|Dec 11, 2012, 08:11 PM|
United States, WI, Wild Rose
Joined Jul 2011
That's awesome "V"! Congrats!
I can't wait to see pictures of it completed!
In testing, did you see problems related to lack of v-stab? Did you see improvement when you added it?
Hard to tell, I'm sure, with just hand tossing it.
Can't wait to hear how it goes from here.
Do you have good sloping opportunities? Or will you need to consider other options to get some height?
Also, if you don't mind my asking, how much effect do you have in pitch control? Roll and yaw? Could you get any feel for it with your hand tosses?
|Dec 11, 2012, 09:40 PM|
Got to take the Eagle to the slope today. It was blowing about 20 kts or so and a little gusty but lots of soaring seagulls were present today.
Two modes of control were programmed into the radio. The first was patterned after the Japanese birds mentioned earlier that used drag flaps and ailerons for turning and the second was conventional differential ailerons only. Both test scenarios used a vertical fin as back up.
All test flights were short. Not by choice either. The first problem was on launch the plane went skyward into a steep vertical stall but was recovered behind the face of the hill and landed. Added ballast to the nose and launched again. This time the plane went into the wind and used full up trim to keep it from diving too hard. This flight used the drag flap aileron approach and had very poor turn response. Almost Nil. Had to hold full deflection to get it to turn. Hopped over the edge of the slope and landed. I then reprogrammed for conventional ailerons and launched again. The ailerons now were making very good turn response. The elevator was OK but somewhat lacking in response. The vertical tail was somewhat flexible and I could see it bending left or right in response to the plane yawing every so often. The wind shifted direction and I had to land again. All these flights are well under a minute.
I removed 1/2 the ballast added earlier to try and get a better CG then launched it again. This resulted in a steep climb skyward (again) and no response to full down elevator that resulted in a deep stall. tried pulling up but it contacted the ground in a 45 degree dive and shattered the left wing.
The conclusion is that this is a forward swept flying wing. It is unstable in the yaw axis and has a very tight CG tolerance resulting in an unstable pitch axis. If the CG is off a fraction of an inch it destabilizes the pitch stability. I can easily rebuild the wing. The fuselage was unharmed. I don't think I'm going to be persuing this project past this point. I got the impression I would be in for alot of frustration trying to get it stable enough to fly right. If the flight got past the launch phase it seemed to fly like any other plane BUT the pitch stability is a real problem.
Every launch I made always resulted in the immediate pitching up of the plane either on the slope or in calm wind on the soccer field except for the flight where it was nose heavy. That flight resulted in a tendancy to dive the whole time. Maybe if I got the CG EXACTLY PERFECT it would be OK but who knows?
Taking a break for now...
|Dec 25, 2012, 07:12 PM|
United States, WI, Wild Rose
Joined Jul 2011
I hope you get back onto the project and see if you can master it... Would you mind helping with a few questions?
I'm still going to move forward on mine, but would of course like to learn from others if possible. Right now I have a workable hand-tossed non-RC redtail hawk glider (about 17" span). I've been playing with it a lot lately trying to see what is different about it vs yours, and what the strengths may be with each design. I can post photos if anyone's interested, and maybe even a video...
Do you have any decalage between the wing and tail? I do, and have never been able to come up with anything (bird-modelwise) stable without it. If my tail is level, the wing leading edge is higher than the trailing edge by several degrees. The tail I'm using for this model is fanned quite a bit as well. Without that, even with positive decalage the nose of the bird always seems to want to tuck under very hard resulting in a crash. I can't really tell from your photos if you built any in or not...
If that's a factor with your bird, maybe you could shim the rear of the tail and get some stability?
If I toss mine gently, it glides straight ahead. I've hinged the tail, and can deflect both sides for up or down "elevator". Doing so on my model results in predictable stall or dive behavior, so I think/hope it will work when I convert to RC? I can make the glider bank and turn as well, which of course equates to a spiral down with my non-RC version.
On "power" tosses though, I worry that I may have similar issues to yours. It always goes up into a loop... It does stabilize and glide straight after that though.
I do see that the angle I've cut my hinges at is different than yours, and wonder if that may also be why it sounds like you don't have much elevator authority?
The third difference (?) between yours and mine may be the aileron/flaps. I can't see where yours are hinged? How large are they, and how much deflection do you get? If you want to make a left-hand turn, does anything happen with the right wing?
I plan to make my hinged wing surfaces quite large in an effort to try to mimic some of the wing movement I see my birds make. But I do plan to use my tail as an elevator, even though I don't see them do that...
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