First we already have a lot of real data. Even once we get his additional data we still need to each, individually, decide on what correction is needed.
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Hi everyone,
Here is my remedy for elevator issue.
The Promodeler DS150CLHV servos arrived today. They are a direct drop in. No modding required. Except they use 4 screws instead of two. 115 oz/in on 4.8V
In regards to the rods, I found a tube I had purchased for 3D printer years ago. Turned out the internal diameter and OD are exact match for the stock carbon tubes and rods. Will prevent the rod from deforming inside the carbon tube.
I removed the super long 60cm elevator extensions and installed super short 13" ones. Was enough considering the length of the servo wire and the aft position of the receiver in the hull.
I have an alarm setup in my radio when flaps are extended AND landing gear is retracted. Prevents flying with flaps extended.
I feel quite comfortable flying it in this configuration.Comment
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It can't hurt though just trying to put some input here.Comment
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Yes I understand that but the heat needs someplace to go . All the testing in the world won't help if it's overheating.Comment
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Changed the wheels to JP 45mm front/ 65mm rear (with brakes)
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I have these on my SU30 and love them however the axle shaft on mine is a bit short and will not reach the other set screw. It hasn't been an issue but I inspect them every few flights to see if if it loosens. What is the length on these and can you show a close up of the axle shaft to wheel assembly?Comment
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I agree. $55 is not cheap. But that's a high end servo, I am planning to use it in other jets in the future. I look at it as an investment into the hobby. This servo is supposed to last for a long time.
The way I see it, any jet would benefit from a servo on a FFS that centers well, and doesn't develop a deadband zone. Resulting in a more locked in feel in the air.Comment
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image_63992.jpgimage_63992.jpg OK, is this what you are showing as an Axle size for your brakes. The main axle is 4mm on my SU30 and I wasn't able to use it and it looks like the same wheels?
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I calculated the CG on the Mig and 140 mm is 25% of MAC. 30% is 165 mm which I think not unrealistic. There is no other reason that this thing should need 6 degrees up elevator just to fly level. It is not surprising the servos are overheating. Maybe using analog servos instead. At least we could have smoke trailsComment
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Eric - Until Firebird gets flight telemetry data later this month, we won’t actually know if the servos are loaded to where they overheat. His static test data taken to date does not show overheating/functional issues until past 6 minutes.
We have good data from Firebird, but we must have the flight data. Then like Evan said, each of us can decide on what correction is needed.
-GGComment
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I mentioned about a week ago about a problem with the MiG. During flight condition with flaps deployed and higher throttle settings, with nose down attitude, the MiG loses elevator control. Please see my previous posts. I was able to reproduce the pitch control instability multiple times. Last Sunday, I had someone take close up burst photos during this maneuver. Unfortunately during my last try, I was not able to pull out of the shallow dive with up elevator input on my transmitter. The MiG was destroyed on impact. I have a picture, moments before impact, that demonstrates a structural problem with this plane. See below. Please note the anhedral configuration of the horizontal stabs. I’m convinced that this is contributing to the loss of elevator control. My advice, please do not fly your MiG with flaps deployed at higher throttle settings
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I think you are onto something... I noted flex In the rear earlier.Comment
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Holy smokes... now that's bad!
And sorry for your loss!Comment
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Borat, very sorry for your loss. Thanks for trying to get more data on the problem
Eric D, I think you are are on to the main problem. Heavy foam jet flown fast with forward CG requiring lots of trim force from the elevator servos, and using cheap micro servos not nearly up to the task.Comment
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Ok, so new questions here come to mind (Motion should send you at least two jets free of charge for your testing and rather tragic discovery)... can you examine the stab mounts after the impact?
What gave way? The foam, the plastic? Was your airframe badly glued? Of course the impact damage may make it hard to tell.
Others having crashed their MiGs, please do this exercise too if you conserve the pieces now that we know what to look for... try to force the stabs into anhedral with your hands and try to identify where is the structure failing.
Good news: Knowing the problem is most of the way to solving it.
Bad news: This probably does not have an easy fix.
Reflection: Wonder why no more jets are falling from the sky considering this structural problem.
Maybe it's just the jets that didn't get properly glued at factory? F-18 case repeating all over again?
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But....Considering that high speed/high throttle condition with flaps down is not a normal nor advisable realm of flight, it appears the MiG is being pushed beyond its design limits.
Sorry for the loss! Thanks for capturing what appears to be a notice for all MiG drivers of a flight condition that must be avoided. Be cognizant that a V(FE) is at play here (max flap extension speed).
-GGComment
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Getting ready to button this one up and maiden. Been reading all the posts on elevator issues. Will do a full ground check with everything moving and see if anything happens with the elevator.
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