Model Forum / General / Rockets / February 2004

} On Tue, 24 Feb 2004 17:23:16 -0500, Doktor DynaSoar
} <targeting@OMCL.mil> wrote:
}
} >Thanks. I've had an interest in the K-F airfoil since the article
} >first came on in OMNI, around 1980 I think. I built a few of the
} >gliders and had good success. Also, the fact that some people did
} >research that refuted some of the (poor) results NASA reported
} >resonated with my sense of conspiracy. It's another hobby of mine.
}
} I have not seen the OMNI article, but I do recall a Kline-Fogelman
} controversy
}
} >There's result data on top and bottom K-F gap airfoils, but I find
} >nothing on having the gap on both surfaces.  Although the L/D ratio is
} >poorer than some other configurations, at low speed and/or high angle
} >of attack it's far  more effective than standard airfoils.
}
} Please cite a reference that suports that claim.

The OMNI article (including paper airplane plans and instructions), an
excerpt from "The Ultimate Paper Airplane" and both of Kline &
Fogelman's patents are here:
http://www.rexresearch.com/klinfogl/klinfogl.htm

I'd found a couple others sources, but this had pretty much everything
I needed to get started, so it's the only one I recorded. Once I get
busy into the project I'll catalog every reference I can find.

} >What I'm hoping for is a configuration that'll allow me to cut down
} >fin size, to reduce drag. If it's higher drag at high speed, but keeps
} >the rocket on track longer as it slows (the famed anti-stall
} >characteristic) then the end result may be a higher flight. It's an
} >empirical question, of course. I could see building a dozen identical
} >replaceable fin sets for a model and launching it over and over with
} >different configurations to test it.
}
} It sounds like you are preparing to do an R&D project.  :)

I'm a professional scientist becuse I figured out how to have a job
doing what I consider to be fun. So my fun ends up looking like a job.
The only difference is, out on the launch range I can hoot and holler.
If I do that in the lab, the subjects get nervous and it messes up the
EEG and MRI.

Of course for a real R&D I'll want to do statistics on the results,
and that means I'll need lots of data point for every different
configuration. And that means LOTS and LOTS of flights.

See how that works out? I love science.

} >And, if it's more detrimental at high than it's helpful at low speed,
} >there's always messing around with variable geometry to keep me
} >occupied. Always looking for that edge, you know?
}
} Well yes, if you could get your fins to shrink as the CG moves
} forwoard, you might reduce drag and increase altitude.

I was thinking more along the lines of a gravity assisted flap. Think
of a fin with a wedge embedded in it parallel to the leading edge and
fee to swing both ways out of the plane of the fin. As the rocket tips
from vertical, the wedge shifts it center line out of the fin plane,
causing differential lift by increasing the K-F gap on one side and
decreasing it on the other. Except maybe it should tilt away from the
vertical line rather than with it. This is going to take some
figuring.

} On Fri, 27 Feb 2004 18:21:30 -0500, Doktor DynaSoar
} <targeting@OMCL.mil> wrote:
}
} >On 24 Feb 2004 18:57:41 -0800, hitch@tda.com (Brad Hitch) wrote:
} >
} >} Doktor DynaSoar <targeting@OMCL.mil> wrote in message news:<0r6l30dtcoi2ptb16vn2p8kp4mq4u10ci2@4ax.com>...
} >} > Has anyone ever experimented with stepped airfoil fins, such as the
} >} > Kline-Fogelman design? I checked the FAQ and the group's usenet
} >} > archives, but didn't see anything.
} >}
} >} NASA published a report back in 1974:
} >}
} >} <http://ntrs.nasa.gov/index.cgi?method=search&limit=25&offset=0&mode=simple&order
=DESC&keywords=kline+fogleman>
} >}
} >} You might be able to find it at a nearby University library (an
} >} engineering school most likely) or buy a copy through NTIS.
} >}
} >}
} >} Brad Hitch
} >
} >Crud, $29.50 with shipping. Too bad we don't have an engineering
} >department here I can con into buying it.
}
} Don't give up so easy.  Ask your librarian about getting it through
} inter library loan.
}
} Alan
}

When I was at Virginia Tech, it would have been no problem. Big
engineering school.

Yale Medical School? They're not going to be so easy to convince.

} Doktor DynaSoar <targeting@OMCL.mil> wrote in message news:<mljv305ldh9jqa6oi9pavtb891mpp9epgo@4ax.com>...
} >
} > More important for safety concerns is high alpha. The K-F does not
} > want to stall.
}
} Well, if the flow separates from the upper surface and forms a
} recirculating bubble or wake, that actually is a stall.  Wings will
} still generate lift when they are stalled, it's usually just not
} enough to keep you in the air.  With a low L/D ratio the drag can get
} so big that you don't have enough power to generate the lift required
} for level flight.  With enough power, however, I can make a brick look
} like an stunt plane or a wingless cylinder fly.  You can also have
} problems with ineffective control surfaces if they are trying to
} operate in a separated flow/wake region - another danger of stalling.

Then perhaps it's better characterized as a controlled stall, along
the lines of Rutan's birds with the higher angle canards.

} It sounds like the K-F airfoil just doesn't have the classic hook
} shape in its lift coef. or moment coef. versus angle of attack (alpha)
} curve and therefore isn't prone to the sudden loss of lift and change
} of moment that classically occurs when most airfoils stall.  Since a
} rocket fin should operate at very low angles of attack anyway, the
} shape with the lowest zero-lift drag is probably what you want - which
} doesn't sound like the K-F.

I'm not so sure that is what I want. For most conditions, yes. But
despite having greater drag, and not being efficient in zero lift
conditions, it might be of a benefit in marginally stable models. The
greater drag would bring the CP back, if the model tips these might be
better for brining it back to vertical, and in general, if it works
well at low speeds, it might keep a bird headed straight up longer. Or
maybe not. These are, of course, empirical questions. I'm planning a
bird with multiple replaceable engine/fin sections so I can do some
systematic testing of various airfoil shapes while keeping the overall
design as similar as possible.

As for regular wing airfoils, I'm building a second pair of gliders
for an Estes 2-glider bird, and making one a top K-F wing and the
other a bottom K-F wing. With a little weight trimming I should be
able to get some fair comparisons out of them.

} Here's the whole cite:
}
Thanks.

} > Others tested it and showed a far better L/D ratio with a top gap.
} > This is at odds with NASA's statement. There were apparently other
} > discrepencies.
}
} It seems to me that a top surface gap toward the back would probably
} stall even easier because the flow is generally decelerating there and
} the boundary layer thickens in the adverse pressure gradient.  These
} are places you sometimes see vortex generators to re-energize the
} boundary layer to prevent stall.

Apparently someone tried a K-F wing on a private plane. I saw the
article but didn't read it, so I'm not sure of it was a top or bottom.

} Most NASA research I have seen published has been competent, sometimes
} stellar, seldom truly bad.  If you allege they screwed up the burden
} of proof is going to be on you to show us where - just saying so isn't
} enough.  You could try contacting the authors directly if you can
} track them down.  They're usually flattered enough that anyone cares
} that they'll send a copy gratis.

I don't claim they did a bad job. I do claim that other research
reports different results. That's mentioned in the article.  One study
is a demonstration. Two studies that show the same result is a
replication; that's science. Two studies that show different results
is a hypothesis waiting to be found and tested. When it's about brain
stuff, that's where I submit my grant proposals.