August, 2003 - RC Soaring

TECH TOPICSDave RegisterBartlesville, Oklahomaregdave@aol.comAPOLECAT AERO’S XP3 DLGlittle while ago one of DennyMaize’s XP3 kits showed up at thehouse. Upon opening the box, a reallyserious round of cussing and carryingon ensued. Cats dove under couches.Paint peeled off the walls. Waterboiled in the pipes.After regaining some composure I hadto admit there was just no way I couldever come close to the quality of thiskit. You try and take pride in your ownworkmanship but when you’re outdone this badly it really hurts. It’ssimply the highest quality kit I’ve everhad the opportunity to own.With the fires somewhat ebbed, let’slook at the details of this very welldone DLG. As readers of “TechTopics” recall, we’ve had a good timeanalyzing HLG’s and DLG’s recently.Mark Drela’s X-Foil has been used toanalyze airfoils. A Visual Basic program was written to estimate launchconditions. Other analyses were doneto estimate performance, wing loadingand optimized planforms.but you will probably choose specialized servos for the wing so yourwiring will be particular to yourinstallation. The channel for theharness is nicely drilled out and theservo wells were perfect. Instructionsfor drilling the peg position and angleare covered on Denny’s web site. Thereare streamlined pegs now available sothe choice of launching peg is up toyou.Although the parts count is low, somecare and preparation should be takenbefore getting into this project. Thefirst thing is downloading and printingthe assembly instructions. Then readthem over several times and visualizeall the assembly details.For instance, notice that the mountingbracket for the horizontal stab fitsproperly in only one direction. Thetaper is subtle but important. If thestab doesn’t clear the vertical fin,you’ve got it on backwards! Do thisassembly dry and then mark theproper end of the fixture for later use(guess who almost got this wrong?).The completed XP3 DLG model out on thefront lawn. It’s 100 these days so not toomuch fun to go out and get flight shots.completely in the well is the Dymond60. Randy McCleave speaks highly ofthese and I have a set of them on order.Also check out your battery, Rx andgyro needs before you get started. Iwound up with a 110maH NiCd packin the nose followed by the gyro andservos under the canopy and a FMAM5 receiver under the wing butThe bottom line is that if I wanted tojammed up against the rear of thedesign something to meet all theNext thing to consider is your choice of servos. You may want to use adhesivecriteria evaluated, it came out lookingtape for anything not nailed down. Theequipment. Micro servos of the S90,an awful lot like an XP3. After a couple HS50/55 JR241 and similar variety are launch forces can get to be many 10’sof e-mails to Denny, a flaperon XP3of G’s so things will move if given aappropriate for the rudder and elevawas on the way.tor. Probably something on the 15 to 24 chance.in-oz torque range would be appropriSorting through the box you’ll find aate (high end for the rudder). If you’ve A NiMh pack (AP 200 square packKevlar fuselage with a carbon boom,style AAAA battery sizes) fromgot the poly version, that covers it. Iftwo of the most gorgeous DLG wingBatteries America will also worknot, read on.halves you’re ever going to see, and(200maH). Denny makes his own packhorizontal and vertical balsa stabs that The wing uses Drela airfoils and isfrom 280maH NiMhs.are faced with light glass fabric. Thequite thin in the servo area. If yourappropriate hardware is supplied forMost everything you need to know forservo is over 9mm thick it willmounting the wings and horizontalassembly is covered by the instrucprotrude a bit. There are only a verystab. Several control linkage optionstions. I’ll just highlight one or twofew models that fit completely in theare also included.things.wing. The JR241 appears to be thepreferred wing servo and at a bit overYou’ll find the instructions on theI would recommend setting up the10mm it will protrude slightly.Polecat Aero web site along withwing peg hole prior to joining theseveral articles on set up, flying andwings. Setting the angle is a lot harderI ordered PS30s from FMA for thistrim all in PDF format. This is a greatwith 60 inches of wing hanging offproject. They are 9mm thick and haveway to do it since the latest updatesyour drill press. To set the angle, I took12 in-oz of torque at 4.8V. They fitare always available to everyone.half the total dihedral angle, set that onperfectly in the existing servo wellsthe drill press base and worked myand were exactly flush with the wingYou supply the wing wiring harnesslower surface. The other servo that fits way up on drill sizes. Glass, KevlarPage 12R/C Soaring Digest

and foam don’t drill real clean so don’thit it with the final size first. I prefer totake it in two steps with the final hole afew thou under the final dimensions soassembly is very tight prior to gluingin the peg.Joining the wing halves worked fine.Choose the dihedral angle that worksbest for you and then epoxy as directed. I had some misgivings aboutthe filled epoxy for the wing bolts.They seem to be OK now but they hada little give after 24 hour cure. I addeda 1/64" ply cap over each bolt hole.All That’s Going in Here? HS55 servos,Gyro, FMA M5 Rx and 200mah NiMh pack.Yup, it All Fits! NiMh Pack SLidesCompletely Into the Nose.Stabilizer Detail - Z-Bends and BalsaSupport for Rudder Linkage.August 2003After tapping the holes in the ply wingsaddle for the wing bolts, hit themwith thin CA. Let that set and then tapagain. Repeat a couple of times untilyou’ve got very hard but accuratethreads in the wood base.Splooging the wing saddle is a highlytechnical term Denny uses for globbingup the gaps in the wing saddle withfilled epoxy. Sand and clean the wingsaddle first to remove any releaseagent. Then cover the bottom of thewing with Saran. Use tape at strategicpoints to stretch it out smooth in thecontact area. Apply some wax orVaseline to the nylon bolts. Mask thefuselage sides around the saddle withtape so the overrun peels off easily.Then mix up a ketchup like consistency of micro balloons in 30 minuteepoxy, slather it on the saddle, bolt onthe wing and go have a couple ofbeers.With the wing mounted, you can nowaccurately glue on the horizontal stabfixture. Mount the stab (get the rightend forward!) and eyeball the stab tobe properly aligned with the wing. Besure you sand the boom under thisfixture so the glue will grab well. Onceyou’ve got the alignment right, hit thefixture with CA and then LEAVE ITALONE FOR ABOUT 15 MINUTES.CA sometimes does not fire off immediately on some carbon surfaces. Addthe adhesive carefully and then backaway from the airplane. Perhapsanother beer is called for here.After the horizontal stab is set, notchthe vertical stab for the boom taper. Ifyou’ve done this right, the vertical stabhas a slight friction fit to the boom soyou can set it properly and not have tosupport it with an external fixturewhile the CA grabs it. Use a right anglePage 13

to be sure you’ve got the vertical ANDhorizontal alignment just where youwant it. Then hit the contact area withthin CA and again leave this alone forabout 15 minutes.ming and launch set up. For me, a gyrois a must. I prefer the near instantaneous response of the gyro duringthose first few fractions of a secondafter launch.As per the instructions, you’re going toCA glass fabric reinforcement on thevertical stab so the initial glue jointdoes not have to be massive. Oh yeah,you did round off the leading edge ofthe stabs before getting to this pointdidn’t you?FLYING THE XP-3shelf life and this one must’ve had it. Itwas fresh from the store but whoknows how long it had been on theirshelf?Repair was my trusty Goop and balsafairing which has never failed me overmany crashes with my own designs.We ran into a few equipment problems Please note that neither the PS30getting the XP3 in the air and this ischatter/drift nor the stab joint failureprobably the place to cover those.were XP3 problems. But they arethings to watch for because this ship isThe PS30 servos had some issues. They just too nice to mess up with stuff likeboth had a very bad buzz near center.that.Linkage is up to the builder. There are The right wing servo would freeze ininstructions for running a pull-pullthe up aileron position (very bad!).With various repairs complete, it wassystem. There’s also Teflon tubing and Thermal drift was quite noticeable.off to the field again. By now it’s 8:45wire for running a stainless steelGoing from the basement to the fieldPM and it’s almost dark but what thepushrod system as used by Mark Drela required about 50% change in subheck. A few hand tosses and every( 0.014" wire). There’s some largertrim. Both servos drifted the samething looks fine. Re-center the PS30’sdiameter tubing for running a 0.020"requiring and the exact sub trimfor the 85F temperature and we’recarbon pushrod system as well (supcorrection is definitely the temperature ready to go.plied in the kit).dependent. The HS55’s in the fuselagedid not exhibit any of these problems.First shot is a gentle spin and releaseMy choice for linkage is 0.055" z-bendand ÖÖ WOW! The XP3 took off like amusic wire for flaperons (supplied)After shortening the servo arms, rescalded cat and I wasn’t even trying.and 0.020" music wire for the stabilizgluing the servos in the wells andGyro setting is perfect as the launch isers (not supplied in lieu of the carbonchanging from metal to nylon clevises, straight and true right from the release.rods). The stab linkage uses the largerthe buzz got down to manageableTurns are great. A little down trim todiameter tubing (yellow supplied with proportions and the right servohandle the rearward CG a bit betterkit). Although I love to fly DLG, at my stopped jamming in the up position.and we’re all set.age I’ll never be competitive so I optHowever, the drift never went away.for something a bit more robust andThe next few launches get a bit morereliable.First outing at the field showed thatvelocity into it. Absolutely everythingthe CG setting was good (I use theworks superbly on this airplane.I used the supplied 3/32" ply horns for most rearward setting I can handle)Launches are incredible. At my age I’mthe flaperons but made my own 1/16" and the elevator throw could be cutin that geezer category where I can’tply horns for the stabs. The longer stab down by 25%. Flaperon differentialget supersonic launch speed but thishorns still provide plenty of travel but was good with no rudder coupling.ship is sure making me look awfullyminimize the effect of play in theI’ve since found that I like just a hair of good!linkage or servo gears.rudder coupling to keep the nosetracking a bit better in the turns. Other Last flight is nearly full force. Well, asThe linkage tubing for the stabs isXP3 flyers prefer no coupling. Flapfull as a fat old guy with a bumrouted through a small opening at thethrow was a bit generous and neededshoulder can get. The plane just keepsbase of the wing saddle and then tackto be cut back. That’s what 1/3 chord going and going and Ö. ooops, it’s soglued with Goop along the carbonflaps will do for you!dark now I can’t see it at the top anyboom. A third tube is also used in thismore. A little strategic positioning andlocation for the Rx antenna to exit theWhat turned out to be the last toss ofthe plane can be silhouetted between afuselage.this outing had a fortuitous glue jointstreet lamp and the full moon for afailure. The landing was in tall grassvery ni

Page 2 R/C Soaring Digest ABOUT RCSD R/C Soaring Digest (RCSD) is a reader-written monthly publication for the R/C sailplane enthusiast and has been published since January, 1984. It is dedicated to sharing . these and I have a set of them on order. August 2003. R/C