Adrian Day Posted January 19, 2012 Author Share Posted January 19, 2012 ENGLISH MR ENGLISH ?? TANGENT??Sorry Steve you have lost me a little .. not 100% knowing .. Im not sure yet will have to have a read up on the offset sorry yes they was fast very happy cant get better than that as soon as i find out will msg back thank you Adrian Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted January 19, 2012 Share Posted January 19, 2012 Ah.....another one who spent his maths lessons staring out of the window watching the girls playing hockey..... Well what we have is effectively a right angle triangle where the opposite side of the triangle is the amount of offset (in distance) that we need & the adjacent side of the triangle is effectively the distance from the firewall to the prop driver. We know this distance (its the length of the motor basically) & we know the side thrust angle (probably 2-3 degrees) so from SOHCAHTOA we know that the Tangent of 2 or 3 degrees equals the Opposite length (which is what we want to find) divided by the Adjacent length (length of motor) so rearranging the formula tells us that the Opposite (or offset in our case) equals the Tangent value of the side thrust multiplied by the length of the motor (Adjacent length).... Probably about 3mm.... This might help........ And you thought working out the watts was difficult!!!! Quote Link to comment Share on other sites More sharing options...
Adrian Day Posted January 19, 2012 Author Share Posted January 19, 2012 you sure you wasn't a maths teacher in a past life well when i was a school life wasn't great and the teacher i had didnt give a hoot as long as the students turned up didnt really set any work . so working out things like this will never be my strong point but it does get in there in the end.. just not as fast as everyone else sorry so in short then the difference in distance back from the left hand side front to the mount and the right hand side front to the mount ??? in deg or mm l Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted January 19, 2012 Share Posted January 19, 2012 Maybe in a past life but definitely not this one...... Hope you don't think I was having a pop at your maths skills......Tis all very much tongue in cheek.... They say a picture is worth a thousand words so heres a thousand words.... Geometry tells us that the Tangent of an angle equals the Opposite divided by the Adjacent thus the Opposite equals the Adjacent multiplied by the tangent of the angle.... Lets put some numbers in....lets say the side thrust is 3 degrees & the distance from the firewall to the prop driver is 50mm.....then the Offset equals 50 x TAN 3.....any schoolboy will tell you that the value for TAN 3 is 0.0524 So 50 x 0.0524 equals 2.62mm So we need to offset our motor centreline on the firewall by 2.62mm to get the propdriver dead central in the cowl......to me thats 2.5mm & if you can work to closer tolerances than that then you're a better man than I Gunga Din..... HTH.... Quote Link to comment Share on other sites More sharing options...
Adrian Day Posted January 19, 2012 Author Share Posted January 19, 2012 according to the drawing the is a motor of set of 1mm to the right hand side of F1 Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted January 19, 2012 Share Posted January 19, 2012 Well Tim might be the one to advise here but that doesn't sound right to me.....if you offset the mounting of the motor towards the right but keep the o/p shaft in the middle you have just applied left thrust.....& I don't think thats what you need... I'll have to take a little look at the plans.... All my theory is applied by looking down on top of the motor whilst stood behind the model... Quote Link to comment Share on other sites More sharing options...
Adrian Day Posted January 19, 2012 Author Share Posted January 19, 2012 thats Ok Steve didnt take it as you was taking a pop its cool npI personally dont think maths is my strongest point im a hands on worker.. and my skills are computers and radio's 19 grade A's and a distinction diploma ACITP. but as i have yet to use it thats near worthless. And the speed at which things are changing in the world of laptops n pc its about as good as a chocolate fireguard .. wow thats some maths there will read that a few times then get back to you if you dont mind?? Adrian Quote Link to comment Share on other sites More sharing options...
ian ludwell Posted January 19, 2012 Share Posted January 19, 2012 Hello to one and all. The Pixie is back on again,nice to see all this activity.Adrian,your build looks very good,i have built one in the past. It flies beautifully, Are going to test fly the Pixie yourselfe or arrange for someone else to fly her? I Quote Link to comment Share on other sites More sharing options...
Adrian Day Posted January 19, 2012 Author Share Posted January 19, 2012 Hi Ian glad to have you aboard the postthank you for you kind comments i like the look of your model seems the blue and white look is a good idea ... have gone and bought blue servos too so it all blends in. . was hoping to test fly this one myself is she a dream to fly ?? may have a word around and see if there is someone close to me that can test it for me as I'm a little new to this..Do you mind me asking what size wheels you have on your model they look like they're smaller than said on the plant that I have .. 1" or 2" cant wait to fly this one Have to say that pictures don't do this model justice. she is better in person. Adrian Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted January 20, 2012 Share Posted January 20, 2012 Ran a ruler & a protractor over my Pix E plan last night.....Tim has set the side thrust at two degrees & the distance from F1 to the front of the cowl is 30mm Using the formula from yesterdays lesson would give us TAN 2 X 30mm which equals 1.047mm.....spookily the offset shown on F1 is........1mm. So that's an extra free period for Mr Hooper & 1 hours detention for the rest of you...... Just a thought too Adrian....the offset shown on F1 is indeed to the right but this is the front view...ie as if you were looking at it from the front. From behind the model the motor base should be offset to the left thus giving some 2 degrees of right thrust. I also checked the length of my motor from mounting to prop driver & its actually 40mm so I will need to move F1 back slightly or build a thicker cowl front. For this motor then the offset should be TAN 2 x 40mm which equals 1.4mm....so fractionally more than the plan..... Now my only problem is to build to an accuracy of 0.5mm.......er... Quote Link to comment Share on other sites More sharing options...
Tim Hooper Posted January 20, 2012 Share Posted January 20, 2012 I only pop in here to learn........Just to qualify what Steve has said; Looking at F1 from the front, the motor is offset to the right by 1mm. However, when installed in the fuselage, and looking down from above, the view changes so that the motor is offset to the left of the fuselage centreline. Mounting F1 slightly askew brings the front of the motor shaft through the centreline.The downthrust is dealt with in the same way. Here's the sidethrust, viewed from above; Adrian, there are lot more pics of the build on my own build thread, than were published in the mag so you might find the answers to some of your queries there. Incidentally, if this is your very first RC model, then you really need somebody to fly it for you to begin with. You've invested far too much time in it to see it crash in the first few seconds of flight! tim Edited By Tim Hooper on 20/01/2012 09:51:57 Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted January 20, 2012 Share Posted January 20, 2012 Posted by Tim Hooper on 20/01/2012 09:50:15: Incidentally, if this is your very first RC model, then you really need somebody to fly it for you to begin with. You've invested far too much time in it to see it crash in the first few seconds of flight! tim Wise words from Mr Tim......this model is quite fragile due to its lightweight construction.....definitely built to fly rather than crash.... It would be a shame to see all that hard work (& maths ) end up as a few broken sticks of balsa..... Quote Link to comment Share on other sites More sharing options...
ian ludwell Posted January 20, 2012 Share Posted January 20, 2012 Hello to all, Just a word about my late Pix-e,which collided with the upcoming field due to signal loss last year. I have been left with,pair of wings,struts,undercarriage,cowl and tail feathers,all in good order. As is suggested by Tim and Steve,this can be fragile if not handled correctly. So i am now rebuilding the fuselage solid in 1/8" sheet balsa. Having fitted the E-Max 2812 1650 Kv motor( with 9x6 SF prop) in place,fitted wings,placed servos and the tray in place between formers,placed tail feathers in situ,the Pix-e balanced on the spar. But there was still the ESC,r/x and Li-Po to locate up front. So now the servos are at the back,leaving room up front or between formers to get C of G correct..Adrian, the wheels are 40mmx10mm light weight foam. Sorry to prattle on..keep up the good work......Ian Edited By ian ludwell on 20/01/2012 12:32:41 Quote Link to comment Share on other sites More sharing options...
Adrian Day Posted January 20, 2012 Author Share Posted January 20, 2012 thank you guys looks like its going to be fun putting this into the plane .. not done this style before.. everything i have done is engine power and cowling not built up.... I have flown about 5 times but some time ago.. So thinking about getting someone who knows what they are doing to test it .. not sure who yet though.. may have a word with Mr C Bliss think there is a lot gone into it from all three sides here both of you and myself.. I know I couldn't have done it on my own.. Very grateful for everyone's kindness in here .. its like a model building family sometimes sound stupid but why do we of set like this ? i have my ideas but im not going to air them as dont want look stupid if I'm wrong Quote Link to comment Share on other sites More sharing options...
Pete B Posted January 20, 2012 Share Posted January 20, 2012 Putting it simply, Adrian ( I know no other way), imagine you are standing behind the aircraft, looking forward. The prop will rotate clockwise as you see it. The torque effect from turning the prop will cause the motor to want to turn anti-clockwise, which will have the tendency to turn the a/c to the left. Setting a bit of right thrust will compensate for this effect.Regarding the down thrust, the thrust line through the prop shaft is lower than the mean incidence of the wing, so that, when under power, the model will tend to rotate upwards around the wing. Setting some down thrust will again compensate for this. I'm ready for the incoming flak from the aerodynamicists! ......... Pete Quote Link to comment Share on other sites More sharing options...
Adrian Day Posted January 20, 2012 Author Share Posted January 20, 2012 Pete B thank you that put in perfect terms understood that one perfectly.. something's just need explaining and then when you do things next time it make life easier .. and gaining know how is always a plus..Aerodynamicists will pull that one apart i guess .. they have terms i would only be able to guess what they would mean or how it would work..again well put thank you Quote Link to comment Share on other sites More sharing options...
Adrian Day Posted January 20, 2012 Author Share Posted January 20, 2012 sorry for the multi post dont know why it did that only clicked send once odd Ian well i have to say i really like the idea of the full sides may do that to not on this model but on another ..i see you have nearly or if not the same motor as me .. what esc did you use im using 18A some say a 20A would be better.. but got it now..thank you for the picture i like to see whats happening rather than just explanations .. for some reason things sink in better 40 mm wheels they look well suited to this model like it.. will look online for some thank you Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted January 20, 2012 Share Posted January 20, 2012 Petes explanation for side thrust is spot on but a little more explanation for downthrust which goes like this........ Because the main drag producer (the wing) is above the main thrust producer (the propellor) then the application of power will cause the model to rotate around the CoG & raise its nose.....we counter this with a little downthrust...... For a low wing aeroplane then you might expect to need upthrust because the thrust line is above the drag line causing the application of power to rotate the nose downwards....in theory this is indeed the case but in practice the thrust & drag lines are quite close together....also low wing models tend to have thinner "slippier" wings which reduce drag hence the moment is reduced to the point where its effect is negligable.....so we don't bother.... These fine chaps had a large range of cheap foam wheels in last time I visited. Can't find 'em on the website so mayhap a phone call is required..... Quote Link to comment Share on other sites More sharing options...
Pete B Posted January 20, 2012 Share Posted January 20, 2012 Thanks for that, Steve - I suspected it was drag but thought that was too simple!Pete Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted January 20, 2012 Share Posted January 20, 2012 Maybe we should pause for a moment & remember the words of Mr R.J. Mitchell "If anybody ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me: it's all balls." Quote Link to comment Share on other sites More sharing options...
ian ludwell Posted January 20, 2012 Share Posted January 20, 2012 Hello, Adrian,i shall couple my trusty Watt meter into the system and see how the power situation looks when running and choose accordingly. Quote Link to comment Share on other sites More sharing options...
Adrian Day Posted January 20, 2012 Author Share Posted January 20, 2012 Posted by Steve Hargreaves on 20/01/2012 14:12:11: Maybe we should pause for a moment & remember the words of Mr R.J. Mitchell "If anybody ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me: it's all balls." laughing @ this comment never heard this one before.. but that's true in a lot of situations Ian i thank you in advance for your testing very grateful ..am wondering if its going to be more than what i have got in.. Steve / Pete thank you for all that info .. well i do think this plane business is more complicated than if first looks ... but with people such as yourselves giving the info does make some of it a little more digestible .. still i think its gong to take some time to work this little lot out.. but from what you have put has giving me a good insight into what i needed to know its good having people all clued up on the ideas at hand .. thank you all Quote Link to comment Share on other sites More sharing options...
Adrian Day Posted January 21, 2012 Author Share Posted January 21, 2012 Posted by Steve Hargreaves on 20/01/2012 09:24:11: Ran a ruler & a protractor over my Pix E plan last night.....Tim has set the side thrust at two degrees & the distance from F1 to the front of the cowl is 30mm Using the formula from yesterdays lesson would give us TAN 2 X 30mm which equals 1.047mm.....spookily the offset shown on F1 is........1mm. So that's an extra free period for Mr Hooper & 1 hours detention for the rest of you...... Just a thought too Adrian....the offset shown on F1 is indeed to the right but this is the front view...ie as if you were looking at it from the front. From behind the model the motor base should be offset to the left thus giving some 2 degrees of right thrust. I also checked the length of my motor from mounting to prop driver & its actually 40mm so I will need to move F1 back slightly or build a thicker cowl front. For this motor then the offset should be TAN 2 x 40mm which equals 1.4mm....so fractionally more than the plan..... Now my only problem is to build to an accuracy of 0.5mm.......er... Sorry!! Just seen this post it was further up the post and I didn't know it was there.. really sorry. thank you for looking into that for me.. how do you get closest to the 0.5mm that's not going to be easy with out a micrometer I would guess that's going to be the only way it could be done that's something I don't have.. The motor that your using is still the same one as I'm using..? or you going with a different one..when you say that the 40mm is from mount to the prop driver, do you mean the back of the prop driver or the tip.. so I can measure my one just to be sure.. ..then i can get my model spot on Too.. Quote Link to comment Share on other sites More sharing options...
Adrian Day Posted January 22, 2012 Author Share Posted January 22, 2012 Well been waiting for more parts to finish this model.. now i have them all i think.. just waiting for the slow fly prop..not got much done today seems that even though i have had some time to myself its not gotten anything done. but least now i have the wheels sorted and the landing gear looking a little better.and a kind friend ((((Steve)))) has sent me some shrink for doing the wiring so thank you there kind Sir.. oh and i have made a small battery holder not sure if its going to work well but .. its a trial and error work in progress .so i got something done how ever little but as they say little each day the model will get finished ... and she will Quote Link to comment Share on other sites More sharing options...
Tim Hooper Posted January 22, 2012 Share Posted January 22, 2012 Adrain, Glad to hear that there's a bit of progress every day - so keep at it! tim Quote Link to comment Share on other sites More sharing options...
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