Chris Lee123 Posted July 8, 2016 Share Posted July 8, 2016 I would like to make my Acro wot quicker, I currently have a 13 x 6.5 prop. Out of these which one would be my best bet to increase speed. 10x10,11x8, 12x8, 13x8, 13x10 or 14x6 . The motor is a Turnigy Aerodrive SK3 - 4250-500kv Brushless Outrunner and I have a 100amp YEP esc. I am using 6s 5000mah packs. I think they are 30 - 40 C Quote Link to comment Share on other sites More sharing options...
Andy48 Posted July 8, 2016 Share Posted July 8, 2016 I did quite a number of tests trying different props and measuring the speed. Guess what? The prop size and pitch made very little difference to the maximum speed, but the current went up a lot with larger props. Don't forget drag is related to the square of the speed, and the efficiency of electric motors drops off at high currents. Quote Link to comment Share on other sites More sharing options...
Colin Bernard Posted July 8, 2016 Share Posted July 8, 2016 Usual analogy is that large diameter/small pitch is like low gear in a car, and small diameter/large pitch is like high gear. So if it is out and out speed you are after then a 10x10 prop may well do the job - but it will be an effort to get there, whereas the current prop easily gets to its top speed but can go no faster. Suggest you just experiment but keep your wattmeter handy and check readings before a flight just to make sure you are keeping within limits! Quote Link to comment Share on other sites More sharing options...
onetenor Posted July 8, 2016 Share Posted July 8, 2016 Dare I suggest a bigger motor ? Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted July 8, 2016 Share Posted July 8, 2016 To make it go faster you will need more power. How many watts is your motor consuming now & at what current? Can you get more power from that motor? A bigger & or pitchier prop will generate more power but can the motor cope with the extra current.? A more powerful motor with a higher kv will help. How fast is the AW now? Most models tend to have a "top speed" above which they are reluctant to go without a lot more power to push them.... Quote Link to comment Share on other sites More sharing options...
Geoff S Posted July 8, 2016 Share Posted July 8, 2016 As Andy points out drag is proportion to the square of the speed which in practical terms means you reach a terminal speed that is almost unaffected by the power of the motor. To get more speed you need to reduce the drag which means redesigning the air frame or, at least, doing things like fitting retracts or changing the cockpit profile as Alex Henshaw did with the Mew Gull. If you was out and out speed you're using the wrong airframe. Geoff Quote Link to comment Share on other sites More sharing options...
ChrisB Posted July 8, 2016 Share Posted July 8, 2016 If you want a fast machine don't choose an acrowot. Thick wing, uc and wide cowl. I've got a Top flite giant p47 with a zen 62. I've flown with several other TF giant P51s and they all leave me standing. The p51 has a thinner wing and streamline cowl, the p47 hasn't...hence its slower. Purely down to drag and design. Edited By ChrisB on 08/07/2016 20:21:30 Quote Link to comment Share on other sites More sharing options...
Former Member Posted July 8, 2016 Share Posted July 8, 2016 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted July 8, 2016 Share Posted July 8, 2016 Can I ask why you want to make it faster? I ask because it might effect the options! BEB Quote Link to comment Share on other sites More sharing options...
Luke Lane Posted July 8, 2016 Share Posted July 8, 2016 Just a couple of clicks of down elevator trim will make it behave like a pylon racer. Luke. Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted July 8, 2016 Share Posted July 8, 2016 What? Fly in triangles? LOL! BEB Quote Link to comment Share on other sites More sharing options...
Former Member Posted July 9, 2016 Share Posted July 9, 2016 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Chris Lee123 Posted July 9, 2016 Author Share Posted July 9, 2016 Posted by Percy Verance on 09/07/2016 07:40:50: Obviously, he's bought the wrong model......... So because I want to make the plane I have fly a little faster that means I have the wrong model???? Quote Link to comment Share on other sites More sharing options...
Chris Lee123 Posted July 9, 2016 Author Share Posted July 9, 2016 Posted by Biggles' Elder Brother - Moderator on 08/07/2016 21:46:02: Can I ask why you want to make it faster? I ask because it might effect the options! BEB Why not. Other than because I would like a little more speed there is no reason. I just wondered given the setup and props that I have, what I could do to increase the speed. Quote Link to comment Share on other sites More sharing options...
Chris Lee123 Posted July 9, 2016 Author Share Posted July 9, 2016 Posted by Steve Hargreaves - Moderator on 08/07/2016 18:56:22: To make it go faster you will need more power. How many watts is your motor consuming now & at what current? Can you get more power from that motor? A bigger & or pitchier prop will generate more power but can the motor cope with the extra current.? A more powerful motor with a higher kv will help. How fast is the AW now? Most models tend to have a "top speed" above which they are reluctant to go without a lot more power to push them.... Watts 900 approx and 40amps ish. The motor is rated at 1350 watts and max amps for the motor is 57. No Idea has haven't tried the speed gun on it. Quote Link to comment Share on other sites More sharing options...
Chris Lee123 Posted July 9, 2016 Author Share Posted July 9, 2016 Posted by ChrisB on 08/07/2016 20:14:48: If you want a fast machine don't choose an acrowot. Thick wing, uc and wide cowl. I've got a Top flite giant p47 with a zen 62. I've flown with several other TF giant P51s and they all leave me standing. The p51 has a thinner wing and streamline cowl, the p47 hasn't...hence its slower. Purely down to drag and design. Edited By ChrisB on 08/07/2016 20:21:30 As I said in my original post I just want to make the plane I have quicker with the parts I have. Quote Link to comment Share on other sites More sharing options...
.. Posted July 9, 2016 Share Posted July 9, 2016 Posted by Chris Lee123 on 09/07/2016 08:00:48: Posted by ChrisB on 08/07/2016 20:14:48: If you want a fast machine don't choose an acrowot. Thick wing, uc and wide cowl. I've got a Top flite giant p47 with a zen 62. I've flown with several other TF giant P51s and they all leave me standing. The p51 has a thinner wing and streamline cowl, the p47 hasn't...hence its slower. Purely down to drag and design. Edited By ChrisB on 08/07/2016 20:21:30 As I said in my original post I just want to make the plane I have quicker with the parts I have. Well unfortunately as suggested a few times above you not really going to be able to....... Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted July 9, 2016 Share Posted July 9, 2016 Posted by Chris Lee123 on 09/07/2016 07:55:53: Posted by Biggles' Elder Brother - Moderator on 08/07/2016 21:46:02: Can I ask why you want to make it faster? I ask because it might effect the options! BEB Why not. Other than because I would like a little more speed there is no reason. I just wondered given the setup and props that I have, what I could do to increase the speed. Well "why not" is because aircraft are designed for specific purposes usually. Features are selected that make that particular aircraft good at what the designer wanted it to achieve. When Chris Foss was designing the AcroWot his objective was to create a model that was: neutrally stable (and hence manouvrable and agile), with a very benign stall behaviour (to enable flight at extreme AoA and low speed - again this promotes agility by making the model able to withstand sudden "pull-outs" etc.) and finally he wanted day-to-day practicality so its tough with a lots of strengtening and a chunky robust undercart etc. (ie a bit "porky"!) All these make the AW a superb acrobatic hack - but none of them make it fast! In fact things like the thick wing ( which give it high lift and good stall behaviour) actually slow it down! Although more slippy than say a Wots-Wot this is in reality still a very draggy aeroplane. Its just not designed or built for speed - nor does it lend itself to adaptation in that direction to be honest. If you really MUST speed it up (using only the existing set up has you asked) the only things I can think of are: 1. Take the undercarraige off - its a major source of drag. This will make a decernable differnce - although how you will land the aircraft is your problem! 2. Decrease the diameter and increase the pitch of your prop - this will make very small difference. The model will have a slightly higher top speed - but at the cost of a considerable reduction in acceleration. Yoiu will gain a few percent more speed for a big loss in flying flexibility - this will not be pleasant to fly. (Dothis with care - you must not exceed the maximum current the ESC and motor can support - use a watt meter to check) So - that's it. If you want to stay with the existing gear - that's about all you can do. It will create a model that is only marginally faster but much less practical and a much worse flyer. To paraphrase an old joke: when asked for directions the man answered "Well if I was going there I would be starting from here" - the same applies to this - the AcroWot is simply not a model that lends itself to speed - it wasn't designed for that, you're trying to turn a Transit Van into a Formula One Car - without changing anything! BEB Quote Link to comment Share on other sites More sharing options...
Former Member Posted July 9, 2016 Share Posted July 9, 2016 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Rich too Posted July 9, 2016 Share Posted July 9, 2016 Posted by Chris Lee123 on 09/07/2016 07:59:03: Posted by Steve Hargreaves - Moderator on 08/07/2016 18:56:22: To make it go faster you will need more power. How many watts is your motor consuming now & at what current? Can you get more power from that motor? A bigger & or pitchier prop will generate more power but can the motor cope with the extra current.? A more powerful motor with a higher kv will help. How fast is the AW now? Most models tend to have a "top speed" above which they are reluctant to go without a lot more power to push them.... Watts 900 approx and 40amps ish. The motor is rated at 1350 watts and max amps for the motor is 57. No Idea has haven't tried the speed gun on it. Hi Chris, It sounds like you have capacity to spare. I am not an expert but you need a higher pitch prop. I would just experiment. I had a look on the net and there are very mixed reviews on that motor, especially on the HK website. I would start with a decent 14 X 8.5 e prop and go from there ( based on a you tube review). Good luck and keep us posted. Ps just ignore the doubters and have fun Edited By Rich2 on 09/07/2016 08:42:50 Edited By Rich2 on 09/07/2016 08:43:19 Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted July 9, 2016 Share Posted July 9, 2016 Ah, but sometimes the "doubters" doubts are based on good engineering principals, knowledge and experience though Rich! It all very well encrouging Chris to "just experiment" the result is likely to be marginal improvement, it could possibly be a blown motor or ESC, it's almost certainly going to be a model that flew well reduced to flying badly. I don't see much fun in that! BEB Quote Link to comment Share on other sites More sharing options...
Chris Lee123 Posted July 9, 2016 Author Share Posted July 9, 2016 Posted by Rich2 on 09/07/2016 08:41:54: Posted by Chris Lee123 on 09/07/2016 07:59:03: Posted by Steve Hargreaves - Moderator on 08/07/2016 18:56:22: To make it go faster you will need more power. How many watts is your motor consuming now & at what current? Can you get more power from that motor? A bigger & or pitchier prop will generate more power but can the motor cope with the extra current.? A more powerful motor with a higher kv will help. How fast is the AW now? Most models tend to have a "top speed" above which they are reluctant to go without a lot more power to push them.... Watts 900 approx and 40amps ish. The motor is rated at 1350 watts and max amps for the motor is 57. No Idea has haven't tried the speed gun on it. Hi Chris, It sounds like you have capacity to spare. I am not an expert but you need a higher pitch prop. I would just experiment. I had a look on the net and there are very mixed reviews on that motor, especially on the HK website. I would start with a decent 14 X 8.5 e prop and go from there ( based on a you tube review). Good luck and keep us posted. Ps just ignore the doubters and have fun Edited By Rich2 on 09/07/2016 08:42:50 Edited By Rich2 on 09/07/2016 08:43:19 Thanks, I think I will try the props I have and see what happens. Quote Link to comment Share on other sites More sharing options...
Chris Lee123 Posted July 9, 2016 Author Share Posted July 9, 2016 Posted by Justin K. on 09/07/2016 08:07:31: Posted by Chris Lee123 on 09/07/2016 08:00:48: Posted by ChrisB on 08/07/2016 20:14:48: If you want a fast machine don't choose an acrowot. Thick wing, uc and wide cowl. I've got a Top flite giant p47 with a zen 62. I've flown with several other TF giant P51s and they all leave me standing. The p51 has a thinner wing and streamline cowl, the p47 hasn't...hence its slower. Purely down to drag and design. Edited By ChrisB on 08/07/2016 20:21:30 As I said in my original post I just want to make the plane I have quicker with the parts I have. Well unfortunately as suggested a few times above you not really going to be able to....... That's only true if its already at its optimum. If the current prop have on it is the perfect size for the motor, esc, lipo and plane then changing it wouldn't have a positive affect I understand that, but I've never said that it is currently the perfect setup. I've also not said anything about wanting a lightning fast plane, I just wanted to make an improvement on the current setup and wondered out of the props listed which would make it faster than it currently is. Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted July 9, 2016 Share Posted July 9, 2016 Some maths then.....if you are currently at 900 watts & can go up to 1300 watts without melting anything that's roughly a 40% increase in power.....as we have already discussed drag goes up with the square of the speed so to double the speed you would need a 400% increase in power..... So your 40% increase should make it faster but not by much...I doubt you'd even notice. On the downside you'd be stressing your components more & flattening your batteries faster..... Maybe it's an age thing but I like my models to have effortless performance rather than speed...rather than have them screaming around I prefer them to fly relatively slowly so I have time to perform the manouevers & to just keep going when the nose points upwards. Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted July 9, 2016 Share Posted July 9, 2016 This is not scientific Chris, nor is it electric, but illustrates, at my club, as other clubs, we have Wot 4s. Mine has a 40 Irvine with a 10 x 6 prop, and my wingman has an SC46 on his, turning an 11 x 6 prop, and you have guessed it, they both keep up with each other at full throttle. It does appear that air frames have an optimum passage through the air Quote Link to comment Share on other sites More sharing options...
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