Just curious how accurate folks found this calculator mrdlg2u posted above? I put in the wing dimentions and accounted for the fues width and seems a bit aft to me to, but I havent done any real world experminting yet. I see he says to move it 2" forward but why have a calc that inaccurate.......lol. I know it is a starting point but has anyone had the balls to try the dimensions that spew out of the calculator......lol.......Just wondering.Originally Posted by mrdlg2u
Last edited by c5galaxy engineer; 17th June 2012 at 12:52 PM.
Brett Hays
www.JosephOregon.com
Did any of you catch Ed's latest build? I like the looks of this one...
View this video on YouTube
"People always talk about individual freedom, but when they see a free individual, it's gonna scare 'em."
Back on post 1 Ed posted the link to go along with his design. there was some discussion later in the thread about why the calculator was off... I don't remember if anyone came up with a good answer.
I did try the CG where the calculator put it, and it felt tail heavy... but with reduced throws it would fly. when I moved it 2" ahead it was very stable. I have never had to use gyros. But, I think Ed does or did.
Later,
Gundy
Thanks Gundy
Brett Hays
www.JosephOregon.com
I'm surprised there is no flex and subsequent control distortion on the elevons. Those look really long and I'm surprised the foam and tape stay stiff. I ran into that problem on a shorter wing. How do you do it?
It's really more for yaw stability than anything. I would say the calculator is pretty good for predicting pitch stability. This plane can actually be trimmed in pitch through a wide range of CG's. The problem is that the vertical stabilizers are so close to the CG they need to be relatively large to be effective, given the short tail moment arm. The further aft the CG is the less effective they become, until the point that there can be some "tail-wagging" at low speeds. If taken very slow, such as during an overzealous flare, the tail can blow out sideways. I like to keep the CG forward for better yaw stability, and it's easy to compensate for the pitch part with the canard angle of incidence being 3 degrees or so greater than the main wing, then dialing in the necessary elevon trim.
Indeed you would think that would happen, I know just what you mean. I myself keep the maneuvering pretty mellow so there's probably not too much wing flex, but it would be interesting to push it and see what happens.
Ed
Awwwwww Yes.......the delicate dance of avaition trade off's......lol.
I had a simple idea that I am going to try and it it is sucessful I will post it but if it isnt I wont so I wont look like an idiot. I just need to find the time to get into the shop to work on my own shti. If it works then it just might fix the "tail wag" With my PD that ctashed I had no wag at all but I had a different design for the virtical stabs. They were very high aspect ratio swept and tapered Armin winged "V" tails set at about 30 to 35 degrees in relation to each other at the center line. The Armin wing type construction of them gave them the stiffness I needed for the aspect ratio I was using. The trade off......?.....I had to use a shoulder type mount for the wings so I could mount the "V" tail on centerline......the other problem was the Vertical stabs were permanently mounted to the fues wich I beleive is NOT in the spirit of the PD wich is suppose to break down into a small package. I am having trouble posting pictures or I would post some of the my belated PD. I did post the video of it crashing from the left wingtip view......lol.
Anyhoooooo........I think I have a plan to use the best of both designs. It really was very yaw stable and looked cool as Hell!!!!!!!!. I will keep you posted. If you want I can email the pictures to you.
Brett Hays
www.JosephOregon.com
Just to throw my two cents worth in again...I just ran my figures through the canard/CG calculator and found that I too must balance my peace drone 2 inches ahead of the calculated results. Maybe because my canard is mounted 2 inches farther forward than the original. My plane likes the CG at 17 inches from the tail.
Just another note. The other day I added my FPV gear and removed the GoPro camera. Didn't want the first FPV flight with the extra weight. But all the FPV gear weighs less than the GoPro and I had to mess around with battery placement for a while to get the CG close. I couldn't quite get it to 17 inches but made it to 16 inches. Well, close enough and I set up all the FPV ground equipment and launched. 16 inches just isn't close enough. It was a real fight to keep it flying and trying to trim it. Flight was short lived and never got to watch the monitor. I've been most of the afternoon repairing the damage. I'll try again another day with yet more weight in the nose.
Airplanes LIKE to fly : Helicopters WANT to kill you.
I've had several OK flights with my beefed-up PD, but today went for low-n-slow and I wasn't pleased. I am using 8" cord wings, with 3 layers of foam board inside the wings, with 1.5" control surfaces. I have the elevator on the 30" canard wing, and ailerons (only) on the main back wing, like my last 3 PD's. This PD is heavier, with more wing surface, as it is heavier, CG set at 16.5" from the rear.
I noticed on this PD that the elevators had less throw than the predecessors.
I noticed that at full throttle it simply climbs steadily, not a bad thing. At 1/2 throttle, it does non-stop shallow dives and climbs, so it drops say 10-15 feet building airspeed, climbs, seems to stall, and repeats. A non-stop series of shallow dives/climbs. Power off it glides beautifully... I don't think it did this dive/climb crap, but I had to hold some up-elevator all the time.
My thought was that the front canard wing might not need as much angle, so I raised the back edge to match the front. Big mistake, I couldn't provide enough up elevator to climb. Tinkering with the angle proved I really wanted the 1-thickness of foam at the canard's front to be able to climb at all, as it was designed and first built.
I then moved the CG back to about 15". accomplished via using one lighter 3.0 amp battery vs. 2@2.2 amp batteries in parallel, this proved to be dangerously unfliable, weight too far rearwards at the 15" point. If anything, the CG should have gone forward (maybe), but couldn't easily try that.
I then realized my motor mount plate was bent a couple degrees, so the motor shaft was a couple degrees lower at the back than at the front. Bending the plate to be roughly parallel to the fuse threw of the elevator, I had to add a TON of up-elevator to fly at all. (Kept nosing down into the ground while it built up airspeed).
So.... is the heavier PD with the thicker wing and deeper cord a bad plan, or do I simply have a thrust-angle alignment issue, perhaps compounded by CG and too-small/inadequate elevator throws?
All ideas are welcomed.
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