Detachable Nose Cone Bug ???

[Bzz]

Hello everyone! I was testing nose cones and wanted to create a detachable nose cone (by adding decoupler / separator under nose cone). The idea was to use nose cone advange while in atmosphere and then detach it when in space.

I was surprised than i saw that rocket with added separator / decoupler performs better than without it !!!

This is also true for other types of small nose cones.

But this doesn't improve larger rockets

Was this already know to someone? Was this intended?

I also made video about this discovery. If photos isn't enough for someone and if You want to see how test was done... I put a link to the video

[FancyMouse]

I guess it's because the wide diameter of lander can - added separator is moving the nose cone a little bit higher, causing the air cone to be able to occlude the lander can more than when without separator.

Could you try a structure that is of the normal size (not like lander can where the model is actually larger) and see is it still the case?

[Streetwind]

Yeah, this is all about occlusion. The 2.5m rocket did not benefit because the nosecone by itself already covered the entire stack.

[Bzz]

@FancyMouse I did test again. Changed lander can for RC-001S Remote Guidance Unit. Here are the rockets and results :

Looks like difference now is way smaller but it still exist. And... can nose cone really impact performanse so much??? Keep in mind that separator adds additional 0.075t mass...

(BTW rocket in left accelerates faster, but rocket on right reaches highermax speed. And this is with small Fuel amount... In larger rockets this difference will be way more noticeble. Its like separator increases max speed...)

Edited July 16, 2015 by Bzz

[FancyMouse]

Higher TWR means lower altitude to hit speed of sound, thus get much more transonic drag, comparing to hitting the same speed at a higher altitude. The difference is even bigger at lower altitudes.

Maybe try both cases 75% or 50% thrust, so that it doesn't hit speed of sound too low? The point is to control the differences of their transonic drag coming from altitude (not because of shape).

[Bzz]

Another test. Same rockets. Thrust changed. first picture Thrust limiter of both rockets set to 74.5. Second picture to 49.5.

Same results again. Even with little bit higher mass rocket with separator performs better... with 50 % throtle it not only have higher speed, but slightly higher altitute too.

[FancyMouse]

the only thing left that I can think of is the SAS module - this 1.25m one has a funny shape, which may be affecting drag in the same way as the lander can. Try swap it with the fuel tank and see what happens. If it still has noticable difference, then I don't know...

[Foxster]

Try it with a shockcone air intake. That's the best performing nose cone - even if you don't need an intake.

[windows_x_seven]

Try it with a shockcone air intake. That's the best performing nose cone - even if you don't need an intake.

That makes SO much sense. Aren't intakes supposed to have lots of drag?

[Foxster]

That makes SO much sense. Aren't intakes supposed to have lots of drag?

Dunno for real but they don't in 1.0+ KSP.

[Wanderfound]

Given sufficient fuel and time to accelerate, maximum speed is reached when thrust = drag. Notice how mass is not a factor in that equation?

It's similar for watercraft; a longer hull is generally faster than a shorter hull, even though it's heavier, due to the reduction in drag (but the shorter/lighter ship will accelerate faster, thanks to superior TWR).

Shaving mass gains you acceleration and ÃŽâ€V by increasing TWR. Increasing maximum atmospheric speed, OTOH, is all about drag and thrust (note, not TWR). Especially if you're dealing with supersonic speeds at relatively low altitudes, a tiny reduction in drag can have a massive effect on speed.

However, because you're aiming to launch rockets vertically instead of set speed records horizontally, you've got gravity as well as drag losses to deal with. Gravity losses are controlled by TWR (the more the better) and ascent path (the more horizontal the better).

As you may notice, the methods to reduce gravity losses are sometimes in direct opposition to the methods to reduce drag losses. Exactly which factor should have higher priority at any given moment is going to vary substantially based upon a host of variables related to ship design and intended mission.

[pincushionman]

Add an RCS tank below the capsule in both vessels, then adjust the monoprop mass until they mass exactly the same. Your performance differences between the two should then be only about the aerodynamics of the front end.

[r4pt0r]

I was just thinking, what if you made your own nose cone with a small empty fairing? where would it fall, efficency wise?

[KerikBalm]

Given sufficient fuel and time to accelerate, maximum speed is reached when thrust = drag. Notice how mass is not a factor in that equation?

This only applies to horizontal flight, with negligible induced drag (otherwise, drag increases as mass increases).

In a vertical climb, if TWR is less than 1.0... you decelerate regardless of how little drag.

For a vertical climb, thrust = drag+ force of gravity.

You need a TWR of 2.0, to reach terminal velocity in a climb. You need a TWR of 0.0 to reach terminal velocity in free fall

[Bzz]

Answer for fairing :

In this pictures :

a) rocket with normal nose cone

with added separator

c) empty fairing. 50 % of possible length in first click

d) empty fairing. 100 % of possible length in first click. (with the smallest hole possible)

e) empty fairing. 3 clicks in length

Quick answer : well, fairings seems to be as good as nose cones with separators. Also obvious fact : fairing performance depends from his shape.

I also did some... stupid tests... to check if adding multiple separators increase performance (I know it shouldn't, but well... I wanted to try it and maybe discover something cool ^^)

Quick answer : Id doesn't

[Sharpy]

How do docking ports compare to separators in that context? (used as decouplers/separators; no port-to-port, just a nose cone stuck to the port's normal "attachment" surface).

As I launch a bunch of modules that fit inline with two Sr. ports on both ends, I tend to stick a nose cone on the "front" port, detach ("decouple node") it in orbit.