Tim Mackey Posted January 11, 2013 Share Posted January 11, 2013 Own design based on a looky-like of the flyingwings bongo etc, I remember many years back having a mick reeves disco too. This one is of course EPP and smaller ( around 16" diameter ), elevons and rudder, electric tractor powered. The front 3 inches or so of the circle are cut out, and about the same amount at the rear to become the elevons. Can anyone suggest a starting point for the COG please. TY Quote Link to comment Share on other sites More sharing options...
Tony Bennett Posted January 11, 2013 Share Posted January 11, 2013 i have a plan for an anular monoplane some where, i will try to find it and see what it says. Quote Link to comment Share on other sites More sharing options...
Martyn K Posted January 11, 2013 Share Posted January 11, 2013 Hi Tim If it is a true circle, then this could also be linearly/logically represented as a plank/square/rectangle (I think). If so, then you need to be looking at 20% wing root as a starter. Not sure what sections or longitudinal stability method you will be using though.. Good luck Martyn Quote Link to comment Share on other sites More sharing options...
Richard Harris Posted January 11, 2013 Share Posted January 11, 2013 Tim, Maybe worth having a look HERE , there are a few PDF's of the model on the first page and give the CG position fr that model. Just a simple case of working it out for yours then. Rich Quote Link to comment Share on other sites More sharing options...
kc Posted January 11, 2013 Share Posted January 11, 2013 I found a file I downloaded a couple of years ago on the Nutball 17 inch dia which said 25 percent of root chord. Never built one myself so I dont know if it's correct. Quote Link to comment Share on other sites More sharing options...
John Cole Posted January 11, 2013 Share Posted January 11, 2013 YOu say ABOUT 16" dia and ABOUT 3" cut off the front and back. If those numbers are right then the length of the cut edge at the front should be 13". Same at the back, and the distance between the 2 cut edges should be 10". I would go for 2.5" back from the front cut edge, which should be 2.5" in front of the centre of the circle. Quote Link to comment Share on other sites More sharing options...
001 Posted January 11, 2013 Share Posted January 11, 2013 Tim, I had a Mick Reeves Disco many years ago, ( very amusing thing to fly) from memory the Cof G was about 1/3 of the way back from the front of the wing. But I think that it was like a delta, very forgiving of the position. Quote Link to comment Share on other sites More sharing options...
Mowerman Posted January 11, 2013 Share Posted January 11, 2013 Tim 2 or 3 years back I built and flew a Nutball from plans downloaded from RCGroups website this was about the same size (17" Dia), Unfortunately, the plan I have has no CG details but I am sure it will still be available on the website. Quote Link to comment Share on other sites More sharing options...
Mowerman Posted January 11, 2013 Share Posted January 11, 2013 Tim Just checked the RCGroups web site. The plan was published in March 2008 Design by 'Goldguy'CG is given as 25% root chord. ( sorry no idea how to attach link) Mine was great fun to fly but as with all depron planes easily damaged. Edited By Mowerman on 11/01/2013 16:47:06 Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted January 11, 2013 Author Share Posted January 11, 2013 Thanks chaps, I'll check the dimensions properly now, and see if I can figure it out LOL I woke this morning and thought, I fancy something new and different for tomorrows indoor meet, so found a sheet of 8mm EPP, spotted a picture of the bongo, and started cutting and building on the hoof as it were. It uses an old home wound CK outrunner, 8x4 slowfly prop 2s 400mahr lipo, and gear found in the bits box. Ive called it "Bonkers", and if it proves worthy, it may get a bit more decoration tomorrow night. Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted January 12, 2013 Author Share Posted January 12, 2013 Flight report. It flies..... sort of...... LOL. Set the COG at around 25% of chord at root, but it flew VERY high alpha, I would say around 10 or even 11 oclock! I moved the battery as far forward as it would go, but that made litle difference, so I ended up with a slight camber on the elevons, instead of the reflex I had set. I think I overdid the down thrust, and the COG is rearward - the motor is also now goosed, so when I replace it I will reduce the downthrust a lot, as well as adjust the balance It was fun and definately worth the effort Now, another question for you guys. Down thrust. A few of us were chatting, and opinions differ as to the reason - especially on a model like this ( flat plate non aerofoil blunt wing ). Some said that downthrust will actually pull the model up, and get the wing into a suitable AOA for flight - the theory being the prop will try to " level out" and hence pull the wing L/E up. Others said its the opposite. So.... for a huge prize, which is correct ? Quote Link to comment Share on other sites More sharing options...
Tom Wright 2 Posted January 12, 2013 Share Posted January 12, 2013 Hi Tim. All my flat wingers need down thrust ,even when the wing to tail incidences are zero zero ...BUT!....all have a long moment and generous tail area , Your model as in effect short coupled and will obviously be more sensitive to the centre of pressure position and any deflections at the rear . There is a theory that suggests a flat blunt l/e damps pitch sensitivity and presents the wing at an aerodynamic positive angle of attack so wether or not any of this is relevant matters not as it's great to see you modelling and posting again. Tom. Quote Link to comment Share on other sites More sharing options...
Martyn K Posted January 12, 2013 Share Posted January 12, 2013 Hi Tim My understanding is that the thrustline should pass through the CoMoments (the single point where thrust, drag,weight and lift can be vectored) (and which will also move as velocity increases/decreases), so if the motor is below the wing, it will need downthrust, if it is above the wing (assuming it is a flat plate) then it will need upthrust (All thing being equal - which they aren't).. BEB will give you a better answer though,,, Martyn Quote Link to comment Share on other sites More sharing options...
Dave Bran Posted January 12, 2013 Share Posted January 12, 2013 I have a dozen or so EPP disc type planes, inc several own designs called NuttyOne, NuttyTwo, etc, Nutballs, RoundOne, PiPlane, etc, etc, all about the size of yours Tim. Firstly, your downthrust looks WAY too much. Secondly, discs are very tolerent of CG, but most of mine close to your size fly OK at about 100-120mm back. I regularly run one disc of about that size back at 140-150 mm and it prop hangs and sits in high alpha perfectly stable with no rock at all like nothing else, but that far back needs a small amount of down held in for speed flight. Does wind up the £100 milled out shockie brigade with its antics though............ Tee Hee........ Many of mine use the A2204 Suppo/SP motor with a GWS 8x4.3 slowfly cut down to 7.5x4.3. Hope this helps........... Quote Link to comment Share on other sites More sharing options...
Dave Bran Posted January 12, 2013 Share Posted January 12, 2013 Posted by Tim Mackey on 12/01/2013 18:28:59: Some said that downthrust will actually pull the model up, and get the wing into a suitable AOA for flight - the theory being the prop will try to " level out" and hence pull the wing L/E up. What it will do depends on where the prop is relative to the CG! Since we are talking front prop, no doubt they also believe the world is flat,and all the planets revolve round the earth. Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted January 12, 2013 Author Share Posted January 12, 2013 Posted by Dave Bran on 12/01/2013 21:22:29: Posted by Tim Mackey on 12/01/2013 18:28:59: Some said that downthrust will actually pull the model up, and get the wing into a suitable AOA for flight - the theory being the prop will try to " level out" and hence pull the wing L/E up. What it will do depends on where the prop is relative to the CG! Since we are talking front prop, no doubt they also believe the world is flat,and all the planets revolve round the earth. What!!! - the earth isnt flat ?? LOL, thanks Dave, and your comments confirm my decision to reduce the downthrust Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted January 12, 2013 Author Share Posted January 12, 2013 Posted by Martyn K on 12/01/2013 19:43:27: Hi Tim My understanding is that the thrustline should pass through the CoMoments (the single point where thrust, drag,weight and lift can be vectored) (and which will also move as velocity increases/decreases), so if the motor is below the wing, it will need downthrust, if it is above the wing (assuming it is a flat plate) then it will need upthrust (All thing being equal - which they aren't). . BEB will give you a better answer though,,, Martyn Ah but will I understand it ? LOL...cheers Martyn Edited By Tim Mackey on 12/01/2013 21:57:09 Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted January 12, 2013 Author Share Posted January 12, 2013 Thanks for your kind words Tom Slowly trying to get things back to normal, but a LONG way to go yet. Quote Link to comment Share on other sites More sharing options...
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