Cjl and myself had a brief discussion about this awhile back, as I too am considering putting electronics in the nosecone. We thought that there is two ways around it...

1. Use an accelerometer based altimeter, like the raven, for deployment. When the nosecone is tumbling down for baro main deploy (if the rocket is DD) then the vent holes should act normally.

2. For baro based apogee, set a generous mach delay, even if the rocket isn't predicted to go supersonic. This way hopefully the rocket has slowed to a "decent" speed where turbulent flow is less than an issue before sampling starts.

I personally have 2 Missileworks RRC2 minis and a 1/4 scale Nike, so im looking at #2 if i use electronics in the future. IDK if i will be investing in a flight computer soon, so I might try with what I have and see what happens. As for vent hole placement, as far away from the nosecone hip as possible. This seems to be about 4" down on my PR kit. I'd like to know how it goes if you try it. Right now mine is strictly motor deploy, so I really don't have any experience to back up my suggestions.

Out of curiosity, what electronics are you using? Is it DD? I was thinking of using a tether device, which would be a good device to have for a rocket like this...

Since this is an interesting problem, and I had a bit of free time, I ran some rough CFD sims on a Nike (this one is 1/4 scale, but the general trends should be valid for any of them that are in that size range, or even remotely close). These plots show surface pressure (and the scales are vastly different between the two).

Mach 0.6
Mach 1.2

(clickable links)

Oh, and the actual pressure that the altimeter should read in those is 101325, so the yellow region in the first and the green region in the second are the locations where a port would read reasonably accurately.

Nice sims, they really illustrate the pressure nicely. I guess that as long as the holes are not located right below the nosecone base, it should work out fine. Do you think these patterns hold truer in lower density/pressures, such as the NCR launch site? I saw that the standard you used was 1013.25 hPa, so these pressures are right on for our launch site in Florida.

The general trends should hold, though you're right that the pressures used were sea level standard. I would think the same idea would be fine for our site though, since that's only a pressure difference of 20% or so.

(I'd still use accel or a generous mach delay though, just to be safe)

Oh, and I'm up for a 4 inch Smoke drag race anytime 😀

OK, first off, thanks Chris for that super cool analysis. That graphic is better than any answer I expected to get. Has anyone done one of these DD or mostly just single deploy? May I ask how you guys set yours up? I know Chris has one, is yours altimeter delpoyment? Anyone else?

I intentionally made mine pretty simple, so it's just motor deploy. I didn't want to have a full electronic deploy or anything. If I were going to make it electronic deploy though, I'd put the E-bay as high as possible, and use the nose cone as the main chute compartment. I'm just guessing here though - I haven't really thought about it too much.

Chris - I think that I am going to try a tether for DD as a side project when I get back to Colorado for the summer...seems like the perfect rocket for one. Right now I'm using a TAC-1 48" which brings it in pretty slow, so DD would be nice (especially for the sod farm in Florida - how I miss the recovery area of the Pawnee Grasslands) I think that along with my Intimidator 5 maiden flight should keep me occupied for a bit 🙂

Side note - have u tried the new CTI White? I just launched today on a Pro38 J290 5 Grain, which was pretty impressive. Here is the video:

https://picasaweb.google.com/ChrisDreher1/NEFARLaunches#5593782708323365234

Can you tell me if this is a choppy video? You can watch it up to 1080p, I'm not sure if it is the camera, Picasa, or my computer (i dont have a dedicated graphics card so HD film is a stretch). Also, good luck with the K2045 - that should be amazing

I have tried the white - I flew an I242 in my Nike, and it was a great boost. The video looks fine to me by the way - nice flight. I still need to race you sometime (assuming mine survives the 2045) 🙂

Batman - I forgot about this thread for a while, but I did finish the tether project over the summer. You can find project pictures here, they might be some help if DD in the Nike is still something you are looking at:

https://picasaweb.google.com/103846431504446049036/NikeElectronicsModification#

I tried to put the pics in the most logical order of assembly, feel free to ask questions. I should have this rocket back in Colorado for the summer and hopefully I can make it to a few launches.

fantastic work.

fantastic work.

Thanks!

So here is a data graph from a Stratologger that was flying in the Nike.

https://plus.google.com/photos/103846431504446049036/albums/5653006273001182769/5713317544085396418

A purely baro-based seems to work fine in a Nike nosecone. My vents are a bit oversized (seen in a different picture within the album). This specific flight used motor deploy at apogee, a few seconds too long from optimal.

Without a drogue, the rocket fell at about 52 feet/sec, and 21 feet/sec under the parachute after the tether released. Those decent rates were based off the altitude changes within the 20-30 second and the 40-50 second intervals respectively, when the rocket appears to be stabilized in each phase the decent. The velocity values seem to be all over the place especially in the drougeless decent, so I'm sticking with the above method to figure out decent rates.