Mike Churchill Posted July 7, 2007 Share Posted July 7, 2007 I recently passed my A Cert with high wing trainer so now moving to low winger. After reading an article in RCME about converting a SpeedAir 40 to electric I thought it would be a good model for my first low winger but in its original IC form.It is now ready to fly but I need to be sure about a couple of points: a)I have installed a JEN 37 (Should have power of 40 ?) Is that enough to get off the ground and fly like a trainer? b)The CG is a tad forward of recommendations (a few mm). Is that a bad thing and should I try to get an exact balance? The trouble is if the answer to a) is I need a bigger engine the CG will be even further forward!Advice would be appreciated Quote Link to comment Share on other sites More sharing options...
Grant Darnley Posted July 7, 2007 Share Posted July 7, 2007 A forward CG is always preferable to a rearward one, but not in extreme measures or you will run out of ele movement on the landing flare. The J'en should be plenty power, one american website quotes the weight as 5.3lbs which is roughly what a trainer weighs. Quote Link to comment Share on other sites More sharing options...
Mike Churchill Posted July 7, 2007 Author Share Posted July 7, 2007 Many thanks for that. My instinct was that forward CG was preferable to rear and anyway it is only a few mm. If I put in the alternative engine, a SuperTigre 42 the CG would be much further forward. Quote Link to comment Share on other sites More sharing options...
Grant Darnley Posted July 9, 2007 Share Posted July 9, 2007 not sure mike, never had one so don't know how heavy it is Quote Link to comment Share on other sites More sharing options...
Myron Beaumont Posted July 9, 2007 Share Posted July 9, 2007 Excuse me, but what you call the CG isn't .What you are all talking about is fore & aft only..If your servo's/battery /everything else are more or less above the thrust line of the engine you will need some dihedral to compensate especially for the "CG" as you call it on a trainer.The CG of any 3-dimensional object can only be located by considering all 3 dimensions .So the CG must be located along all 3 axes. Keep the CG BELOW the centre of lift(trainers only)) whether it's high or low wing and the stability (for a trainer )will be OK.It doesn't matter which configuration. To those that might disagree - Imagine a low winger with 20 degrees of dihedral ? Wouldn't it be better than a high winger with anhedral wings ?? Quote Link to comment Share on other sites More sharing options...
Mike Churchill Posted July 9, 2007 Author Share Posted July 9, 2007 Many thanks for that. I don't think I have a problem with regard to balance on the axes other than fore and aft. I understood the fore and aft balance point to be fairly critical as it is the one usually specified by model designers. Perhaps I used the term CG loosely? Quote Link to comment Share on other sites More sharing options...
Myron Beaumont Posted July 9, 2007 Share Posted July 9, 2007 Hi Mike Of course it's critical_ the fore & aft thing , but I think you've missed the point ,I think (correctly) that High wing Versus low wing is an issue based on the CG above or (& I mean)ABOVE "the datum come -thrust line" otherwise it will fly better inverted .Look at how birds fly ! Maybe we could start a thread on high versus low wing thread & I will start by saying that it all depends what you really want .A totally stable flying m/c upright or inverted OR a 2nd model with a low wing THAT RESPONDS LIKE A HIGH WINGED CESSA type thing that I thought you were after info about for your 2nd model !? Quote Link to comment Share on other sites More sharing options...
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