Official Freewing MiG-29 Fulcrum Twin 80mm Thread

[Gringotuerto]

Another video of Mig-29, this time flying with an F-16 and a Eurofighter. Great shots of the anti-FOD doors in action.

[Skosh25]

The cone shaped washer/ spacer should go between the ball and horn if you use it. Allows the ball link to be used at greater angles.

Good catch. Thank you!

[Molly914]

I am probably one of many with an unexplained non-responsive elevator leading to a crash. My Mig 29 had around 10 flights on it with the MRC upgrade servo's installed from day one as per MRC instructions.
A diving then low height 3 feet pass along the runway at full power, gave no elevator response. She would not pull up. Ended up going for about a 120mph slide down the runway.
It happened right in front of me at close range less than 50 yards, and flight telemetry data logging records show a perfect radio connection throughout the flight duration.
Based on all the posting I read here, this is not new. I guess I should be happy it's not a total loss, just severe gravel rash on the fuselage belly.

[xviper]

I am probably one of many with an unexplained non-responsive elevator leading to a crash. My Mig 29 had around 10 flights on it with the MRC upgrade servo's installed from day one as per MRC instructions.
A diving then low height 3 feet pass along the runway at full power, gave no elevator response. She would not pull up. Ended up going for about a 120mph slide down the runway.
It happened right in front of me at close range less than 50 yards, and flight telemetry data logging records show a perfect radio connection throughout the flight duration.
Based on all the posting I read here, this is not new. I guess I should be happy it's not a total loss, just severe gravel rash on the fuselage belly.

Flaps?

[themudduck]

I am probably one of many with an unexplained non-responsive elevator leading to a crash. My Mig 29 had around 10 flights on it with the MRC upgrade servo's installed from day one as per MRC instructions.
A diving then low height 3 feet pass along the runway at full power, gave no elevator response. She would not pull up. Ended up going for about a 120mph slide down the runway.
It happened right in front of me at close range less than 50 yards, and flight telemetry data logging records show a perfect radio connection throughout the flight duration.
Based on all the posting I read here, this is not new. I guess I should be happy it's not a total loss, just severe gravel rash on the fuselage belly.

That's VERY interesting, thanks for your report. To comment on a few points:

• You were flying level, apparently without flaps deployed, so there's no aerodynamic "blanking" of the stabs - reinforcing the idea that this is NOT an aerodynamic issue (at least not this time)
• Your telemetry shows no failure of the radio connection - no faults - so that seems to indicate that wasn't the issue (at least not this time)

So why do both elevators servos simply stop working, at the same time? What a mystery.

[kallend]

I am probably one of many with an unexplained non-responsive elevator leading to a crash. My Mig 29 had around 10 flights on it with the MRC upgrade servo's installed from day one as per MRC instructions.
A diving then low height 3 feet pass along the runway at full power, gave no elevator response. She would not pull up. Ended up going for about a 120mph slide down the runway.
It happened right in front of me at close range less than 50 yards, and flight telemetry data logging records show a perfect radio connection throughout the flight duration.
Based on all the posting I read here, this is not new. I guess I should be happy it's not a total loss, just severe gravel rash on the fuselage belly.

How are the elevator servos connected to the receiver?

[viper1gj]

Does anyone have a photo of the Home Depot touch up paint code for the stock Mig-29 grey color?

[Gringotuerto]

Does anyone have a photo of the Home Depot touch up paint code for the stock Mig-29 grey color?

Here it is, posted by Rudy:

For anyone looking for a paint match, I got the fuselage done at Home Depot today and picked up Tamiya X10 Gunmetal which is basically an exact match for the exhaust nozzles.

[Molly914]

Flaps?

No flaps deployed, it was a full throttle level pass

[Molly914]

That's VERY interesting, thanks for your report. To comment on a few points:

• You were flying level, apparently without flaps deployed, so there's no aerodynamic "blanking" of the stabs - reinforcing the idea that this is NOT an aerodynamic issue (at least not this time)
• Your telemetry shows no failure of the radio connection - no faults - so that seems to indicate that wasn't the issue (at least not this time)

So why do both elevators servos simply stop working, at the same time? What a mystery.

The thing that maybe slightly out of the ordinary was 3mm of reflex I added into the aileron and flaps, and hence slight elevator trim adjustment to compensate for the reflex.
I also had the MRC 'Upgrade' elevator servos. The servos are on one channel on a Y connector.

[xviper]

The thing that maybe slightly out of the ordinary was 3mm of reflex I added into the aileron and flaps, and hence slight elevator trim adjustment to compensate for the reflex.
I also had the MRC 'Upgrade' elevator servos. The servos are on one channel on a Y connector.

I kinda doubt that 3mm reflex is going to affect the elevators. This is somewhat disconcerting. I've got the upgrade servos and also the ELE "Y'd" together directly to the RX. The mystery continues.

[Firebird]

I attached a picture comparing the diameter of the stock elevator Y-cable to a regular servo cable diameter. This thin power and signal line of this cable is responsible for the most importend control surfaces of your 6KG / 125mph RC-jet. A 5V, few mAh, thin signal line bypassing a 4000watt power system from the front to the tail of the aircraft - even directly underneath the esc...

The fact that hunderts of migs are flying without issues doesn’t automatically mean that their elevator singnal at the tail is clear and strong - it might be just barely strong enough to not lose the signal.

[themudduck]

I attached a picture comparing the diameter of the stock elevator Y-cable to a regular servo cable diameter. This thin power and signal line of this cable is responsible for the most important control surfaces of your 6KG / 125mph RC-jet. A 5V, few mAh, thin signal line bypassing a 4000watt power system from the front to the tail of the aircraft - even directly underneath the esc...

The fact that hundreds of migs are flying without issues doesn’t automatically mean that their elevator signal at the tail is clear and strong - it might be just barely strong enough to not lose the signal.

Nearby RF energy interference is not going to stop the voltage from getting through the lines. (I agree that the larger-gauge wires are superior, especially for longer cable runs. Less voltage loss.)
.
But, for the sake or argument lets imagine that the servo cables are picking up RF interference. Will that make the servos simply stop working (turn off)? if they were picking up RF interference from the ESCs I'd expect them to be twitching. And not equally.
Any of you electronic ubergeeks want to contribute some knowledge?

[Firebird]

Nearby RF energy interference is not going to stop the voltage from getting through the lines. (I agree that the larger-gauge wires are superior, especially for longer cable runs. Less voltage loss.)
.
But, for the sake or argument lets imagine that the servo cables are picking up RF interference. Will that make the servos simply stop working (turn off)? if they were picking up RF interference from the ESCs I'd expect them to be twitching. And not equally.
Any of you electronic ubergeeks want to contribute some knowledge?

I could imagine that the way the servo reacts on a interrupted or weak signal depends on the design of the servo itself. As we are using digital servos, this particular servo might react with stoping movement until the signal is getting clear enough again (cutting engine power was reported to help regaining control) to securely identify the command send by the receiver.

We had several cases now of crashes losing elevator control recorded by telemetry systems stating that there had been a clear TX/RX communication and no loss of voltage in the system. As this owners did uses different rc system with same result (loss of elevator control) the core of the problem seams to be downline the elevator out of the receiver. As both elevator servos stop working same time (in level or almost level flight) I don‘t suspect the servos itself failing.

So what is left then - the servos cables itself and their position in the aircraft. And those cables are very long and very thin. And they bypass a 4000Watt power system and the esc‘s on the way back to the elevator servo - which might be trying hard to do the best out of the possibly disturbed signal.

[GliderGuy]

Such a mystery. We were blessed with beautiful weather here, so I flew most of the day. MiG, F-4, P-38. Mostly the MiG, however.

I wanted to test out the “shielding” added to the ESC area (see prior post above) and the added RF chokes placed right at the elevator servos.

Low passes, slow passes, high speed passes, level passes, diving passes, acrobatics, flaps and gear down for approaches (maneuvering).....

Nothing out of the ordinary happened. Always had full control authority...and I was watching closely.

I made one really low pass VERY close by me on the way to touchdown. I wiggled the elevator, and she responded as expected. No elevator blanking detected

Total loss as to what’s going on that’s causing the problem.

-GG

[kallend]

.
But, for the sake or argument lets imagine that the servo cables are picking up RF interference. Will that make the servos simply stop working (turn off)? if they were picking up RF interference from the ESCs I'd expect them to be twitching. And not equally.
Any of you electronic ubergeeks want to contribute some knowledge?

With digital servos, they would do what their firmware is programmed to do in case the signal goes outside the normal parameters.

I've never programed a servo but I have programed Arduino and PIC devices that read PWM signals to control other stuff. In each case they are programmed to enter a defined state if the signal goes out of spec, typically some kind of fail-safe.

[HK111]

I am probably one of many with an unexplained non-responsive elevator leading to a crash.

Thanks for the report, and I am glad that the plane is still there. Just curious, did you bypass the blue box, i.e. power the elevators directly from the receiver?

BTW, does the Blue Box have a failsafe mechanism (e.g. "hold last position") built in?

Cheers,
Henrik

[HK111]

Very long elevator wire, thin wire, but no loss of voltage in the system, maybe induction from the power wires, temporary voltage drop in wire, servo goes to failsafe?

[xviper]

Thanks for the report, and I am glad that the plane is still there. Just curious, did you bypass the blue box, i.e. power the elevators directly from the receiver?

BTW, does the Blue Box have a failsafe mechanism (e.g. "hold last position") built in?

Cheers,
Henrik

No. It's a sort of collector board. It serves as "Y's", reversers, gear sequencer, power for lights and light flashing type, nose steering defeat. Signal in, signal out - sometimes.

[HK111]

Here some calculations, inspired by an post from skyfox60 from rc-network.de comparing the effect of LV and HV servos in general:

• Assume a standard low voltage setup with 5 Volts at the receiver
• Assume the tail servo wants 15 Watts, which means it pulls 3 Amperes
• Assume the length of the elevator wire is about 1m (I just roughly measured the distances: it is about 70+cm from the rear to the blue box, and another 30cm for the wire from the bb to the rx)
• We use 2m for calculation, because the current has to go 1m to the servo and 1m back
• Assume the thin wire has a cross-section of only 0.14mm²
• 2m of copper wire at 0.14mm² have a resistance of about 0.244 Ohm
• Voltage drop due to the wire is 0.244 Ohm * 3A = 0.732V

So our servo at the tail has to get by with 4.27V, not 5. Assume that for some reason it wants more power and pulls a larger current, e.g. 4A or 5A, then it hits 4V or even less. That is marginal.

So a way forward would be:

1. Can somebody measure the voltage at the elevator servo?
2. Can somebody measure how many Amperes the elevator servo eats when under heavy load or obstructed?

Remedies:

1. Thicker, heavier wires
2. Shorter wires, by bypassing the blue box, or moving the receiver into the rear compartment and possibly exchanging the servo wires
3. Increase BEC voltage by 0.5V so that more reaches the "far away" servos and hope it doesn't fry the nearer servos nor the landing gear drives
4. Switch to high voltage servos.

Hmm...