SCAT Electronic News 6 Nov 2001 issue 639
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SCAT Electronic News 6 Nov 2001 issue 639
Table of Contents
=================
Eurofly Worldcup 2001 Results - Sager
Martin Symons challenge on CG position - Montes and Wantzenriether.
Brits at Lost Hills - Dilly
Winding F1B - Crowley
Free Flight CG positions. - O'Connor and Wantzenriether.
Worldcup 2001 Results
======================
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Please find attached the results from the euro-fly 2001 Worldcup
Best regards
Kurt Sager
Worldcup euro-fly 2001 - 03./04. Nov. 2001
Results F1A
Name / First Name ## ## ## ## Total Final
1 Rink Andreas GER 180 300 300 300 1080 +334 1080
2 Valo Jari FIN 180 300 300 300 1080 +277 1080
3 Aringer Gerhard AUT 180 275 300 300 1055 1055
4 Hofmann Felix GER 180 300 300 257 1037 1037
5 van Eldik Anton NED 180 242 300 300 1022 1022
6 Züger Erich SUI 180 300 300 240 1020 1020
7 Walliser Rolf GER 180 247 300 270 997 997
8 Bachmann Christoph SUI 180 300 293 205 978 978
9 Adametz Frank GER 180 251 244 300 975 975
10 Kretz Ivo NED 180 300 300 185 965 965
11 Chabot Sylvain FRA 180 300 235 240 955 955
12 Maurer Andreas SUI 180 300 300 174 954 954
13 Brussolo Vittorio ITA 180 300 237 223 940 940
14 Godinho Jean FRA 180 286 300 170 936 936
14 Trumpf Daniel SUI 96 300 300 240 936 936
16 Gerlach Wolfgang GER 180 203 300 244 927 927
17 Mächler Josef SUI 152 260 300 212 924 924
18 Aberlenc Frédéric FRA 180 189 295 251 915 915
19 Szekelyhidi Attila HUN 180 300 131 300 911 911
20 Fuss Helmut AUT 180 272 200 238 890 890
21 Seren Paul GER 180 168 300 233 881 881
22 Reuss Steffen GER 180 121 300 264 865 865
23 Vesa Varuskivi FIN 180 260 172 246 858 858
24 Van Dijk Maarten NED 180 159 300 218 857 857
25 Van de Kerkhof Bram NED 180 300 192 178 850 850
26 Bellen Win NED 180 300 114 240 834 834
27 Camenzind Josef SUI 180 300 201 140 821 821
28 Bachmann Gottfried SUI 180 300 147 190 817 817
29 Bailly André FRA 140 300 213 159 812 812
30 Weisheit Volker GER 180 41 300 288 809 809
31 Gugger Christian SUI 180 276 141 190 787 787
32 Bleuer Heinz SUI 180 300 130 176 786 786
33 Maassen Jürgen NED 180 300 135 167 782 782
34 Nüttgens Ansgar GER 180 224 285 91 780 780
35 Besnard Anne FRA 180 300 166 133 779 779
36 Rotteveel Bart NED 180 235 46 273 734 734
37 Bürgi Walter SUI 180 140 263 144 727 727
38 Pshenychnyy Oleg UKR 180 110 249 182 721 721
39 Ragot Emmanuel FRA 180 300 153 76 709 709
40 Kleine Ralf GER 180 78 300 136 694 694
41 Tschuor Georg SUI 145 125 225 194 689 689
42 De Boer Pieter NED 180 21 163 300 664 664
43 Challine Jean-Pierre FRA 141 244 135 130 650 650
44 Schuermanns Leo NED 180 0 300 165 645 645
45 Kamp Wilhelm AUT 86 300 139 99 624 624
46 Schellekens Bert NED 180 116 123 182 601 601
47 Stierlin Roger SUI 180 171 30 153 534 534
47 Kretz Ron NED 123 143 96 172 534 534
49 Waser Josef SUI 180 127 80 138 525 525
50 Burri Werner SUI 180 0 224 64 468 468
51 Csanyi Jozsef HUN 180 221 0 0 401 401
52 Schalkowski Josef GER 124 97 79 62 362 362
53 Kravchenko Alexander RUS 154 201 0 0 355 355
54 Stoffels Horst GER 180 68 0 0 248 248
55 Schoder Hans SUI 141 0 0 0 141 141
F1A - Juniors
1 Bajorat Lennat GER 177 148 300 212 837
2 Wächtler Mario GER 162 133 300 137 732
3 Wächtler Marcel GER 81 107 260 188 636
Worldcup euro-fly 2001 - 03./04. Nov. 2001
Results F1B
Name / First Name ## ## ## ## ## Total Final
1 Silz Bernd GER 240 240 240 240 300 1260+420 +405 1260
2 Schoder Hans SUI 240 240 240 240 300 1260+420 +353 1260
3 Sarpila Teppo FIN 240 240 240 240 300 1260+420 +238 1260
4 Kolic Ivan YOU 240 240 240 240 300 1260+417 1260
5 Zilberg Igor GER 240 240 240 240 300 1260+415 1260
6 Mönninghoff Peter GER 240 240 240 240 300 1260+266 1260
7 Rosonoks Viktor LIT 240 240 240 240 300 1260+257 1260
8 Aslett Bernard GBR 240 240 226 240 300 1246 1246
9 Lovato Mario ITA 240 240 240 240 285 1245 1245
10 Seifert Marcus GER 240 240 240 240 275 1235 1235
11 Andriukov Alex USA 240 240 240 240 266 1226 1226
12 Wiesiolek Thomas GER 205 240 240 240 295 1220 1220
13 Ghio Walt USA 240 240 240 240 256 1216 1216
14 Wiesiolek Rainer GER 240 220 240 240 275 1215 1215
15 Tedeschi Serge FRA 240 240 240 240 230 1190 1190
16 Waltonen Yrjo FIN 240 240 240 240 227 1187 1187
17 Kulakovsky Oleg UKR 240 240 240 240 225 1185 1185
18 Siebenmann Dieter SUI 240 240 197 240 266 1183 1183
19 Laurynas Gircys (J) LIT 240 240 150 240 300 1170 1170
20 Lucassen Roel NED 234 190 240 167 300 1131 1131
21 Kolobyanin Vadim RUS 211 240 240 231 204 1126 1126
22 Van Eede Ton NED 158 180 240 240 300 1118 1118
23 Van Horn Henk NED 240 240 240 240 154 1114 1114
24 Trumpf Rudolf SUI 240 214 201 240 218 1113 1113
25 Schwendemann Bernh. GER 240 216 160 240 252 1108 1108
26 Seifert Rolf GER 240 240 196 240 183 1099 1099
27 Koppitz Albert FRA 229 240 220 178 212 1079 1079
28 Rolandas Mackus LIT 240 55 240 240 300 1075 1075
29 Boos Jean FRA 146 224 206 220 278 1074 1074
30 Pineau Aurelien FRA 225 229 153 162 280 1049 1049
31 Hoffmann Manfred GER 240 191 240 240 130 1041 1041
32 Meerkestyn Piet NED 230 211 153 240 204 1038 1038
33 Ruyter Pim NED 240 240 240 172 138 1030 1030
34 Sager Kurt SUI 237 203 42 240 191 913 913
35 Evatt Michael GBR 192 131 137 240 200 900 900
36 Bauer Balazs HUN 0 240 150 110 204 704 704
37 Bjelic Branko YOU 240 240 212 0 0 692 692
38 Fux Christian (J) GER 166 146 180 90 110 692 692
39 Gostojic Svetozar YOU 197 0 0 0 0 197 197
Worldcup euro-fly 2001 - 03./04. Nov. 2001
Results F1C
Name / Vorname ## ## ## ## ## Total Final
1 Cuthbert John GBR 240 240 240 240 300 1260 1260
2 Seydel Sigurd GER 240 240 211 240 300 1231 1231
3 Gretter Claus GER 240 233 237 240 262 1212 1212
4 Zsengeller Gabor HUN 240 240 191 240 300 1211 1211
5 Meissnest Dittmar GER 240 240 226 240 252 1198 1198
6 Truppe Reinhard AUT 240 240 240 240 235 1195 1195
6 Wächtler Claus- Pet GER 240 240 212 203 300 1195 1195
8 Kuhl Kurt GER 240 195 240 240 268 1183 1183
9 Reinwald Stefan GER 240 240 200 240 223 1143 1143
# Maurer Peter SUI 240 207 154 240 300 1141 1141
# Meissnest Rolf GER 217 238 240 240 198 1133 1133
# Niiranen Timo FIN 164 240 184 240 278 1106 1106
# Stetz Hans GER 115 240 240 130 212 937 937
# Schalkowski Josef GER 220 210 75 217 199 921 921
# Stäbler Rolf GER 240 240 240 38 90 848 848
# Aringer Gerhard AUT 231 124 155 37 0 547 547
Martin Symons challenge on CG position
=======================================
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Dear Roger,
Could we ask you to print another answer to Martin Symon's challenge?
I hope that the table survives the printing in SCAT, something that is
very difficult to predict, as the page set-up may differ between my
browser's
editor ( Netscape 4.75) and yours.
regards
Sergio Montes
=============================================
This reply to Martin Symons's challenge is a joint effort between Jean
Wantzenriether (JW) and myself, and we apologize for the length of the
reply, but feel that SEN affords a unique forum for a very important
question that deserves the attention and respect of interested
modellers. And thanks to Martin and Bill Gieskieng, for initiating this
debate.
One of the implicit assumptions in Martin's challenge is that a FF
contest model has but one single task to accomplish, and that is to
glide at minimum sink speed.
In that case it is not difficult to conceive, theoretically at least, a
type of model for which Martin's diagnosis is correct. The minimum sink
speed would be achieved by a short model, with a symmetrical stab of
small proportions. The only additional factor that the designer has to
worry is that some criterion for stability is satisfied. Static
stability demands (see for example Milne-Thompson "Theoretical
Aerodynamics", 1958) that the CG be located forward of a point whose
distance to the LE is x0 = c*(TV + 0.25).
Here c = wing chord, TV = Tail Volume = l*St/(c*Sw)
l= moment arm, St = Stab area, Sw = Wing area
This criterion is easily satisfied in most models, and furthermore
static stability increases with a forward position of the CG. Hence the
30% CG, short-coupled model with symmetrical stab of small size (that
would mirror full-size glider practice) would theoretically be suitable.
But this remains in the realm of theory, because in practice a FF model
is expected to do many things besides just glide in a straight line.
1) Models must climb: power models with or without bunt, towline with
zoom and bunt, rubber models under very variable power conditions.
2) Models must glide
3) Models must dethermalize well, which requires a sharp stall due to a
large stab. The stability of the dethermalized descent also depends on
the area of the stab, and is quite marginal for small stabs, a common
observation.
Rubber and glider models also demand long moment arms, the rubber models
due to prop-normal effects which are destabilizing in the climb, the
gliders to allow the small fin area to be effective under tow.
These requirements of climb and glide have led to a model configuration
that is quite at variance in its proportions to those advocated by
Martin. This prompts a reflection on his "fashion" theory. Martin said:
"Until I am proved wrong, I shall go on supposing that free flighters
have been copying old and false theories, in this respect, for nearly
seventy years. The tradition goes back to about 1935 and I suspect it
is just that - a tradition, and nobody so far seems to have
questioned it. I do question it now!."
It is unlikely, we would say extremely unlikely, that a large body of
astute practitioners of a sport (any sport) would follow for some 65
years a wrong theory, just because of "fashion". Quite the contrary, in
competition model flying, the "fashion" has changed gradually throughout
the years, following many, many field tests in several countries. The
unsuitable characteristics of certain models have been discarded, one
does not speak further of them. The good characteristics of others are
retained, they become statistics when the model has done well in
competition, and the design is published and analyzed. The importance of
these statistics is very considerable, and one would deviate from them
at considerable peril, witness the uniformity of design seen in later
years at the World Championships.
The literature of model aviation is considerably more extensive than the
issues of the NFFS Symposia, admirable though they are, and this
richness is not only confined to English-speaking articles and reports.
Examples from the archives of JW are also interesting in this sense: 5
published F1A models with CG at 30% against more than 100 with CG
position between 50 to 80%...beginners models with CG at 30% kitted in
France during the decade 1945-1955; they were extremely difficult to
trim and such designs were quickly forgotten. The argument between the
"close-coupled" models and the long models ("tooth-pick" models after
the famous 1950's model of Oskar Czepa) was decisively decided for the
latter configuration, on the strength of all-around superior performance
of the long models. Much the same has happened with F1B and F1C designs.
The shorter models with advanced CG position have been found wanting in
stability about the three axes, such cases have been documented by JW in
the NFFS Symps.
To determine the optimum position of the CG for any model, I have
developed a computer program. The program considers purely the gliding
situation, under which the total pitching moment about the CG is zero,
as in Martin's assumption. For a given model configuration and CG
position the program calculates the decalage that assures the minimum
sink speed. There are some problems inherent in this calculation,
especially the estimation of the downwash angle. The calculations give
somewhat different results depending on the downwash angle formula used,
I have used Von Mises equation. A typical F1B model has been chosen,
with 16.2 dm2 wing of 1450 mm span, 2.6 dm2 stab and a long fuselage
(moment arm 1000 mm) and an AA-type wing airfoil, with a flat stab. The
results are as follows:
CG pos Vsink (m/s) decalage(deg) Vflight CL Re alfa(deg)
30 0.449 9.75 4.842 0.964 36387 8.2
35 0.437 8.75 4.947 0.919 37241 7.6
40 0.427 8.00 4.969 0.906 36659 7.4
45 0.418 7.5 4.920 0.919 36846 7.5
50 0.411 7.00 4.840 0.944 36932 7.90
55 0.411 6.75 4.695 0.918 36818 7.2
60 0.398 5.50 4.943 0.896 37167 7.0
65 0.392 4.75 4.976 0.879 37032 7.4
70 0.388 4.25 4.879 0.866 37632 6.8
75 0.384 3.50 4.974 0.909 36575 7.4
80 0.380 3.00 4.848 0.878 37042 7.0
85 0.378 2.50 4.641 0.909 35531 8.5
90 0.381 1.75 4.665 0.969 35173 8.3
95 0.411 1.25 4.432 1.064 33323 9.7
100 0.428 0.87 4.217 1.198 31271 11.6
The computations show that for this "modern" F1B there is a discernible
CG effect in the minimum sink speed, the minimum being realized at an
85% location. This minimum sink speed is 16% better than that with a
forward position of the CG at 33%.
Can we believe these figures? There is some confirmation from flight
tests. In the first place the computed flight speed "Vflight" is very
close to the value of 5.0 m/s measured by JW in 1988. This was done by
frame by frame analysis of a flight film on a similar F1B model. The
computed flight angle of attack is 6.8 degrees at CG position of 70%,
which again agrees with many flight tests going back to Frank Zaic in
the 1940's. The flight angle "alfa" increases as the CG moves aft, and
the flight speed is reduced, reaching 11.6 degrees at a CG position of
100%.
The performance computed for this "short" model (climbing to an assumed
115 m) would be about 350 seconds in still air, which, it is true, is
bettered by the longer span models used today. For a "long" model of
1800 mm span the calculated minimum sink speed using otherwise the same
model data is close to 0.330 m/s, with a total flight time of 400
seconds, which is a reasonable simulation of present fly-off time
capabilities.
In summary, performance considerations other than minimum sink speed
have dictated CG positions aft of the full-size glider optimum of 33%.
Calculations show that some improvement on the sink speed is possible
with further aft displacement of the CG to about 85%, but there may be
climb stability arguments for the typical 55-60% positions chosen in
most cases for F1B models. It is not without interest that Richard
Blackam's very successful Spirit 22 sports a 72% CG position!
Sergio Montes and Jean Wantzenriether.
PS: We are gratified to see that Chuck Markos' simple experiment gives results
that also agree with the above calculations. His experiment has the merit
that it can be closely controlled, something very difficult to achieve in the
field.
Brits at Lost Hills
===================
Sender : This email address is being protected from spambots. You need JavaScript enabled to view it.
On behalf, I'm sure, of all teams at Lost Hills this year, could I use SEN
to thank all the US free-flighters who helped us with chasing, support,
tolerance of odd tantrums and general kindnesses.
In the case of the UK team Mike Mulligan was the Man With The Bike, and he
was invaluable, so a special thank you to him from all of us. In the heat
(well, it wasn't that bad this time, actually=85) of the flying we tended to
take it for granted that the models would all somehow get back to the line,
and sometimes ignored the efforts that made that happen.
Thanks too to Jon Davis and Don Zink for the sunshades, a truly generous
gesture. Ours now has a new home and will doubtless appear over future UK
teams worldwide.
Martin Dilly
Team Manager, UK
Winding F1B
===========
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The problem I have with the rules as they now stand is their inconsistency.
You can wind before the round starts for the first seven rounds which are
normally one hour long ,but for fly-offs, ten minute window, you can't. It
doesn't make sense to me. I am in favor of changing the rule as proposed.
And sportsmen lets focus on the issue, not who might have made the proposal.
Someone saw what they thought was an unfairness in the F1B rules and is
suggesting it be changed, that's all.
Paul Crowley
Free Flight CG positions.
=========================
Author : This email address is being protected from spambots. You need JavaScript enabled to view it.
Appologies for the length of this piece.
I think that the answer to Martin Simon's question goes like this.
Over the last 50 years many modellers have tried
small tails and / or forward CGs.
Jean Wantzenriether described some
cases in the e-mail appended below.
Markku Tahkapaa flew an A2 of this type in the 59 world champs. The July 57
Aero Modeller has information about an
East German design on pages 365 and 383.
Then of course there is George Matherat's Wakkisme.
It seems that Haklinger, Lindner et al, with Eppler in the
background, must have at least considered such an
obvious way to reduce sinking speed.
Then what about all those scale models, especially the FAC sort.
It would seem, that as in other areas of life,
failed and /or imperfect experiments don't get reported.
Free flight is possible because small, lightly loaded aircraft
can be made auto-stable if suitably designed.
In contrast, an auto-stable aircraft of the size and weight
of a full size light plane is not possible.
A significant aspect of this is that the phugoid oscillation
in lightly loaded model aircraft, can be controlled.
This oscillation decays exponentially with a time constant
of 2 - 3 sec for a typical FF competition model.
In contrast to the full size case where the lift coefficient (CL)
is nearly constant, CL varies significantly in model phugoid motion,
reaching peak values at the tops of the roller coaster.
Some time after a sufficiently big disturbance
CL will become so large that a model wing stalls.
If the phugoid period is too short then the subsequent
recovery will lead to a second stall and so on.
A classical relaxation oscillation mechanism.
Provided the period of the oscillation is long enough
compared to the damping time, the aircraft can
recover from quite extreme initial distubances.
Another contrast to larger aircraft, is that at Re # below
50,000 airfoil characteristics can be very unstable.
It seems that the tail sizes that have become 'classical'
in the last 20 yrs (3 dm2 for F1B and 4 to 4.5 for F1A)
may well be those that combined with the tail moments
in current use, just suffice for worst usable case wing
section characteristics.
An F1A with a truely neutral tail, of say 10%, on a
conventional moment will oscillate too rapidly to be
flown near its optimal CL and will always be flipped
into never ending stalls by a strong disturbance.
With a 2 dm2 tail (6%), the phugoid may be manageable,
but the static margin could be quite small, less than 20 mm.
[40 - 50 mm is the norm on conventioal gliders]
Then slight purturbations to the CG due to humidity say,
or purturbations to the AC location (which can change due to background
turbulence level causing changes in lift curve slopes),
will cause unacceptable trim changes.
Worse, the tow line attatchment point will have to be
very close to the CG and also be very sensitive.
Similar practical considerations apply to the other classes.
Experiments with dynamic free flight simulation show that
with conventional tail sizes tail CLs fluctuate by less than
+ or - .2 in quite violent disturbances except for very brief
intervals, so the chance that some gust may stall the tail
before the wing is quite slight.
Smaller tails would be more efficient in the sense that
they would use a larger part of their polars,
but would be more at risk of acidental overload.
On the other hand the excess drag due to a tail of 15%
working at a CL of .1 - .3 may reduce potential
performance by 1% or so, and in those classes where
the total area is fixed, the reduction in wing area will
have at worst a 3% detrimental effect relative to the ideal.
I don't think many FFers who have thought about it actually
think that they can get somthing for nothing by using a lifting
tail, although experience might suggest that this is possible.
Many modellers will have found that the perfomance of a
model was improved by a rearward CG shift and retrim.
The reason is that with a forward CG, the phugiod period
is too short and the model must be trimmed well below its
optimum CL to avoid the repeating stall effect.
Moving the CG back lengthens the period, making it possible
to trim closer to the optimum CL.
Calculations suggest that tails as small as 2 dm2 for F1B and
3 dm2 for F1A might be practicle if used with wing sections
having favourable stall characteristics.
Thermals
Sean
From:
To: "FFML"
Subject: Re: upside down stab
Message-ID: <000b01c0c3f0$127ca5a0$efcafac1@default>
Original From: "Ben Humphries"
>> One of the kit planes on display was a STOL design_ The
inovatative thing I noticed was that the horiz stab airfoil was upside
down_ So has anybody ever tried this? <<
An *upside down stab* was used on the F1A model "Greenhorn" by Rene
Butty, Switzerland, see Aeromodeller april 1979_ The goal was to
reduce the stab drag by holding its area as small as possible : 2 dm2_
The CG therefore is placed at 25 percent of the wing mean chord_ This
gives a further advantage : a towing with well forward placed CG is
far easier in strong winds_ But a great handicap has prevent this 25
percent CG from living a longer time, for booth glider and rubber
powered models : the D/Ting is miserable, in continuous loops_ In
France Jean-Francis Frugoli flies F1G models showing 25 percent CG and
reversed stab, with great success but also many wing breakings due to
the wild D/Ting_ He says the trimming is quite easy for the glide as
well as for the climb_
The interesting question is : Why a reversed stab ? The basic idea
was published in Europe by Arthur Schaeffler, 1963_ For good
efficiency and low drag, a stab must work approximately in the center
of the *straight part* of its lift line (i_e_ the curve of the lift
coeff in relation with the angle of attack, in its 3D configuration)_
This leads to the following trends_ For a 75 percent CG, the stab
working CL (lift coeff) is 0,30 or so, therefore use a well cambered
stab profile for which the lowest drag lies at high CL_ For a 50
percent CG, the CL is 0,17 or so, use a *flat* stab like a thinned
ClarkY_ For a 40 percent CG, the stab flies with zero CL, therefore a
symmetrical airfoil is superior (see the F1A of Uwe Rush, for
instance, placed 5th at the WC 1985)_ And for a 25 percent CG, the
stab works with a slight negative CL, so a reversed airfoil is
superior_ In conjunction with this, Butty used a curved plate airfoil,
which gives a stronger lift gradient and allows to reduce the stab
area further_
Be sure that the advantage in drag is very, very, very small ! The
same for the total CL wing & stab, high CL stabs do not add much to
the sinking performance_
Concerning the kit plane in Florida, maybe the strong airstream
behind the prop gives a supplementary control for the longitudinal
balance, if the stab lies in it_ This happens by our gas models_ For
rubber powered models the airstream has definitely no recognizable
effect, please trim with other parameters in your mind (torque,
decalage, etc)_
--
Jean Wantzenriether, E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
................
Roger Morrell
