Atlas 5 - 401 & 551 (BT-60 w/ 2x 18mm cluster + BT-20 Boosters w/ 13mm mini engines)

[BigMacDaddy]

For my latest project I decided to take a crack at a NASA launch vehicle. The Atlas 5 is interesting since it has both the 400 and 500 series which have significantly different looks. Also the variety of booster configurations and different sized nosecones add even more variety. I was really surprised that I could not find an Atlas 5 model rocket out there (although you can purchase a display model from ULA).

I am planning to do both the 401 and 551 versions initially (and maybe a Skyliner). I scaled my design to a BT-60 main airframe w/ BT-20 boosters (the 401 also has a segment of BT-55 tube near the nosecone). These are just my first sanity check prints so still a bunch more work to do.



I sized the main engines to fit a cluster of 2x 18mm engines per the prototype and fit 13mm mini engines in the boosters (tight fit to get retainer caps in there).


I am hoping to make the boosters eject / separate from the main rocket. The goal is to offer multiple positions around the model so that it is possible to move the boosters into a more prototypical position but space them out for a launch. I am also hoping to incorporate two positions so that the boosters can be placed closer to the model for a prototypical look but moved away from the model for launch to help with stability.


Some inspirations pictures of the prototype (and ULA's model)...

 

[kuririn]

 

[burkefj]

That's great, love boosters!

 

[BigMacDaddy]

I do have a question -- Can side boosters like these work like fins to stabilize the rocket or will I need to include clear plastic fins? As I said above I was thinking I could move the boosters out away from the main body some for launch.

OR seems to ignore the stabilizing impact of the rear boosters.



If I add in fins the same size / distance from rocket as the boosters it looks much more stable (no surprise there I guess)...

 

[BigMacDaddy]

That's great, love boosters!

Thanks Ron -- for my first test build I permanently connected them to main body (at least in front) but am playing with brackets to allow them to be moved around or added / taken off from rocket.

 

[Cape Byron]

You had me at 'cluster'.

 

[cls]

Really nice!!

 

[BigMacDaddy]

I taped the model together and did a swing test this morning. Trying to figure out how much the side booster tubes contribute to stability. No motors or anything -- I can always increase nose weight to offset any motor weight in the final build (assuming I do not get too heavy for motors to lift).



Anyway, here is what OR says is the CP position (ignore CG in this since there are some build details that are not input into OR - I will override with final build details):



I hypothesized that I might be able to simulate fins with around the same area as the booster tubes (I assume something a bit smaller but this is all just an experiment). This would put the CP around here:



If I use the base drag hack it shifts CP back even more than the mock fins (somewhat surprising since those were pretty big, albeit not so tall, fins). What size should the cone be here? Should I put drag cones on all the boosters as well as main body?



So for my swing test... My initial build with no nose weight put the CG around 39cm back (just in front of the nose on the boosters and about where it shows in the initial base drag hack above). Swing test showed the rocket was marginally stable with CG here. It would fly forward if it started facing forward and would fly backwards if it was facing backwards to start. It also took a little while (a little speed) to aim forward. I added 6 pennies to the nosecone which put the CG at 34.5cm and then the model flew very stable.

I have not done enough swing tests to know how half a caliber rockets tend to fly vs a quarter vs 1 full caliber. If I had to guess right I would say the CP is at or less than half a caliber behind the original CG location - so somewhere between 39 and 42cm.

Now if I wanted to eject the boosters I guess I would definitely need some clear fins on the sustainer.

 

[bad_idea]

Building a scale model of an orbital rocket without using clear fins is a feat well worth dispensing with booster ejection, IMO.

 

[BigMacDaddy]

Building a scale model of an orbital rocket without using clear fins is a feat well worth dispensing with booster ejection, IMO.

Thanks -- that was my thought as well...

Sadly, I have my doubts that I could make the 551 version with that massive nosecone stable with just the boosters.

 

[mh9162013]

Cool stuff!

Looking forward to your 551 build; that's one of my favorite "real world" rockets.

 

[cls]

Yep! Atlas 551 launched my favorite mission, New Horizons to Pluto, the fastest launch ever. Wow.

https://en.m.wikipedia.org/wiki/New_Horizons

 

[jqavins]

I do have a question -- Can side boosters like these work like fins to stabilize the rocket or will I need to include clear plastic fins? As I said above I was thinking I could move the boosters out away from the main body some for launch.

OR seems to ignore the stabilizing impact of the rear boosters.

View attachment 557968

If I add in fins the same size / distance from rocket as the boosters it looks much more stable (no surprise there I guess)...
View attachment 557969

If I were you, I would first swing test the prototype. If it seems stable, I would launch the prototype as most definitely a heads-up launch.

Also, in OR I would add fins that represent the struts. I don't know what the heck is happening to the air in between the common core and strap-on boosters, but at least the renders would look right.

These have a special place in my heart because I was part of the project team that designed and built the satellite that was on board the Atlas V family's third mission. It was a 521, which was the first with the five meter fairing and the first with strap-ons; that is, the first two launches were both 401s. The payload was the Rainbow-1 satellite; I was it's electrical integrator and C&DH lead, and when it's chief engineer took ill four or five hours before launch I started doing his part as well.

 

[BigMacDaddy]

If I were you, I would first swing test the prototype. If it seems stable, I would launch the prototype as most definitely a heads-up launch.

Also, in OR I would add fins that represent the struts. I don't know what the heck is happening to the air in between the common core and strap-on boosters, but at least the renders would look right.

These have a special place in my heart because I was part of the project team that designed and built the satellite that was on board the Atlas V family's third mission. It was a 521, which was the first with the five meter fairing and the first with strap-ons; that is, the first two launches were both 401s. The payload was the Rainbow-1 satellite; I was it's electrical integrator and C&DH lead, and when it's chief engineer took ill four or five hours before launch I started doing his part as well.

That is so cool that you worked on that project. I will ask for your feedback on how close to prototype my model looks when it is done.

I could also use some help on understanding what details I should incorporate since they vary picture-by-picture quite a bit.

Great minds think alike -- yep, swing test complete, adjusted nose weight, next swing test was quite stable... Pictures / details middle of thread above along with hypothetical OR adaptations.

 

[KenECoyote]

FWIW I believe it can be made more stable if you shorten the pods and/or make them wider (not sure how much to scale the pods on your current version are). This should give you more options in addition to moving them outwards, which I believe helps as well.

 

[BigMacDaddy]

FWIW I believe it can be made more stable if you shorten the pods and/or make them wider (not sure how much to scale the pods on your current version are). This should give you more options in addition to moving them outwards, which I believe helps as well.

Thanks...

I started with main body scaled to BT-60 (around 1:91 scale) and the top transition part on the 401 scaled perfectly to BT-55 (less than 1% larger). The booster pods are BT-20 which is 8% larger than scale. BT-50 was 50% larger than scale if I used them in the boosters. If I decide to use a BT-80 for the nosecone on 551 version that is 11% larger than scale (BT-70 would be around 5% smaller than scale).

The biggest change is that the booster pods are pushed around 1cm further from body than they are on the prototype (although they are far out on the ULA model as well).

 

[jqavins]

That is so cool that you worked on that project. I will ask for your feedback on how close to prototype my model looks when it is done.

I could also use some help on understanding what details I should incorporate since they vary picture-by-picture quite a bit.

We were all given desktop display models after the launch. Based on that, the 521 in this picture it quite accurate. I can only presume the other variants are as well.

 

[mikec]

https://axmpaperspacescalemodels.com/index.php/atlas-v/ is a good source for paper models of the Atlas V, with all the fairing art, etc.

 

[Ez2cDave]

A few items . . .

Dave F.

 

[BigMacDaddy]

A few items . . .

Dave F.View attachment 558441View attachment 558442View attachment 558443

Thank you for sharing this -- Great picture of the bottom of the boosters that I had not come across. I did not realize that the side shrouds are similar size to the main engine shrouds.

I needed to make the main and booster shrouds a little larger to fit the 18mm and 13mm engines in there but was thinking about making display versions of both types of shrouds so you could swap out for launches.

 

[neil_w]

Presently the pod tubes are treated as body tubes, which don't contribute to stability according to Barrowman.

Do side tubes really behave more like fins with equal profile? I don't know for sure but I seriously doubt it.

 

[Ez2cDave]

Thank you for sharing this -- Great picture of the bottom of the boosters that I had not come across. I did not realize that the side shrouds are similar size to the main engine shrouds.

I needed to make the main and booster shrouds a little larger to fit the 18mm and 13mm engines in there but was thinking about making display versions of both types of shrouds so you could swap out for launches.

I am uploading all of my ATLAS V data to "MEGA".
As soon as the upload is finished, I will send you a link, so you can download the data.

Dave F.

 

[jqavins]

Presently the pod tubes are treated as body tubes, which don't contribute to stability according to Barrowman.

Do side tubes really behave more like fins with equal profile? I don't know for sure but I seriously doubt it.

Are the nose cones on the booster tubes accounted for? The nose cone at the top of a rocket moves the CP up, while a diameter expansion at the rear moves it aft. So even if the effects of the tubes are negligible (a debatable point, but it's what Barrowman says) the nose cones are not.

 

[neil_w]

Yes, nose cones and everything else on the pods are accounted for.

 

[BigMacDaddy]

https://axmpaperspacescalemodels.com/index.php/atlas-v/ is a good source for paper models of the Atlas V, with all the fairing art, etc.

This is a great site and great source for potential decals. The 1:96 scale should be very close to the scale I am working in (which is around 1:91.5)

 

[mikec]

For my 1:48 Atlas V model, I scaled up the files from https://axmpaperspacescalemodels.com/index.php/atlas-v/ in Inkscape and printed them on full vinyl wraps. It worked pretty well, but despite clear-coating, it faded badly in 2-3 years, so some combo of my printer and the vinyl wasn't a good idea. (BTW, I used clear Lexan fins on mine.)

 

[bguffer]

This is a great site and great source for potential decals. The 1:96 scale should be very close to the scale I am working in (which is around 1:91.5)

I've used that site, InkScape to decompose and scale the graphics, and then print graphics as decals using laser printer. Falcon 9, Falcon Heavy, and Space Shuttle done that way with great results. I did clear coat over the decals.

I also pick a mission, and then use search engine to locate company logos and mission graphics that are not available from axmpaperspacemodels, and then load into Inkscape, scale, print.

You do have to be careful (like with any decals) that base paint color doesn't bleed through decal too much. Any transparent decal with color printed onto it, applied onto black base paint coat, doesn't look good/right. Applied over white, no problem. Applying over dark color, probably best to print onto a non-transparent background, or possibly just onto sticker paper.

LIke mikec i gave up and used clear lexan fins on scale rockets. They don't show up much in launch photos, and i ensure i can remove the fins after launch for display purposes. I launch once, remove the fins, and then place on permanent display. Threw the wall fins, with the fins only glued against motor mount, allows breaking the glue joint, without marring paint on the airframe.

I'm also finding https://evergreenscalemodels.com/ strips, half rounds, dowels are very convenient for detailing. Local hobby shop has them available in the train section. Bob Smith Industries gold super thin crazy glue works very well for applying the strips, etc. Place the strip where you want it on airframe, then apply glue near piece, and glue will just wick under the piece. Wipe with paper towel, and done.