Official Freewing MiG-29 Fulcrum Twin 80mm Thread

[HK111]

Here's some clips from flying this morning

Thanks. A clear correlation of elevators bending downwards when the flaps are deployed, easily spottable by tracking the outer tip of the elevator. It doesn't look too bad, though.

I still wonder how to best reinforce the fuselage tail that carries the elevator (thanks to the other posters who showed their improvements), and if the elevator itself should get a bit of reinforcement with thin carbon fibre strips. The other improvements, namely better servos, better pushrods, shorter and thicker servo wires, bypassing of the blue box for the tail surfaces and a slightly higher voltage are all done.

[paulrkytek]

As long as we're wondering....I wonder what would happen if the full size Mig dropped flaps at Mach 1?

Perhaps the Russians were not that suicidal !!!

[GliderGuy]

Great video mshagg - IMO the tail loading indicated FOR THE FLIGHT CONDITIONS captured is not excessive for the FFS structure. It bends a little, but it is a piece of foam.

My concern / Due to the speed potential of this jet....if you start messing with the FFS by beefing it up are you not changing the flutter characteristics?

Mass balance of a FFS is critical in determining flutter chacteristics of a FFS. Unless you know what you are doing, CAUTION CAUTION. A fluttering FFS is much worse than the small amount of flex shown in the video.

Youtube has several FFS flutter videos, and the planes eat dirt thereafter. Flutter = loss of control and/or parts leaving the aircraft!

If you are experienced with FFS flutter and know how to mass balance after adding material to the FFS, would you share how to do it?

I am not messing with the FFS unless I could know what I am doing. Flutter is ugly! A little flexing is acceptable for NORMAL flight conditions.

-GG

[Jet jocky]

Yes HK111 very happy with the outcome. Stopped the flexing significantly, and with the pro modeler servos should help with the issue's. But still don't fly with flaps down can't stress this enough.

[Jet jocky]

Can anyone tell me what the yellow bars mean under the members box on some of the members?

[Saxamadmac]

Would running one of these over the surfaces show anything i wonder, you wouldn't have to take off ! https://youtu.be/kDtQknRSVys Obviously it's not running full chat here, its an fms 70mm 6s with a hobbywing 80a. It should be putting out about 150 mph at full power

[Captain Moron]

Just watched a video on You Tube of someone flying the Freewing Mig 29 with a rear facing camera and you can see the 2 rear fins fail causing the Mig to crash .The 2 rear fins just collapse under the pressure and he was not doing any high G moves .What with the elevator problem and now watching this video of the fins collapsing .(Maybe this person did not install the fins correctly .I do not know ) Really want to buy this Mig 29 when it comes back" In Stock" but at around £600 want to make sure all the teething problems are sorted out before I buy one ,That why I never buy the first batch of a new model . I hang on and see what happens first and at the moment there seems to be a lot of strange crashes with the Mig 29 ?????? Has anyone else crashed due to the 2 fins collapsing or maybe they have had a strange crash and not know what caused it

[Airguardian]

Captain, please could you share the link to that video?

I am concerned about inducing flutter if messing with the stab mass balance.

How are you avoiding the potential for flutter if changing up the FFS? Re-mass balancing? Should this be a concern?

I wouldn't be too concerned. Stab balancing does little in that regard and making the stab more rigid to torsion by glassing it should in fact help prevent flutter, and there hasn't been any to begin with so...
Guess I'll find out when I maiden mine, eventually.

That’s why I added CF only to the bottom to stave off rectangular box / foam glue joint separation.

The reinforcement you made doesn't prevent the two foam halves from delaminating, but most importantly doesn't limit deformation due to torsion where it would help most which is in the top-side, not the bottom one IMO. :'(

[GliderGuy]

Hi CM - Many are having a blast with this bird. It flies nice and looks awesome. While there remain a few unexplained crashes, if you read the most recent pages of this forum, flying fast with flaps down appears to be the culprit.

Take some time and read all the pages of this forum then make your decision. If you don’t, you will be missing a lot of good knowledge.

-GG

[kallend]

Just watched a video on You Tube of someone flying the Freewing Mig 29 with a rear facing camera and you can see the 2 rear fins fail causing the Mig to crash .The 2 rear fins just collapse under the pressure and he was not doing any high G moves .What with the elevator problem and now watching this video of the fins collapsing .(Maybe this person did not install the fins correctly .I do not know ) Really want to buy this Mig 29 when it comes back" In Stock" but at around £600 want to make sure all the teething problems are sorted out before I buy one ,That why I never buy the first batch of a new model . I hang on and see what happens first and at the moment there seems to be a lot of strange crashes with the Mig 29 ?????? Has anyone else crashed due to the 2 fins collapsing or maybe they have had a strange crash and not know what caused it

Can you provide a link to the video?

[GliderGuy]

Hi Airguardian - After watching Fred’s video and mshagg’s video, I am not seeing much support area deformation. That’s why I didn’t add CF other places.

As to mass balance/flutter, the Standard Austria sailplane and others with FFS had external anti-flutter mass balancers.

No flutter in the MiG FFS, for sure. That’s why I have concerns about messing with a good thing. Mass balancing must be important or why would the designers add external masses to ensure flutter wouldn’t occur. I present this as a precaution to be considered before changing the mass of the MiG’s FFS.

See photo for anti-flutter mass balances on the FFSs.

Edit: Adding a snip from a Standard Cirrus POH about how and where to add weight after a repair and repainting of the FFS to ensure mass balance is maintained....to avoid changing the flutter characteristics.

[Reaper911]

Can you provide a link to the video?

at 2:34 in a shallow dive he drops the flaps and the horizontal stabs deflect down (anhedral) a lot.

Perhaps they bind up at that severe deflection making them inoperable?

https://www.youtube.com/watch?v=sEGz_euefdY&t=166s

[janmb]

at 2:34 in a shallow dive he drops the flaps and the horizontal stabs deflect down (anhedral) a lot.

Perhaps they bind up at that severe deflection making them inoperable?

https://www.youtube.com/watch?v=sEGz_euefdY&t=166s

This is Fred's video. Very very relevant, but not news.

[xviper]

Would running one of these over the surfaces show anything i wonder, you wouldn't have to take off ! https://youtu.be/kDtQknRSVys Obviously it's not running full chat here, its an fms 70mm 6s with a hobbywing 80a. It should be putting out about 150 mph at full power

Maybe, but I doubt it. That thing might put out 150mph but that's right at the nozzle. Once the air gets about a foot away and beyond, the velocity gets cut down to a fraction of that. In an experiment like this, you'd want the air to be blowing past the main wing and then past the tail surface. Next, it's not just air velocity that's the only factor, it's also the air volume that can be produced. I typically use a Stihl back pack leaf blower to clear snow from sidewalks. The nozzle velocity on that is 238mph and the air volume is 677cfm. There is now an even more powerful blower. The nozzle velocity is the same but the air volume goes up to 912cfm. The point is, you need a lot of air volume to produce the desired effect. What it puts out at point blank range (within a couple of inches) and what it can do at a couple of feet are vastly different. Speed and volume decrease exponentially.
I've thought about tying my MiG down to something and giving it a blast from just in front of one wing to see what happens. By the time the air gets back to the elevator, it's likely still going 150mph. But then, I decided it's just a foam airplane. I do what I can to make it strong, add safety margins and try not fly it in any abnormal ways but after that, if it goes splat, well, on to the next plane.

[Airguardian]

Hi Airguardian - After watching Fred’s video and mshagg’s video, I am not seeing much support area deformation. That’s why I didn’t add CF other places.

Check this video by Mshagg again. Minute 1:00

Watch carefully and replay a few times if need be. When flaps are lowered not only stabs deform, the whole fuselage / vertical stabs bloc is shifting down. From this angle you don't really appreciate it as torsion... but it is mostly torsion of the entire thing. Some flex too, but mostly torsion IMO.

And that's the reaction to stabs that are deformed (thus they produce less force than if they were keeping shape) plus being flown at low speeds. Add stab rigidity and speed and picture that deformation again, but increased tenfold.

As to mass balance/flutter, the Standard Austria sailplane and others with FFS had external anti-flutter mass balancers.

No flutter in the MiG FFS, for sure. That’s why I have concerns about messing with a good thing. Mass balancing must be important or why would the designers add external masses to ensure flutter wouldn’t occur. I present this as a precaution to be considered before changing the mass of the MiG’s FFS.

Not saying it is not important, just voicing an opinion that I doubt this is going to be a problem here on this particular build and that other considerations apply to flutter which may be more relevant than mass balancing. I assume pilots are limited in what they can (or are allowed to) do to an existing design and built aircraft to deal with flutter.

Rigidity to torsion plays a huge part, the way the mechanical linkage transmission is laid out, aerodynamic/aeroelastic considerations, the relation between stab inertia and actuator response time, etc, etc.

Mass balancing is 'another step in the ladder', not necessarily the most important one as far as I understand it. Of course, it is relevant and some of the problems may be limited through that approach when others are not available. ;)

[GliderGuy]

Yep...at 1:00+ you CAN see the support structure squat in a downward motion in the slow mo speed. Not a lot, but you can definitely see it. Thanks. Good eye!!! More info to consider.

All the more reason not to fly fast with flaps down which exacerbates what the video shows is happening at these slower air speeds (as ascertained by the sound in the video).

-GG

[Colorc]

If I were MRC, I might say something like...“Operating as to cause the ROC to be exceeded is not recommended. Operation outside the ROC may induce stresses which may impact successful operation.” In other words....not guaranteed.
-GG

Haha, im kinda late to the forums. Been having too much fun flying the mig instead of talking about it.
Flex innovations say something similar to the qoute above with their flex jet. Im sure that keeps their pilots aware that the plane has enough power to destroy itself if not flown in the ROC. (which i find hilarious and kinda bad donkey and i would still buy the mig if freewing had that caution) The flex jet seems like it was meant to have enough thrust to give it amazing verticle climb and punch, but if going flat out level or in a shallow dive, something not so fun will happen.
This is probably one of the many reasons why rc manufacturers dont put a stock power system in their planes that will give it that 1:1 power to weight ratio or ballistic performance is because the average pilot will think that the plane should survive full throttle flying no matter what because its the stock power system. Although that high performance version mirage can actually handle wot all day long. The guys that do stuff more powerful systems in their planes understand common airframe limitations and beef up these areas to prevent failure.
I know that for those that have lost their migs to whatever scenario may get bent out of shape by this comment, but i dont mean it to be patronizing. I am grateful to all that have posted their failures to help the rest of us to prevent failure. I do agree though that if the system as a whole on this mig is not balanced in some way, like the flex jet, then the manufacturer should state that. Be it the fans are powerfull enough to push the plane too fast to control, flaps down moderate speed will cause progessive loss of elevator control or whatever it may be.
i think this is a pretty good value for the size and complexity of this jet even if its not a true pnp in the sense that you just screw it together, put a battery in, and go. Then again, i fly $3000 gassers that i still had to do extra build mods, based on experience of others, to ensure that my plane could endure and handle the flying style i intended to put it through
Maybe my tune will change if i crash mine.😂

[leithalweapon]

Captain, please could you share the link to that video?



I wouldn't be too concerned. Stab balancing does little in that regard and making the stab more rigid to torsion by glassing it should in fact help prevent flutter, and there hasn't been any to begin with so...
Guess I'll find out when I maiden mine, eventually.



The reinforcement you made doesn't prevent the two foam halves from delaminating, but most importantly doesn't limit deformation due to torsion where it would help most which is in the top-side, not the bottom one IMO. :'(

You should fly yours, it really does fly well.

[Reaper911]

This is Fred's video. Very very relevant, but not news.

Yes, I realize that. Kallend had asked for a link to the video

[kallend]

at 2:34 in a shallow dive he drops the flaps and the horizontal stabs deflect down (anhedral) a lot.

Perhaps they bind up at that severe deflection making them inoperable?

https://www.youtube.com/watch?v=sEGz_euefdY&t=166s

That doesn't seem to be the one Capt. Moron referred to, going by his description.