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Understood. I want to make it clear that I'm not assigning blame to Freewing, I have no clue as to what occurred. All I know is I ran out of elevator at some point in time. I posted my accident as a caution to everyone out there more than anything else. I do know that whatever happened, I did not have enough elevator to pull out of a very normal diving decent. It would be easy to say that the CG was too far forward, but what's puzzling is that I didn't have to put ANY nose up / down trim into the model. I just verified that by looking at my transmitter which still holds the trim settings I was using for the MiG.
I don't know my dudes....Comment
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Still a real shame this had to happen. If everything else seemed to work, except for the elevators, I'm putting my money on that "blue box syndrome". This discussion has been going on for a very long time, ever since these "control boxes" first appeared. I called it "signal/ground leaching" from one circuit within the control box to another circuit. Sometimes one thing stopped working while other things continued to function. Some guy (or girl) sits at his/her work station soldering hundreds of these things every shift. They are minute solders that need to be precise. If there is just a tiny bit of solder/flux bleeding along the surface of the circuit board, electrical current may bleed over to the next circuit and not enough gets to the servos that's suppose to get it. If you take an old circuit board, even one done by robotics, look at it under magnification, you can see just how close some circuits come to another. I've looked at some of these boards out of RC planes and in some cases, there appears to be some sort of leaching (as indicated by discoloration) between two circuits at or near solder points. Well, that's my take on it.Comment
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At this point I'm beginning to suspect there could be an aerodynamical problem other than servos not being strong enough or lacking electrical power.
Insufficient throws with nose-heavy CG may be playing a part, possibly coupled with there being a problem with wing wake blacking out the stabs since they are straight in-line with the wings (unlike, for example in the Su-35 where they are placed underneath it to get cleaner airflow).
If that is the problem, then setting a more rearwards CG and increasing throws (maybe increasing expo) could offer, if not a total cure, at least a mitigation.
Cutting throttle off, could also help survive the situation by allowing the bird to decrease speed.Comment
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It's just a theory, but at this point and with at least some reported failures following the same pattern with the improved servos, I think we would have to consider the option at least.
So we'd be talking a high speed stall, not a low-speed one...
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Falcondriver - Can you tell us your flap settings / take-off, etc. Alpha or James mentioned an elevator blanking related to flap settings as I recall. I could be dreaming, too.
My MiG doesn’t go full throw flaps down. I have a glued stop at 1/2 travel on the vernier knob on my transmitter body to accommodate another bird’s set-up.
-GGComment
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Or flap-induced... good point, that could be an option too.
Many of the crashes have been with flaps deployed I think?Comment
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Full flaps according to the manual is only 39mm. It is easily capable of much more. If it is not actually measured, it would be very easy to give it more while thinking it is good and possibly blanking out the stab. I almost did it myself. Not saying it was set up that way just that 39mm didn't seem like much for full flaps on this bird. It may have been limited to 39mm to keep it from happening.Comment
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Also...Corsair Nut / My flaps are slightly negative. One of my flap push rods was a tad long, and I didn’t want to mess with modifying it. So I adjusted the other flap to match. I did not adjust the ailerons to match the flaps.
The amount of negative flap is exactly what you show in your video. And, like yours, it seems to be a perfect set-up. No pitch changes while changing throttle while cruising.
A possible golden nugget?!
-GGComment
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Falcondriver - Can you quantify take-off flaps? What are your flap travel/deflection measurements? I have seen some photos that show a lot of deflection. My bird....not so much so.
-GGComment
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Stab flutter is usually associated with a buzz. Don’t hear that in any of those crashes. The aerodynamic blanketing makes the most sense out of anything else. Plus that, postmortem revealed zero play between the servo and the elevator. The elevators were held firmly in their last commanded position.
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Has anyone had a crash that bypassed the MCB-e? Chinese made electronics sound more likely than an intermittent aerodynamic problem. I think we will see more crashes if it is a flaw with the design.Comment
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The same MCB-e is used in the F-22. To my knowledge they have not had a rash of unexplained elevator failures and they came out even before the F-18. If the blue box was the issue wouldn't we be seeing more reports of similar problems with the F-22?Comment
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VERY good point. Via the magic of the Internet, the blue box might be named a witch without any hard evidence.
I flew an RC sailplane that would suddenly appear to lose elevator control and dive for Mother Earth. I nearly tore the wings off in the tight loop that resulted from holding full up elevator and control returned. Eventually, I learned to simply to roll in full up trim and let her fall....she would return to controlled flight on her own.
My point is....her wing and horizontal tailplane were IN LINE with each other. Mean anything? Only time will tell. We are grabbing at ANYTHING that might be a solution whether or not it is correct. Is there some weird aerodynamic coupling that results from this arrangement? If there is, you will eventually see a post from me about a crash due to loss of elevator control because I intend to fly her a lot! My meaning? If the beast is there, likely it’ll bite me too.
At that point (and I hope it doesn’t happen), I would install vortex generators on my next MiG to forestall the wing/tailplane alignment interaction. Just a thought. :D
Keep all possibilities under consideration and settle on NONE without justification. CG to blame? Why am I not seeing issues, and I am flying right on factory CG? Right now, we are only guessing. And that’s good to have the dialogue. Eventually, it will be figured out. At this point, it is anybody’s guess.
-GGComment
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