On Monday 25 August 2008, Curtis Olson wrote: > On Mon, Aug 25, 2008 at 3:58 AM, Robert Black <[EMAIL PROTECTED]> wrote: > > Thought this would be of interest about the UAV flight record > > being broken. > > > > http://news.google.com/nwshp?tab=wn&ned=us&ncl=1239453441&hl=en > >&topic=t > > I saw a movie of the launch and it took 3 people running to > launch it. I was amazed that something so big could be launched > at jogging speed. > > By the way, I had an interesting weekend. For the marinized UAV > project I'm involved with, we needed to do some airframe > performance tests (flown manually.) One of the guys that is > helping lives in Indiana and he got in touch with a guy out there > that has his own 2000' grass runway in the middle of a corn > field. This guy has a '46 Luscome 8A, a 7/8th scale Tiger Moth, > and two other home built aircraft. It turns out he was the first > one to fly with a parafoil parachute when that was being first > developed and had been involved in a number of aerospace research > projects over the years, and had even been in the northrup flying > wing. Since our UAV airframe was also a flying wing he was > really interested in what we were doing and hung around much of > the time we were there to watch. (He was very polite and just > kicked back and watched, even though he probably could have > pointed out all the things we were doing wrong.) :-) > > Friday we tested our wing with winglets versus moving the > vertical fins inboard. I won't get into all the details, but > winglets suck if that is your only vertical stabilizer on your > wing, and more central fins really rock. The guy who owned the > field ran inside, pulled out a book on northrup flying wings, > pointed to the ones he'd been in and also showed us how they also > moved to inboard vertical stabilizers. So we are a little slow > (like 60 years behind the curve), but having fun learning this > stuff over again. > > http://baron.flightgear.org/~curt/UAS/Malolo2/2008-05-05--13.28.4 >6/IMG_0891.JPG > > So with inboard vertical stabs, our airframe was transformed into > an entirely new airplane ... it flew like it was on rails, I > could do agressive loops, rolls, and inverted flight (and > combinations of those things.) It became almost impossible to > stall. It really was amazing the difference this made.
Winglets are primarily used to improve the efficiency of the wing by effectively increasing it's aspect ratio without increasing the span (by much). They can also be used to change the wake characteristics too, but they don't do anything for longitudinal stability, as you've found out:) Actually, they look a bit over-sized for that size of wing and much smaller ones, with a smoother transition to the wingtip join i.e. with a couple of inches radius would probably be more efficient, weigh less and cause a lot less drag. For stability, you could try adding couple of smaller fins at the fuselage/wing join line and set them as far back as you can securely fix them, so that they overhang the trailing edge. You could experiment with canting them outwards, out of the vertical, as well, to give the prop a bit more space. The Northrop flying wings had problems with yaw too, developing in to a yaw and roll oscillation that could take the pilots several minutes+ to control. From their cockpit viewpoint, the pilots could see that the wingtips were actually tracing out a circle. As the wing yawed, one of the tips would be moving forward and the other backwards, which meant that the one moving forwards would gain a little extra lift while the one moving backwards would loose a little, adding the roll. Apparently, sea-sickness could be a real problem at times. LeeE ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ Flightgear-users mailing list Flightgear-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-users
