SEN-424 June 4 2000
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News and Reports 2000 - First half
SCAT Electronic News 4 June 2000 issue 424
Table of Contents
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SEN Issues 421- skinny rubber - Ackery
Rubber Models - Fantham
Caveat Emptor
2 more cents worth of spin re Phillips entry stabs - Himes
More Stab Science - Linkosalo
New Northest Free Flight Field ! - FAI Model Supply
Thanks
SEN Issues 421- skinny rubber
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Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
Regarding Klaus's question on the use of 1/16 rubber.
The only time I have tried something like this was about 6-7 years ago when
someone sold me a large skein of Chinese rubber, which was roughly that
size.
It was rather tedious to make up motors, partly due to the size, and partly
because it was a skein rather than looped in a box.
And then to load all those strands onto a winding hook was annoying,
And after that it was quite easy for a couple of strands to break, which
reduced the fun even further.
I think a major part of the problem was that the rubber was not very good,
apart from the size, but I did not enjoy the experience.
I ditched that batch of rubber rather quickly, selling it on cheaply to
indoor scale fliers where I though they could get some use out of it, and I
have been happily using 1/8 ever since.
Perhaps a better place to do comparative tests would be in smaller models
like Coupe or P30.
cheers
David Ackery
New Zealand
Rubber Models!
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Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
Hi Roger,
Because this touches my area of expertise, I can help by telling you that
the guy who sent you the message below is looking for a Finite Element (FE)
structural analysis simulation program that handles the properties of
rubber as a structural material. This is a specialised field because of
the high Poissons Ratio effects that occur. (The stuff gets narrower when
you pull it!). I doubt that we can help him.
I guess he typed 'rubber model' into his browser.
I wonder what the SM lot are making of his enquiry there.........?
Regards
Mike Fantham
Caveat Emptor
=============
Mike's message, along with some others that I have recieved over time
remind me to mention that SCAT Electronic News does not endorse
any of the products or services advertized on the Web Site or in SEN.
We do not have a way of verifing how good the deal is so it is
impossible for us to be selective. We make that
information available as a service to the readers. We do not charge
for the 'advertizements'. It is the reader's responsibility to verify
how reputable the person is. We have heard some people say a particular
product is no good yet others say it is the greatest thing ever. Obviously
many of these decisions are completly personal and depend on
individual circumstances. If you have doubts you can ask the person
for a reference. Our Free Flight community is very small so it is not
too difficult to find a mutual friend.
2 more cents worth of spin re Phillips entry stabs
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Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
I am very OK with what the astute Mr Gregorie had to say (SEN 423), in
fact the very same sequence of events took place in my design phases
during the 70s and 80s with zoom-type Nordics.
My early designs(Ultimax I &II for the long-term crowd) had an
undercambered stab
airfoil and 4 deg decalage, which gave a tight spiral/low height gain
launch as well.
Lars-G Olaffson used to call me from his fire marshall post @ 3-4am
Swedish time
and we would talk for hours on all things, especially freeflight.
During a call I said
I was getting no real height on launch & he said a similar thing had
happened with
him using a u/c stab which broke in a tree and he swapped it for a stab
with some
Phillips entry(the airfoil is Rhodes St Genese 29). This cured the
loopy zoom, giving
more altitude and was still bouncy in thermals, he said.
Well, this was also during my Mean Machine development of '77-78 when
the first stab
was terrible(6% thin flatbot), so I tried the RSG 29---it worked!
Launches were more
open and clicked out cleanly on top very reliably and comfortingly.
Decalage now
equalled 2.5-3 degrees, which agrees with Martin's findings. Also, I
believe the CG
shifted slightly forward, but can't be recall if this was on purpose or
the result of the
stab being slightly lighter.
Go forward a couple years: During the 79FFWC @ Taft I met Arno Hacken,
an excellent Dutch glider flyer, who could runand tow about as fast as
anyone I ever saw.
I noticed his zooms didn't pitch up as much as most others and asked to
look at his
plane and if he could explain the reason. To my surprise he had gone
thru similar
experiences as Lars-G and I, finding by trial & error, that upsweep of
the stab LE
(ie, excessive Phillips entry) combined with a slight CG forward bias
gave him the
flatish zooms he was looking for. Furthermore, he had a computation
which told him where to locate the CG when he changed from u/c to
upswept stab airfoil types!
Well, this turned out to be the popular Jossien CG Method, which he
translated from
French to English for me in 1980 upon his return to NL. It was
published in the NFFS
Digest and I strongly recommend it to all.
Now to get specific re the spinning problem with a Phillips entry stab
airfoil which
was corrected by changing to a flatbottom section: The Jossien Method will
quickly show that using a more forward CG should be used with lower mean
camber stabs; ie, going from u/c to flatbot % CG fwd 1%, then again,
going from flatbot to Phillips entry stab % CG fwd 1% again.
So even tho the overall decalage is lower, retrimming the glide for the
more forward CG gives the margin of stability just enuf to keep the glide from
spinning in, is how
I would put it, in slightly different words than Martin used.
Isn't freeflight science wonderful?
Ciao,
LEE
More Stab Science
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Sender : This email address is being protected from spambots. You need JavaScript enabled to view it.
> Decalage (Was: Phillips entry stabs)
>=======================
> Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
> I can see why it could result in spinning in as well. My current F1A
> series originally flew with a B8403 stab and 4 degrees decalage and had
> a very tight catapult launch with little height gain.
> In consequence, the next model I built had an 8% Clark-Y stab (Philips
> entry!) which resulted in even less centre line camber. This setup
> flies on all of 2.5 degrees geometric decalage and has an even more
> open catapult pattern with good height gain.
Another way to reduce the decalage in order to get more "open" launch
pattern is to reduce the aspect ratio of the tailplane. This makes it less
efficient at slow speeds, so decalage is reduced, but the higher RE-number
due to wider chord makes the tailplane more efficient at higher speeds
during the launch.
The problem with this, at least with F1H gliders is that with small
decalage the model seems to be less capable to carry the weight and drag
of the towline, so that the model will make the tow cicles in slight
dive. Not good for air-picking. I wonder if playing with airfoil AND
aspect ratio would produce a setup that has low pitching moment in launch
(i.e. open launch pattern) and still be resistant to the CG moving forward
(the towline effect)?
-Tapio-
New Northest Free Flight Field !
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Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
"AH , THERE'S GOOD NEWS TONIGHT !" The SkyScrapers et al, thanks to a
knight in shining armor, have a new flying field ! The KNIGHT is none
other than Sir Andrew ( as in Barron ) . The first inaugural
get-together was held this past Saturday, at the Wawayanda, NY site.
Approximately 20 people showed up to talk, fly and kibitz.
The Wawayanda site is only a few miles from the now defunct Galeville
site . The location is approximately 5 miles off of route 84 , three
miles south of NY 17.
Andrew has purchased 277 acres , and has a gentlemen's agreement for
fliers to also have access to 458 additional surrounding acres .
Andrew's land is leased to a sod farmer and the surrounding land is very
flat farmland . Everyone using the site is urged to leave the premises
just the way they were found . Chase bikes are restricted to the many
farm roads on the site .
Renewed interest in competition was evident in all that were able to
attend the short notice gathering . Several were talking Wakefield
models with Dave and Art Ellis, Vic Nippert, Bob Hatschek, Larry
Pelatowski, Ron Felix, newcomer Lee Wang, and out-of-retirement Krine
Laffler.
Maybe the New England Wakefield Group will be reborn .
Several power fliers were also at the gathering , a few of whom were :
Bob Gutai, Jean Pailet, Alan Abriss, Peter Ferrara .
All in attendance gave a toast and a hearty round of applause to Andrew
and his family !!
John Clapp
Thanks
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Thanks to Michael Jordan [of Florida!] for his donation.
........................
Roger Morrell
