Extra-large reaction wheels

[valenti_scott]

Hello-
I'm not seeing any extra-large reaction wheels in the game. However, there are extra-large engines and fuel tanks. So maybe they are built-in, or they are not needed for some reason, or you can use the large reaction wheels?
-Scott

[Razamanaz]

I just use the largest ones you have and put inside a piece of structural tubing.

[valenti_scott]

Is there an extra-large structural tube?

[poruatokin]

Originally posted by valenti_scott:

Hello-
I'm not seeing any extra-large reaction wheels in the game. However, there are extra-large engines and fuel tanks. So maybe they are built-in, or they are not needed for some reason, or you can use the large reaction wheels?
-Scott

There are two very large remote probes available (3.7 or 5m) that have powerful reaction wheels (but that might just be in the Restock mod I am running).

[Wobbly Av8r]

You can stack any of the available reaction wheels to "accumulate" their effect and that's probably what you're gonna have to go with, but keep in mind that when attaching a smaller reaction wheel to a larger diameter tank or fuselage section below it, the amount of calculated drag will be significantly increased as though the difference in area of the two cross-sections are directly exposed, even if it is made to appear as though it does not...

The most elegant solution I've found for large-diameter bodies is to use the appropriate size engine plate (not as an engine plate but as an aerodynamic cover to attach to smaller diameter sections) if you have the Breaking Ground Add-On with a shroud for the "guidance" unit and/or reaction wheels.

[Razamanaz]

T-50 Structural Tube is the same size as S4 Tanks.

Originally posted by Wobbly Av8r:

when attaching a smaller reaction wheel to a larger diameter tank or fuselage section below it, the amount of calculated drag will be significantly increased as though the difference in area of the two cross-sections are directly exposed, even if it is made to appear as though it does not...

The reaction wheel/s should be attached to the upper section and the lower section only attached by the structural tube. Are you saying that structural tubes don't affect aerodynamics?

[Wobbly Av8r]

Originally posted by Razamanaz:

Are you saying that structural tubes don't affect aerodynamics?

No, I'm saying that structural tubes DO affect aerodynamics and rather adversely in certain cases like the one in question.

I built a test rig and then modified only the manner in which I mounted an Advanced Reaction Wheel Module (ARWM) to it:

1. Simply place the ARWM between larger diameter sections
2. Same as 1. above but then moving the larger diameter sections so that the reaction wheel was "covered up".
3. T-50 structural tube mounting, both top and bottom.
4. Engine plate (with shroud) upon which the ARWM was mounted.

In all these configurations the clear winner was the engine plate mounting by a significant margin. If you turn on the debug drag menu, you will also see that that configuration definitely poses the least drag (and effect on stability from drag) than all the other configurations, including the baseline rig because the ARWM kept the rig in better aerodynamic alignment than the baseline.

In the super-nerdy but how about that? category, I found that mounting the engine plate inverted created noticably lower drag than the default upright position!

[Razamanaz]

Originally posted by Wobbly Av8r:

Originally posted by "Razamanaz":

Are you saying that structural tubes don't affect aerodynamics?

No, I'm not saying that structural tubes DO affect aerodynamics and rather adversely in certain cases like the one in question.

I built a test rig and then modified only the manner in which I mounted an Advanced Reaction Wheel Module (ARWM) to it:

1. Simply place the ARWM between larger diameter sections
2. Same as 1. above but then moving the larger diameter sections so that the reaction wheel was "covered up".
3. T-50 structural tube mounting, both top and bottom.
4. Engine plate with shroud upon which the ARWM was mounted.

In all these configurations the clear winner was the engine plate mounting by a significant margin. If you turn on the debug drag menu, you will also see that that configuration definitely poses the least drag (and effect on stability from drag) than all the other configurations, including the baseline rig because the ARWM kept the rig in better aerodynamic alignment than the baseline.

In the super-nerdy but how about that? category, I found that mounting the engine plate inverted created noticably lower drag than the default upright position!

That seems odd. I never checked the numbers but I never noticed any problems either. If that's the case I wonder what the drag is like if you leave the ARWM magically floating inside the tube without actually touching the top or bottom sections.
I guess I'll have to go try it now.

[Razamanaz]

Well, I just tested that and 2 ARWM without T-50 (just a big gap) had the same amount of drag as it does with the T-50. Only difference was I hit my target speed at 100m higher altitude due to the extra weight. Leads me to conclude that the structural tubes have no aerodynamic properties at all and are purely cosmetic. Although they do add a bit of detrimental weight.

The engine plate only had about 25% the amount of drag and hit the target speed around 550m sooner than nothing at all and 650m sooner than using the T-50. Evidently the shroud does have aerodynamic properties unlike the tubes.

That almost seems like a bug to me. BTW leaving the reaction wheels floating made no difference.

[Wobbly Av8r]

The reason I made my original statement regarding drag was because the performance penalty is not immediately apparent and is one of those things that can make the game very frustrating if not understood.

One would *think* that if a smaller diameter part is "tucked inside" other components that the drag has been eliminated but that appears to not be the case. From an aerodynamic point-of-view, structural tubes are just that - structural. If you want to "streamline" then its important to use a payload fairing or the lesser-known engine plate.

[valenti_scott]

I gather that you are saying that I should take a large reaction wheel and place it inside an extra-large engine plate. I haven't used engine plates yet; I'll keep all this in mind, and look forward to playing with engine plates.

[Razamanaz]

Originally posted by valenti_scott:

I gather that you are saying that I should take a large reaction wheel and place it inside an extra-large engine plate. I haven't used engine plates yet; I'll keep all this in mind, and look forward to playing with engine plates.

That seems to be the case. I even tried a fairing and even though it should be lighter, an engine plate with shroud still had a slightly better drag and slightly better performance.

The only benefit I see now to using the T-50 is that it should give a more rigid body. Probably a moot point if you are using autostruts.

Keep in mind none of these results are actually Kerbin shattering but may help you reach orbit with a little bit more ▲v.