Butterfly stabilizer

[wnderer]

I've been using these to hold down my rocket's tail. I call them butterflies. They add drag so there is a fuel cost. Anyway, I was wondering what other people think of this technique.

[TheXRuler]

cool idea, however as you said drag is an issue, I would reccommend replacing the girder with a similar sized wing segment. Shouldn't lose you any stability and is still more aerodynamic

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From your screenshot it is not quite clear but I assume the air flows over it roughly from where the camera is?

[Ferdoni]

Can you post some more screenshots?

[wnderer]

I have three butterflies on the big orange rocket. The air flows from top to bottom. The air is funneled through the gap in wings.

[Red Iron Crown]

You could probably do something similar without the cubic strut, just mount them directly to the tank and angle them.

[TheXRuler]

Ah well that will (or should anyway) produce a massive amount of drag. The idea is very interesting, although I doubt it would work very well with more realistic supersonic aerodynamics, however, most stock designs don't work well with that so forget that.

I would think that oyu might actually get more stability if you put the larger fin directly on the tank, and a similarily shaped wing segment (or another fin) infront and then added the little fins to the top of that to create double tail, similar to the F-22

[wnderer]

You could probably do something similar without the cubic strut, just mount them directly to the tank and angle them.

I don't have the cubic strut yet. I'll try that when I get them.

Ah well that will (or should anyway) produce a massive amount of drag. The idea is very interesting, although I doubt it would work very well with more realistic supersonic aerodynamics, however, most stock designs don't work well with that so forget that.

I would think that oyu might actually get more stability if you put the larger fin directly on the tank, and a similarily shaped wing segment (or another fin) infront and then added the little fins to the top of that to create double tail, similar to the F-22 https://defenseissues.files.wordpress.com/2012/10/f-22.jpg

I'm not sure the program will let me build something like that. I stumbled on this by accident. Put the basic fin on crooked and the blue center of lift shot down the rocket. It would be nice to be able to control the angle and the drag.

[Red Iron Crown]

Sorry, scale issue. I mean you don't need the girder piece that the fins are mounted to, you could just mount them directly to the tank at an angle.

[TheXRuler]

You can use the rotation and offset tools in the editor (the 4 icons at the top left but right of the part list) to put almost any part in almost any position you want (though there are some really weird bugs sometimes ^^)

[rofltehcat]

Wait, isn't the whole point of winglets their high angular drag multiplier + angular drag bonus? If I read the files correctly, they have pretty low drag (thus saving fuel) until the air is coming from an angle, in which case their drag is a lot higher ( and so they pull the rocket back into the air stream.

The way you are mounting the small winglets you're basically keeping them in constant angle mode so they are slowing you down constantly vs. just when the rocket starts to wobble.

Of course that will stabilize the whole thing by braking the tail but have you tested if the stabilizing effect is actually that much better than mounting the winglets normally or just at a slightly sub-optimal angle? A third winglet would also cost the same $ and part count at the girder segment while having a lot less inline drag and a lot more angular drag, so I'd also test if having 3 fins don't do the job.

Normally I just slap on cheap fins at the very bottom of the boosters until it is stable enough if I run into problems.

Or is this in FAR?

[DancesWithSquirrels]

Reminds me of the Soviet style grid fins, which pull the back end of the rocket to keep the front end pointed fronty:

It's a drag device, rather than a lift device, and will cost you delta-V accordingly. Probably more efficient to replace them with larger (or more) fins. Airfoils produce far more lift than drag, and pushing the rear back into line for stability will be much less drag than pulling with plain drag as you're doing now.

Edit: Upon further reading, actual grid fins are grids of tiny airfoils, so they are also (rather odd looking) airfoils acting with lift - albeit ones that are more easily folded against the body. Your butterfly stabilizer is perhaps better compared to small drogue parachutes slowing the rocket back end, keeping the front end fronty.

Edited June 3, 2015 by DancesWithSquirrels

[wnderer]

Here are some numbers. I stripped off the solid boosters and launched straight up until the fuel ran out and took a screenshot. The mass really didn't change with the number of fins from 81.1t.

fins top speed apoapsis

0 980.5 m/s 93793 m

1 vertical 977.9 m/s 93471 m

2 butterfly 953.5 m/s 89228 m

3 bf + vert 952.3 m/s 88918 m

I'm not sure how to measure stability. With the butterfly, the center of lift is at the butterfly. Without the butterfly, the center of lift is above the center of mass.

[Geschosskopf]

The problem with the rocket in the OP is that it's got too much mass too low. The 1.0.2 aero doesn't like short, wide booster clusters. You can counter this to some extent by sliding the boosters up the core as far as you can because KSP doesn't model radiant heat from rocket flames, so the tank adjacent to the exhaust (but not in line with it) won't feel a thing. In general, though, it's usually better practice (and looks better) to just add stack stages than a wad of radial SRBs.

Think of an arrow. It's heavy at the front (the arrowhead) and has tailfeathers. The important thing for rockets is that the CoM be above the CoL as much as possible, like an arrow. Low CoMs can be countered by adding more fins. In extreme cases, it might even be necessary to use detla wings and control surfaces. From what I can tell, these don't add as much drag as deliberately trying to make drag, but serve the real purpose of moving the CoL as low as possible.

[wnderer]

Think of an arrow. It's heavy at the front (the arrowhead) and has tailfeathers.

What I need is a structural fuselage that fits the Rockomax rockets. I don't know if there is one ahead of me when I get more science.