Official Freewing MiG-29 Fulcrum Twin 80mm Thread

[GliderGuy]

HK111 - Is it possible to obtain more of the set-up / system details?

Thanks

[Colorc]

An old anecdote that ive heard from a bunch of rc pilots over the last 14 years is to not use y connectors as much as possible. Its something ive followed over the years and the only reasoning that the older "experienced" pilots had was that adding more connectors to a wire is just adding another point of failure. Be it the amount of contact that the connector can make to the quality of metal used to pass the signal and current through. I have choosen to follow this with my builds over time and hope that it saves me from whatever issues have been hapoening with others migs. i have put my elevators on seperate channels on the rx and the throttle connectors have been soldered together into one connector instead of using a y. Im even tempted to take out the elevator connector and solder the servo leads directly to the extension just like my gassers. If you believe in rf chokes or not, or y connectora or not, or using battery power supply for rx, a stand alone bec, or esc bec; im sure they all have there bit of evidence in working. Whatever gives you piece of mind.

[Colorc]

There are those with hundreds of flights without accidents too. Unfortunately, since we don't know what the issue is, it is also hard to say exactly why it haven't occurred for them (yet)

its just so random these crashes. As stated before, each set up was different. Something im interested in is if the rx failsafes were set after doing all the trimming for level flight. I found that i needed some up elevator trim on the maiden after setting up by the book. I feel like the majority of us are doing to same thing until we more the cg back a little. Maybe these crashes are the rx losing signal, going into failsafe and setting everything to the first time they bound their rx. Ive only ever flown spektrum and know that setting failsafe is done that way.

[Evan D]

I redo the bind and failsafe anytime I change programming especially servo subtrims.

[Bushong572]

This is my setup after numerous experiments.

Upgraded linkages 4-40 (I don't think the stock elevator linkage has any business on a 13 lb/100mph plane), upgraded (Motion) elevator servos, CG 12mm aft, 1/8" reflex (ailerons and flaps), and low rate elevator
I always glue (Goop) the connectors to the MCB.

It flies much better now....does not want to dive like it used to on high speed passes. I was also able to reduce my up trim from 5-6mm to 3mm.

[crxmanpat]

Both with the original servos and with the upgraded servos, I noticed the plane wanted to "nose down" after making an approach for a high speed level pass, requiring some slight back pressure on the elevator to level off. I only had 4 flights on it before taking it to an event in St George, UT where myself, JLamb, JLink and corsair nut all had our Migs there. Brent suggested moving the CG back, which I did by moving the forward battery on the middle tray as far back as it would go. This gave me a CG about 10mm back from the marked CG on the wings. The first thing I noticed was that the Mig no longer tucked the nose during a pass. Between the 4 of us, we got about 100 flights on our Migs. They were all stock with the new servos.

So I think the mitigating factors are:

1. Factory CG is nose heavy. Needs to be moved 10-20mm back.
2. Control rods are still too flexible even with the CF tube over them because of the ID of the tube.
3. The angle of the control rods in relation to the servos and control horns is not optimal.

I believe some of the first crashes in Taiwan were due to being nose heavy (even more so if the battery was put in the forward tray and the marked CG was not set properly), the fact that most were putting the control rod in the outer hole of the servo arm, and the fact that the control rods were still allowed to flex, even inside the CF tubes.

These are my opinions based on personal experience and reading the posts here and on RCG.

[Bushong572]

I think there is definitely an incidence/thrust line issue with the plane. I was not too impressed with the flying qualities (stock configuration). I feel the factory CG is way too nose heavy. I had 5-6mm up trim to fly level with the stock CG. That has to be a big strain on the elevators and alot of drag. I also noticed the pronounced dive on high speed passes. I could not get the elevator to trim well at all.
I'm pretty happy with the plane after my above mentioned changes. The only other mods I have planned are new front wheels (JP 45mm) and brakes (JP 65mm). I hate the stock wheels and tires. I really like brakes on my EDFs......hate adding the weight though.

I'm a big Freewing fan. I've owned just about all of their 90mm EDFs and several 80mm.......but I think this plane could have benefitted from a little more development.

[kallend]

I've seen a whole lot of great flights. Even Pilot Ryan posted a great flight. I didn't see any flight issues during his flight. .

At the risk of sounding like a broken record, that is totally irrelevant.

Most Boeing 737 MAX flights went off without a hitch.
Most Audi 5000s didn't kill their occupants with unexpected acceleration
Most Ford Pintos didn't incinerate their occupants.
Most Takata airbags didn't blind the passengers.
Most 2000 model Ford Explorers didn't roll over.

[HK111]

HK111 - Is it possible to obtain more of the set-up / system details?

I'll forward it if I get it, but there was only follow-up chatter at RCN sofar.

One interesting observation: Suppose the crash is really related to the other crashs. Then we know a lot because the guy flew with a turbine. So he does not have the ESC and the fan sitting over the wires going to the elevators. That reduces the space of possibilities a lot. It could still be "generic electrical weakness from long wires", but it would rule out the "ESC, fan and/or large currents from the battery induce bad signals in the wires". And it would still leave room for "purely mechanical" explanations, some bad combination of angle of attack of the elevators, weak/bending links or so. The mechanical explanations might also be compatible with the observation that both elevators seem to stop working synchronously, which was a partial counterargument against electrical interference on one power train.

Hmm.

[HK111]

PS: What if the rear of the fuselage is bending, the part that houses the rod that carries the elevator? I noticed during assembly that it was looking weak and could be bent easily. The part became reasonably stable only after screwing in the rudders. Maybe the rudders should be glued in to get more stability of the rear fuselage / elevator carriers.

[Mizer67]

I don't understand how a purely mechanical failure would occur on both elevators simultaneously. Particularly given the rods and ball links are still attached in almost all of the crashes and many (most?) of the components still work when plugged back into a power source.

Contributing cause, yes. The root cause, I can't wrap my head around that one.

[GliderGuy]

There are those with hundreds of flights without accidents too. Unfortunately, since we don't know what the issue is, it is also hard to say exactly why it haven't occurred for them (yet)

But it has happened to me. My 90 mm F-4 (once) and twin 80 mm A-10 (twice) crashed with almost the exact characteristics of the somewhat common MiG crashes characteristics.

The common denominator in all these = high current ESC systems.

But the turbine MiG crash flies in the face of this comparison. Unless stock pushrods were used.

-GG

[bandetx]

I don't understand how a purely mechanical failure would occur on both elevators simultaneously. Particularly given the rods and ball links are still attached in almost all of the crashes and many (most?) of the components still work when plugged back into a power source.

Contributing cause, yes. The root cause, I can't wrap my head around that one.

Depends what you define as a "purely mechanical failure"

Is servos not having proper leverage because of the linkage design mechanical failure? If so, then it makes PERFECT sense for both elevators to fail.

[themudduck]

I guess I'll repeat my story, sorry for being that way, but luckily my Mig didn't crash - both elevators failed while I was flying at a relatively low speed, heading downhill at maybe a 20% down angle. I had no elevator control for about 2 butt-puckering seconds and then I regained control in time. I had done all the mods and I'd bypassed the blue box. I'm flying slightly nose heavy (balanced with the CG close to the marks) The only thing I can think of now is to replace the Y-cable. here are some things I can eliminate as possibilities:

• the elevator pushrod didn't come off and the pushrods were not flexing or bending - I have the HD 4-40 rods and connectors and I wasn't flying fast enough for that to be a factor anyway
• the elevators were not "blanked out" by flaps - the flaps were up
• the elevators were not stressed by aerodynamic forces due to high speed or a dive - I wasn't doing either
• I had not preceeded the incident with a bunch of high-speed stressful maneuvers. Just relaxed flying.
• I doubt it was RF interference in the servo wires because I wasn't pulling tons of amps - I was basically just above idle, losing altitude.
• I don't think the servos "stalled" because they weren't working hard when this happened (before the incident I was flying level, not puling through a turn.)

how could both servos stall at exactly the same time? How could they both be interfered with equally at the same time? Like Mizer67 said, a mechanical failure would be unlikely to affect both elevators equally at the same time. My feeling is that maybe the Y-cable is bad or it could have been a receiver glitch. (I don't know because I didn't have time to check all the controls) But if it was a receiver glitch why would this same elevator thing be happening to different modelers who have many different brands or receivers, and only with the elevators?? But most of us are probably all using a Y-cable on the elevators. MAYBE that is the common thing here.

I really have no idea. I'm just tossing this out because I have nothing better to do.... Maybe the interference is hitting the Y-cable.

I had an elevator failure on my F4 Phantom soon after I got it, because the pushrod's plastic keeper fell off. I could see that as a possibility with the Mig and stock setup, but in my case both elevators stopped working and there were no problems with any of the mechanical functions - when control came back I simply flew it normally again and landed it completely normally. (My nerves on the other hand were not normal at that point)

[leithalweapon]

Is it possible that one servo stopped and somehow, because of the Y cable, caused the other to stop?

[xviper]

Is it possible that one servo stopped and somehow, because of the Y cable, caused the other to stop?

I doubt it. Take a "Y", any "Y" and plug a good servo into one side and a dead one on the other. The good one still works. A "Y" is a parallel circuit. Kill one side and the other works. If it were a serial circuit, that's another story.

[Captain MoMo]

MRC - can one of you please comment on what is being done to address these Mig 29 crashes? Do you have any recommendations for pilots now on what they can mod to help with this situation? We just want to get this issue resolved sooner than later and any input is most welcome.

[fredmdbud]

Have any of the crashes involved stabilator (differential elevator) setups?

[leithalweapon]

Have any of the crashes involved stabilator (differential elevator) setups?

Evan D did a poll to get some data. Maybe he can chime in and let us know how many crashes involved diferential elevator versus the total number of crashes.

[Firebird]

Just a different approach until we figure out what is causing the loss of elevator control:

Why does the aircraft need this much up elevator in level flight at all? We saw crash videos of Mig‘s flying perfectly straight and level at medium speed entering the dive. In general - the reason why aircrafts lower the nose is that the center of lift above the wing is not located at the cg (aft of the cg in most cases). To counterbalance, the horizontal stabilizer creates inverted lift - means pulls the tail down.
If we want the aircraft to fly at least straight and level in an event of momentarily loss of elevator control, we need to moved the cg far more backwards. I expect the servos to enter fail save (means the programmed fail save reaction of the servo itself - not the receiver) which might with this servo just be „stop movement until signal is clear“. That means that the elevators might move back in aerodynamic center position forced by airflow. In order to at least win a bit of time during the event for the servos to reestablish communication with the receiver, it might help to balance the aircraft (move cg backwards) in a way that the aerodynamic center position of the elevators are equal to the elevator position you would anyway need to fly straight and level.

Another idea would be - if you use programable digital servos: Program the fail save of the servo itself (not fail save of the receiver) to move the elevators in - in case of loss of communication with the receiver (signal line) - to the position you require for straight and level flight according to you cg.