Fairing or no fairing?

[Fadly]

I'm building a spacecraft/lander using Mk1-2 command pod. Things like batteries, monoprop tank and reaction wheel I kept inside the service bay. but some protruding equipment like folded landing legs, folded solar panels and radiators are expose outside. I wonder if this equipment is a significant drag to my rocket during ascent? What if I cover it with a fairing? Will the extra weight from the worth it?

Edited May 1, 2018 by Fadly

[Snark]

13 minutes ago, Fadly said:

I wonder if this equipment is a significant drag to my rocket during ascent? What if I cover it with a fairing? Will the extra weight from the worth it?

From your description, I'd say it's probably not worth the bother.  Yes, landing legs and such will add a bit of drag, but if the rocket is otherwise reasonably streamlined, it's probably not worth the extra complexity of adding a fairing.  In fact, depending on the shape of the design, it's possible that adding a fairing could actually make drag worse (since the fairing will need to be wider than the current rocket in order to fit everything).

The usual rule of thumb is:

• Mostly-aerodynamic thing that happens to have a few minor draggy bits on it?  Don't bother with a fairing.
• Horribly un-aerodynamic mess?  Put a fairing around it.

An example of a good case to use a fairing is, for example, if you're putting up a communications relay satellite that has one of the big fixed dishes on the front end-- that's a horribly draggy contraption, so a fairing would be a major boon.

[Geonovast]

There's also a pretty good chance you can ditch the radiators.

What's the ship's mission?

 

[Fadly]

Sandbox actually. I'm just wondering, that's all. My career research haven't yet pass the third stage research. Unlike most people here who tend to overengineered their rocket, I prefer to get as bare bone as possible. I consider it a peak of accomplishment if I spend all my fuels at mission completion with not a drop of fuel left in the tank. 

[blakemw]

My rule of thumb is: use a fairing.

Only real exception is for early career when there are no fairings, and for fuel tankers which can be made entirely from streamlined adapter pieces.

Most parts which aren't inline fuel tanks or aircraft parts - things like science lab, hitchhiker can, etc generate quite a lot of drag even if they look like they fit the stack. Also there are some gotchas around surface attachment which can cause surface attached parts (solar panels, parachutes etc) to generate a lot more drag than you'd expect, you can learn all the gotchas and work around them.... or you can just use a fairing. Fairings also let you use vacuum optimized parts which are usually lighter than atmospheric parts and generate more drag during reentry making reentry safer (which is somewhat paradoxical, particularly as the part description usually warns you not to use these parts for reentry, but in KSP there is neither enough heating nor enough pressure to threaten vacuum optimized parts under normal reentry conditions).

I've played hard career a lot and generally found fairings a good investment in that context, they reduce the possibility of things going wrong and improve the consistency of launches, so even when paying for the things I reckon they're good value.

Edited May 3, 2018 by blakemw

[Foxster]

7 hours ago, blakemw said:

My rule of thumb is: use a fairing...

My rule of thumb is: Don't use a fairing. 

They are heavy and draggy. Often this negates their advantage on many craft. 

Fair enough if you are putting a rover into orbit, otherwise it's often a lower-dV solution to not bother with a fairing. 

[blakemw]

3 hours ago, Foxster said:

They are heavy and draggy.

 

You might want to make them pointy, nothing is less draggy than a pointy fairing.
They also aren't heavy, for example, a mk1 landing can enclosed in a pointy 1.25m fairing is lighter than a mk1 command pod. Because of square-cube law the larger ones are even lighter by volume enclosed, fairing walls don't get thicker with larger fairings so a mk3 fairing can end up weighing ridiculously little for the volume enclosed.

Edited May 3, 2018 by blakemw

[Curveball Anders]

4 hours ago, Foxster said:

My rule of thumb is: Don't use a fairing. 

They are heavy and draggy. Often this negates their advantage on many craft. 

Fair enough if you are putting a rover into orbit, otherwise it's often a lower-dV solution to not bother with a fairing. 

Testing the same payload with an without a fairing my results are always use a fairing.

YMMV, but I've always found em effective.

[Gargamel]

12 hours ago, blakemw said:

You might want to make them pointy, nothing is less draggy than a pointy fairing.

But for most payload that are already pointy, the difference in drag losses is easily out weighed by the extra mass a fairing brings.   

Some payloads scream Fairing!  Some payloads do better without.  You really have to take it on a case by case basis.