Official Freewing MiG-29 Fulcrum Twin 80mm Thread

[RudyD54]

Yes, the slight flap reflex does indeed affect the elevator trim (positively)

I had no signs of the model wanting to sit on her butt, neither during turns or when slowing down. That would have been a good sign imo - a neutral or close to it model typically does.

I don't consider it a fault or drawback if a model hangs it's tail if you bank and yank though. A balanced model *should* do exactly that if you don't use your rudder. If a model tracks through a turn, having the nose seek into the turn during bank and yank, it is nose heavy.

There are far better ways of actually testing balance, but this too is a nice little tell to look for.

Good to know....I'll probably experiment with the CG some more now that I've got the expo and trim sorted out. Unfortunately it looks like it'll be a couple of weeks before South Florida gets a break from the poor weather and high winds. 😭

[janmb]

Argh, sorry to see that fishface.

Clearly an issue somewhere still.

Great if you can fill in your details on Evan D's poll here: https://www.rcgroups.com/forums/show...d-a-FW-Big-Mig

[GliderGuy]

Man....that sucks. Can you provide the group as much detailed information about your set-up as possible.

Also....details about your flight. Thanks and sorry for your loss.

-GG

[Evan D]

So sorry too... If you have a chance can you add your info to the crash page please?

https://www.rcgroups.com/forums/showthread.php?3742755-If-you-have-crashed-a-FW-Big-Mig

[john2kx]

So sorry for your loss. I’m bothered every time I walk by that pile of foam and electronics in my shop. It’s been a few weeks but it still stings.

john

[lusek_pl]

Sad and falling Mig: / It's also surprising that the model was supposed to be available in Europe at the beginning of October, and it's November and it's still out of stock? Could MotionRc have suspended the sale due to accidents. Because for a long time there has been silence from their steones ... In my opinion, the only solution that will give us 90% certainty is the camera directed at the elevator. During a break in the elevator operation, or an accident, how did the controls behave during a stop. Then you can slowly break down the first breakdowns based on the frame rate. Although maybe I am not a modeler with 30 years of experience, I would insist that the servos on the tail are too weak for such a large and fast model. For example, but I have a foam mig29 with a 600g weight propeller. 2 servos 9g per tailerons at the beginning withstood up to 10 flights before they seized or overheated, until I exchanged for the branded 17g, but I repeat the 600g model. And the mig 29 is designed for mega dynamic flying, so I would focus on the serves. We know well that servo servos are not equal either. With such a model with such weight and dimensions, there is no room for the cheapest Chinese equipment ...

[MANFRED]

What are the odds that both servos would lock up in the down position at the same time? AS the famous pilot once said "something Wong"

[nuts-n-volts]

Again, so sorry to hear of yet another crash. This sounds like almost all the rest. Please post everything you can remember about the incident to the crash page. We get better data the more that do. Unfortunate, that maybe you didn't see this blog earlier. We are really trying to help folks understand the idiosyncrasies of this plane before they put them up for the first time.

...and again, I don't believe they're locking or getting interference. They are being overworked with not enough power and simply shut down. They slowly trail with the wind stream thus the slowly falling off dives. Full throttle is probably adding to this as it draws from the ESC/BEC, never letting the servos regain power. This is also why some servos regain power when the throttle is reduced.

[HK111]

A ton of sorry. I was at our field today, just for 5 minutes, without a plane. I wondered then if I had maidened the plane in its current unsatisfactory condition, and what it would be like to pick up the pieces from the grass. You did the maiden, you picked up the pieces. Oh man.

[HK111]

And by the way:

MOTION RC SAY SOMETHING!!

[janmb]

What are the odds that both servos would lock up in the down position at the same time? AS the famous pilot once said "something Wong"

Who said anything about servos being in a (pitch) down position at all? (there are other ways for a model to enter a dive, especially when nose heavy af)

And there ways both elevators could mess up at the same time:
- aerodynamic issues
- low volt cutoff on the servo end (thin, long leads)
- RF noise from ESCs or other components
- underpowered servos stalling under pressure

[john2kx]

A ton of sorry. I was at our field today, just for 5 minutes, without a plane. I wondered then if I had maidened the plane in its current unsatisfactory condition, and what it would be like to pick up the pieces from the grass. You did the maiden, you picked up the pieces. Oh man.

[themudduck]

Well In my opinion something is still wrong with this jet!. I just got back from flying it and it went down. I flew it last week and it did a little dive on its own but i was able to compensate and land it ok. I figured maybe i was flying it to fast and hard so today I went and flew it scale like and it did a dramatic dive and i was able to get it pulled out and it did it again and i could not save it.

I have the updated servos and the updated rods and links. Hopefully some one can get this figured out.

Dear Fishface, I am very sorry to hear that this happened to you. Could you let us know a little more: you said it went into a dive and that you recovered, but then it did it again. Did you cut the throttle in your dive? Were the elevators working? Did they seem to work after the first dive? Did the model go into a steep dive all by itself or was it already going down and then stopped responding to the elevators? Where was the receiver located and did you check the battery voltage afterwards? (I'm not suggesting anything, just wondering if you checked)

[john2kx]

It’s a long walk. Mine went in at a Star Bucks plant. Required some prison break out techniques to get to the MiG. Your pic and description are so familiar.

[GliderGuy]

Completed the elevator wiring upgrade to twisted 20 AWG. Hopefully, this will help decrease the chances of having low-voltage at the elevator servos in case of a heavy servo load. The gold contacts should help a bit, too.

I decided to not reroute and did a straight replacement pull (hint: Easier to pull the new wire forward from the tail.) since I wasn’t having issues and I previously added some “shielding” around the ESCs (aluminum pipe tape).

Since the MRC “Y” is short, not much IR drop in a short length, so I kept the MRC “Y”.

HK111 - What would MRC “say”? I doubt they have any better knowledge of the cause of the crashes at this point. If they knew something to tell us, I feel sure they would.

Pix and link follow:

-GG

https://www.hacker-motor-shop.com/Se...0025050&p=8312

IMPORTANT: Get the 80 cm length! Perfect length.

[Airguardian]

Congrats on the maiden Jan!

My point is that they are not being overloaded to the point of failure on a regular basis. Its an unusual and rare occurence. Both servos simply stop working seemingly at random.

My guess is the servos are being constantly overloaded as Kallend suggests and when certain conditions occur/converge on the whole power distribution system, further taxing available voltage/current, then that is too much for the servos and they give up, being unable to deliver the required torque to keep servos 'trimming the jet'. Thus the airflow deflects the tailerons to the point where they exert no moment on the hinge and that sends the jet diving. So the amount of the jet diving is exactly the required trim, so to speak, which went missing when servos overloaded. That would also explain why the jets don't just keep flying straight but rather dive. The nose-heavier the jet, the worse it will dive in such conditions.

I have a rebuttal I think, I can easily stall a 50 in/oz torque servo using just a finger 50in/oz = 3.1 in/lbs the upgraded servos in this A/C are around that torque, therefore all your high load load on the servos is pure theory otherwise we would have many A/C in pieces all over the place, as it is we only have a few, thank goodness.

I think you are forgetting that a number of factors may add up.
In this particular case, long-thin wires are causing the stab servos to run at lower voltages than they should, plus the UBEC running of a main Li-Po pack powering the EDFs may see conditions where it struggles to provide the required amps. This coupled with flap servos also demanding extra amps and long wires all over the place straining the whole system way too far. Those servos you referred to probably weren't installed in such a weak system. Also not all servos are equal. There is variance in production. Maybe most servos come out fine enough to survive those dire conditions but a few units in the thousands made will not. And there are your crashes.

Hi Guys I just measured the wing incidence on the Mig . At 0 degrees on the wing the stab is at 6 degrees negative. To my thinking the CG is way off or this plane does not have enough wing area to support it's weight. I can see why the servos are possibly overheating.

I think the former. CG is off, as it mostly always is on manufacturer recommendations, Freewing or otherwise. The plane clearly has wing enough to hold its weight judging by rather low landing speeds from available videos ;)

Assuming the mig needs about 100gram downforce at each elevator tip for straight and level cruise, the servo might be close to stall after continuous stress. At around 5:50minutes the servos didn’t correctly follow their commands anymore until they fully stopped to follow at around 8minutes. The measured temperature at the servo rised from 21,7 c at the beginning to 36,2 c (f) at the end of the test.

Outstanding work, very well done!
Doesn't seem like the temperature is the culprit (unless internally some part of the circuitry or motor is getting much hotter, unnoticed) but this clearly shows and documents that the servos are suffering to give the apropriate torque under stress. Flight loads will likely be worse than those of the test (and cyclic), plus the whole power distribution system may be more taxed out than what you tested here (only 2 servos under load) and cause them to struggle in even more dire conditions.

My proposed solutions:
- Move CG back to at least >10mm to reduce elevator trim loads.
- Use a 20A UBEC from a SEPARATE receiver 2S Li-Po pack.
- Use thicker gauge wires to power stab servos.
- Reduce servo wire lengths were possible, not just for stab servos.
- Install more capable, higher torque servos for the stabs.
- Run the jet at 6V to add more voltage margin and reduce losses due to heat. Use a separate 5V UBEC (stock one for instance) to power BB and all that hangs from it. Pull red wires from channel inputs into the BB so things don't go *ka-boom*.
- Ideally, get a proper control box (Jeti CB200, Powerbox Pioneer, FrSky RB20...) to power the servos.
- Install CB on the aft battery compartment to be able to shorten wire length. Use SBUS or comparable receivers to get the signal from the nose of the jet to the CB in the aft compartment using a single servo wire.
- And since we're at it, beef up the pushrods and add ferrite chokes to the ESC-rx leads, just in case.
- Also probably a good idea to add caps next to the stab servos to help them out.

[Captain MoMo]

Well In my opinion something is still wrong with this jet!. I just got back from flying it and it went down. I flew it last week and it did a little dive on its own but i was able to compensate and land it ok. I figured maybe i was flying it to fast and hard so today I went and flew it scale like and it did a dramatic dive and i was able to get it pulled out and it did it again and i could not save it.

I have the updated servos and the updated rods and links. Hopefully some one can get this figured out.

This really sucks. I am very sorry to see you crash as well. Been there and know exactly how you feel. Mine went down two weeks ago. My advise is to contact MRC and give as much details as you can. MRC was great with my issue and helped me a great deal. They are truly trying to figure this out - including some very intense discussions with Freewing. We just need to keep reporting the crashes and details. Please have a look at the elevator horns. Is the pic above after the crash or before? ... are they bent post crash? Any more close up pictures of the wreckage is welcome.

[awat70]

Can anybody tell me the diameter of the wheels on this jet?. I want to add brakes to it.

[fishface5]

I was flying out of a turn and going level and then it did the dive all by itself i was able to pull back on the elevator and get it going straight up and then level and it did it again and then it was a struggle to get it recovered i got it to go inverted then got it turned right side up and then it was diving again and would not recover. I replaced the factory BEC because i have had troubles with that brand. I was using a castle 10amp bec. I have several large EDF Jets and the HSD F16 has similar size elevator stabs and on that jet they are using 25g servos. I wonder if this is what is needed on this jet

[fishface5]

This really sucks. I am very sorry to see you crash as well. Been there and know exactly how you feel. Mine went down two weeks ago. My advise is to contact MRC and give as much details as you can. MRC was great with my issue and helped me a great deal. They are truly trying to figure this out - including some very intense discussions with Freewing. We just need to keep reporting the crashes and details. Please have a look at the elevator horns. Is the pic above after the crash or before? ... are they bent post crash? Any more close up pictures of the wreckage is welcome.

The picture of the elevator rod setup is post crash