Official Freewing MiG-29 Fulcrum Twin 80mm Thread

[GliderGuy]

Did you measure the maximum current drawn by the stalled servos?

This video does measure stalled servo current. CAUTION: NOTHING WRONG WITH THE SERVOS. They are behaving normally....changing direction as they should. I timed the stall time. It is long enough fo allow for the “reverse” drive signal to tell the servo to reverse. Which it does BEHAVING CORRECTLY!

Just watch it for the ammeter readings.

https://youtu.be/0c5aI7DpqkY

-GG

[Yellowbird911]

We are doing a turbine conversion on the Mig29 also using a single K45. Here is the forward section of the center line tank we have come up with, this portion of the tank will hold fuel. Will be printed in PETG and thicker than pictured, should hold around 45 ounces of fuel. Plan to use a 8 or 12 ounce tank at the rear of the battery compartment as a hopper tank, the center line tank will have a fixed pick up. Will post files on Thingiverse when complete which should be with in the week or so.

Elevator servos are definitely getting replaced!!

[RC30Flyer]

Did you measure the maximum current drawn by the stalled servos?

Kallend... I did not test current/amp draw only voltage sag. Most of the servos I tested were high voltage on a 3S lipo. And I was just verifying the torque specs before the vendor put them on website for sale.

[Waconut]

I have to say watching what’s going on in this thread is interesting. I am sure the true cause of these crashes will be discovered and resolved. Until then I will sit on the sidelines and watch. The plane in my Avatar was my pride and joy but I was afraid every time I put it in the air. The first flight of every session scared the hell out of me, after that I would enjoy the flights.
I don’t need another plane that I am afraid to fly. Maybe before spring I will feel comfortable ordering the MiG.

[hmarmaizmd717]

I just maiden my Mig29 last Sunday, and gave it a second flight. This is an awsome jet. Did the modifications to the elevators
pushrods. Nothing to worry about. Lands very easily.. Vry good buy.

Hector

[hmarmaizmd717]

Has anyone installed brakes in this plane? Which ones??

Hector

[Skosh25]

Would be interested to see what the flight condition was at the time of elevator loss in these crash reports. Common theme seems to be coming out of a dive into a high speed pass. Was power on or off in dive preceding the high speed pass? My basic uninformed running theory is there's a speed limit here of sorts at which point the elevators don't mechanically stop working, they simply blank and lose effectiveness (not unlike compressibility issues experienced by WW2 fighters in high speed dives before supersonic flight was understood) . Has this been ruled out? This bird carries her momentum well and accelerates quickly, especially downhill.

I've had no problems with vertical maneuvers like Split S, Cuban 8, loops, but power is always idle on the downline before I attempt a full throttle pass down the runway. May be a factor.

Have there been any reports of loss of elevator effectiveness during a high speed pass which was preceded by a turn in level flight?

@Hector, regarding brakes in my experience this thing slows down so well on final brakes aren't needed. Uses up less runway than my L-39.

[Mizer67]

My basic, somewhat informed opinion is that this is not aerodynamic.

Electrical most likely, mechanical may contribute.

I think the working theory that best explains the failure mode is that a voltage drop to the elevator servos is possible. There's not a lot of other failure modes where something like this would occur and both elevator servos would go down simultaneously, but the pilot would retain control of other surfaces and power to the motors.

Given the elevators servos are Y-ed together, a simultaneous loss/drop of signal is possible. It's less likely they overheat or stall simultaneously.

[hmarmaizmd717]

Got it. Just asking, Skosh. No problem since our runway is 750 feet.

Hector

[Skosh25]

Worded differently: Has anyone attempted a full throttle (or simply power on) dive into a high speed pass and noticed loss of elevator effectiveness? Every crash video I've seen has been during a ramp up to a high speed pass. I've done this countless times in my L-39, 8S Raptor, T-33, etc. but not with the MiG.

Regarding the voltage drop, the rudder servos are the same distance from the RX as the elevators, actually even a little bit further away. Has anyone tested this theory with the rudders? I don't see how the elevator would be affected but not rudders if voltage drop was the culprit.

There have been crashes with Y and without. Evan's preliminary poll results indicated 3/5 reported crashes have elevators direct to the BB, not Y to receiver.

[Airguardian]

I am more inclined to belive as of now that the fault is electrical in nature (noise, EMI, etc).

There's no need to ask for forgiveness for posting Hugh.

Some would have it that way but don't give them the pleasure!

[GliderGuy]

Skosh25 - I have done all sorts of passes in many throttle, speed, nose angle, inverted, diving, and level configurations. Always had solid control response...all axis (several hundred flights logged).

I have not done high speed flaps down, but I always put flaps down (30 mm) at 1/2 throttle then lower the gear for approach after she slows down. She’s clipping along pretty fast at 1/2 throttle.

Gut feeling....It is not an aerodynamics issue.

-GG

[kallend]

This video does measure stalled servo current. CAUTION: NOTHING WRONG WITH THE SERVOS. They are behaving normally....changing direction as they should. I timed the stall time. It is long enough fo allow for the “reverse” drive signal to tell the servo to reverse. Which it does BEHAVING CORRECTLY!

Just watch it for the ammeter readings.

https://youtu.be/0c5aI7DpqkY

-GG

Well, IMO that isn't enough current draw when stalled to cause a voltage drop along the wires enough to cause the servos to quit altogether, or to overload the BEC.

[Yellowbird911]

Not sure if this could be related but the power leads are very long which can produce a bunch of RF noise. on the Freewing Mig21, that also had really long leads, I would get lock outs. Could it be a contributing factor for either servo signal issues or receiver issues?? I bought the ARF version as I am doing a turbine conversion so I don't know how the power leads run. Do they run along side the elevator servo leads from front the back? Just a thought.

[bandetx]

This is kind of what happens though?

They are diving, and then they have no elevator. Because the servo "gives up", or the pushrod gives up or something. And then later when tested the servos are fine.

It could be the geometry of the linkage not allowing the servos to get proper leverage and the servos themselves aren't fine. People who have upgraded servos still crash.

[Airguardian]

Well, IMO that isn't enough current draw when stalled to cause a voltage drop along the wires enough to cause the servos to quit altogether, or to overload the BEC.

Thus why I'm leaning towards the EMI/noise explanation.
Of course, all speculation still. :'(

On that note, if we want to protect the stab servo leads from EMI, where should we place the ferrite rings/clips... on the servo side or the receiver side? ...or halfway?
I guess servo side (to protect servo) and receiver side (to protect receiver) but I'd like someone with better knowledge on the topic chiming in.

[GliderGuy]

See photo / also placed one near the green ring near the receiver and recently added near tail servo.

They are light and easy to install. Put on the ESC wires where ALL is marked...a total of 3 up front snd 2 in the rear...can run multiple wires thru one choke.
Place the 2 larger ones on each side of the rear battery...plenty of room. One per ESC.

Enter “ferrite”! in the search window for more details in other posts.

Here is the link:

https://www.amazon.com/Cedmon-Pieces...8870654&sr=8-4

[Firebird]

Short update: The telemetry servos arrived today, unfortunately i found out that the actual firmware version of my Rx (jeti rex 12 assist) does not support servo telemetry yet. So - a new receiver is on the way now...
Find attached some pics of my servo and cable installation (drilled 20AWG) and the added ferrite rings on the elevator and rudder cables. I will exchange the pushrods as well, just installed them for testing.

[leithalweapon]

This is kind of what happens though?

They are diving, and then they have no elevator. Because the servo "gives up", or the pushrod gives up or something. And then later when tested the servos are fine.

It could be the geometry of the linkage not allowing the servos to get proper leverage and the servos themselves aren't fine. People who have upgraded servos still crash.

in these cases the pilot isn't initiating the dive. The loss of elevator causes the dive. Loss of elevator control from level flight until it hits the ground.

[Airguardian]

Short update: The telemetry servos arrived today

That will provide very valuable information, thanks for the effort!

I think since your servo is bigger it looks like the angle of attack of the pushrod also decreased which will help out but gotta have that in mind when translating the loads to a stock setup.