TASK 2000 12 - Southern Ontario Glider Group

TASK
Official Newsletter of the Southern Ontario Glider Group Inc.
Volume 16 Issue 6
December 2000
Inside This Issue:
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Greetings from SC
Square-Cube Law Stuff
Classic Designs
Membership List
Events Calendar
For Sale
MERRY CHRISMAS TO ALL OUR READERS
If you recognise the tune, Sing along!.
Task 2000
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Official Newsletter of the Southern Ontario Glider Group Inc.
Volume 16 Issue 6
December 2000
THE SQUARE-CUBE LAW & SCALING FOR RC SAILPLANES
by Michael Selig, © Copyright 1990 and 1998
This past summer I, unfortunately, found myself at the controls of someone else's large Sagitta XC after having been
calibrated for years to fly my 2M Prodigy. The sailplane was high and downwind when I pushed the nose over to
penetrate upwind. I had just reached what seemed to be a moderate and safe speed when suddenly the wings folded
and the glider tumbled to the ground in pieces - a fuselage and two wings. The problem was that I attempted to fly the
large XC at speeds that appeared to be on the order of my small 2M. On another occasion, a friend of mine scaled a
2M Prodigy up to XC size. His initial reaction to the first few flights was that the 2M flew better - it "seemed" to fly
faster than the XC. As further examples, a scale model sailplane looks faster than the full scale, a sparrow looks faster
than a crow, and a Learjet looks faster than a DC-10.
So that you will not be easily deceived by what you see, it is worth going over why large aircraft appear to fly slower
than small aircraft.
If we consider a class of aircraft of similar geometry and construction (for example, balsa and MonoKote or fiberglass
and foam), the weight will scale as the cube of a characteristic length. This follows generally from mass being equal
to density times volume. Taking the wing span as the characteristic length, we can therefore write:
Likewise for the wing area we have
These relations form what is often called the "square-cube law," from which a wealth of useful information may be
derived. For instance, these equations can be combined to give
Thus if a model is scaled up to twice its size, the wing loading will be double if the construction materials are similar.
This relationship can be used to estimate the weight of new designs based on old ones. It is only necessary to
determine the proportionality constant. Also, since
and L = W, we have
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Official Newsletter of the Southern Ontario Glider Group Inc.
Volume 16 Issue 6
December 2000
This shows that if we increase the span and keep geometrically similar models with the same type of construction,
then the speed at a given lift coefficient will increase with wing loading. It does not yet show why large aircraft look
slower than small aircraft.
When an aircraft is flying, the only relative measure of length or size is the aircraft itself. Therefore, we can only base
the speed on how long it takes the aircraft to cover some distance relative to its size. We can write that the time it
takes for the aircraft to travel the length of one wing span, b, is
From (4) we can than then write
Immediately we see that as the span increases so too does the time it takes to travel a distance of one wing span.
Finally, we can compare the "speeds" of a 2M and XC sailplane by forming the ratio
If the wing span of the larger plane (denoted as 1) is twice the smaller (2), then the time it takes the larger plane to
travel one wing span is 41% longer than the smaller. Although it is actually flying 41% faster (see equation (4)), it
looks 41% slower. That is a big difference.
(Read, and inwardly digest – especially after a huge Christmas Dinner. – Ed.)
Werner’s Big Bird……………………………………………………Relaxing!
Task 2000
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Official Newsletter of the Southern Ontario Glider Group Inc.
Volume 16 Issue 6
December 2000
Is there anybody out there? – Who has an article inside just bursting to get out
- We publish for free!
For Sale: Want Ads: Personals
For SALE:
This could be your add here!
Lowest Rates in Town
Latest project – 7/8 Scale Cessna, powered by 850 Speed 400’s – great search plane!
The Southern Ontario Glider Group is a chartered club of MAAC
Task 2000
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Official Newsletter of the Southern Ontario Glider Group Inc.
Volume 16 Issue 6
December 2000
2000 SOGGI Executive
President:
Bud Wallace
1060, Eastmount Avenue
Mississauga, Ont.
L5E 1Z3
Vice President: Werner Klebert
69, Byron Avenue
Stoney Creek, Ont.
905-274-3177
905-578-9431
L8J 2T1
Treasurer:
Derek Hartwell
39, Isaac Brock Drive
Stoney Creek, Ont. L8J 2P1
905-578-7991
Secretary:
Cliff English
24, Blackwood Crescent
Hamilton, Ont.
L8S 3H5
905-522-4561
Editor:
Dick Colley
101, Braeheid Avenue
Waterdown, Ont.
L0R 2H5
905-689-7761
Deadline for February Issue of Task:
January 22nd 2000
2000-2001 Calendar of Events
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Dec 17
2001
Jan 14
Feb 11
Mar 11
Apr 15
May 9
June 3
June 13
June 24
July 11
Aug 15
Sept 2
July
Task 2000
Membership Meeting
Rockton Library,
2.00pm
Membership Meeting
Membership Meeting
Membership Meeting
Membership Meeting
Contest dates to be confirmed
One Design
CD
Club Day
CD
One Design
CD
Golden Oldies
CD
One Design
CD
One Design
CD
Big Bird Bash
CD
Bird of Time Postal Contest CD
To be held during July
Rockton Library,
Rockton Library,
Rockton Library,
Rockton Library,
2.00pm
2.00pm
2.00pm
2.00pm
Zivko Rizoniko/Cliff English
Stan Shaw
Zivko Rizoniko/Cliff English
Bud Wallace
Zivko Rizoniko/Cliff English
Zivko Rizoniko/Cliff English
Werner Klebert
Stan Shaw
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Official Newsletter of the Southern Ontario Glider Group Inc.
Volume 16 Issue 6
December 2000
TASK
MEMBERSHIP LIST
Keith
Peter
Roy
Joseph
Robert
Rob
Dick
Cliff
Richard
Fred
Albert
Arnold
Don
Bob
Derek
Werner
Herb
Werner
Otakar
Herb
Jack
Ken
Tom
Mike
Paul
Bryn
Zivko
Ann
Bob
Mike
Walter
Juri
Bud
Stewart
Doug
Bill
Armstrong
Ashton
Auwaerter
Baltaza
Batt
Campbell
Colley
English
Fahey
Freeman
Fund
Gardner
Guthrie
Hammett
Hartwell
Hildesheim
Jenkins
Klebert
Koprnicky
Lentfer
Linghorne
Lockwood
McCann
Penney
Penney
Rennie
Rizoniko
Tekatch
Thayer
Thomas
Tremmel
Vosu
Wallace
Watson
Wilkins
Woodward
219, Governors Road
200, Edwin Street
9, Jamieson Drive
19, Gaitwin Street
612, Blue Forrest Hill
34, Hopkins Court
101, Braeheid Avenue
24, Blackwood Crescent
827, Shadeland Ave.,
511-120 Strathcona Ave N
73, Beech Street
202, San Pedro Drive
RR4
183, Uplands Drive
39, Isaac Brock Drive
4, Foster Crescent
238, Lloyminn Ave.,
59, Byron Avenue
75, Hazelwood Crescent
23, Walsh Court
55, Angelsey Boulevard
29, Cross Creek Blvd.,
2206, Towne Blvd.,
388, Massey Drive
388. Massey Drive
22/1255 Upper Gage Avenue
479, Fendalton Street
19, Pheasant Place
4108, Millcroft Park
61, Alhart Drive
56-600 Silvercreek Blvd
3291, Candela Drive
1060, Eastmount Avenue
26, Juanita Drive
8448, Twenty Road
520, Pine Street
DUNDAS
Kitchener
DUNDAS
Brantford
Burlington
DUNDAS
WATERDOWN
HAMILTON
BURLINGTON
HAMILTON
CAMBRIDGE
HAMILTON
Belwood
KITCHENER
Stoney Creek
CAMBRIDGE
ANCASTER
STONEY CREEK
CAMBRIDGE
BRANTFORD
ISLINGTON
Guelph
OAKVILLE
ANCASTER
ANCASTER
HAMILTON
MISSISSAUGA
Hamilton
BURLINGTON
ETOBICOKE
MISSISSAUGA
MISSISSAUGA
MISSISSAUGA
HAMILTON
HAMILTON
Cambridge
Ont
Ont
Ont
Ont
Ont
Ont
Ont
Ont
Ont
Ont
Ont
Ont
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Ont
Ont
Ont
Ont
Ont
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3J7
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1A9
4H3
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2H5
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3J5
1X6
2E1
1J0
4X3
2P1
4R1
1J1
2T1
8A4
5Y1
3B8
6J2
5H4
3J9
3J9
3C7
2L8
4Y4
3V9
2N1
2B4
2V1
1Z3
2G3
1H7
2S6
905-627-4011
519-576-6750
905-627-8496
519-751-3698
905-632-8790
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905-689-7761
905-522-4561
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519-576-7636
905-578-7991
519-623-2663
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519-753-2856
416-233-0230
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905-648-5843
905-648-5843
905-385-3365
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905-575-5433
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416-748-2833
905-270-5959
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519-653-4251
Correction Notice:
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POSTAL CODE:
PHONE:
e-mail:
Task 2000
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Official Newsletter of the Southern Ontario Glider Group Inc.
Volume 16 Issue 6
Task 2000
December 2000
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