TASK 2000 12 - Southern Ontario Glider Group
Transcription
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: • • • • • • 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 Page - 1 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 Task 2000 Page - 2 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 Page - 3 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 Page - 4 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 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 Page - 5 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 Ont Ont Ont Ont Ont Ont Ont Ont Ont Ont Ont Ont Ont Ont Ont Ont Ont Ont Ont Ont Ont Ont Ont Ont L9H N2H L9H N3P L7L L9H L0R L8S L7T L8R N3C L9C N0B N2M L8J N1R L9G L8J N1R N3T M9A N1H L6H L9G L9G L8W L5B L9A L7M M9V L5A L5A L5E L9C L9B N3H 3J7 4P2 5A1 1A9 4H3 5M5 2H5 3H5 2M2 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 905-627-9435 905-689-7761 905-522-4561 905-637-5469 905-525-6509 519-658-9495 905-383-4418 519-843-4537 519-576-7636 905-578-7991 519-623-2663 905-648-6123 905-578-9431 519-740-9504 519-753-2856 416-233-0230 519-821-9947 905-257-2101 905-648-5843 905-648-5843 905-385-3365 905-275-0597 905-575-5433 905-336-3290 416-748-2833 905-270-5959 905-279-9549 905-274-3177 905-385-8214 905-679-4973 519-653-4251 Correction Notice: NAME: ADDRESS: CITY/TOWN: POSTAL CODE: PHONE: e-mail: Task 2000 Page - 6 Official Newsletter of the Southern Ontario Glider Group Inc. Volume 16 Issue 6 Task 2000 December 2000 Page - 7