will get quite high, bleeding off the kinetic energy fairly rapidly after motor burnout.

As far as making them, you would have to make them like the dividers for Christmas ornaments. A rectangle with equidistant slots that go halfway into the long side, then interlocking them.

Greg

The big issue I would see is that your simulator's aren't designed for them and thus your altitudes and delays would be way off. Certainly the rocket would be kept at a lower speed and altitude. But in the name of science you should definitely try them. Just put in an altimeter for deployment.


Sent from my iPad using Rocketry Forum

Here's a recent, full scale use of steerable grid fins on the Falcon 9 Reusable rocket from SpaceX - though only used on the descent - wait until about 1:10 in the video. My understanding of them is minimal, but one can imagine that there's a lot of surface area to use.

[video=youtube_share;DgLBIdVg3EM]https://youtu.be/DgLBIdVg3EM[/video]

Yes, Kevin, I remember 3D printed grid fins on at least one USLI rocket at a recent event, perhaps also on a Midwest or Wisconsin Space Grant competition rocket. I'll dig and see whether I can find a photo or other reference.

Mark

However, if your rocket is capable of passing the sound barrier, then grid fins produce less drag then planar fins. Also its probably more trouble than its worth, where normal fins are cheaper, stronger and proven effective. However it would be interesting to use them on a steerable rocket in a configuration like the ones below. And i found the site of the university of alabama rocket girls and their rocket uses grid fins: https://rocketgirls.eng.ua.edu/Rocket and Payload.htm

Can't find any active links to details about this Cal Poly Pomona NASA USLI project. Anyone else with any info on it?:

[video=youtube;xtbxDtibI3M]https://www.youtube.com/watch?v=xtbxDtibI3M[/video]

Winston said:

Can't find any active links to details about this Cal Poly Pomona NASA USLI project. Anyone else with any info on it?:

Click to expand...

I didn't see any team this year using static grid fins for boost.
Auburn had flip out grid fins for altitude targeting I believe.

For a challenge where they only need to go 1 mile, I can see why students are attracted to these draggy structures.

Clip the corners and sweep 'em back, ensure the depth of your grid does not exceed the width or height of your grid cell.

They're not particularly draggy except at transonic speeds. (where shock waves constipate air movement through holes)
At least according to Wikipedia.

I think airbrakes would be more effective if they were going for flip out drag inducing structures.

Nytrunner said:

I didn't see any team this year using static grid fins for boost.
Auburn had flip out grid fins for altitude targeting I believe.

For a challenge where they only need to go 1 mile, I can see why students are attracted to these draggy structures.

Click to expand...

These I believe.

Jim

Nytrunner said:

I didn't see any team this year using static grid fins for boost.
Auburn had flip out grid fins for altitude targeting I believe.

For a challenge where they only need to go 1 mile, I can see why students are attracted to these draggy structures.

Click to expand...

There's another thread here about intentionally draggy designs for small field and impressive low altitude propellant burners that aren't just spools. Grid fin fin cans would be easy to 3D print after STL creation using an openSCAD script which would allow easy scaling and parameter changes by the user prior to generating the STL.

JimJarvis50 said:

These I believe.

Jim

Click to expand...

That's them!

I didn't talk to that team, do you know if they were for altitude targeting or some other purpose?
(other than mimicking SpaceX which pops up every now and then on college teams)

Nytrunner said:

That's them!

I didn't talk to that team, do you know if they were for altitude targeting or some other purpose?
(other than mimicking SpaceX which pops up every now and then on college teams)

Click to expand...

I think they were just for altitude targeting, at least for the time being. I don't recall how the flight went (it was often difficult to hear the PA).

Jim

A scale MOAB would be cool.

I'm an advisor for an IREC team that is using grid fins and active roll control. They are very cool.

Here is a link to what the first iteration looked like. These were static and the flight was performed to better estimate CP.

https://imgur.com/a/4GCMS

They are using a water jet to cut their fins out of aluminum instead of CNC machine them. They can make the lattices thinner.

Edward