The following is a summary of some very obvious things that unfortunately, were learned mostly the hard way. Some of the more experienced will laugh and say "everybody knows that" Well, I to would likely think that today but, 3 years or so ago when discus launch began becoming popular a lot of this stuff had to be learned the hard way. I get questions and horror storys every day that indicate that we can possibly help someone avoid the steep part of the learning curve. Pay attention and you will have a that flys better, launches higher and doesn’t plague you with small problems during each flying session.
Wing to fuse
The wing saddle is definitely the single most "stressed" part of the air frame. During launch the tail is trying to leave the plane from centrifical force and in the front of the plane the battery is trying to do the same thing. All this stress is focused at the wing saddle.The more "solid that you can make the wing to fuse joint, the less likely that the fuse can flex in this area and create a problem. I strongly recommend on any DLG that you take the time to seat the wing to the fuse. Simply protect the bottom of the wing with sarab wrap or packing tape, apply a small amount of epoxy and microballoons to the wing saddle and bolt the wing down. The ‘splooge" mixture will create a perfect fit for the wing. I have seen this simple modification increase launch height, eliminate strange directional launch problems and with the solid mount the fuse will last a lot longer under stress.
Use the best servo that you can in this application. With the new airfoils and almost all DLG’s now being flaperon, centering and resolution are critical. When you are moving 1/4th to 1/3rd of the wing, the tiniest bit of poor centering or slop can create two completely different airfoils from panel to panel requiring constant correction. Any control input creates drag and should be avoided unless it is necessary. On the XP-3 I do most of my flying with rudder elevator except in windy conditions and situations requiring a quick correction. My personal choice for aileron servos is JR 281 Digital or JR 241 analog. These servos have the best resolution and centering of any I have tried.
Assuming a good servo without slop, ALL play must be removed from linkage. If this requires drilling your own holes in servo arms and control horns to eliminate slop, so be it. Any other questions, refer to the first sentence.
Simply the same as the aileron linkage. NO slop. Most DLG’s are now using pushrods that are routed outside the boom and can easily be firmly attached the whole length of the housing. At either end the push rod should be unsupported ONLY enough to compensate for travel and the housing should be supported all the way to the end. .030 carbon makes a very good pushrod material or some of the more serious guys go to .020 music wire. Either one can be made slop free and will work fine. Do not let a large area of unsupported housing in the wing saddle area or play will result. Again, if you have to drill your own holes in the horns and servo arms, do it. The result will be better launching, more precise control and a generally better flying plane.
Vertical and horizontal tail
These come bagged and shaped to outline with an airfoil taper already in the aft section. TAKE THE TIME to correctly shape the leading edges for a big decrease in drag and increase in efficiency. Instead of simply rounding them off take the time to sand in a nice oval or "egg" shape. After I do this I like to seal the edges with thin CA. It waterproofs the area and greatly adds to the stiffness of the surface.
On the vertical fin, slot the boom half way for the mounting and the fin the other half. Attach as normal and THEN take the time to put one or two quick wraps of kevlar thread around the boom at the front edge of the fin and attach with thin CA. This will GREATLY reduce the chances of splitting the boom if the plane is skidded sideways on landing.
Most recievers are run "out of the case" Simply put a wrap of tape around the reciever to secure the crystal. I know of MANY planes lost because the crystal came out of the reciever.
Make sure the battery and any balancing lead are SECURELY fastened, it WILL move!
After the Above
- TRIM THE PLANE
- TRIM THE PLANE
- See #1 and #2
I’m always amazed at the amount of airplanes I come across at contests and such that fly and launch poorly and after we spend a little time trimming, it’s a whole new plane! Folks tell me "I don’t use camber because it doesn’t make any difference" Good Lord man, on a modern airfoil created to utilize reflex and camber, if you don’t see a difference, the Dang plane needs some serious trimming! It’s that simple. There are good trim and set up articles on the site by Mark Drela, Craig Greening and others. Read them, if you don’t understand, e-mail or call and tell me what the problem is and most times it’s a simple fix.
Guys, I don’t claim to be an expert, these are things learned by trial and error and some application of common sense. If you dissagree, so be it. If you do the above you will increase launch height, dead air time and generally enjoy your plane much more.