Build thread: Blackfish

[neil_w]

I'd forgotten that the aft fins are on the boat tail, so lugs alongside them obviously wouldn't work. Looks good, and I"m sure it'll work great too.

I could have floated it up onto the fin, but I didn't think it would really work or look any better than where I put it. Plus it's way easier to just shove it in against the fin root.

 

[jqavins]

I hadn't - wouldn't - even consider(ed) pushing up the fin.

 

[neil_w]

Still thinking about lug placement today, as I saw Chris's blog post today putting the lugs on the Doorknob.

When using a single lug, it occurs to me that a prime motivation for positioning a single lug at the CG is to allow the rocket to sit neutrally on the rod. With the lug too far behind the CG, the rocket will want to tilt, possibly causing binding. An extreme example would be with the lug all the way in the back: you would expect that rocket to want to lean over and pull on the lug. With the lug much in front of the CG, it'll probably sit on the rod OK but the lug will also leave the rod earlier, which also isn't ideal. And so right around CG is a good balance.

With two lugs, the latter issue is typically eliminated because the rear lug is usually place way back. The former issue is still there but reduced, because you get a much larger span across the two lugs and they're going to do a better job of holding the rocket in position, regardless if the CG above the front lug is going to apply a bit of torque to the rocket airframe.

In all these cases, things will probably work most are all of the time, but it's a matter of minimizing opportunities for anything interfering with a clean launch.

For this rocket, my lug placement is sort of a hybrid. The front lug is about 3.5" being the CG, which isn't too bad, and probably not enough to get too much torque on the rocket. Also this rocket is fairly light, which should help a bit as well. The span between the two lugs totals about 4.5", which isn't really that much but should be enough to hold the rocket straight on the rod without undue pressure on the lugs.

 

[lakeroadster]

How about combining the two to just have 1 big long lug that looks like a cannon?

Pew... Pew... Pew...

 

[BABAR]

I call it the Babar principle: You can get away with a lot at low power.

Love it! ROFL LMBO
You made my day!

 

[BABAR]

I dunno if this is the best or smartest or best-looking I could have done, but I think it'll work OK. As it turned out, I couldn't really get a 2" lug next to the front fin without it looking horrible, so I went with two smaller ones, each about 3/4" long plus or minus.
View attachment 419116

We're almost ready for paint.

I put launch lugs in the fin/tube joint whenever possible. Makes the lug-tube joint AND the fin-Tube joint stronger. I theeeeeenk but I am not sure that, although it messes with the flow dynamics over a smooth fin with a nice fillet, it is still less drag than just sticking the lug on the side of the tube itself. Plus, assuming the FIN is on straight, the lug is automatically perfectly aligned. So, stronger, less draggy, straighter.....what’s not to like? Also most rockets, including YOURS, Frequently have one side that for one or more reasons is more “photogenic”, so unless the lug is part of the design, it’s easy to “hide” on the far side in a fin joint,

Good example of an integrated cosmetic lug placement I think was a design by @lakeroadster , I was thinking he put lugs on both sides to simulate laser cannons. Voila, an ambidextrous rocket!

 

[BABAR]

For the record the preceding post was written BEFORE i read post 154.

 

[jqavins]

Also this rocket is fairly light, which should help a bit as well.

Wrong; it will help A LOT. Remember Babar's Principle and don't overthink it (says one chronic overthinker to another).

 

[neil_w]

Wrong; it will help A LOT. Remember Babar's Principle and don't overthink it (says one chronic overthinker to another).

Agreed, not super critical for this rocket, but I am forever in search of True Launch Lug Enlightenment.

 

[BABAR]

Still thinking about lug placement today, as I saw Chris's blog post today putting the lugs on the Doorknob.

When using a single lug, it occurs to me that a prime motivation for positioning a single lug at the CG is to allow the rocket to sit neutrally on the rod. With the lug too far behind the CG, the rocket will want to tilt, possibly causing binding. An extreme example would be with the lug all the way in the back: you would expect that rocket to want to lean over and pull on the lug. With the lug much in front of the CG, it'll probably sit on the rod OK but the lug will also leave the rod earlier, which also isn't ideal. And so right around CG is a good balance.

With two lugs, the latter issue is typically eliminated because the rear lug is usually place way back. The former issue is still there but reduced, because you get a much larger span across the two lugs and they're going to do a better job of holding the rocket in position, regardless if the CG above the front lug is going to apply a bit of torque to the rocket airframe.

In all these cases, things will probably work most are all of the time, but it's a matter of minimizing opportunities for anything interfering with a clean launch.

For this rocket, my lug placement is sort of a hybrid. The front lug is about 3.5" being the CG, which isn't too bad, and probably not enough to get too much torque on the rocket. Also this rocket is fairly light, which should help a bit as well. The span between the two lugs totals about 4.5", which isn't really that much but should be enough to hold the rocket straight on the rod without undue pressure on the lugs.

I see your point, but also see @Nytrunner ‘s point about being on the CP. Especially for a rocket at a club launch, that may be sitting on the rod or rail for a long time, if your lugs or buttons are too far from the CP, and there is any wind (and it seems like there is ALWAYS wind), a single short lug can get “torqued” off pretty easy. Especially if I put it on and forgot to sand off the glassine body tube coating

 

[BABAR]

Wrong; it will help A LOT. Remember Babar's Principle and don't overthink it (says one chronic overthinker to another).

Now wait just a cotton picking minute!.........

 

[BABAR]

https://www.apogeerockets.com/downloads/PDFs/launch-lug-drag.pdf
Tim Van Milligan presentation on launch lugs presented at NARCON.

still doesn’t answer the question of WHERE TO PUT IT, but some interesting points on lug length, shape, and chamfer (strongly recommend skip to page 30 of 34.)

 

[jqavins]

I see your point, but also see @Nytrunner ‘s point about being on the CP...

So, use the double lug method for a long moment arm, with one at the CP an the other at the CG. And then just push the darn button.

Suddenly, I can't believe I didn't say this sooner. For that matter, I can't believe no one else did either.

Fly-away rail guides.​

OK, there's still the question of where along the rocket's length, but the importance of that is greatly reduced by it's length (i.e. long moment arm) and the drag and aesthetics questions disappear entirely.

 

[BABAR]

So, use the double lug method for a long moment arm, with one at the CP an the other at the CG. And then just push the darn button.

And duck!

 

[Nytrunner]

theeeeeenk but I am not sure that, although it messes with the flow dynamics over a smooth fin with a nice fillet, it is still less drag than just sticking the lug on the side of the tube itself.

I also recall an article about experimenting with lug position.
For aerodynamics:
-Best: no lug
-Better: Lug along root (there's fin/body interference there anyway)
-Worst: Free standing lug somewhere on the body (normal)

I also recall that apogee article and have been angling the front end of my lugs leaving the back side flat ever since. Does it matter? not really, but it's something to do.

The real exciting stuff is in pop lugs! (If I ever get to go fly them....)

 

[kuririn]

Suddenly, I can't believe I didn't say this sooner. For that matter, I can't believe no one else did either.
Fly-away rail guides.

Pros:
1. Aerodynamics, less drag.
2. Aesthetics.

Cons:
1. Needs a rail.
2. Guides sometimes hit the ascending rocket when they fly off.
(In particular the fins).
Same benefits can be found on a tower launcher.
Pros:
Same as above.
Cons:
May not work with rockets with unusual body or fin configurations.
Can be pricey.

For both, the incremental added benefit might not be worth the hassle of buying/making additional hardware and lugging to each launch.

 

[lakeroadster]

Good example of an integrated cosmetic lug placement I think was a design by @lakeroadster , I was thinking he put lugs on both sides to simulate laser cannons. Voila, an ambidextrous rocket!

I did that on the X-Wing... pew... pew

Also, I used 2 lugs on the Hammerhead, the Sled Rocket and the F-79. Symmetry = Balance

I originally had planned to put the launch lugs on the F-79 down low at the root of the two ventral fins. I was worried about weather cocking / snap off the launch rod.. so I stretched the lugs out and mounted them higher.

Cutting them at an angle makes them look like they're doing something more aero too.

They can look cool if they are designed into the rocket early on.. instead of only being thought of as a means to an end.

 

[jqavins]

Symmetry = Good Aesthetics, even without a "story", like them are cannons. Your integration of launch lugs is cool and lovely. That said, I can't believe that the imbalance introduced by an ordinary launch lug, in mass and drag combined, amounts to all of a drop in the bucket.

 

[lakeroadster]

Symmetry = Good Aesthetics, even without a "story", like them are cannons. Your integration of launch lugs is cool and lovely. That said, I can't believe that the imbalance introduced by an ordinary launch lug, in mass and drag combined, amounts to all of a drop in the bucket.

Depends on the size of the drop... and the design of the bucket. Like a wise man recently so eloquently stated:

Power and nose weight rule! Solves 95% of yer problems and that ain't bad!

 

[Daddyisabar]

Depends on the size of the drop... and the design of the bucket. Like a wise man recently so eloquently stated:

Unfortunately asymmetric drag and finding a way to attach lugs/buttons fall into the 5% trouble category. Rocket science is so cruel!

 

[BABAR]

Symmetry = Good Aesthetics, even without a "story", like them are cannons. Your integration of launch lugs is cool and lovely. That said, I can't believe that the imbalance introduced by an ordinary launch lug, in mass and drag combined, amounts to all of a drop in the bucket.

Symmetry is overrated. You want to see cool! Look at the FlisKits Night Whisper

And who can forget the SpitFire

ANYBODY can build a symmetrical rocket and get it to fly. That’s mostly science. Making a beautiful Asmmetrical rocket that flies—- that’s Science and Art (or Insanity!)

From

https://www.rocketryforum.com/threads/fliskits-acme-spitfire-steampunk-style.9710/

 

[neil_w]

Random unsolicited opinion: I find the Night Whisper, and a number of other of the Fliskits sci-fi kits, to be overdesigned. Just my own personal taste.

In the meantime, the rings are ready for paint. They'll get sprayed white on the outside, and than brush-painted on the inside.

 

[BABAR]

Random unsolicited opinion: I find the Night Whisper, and a number of other of the Fliskits sci-fi kits, to be overdesigned. Just my own personal taste.

View attachment 419301

I’ll spot you he overdoes the doodads, but I like the overall lines of the Night Whisper.

“Elegance is complimented by simplicity”
Les. S. Moore

 

[jqavins]

I go back and forth on the FlisKits sci-fi series. Some days I agree with you, and some days I'm knocked flat by them (in a good way). One day I critically think "Too fiddly", and the next day " Ooh, puuurdy ".

 

[neil_w]

PAINT, PT. 1

Had a nice opportunity to paint today, gorgeous weather and alone in the house.

I was masked and ready:

I had some annoyingly small bits of Tamiya tape on the areas where the rings will be glued eventually (red boxes), and this time cut custom lug-fillers for my two odd-shaped lugs. I don't like any spray to get into my lugs; I'll blacken the visible bits later with Sharpie, and a bit of brush paint only if necessary.

And so now the rocket is black:

Surface doesn't look like my best paint job ever, but not the worst either. Unless something weird happens while it's curing it'll be fine. And no drops or dings this time!

And the rings are white:

My perfect record with Rusto 2x Gloss White continues.

Now things really slow down. In addition to waiting for the paint to cure, I need to acquire some white craft paint for the interior of the rings, and I have no idea when I'll be able to get it. Also some orange paint for the tips of the pods (same story), and I need to print my decals at work, a long-lost place that I have vague memories of.

But I was glad to get this done.

 

[bobbyg23]

PAINT, PT. 1

Had a nice opportunity to paint today, gorgeous weather and alone in the house.

I was masked and ready:
View attachment 419809
I had some annoyingly small bits of Tamiya tape on the areas where the rings will be glued eventually (red boxes), and this time cut custom lug-fillers for my two odd-shaped lugs. I don't like any spray to get into my lugs; I'll blacken the visible bits later with Sharpie, and a bit of brush paint only if necessary.

And so now the rocket is black:
View attachment 419810
Surface doesn't look like my best paint job ever, but not the worst either. Unless something weird happens while it's curing it'll be fine. And no drops or dings this time!

And the rings are white:
View attachment 419811
My perfect record with Rusto 2x Gloss White continues.

Now things really slow down. In addition to waiting for the paint to cure, I need to acquire some white craft paint for the interior of the rings, and I have no idea when I'll be able to get it. Also some orange paint for the tips of the pods (same story), and I need to print my decals at work, a long-lost place that I have vague memories of.

But I was glad to get this done.

Looks great!

 

[lakeroadster]

PAINT, PT. 1

Had a nice opportunity to paint today, gorgeous weather and alone in the house.

I was masked and ready:
View attachment 419809
I had some annoyingly small bits of Tamiya tape on the areas where the rings will be glued eventually (red boxes), and this time cut custom lug-fillers for my two odd-shaped lugs. I don't like any spray to get into my lugs; I'll blacken the visible bits later with Sharpie, and a bit of brush paint only if necessary.

And so now the rocket is black:
View attachment 419810
Surface doesn't look like my best paint job ever, but not the worst either. Unless something weird happens while it's curing it'll be fine. And no drops or dings this time!

And the rings are white:
View attachment 419811
My perfect record with Rusto 2x Gloss White continues.

Now things really slow down. In addition to waiting for the paint to cure, I need to acquire some white craft paint for the interior of the rings, and I have no idea when I'll be able to get it. Also some orange paint for the tips of the pods (same story), and I need to print my decals at work, a long-lost place that I have vague memories of.

But I was glad to get this done.

Amazing! With that vegetation and the black paint ... you could also call it The Black Mamba.

 

[Wally Ferrer]

I just caught up with this build, very impressive. I wish I had the patience for this level of attention to detail. I console myself knowing once it hits 1,000 feet or so, it's hard to notice...

 

[mbeels]

And so now the rocket is black:

Nice, that is a satisfying milestone. Although waiting for the final details will take some patience! It's so close....

 

[neil_w]

Nice, that is a satisfying milestone. Although waiting for the final details will take some patience! It's so close....

I have been forced to learn great patience with this sort of thing.

Time to focus on developing some new designs to avoid insanity.