Simming camera shroud in Rocksim

I created a fin in Rocksim to be able to sim my Mobius shroud from Additive Aerospace. Weight, dimensions, radial placement, all accurate. I threw the mod on my Madcow Blue Iguana, 2.6" w/54mm motor mount. On an L935, it sims to 17,250' without the shroud. With the shroud, it doesn't even hit 7,500'. I tried a J250 to check low and performance and without the shroud it sims to 7,300' and with it, 3,600'.
The drop off seems hugely excessive to me. Anyone have any flight data with and without a shroud?

Post the Sim? I suspect squared edges and/or rough finish, but that's a blind guess.

Rounded the edges and took apogee on the J250 from 3599 to 3900 even. It was already set to smooth finish.

I have one actual flight on the airframe...Rocksim predicted between 12,200 and 12,600 and i flew to 12,362' so the base modeling is on point.

I’ve flown a 3” Frenzy a few times with & without a shroud on same motor (J525). Lost about 500’ each time when flown with shroud. I’ll have to look at flight data but was like 3800’ without & 3300’ with shroud off top of my head.

timbucktoo said:

I’ve flown a 3” Frenzy a few times with & without a shroud on same motor (J525). Lost about 500’ each time when flown with shroud. I’ll have to look at flight data but was like 3800’ without & 3300’ with shroud off top of my head.

Click to expand...

I buy a 500 foot loss with that motor, 100%. But a 9,000 foot loss for 41 grams (disregarding the aerodynamic forces) on an L935?!? (sim didn't even include the camera, it was just the shroud and hardware).

I fly in 10 days with the J250 DMS, I suppose I will find out how much of an altitude penalty I will pay. I really don't want an internal camera with a mirror...ugh.

Thick fin approximations for things like that are weird. I wouldn't trust that simulated altitude.

Run it on RASAero II.

In the new version of RASAero II (Version 1.0.2.0) we added new Protuberance Drag models, including Streamlined - With Base Drag Protuberance. A Cineroc camera shroud is shown as an example of Streamlined - With Base Drag Protuberance. See Pages 24-29 in the RASAero II Users Manual.


Charles E. (Chuck) Rogers
Rogers Aeroscience

As a note the modeling of the additional drag from the Protuberance is done for subsonic, transonic, supersonic and hypersonic Mach numbers. (If your camera shroud is still on at hypersonic speeds.)

Remember that when you import the Rocksim file into RASAero II, you'll need to add rail guides/launch shoes, and you'll need to put in the correct fin airfoil.


Charles E. (Chuck) Rogers
Rogers Aeroscience

Chuck Rogers said:

As a note the modeling of the additional drag from the Protuberance is done for subsonic, transonic, supersonic and hypersonic Mach numbers. (If your camera shroud is still on at hypersonic speeds.)

Remember that when you import the Rocksim file into RASAero II, you'll need to add rail guides/launch shoes, and you'll need to put in the correct fin airfoil.


Charles E. (Chuck) Rogers
Rogers Aeroscience

Click to expand...

I'm on it! Can't go wrong with an expert recommendation.

Modeling as a fin will probably confuse rocksim. Check the flight profile. It may be instability causing the low altitude.

I will send you my sim file for my 3" Dark Star, that has the same Mobius and Addictive shroud, when I get home later this evening. It sims +- 10%

Buckeye said:

Modeling as a fin will probably confuse rocksim. Check the flight profile. It may be instability causing the low altitude.

Click to expand...

Flight data looks stable, no odd Cg/Cp conflict. But I'm sure the abnormal fin is giving the program fits.

Finally flew my rocket...4,331 feet. 59% of projected altitude.

Rocket didn't spin or twist abnormally during flight which says to me the loads were at least symmetric.

What the video doesn't show well is the fact that when the rocket was about 100 feet off the ground it angled hard into the direction of the shroud (which tells me it was more aerodynamics than weight affecting flight). The rocket headed due west and landed half a like from the pad.

I'm going to push it hard on a CTI L805 at Black Rock in two weeks and if I get less than 10,000' (80% of predicted altitude) I'm going to remove the shroud.