Tim Mackey Posted April 13, 2009 Share Posted April 13, 2009 Hi Brian and welcome aboard . Having read your article, I found it entertaining and interesting, and indeed further proof again that electric to IC "equivalent" is notoriously difficult to achieve for a variety of reasons. Not least - unlike an IC engine, which tend to be suited to just one fairly narrow power band and consequent very limited prop range, an electric motor can be made to behave quite differently using a variety of props and cell counts, even though the constant Kv remains the same. I have no experience of contra rotating props so can offer no commment on the results of your experiments, but the idea is indeed interesting. Others here have also done a fair bit on this concept - not least Roy Thompson, whose video tutorial we recently hosted on the forum. Another "system" which I have used from time to time is the "double up add zero" method, ( not mine I hasten to add, but borrowed from an active electric flight modeller across the big pond ) and this can work pretty well and maybe fits a little closer with the reslts you found? Take an IC engine of say .35 size. double it to 70 and add 0 results? = 700. A ball park figure of 700 watts which is pretty close to your reckoning on the .25 size engine of 600. This "double add zero" system would show of course 500 watts for the .25. Another big factor in trying to make these simplified comparisons is the vast difference in power outpouts between different engines - a cooking plain bearing old .40 Merco will behave somewhat differently to a Rossi rear induction of the same capacity! Anyways, glad you found the whole project interesting and that my article did not give you too much of a bum steer Cheers.... Tim.Edited By Timbo - Moderator on 14/04/2009 11:03:40 Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted April 14, 2009 Share Posted April 14, 2009 Hi BRian. Very interesting article. I always knew that i.c was so much simpler than electrics A couple of comments. The CAP 21 really needs a .32 for the full aerobatic potential. The undercarriage plate is one piece as shown on the sketch of the plan. For your contra props, how about a Supermarine Seafire Mk 42. THis is just a Spitfire 21 which can either be flown with a 5 blade single prop or a 6 blade contra prop. Another alternative is the Westland Wyvern Quote Link to comment Share on other sites More sharing options...
brian squelch Posted April 14, 2009 Share Posted April 14, 2009 I thank you and Tim for your kind remarks. I'm a bit of a timid flyer so the power available will probably be enough for me. I did fit the U/C plate as one piece. I got the fore/aft angle about right but the transverse one was too great. and the model has a bit more dihederal than your plan showed. nevertheless, it still looks fine. I think its a very 'pretty' model. The models you suggest are good candidates for contra-props but a total of 400watts seems a bit on the small side. To do a semi-scale for that power would be a bit 'fiddley' I think. It would break my heart to 'prang' such a model. Regards Brian Quote Link to comment Share on other sites More sharing options...
brian squelch Posted September 11, 2009 Share Posted September 11, 2009 Dear Peter, As of October BT are withdrawing their free web facility. Since, in order to read the article I wrote concerning the CAP 21 electrification, the first posting links to my Geocities BT web-site, the thread will soon become defunct. It has probably served its purpose and should be deleted. As the Moderator will you please delete this thread (or advise me how to do so). I may be able to put it on a club web-site in future. On another topic. Over the summer I worked on a project to scratch-build a glider tug. It flew its final test in August and my test pilot said it flies similarly with and without the glider attached. In its final form it looked like a 'Roamer' on steroids with an additional lower wing. I have never seen a description of such a 'type' in any model magazine. I have written-it-up and rather hoped you might look it over. It has an I/C engine (Tiger 60)and the design is functional rather than pretty. If you would take a look and 'polish' some plans I would be grateful. In the past I have attached the article to an email. Its about 14 Meg and takes about 5 mins to down load. If you would take a look, please let me know the address to which I could send it. Regards Brian Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted September 11, 2009 Share Posted September 11, 2009 I have PMed you Peter Quote Link to comment Share on other sites More sharing options...
brian squelch Posted September 12, 2009 Share Posted September 12, 2009 Dear Peter, I don't know what 'PMed you' means. Should Gordon Brown be worried? Regards Brian Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted September 12, 2009 Share Posted September 12, 2009 IT means that I sent you a personal message with my address. Quote Link to comment Share on other sites More sharing options...
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