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Boat tail aesthetics.

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Senior Space Cadet

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Some people think that a boat tail improves the look of a rocket. Might improve aerodynamics too. Some prefer a tailless rocket.
My personal feeling is that it can improve the looks or detract from them, depending on how it's used.
My favorite look is a long boat tail with the fins attached to it, rather than the body tube.
But, suppose you want to use a BT-60 slotted tube and an 18mm motor.
Balsa Machining sells a 3" V2 boat tail that I think looks way out of proportion.
Screenshot 2020-11-23 06.53.30.png

If you shorten it to 1.5", I think it looks much better.
Screenshot 2020-11-23 06.55.30.png
 

dr wogz

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Senior,

think about the aerodynamics. A boat tails helps the airflow off the tail end of the object. Think planes, race cars, the ballast bulb on a sailboat's keel.. the body is wide to accommodate whatever it needs to accommodate. The boat tail reduces the width to the minimum dia needed in a sleek & sexy way. Otherwise, it's not really needed. Again, what is the goal of the boat tail? The rocket itself?

In our case, they are a bit of a pain to build it / design / fabricated, etc.. so most "toy" rockets opt to leave them off for simplicity in the build. (And the fact that their benefit is small, but over time, have an advantage.)

It really, at this point, its more of an aesthetics thing more than a functional thing.. And, adding a plastic bot tail adds weight where you don't want it.. especially for a short rocket!


I've done some boat tails with just a paper shroud. a transition if you will, to get the effect I want.

Look at What Giant Leap offered a few years ago for inspiration:
 

K'Tesh

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If you want to see what a boat tail can do for a rocket, compare the Binder Design Raptor to the Velociraptor... Mind you these are my downscales of the kits, and the forwardmost fins of the Raptor are not accurate to the actual kit.

1606148292588.png
1606148396700.png
 
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K'Tesh

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what about moving the fins aft where they are on the boattail itself?
I have a feeling that this is going to result in someone needing some help in OR... If only there was a tutorial....

 

Jay Rairigh

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Cadet...not to complain, but you talk 1" this, 1.5" that, 3" the other, and then the screenshots that you post of OR are always in metric, so I have to convert it to picture what size your stuff is.

Any reason you don't use inches in your OR?
 

K'Tesh

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For my downscale of the Binder Design Velociraptor, I cut off the tip of a PNC-60RL. However, the same shape can be derived by using a PNC-60AH, or the PN 072665 nosecones (the one from the QCC Explorer). Binder Design's actual 16" nosecone is used for the full size kit.
 

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Cadet...not to complain, but you talk 1" this, 1.5" that, 3" the other, and then the screenshots that you post of OR are always in metric, so I have to convert it to picture what size your stuff is.

Any reason you don't use inches in your OR?
Most of the parts I use, nosecone, transitions, boat tails, all come measured in inches, not centimeters, so that's how I spec them on the Open Rocket design. Body tubes diameters are measured in millimeters, such as 24mm or 33mm, so I keep tube measurements metric. It's just easier for me that way. Sorry!
 

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Senior,

think about the aerodynamics. A boat tails helps the airflow off the tail end of the object. Think planes, race cars, the ballast bulb on a sailboat's keel.. the body is wide to accommodate whatever it needs to accommodate. The boat tail reduces the width to the minimum dia needed in a sleek & sexy way. Otherwise, it's not really needed. Again, what is the goal of the boat tail? The rocket itself?

In our case, they are a bit of a pain to build it / design / fabricated, etc.. so most "toy" rockets opt to leave them off for simplicity in the build. (And the fact that their benefit is small, but over time, have an advantage.)

It really, at this point, its more of an aesthetics thing more than a functional thing.. And, adding a plastic bot tail adds weight where you don't want it.. especially for a short rocket!


I've done some boat tails with just a paper shroud. a transition if you will, to get the effect I want.

Look at What Giant Leap offered a few years ago for inspiration:
I understand all that, not as well as you, but I have the drift. That's why my thread is strictly about aesthetics and not aerodynamics. I'm speaking strictly about looks.
 

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I just got another V2 BT-60 boat tail yesterday and measured it and it's actually 3.5".
Lengthening the rocket, which you'd need to do anyway, since the boat tail moves the CP back, and sweeping the fins back, makes the long boat tail look better.
Screenshot 2020-11-24 05.41.09.png

I'm not sure a short conical boat tail cone might not look better than an ogive. If you had a conical nosecone, it definitely would. I like to mirror the shape of the fins with the nosecone too. So, with an ellipsoid nose cone I normally use elliptical fins.
 

pbahorich

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If you want to see what a boat tail can do for a rocket, compare the Binder Design Raptor to the Velociraptor... Mind you these are my downscales of the kits, and the forwardmost fins of the Raptor are not accurate to the actual kit.

View attachment 439464View attachment 439465
The comparison above also illustrates the potential drawback of boat tails. The boat tail causes the motor to move aft in relation to the fins. Compare the two stability margins 1.94 and 1.13. Once weight is added to the nose of the Velociraptor so that it has a stability margin of 1.94 like the Raptor, the max velocity will be lower than the Raptor, and the apogee will probably also be lower.

Also, it looks like the Velociraptor has a higher thrust motor used (and probably higher total impulse) in the example. I don't see any other way that the 8.81 oz Velociraptor accelerates at 571 ft/s^2 while the lighter 6.83 oz Raptor accelerates at only 452 ft/s^2.
 

K'Tesh

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The comparison above also illustrates the potential drawback of boat tails. The boat tail causes the motor to move aft in relation to the fins. Compare the two stability margins 1.94 and 1.13. Once weight is added to the nose of the Velociraptor so that it has a stability margin of 1.94 like the Raptor, the max velocity will be lower than the Raptor, and the apogee will probably also be lower.

Also, it looks like the Velociraptor has a higher thrust motor used (and probably higher total impulse) in the example. I don't see any other way that the 8.81 oz Velociraptor accelerates at 571 ft/s^2 while the lighter 6.83 oz Raptor accelerates at only 452 ft/s^2.
Part of that is likely due to the shenanigans I had to do to *make* it a two stage rocket.
 

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I wonder how the term "boat tail" was ever injected into rocketry? Rear Conical Reducer.. sure. Boat Tail... huh?
 

HHaase

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It pre-dates rocketry by a long shot. The concept was from the late 1800's as part of rifle bullet design, also called a spitzer.

Probably took on the name boat-tail because it looks like a tapered transom on a boat.

-Hans
 

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121551736_3668927679808205_5882987494108085173_o.jpg

They not only look good, but improve altitude. I was 250' higher on a ~3000' flight with a boattail vs. without. They can shift Cp though, so make sure to run sims!
 

Jay Rairigh

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so that's how I spec them on the Open Rocket design. Body tubes diameters are measured in millimeters, such as 24mm or 33m
SSC, did you know that all your body tubes, nosecones and most other parts are already in OR for you to use, 'spec'ed out' with O.D., I.D., wall thickness, weight etc., catalogued/named by manufacturer....BT-60, BT-80, LT-200, 2.6", whatever the manufacturer calls them. In inches.

In rocketry, motors themselves are dimensioned in mm but that's about all I've seen. 24mm goes in a bt-50, 18mm in a bt-20 is about all the metrics you'll need for LP rockets.
Some people enjoy using the metric system, I dread it because I have to always convert it to work with it.
 

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SSC, did you know that all your body tubes, nosecones and most other parts are already in OR for you to use, 'spec'ed out' with O.D., I.D., wall thickness, weight etc., catalogued/named by manufacturer....BT-60, BT-80, LT-200, 2.6", whatever the manufacturer calls them. In inches.

In rocketry, motors themselves are dimensioned in mm but that's about all I've seen. 24mm goes in a bt-50, 18mm in a bt-20 is about all the metrics you'll need for LP rockets.
Some people enjoy using the metric system, I dread it because I have to always convert it to work with it.
If you go back to when I first started on this forum, and rocketry, I made it pretty obvious that computers weren't my thing. Yes, I kind of did know that there were a lot of part specs already in Open Rocket. I think I tried to find one, that I was using, and it wasn't there and never tried again.
I could also convert everything to metric, for anything I post, but for this, since it was about aesthetics, I didn't think it would matter.
A while back, I bought a gram scale, and when I'm feeling anal, I weigh all the components and then I'm sure.
 

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My personal feeling about boat tails is they are a pain in the behind, except for one way of incorporating them.
The one thing I really like to do is take one of the long V-2 boat tails and and attach the fins to it.
I like the look, it probably streamlines it, and it almost makes the build easier since I can glue the engine mount directly to the boat tail, with no spacers.
Oddly enough, I've found that it is much harder to glue balsa fins to a balsa boat tail than to a paper body tube. Not sure what I need to do about that.
 

jqavins

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think about the aerodynamics....
I understand all that... I'm speaking strictly about looks.
My thought on the looks is that since you like putting the fins on the boat tail, if you were to do that with a long boat tail like the one in the OP, maybe it wouldn't look out of proportion anymore. Kills three birds with one stone: keeps the aerodynamic benefit, puts the fins all the way back helping stability, and fixes the look.

When a boat tail sticks out aft of the fins, I agree with you that keeping it short looks better.

My personal feeling about boat tails is they are a pain in the behind.
Agreed, unless you stick an off-the-shelf one aft of the motor mount, which we have already agreed doesn't look so good.
The one thing I really like to do is take one of the long V-2 boat tails and and attach the fins to it. I like the look, it probably streamlines it
Definitely
and it almost makes the build easier since I can glue the engine mount directly to the boat tail, with no spacers.
By spacers, do you mean centering rings? One can use the opening in a boat tail to hold the aft end of a motor mount, but don't you still need a centering ring on the forward end, since the boat tail is bigger there?
 
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