SEN-447 July 31 2000
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News and Reports 2000 - second half
SCAT Electronic News 31 July 2000 issue 447
Table of Contents
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Coming Up
Allison "Radio Eyes" article - Ramrod250
FFML - Gregorie
More Stab Airfoil History - Andresen
Lost Hills FF Assoc ? - Norton
Biggles Martin, etc - Bogie
Coming Up
=========
Now at Muncie the AMA Nats
Next Weekend at Lost Hills - Hector Diez's SCAT MidSummer Madness
Allison "Radio Eyes" article
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Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
Rick Allison's piece was one of the last features I worked on before I left
Model Aviation. He's an excellent, perceptive writer who knows whereof he
speaks.
As to Walt Rozelle's comment about the article not discussing effective color
schemes for timer visibility, remember that Rick is primarily a Pattern
flier, and thus his focus is on schemes that will work within the "box" where
Pattern maneuvers are executed.
Still, there are many useful points in the article for all of us. One I
particularly identified with was the idea that each of us perceives colors
differently. I used to have a terrible time tracking/chasing my Dad's models,
which had yellow wings and stabs. Against many backgrounds I could hardly see
his models, until he added some red to the wingtips; I "see" red much better,
though he had no trouble at all with yellow.
With the long, skinny models flown in the FAI classes, visibility is even
more improtant than ever, and color schemes are worth careful thought.
Jim Haught
FFML
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Roger,
I notice that every so often the SEN gets requests for help from sport or
scale fliers. These people may get more timely help from FFML members as
their requests are a better match with the majority of FFML folks.
Although there are some people who subscribe to both mailing lists I have
the impression that these are usually not the sport fliers and scale people.
It might be useful if you could add a note to the SCAT website and to your
periodically posted description of SEN that mentions the FFML and its usual
subjects.
Thermals,
Martin
Harlow, UK
[The FFML - Free Flight Mailing List this Martin refers to above
was started by Theyer Syme. It is hosted by AirAge.
You can get more information, including how to subscrible at :
http://www.sirius.com/~thayer/ffpages/lists/subscribe.html
Typically they talk about small field and scale models]
More Stab Airfoil History
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Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
Gail Cheesman, an NACA research scientist presented 20A-08 in the 1951-52
Zaic YB as a stab airfoil. It was blunt nosed, 20% HP and 8% thick. Had
slight top curvature to TE, however. I used his 25-1.00-10 wing airfoil,
with not quite the extreme stab on my most successful rubber model.
Later, when AMA rules were changed to "limited rubber" I sorta scaled down
the model, but used an Issacson sp? sharp LE stab. Was supposed to be self
turbulating off the pointed LE. After trying to eliminate the Phugoid with
CG & incidence changes, to no avail, I sanded a generous radius on the stab
LE. The model behaved after that. Too good as it was still climbing as it
crossed the fence at '54 Glenview Nats.
Hoerner shows examples of improvement in lift slope with blunt, foreward HP
and actually shows improvement on boat rudder with 15% cylinder LE followed
by straight top & bot to pointed TE.
Have run a number of indoor glider tests showing importance of HIGH stab AR
for stability. Best had stab AR several times higher than wing AR, but
that's another story.
Keep up the good work.
H
Lost Hills FF Assoc
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Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
Can someone give me the address of the Lost Hills Free Flight Association,
there`s someone here that wants to join.
thanks,
bob norton
Biggles Martin, etc
===================
Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
Yes, I saw Martin in the September issue of Model Aviation as well as the
August issue.
Aram Schlosberg discusses the Ritz stab and gives the ordinates. It looks
like a structural front end with a deflected flap in the rear. For that
reason, it is likely that the section has considerable lift at zero angle of
attack ( and hence a goodly negative angle at zero lift) and the basic reason
we see negative incidence in stabs relative to the wing. The nose is too big
a radius to have leading edge separation. Of course, Gerry Ritz did not bunt
models in his hey day. He just developed the 'Ritz Turn.'
Walt Rozelle discusses model visibility in the distance. At Lost Hills, a
clouded sky is a rarity. Blue most of the time. My experience in gazing
through binoculars at fading models, trying to see the model straight on or
going away is the toughest when the mountains are in the background. Silver
tape on the leading edge and on the fuselage side allows a model to wink when
the sun is out, again 99.9 percent of the time at LH. Knowing what the
bottom of the wing looks like is necessary when converting from eye balls to
binoculars.
Bob Mates wonders about Reynolds number and aspect ratio effects when
choosing a span for the model. The Supermarine Spitfire in the early 1940s
had an elliptical planform. Aerdynamics had advanced to the point of showing
that an elliptical span loading on the wing would give the least drag due to
lift. This means that for the Spit planform, the wing would not have any
twist, thus the angle of attack was constant from wing body junction to the
tip. Without twist, the wing tips will stall first, thus diminishing or
losing aileron control. With models, the Reynolds number varies with the
chord length. and so does the speed for minimum sink. Therefore, for a model
in glide with an elliptical planform, the optimum speed for min sink would be
compromised.
For glide purposes, I think it is better to keep a constant chord. I believe
that skin friction, being a direct function of Reynolds number probably
produces more drag than does the drag due to lift. On the other hand, there
are structural considerations that say to put the large chord at the root
and the smaller tip. If the wing can be made sufficiently stiff and still be
down to minimum weight, then higher aspect ratio should be used. There just
is not sufficient aero data to optimize the wing. It must be built and tried
in flight. Just look at current models.
Bill Bogart
......................
Roger Morrell
