Variable Drag Project

[Rocketjunkie]

Sad ending. This has been a greta project to follow and a good concept to keep rockets on a smaller field. You can test a higher flying motor without a trip to the trees.

Not done yet. Will repair the 4" and build a 7.5". The 7.5" will probably test on 75-3 grain motors. Still have some BT60 size in flyable condition.

 

[jmasterj]

Any updates since last year? This is a really cool project!

 

[Rocketjunkie]

I flew the TV400-6 on a research J220 (54-2G) to 395' Saturday. Had a shroud line tangled over the canopy resulting in a nylon wad recovery. Broke the tube fins off, 5 min epoxy will fix. Still planning on building the 7.5" for the N motor. Will test with 75/3680 research motors. I still have 3 of 4 TV60s flyable. I've been working on my 18 mm motors lately. If you have research forum access, 18 mm motors are in this thread https://www.rocketryforum.com/threads/18-mm-motors.158722/

 

[Rocketjunkie]

I flew the 4" TV400s in all 4 configurations, 0 to 6 plates. All on 54/1280 J330 motors at the SC Freedom launch.
0 plates, 3700'
2 plates, 822'
4 plates, 622'
6 plates, 544'

 

[Sandy H.]

I flew the 4" TV400s in all 4 configurations, 0 to 6 plates. All on 54/1280 J330 motors at the SC Freedom launch.
0 plates, 3700'
2 plates, 822'
4 plates, 622'
6 plates, 544'

Awesome, if you flew the 6 plate on Saturday, I think I saw it, but thought it recovered closer to the 2 plate in the video. Maybe I saw more than one while we were prepping.

I noted a few posts above you mentioned it seems like a 0 plate or 6 plate design. I'm assuming that's because 0 plates is full send and the difference between 2 and 6 plates is kind of trivial, so fly it with all 6 and be very stable.

Have you considered an iteration where you put centering rings in couplers and then insert those in some of the tube fins? I could maybe see using a 38 or 54mm 4" centering ring in 3 of the 6 tubes as maybe a flight that could be closer to 2500' (a guess) if that was a desired.

I think your test-vehicle is awesome. I love the ideas of different inserts for the tubes to achieve different results. I hope you continue down this path and also try some different inserts if they seem interesting.

Sandy.

 

[Rocketjunkie]

The purpose of the project is to build a 7.5" version with a 98 mm mount. Eventually, I should get over 10,000' with no plates and around 1500' with 6 plates on an N800. This will allow an N on almost any field The 7.5" will have 6 plates available, I will use the amount appropriate to the field. I do not plan on carrying this beyond the N motor on small field plans. Others can experiment with different shapes, etc.
Time to build the 7.5"

 

[Rocketjunkie]

Awesome, if you flew the 6 plate on Saturday, I think I saw it, but thought it recovered closer to the 2 plate in the video. Maybe I saw more than one while we were prepping.

I flew the 0 and 6 plates on Saturday, the 2 and 4 plates on Sunday.

 

[Rschub]

I thought about putting a 7.5 in drag plate on my 5.5 in Minnie-Magg for my level 2 cert flight since our field is smallish, I think it might be considered an oddroc though.

 

[lakeroadster]

Feb 8-9 Camden launch. Flew all 4 on E12-4s

No plates 955 ft.
2 plates 261 ft.
4 plates 192 ft.
6 plates 151 ft.
I was still not able to get the Estes altimeters to work, none of them got data on the field. All data was from the PerfectFlite Fireflys.
Time to construct the 4" from LOC parts, 54mm mount and power will be 2 grain 54 mm motors (J244, J275, or Rx J220).
Except for turbulence effects, the forces on the plates won't exceed the thrust of the motor. The 4" involves increasing the glue area and the 7.5" includes stepped bulk plates and threaded rods (in tension). The 7.5" test flights will probably be on Rx M1100s (98/7680).

Way cool. I like how you could see the rocket coning with 4 plates. Ye ole tail wagger!

 

[cjl]

Yes, do this. I don't know about a "very good" measurement of CD, but having accel numbers will be your best chance to compute it from flight data. Be prepared to smooth the accel data before working with it.

Wind tunnel or CFD simulations would be the best choice for drag prediction.

Honestly, I'd trust post-burnout deceleration data more than CFD, unless you are the kind of person that runs CFD all the time for your job or something. CFD is finicky to set up and results are highly dependent on a ton of factors.

Wind tunnel data would be great, but you'd need a pretty big tunnel to get representative free-air data without the model blocking too much of the tunnel cross section.

 

[Buckeye]

Honestly, I'd trust post-burnout deceleration data more than CFD, unless you are the kind of person that runs CFD all the time for your job or something. CFD is finicky to set up and results are highly dependent on a ton of factors.

Wind tunnel data would be great, but you'd need a pretty big tunnel to get representative free-air data without the model blocking too much of the tunnel cross section.

True, CFD is not for the casual hobbyists nor the faint of heart.

Unfortunately, we don't see any of these 3 methods discussed very often on TRF. Someday, I hope to see a hobby-level CFD software for model rocketry (with GPU computing?) and we can put to bed the ancient empirical models and aero estimations used today in the flight simulators.

 

[cjl]

Maybe? I question whether we're anywhere close to being able to do that though. Meshing is still somewhat of a black art to get right, and there are so many fiddly little things with CFD that I'm really not sure a "beginner-friendly" package could do all that much better than we already have with existing sim programs. It is getting better all the time though...

 

[dhbarr]

Maybe? I question whether we're anywhere close to being able to do that though. Meshing is still somewhat of a black art to get right, and there are so many fiddly little things with CFD that I'm really not sure a "beginner-friendly" package could do all that much better than we already have with existing sim programs. It is getting better all the time though...

+1, I keep hoping someone will come up with a pretty-okay OpenFoam recipe that I can follow. Nothing so far, and it's definitely not my area of expertise.

 

[Rschub]

+1, I keep hoping someone will come up with a pretty-okay OpenFoam recipe that I can follow. Nothing so far, and it's definitely not my area of expertise.

https://github.com/jaheyns/CfdOF
https://forum.freecad.org/viewforum.php?f=37

 

[dhbarr]

https://github.com/jaheyns/CfdOF
https://forum.freecad.org/viewforum.php?f=37

HRMMM

 

[Rschub]

I know where all the rabbit holes are....

 

[ljwilley]

wow, cool to hear that someone figured out how to make an estes altimeter work.. no one i know ever did

Don't even try to buy that junk. You can get jolly logic altimeter II which calculates pretty much everything you could want for only $80 which is a good price for what your getting. The Estes altimeter is overpriced for what it is and INSANELY finicky. The jolly logic gives you many times the info about your flight and is much easier to use. I don't know how to get the Estes one to work and I'm not sure I ever will or at least ever want to.

 

[Rocketjunkie]

I wasn't able to get the Estes ones to work. Perfectflite Fireflys work the same way and are reliable and slightly cheaper.

 

[anbhtblr]

For interest in controlling apogee via drag adjustment I suggest checking out the Vanderbilt University SLI team's approach. At this years SLI launch near Huntsville, AL they came within 5' of their predicted apogee in a 4k flight.