Archive/OldMag/CAP 3D Conversion

<body topmargin=0 leftmargin=0 marginheight=0 marginwidth=0> <table cellpadding=0 cellspacing=0 border=0><tr> <td valign="top" rowspan="2" width=156 BGCOLOR="#FFFFFF" TEXT="#080000" bgproperties="fixed" background="00e9cc00egerdp.jpg"> <div> <B> <STYLE>  </STYLE>  </B></div> <bR> <bR> <bR> <bR> <bR> <div> <B> <TABLE BORDER="0" CELLPADDING="2" CELLSPACING="1" WIDTH="97" BORDERCOLORLIGHT="#C0C0C0" BORDERCOLORDARK="#808080" FRAME="BOX" RULES="ALL" HSPACE="0" VSPACE="0" > <tR> <tD VALIGN=TOP HEIGHT= 313 ><NOBR><div> <A HREF="index.htm" TARGET="_top" TITLE="Home Page"><U><B>Home</B></U></A></div> <div> <A HREF="id2.htm" TARGET="_top" TITLE="Archive"><U><B>Archive</B></U></A></div> <div> <A HREF="id5.php" TARGET="_top" TITLE="Contact"><U><B>Contact</B></U></A></div> <div> <A HREF="id6.htm" TARGET="_top" TITLE="Downloads"><U><B>Downloads</B></U></A></div> <div> <A HREF="id7.htm" TARGET="_top" TITLE="Events"><U><B>Events</B></U></A></div> <div> <A HREF="id8.htm" TARGET="_top" TITLE="For Sale"><U><B>For Sale</B></U></A></div> <div> <A HREF="id9.htm" TARGET="_top" TITLE="Galleries"><U><B>Galleries</B></U></A></div> <div> <A HREF="id14.htm" TARGET="_top" TITLE="Games"><U><B>Games</B></U></A></div> <div> <A HREF="id15.htm" TARGET="_top" TITLE="Links"><U><B>Links</B></U></A></div> <div> <A HREF="id16.htm" TARGET="_top" TITLE="Magazine"><U><B>Magazine</B></U></A></div> <div> <A HREF="id17.htm" TARGET="_top" TITLE="Newsletter"><U><B>Newsletter</B></U></A></div> <div> <A HREF="id18.htm" TARGET="_top" TITLE="Reference"><U><B>Reference</B></U></A></div> <div> <A HREF="id88.htm" TARGET="_top" TITLE="Video"><U><B>Video</B></U></A></div> <div> <A HREF="id19.htm" TARGET="_top" TITLE="Weather"><U><B>Weather</B></U></A></div> </NOBR></tD> </tR> </TABLE></B></div> <bR> </td> <td valign="top" colspan=2 height=100 BGCOLOR="#FFFFFF" TEXT="#080000" bgproperties="fixed" background="00f00640egerdp.jpg"> <bR> <bR> <bR> <div> <I><B>Archive </B></I></div> <div> </div> </td> </tr><tr> <td valign="top" height=380 colspan=2 BGCOLOR="#FFFFFF" TEXT="#080000"> <div> <FONT SIZE="2" COLOR="#000000" FACE="Arial" > <STYLE>  </STYLE>  </FONT><A HREF="id78.htm" TARGET="_top" TITLE="Archive/Old Mag/CAP 21 Part 3"><U><B><< </B></U></A><B>  </B><A HREF="id53.htm" TARGET="_top" TITLE="Archive/Old Mag/Your Eyesight"><U><B> >></B></U></A></div> <div> <TABLE BORDER="0" CELLPADDING="10" CELLSPACING="1" WIDTH="602" BORDERCOLORLIGHT="#C0C0C0" BORDERCOLORDARK="#808080" FRAME="BOX" RULES="ALL" HSPACE="0" VSPACE="0" > <tR> <tD VALIGN=TOP HEIGHT= 2656 WIDTH="580"><div> <B> <A NAME="cap_21_part_4___3d_conversion"><IMG BORDER="0" SRC="1x1.gif" HEIGHT="1" ALIGN="bottom" WIDTH="1" HSPACE="0" VSPACE="0" ></A></B><FONT SIZE="3" COLOR="#009900" FACE="Arial" ><I><B>CAP 21 Part 4 - 3D Conversion</B></I></FONT></div> <bR> <div> <IMG SRC="3ae3aed0.jpg" border=0 width="314" height="237" ALIGN="LEFT" HSPACE="5" VSPACE="5">I finished the last article on this `plane by saying, “… what more could one ask?”. Well, I'll tell you; 3D matey, that's what! </div> <div> (<FONT SIZE="2" COLOR="#0000CC" FACE="Arial" ><A HREF="id52.htm" TARGET="_top" TITLE="Archive/Old Mag/CAP 21 Part1"><U>Click Here for Parts 1, 2, & 3</U></A></FONT>) When the CAP was originally finished there wasn't much in the way of 3D flying at that time, and even though I was hovering all over the place with a Limbo Dancer, to the consternation of many of our more wimpy members, the thought of hovering and 3D'ing the CAP never entered my feeble mind. After all, we're talking about a 30 year old design here, not some modern smart arse new kid on the block 3D A.R.T.F. Pat French may have been a good designer, but he couldn't have foreseen the development of 3D way back then.</div> <bR> <div> <IMG SRC="3b33aec0.jpg" border=0 width="314" height="236" ALIGN="RIGHT" HSPACE="5" VSPACE="5">When flying the CAP I'd noticed that the verticals eventually ran out of steam. Sometimes I'd try to prop' hang, at great height you understand, and it'd slide back after a few seconds every time. Also, it had a few frightening traits, namely a huge pitch down on the application of rudder, due I think, to the wing/tail incidence problem I mentioned in the previous article. This made snap rolls interesting as an inverted flick would get you an extra 180 degrees of rotation for exactly the same stick input as an upright flick - not something you want when hot dogging on the deck! Even stall turns would require full up at the point of rotation to stop it tucking under.</div> <bR> <div> Long after I'd stopped flying it in favour of more modern 3D'able designs, i.e. Funtana, I was wondering what I could get for it on E-Bay when the thought, “Pity it won't 3D.” slipped through my mind. Even before the thought had evaporated I had the tape measure out and was comparing elevator and rudder volumes with Funtana, Edge, Extra etc. </div> <bR> <div> <IMG SRC="3b23aec0.jpg" border=0 width="314" height="236" ALIGN="LEFT" HSPACE="5" VSPACE="5">I had an idea I could bevel the tail and fin to get more elevator and rudder movement. I also figured I could do it without unhinging the control surfaces, and that's just what I did! I just cut the corner off with a Stanley knife, gave it a light sand and covered with a strip of matching film that slotted between the hinges. I got about 50 degrees each way for the rudder and elevators. The ailerons, although looking a little small for 3D, were nonetheless pretty big for a normal aerobatic model. Really I needed to cut into the wing and make new and bigger ailerons, but, as I'm a lazy S.O.B. I decided not to worry about it right now and just get everything else done first!</div> <bR> <div> <IMG SRC="3b53aec0.jpg" border=0 width="314" height="236" ALIGN="RIGHT" HSPACE="5" VSPACE="5">The separate elevators were originally driven by a pair of heavy duty snakes, but they wouldn't bend enough with the big arc described by the control surface horn at 40 degrees plus each way. It looked as though twin elevator servo's mounted in the rear fuselage was the only way to go. I wasn't keen on this as two servos and linkages in the tail would make it tail heavy. That'd mean lead in the nose and the weight increase wouldn't help 3D'ability at all. So what to do? In the end I joined the elevator halves with a 6 gauge piano wire joiner and drove them via a carbon push rod, with ball joints either end, from the single servo mounted under the wing seat in the fuselage. And it works brilliantly and saves the weight and cost of an extra servo! The rudder remains pull/pull cable driven.</div> <bR> <div> <IMG SRC="3b73aec0.jpg" border=0 width="314" height="236" ALIGN="LEFT" HSPACE="5" VSPACE="5">The next problem was - could it make enough thrust to hover? The model weighs 14.5 pounds and from everything I'd read on internet forums a 30cc (1.80) glow engine should have just enough. Obviously then - unless Super Tigre's were inferior to everything else - it should just be about the careful selection of the propeller. And at the 2004 Nat's I found just the thing in the shape of a brace of wooden 20 x 6 Smart propellers for a tenner - beat that! </div> <bR> <div> The next snag was the notorious Super Tigre rich midrange problem. A quick sortie on the internet to the Perry (carb' and pump) website revealed exactly the Perry carb' I needed for an unpumped installation (Part: 5001). I had to wait a couple of weeks for Just Engines to get one in stock, but it arrived exactly when they said it would. Hopefully, it would solve the problem.</div> <bR> <div> <IMG SRC="3b83aec0.jpg" border=0 width="314" height="236" ALIGN="RIGHT" HSPACE="5" VSPACE="5">The bigger propeller was now grazing the deck so a taller undercarriage was needed. Fortunately I had just the thing in the shape of a two piece ally job that had an extra couple of inches of lift and gave adequate clearance. Phew!</div> <bR> <div> So, back to the wing. I decided to bite the bullet and correct the wing incidence problem. The job wasn't as bad as I'd imagined it would be. I cut out toward the trailing edge of the wing seat and filed out the wing dowel mounting holes until I had 1 degree of positive incidence. After filling and sanding I found I now had 1.5 degrees! Ho hum! It still flies with down elevator but only a 10th of that used before. By the time I'd sorted the wing incidence problem I didn't have the enthusiasm left to hack out my wing for new and bigger ailerons. I decided to just double bevel them as per the tail surfaces and see how we went with that. 40 odd degrees each way was achieved and it certainly looked plenty enough! I also sealed the hinge lines with film on both ailerons and elevators.</div> <bR> <div> <IMG SRC="3b93aec0.jpg" border=0 width="314" height="236" ALIGN="LEFT" HSPACE="5" VSPACE="5">So, how's it fly? Well, still quirky but a lot of fun. Harrier rolls are difficult to maintain, probably because of those slow old Hitec jumbo servo's not keeping up, plus I'm no expert! It hovers and torque rolls okay, the 20 x 6 prop' developing loads of thrust compared to the original 18 x 8. I haven't done any low hovering yet because of issues with the Perry carb'. The Super Tigre 3000 runs and throttles nicely throughout the range on its Perry carb' but leans out a lot when the nose is vertical, even when it's stumbling rich in level flight. I should have bought the pumped version! Also the needle valve has a habit of unscrewing itself in flight. Its only restraint is the rubber sealing ring - maybe I got a slack one. Consequently, I daren't trust it in a low hover. I'm told the O.S. 7D carb' is the one to have, so may try this later. When everything is right, however, it runs beautifully!</div> <bR> <div> <IMG SRC="3b0e3350.jpg" border=0 width="227" height="309" ALIGN="RIGHT" HSPACE="5" VSPACE="5">The motor has now had a season running on fuel containing 9%castor, 9% synthetic and 5% nitro. Despite dire warnings from the importer there have been no adverse effects. The recommended 11% total oil content runs too hot for me, the engine not sounding or feeling happy. You tend to get picky about things like this when it's hanging on the prop' five feet off the deck!</div> <bR> <div> The ailerons turned out to be just effective enough when hovering unless a gust of wind pushes it round. Interestingly the last one third of aileron movement seems to have no noticeable effect, so the only way to get more aileron power would be broader chord ailerons. All in all I'm pretty happy with it, quirks and all. It does the most amazing waterfall, when I can nail it, rotating around the C.G. absolutely on the spot just like the full size. This is the only model I've ever had that would do this. Oddly, It'll only do it inverted; it won't even consider it upright! The relatively heavy wing also likes to carry on rotatating in flick manoeuvres, making low level larking about a bit dangerous. The upright to inverted flick difference is still there but not as extreme as it was.</div> <bR> <div> So overall it's a success. It gets me used to the look and feel of a largish model, has expanded its repertoire to include 3D manoeuvres, untidy but do-able nonetheless, and I'm looking forward to flying it again this season. I feel better servo's would make a big difference to it, but have you seen the price of 10kg digitals? Phew! <I>G:-)</I></div> <div> <I>FF-27-4-06</I></div> </tD> </tR> </TABLE></div> <div> <A HREF="id78.htm" TARGET="_top" TITLE="Archive/Old Mag/CAP 21 Part 3"><U><B><< </B></U></A><B>  </B><A HREF="id53.htm" TARGET="_top" TITLE="Archive/Old Mag/Your Eyesight"><U><B> >></B></U></A></div> <bR> </td> </tr></table></body>