Official Freewing MiG-29 Fulcrum Twin 80mm Thread

[kallend]

There is a common denominator in every single one of these crashes and it is mostly being ignored:

The airframe.

[PieterO]

Since we still don't have a clue about what really caused these crashes, I thought of a somewhat strange solution that would mitigate almost all of the possible causes that I have read in the past few days:

How about putting a small (2-channel) receiver in the back of the plane for the elevators only? This receiver could be powered by a small receiver pack, also located in the back of the plane. In my case i could use this 6 grams Futaba R202GF S-FHSS and put each elevator on it's own channel.

This would solve/mitigate the issue, if it's caused by one of these many options:

- faulty y-cable
- problems with bluebox
- interference/rf noise in the elevator servo cables
- voltage drop because of long elevator servo cables
- BEC overloaded
- receiver/antenna's blanked out by large batteries
- receiver brown out because of flying high speed with flaps deployed
- and I possibly forgot a few

What do you think?

*Edit: I just noticed that the R202GF isn't suitable for planes, but you get the idea :-)

[janmb]

There is a common denominator in every single one of these crashes and it is mostly being ignored:

The airframe.

Well, I have a really hard time seeing this being an aerodynamic issue, considering the attitude, speed variation, and various flap settings too. Impossible - certainly not. But definitely don't see it as likely at all.

It takes a fair bit of turbulence to blank out a fully deflected elevator of this size. And therein lies the issue - we are not seeing a lot of deflection at all in those videos - despite the pilot surely must be pulling frantically

[GliderGuy]

There is a common denominator in every single one of these crashes and it is mostly being ignored:

The airframe.

My money is on the other common denominator - That being the variability of the installed electronics.

PieterO - Cool suggestion, but I am not sure many owners would be willing to do this. If a lot of folks don’t do it, then the data points will be restricted to the one-off experimenters who choose to try it. But I like your thinking outside the box suggestion.

FYI - I did a very short look at other EDF forums. The MiG apparently isn’t the only new MRC bird seeing weird loss of control issues. Again...see paragraph #1 above.

Statistically, if it were an airframe/design issue...it would VERY probably caused mine to crash given the high number of flights I have flown. And, I don’t just loiter around the pattern.

-GG

[HK111]

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

• Used the replacement servos
• Used the new servo horn and recommended middle hole in the shortened horn
• Control via blue box
• Reinforced pushrod for the elevators
• CG at stock location
• Flaps up, in normal position

He mentioned that during the crash, he pulled full up elevator, but nothing changed, "nothing, not even minimal". Some other commenters wondered whether his CoG was too far forward, but he mentioned that he had the CoG even a bit further forward in earlier flights, where it did feel wrong, but had moved it back and was happy with it during the flight where it crashed.

He also mentioned that he had the impression that when going down, flying less than horizontal, the effectiveness of the elevators seemed reduced.

HTH,
H

[kallend]

Well, I have a really hard time seeing this being an aerodynamic issue, considering the attitude, speed variation, and various flap settings too. Impossible - certainly not. But definitely don't see it as likely at all.

It takes a fair bit of turbulence to blank out a fully deflected elevator of this size. And therein lies the issue - we are not seeing a lot of deflection at all in those videos - despite the pilot surely must be pulling frantically

Doesn't have to be aerodynamic in the sense of fluid mechanics. Could be aeroelastic/structural/geometrical.

[kallend]

My money is on the other common denominator - That being the variability of the installed electronics.

That is the opposite of a common denominator.

[GliderGuy]

That is the opposite of a common denominator.

LOL - Weak attempt at humor.

Point being....nothing definite that we can point to as a cause, yet. Not, from what I see on other forums for other EDF models having loss of control, either.

-GG

[Firebird]

Since we still don't have a clue about what really caused these crashes, I thought of a somewhat strange solution that would mitigate almost all of the possible causes that I have read in the past few days:

How about putting a small (2-channel) receiver in the back of the plane for the elevators only? This receiver could be powered by a small receiver pack, also located in the back of the plane. In my case i could use this 6 grams Futaba R202GF S-FHSS and put each elevator on it's own channel.

This would solve/mitigate the issue, if it's caused by one of these many options:

- faulty y-cable
- problems with bluebox
- interference/rf noise in the elevator servo cables
- voltage drop because of long elevator servo cables
- BEC overloaded
- receiver/antenna's blanked out by large batteries
- receiver brown out because of flying high speed with flaps deployed
- and I possibly forgot a few

What do you think?

*Edit: I just noticed that the R202GF isn't suitable for planes, but you get the idea :-)

I do agree Pieter - a second, independent and battery powered receiver in the tail for the elevator servos could be a solution as well.

[Captain MoMo]

You can rule out pilot error on 99% of these recent Mig 29 crashes.

[Evan D]

Everyone that has answered the poll has had the elevators through the MCBe (a Y in a box) or used the Y, so no one was using tailerons.

As an aside I do use them every flight, take off normal and then flip to high rate aileron which kicks in tailerons.

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.

[hmarmaizmd717]

Hi, colorc, sent you a photo of my mods. to the elevators. I couldn't post it in the forum. Also changed the steering lead to
an aux. channel and mixed it to the rudder with a rotary knob.

Hector

[Waconut]

Well I guess this is like Covid-19, 99% will be just fine. If your unlucky you will be in the 1%. It is 2020 after all. Hell maybe after the election all the crashes just may stop.

[Jet jocky]

Way to nose heavy in a high speed dive is accident waiting to happen . Your elevators are working they just can't overcome the speed and g force acting upon them. I'm inclined to beleave it's pilot error not anything to do with the electronics. Fly the thing don't abuse it . Sure you love the speed and everyhing about it but it's not meant to fly it the way some of you are doing. Just my opinion.

[janmb]

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.

The main reason I doubt failsafe being a thing here is because most pilots are indeed flying spektrum, and even if subsequent trimming would somewhat invalidate failsafe positions for the control surfaces, 99% of those pilots would have a throttle that goes to -100 (or even -130 depending on whether or not they bound with default throttle cut setting). In short, even fresh or less gifted pilots will typically struggle to get failsafe wrong for throttle on spektrum systems. It basically is right unless you deliberately try to sabotage it (contrary to a lot of other radio systems, where you have to actively remember to set it up right).

And all the crashes I've seen have one thing in common: Motors don't cut.

[Firebird]

Servotelemetry - test 1

The new receiver arrived and i‘m able to provide servo telemetry data now.

I just made a quick voltage check at the servos to show the voltage difference at the servos under same conditions - Test 1 connected to the stock elevator servo cables via y-cable compared to my upgraded and rerouted elevator cables (will follow soon in Servotelemetry part 2)

Following setup for test1:

Stock BEC directly connected to jeti rex12 receiver. Both telemetry servos connected via the stock elevator servo cables and plugged into one receiver channel via the y-cable provided with the MRC upgrade servos. No other equipment connected to the receiver. No Bluebox. Voltage at the receiver 4.9Volt.

1. Servos in idle - no servo movement: V at the servo 4,7Volt at 0,2ah (each servo)

2. Servos moving free in servo test mode at half speed: Voltage at the Servo: 4,6Volts at 0,7ah (each servo)

3. Servos forced by hand to stall: Voltage at the servo 3,5Volt at 2,5ah (each servo)

[janmb]

Servotelemetry - test 1

The new receiver arrived and i‘m able to provide servo telemetry data now.

I just made a quick voltage check at the servos to show the voltage difference at the servos under same conditions - Test 1 connected to the stock elevator servo cables via y-cable compared to my upgraded and rerouted elevator cables (will follow soon in Servotelemetry part 2)

Following setup for test1:

Stock BEC directly connected to jeti rex12 receiver. Both telemetry servos connected via the stock elevator servo cables and plugged into one receiver channel via the y-cable provided with the MRC upgrade servos. No other equipment connected to the receiver. No Bluebox. Voltage at the receiver 4.9Volt.

1. Servos in idle - no servo movement: V at the servo 4,7Volt at 0,2ah (each servo)

2. Servos moving free in servo test mode at half speed: Voltage at the Servo: 4,6Volts at 0,7ah (each servo)

3. Servos forced by hand to stall: Voltage at the servo 3,5Volt at 2,5ah (each servo)

That is quite a nasty drop. Considering how much force improves from 4.8 to 6.0, the drop in performance from around 5 down to 3,5 must also be quite significant. And considering the servos have a hard time even at 6V, this tells quite a nasty story imo

[Firebird]

Servotelemetry - part2

Setup:

Stock BEC directly connected to jeti rex12 receiver. Both telemetry servos connected via my upgraded and rerouted servo cables into the receiver. Each servo is connected to it’s own channel at the receiver. No other equipment connected to the receiver. No Bluebox. Voltage at the receiver 4.9Volt.

1. Servos in idle - no servo movement: V at the servo 4,9Volt at 0,1ah (each servo)

2. Servos moving free in servo test mode at half speed: Voltage at the Servo: 4,8Volts at 0,6ah (each servo)

3. Servos forced by hand to stall: Voltage at the servo 4,3Volt at 3.0ah (each servo)

Servo telemetry test 1 (previous post) compared to servotelemetry test 2 shows that the voltage at the servos might drop low using the y-cable together with the stock elevator cables.

[bandetx]

The main reason I doubt failsafe being a thing here is because most pilots are indeed flying spektrum, and even if subsequent trimming would somewhat invalidate failsafe positions for the control surfaces, 99% of those pilots would have a throttle that goes to -100 (or even -130 depending on whether or not they bound with default throttle cut setting). In short, even fresh or less gifted pilots will typically struggle to get failsafe wrong for throttle on spektrum systems. It basically is right unless you deliberately try to sabotage it (contrary to a lot of other radio systems, where you have to actively remember to set it up right).

And all the crashes I've seen have one thing in common: Motors don't cut.

Also, modern radios wouldn't be losing signal at the rate of these crashes. It's exceedingly rare.

[Captain MoMo]

Way to nose heavy in a high speed dive is accident waiting to happen . Your elevators are working they just can't overcome the speed and g force acting upon them. I'm inclined to beleave it's pilot error not anything to do with the electronics. Fly the thing don't abuse it . Sure you love the speed and everyhing about it but it's not meant to fly it the way some of you are doing. Just my opinion.

I think you should do more reading on this topic before throwing out your opinion like this. It is not pilot error as all of the crashes occurred on a straight approach to the runway and mine (as well as others) were balanced at the recommended CG or aft of it.