Quantcast

Jeff L's unbaked design thread

The Rocketry Forum

Help Support The Rocketry Forum:

kuririn

BARGeezer
TRF Supporter
Joined
Oct 3, 2016
Messages
4,821
Reaction score
2,432
Location
Hawaii
Also the MPC Star Trek rockets comes to mind.
 

Jeff Lassahn

Well-Known Member
TRF Supporter
Joined
Jul 5, 2020
Messages
175
Reaction score
198
Location
Portland OR
Trying out different lengths for the interplanetary ship.
The original -- longer -- and no really lets stay _way_ away from that reactor longer
interplanetary_lengths.png

Currently my favorite is the really long one.

Also thinking that maybe the radiator fins on the rear should be a ring instead of panels. Real spacecraft always use boring easy to make rectangular panels, but rings are cool.
 

jqavins

Joseph Avins
TRF Supporter
Joined
Sep 29, 2011
Messages
3,984
Reaction score
1,467
Location
Howard, NY
I also like the long one best. And the short one least. It looks like a gooney version of the long one.

The real spacecraft use boring panels not just because they're easy, but also because they're efficient as to radiator area per mass. And yes, rings are cool. So how about anther reason for the ring? How about the ring is there to provide additional radiator area as well as a thermal conduction path to equalize the panel temps. And then it would make sense to have two or three concentric rings, with the panels extending beyond the outermost ring.

(And don't look too closely at the "real" thermal performance, with things like shadowing.)
 

Nytrunner

Pop lugs, not drugs
Joined
Oct 15, 2016
Messages
7,023
Reaction score
2,460
Location
Huntsville AL
Whats your approach for creating that latticed body, and where would the ejection break be?
 

Jeff Lassahn

Well-Known Member
TRF Supporter
Joined
Jul 5, 2020
Messages
175
Reaction score
198
Location
Portland OR
I'm thinking the lattice is glued up out of 1/8" wooden dowels.
The motor mount tube extends to the middle section (you can see the tube in grey inside the rear lattice), and there would be a parachute in that middle section.
 

neil_w

Chuffed as ninepence
TRF Supporter
Joined
Jul 14, 2015
Messages
9,784
Reaction score
2,894
Location
Northern NJ
Wouldn't there be some sort of walkway to go between the front and middle parts?

I like the look, but confess I would be nervous about the whole thing surviving a landing.
 

Jeff Lassahn

Well-Known Member
TRF Supporter
Joined
Jul 5, 2020
Messages
175
Reaction score
198
Location
Portland OR
The front section is the only habitable part. It's got atmosphere, some shielding and part is a drum that's under spin to provide gravity.
The rear section is a nuclear reactor and plasma drive, the environment there is considerably less safe than just stepping outside into interplanetary space.
The middle section is [the parachute compartment], um I mean general drive and power generation equipment mumble vitally important mumble, and is also not habitable. I suppose there could be an access tube but you'd still need a full spacesuit to even think about going there so it's probably safer to drive one of the obligatory pods down there if you need to mess with stuff and count on the ship's computer to let you back in when you're done.

I'm thinking the rough scale of this thing is about 20 meter diameter for the habitat module, which makes the total length something like 350 meters.
 

Jeff Lassahn

Well-Known Member
TRF Supporter
Joined
Jul 5, 2020
Messages
175
Reaction score
198
Location
Portland OR
I would be nervous about the whole thing surviving a landing
I also am nervous about that. And, pretty much everything else about building and flying this thing...

I'm toying with running some shock cord half way up the front lattice so the whole front section hangs sideways when it comes down, and I'm also wondering if that means the front and rear section can collide hard and tangle with each other after ejection.
 

lakeroadster

Lonewolf.... No Club
TRF Supporter
Joined
Mar 3, 2018
Messages
2,159
Reaction score
965
Location
Central Colorado
.... The whole thing is clearly too stubby .....
Say what? The less a rocket looks like a rocket... the better. I guess another way to look at this is to say opinions vary.

Once you're beyond the surly bonds of gravity... center of pressure isn't a concern. So for space travel... stubby is fine.

As an example.. see LEM.

I'm a huge oddroc fan though. Kind of tired of seeing rockets that look like an arrow.
 
Last edited:

neil_w

Chuffed as ninepence
TRF Supporter
Joined
Jul 14, 2015
Messages
9,784
Reaction score
2,894
Location
Northern NJ
Say what? The less a rocket looks like a rocket... the better. Once you're beyond the surly bonds of gravity center of pressure isn't a concern. So for space travel... stubby is fine.
I was just talking proportions and aesthetics, not evaluating its flightworthiness or verisimilitude.
 

lakeroadster

Lonewolf.... No Club
TRF Supporter
Joined
Mar 3, 2018
Messages
2,159
Reaction score
965
Location
Central Colorado
I was just talking proportions and aesthetics, not evaluating its flightworthiness or verisimilitude.
Verisimilitude definition, the appearance or semblance of truth; likelihood; probability: The play lacked verisimilitude.
 

Jeff Lassahn

Well-Known Member
TRF Supporter
Joined
Jul 5, 2020
Messages
175
Reaction score
198
Location
Portland OR
Or "this weird rocket design with a disconnected glowing orb in the center lacks verisimilitude"
 

Jeff Lassahn

Well-Known Member
TRF Supporter
Joined
Jul 5, 2020
Messages
175
Reaction score
198
Location
Portland OR
Messing around with two designs that depart from sanity in completely opposite directions...
The Googie nightmare that OpenRocket seems to think is completely flyable
googie.png

and the scale-like sensible workhorse heavy lift rocket, that is _maybe_ flyable with a bunch of nose weight
booster1.png

verisimilitude, in deed. How do you feel about "ineffable"?
 

neil_w

Chuffed as ninepence
TRF Supporter
Joined
Jul 14, 2015
Messages
9,784
Reaction score
2,894
Location
Northern NJ
verisimilitude, in deed. How do you feel about "ineffable"?
I dunno, I have a hard time wrapping my arms around "ineffable".

BTW, if you like that word you should read Good Omens (or watch the excellent 6-episode adaptation on Amazon Prime), if you haven't already. You'll get your fill of it. :)
 

jqavins

Joseph Avins
TRF Supporter
Joined
Sep 29, 2011
Messages
3,984
Reaction score
1,467
Location
Howard, NY
I like the frog leg fins. There is a certain ineffable verisimilitude in their proactive and synergistic paradigm.
 

Jeff Lassahn

Well-Known Member
TRF Supporter
Joined
Jul 5, 2020
Messages
175
Reaction score
198
Location
Portland OR
if you like that word you should read Good Omens
The word's probably coming to mind because I watched the miniseries about a month ago. I quite enjoyed it.

I wonder if the problem is that "ineffable" lacks verisimilitude.
 

jqavins

Joseph Avins
TRF Supporter
Joined
Sep 29, 2011
Messages
3,984
Reaction score
1,467
Location
Howard, NY
I've got this notion that you can estimate the CP contribution of rounded objects (like pods or even the main rocket body) by assuming they have about half the contribution of a flat plate of the same plan area. I'd like to validate that against some real experimental data at some point...
I too would like to see experimental data. I have some RockSim 9 results. I'm working on upgrading to RS 10, but it's a PITA with one's PC off line (and the instructions Apogee sent me didn't work).

I started with a pretty normal 3FNC+Pods (and a boat tail; why not?):
Pod CP 1 Full.JPGPod CP 1.JPG
The CP is at 457.19 mm and the CD at zero speed is 0.446.

Next, I replaced to pods with flat fins of the same silhouette, still attached as additions on the tips of the regular fins:
Pod CP 2.JPG
I did not know, and would not even hazard a guess as to how mich difference this would make. I got the only result that could surprise me, which is (virtually) no difference at all.

The CP is at 458.32 mm and the CD at zero speed is 0.449.

Finally, I removed all of that and replaced it with a single piece complex shaped fin with, again, the same silhouette:
Pod CP 3.JPG
This time, the results should have been exactly the same at those in the second case, but they were actually quite different. The CP is 472.80, and the CD is 0.484.

What this shows is that RS 9 is not handling the CP and CD contributions of pods correctly, and therefore only the third case result should be trusted. The first case might be right, though I wouldn't count on it, and the second case is almost surely wrong. Unless it's getting the complex one piece fin wrong, which I think is by far the least likely.

In case someone would like to test these cases with RS 10, or look for errors in my work, I'm attaching the three design files.
 

Attachments

Jeff Lassahn

Well-Known Member
TRF Supporter
Joined
Jul 5, 2020
Messages
175
Reaction score
198
Location
Portland OR
I believe the most important thing we as a community can do to improve these programs is to create a set of test cases (and corresponding correct answers) to use with them.
We all know that neither RockSim nor OpenRocket gives good results in all cases, but everyone has to base their beliefs about _which_ cases to trust on hearsay.
 

Jeff Lassahn

Well-Known Member
TRF Supporter
Joined
Jul 5, 2020
Messages
175
Reaction score
198
Location
Portland OR
My favorite "how to break OpenRocket in 5 minutes" exercise is this:
Screen Shot 2020-09-27 at 3.41.45 PM.png
Screen Shot 2020-09-27 at 3.43.39 PM.png

These two designs are identical except the second one splits the fins into two pieces. The actual surface geometry is identical, just one is made by splicing two pieces front to back. The CGs are the same (as expected), but the CPs differ by 0.74 calibers.

So beware when simulating that Astron Avenger clone...
 

jqavins

Joseph Avins
TRF Supporter
Joined
Sep 29, 2011
Messages
3,984
Reaction score
1,467
Location
Howard, NY
Day-om! I just tried it in RS-9 and got a similar result.

Maybe we've hijacked Jeff's thread enough with this. I'll start a new thread. (Oh, wait, that was you with the second one. I'll start a new thread anyway.)

EDIT: Here it is.
 
Last edited:

Jeff Lassahn

Well-Known Member
TRF Supporter
Joined
Jul 5, 2020
Messages
175
Reaction score
198
Location
Portland OR
It probably more accurate to think of it as a lift effect rather than a drag effect. The rear half is in the downwash of the front half, so the center of lift is biased towards the front of the fin. The Barroman equations handle this effect for single isolated fins but don't handle cases where two fins interact.
 

neil_w

Chuffed as ninepence
TRF Supporter
Joined
Jul 14, 2015
Messages
9,784
Reaction score
2,894
Location
Northern NJ
I’m not convinced what’s going on. Will file an issue with OR.
 

jqavins

Joseph Avins
TRF Supporter
Joined
Sep 29, 2011
Messages
3,984
Reaction score
1,467
Location
Howard, NY
Oh, that's gorgeous. I'd worry about burning the inside edges of the tail feathers.
 

Jeff Lassahn

Well-Known Member
TRF Supporter
Joined
Jul 5, 2020
Messages
175
Reaction score
198
Location
Portland OR
I also fear that. I should probably look at Daddyisabar's crazy traction motor designs to see what one can get away with.

Also trying to decide whether to make a joke about the rocket becoming less unbaked, or a John Cleese quote about dead parrots.

Beautiful plumage, though, you do have to admit.
 

jqavins

Joseph Avins
TRF Supporter
Joined
Sep 29, 2011
Messages
3,984
Reaction score
1,467
Location
Howard, NY
That would be a Michael Palin joke. And anyway, the plumage don't enter into it.
 

Nytrunner

Pop lugs, not drugs
Joined
Oct 15, 2016
Messages
7,023
Reaction score
2,460
Location
Huntsville AL
Aluminum foil tape wrapping around the inside edge of the rear plumes. Offers some protection, looks shiny, and shouldn't be too hard to clean either.

Biggest risk is those tips snapping off.
 

neil_w

Chuffed as ninepence
TRF Supporter
Joined
Jul 14, 2015
Messages
9,784
Reaction score
2,894
Location
Northern NJ
It is very pretty... if you could make it survive it'd be a winner.
 
Top