# 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?
--
Darren J Longhorn http://www.geocities.com/darrenlonghorn /
NSRG #005 http://www.northstarrocketry.org.uk /
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A cone has no concave angles, so the airflow is smooth.
-- David

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wrote:

I'm not sure what you mean by that? Where are the concave angles on an ogive cone?
--
Darren J Longhorn http://www.geocities.com/darrenlonghorn /
NSRG #005 http://www.northstarrocketry.org.uk /
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I would ignore that comment as confusing.
--
Jerry Irvine, Box 1242, Claremont, California 91711 USA
Opinion, the whole thing. <mail to: snipped-for-privacy@gte.net>
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wrote:

I'd rather try and understand what he meant.
--
Darren J Longhorn http://www.geocities.com/darrenlonghorn /
NSRG #005 http://www.northstarrocketry.org.uk /
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"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.
--
Jerry Irvine, Box 1242, Claremont, California 91711 USA
Opinion, the whole thing. <mail to: snipped-for-privacy@gte.net>
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Jerry Irvine wrote:

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
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-\$40k in the bank
It seemed sooo offtopic at the time :)

Ahhh, come on David. In your case you are forgiven.
Jerry
--
Jerry Irvine, Box 1242, Claremont, California 91711 USA
Opinion, the whole thing. <mail to: snipped-for-privacy@gte.net>
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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.
-- David

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

--
Jerry Irvine, Box 1242, Claremont, California 91711 USA
Opinion, the whole thing. <mail to: snipped-for-privacy@gte.net>
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wrote:

I guess I can see why conical is convex, but not why elliptical is concave? Seems that with an elliptical transition the angle at the join is 180 degrees?

That's fine, thanks for taking the time to answer.
--
Darren J Longhorn http://www.geocities.com/darrenlonghorn /
NSRG #005 http://www.northstarrocketry.org.uk /
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A transition with a 180 degree angle is just a coupler. A transition goes from one size tube to another. The joint at the larger tube is convex; the joint at the smaller tube is concave (or else the transition itself has a concave angle somewhere in it). You can't have a transition without a concave angle or curve somewhere.

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wrote:

I understand what you're saying now, I thought you were just referring to the angle where the transition joined the aft bodytube.
--
Darren J Longhorn http://www.geocities.com/darrenlonghorn /
NSRG #005 http://www.northstarrocketry.org.uk /
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wrote:

I've never heard the terms "concave" and "convex" used to refer to angles before. I've only heard them in terms of surfaces.
The terms I've heard for angles are:
Acute angle (less than 90 degrees) Right angle (exactly 90 degrees) Obtuse angle (greater than 90 and less than 180 degrees) Straight line (exactly 180 degrees) Reflex angle (greater than 180 degrees) Those Northumbrian bastards (usually spoken by Saxons)
The cross-section of every rocket transition I've ever seen has had a pair of reflex angles (going from the largest tube to the transition shroud), and a pair of obtuse angles (going from the transition shroud to the smaller tube:
______ \ \_______
_______ / ______/
The surface of the rocket in a small patch centered on a point on the vertex of the large-to-shroud angle is definitely convex, as you stated. However, the surface of the rocket in a small patch centered on a point on the vertex of the small-to-shroud angle is most definitely *not* concave. It is, rather, saddle-shaped, like a Pringle's potato crisp. It curves downward to the sides, and upward to the fore and aft.
- Rick "Amateur topologist" Dickinson
--
Engineers think that equations approximate the real world.
Scientists think that the real world approximates equations.
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Some transitons can themselves be sections of ogive nose cones (ie Bumper V-2 w/Wac Corporal, or other shapes).
(going from the largest tube to the transition

--
Jerry Irvine, Box 1242, Claremont, California 91711 USA
Opinion, the whole thing. <mail to: snipped-for-privacy@gte.net>
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The deflection of the wind off a cone acts like a fin via "induced drag"
Sorry for the tech post!!
Jerry
--
Jerry Irvine, Box 1242, Claremont, California 91711 USA
Opinion, the whole thing. <mail to: snipped-for-privacy@gte.net>
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wrote:

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?
--
Darren J Longhorn http://www.geocities.com/darrenlonghorn /
NSRG #005 http://www.northstarrocketry.org.uk /
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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:)
--
Jerry Irvine, Box 1242, Claremont, California 91711 USA
Opinion, the whole thing. <mail to: snipped-for-privacy@gte.net>
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wrote:

Well that;s what I was looking for.

Mine too.
--
Darren J Longhorn http://www.geocities.com/darrenlonghorn /
NSRG #005 http://www.northstarrocketry.org.uk /
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wrote:

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