Conical vs Ogive, or eliptical or von karman...

Been playing around in Rocksim with rockets built up primarily of transitions.

Could someone give me an explanation, in layman's terms, of why a cone is so much more stable than say an ogive transition?

Reply to
Darren J Longhorn
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A cone has no concave angles, so the airflow is smooth.

Reply to
David

The deflection of the wind off a cone acts like a fin via "induced drag"

Sorry for the tech post!!

Jerry

Reply to
Jerry Irvine

I'm not sure what you mean by that? Where are the concave angles on an ogive cone?

Reply to
Darren J Longhorn

Ok, so the cone presents more surface area behind the cg. Especially compared to any kind of ogive or elliptical shape, which are naturally almost parallel to the air flow at the base? Does that make sense?

Reply to
Darren J Longhorn

Kinda, in layman's terms.

Len could probably post oddles of equations, but I find that thinking of the wave from induced drag as being "attached" to the rocket is helpful. It is not "aerodynamically opaque" like a fin is. It is aerodynamically translucent.

Jerry

Simple terms. Simple minds. Like mine:)

Reply to
Jerry Irvine

I would ignore that comment as confusing.

Reply to
Jerry Irvine

I'd rather try and understand what he meant.

Reply to
Darren J Longhorn

Mine too.

Reply to
Darren J Longhorn

"A cone has no concave angles, so the airflow is smooth."

Means "no divits".

Smooth is a relative term. EVERYTHING in aero is a relative term. The cone/tube transition is not smooth. The tip of the cone is a transition that is not smooth. Even the relatively smooth cone surface is a series of wave impact points for air hitting it at an angle of attack.

Sometimes a divot or valley actually can act as a TURBULATOR thus lowering overall drag by sucking the boundry layer closer to the object.

LIKE ON A GOLF BALL.

Jerry

Aero in the brain. Econ on the sheepskin. Propellant on the hands.

Reply to
Jerry Irvine

DOT in the wallet...

(Sorry, Jerry, particularly on a valid tech post -- but it was like being given a slow one right over the plate...)

David Erbas-White

Reply to
David Erbas-White

I shoulda added

-$40k in the bank

It seemed sooo offtopic at the time :)

Ahhh, come on David. In your case you are forgiven.

Jerry

Reply to
Jerry Irvine

This entire thread makes no sense. It is all BS, but the stench is preferable the usual political BS.

Reply to
Alan Jones

It is not.

Reply to
Jerry Irvine

Then perhaps you'd like to enlighten me?

Reply to
Darren J Longhorn

No, but because you asked, an ogive shaped transition has more wetted surface area that a conical transition of the same length and front and rear diameters. Drag has little to do with stability. Angles are not concave or convex, they can be acute or obtuse... "Smooth airflow", is not saying much, but Barroman and similar CP stability methods are not valid for separated flow.

Alan

Reply to
Alan Jones

The concave angle I mean is the angle where the upper body tube meets the transition. That creates an area of turbulence that doesn't exist if you have all convex angles.

I understand this is a very simplified view, but the original question asked for "layman's terms", so I assume that implied a simple answer.

Reply to
David

However, and back to the topic, that particular turbulence causes induced drag and also increases dynamic stability.

Reply to
Jerry Irvine

I am new to the hobby, but I believe I can combine the given answers into a single post, and add a thought of my own. The contribution to stability from the nose is lateral area (perpendicular to direction of flight). The cone has less, the ogive has more (For the cone, the center of pressure is further back than the other two forms). The rest of the replies seem to deal with drag. Any drag on the cone will be radially symmetric (the cone it self will not have lateral force). Then the question is how fast will the rocket be going. The cone has a smaller drag coeffient at super sonic speeds, where the ogive is best at subsonic. This also has a great effect on the boundary layer at the surface. I haven't done the math (Not sure i could), but it seems speed is the most important factor in cone selection.

Reply to
James M. Devine

Yes.

Reply to
Jerry Irvine

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