Mobius Shroud Effect on Flight?

[Starfire73]

I just went from a Universal Astrocam, which is quite small and light, to a much bigger Mobius ActionCam. I tried my first flight with the Mobius on my 4" LOC EZI-65, on an I140W.

I have to say, I was very disappointed in the flight. OR simmed it out at about 2,200' at apogee. However, I only got about 1,600 and more importantly the rocket went about 1,200' up wind. It was nearly horizontal at the end of the thrust phase.

I don't think it weather cocked per se, but it did have the appearance of a strong weather cock. I think the Mobius camera shroud/mount acted like an air-brake on one side of the rocket and pulled the rocket in the direction it flew. The winds were only 5 mph, and this rocket never noticeably weather cocked in three flights with the much smaller Universal Astrocam.

What are your thoughts on it? Do you have any experiences like this? Is the asymmetrical drag of the Mobius pulling the rocket off course from straight up?

 

[Titan II]

No problems here with similar camera and various rockets.

 

[kjhambrick]

Interesting topic @Starfire73 !

But I have nothing but questions and a lot of silly conjecture.

Following this thread.

Q[1]: did the motor start cleanly ?

Q[2]: how long is your launch rail / rod ?

Q[3]: what was the 'Velocity off the rod' reported by your OR Sim for your launch rail ?

Q[4]: could you see the position of the camera housing while the rocket was in flight ? If so, did it seem to be upwind, downwind or neither ?

Q[5]: EDIT: which Moibus Action Cam did you purchase ?

Q[6]: EDIT: what are the dimensions of the housing ?

-- kjh

p.s. Thanks for the .ork file: @Starfire73's EZI-65 OR File

 

[Buckeye]

Q[7]: What was the measured mass of the rocket, sans motor?

Many people fly big cameras on small diameter rockets with little effect on trajectory. I don't think asymmetric drag is the problem here.

 

[kjhambrick]

@Buckeye --

That's the best Q of all

-- kjh

 

[jkovac]

I have flown a number of rockets with Mobius cameras in Additive Aerospace external shrouds, and I have not seen what you are describing.

 

[Banzai88]

I have flown a number of rockets with Mobius cameras in Additive Aerospace external shrouds, and I have not seen what you are describing.

I have flown a number of rockets (several in the EZI-65 category, and many smaller) with RunCam2 4K cameras, which are much bigger than the Mobius, also with Additive Aerospace shrouds, and I have also not seen anything like the OP describes.

 

[Starfire73]

Thanks for the assistance and for diving into this with me. I will try to answer these as succinctly as possible.

Q[1]: did the motor start cleanly ?

R: Yes, it was an AT I140W-10

Q[2]: how long is your launch rail / rod ?

6’ 10/10 Rail

Q[3]: what was the 'Velocity off the rod' reported by your OR Sim for your launch rail ?

R: 65.1 fps

Q[4]: could you see the position of the camera housing while the rocket was in flight ? If so, did it seem to be upwind, downwind or neither?

R: The Mobius Camera was mounted on the NW facing side of the rocket. The pink lines in the photos indicate north. Wind was from the WNW at 5 mph.

Q[5]: which Mobius Action Cam did you purchase?

R: Not sure on more specifics, photo attached.

Q[6]: what are the dimensions of the housing?

R: Inverted Pursuits Lab, Mobius ActionCam Shroud. 102 mm long, 39.3 mm wide, 26.4 mm high

Q[7]: What was the measured mass of the rocket, sans motor?

R: 4.6 lbs.

• Launch Data from OR is attached.
• .ork file (customized for this launch only) is attached. You'll notice I added the camera in the OR file. It's the right length, but the width and height were adjusted to reflect the same surface area in of a square object simmed in a round shape.
• I will provide a link to the onboard video when it's uploaded to YouTube

 

[Starfire73]

YouTube video of onboard camera.

EZI-65 on board video, YouTube

This was one of the few launches (unfortunately) in which I did not get any video from the ground.

 

[OzHybrid]

It's a white lightning composition. Did it do any chuffing before taking off?
Edit: video shows clean ignition.

 

[kjhambrick]

@Starfire73 --

Did you ever fly your EZI-65 with the Universal AstroCam ?

Q8: The video where it was damaged was from a different rocket but maybe you've got video from a similar flight ?

The video you posted for the I140-W flight did roll a bit but not too bad ...

Your @Starfire73 EZI-65 file listed the dry mass of your EZI-65 as 1.5 Kg but the new dry mass for this I140 flight was 4.6 Lb / 2.1 Kg.

The Mass and CG were overridden for the Stage in your .ork file.

When I changed the Mass Override for the Stage from 1.5 Kg to 2.09 Kg, the velocity off the rail was only 44 ft/sec or 30 mph.

Attached your .ork with a new mass override.

If the wind was 5 mph, then the initial AoA off the rail would be about 9.5 deg ...

Maybe the extra mass and lower speed off the rail explains the weathercocking / gravity turn and more thrust will 'fix' it ?

HTH !

-- kjh

These are the new sims from your original .ork with a 2.09 Kg Dry Mass:

$ get-or-sims.sh -SA /home/tmp/EZI-65_LOC_PRECISION_PK-64.ork

# Title     | Flight Sim Data Extracted from /home/tmp/EZI-65_LOC_PRECISION_PK-64.ork -- Dry Mass = 2.09 Kg ( Version = C30725 )
# Command   | /home/konrad/prj/app/dev/blueraven/tst/get-or-sims.sh -SA /home/tmp/EZI-65_LOC_PRECISION_PK-64.ork
# Sorted by | Altitude
# RunDate   | Thu Jul 27 06:07:16 CDT 2023
#
# Config       |    MaxAlt |   VelRail |    VelMax |   GMax |      Mach |  ApogeeAt |    LandAt |   VelLand | MotSize | Delay | SimName
  G80T         |       434 |      34.2 |     142.7 |   3.66 |      0.13 |       5.9 |      21.9 |      26.8 | 29x124  |   6.0 | Simulation 2
  H100W_DMS    |      1055 |      37.7 |     239.9 |   4.69 |      0.22 |       8.9 |      47.5 |      27.1 | 38x153  |   8.0 | Simulation 1
  HP-H45W      |      1542 |      28.7 |     239.9 |   2.62 |      0.22 |      11.6 |      65.6 |      27.6 | 38x203  |   8.0 | Simulation 3
  HP-H135W     |      1618 |      49.2 |     351.8 |   8.14 |      0.32 |      10.1 |      79.6 |      23.3 | 29x216  |   8.0 | Simulation 1 (5-10)
> HP-I140W     |      1832 |      44.3 |     360.0 |   6.53 |      0.32 |       9.5 |      73.9 |      28.5 | 38x203  |   6.0 | I140-6W - SU 38x203mm
  HP-I205W     |      2052 |      55.7 |     404.2 |  13.00 |      0.36 |      11.2 |      86.5 |      27.2 | 29x305  |  10.0 | Simulation 4
  J450DM       |      5549 |      64.3 |     905.1 |  15.68 |      0.82 |      16.6 |     191.9 |      30.7 | 54x359  |  14.0 | Simulation 5

 

[Buckeye]

@kjhambrick is correct. This rocket was underpowered at rail exit.

A quick sim on Thrustcurve yields a rail speed of 43 ft/s, not 65. You need to fix the mass in your ork file.

I assume the length of the 1010 rail is 6 ft. The effective guidance length is from the top button to the top of the rail. I used 5 ft in the simulation, which is still probably generous when looking at your pics.

Assuming you launched in the afternoon on 7/22/2023, the wind measured at Flint Bishop Airport averaged more like 10 mph during this time.

All these things add up to low rail speed and some AOA that sent the rocket on a slow, arcing, trajectory.

 

[Starfire73]

The latest ,ork file (the "TRF" version) is the actual flight. Since the original post of the .ork file I added the Mobius, Camera Shroud, and a Featherweight Tracker and sled in the payload bay; hence, the TRF version. This added another appx. 5 oz.

OR Data:

• The "TRF" version of the file shows me: 60.9 oz w/o motor, 73.9 oz (4.6 lbs.) with the I140W.
• The velocity off the rail (adjusted down to 5') is showing 48.6 fps
• Winds did show WNW at 5 mph at the time of the launch 11:57, and I would agree with that based on my observations at the time of launch.
• I am getting an AoA in OR of about 8 degrees at launch rod clearance, but to be honest, I'm not 100% confident I'm interpreting AoA in OR correctly. I think it's the angle of the rocket as compared to the flight path of the rocket (sort of like a yaw for rockets) isn't it? So what would show the angle of the flight path in OR? Would that be Vertical Direction (Zenith)
• KJH - what did you use to generate that sim data? Is that from Thrust Curve?

Finally, I have launched this rocket on an H135, a G80 (12 mph winds) and an H100, all with the smaller Universal AstroCam and all under wind conditions at least as windy is the I140, and in all three flights it flew relatively straight up with no weather cocking. Maybe I got lucky? If you look at the Google Earth flight path of the I140 flight (w/Mobius) below, the rocket trajectory was practically 20-30 degrees from vertical. That's why even though it only reached an altitude of 1,680' it traveled over 1,100' to the west.

Thank you guys for taking the time to look through this, I'm really learning a lot here!

 

[Buckeye]

You are lucky, or your definition of a straight flight is different than mine. The motors you mention are very wimpy for a 4" L2 sized rocket. G80? That's barely 40 ft/s off the rail into 12 mph wind.

Still not clear to me if you actually measured the mass of the rocket, or you are quoting what the ork file "shows" you. I am assuming the best-case scenario for you in Thrustcurve based on what you mentioned so far: 56 oz without motor (61-5).

 

[Starfire73]

You are lucky, or your definition of a straight flight is different than mine. The motors you mention are very wimpy for a 4" L2 sized rocket. G80? That's barely 40 ft/s off the rail into 12 mph wind.

Still not clear to me if you actually measured the mass of the rocket, or you are quoting what the ork file "shows" you. I am assuming the best-case scenario for you in Thrustcurve based on what you mentioned so far: 56 oz without motor (61-5).

I actually weighed the rocket (sans motor) fully equipped. I did the mass override based on the 60.9 oz dry weight. OR added the motor weight for the total of 4.6 lbs (which was confirmed at the LCO table).

For the previous flights (H135, H100, G80) the rocket was about 6 oz lighter (NO featherweight/sled in the payload bay) and had less drag with the much smaller camera. Even on the G80 flight it flew straight up, an excellent flight to 700’ (JL Alt2).

 

[kjhambrick]

The latest ,ork file (the "TRF" version) is the actual flight. Since the original post of the .ork file I added the Mobius, Camera Shroud, and a Featherweight Tracker and sled in the payload bay; hence, the TRF version. This added another appx. 5 oz.

OR Data:

• The "TRF" version of the file shows me: 60.9 oz w/o motor, 73.9 oz (4.6 lbs.) with the I140W.
• The velocity off the rail (adjusted down to 5') is showing 48.6 fps
• Winds did show WNW at 5 mph at the time of the launch 11:57, and I would agree with that based on my observations at the time of launch.
• I am getting an AoA in OR of about 8 degrees at launch rod clearance, but to be honest, I'm not 100% confident I'm interpreting AoA in OR correctly. I think it's the angle of the rocket as compared to the flight path of the rocket (sort of like a yaw for rockets) isn't it? So what would show the angle of the flight path in OR? Would that be Vertical Direction (Zenith)
• KJH - what did you use to generate that sim data? Is that from Thrust Curve?

Finally, I have launched this rocket on an H135, a G80 (12 mph winds) and an H100, all with the smaller Universal AstroCam and all under wind conditions at least as windy is the I140, and in all three flights it flew relatively straight up with no weather cocking. Maybe I got lucky? If you look at the Google Earth flight path of the I140 flight (w/Mobius) below, the rocket trajectory was practically 20-30 degrees from vertical. That's why even though it only reached an altitude of 1,680' it traveled over 1,100' to the west.

Thank you guys for taking the time to look through this, I'm really learning a lot here!

@Starfire73 --

You're welcome -- I am learning a lot too so please take my comments with a grain ( or a shaker full ) of salt.

Thank you for sharing your flight data !

One more ... Q[9]: did you fly an accelerometer ?

When someone asks an interesting Q about OR, I try to find an OR.ork file for their rocket.

This is what I recall ...

I found Your EZI-65 OR.ORK File here on TRF ( ! woo hoo ! ).

I ran the I140 Motor and got very reasonable results. The reason I didn't ask @Buckeye's Q[7] is because you had a Dry Mass Override ( 1.5 Kg ) and a CG Override so I assumed it was for this same rocket. Then you answered Q7: A7 = 4.6 lns sans motor ( 2.09 Kg )

I had a little difficulty modifying the dry mass because I didn't know about setting overrides for the Stage but I found it and changed the Mass Override:



I also didn't notice that you posted a new .ork file on Post #8 in this Thread so I used a different .ork than you.

The motor thrust curve is whatever was provided with OR.

If you're asking about the 'sim summary' for your EZI -- that is the output from an awk script I wrote to extract 'interesting' goodies from an OR.ork file.

I've posted it here on TRF: OpenRocket feature idea: cert flight packet

One new thing I see from your .kml plot is that your rocket traveled 'west' during boost, coast and drogue but then it took a -135 degree turn ( ese ) when the main came out ???

These google earth plots are new to me -- I've not seen a lot of them -- Isn't that an odd trajectory for the full boost-coast-recovery cycle ?

Anyhow, trust in thrust

More discussion please !

Thanks !!

-- kjh

p.s. EDIT - I just now opened your new PK-64_EZI-65-TRF_Version.ork from post #8 and I see the 80 gm moibus as well as the updated mass.

Very clever OR tricks to add the 'moibus wart' to the rocket

Thanks @Starfire73 !

 

[Starfire73]

Quick clarification on Q7 respoonse. I misspoke - the 4.6 lbs actual (and sim), was with the I140 motor. It was 60.9 oz (3.81 lbs) actual, without the motor.

For the flight (and KML file):

• Rocket traveled 1,232' west during boost and coast, came down fairly quick and landed about 115' east of it's western most point. The rocket landed 1,136' west if the launch pad.
• The intent was a JLCR @ 300’; however, the chute got tangled up in the shock cord and never fully deployed. Thankfully it landed in some pretty tall grass/bush (yup… got the poison ivy and paper cuts to prove I trudged through a thousand feet of brush). I think the chute got pulled out of the chute release at ejection. Maybe because of the more violent higher speed ejection? Maybe because of the tangled mess it was in? I know one contributing factor was the stupid way I packed the cute and shock cord. I've been in rocketry for 50 years, and for some stupid reason I slid the chute and protector burrito in first and put all that shock cord in last. The chute got ejected right in to the bulk of the coiled up shock cord... duh! I know better... not sure what I was thinking on that one.
• The 10 second motor delay was way too long for a rocket on that trajectory (it was drilled for 10 seconds, but actual observation was 12 seconds). Probably would have been just right if it had stayed vertical.
• I isolated my EZI flights on my JLAlt2 log if anyone is interested (attached). This might have the acceleration data you were looking for.

 

[kjhambrick]

One last Q and I can't think of more ...

There is a CG Override in the STAGE Section for the updated .ork at 35 inches but when I look at the Rocket Design view it is listed as 38.335 inches from the nose.

Do you understand how that works in OR ?

Q[10] - where was the actual flight-ready CG ?

-- kjh



p.s. thanks for the additional data. There is acceleration but IIANM, it is the 2nd derivative of altitude-vs-time so it doesn't tell much

 

[Starfire73]

One last Q and I can't think of more ...

There is a CG Override in the STAGE Section for the updated .ork at 35 inches but when I look at the Rocket Design view it is listed as 38.335 inches from the nose.

Do you understand how that works in OR ?

Yes, the ”Stage” CG measurement is determined and set w/o motor. That way you can plug different motors in to the motor mount and see how the CG is affected. I’ll bet if you select no motor under the Flight Configuration drop down, it’ll go back to 35”.

Q[10] - where was the actual flight-ready CG ?

-- kjh



p.s. thanks for the additional data. There is acceleration but IIANM, it is the 2nd derivative of altitude-vs-time so it doesn't tell much

The actual total weight of the rocket with the motor added was exactly what OR predicted, so I didn’t physically check the CG after determining the CG without the motor and doing the override.

 

[mikec]

As best I can tell from the video, and this is consistent with the tracker info, it left the vertical pretty much right off the rail. I don't think the camera shroud would have much effect aerodynamically (I've flown them a lot and never seen anything noticeable) but even if it did, I wouldn't expect it to be so strong at low speed. I think this was something else.

I'm also not sure if OR can appropriately model an asymmetric surface like this.

I'd try flying it again with the same motor and see if you get similar behavior.

 

[Starfire73]

Agreed @mikec! I’m confident OR can model the drag, effect of CP, CG, Mass, etc. But you’re right. I don’t think OR can simulate the pull (if any) an object‘s asymetrical drag will cause.

I will try another flight with it, but probably not until winter when we can go to our winter launch site - empty farm fields. I’m not risking trudging that far through the brush again.

 

[waltr]

I have seem many flights where the rocket left vertical just past the rail. And many where the same rocket with same motor and no other mods went straight off the rail.
Why? We don't know that except sometimes the fight does not go as planning or as it went previously.

 

[Starfire73]

I have seem many flights where the rocket left vertical just past the rail. And many where the same rocket with same motor and no other mods went straight off the rail.
Why? We don't know that except sometimes the fight does not go as planning or as it went previously.

Ya‘ know… that sums it up quite well!

 

[b.wieting]

I had the same question when I first flew a Mobius/Additive on a smaller (4inch) rocket.
Your video shows an interesting shift at about 6 seconds--the rocket appears to freeze or even reverse roll before roll sets in.
I first flew mine on my MegaMagg L2 cert flight. Video shows pretty vertical with fairly slow roll (~ 1/3 rps). Stretched for DD, subsequent flights have had scattered landings, from 1/4mile to 20ft from the pad.
Fitting the Mobius to my old Polecat V2, video showed much greater roll rate (~2.5 rps).

 

[kjhambrick]

Very interesting ... Good eye, @b.wieting !

There are better frames in the video but I am not as good at capturing YouTube as @tsmith1315

The smoke trail starting at ground level should follow the rail -- it should be more or less vertical.

But then @Starfire73's EZI-65 made a sharp turn just before this frame:



Not an arc -- it was a sudden tilt.

I dunno what it means but it is there in the video.

Interesting stuff !

-- kjh

 

[teepot]

Two things. How can you measure Cg without a motor in it? Or do you not balance the rocket on a knife edge to find CG. And my gut feeling when I heard the weight and motor was, that's not enough motor. I don't use any computer sims when I build my rockets. Just graph paper and experience. I do use Thrustcurve though.

 

[OzHybrid]

Two things. How can you measure Cg without a motor in it? Or do you not balance the rocket on a knife edge to find CG. And my gut feeling when I heard the weight and motor was, that's not enough motor. I don't use any computer sims when I build my rockets. Just graph paper and experience. I do use Thrustcurve though.

In OR when you override the cg for the whole rocket(sustainer, edit) it should be without the motor loaded. When you then load the whole motor in the sim, it will be correct. You can balance it horizontally on your finger for close enough to be able to check if you are in the right ballpark with at least 1 caliber.

 

[Starfire73]

Two things. How can you measure Cg without a motor in it? Or do you not balance the rocket on a knife edge to find CG. And my gut feeling when I heard the weight and motor was, that's not enough motor. I don't use any computer sims when I build my rockets. Just graph paper and experience. I do use Thrustcurve though.

The I140 is plenty of motor. I’ve had the EZI up on a G80, H100, H135 prior to the I140. All (except the I140) flew pretty much straight up vertical. See post #17, my flight logs from the Jolly Logic Alt2 are attached.

 

[teepot]

In OR when you override the cg for the whole rocket(sustainer, edit) it should be without the motor loaded. When you then load the whole motor in the sim, it will be correct. You can balance it horizontally on your finger for close enough to be able to check if you are in the right ballpark with at least 1 caliber.

Oh. I tried OR. Couldn't get past go. To find CG I load the rocket flight ready. Then balance the rocket on the edge of a drafting triangle. I put the biggest motor I would fly in it to do the balancing.

 

[Starfire73]

I just balance it on my finger. With no motor, but everything else loaded and ready. I’m thinking that balancing on my finger is accurate to +/- a quarter inch. That’s close enough for me. The main point is the relation of the CG to CP, and I’ll never call it so close that a quarter inch either was makes the difference.