Martin Harris - Moderator Posted May 6, 2012 Share Posted May 6, 2012 Looking through the latest mag, I was very taken by Alex Whittaker's description of the new Black Horse Sea Fury. Checking some details, it seems this is a model of around 77 inches span and just under 15 lbs weight. As I've got an ASP 180FS currently unemployed, my mind started ticking over (probably idly as I'm a bit short of storage space and brownie points). So, is a 35 - 40cc petrol engine really necessary? I'd have thought that this should fly reasonably on a 120 FS glow and very well on a 180 but the figures don't seem to put a 180 on the same footing as even a 30cc petrol on the figures I can find! I know petrol engines are more economical to run but I really prefer a 4 stroke for a scale model of a piston engined aircraft and steadfastly continue to reject electric power for these applications (heart ruling head here). So, are petrol engines generally overstating their power output, less efficient using typical sized props or am I miles wide of the mark in my estimation of the power required? Looking at the power requirements stated for similar sized plan builds seems to back up my original thoughts... Quote Link to comment Share on other sites More sharing options...
Alan Cantwell Posted May 6, 2012 Share Posted May 6, 2012 What you have to remember is the sea fury has a chopped down tempest wing, it had a fair chunk of the centre section taken out, so, it is about an 84inch tempest, which makes the fuzz BIG sea fury was 38ft 43/4 span, tempest was 41 foot, i will let you do the maths today, i test flew a world models Zero, fitted with a zenoah 38--82inch, it wasnt overpowered!! a 120 in it would have been useless, my YT birds sports 26cc mvvs engines, some could do with more, and they are 72inch Edited By Alan Cantwell on 06/05/2012 23:40:14 Edited By Alan Cantwell on 06/05/2012 23:50:53 Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted May 6, 2012 Share Posted May 6, 2012 Hi Martin, I have the Blackhorse Chipmunk at 86" and that is stated as requiring a 45cc petrol. Now I have seen one flying more than happily on a 1.20 FS. Now the Chipmunk hasn't got the same presence as the Fury, but i think you are probably right in thinking this doesn't need this sort of power. The way I see it, and this is just how my mind works. A 15lb model will need around 1500 - 2000 watts if done electric. 1hp = 746 watts so therefore you will need around 3hp Cheers Danny Quote Link to comment Share on other sites More sharing options...
Alan Cantwell Posted May 6, 2012 Share Posted May 6, 2012 its a fighter Danny, you can throttle back, but yer cant boot it if you aint got it, Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted May 6, 2012 Share Posted May 6, 2012 I agree it has more "need for Speed" than the Chippy, and the fus will be bigger so more drag, but I reckon it would fly on 3hp quite happily Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted May 6, 2012 Author Share Posted May 6, 2012 Posted by Alan Cantwell on 06/05/2012 23:33:23: What you have to remember is the sea fury has a chopped down tempest wing, it had a fair chunk of the centre section taken out, so, it is about an 84inch tempest, which makes the fuzz BIG sea fury was 38ft 43/4 span, tempest was 41 foot, i will let you do the maths Just over a foot off each side on those figures? Doesn't seem too significant to me even if it's at the wide bit... There seem to be plenty of Spitfire plans around that size/weight designed for 120s but I suppose their fuselages would be a lot less draggy...maybe some of these ARTF models have much thicker wing sections than the plan builds? Quote Link to comment Share on other sites More sharing options...
Alan Cantwell Posted May 6, 2012 Share Posted May 6, 2012 cant speak for the BH stuff, but i know we play with the wing sections, the aim i to give a good flying model, thats has an accurate outline, roughly working it out, i would put a tempest at nearer 80inch, the fury has a very fat fuzz compared to a spitfire, 180 fourstrokes have been put into the YT series of 72inch fighters, they have gone really well, if you can get this sea fury dwon to 15lb, then the 180 will do, but, bet its nearer 18-20 To be honest, i prefer a heavy fighter, it has more presence in the air, the zero i flew today was no lightweight, it grooved along superbly, and had that air about it, if i was buying this my choice would be a 40cc petrol Edited By Alan Cantwell on 06/05/2012 23:59:47 Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted May 7, 2012 Share Posted May 7, 2012 There's nothing to choose between the weight of the MVVS30 (plus electronic ignition) say and the ASP180 - both just over 1Kg. The ASP might need a larger tank - lets say the AUW with the ASP180FS tips the scales at 16lbs to be on the safe side. According to the 2005 RCM&E review - the ASP180 dishes out 2.8hp, thats 2089W. So that works out at 130W/lb. Now there's no doubt at all - it will fly on that, and it wont be in anyway dangerously underpowered. But it certainly wont be overpowered either! You're not going to get a electrifying performance out of 130W/ib. Will it be enough? Well it depends on how you want to fly it! My guess is it would be "OK" - but maybe a bit of a "damp squib" as a model of a fighter on that sort of power to weight ratio. To emulate a high performance WWII piston engine figther in the air I think you'd need nearer to 180W/lb. That's around 3.9hp. BEB Edited By Biggles' Elder Brother - Moderator on 07/05/2012 00:28:18 Quote Link to comment Share on other sites More sharing options...
Lindsay Todd Posted May 7, 2012 Share Posted May 7, 2012 I wouldn't consider going less than 180 4 stroke or 30cc petrol as a minimum for any type of reasonable performance. I have seen a couple fly now and most people have gone for the higher end. As Alan rightly say's you can always throttle back and this is a large bulky model. I have several warbirds in the 80" span size all with 30cc plus engines and would not consider any of them excessive with weights from 18 to 22lb. Linds Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted May 7, 2012 Author Share Posted May 7, 2012 Posted by Biggles' Elder Brother - Moderator on 07/05/2012 00:26:59: Now there's no doubt at all - it will fly on that, and it wont be in anyway dangerously underpowered. But it certainly wont be overpowered either! You're not going to get a electrifying performance out of 130W/ib. Interesting choice of adjective BEB - don't the electric boys usually quote 100W/lb as giving excellent performance? Maybe Alan's suggestion that the AUW might be "optimistic" goes some way to answering my question? Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted May 7, 2012 Share Posted May 7, 2012 BEB quoting watts per lb......I feel faint.....have I stumbled into a parallel universe.... Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted May 7, 2012 Share Posted May 7, 2012 While I do not know anything about large models and big petrol vs glow engines I can add one bit of useful information. Properly designed radial cowlings are not as draggy as people seem to think. The most streamlined shape at the speeds we are working at is a tear drop with a ratio of about 4 or 5:1. Look at the Gee Bees, some of the fastest racing aircraft of their day. I have flown models with radial cowlings that only allowed a little bit of the prop outside the diameter of the cowl. They went like stink. Quote Link to comment Share on other sites More sharing options...
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