Official Freewing MiG-29 Fulcrum Twin 80mm Thread

[DCORSAIR]

WoW DCORSAIR..we must be of the same era.. That is exactly what happened to my Byron Mig on its maiden in 1980!

cheers
dw

Yes, it was a long time ago...... I also had the Yellow Aircraft F-4 DF, it did not like to much flap on landing, it would blank out the elevator on your flare, yes stabs were balanced, I balanced all my stabs since those days, even the Freewing F-4, just throwing it out there, with the pivot point being off and weak servos on a big jet like the Mig, never know what is going on but I do wish someone can get this one solved soon, because it might still be a problem when the next big EDF from Freewing comes along.

[GliderGuy]

Tomorrow is forecast to be light winds and good weather. I’ll be trying out the MiG’s new configuration which consists of:

- 20 AWG (0.5mm) twisted tail servo drive wires
- MRC supplied Y
- FFS servo control rod on inner servo arm hole
— 4-40 threaded rod with heavy duty DuBro ball link and Kwik-Link safety lock ends driving the FFS
- CG 15 mm aft of wing mark / wheels down
— Since I am using Admiral Pro 6000, this required adding some weight to the tail area (not a lot)
- MRC upgrade servos (they have served me well so far)
- 4 mm of FFS trim removed / We’ll see where the trim ends up after the first flight
- 5 RF chokes (each ESC, each rear servo in the tail and one by the green ferrite ring)

Thanks for everyone’s inputs.

Until I upgrade TX/RX, this is about as far as I can “improve”.

Stay tuned.

-GG

UPDATE : The weather was as forecast.....perfect! Started at sunrise and now taking a lunch break.

P-38, F-4 and MiG-29 were flown.

No issues at all with the MIG’s CG @ 15 mm aft of marks. This CG adjustment gave an 80% reduction in FFS trim. Still carrying a touch (1 mm or less). You need to pay attention right after lift-off as the nose wants to over-rotate just a bit. After a couple of flights...this became a non-event.

Now to spend some time filling, sanding, painting the underbelly at the tail where I added the weights.

Thanks again for everyone’s inputs.

-GG

EDIT - Servo arm on innermost hole for FFS.

[Eric D]

With moving the CG aft will probably need a elev. travel reduction.because of the increased effectiveness.

[GliderGuy]

With moving the CG aft will probably need a elev. travel reduction.because of the increased effectiveness.

With the FFS servo arms on the inner hole, it felt pretty good. Basically....what you said.

Thanks!

-GG

[lusek_pl]

With these flaps and full throttle. What do you say?
https://youtu.be/ZPlFVV9zvQs 3:55
Polish captain Adrian Rojek, known for vertical take-offs, makes a departure in 4 minutes on full flaps, afterburner plus a slow barrel ... In general, the flaps increase the lift force and when working properly they should put up resistance and lift the plane up with increasing thrust. remember, however, that the critical angle of attack is decreasing. Therefore, the mere use of them at high speeds should not be a problem, as long as we correct the angles appropriately.

[janmb]

With moving the CG aft will probably need a elev. travel reduction.because of the increased effectiveness.

Yes, and that is a very good thing

[janmb]

With these flaps and full throttle. What do you say?
https://youtu.be/ZPlFVV9zvQs 3:55
Polish captain Adrian Rojek, known for vertical take-offs, makes a departure in 4 minutes on full flaps, afterburner plus a slow barrel ... In general, the flaps increase the lift force and when working properly they should put up resistance and lift the plane up with increasing thrust. remember, however, that the critical angle of attack is decreasing. Therefore, the mere use of them at high speeds should not be a problem, as long as we correct the angles appropriately.

I agree that this shouldn't be as marginal as it is, but that clip shows very slow flight though. The opposite of what we have seen when people crash the model.

[PieterO]

For the guys who installed afterburners: how did you get the wires from the afterburner unit to the battery/receiver compartment? It's quite a distance and it seems a narrow duct...

[kallend]

Saw a crash today at our club field. Following a very high alpha pass about 3 minutes into the flight, the MiG wouldn't respond to down elevator and just descended tail first, slowly into the weeds. Repairable. Experienced pilot.

[GliderGuy]

Saw a crash today at our club field. Following a very high alpha pass about 3 minutes into the flight, the MiG wouldn't respond to down elevator and just descended tail first, slowly into the weeds. Repairable. Experienced pilot.

Yep...been there, done that. Almost didn't recover. Several have posted warnings about this characteristic in the past...including me. The posts also show the recovery method....chop the throttle. The thrust line is such that once into the high alpha, deep stall, falling leaf realm, adding power only holds the nose up and keeps the alpha high...not recoverable. There is no response to any control input other than throttle.

So....#1...keep your altitude if you are playing around with high alpha and #2...Be prepared to chop the throttle and allow the nose to fall through...then gently add power to begin flying again.

Several warnings and how-to recovery videos are in this forum. Hard to talk yourself into chopping the throttle, but that's how the recovery is done...assuming enough altitude is in hand. Nothing to be scared about...Just be aware.

-GG

[AirHead]

Like these?

There Ya Go!...lol

[JLambCWU]

Saw a crash today at our club field. Following a very high alpha pass about 3 minutes into the flight, the MiG wouldn't respond to down elevator and just descended tail first, slowly into the weeds. Repairable. Experienced pilot.

EXACTLY what I warned people about in my EXTENSIVE write up on flying the early Mig models to arrive.

All of the keyboard experts wanted to voice their zero experience opinions though...

[HK111]

Putting the FFS pivot axis close to the CP would eliminate most of the above issues.

So how do we do that? I mean, without having two dysfunctional elevators after botching up the operation 😁.

[janmb]

Saw a crash today at our club field. Following a very high alpha pass about 3 minutes into the flight, the MiG wouldn't respond to down elevator and just descended tail first, slowly into the weeds. Repairable. Experienced pilot.

That is a known problem and simply boils down to thrust line.

[janmb]

For the guys who installed afterburners: how did you get the wires from the afterburner unit to the battery/receiver compartment? It's quite a distance and it seems a narrow duct...

Use a pulling wire. (most of the larger freewing models have been supplied with one)

[PaulZ]

Yep...been there, done that. Almost didn't recover. Several have posted warnings about this characteristic in the past...including me. The posts also show the recovery method....chop the throttle. The thrust line is such that once into the high alpha, deep stall, falling leaf realm, adding power only holds the nose up and keeps the alpha high...not recoverable. There is no response to any control input other than throttle.

So....#1...keep your altitude if you are playing around with high alpha and #2...Be prepared to chop the throttle and allow the nose to fall through...then gently add power to begin flying again.

Several warnings and how-to recovery videos are in this forum. Hard to talk yourself into chopping the throttle, but that's how the recovery is done...assuming enough altitude is in hand. Nothing to be scared about...Just be aware.

-GG

Thanks for this, had the same thing happen on landing approach in very high wind. The plane would not recover from very high alpha. Adding throttle made it worse...I was lucky and it landed on the mains eventually. There was very little response to down elevator.

[Airguardian]

I spent some quality time evaluating the MiG-29 stab housing and now that I know what to look for, it is pretty darn obvious to me what is wrong and I'm kinda surprised/upset that this was overlooked or outright ignored by Freewing/MRC.

There is indeed a structural issue as a result from a design flaw derived from choosing not to implement the scale stab shaft axis for whatever reason.



The thing is, with the 'scale' pivot axis, the stab would unload the forces directly to the strong part of the rear fuselage but with the 90º shaft placed further aft, the thin foam+plastic box that should be basically only there for cosmetic and aerodynamic purposes becomes the responsible for keeping the stabs in place. If that little piece of foam and plastic fails, the stabs will deflect producing anhedral and that probably messes the linkage geometry to the point that the stabs cannot simply be moved to produce the restoring downwards lift required for level flight or pulling out of a dive, regardless of whether the servo is operating properly or not.



To make things worse, the piece of foam that has to take the torsional load has been 'emptied' to allow the 'aligning' vertical stab insert.
This reduces the total cross section of the piece and makes it act as an open U-shape profile (as if EPO flexing wasn't already bad enough). It can be clearly observed from manual application of forces to the stab axis that this piece is deforming. If the glue responsible for joining the of the two fuselage foam halves and/or the one gluing the plastic stab housing to the foam fails, then that will provide basically zero structural resistance. That's the underlying reason for the dive-crashes witnessed so far IMO.



The foam being cut open to host the vertical fin only makes it worse as it 'opens' the profile, killing its ability to withstand torsion which was already marginal to begin with for the flexible foam.

Shifting the shaft more aft without changing the sweep angle will only make things MUCH worse.

Putting the FFS pivot axis close to the CP would eliminate most of the above issues. Reducing the loads reduces the servo currents, reduces the heating, reduces the flexing.

Being that the most likely culprit of jets going down is structural, switching the pivot shaft aft while keeping it at 90º will only make it much worse.
The 'good' solution would be to cant the axis as it is on the fullscale jet and should have been the stock design.

Challenging? Sure, but perfectly doable IMO.

Since that's quite a lot of work, I will provide an alternative in my next post.

If this really is the main issue couldn't (shouldn't) motion/freewing sell a new ffs set with a redesigned pivot axis?

I do think this is indeed the problem and yes, that would be ideal but I don't think MRC/FW will go to such lengths unfortunately.
Apparently they are happy enough that the 'casualty rate' of the MiG is pretty low percentually speaking if compared to other jets despite this design flaw.

But from the nature of the beast, I'm predicting we will see the number of MiGs crashing from this problem keep to grow as airframes age and the structure is further stressed out, unless dealt with and reinforced.

[Airguardian]

This would be my proposed solution, or at least what I'm planning to do on mine after thinking it out...

First I thought about just epoxy-gluing the vertical stabs in but being unable to dismount them is a huge compromise and that doesn't impede the halves from delaminating if glue fails anyway.

The idea is to close the stab assembly cross-section-profile, on one hand to prevent delamination, on the other to make sure torsional loads transmit properly from the shaft section forward.
This should make the assembly much more rigid and reliable.

This (or a similar fix on these lines) should be mandatory for those considering the kero upgrades, and more than advisable for those that will stick to EDF as well IMO. Do as you please of course.

This mod will obviously require doing paint touch-ups later on, but it is what it is. I think there's already been like 20 to 30 reported lawn-darting crashes.
Even if that only represents a small percentage of all the MiGs flying, I'm not taking the chances, and honestly, neither should anyone considering that this is a small 6kg missile.


Step 1:



Step 2:

[viper1gj]

This would be my proposed solution, or at least what I'm planning to do on mine after thinking it out...
This (or a similar fix on these lines) should be mandatory for those considering the kero upgrades, and more than advisable for those that will stick to EDF as well IMO. Do as you please of course.

I just spent some time planning how to do exactly this on mine today. Now I have a step by step guide with pictures. Thanks!

[GliderGuy]

Airguardian - Thanks....I’m gonna!!!! Also, with the large number of flights on mine, I am going to take a close look at the integrity before I implement the strengthening. If I find anything, I will post it.

-GG