Lakeroadster's Cygnus Probe Ship

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lakeroadster

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Spurred on by @jgavins odd roc challenge thread here and another discussion about the Cygnus Probe Ship here I'm going to take a stab at building a Cygnus Probe Ship.

It's a BT-55 based and 29mm powered. I won't know until I get it mocked up just how much nose weight it will need since Open Rocket doesn't take into account the stability increase due to the conical rear segment.

I did a quick CAD sketch in order to pull dimensions to input into Open Rocket.

Next up, I'll make some drawings so I can start the build.

Cygnus Probe CAD 003.JPG

2022-01-17 Cygnus Probe Open Rocket Simulation.jpg Cygnus Probe Dwg Sheet 1 of 2 Rev 00.jpg Cygnus Probe Dwg Sheet 2 of 2 Rev 00.jpg Estes Cygnus Probe 001.jpg
 

Dotini

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Spurred on by @jgavins odd roc challenge thread here and another discussion about the Cygnus Probe Ship here I'm going to take a stab at building a Cygnus Probe Ship.

It's a BT-55 based and 29mm powered. I won't know until I get it mocked up just how much nose weight it will need since Open Rocket doesn't take into account the stability increase due to the conical rear segment.

I did a quick CAD sketch in order to pull dimensions to input into Open Rocket.

Next up, I'll make some drawings so I can start the build.

View attachment 500301
View attachment 500302 View attachment 500303 View attachment 500304 View attachment 500307
Very nifty!
I'm quite taken with those landing pads. I bet they would be a very useful source of base drag.
 

lakeroadster

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@neil_w the Open Rocket simulation I did shows poor performance in regard to apogee, even with a 29mm motor. I find that kind of strange, for a rocket that only weighs 5.5 ounces without a motor?

I know this rocket is a turd from an aerodynmaic perspective, and I'm ok with a low apogee, but what's your take on the simulation?
 

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neil_w

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@neil_w the Open Rocket simulation I did shows poor performance in regard to apogee, even with a 29mm motor. I find that kind of strange, for a rocket that only weighs 5.5 ounces without a motor?

I know this rocket is a turd from an aerodynmaic perspective, and I'm ok with a low apogee, but what's your take on the simulation?
Wow, that is some model.

With so much going on it is hard to pinpoint any one thing but it is reasonable to guess that the accumulation of drag from the many discontinuities is the reason. Here's a small experiment to support that theory. First, the sim as-is:
1642602162061.png

I changed the forward ring ("External Ring BT-55 Body Tube") to be the BT55, to eliminate that particular discontinuity, and got this:
1642602279799.png

So that's an extra 27' (on the F) just from eliminating one out of very many discontinuities.

I would speculate that the error bars on the simulation get larger and larger with each discontinuity, so I'm not sure how much you can trust what you're getting there, other than the general conclusion that "this rocket is draggy". :) What I would do is create a second version of this, with discontinuities removed completely, to give you a "best case" sim, and then figure that real-world performance will be somewhere in between the two. This is similar to what I did on my Shear Insanity build, which suffers similar problems.
 

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Just took a quick look at this but wondering - Do body tubes factor into CP? I do not think they impact CP in the same way as transitions do. May need to put minimum length transitions on either end of a body tube to get it to factor into CP.
 

lakeroadster

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Just took a quick look at this but wondering - Do body tubes factor into CP? I do not think they impact CP in the same way as transitions do. May need to put minimum length transitions on either end of a body tube to get it to factor into CP.

To test your theory I went into the model and added transitions (that are 0.001 long), between the stack of body tubes that made the flat heads between the mast and the BT-55, re-ran the simulation and it changed the apogee from 437 feet... to 306 feet. :dontknow:

Went back to the base simulation and changed the stack of body tubes that made the flat heads, bewteen the mast and the BT-55 into transitions, and re-ran the simulation. The apogee changed from 437 feet... to 436 feet. So negligible change.

Wow, that is some model.
Thanks! A bit time consuming to create, but a lot of fun.

What I would do is create a second version of this, with discontinuities removed completely, to give you a "best case" sim, and then figure that real-world performance will be somewhere in between the two. This is similar to what I did on my Shear Insanity build, which suffers similar problems.

I changed the stack of rings (body tubes) at the top of the barrel section to a single transition and deleted the landing gear. The simulation now shows an apogee of 770 feet, instead of 437 feet. My mindsim senses somewhere between the two.

On a side note: This version looks like Major Nelson's Genie's Bottle.. maybe another build.. for another day?

2022-01-19 Cygnus Aero 001.jpg 1642612387503.png
 
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BigMacDaddy

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To test your theory I went into the model and added transitions (that are 0.001 long), between the stack of body tubes that made the flat heads between the mast and the BT-55, re-ran the simulation and it changed the apogee from 437 feet... to 306 feet. :dontknow:

Went back to the base simulation and changed the stack of body tubes that made the flat heads, bewteen the mast and the BT-55 into transitions, and re-ran the simulation. The apogee changed from 437 feet... to 436 feet. So negligible change.


Thanks! A bit time consuming to create, but a lot of fun.



I changed the stack of rings (body tubes) at the top of the barrel section to a single transition and deleted the landing gear. The simulation now shows an apogee of 770 feet, instead of 437 feet. My mindsim senses somewhere between the two.

On a side note: This version looks like Major Nelson's Genie's Bottle.. maybe another build.. for another day?

View attachment 500543 View attachment 500544

The reason that the first big change happened is that OR is not calculating any resistance / drag or CP for the nose unless it has a nose cone or transition. I think the same thing happened with your Bottle Rocket simulation - until you put a really short / flat nose cone on there it basically ignores the impact of the front of the rocket and forecasts unrealistic altitudes and gives inaccurate stability estimates (not that the final estimates are totally accurate either).

The other CP effects may cancel each other out a bit since there are draggy rings in front and rear -- I am more thinking about CP location than max altitude so the .001 transitions will better take into account drag across model I think.

I also noticed something as I was messing with this -- putting transitions on front and back of element does not affect CP much but just putting a transition on the back of the body-tube piece seems to have the biggest impact and shifts CP more. I am not sure why.
 

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The reason that the first big change happened is that OR is not calculating any resistance / drag or CP for the nose unless it has a nose cone or transition. I think the same thing happened with your Bottle Rocket simulation - until you put a really short / flat nose cone on there it basically ignores the impact of the front of the rocket and forecasts unrealistic altitudes and gives inaccurate stability estimates (not that the final estimates are totally accurate either).

The other CP effects may cancel each other out a bit since there are draggy rings in front and rear -- I am more thinking about CP location than max altitude so the .001 transitions will better take into account drag across model I think.

I also noticed something as I was messing with this -- putting transitions on front and back of element does not affect CP much but just putting a transition on the back of the body-tube piece seems to have the biggest impact and shifts CP more. I am not sure why.

The top of the mast, on the original sim that I posted.. is a nose cone.

I'm not really worried about CP. It's seemed to me based on past sim's that OR doesn't sim base drag well. I'll swing test it once it is built, and add nose weight to make it stable. Then I can plug that data into OR and see what it states. Reverse Engineering.

The fact that Estes built a working prototype gives me confidence the profile will be stable. But we'll see.
 
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jqavins

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Open Rocket doesn't take into account the stability increase due to the conical rear segment.
That doesn't ring true. If OR doesn't account for a transition's effect on CP then it's pretty useless, and I know it's not useless. How did you model the back end? It looks like a pair of transitions, one increasing (as you move aftward) and one decreasing. The increasing one pulls the CP down and the decreasing one pushes it back up.
It's seemed to me based on past sim's that OR doesn't sim base drag well.
Now that I believe. I can't speak to OR, but I know that RS doesn't take base drag into account at all in computing the CP. And there's a work-around for it. See Peak of Flight # 162. That will make the model even draggier, so ignore the altitude results.

I changed the stack of rings (body tubes) at the top of the barrel section to a single transition and deleted the landing gear...
View attachment 500543
It also looks like an astronaut's capsule with a launch abort tower on top. Maybe you could... Never mind.
 

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If OR doesn't account for a transition's effect on CP then it's pretty useless, and I know it's not useless. How did you model the back end? It looks like a pair of transitions, one increasing (as you move aftward) and one decreasing. The increasing one pulls the CP down and the decreasing one pushes it back up.Now that I believe.

Thanks Joe, that makes sense.
 

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The increasing one pulls the CP down and the decreasing one pushes it back up.
Correct.

OR *will*, to the best of my understanding, model the base drag' contribution to Cd. What it will *not* do is model the effect of the base drag on Cp. That's where the base drag correction hack comes in. Not sure if it's needed here; the tail end is not that large.
 

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Correct.

OR *will*, to the best of my understanding, model the base drag' contribution to Cd. What it will *not* do is model the effect of the base drag on Cp. That's where the base drag correction hack comes in. Not sure if it's needed here; the tail end is not that large.
Don't forget about the landing pads.
 

lakeroadster

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Mike Dorffler's posted on the Ye Olde Rocket Forum, 04-15-2009.... (Here's a link )

"The Cygnus Probe got killed by the Disney marketing people too. This was after we had actually produced about 5,000 kits and were in the warehouse ready to ship. Disney, after the initial approvals in the early work, decided to change their mind, They didn't like Wayne's rendition afterall, hated the kit panel, and didn't like the decal either. They decided it wasn't represenative enough of the movie vehicle and since they had the final word, it was killed. We had considered changing the name and repackaging it but decided it wouldn't work. End of Cygnus. Sorry again, guys. "

I modeled the Estes version.

I spent some time on the internet trying to find actual photo's of the Cygnus Probe from The Black Hole Movie. There aren't many views of the probe in the movie, but the one's there are show that the movie version is quite different than the Estes catalog version. The movie probe ship appears to be more aerodynamic with respect to the nose cone and the external rings near the top of the ship.

Also where the legs attach are different, that was an oversight on my part.

I revised the model to look more like the actual movie version. I also rented the movie for $3.99... Spoiler Alert... it's pretty horrible when compared to the 1st Star Wars movie that was released 2 years earlier in 1977, from a special effects perspective. The best part of The Black Hole is Slim Pickens as robot B.O.B. ...

Cygnus Probe Ship From The Black Hole Movie 001.jpg Cygnus Probe Ship From The Black Hole Movie 002.jpg Cygnus Probe Ship Rev 00 vs REv 01.jpg Old_B_O_B_Screencap_13.jpg
 
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lakeroadster

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lakeroadster

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OK, if that's the actual model, then what the heck was Disney's problem with the proposed Estes design? Looks like a pretty good approximation to me (at least from the one existing catalog pic).

Agreed.

The Estes model is a bit wider in the lower barrel area.. maybe they had to do this to make it stable?

Maybe because it was silver and not gold?

:questions:

Cygnus Probe Disney vs Estes.jpg
 
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lakeroadster

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Upon further review... Disney's own models must have been different. If you superimpose their own model, onto an actual screen grab from the movie, they don't appear to match.

Look at the top domes... not even close.

Cygnus Probe Disnet vs Disney.jpg
Cygnus Probe Ship JPS vs Disney.JPG
 
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