|Jul 14, 2014, 04:40 PM|
Nearly ready for another maiden attempt....
Note new position for rudder servo. The foam block holding the rudder server is mounted via magnets, to enable "top" access to the Guardian Stabilizer, which will be positioned directly below this position.
Maybe maiden tomorrow evening if I can finish up a couple things tonight and the weather cooperates tomorrow.
Covering is a little rougher than I like where I tied in the new tail section and covered over the top surface of the wing where the previous nacelle was mounted.
|Jul 15, 2014, 03:17 PM|
The shortened fuselage compartment doesn't leave much room to spare, but I got it all in there...but barely!
I think its ready to maiden now... just looking for some calm/light wind conditions.
If she flies well enough, I'll want to do something to finish out the shell of the nacelle, as this is the one "dirty" spot on the plane currently (aerodynamically speaking of course).
Maybe tonight yet... who knows....
|Jul 17, 2014, 04:07 PM|
Well, there's good news and not so good news.
The MacroSpot has now flown and it flew nicely!
With assistance from a local club member, we did a hand launch and got airborne with no problem. I quickly got into an oscillation issue (over controlling) from the Guardian Stabilizer. So it was a wild ride for a second or two before I got that switched off. Once turned off, I got some altitude and began getting it trimmed out.
After about 2-3 times around the field at something less than full power, it was certainly quick but feeling pretty well.
So, the plane was flying very stable, responsive and fast....
Then I got into a turn, and for whatever reason got a bit disoriented. I'm not sure if I turned too far (360) or what... but I instinctively backed off on the power to try to sort it out. Well, I put it into a tail spin, presumably from reaching the stall speed, In retrospect I might have been able to power up and pull out... but who knows. I ended up killing all power and it spun in.
Overall the damage wasn't nearly as bad as I expected, once we found it in the weeds. The nose predictably broke, but the air frame is fine and there's only a little damage to the [newly redesigned] EDF mounts. No damage to the tail at all.
So, we're far from done with this. Not sure when I'll be ready for the "third time's the charm" event, but will keep you posted.
My biggest concern with this now is just the question of what the minimum flying speed is really going to be for this bird. Landings are probably going to be a real challenge, now that I know it stalls out pretty easily. Will have to do some thinking on that... but unless I were to add a canard winglet, there's not much I can do to address that without starting all over.
While I had it under power and in a trimmed state (with the stabilizer off) it looked great, flew great, and the guys in the club were very impressed with its speed.
Thanks for all your interest and support!
|Jul 18, 2014, 02:15 PM|
Lest people get the wrong impression about my comments on the Guardian Stabilizer....
Getting Oscillations at higher speeds is to be expected with this unit until you get the gains "dialed in". So the oscillations ("wagging its tail quickly") were not a surprise per-se, I just didn't expect to get them so quickly after launch.
Rather than just turning the stabilizer off I could have turned the gains down as a first step, but I didn't have much altitude or time to play with. So just turning it off was probably best... but luckily the plane wasn't that far out of trim. If it had been, I could have easily just run it into the ground (was probably less than 12 feet of altitude at that point). Actually, I nearly mentally gave up ... but luckily managed to get the stabilizer off in time to recover.
FYI .... right now I've got hi-lo settings tied to my gear channel. On my other test flights with the Guardian, I was able to get out of oscillations must by cutting to my "gear up" setting.
All comments about the Guardian, including its own documentation, reference the fact that it takes a few flights to get the ideal gain settings figured out. It is a bit easier if you have a gain "knob" you can use in flight. But since my DX-7 only has 2 or 3 position switches, it takes a little more trial and error. Ideally the manual recommends getting into the air BEFORE you turn on the Guardian the first time. As this was a maiden via a "hand toss", I opted for the Guardian to be on (in 3-D mode) just to help avoid a bad toss. It certainly launched great so let's split the credit between my helper and the Guardian for that!
FYI '3-D' mode just means "keep the current heading and attitude". With a quick preset "click" before launch such as holding it 45 degrees up, wings level, in "that direction" the unit will then control the surfaces a best it can to keep that heading & attitude..
After-the-fact observation that might have prevented the spin and crash..... what I should have done, once I was disoriented... was to flip to "2-D" mode (combined with keeping the power "on"). Having been pre-set on the ground to know "straight and level" (definition of 2-D mode), one of the primary purposes of the unit is to enable just that... recovery from disorientation.
I've only had a couple test flights on a different plane with the Guardian, and that "OMG" reaction wasn't yet calibrated to do that.
Instead, I powered back, and then ended up in the spin. It does seem the plane spun all the way in, even though I'm pretty sure I neutralized the sticks at some point.
Final "should have known better" comment to myself is that this isn't the first time I've lost an EDF due to cutting the power. My first EDF was a foamy "Tigershark". I lost it in similar conditions.... I throttled back and turned away from a trainer that I felt I got "too close to". That quickly led to losing control (in a stall) as well. In that case I was way too low to even have a moment to try to recover.
So... one more "note to self".... keep the power on ... unless there is a LOT of altitude to play with. Obviously I do need to understand where the minimum flight speed is.. and how much I can play with "high alpha" when under power... But I'm going to need to do those learnings from a good-safe altitude!
Rebuild is already well under way. I've cut out the crunched balsa, completed most repairs in the EDF mount, and have the replacement nose assembly started. Maybe by Sat/Sunday I can have it back together... we'll see!
|Jul 20, 2014, 05:30 PM|
Third time's NOT the charm!
Well, sorry to say I haven't got it right yet. After a quick rebuild, I went out for another attempt today.
After a fairly successful hand launch (with the Guardian turned on again in 3-D mode) I got to the point where I was flying fairly straight and level, at a fairly good speed. But I was still pretty low.
Although I had turned the gains down substantially on the Guardian, since it was building speed I really didn't want to take the risk of oscillations occurring again, so I switched off the guardian and attempted to "climb out".
I almost immediately lost ability to control the plane. I fought it for horizontal control (rolling left/right) but contrary to the previous flight, it just was not stable at all! A quick attempt to turn the Guardian back on (to 2-D mode) didn't seem to correct anything, so rather than likely run it into the ground under full power, I cut power and it again "tail spun" in.
The 2-D mode may have help somewhat, as when we found it it had gone in nose first, but seemingly not at too far of a downward pitch. Didn't break the nose off completely this time, but crunched the fuselage sides again. A lot less damage than last time though.
I know that "flying wings" need to have some reflex designed in for stability. The most common way of doing that is to just put "up pitch" in both elevons in their neutral state. So I've got a few clicks of that. But in the end, this could just be acting like "up elevator" without giving it the stability it needs... ie: as soon as the elevons are near neutral position, such as with a little "down"... maybe the stability is just lost... especially at slower speeds?
Other thoughts at the club (from Toni) was that will all my "gear" being topside, and the battery even standing on its side, this could contribute to the plane just wanting to flip over. His suggestion was to "lower" the battery, which I could do but would substantially re-design things and would cut into the wing core, reducing its strength.
Since I have some good stable flight time in my first attempt, right now my initial thoughts would be the cut the outer couple inches of each elevon, and re-glue them with a few degrees of "up" relative to the rest of the control surface. This should give it some permanent reflex regardless of elevon position.
There was one physical difference in the two flights. I "raised" the nose by putting a 3/8 inch balsa riser on the nose wheel. The intent was to increase the angle of attack to hopefully make it more likely to lift off the runway. but we ended up with some cross wind, and I couldn't keep the plane down the center today. Although I taper-cut the balsa.. almost "airfoil" if looking at its profile from the bottom, is it possible that this disrupted the airflow enough to make it unstable? (but then it flew OK while the Guardian was on...).... Picture of this is attached...
But... open for any other thoughts...
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