breadneck Posted March 17, 2022 Share Posted March 17, 2022 If the real size 1:1 machine is 10 tons, what would it weigh in at in the various modeling scales? Say a 1:1 scale Avro Lancaster weighs 25.000 KGs, what should in theory a 1:72 scale model of a Lancaster weigh? I don`t even know if there is anything called "true to weight" but it would be fun to know. Are our plastic models lighter or heavier then what they should have been following the logic of "true to weight" ? I hope i got my question through to y`all out there, lol. Quote Link to post Share on other sites
southwestforests Posted March 17, 2022 Share Posted March 17, 2022 I know of 2 previous conversations on the theme, there is math included, from 2010, https://archive.armorama.com/forums/164001/ and from 2005, https://cs.trains.com/mrr/f/88/t/45420.aspx I wouldn't worry about scale weight until manufacturers start giving you scale fuselage skin thickness. Quote Link to post Share on other sites
Joe Hegedus Posted March 17, 2022 Share Posted March 17, 2022 FWWI, a 1/72 model of a 25,000 kg 1:1 subject would have a mass of approximately 70 grams. length scales proportionally to a given unit (feet, meter, etc.) area scales proportionally to the square of a given unit volume (and by extension mass assuming a consistent density to the overall subject) will scale by the cube of a given unit. So, your scale weight would be: 25,000 kg x (1/72**3) = 25,000/(72**3) = 25,000/373,248 = 0.069 kg. With 1000 g/kg, the 1/72 version should have a mass of ~67 g So, I'd venture to say that most airplane models are far heavier than scale. Quote Link to post Share on other sites
breadneck Posted March 18, 2022 Author Share Posted March 18, 2022 (edited) Well to be honest this issue popped up in my head when i accidentally dropped a single engined model straight down onto the wooden floor and thought to myself aerodynamic my arse. I couldn`t help wonder why it just fell to earth like a rock. I guess physics plays a part in this. Maybe if the model i dropped would have been true to weight it somehow would have magically crashlanded on the floor without any damages, lol. I get strange thoughts in my head like that from time to time, hahaha. Edited March 18, 2022 by breadneck Quote Link to post Share on other sites
habu2 Posted March 18, 2022 Share Posted March 18, 2022 I concur with Joe’s volumetric analysis. 👍 Quote Link to post Share on other sites
Helmsman Posted March 18, 2022 Share Posted March 18, 2022 14 hours ago, Joe Hegedus said: FWWI, a 1/72 model of a 25,000 kg 1:1 subject would have a mass of approximately 70 grams. length scales proportionally to a given unit (feet, meter, etc.) area scales proportionally to the square of a given unit volume (and by extension mass assuming a consistent density to the overall subject) will scale by the cube of a given unit. So, your scale weight would be: 25,000 kg x (1/72**3) = 25,000/(72**3) = 25,000/373,248 = 0.069 kg. With 1000 g/kg, the 1/72 version should have a mass of ~67 g So, I'd venture to say that most airplane models are far heavier than scale. This depends on scale. Same 25000 kg will be 226 gr in 1/48 and 763 gr in 1/32. None of my built 1/32 models weigh this much, they're in the 400-700gr range (F-15 is 680gr but it is way more heavy then 25000kg). AMK 1/48 MiG-31 with full missile load and no pilots weighs about 290 grams which corresponds to 32071 kg while it max TOW is 41000kg. KittyHawk 1/48 Su-34 weighs 275 gr with bunch of bombs and missiles, this gives ~30400kg where max TOW is about 45000kg. Quote Link to post Share on other sites
pigsty Posted March 18, 2022 Share Posted March 18, 2022 18 hours ago, breadneck said: I couldn`t help wonder why it just fell to earth like a rock. Two reasons. The first is: not enough speed. Your average large modern aircraft needs to be doing well over 100mph, sometimes as much as 200, to get airborne. It was less in WW2 but still good and fast. If you drop a four-ounce model from waist height it has only three feet to pick up speed before it hits the deck. It won't get anywhere near its unstick speed. Plus, you have to remember, if it's falling nose-down any lift the wings do manage to generate will act sideways, so while it might deflect slightly, it certainly won't lift the nose and start flying level. The second is balance. While the calculations above are correct, they only give you an overall figure for mass. They don't say anything about how it's distributed. Your kit's weight is far more evenly spaced out than its real-life counterpart, so the centre of gravity will be in a very different place and the way it reacts to lift will be completely different. At a guess, without an engine in front, a model of a single-engined fighter would be far more tail-heavy than the real thing, so it would flick its nose up and stall at once. Quote Link to post Share on other sites
Joe Hegedus Posted March 19, 2022 Share Posted March 19, 2022 10 hours ago, Helmsman said: This depends on scale. Same 25000 kg will be 226 gr in 1/48 and 763 gr in 1/32. None of my built 1/32 models weigh this much, they're in the 400-700gr range (F-15 is 680gr but it is way more heavy then 25000kg). AMK 1/48 MiG-31 with full missile load and no pilots weighs about 290 grams which corresponds to 32071 kg while it max TOW is 41000kg. KittyHawk 1/48 Su-34 weighs 275 gr with bunch of bombs and missiles, this gives ~30400kg where max TOW is about 45000kg. That's why I specified 1/72 in the first line of my post; the OP also specified 1/72 scale in his question. As the scale gets larger, the plastic doesn't necessarily get thicker so the weight may approach scale (or less, depending on how much "stuff" is included in the model). True, modern airplanes are in general more dense overall than those of the WWII-ish era, the earlier airplanes had a lot more empty space inside whereas modern military airplanes have pretty much all the internal fuselage volume, and a good bit of the wings, occupied with something. So maybe my "most models being heavier than scale" is a bit of a stretch. Quote Link to post Share on other sites
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