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Model Forum / Radio Controlled / Air Models / October 2008P-40 (Pica????)
Being a sucker, I recently acquired a P-40 that the seller claimed it was a Pica, but I don't recall them doing that particular bird unless it was many years ago. I missed out on their P-51 but did get the Spitfire. This bird seems to be all wood with plastic in the cowl area and guns only. The bird appears to be in reasonably good shape except for some glaring problems with rudder/elevator movement conflicts and other controllability issues. Some dummy hot glued the servos in and used easy connectors on all the surfaces. I am in recovery mode and will fly this bird as soon as I am satisfied that all the decencies are corrected safely. That being said, I need some information. Where should the CG be and what should the control throws be? If you have this kit hiding in the attic, please post answers for me. I can (and if necessary will ) use the TLAR method, but actual real values tend to be better. TIA, Jim Branaum AMA 1428 > Being a sucker, I recently acquired a P-40 that the seller claimed it was a > Pica, but I don't recall them doing that particular bird unless it was many [quoted text clipped - 14 lines] > (and if necessary will ) use the TLAR method, but actual real values tend to > be better. Inspect it carefully for alignment and twist, then. I've found that the biggest impact I can have on the flyability of a built airplane is to adjust the CG, so I only consider the kit recommendation to be a starting point. So TLAR may be the best starting point of all, if you follow it with some serious test & trim flights. A P-40 is conventional enough that setting the CG to 25% back of the chord at the root should be super-safe, 30% back should be OK. Then go flying to figure out what you really want. You can learn a lot about the CG location by doing dive tests similar to what the sailplane guys do. Get it trimmed to fly nice and level at moderate throttle, then without touching that throttle put it in a moderate dive & let it build up a bit of speed. Then let go of the elevator stick and watch -- if it immediately zooms up or tries to loop then the CG is way forward. If it _gently_ recovers from the dive then the CG is probably about right for sport flying. If it stays pointed right where it was then it's about right for aerobatic flight. If it tucks under, land the plane as immediately and gently as you can and put some weight in the nose! Getting a long gentle recovery, or a straight dive, will give you a plane that can be snap-rolled or stalled at will. This is really good when you want to wring it out (snap rolls are FUN), but it is really bad if you have bad flying days (my last FUN plane succumbed to one of those "I shouldn't be flying today" takeoffs on a high-pollen allergy day; I'll fix the nose when I have something I can fly when my brain is working at half speed). If the notion of a plane that must be watched like a hawk gives you the willies, then put the CG forward -- something that lets it recover from that dive nicely, without being so far forward that it half-loops into a mushy stall, is what I'm currently aiming for in my "allergy day" plane. I try for medium control surface throws at first (+/- 20-30 degrees), and I try to adjust them for nice flight characteristics _after_ I've established a CG. _First_ you get it so that it has the stability properties that you want, _then_ you mess with throws. Hope this helps.  SignatureTim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" gives you just what it says. See details at http://www.wescottdesign.com/actfes/actfes.html > Being a sucker, I recently acquired a P-40 that the seller claimed it was > a Pica, but I don't recall them doing that particular bird unless it was [quoted text clipped - 20 lines] > Jim Branaum > AMA 1428 Hi Jim, If the wingspan of your P-40 is 71 1/4 inches, it's a1/6th scale Pica, the 1/5th is 86 inches. I have the 1/6th kit and the following info is from that kit. The root chord of the wing is 16 5/8, and the plans show the c/g at 3 3/32nd from the front. The c/g shown is at the forward edge of the front spar's WEBBING, but you are allowed a "safe" range of 3/8in either side of the c/g marking. Start at the c/g and adjust for your flying habits. Elevator - 1 to 1 1/2 in. each way. Rudder - Full throw Aileron - 3/4 to 1 in. each way. Flaps - no more than 35 degrees. Good luck, Harry >> Being a sucker, I recently acquired a P-40 that the seller claimed it was >> a Pica, but I don't recall them doing that particular bird unless it was [quoted text clipped - 41 lines] > Good luck, > Harry And let us know how it goes, eh? SignatureTim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" gives you just what it says. See details at http://www.wescottdesign.com/actfes/actfes.html >>> Being a sucker, I recently acquired a P-40 that the seller claimed it >>> was a Pica, but I don't recall them doing that particular bird unless it [quoted text clipped - 43 lines] >> Harry > And let us know how it goes, eh? THAT is the one! Thank you Harry. Yes, I will let everyone know how it goes. It might take a month or two to repair this one because there are several things I do not like that will be changed before it gets airborne, but it is in progress. Tim, my general rule is that tail heavy birds will always fly once while nose heavy birds are just hard to fly. I have already determined that there WILL be a significant change in the CG as all tail feather servos are mounted, you guessed it, in the tail. Simply moving them forward changes the CG significantly. Knowing the proper location helps in determining reality, even though I am one who is addicted to full throttle snaps. -- snip -- > Tim, my general rule is that tail heavy birds will always fly once while > nose heavy birds are just hard to fly. I have already determined that there > WILL be a significant change in the CG as all tail feather servos are > mounted, you guessed it, in the tail. Simply moving them forward changes > the CG significantly. Knowing the proper location helps in determining > reality, even though I am one who is addicted to full throttle snaps. You definitely want to start out nose heavy and work back. Rebuilding a shattered nose _does_ move the CG forward, but it's kind of an inefficient way to do it from an hours-of-labor point of view. SignatureTim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" gives you just what it says. See details at http://www.wescottdesign.com/actfes/actfes.html > Being a sucker, I recently acquired a P-40 that the seller claimed it was > a Pica, but I don't recall them doing that particular bird unless it was [quoted text clipped - 20 lines] > Jim Branaum > AMA 1428 Jim, did you happen to go to the first annual Austin swap meet this last weekend? I didn't go but two buddies went. They weren't real impressed with the turnout. I thought maybe that's where you got the plane. mk >> Being a sucker, I recently acquired a P-40 that the seller claimed it was >> a Pica, but I don't recall them doing that particular bird unless it was [quoted text clipped - 27 lines] > I thought maybe that's where you got the plane. > mk Nah, I picked it up in west Texas when my ageing Pitts died a horrible death due to a switchology error. The Austin swap meet is in direct competition to the Georgetown meet in January so what your friends reported is not a surprise. The Pitts replacement will be in the air before Christmas, just after this bird that was supposed to be ready to mount radio, engine, and battery packs and fly. So far, I have managed to remove one servo and lots of really bad wiring that was glued into place, which plays havoc on insulation.. I will have to remove 5 more before this is all over. I am probably going to leave the retract servo as is because it is hard to get to. Knowing my luck, vibration will kill it soon. Hopefully with the gear down. My test of the retract system shows it to be tight and operational and I am a firm believer in the old "if it ain't broke, don't fix it" saw. Anyone know an easy way to defeat hot glue? Hot glue ( which I like ) can be removed easily with a flat bladed razor knife..heated by a heat gun or a hair dryer..and sliced through the edges of the servo walls. regards, Rich > Hot glue ( which I like ) can be removed easily with a flat bladed razor > knife..heated by a heat gun or a hair dryer..and sliced through the edges > of the servo walls. regards, Rich ----------- One of the reasons that hot glue is generally unacceptable for powered model usage is because it cools too fast to penetrate the balsa or ply. Without penetration, the strength of the bond is very weak. Over time, vibration tends to loosen the bond of the hot glue to the point that the joints can fail and separate. Not a good situation. Ed Cregger Well... for foam construction...it penetrates well into the foam and you cannot pull the joint apart without destroying the foam ( unless you use the heated knife method). So, it works for one material and not well on others. Many new electric models are made completely of foam these days. regards, Rich > Well... for foam construction...it penetrates well into the foam and you > cannot pull the joint apart without destroying the foam ( unless you use > the heated knife method). So, it works for one material and not well on > others. Many new electric models are made completely of foam these days. > > regards, Rich ********** I assume that you are talking about hot melt glue, correct? If so, you make a great point. Ed Cregger Yes..Hot melt glue......but ...far more specifically .... Low Temperature Hot Melt Glue. Many glue sticks sold now will melt at either a high or low setting. Many inexpensive guns ( $10.00 or so ) are dual temperature tools. CAUTION..do NOT use HIGH TEMPERATURE hot melt glue on a foam airplane . The too hot glue will melt a hole in your project. Don't ask me how I know this fact.....Ha Ha Rich > Anyone know an easy way to defeat hot glue? A good way to get the stuff out of it is to use a hot glue gun with no glue in it. Just use the tip to melt stuff out of the glue. A low power pencil tip soldering iron will do, but is a bit hot. That said, get the glue hot then stick some strips of cloth into the glue and pull it out before it gets real hard again. There is nothing that will avoid some cutting and shaving the glue away. My best advice is to get the stuff out that is holding unwanted parts in place, shave enough out to get the worst of it out, and leave the rest. If you get too involved, there will be some slips that remove wood that you did not want to remove! After all, a little left in place will hold splinters in place, that were created in that upcoming crash! <g> SignatureJim in NC |
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