Official Freewing MiG-29 Fulcrum Twin 80mm Thread

[Airguardian]

I still have it to implement it myself and see that it really beefs it up properly.

But the test is rather easy... as it comes stock, you just put the shaft in and can bend it with your hands rather easily... if it doesn't bent that easy after the mod, then it was succesful!


Otherwise... gotta think of a tougher solution.

Think I'll be attempting this tomorrow, hopefully I can give some feedback on the outcome if you don't want to jump straight into it as it will damage looks and so forth...

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

Expo is your friend.

[GliderGuy]

I removed both FFS and loaded the rod. I did not see any glue delamination/cracking. Nor any signs of fatigue cracking anywhere. Good news as this bird has 400+ flights on it.

Considering using thin CF sheeting vs fiberglass due to it being a more stiff material than fiberglass.

-GG

[leithalweapon]

I removed both FFS and loaded the rod. I did not see any glue delamination/cracking. Nor any signs of fatigue cracking anywhere. Good news as this bird has 400+ flights on it.

Considering using thin CF sheeting vs fiberglass due to it being a more stiff material than fiberglass.

-GG

I was thinking a CF sheet on the underside. Add holes for the screws. Use longer screws with washers after it's glued on.

[Scale Master]

I am working with my friend Keith (Yellowbird911) to make the Mig-29 a turbine conversion. We are both using the K-45G3 turbine. So far this has been a very easy conversion with a simple turbine mount between the engine nacelles and lots of room on top for all the extra stuff. Not much foam carving is needed. This is possible because we are using an external centerline tank as the main fuel tank. This external tank holds about 45 oz and will feed a 12-14oz header tank in the rear battery compartment and then feed the air trap tank and pump in the nose. Most fuel will be near the CG and its great not to have to carve foam to stuff all the fuel on the insid

Keith has designed and 3D printed tanks for several foamy turbine conversions before. The process is to print the tank and then coat the inside and outside with epoxy resin. For the Mig-29 he designed a semi scale center line fuel tank from photos that also functions as a FOD shield for the rear undermounted turbine. The tank has anti slosh baffles.

My tank arrived today. At first look it look fits perfect and looks great and scale. Keith will be posting the CAD and 3D print files on Thingiverse so it can be downloaded and printed if desired. This conversion is still a work in progress and I will post a full build thread somewhere when it is complete. For now here are some photos of the 3D printed tank.

Gary

Hi Gary how do I get one of those functional centerline fuel tanks? I wondering is the designer has a version without the non scale fod shield, because I don't need it as I'm running two turbines in her.

Thanks.

TSM

[GliderGuy]

I was thinking a CF sheet on the underside. Add holes for the screws. Use longer screws with washers after it's glued on.

Using 0.5 mm CF sheeting, I believe there is room to build either an L-shaped or a U-shaped “wrap-around” of the sides and bottom only...leaving the top unaltered. That’s got to be stiff enough and will prevent glue line separation, too. I just ordered some.

Thoughts?

-GG

https://www.amazon.com/dp/B082PX95QL/ref=cm_sw_r_sms_api_fabc_.u4PFbNMECV80

[Radar-Guy]

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.

FWIW: I brought this up in the Discord chat on 12 Sep and asked Alpha about the reasons for not following the original design (which has been replicated in other RC MiG-29s). The answer given by Alpha back then was:

“Regarding the pivot point, you're right, the scale point is impossible for us to replicate, so we recalculated based on our 17g. We have all the math for all our other birds which use the 17g with full flying stabs”.

[fredmdbud]

Using 0.5 mm CF sheeting, I believe there is room to build either an L-shaped or a U-shaped “wrap-around” of the sides and bottom only...leaving the top unaltered. That’s got to be stiff enough and will prevent glue line separation, too. I just ordered some.

Thoughts?

-GG

https://www.amazon.com/dp/B082PX95QL/ref=cm_sw_r_sms_api_fabc_.u4PFbNMECV80

Isn’t there already a plastic plate/bracket there. It’s where the fixed axle rod is anchored.

[GliderGuy]

Isn’t there already a plastic plate/bracket there. It’s where the fixed axle rod is anchored.

Yes—The last few posts are discussing the advisability to strengthen this area and to harden it for flight loads. Deformation or failure of this area may lead to a loss of control.

Also need to ensure the area will withstand a lot of flights without glue joint delamination or fatigue cracking over time. The other posts indicate the design of this area may be lacking in robustness.

MiG pilots should review the last couple of pages and decide for themselves.

Example of high flight loads causing deformation (anhedral) was posted by Borat in #2794 and reposting his photo below as he lost control and subsequently crashed (high throttle with flaps down and nose down "experiment"). Borat gave the ultimate sacrifice to extend the knowledge about this bird. As others have posted, high speed, high throttle with flaps down is not generally considered advisable. But pilots may forget to put the flaps up.

I am also concerned about hardening this area against fatigue, since I fly a lot! I will be adding some thin carbon fiber sheeting to the sides and bottom of this area. Easy to do for added piece of mind. Other methods to add strength were previously discussed in recent posts.

-GG

[Bushong572]

I've been flying my Mig for a while with 0 problems. I've been watching for any flex or anhedral in the tail and have not noticed any.
I glued my vertical stabs in from the beginning....including the rear section to the top of the fuse. This may help the situation.

[Yellowbird911]

TSM, I have it without the FOD screen as well. Will put on thingiverse soon. This is designed in the free version of Fusion360 so I can't actually sell one. PM me if you have more questions.

[DForbes]

I thought someone mentioned using thin metal sheeting which would probably be easier?

[GliderGuy]

I thought someone mentioned using thin metal sheeting which would probably be easier?

Metal might be more susceptible to fatigue cracking vs thin carbon fiber sheeting.

[kallend]

FWIW: I brought this up in the Discord chat on 12 Sep and asked Alpha about the reasons for not following the original design (which has been replicated in other RC MiG-29s). The answer given by Alpha back then was:

“Regarding the pivot point, you're right, the scale point is impossible for us to replicate, so we recalculated based on our 17g. We have all the math for all our other birds which use the 17g with full flying stabs”.

As far as I have been able to tell, none of their "other birds" with full flying stabs have their pivots so far from the center of pressure, and if all their math were correct why require the servo upgrade?

[kallend]

Yes—The last few posts are discussing the advisability to strengthen this area and to harden it for flight loads. Deformation or failure of this area may lead to a loss of control.

Yes it may.

The deformation may also just be another symptom of high loads but not the actual cause of the crashes. This remains to be proven.

However, stiffening the area certainly can't hurt.

[Nickc2023]

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:

I can definitely see from what you have illustrated how the problem is most likely structural. While reinforcing is a bit of a challenge it certainly isn't impossible. I did however have a thought on this. Wouldn't the assist in control from the soon to be released TV nozzles remove a great deal of the stress on the elevators? If so then perhaps motion should give us a bit of a discount on the upgrade as it helps to mitigate a safety issue? 😉 I know tv requires some radio mixing and more rx channels but those not looking for "extreme" control could just have them work with the elevator channel. It would probably be easier (and maybe cheaper) than rebuilding the rear of the airframe. Thoughts?

[GliderGuy]

I know tv requires some radio mixing and more rx channels but those not looking for "extreme" control could just have them work with the elevator channel. It would probably be easier (and maybe cheaper) than rebuilding the rear of the airframe. Thoughts?

My thoughts...I've ordered some thin 0.5 mm carbon fiber sheeting. I intend to epoxy this to the bottom and side areas and call it done. This will be easy...not a rebuild of the area.

My goal is to add stiffness and also reduce the chance that the plastic mount may delaminate due to glue joint failure in this area. If the end result is not stiff enough, then I will look at messing with the top of the area.

Each will need to evaluate and decide on the approach to take, if any.
-GG

[Nickc2023]

My thoughts...I've ordered some thin 0.5 mm carbon fiber sheeting. I intend to epoxy this to the bottom and side areas and call it done. This will be easy...not a rebuild of the area.

My goal is to add stiffness and also reduce the chance that the plastic mount may delaminate due to glue joint failure in this area. If the end result is not stiff enough, then I will look at messing with the top of the area.

Each will need to evaluate and decide on the approach to take, if any.
-GG

I kinda meant thoughts on if the TV nozzles would provide significant stress relief on the elevators. For example, if in flight the elevators fail for whatever reason (servo, pushrod, structural failure) would the TV alone allow you to keep control? Or would the assist from the TV prevent the high loads that cause elevator failure in the first place?

[t33jetman]

I can definitely see from what you have illustrated how the problem is most likely structural. While reinforcing is a bit of a challenge it certainly isn't impossible. I did however have a thought on this. Wouldn't the assist in control from the soon to be released TV nozzles remove a great deal of the stress on the elevators? If so then perhaps motion should give us a bit of a discount on the upgrade as it helps to mitigate a safety issue? 😉 I know tv requires some radio mixing and more rx channels but those not looking for "extreme" control could just have them work with the elevator channel. It would probably be easier (and maybe cheaper) than rebuilding the rear of the airframe. Thoughts?

I like your idea.
But take a step further, not to just reglue the foam cutoff part back, but replace it with a solid peice of wood glued in. I added a embedded carbon spare for just in case.

Pretty stiff back there now.

[Eric D]

Here is my collection of mods so far. HT 5245 servos and moved out. 22ga servo extensions on separate channels. 4-40 threaded rod inside close fitting carbon tube. Control horn reinforcements 3-32 phenolic . 3-16 carbon rod going through stab mount into tailpipe 2.5" long. Rear portion of fins glued also I also noticed that both my stabs have anhedral built in at production..Sight down your leading edges.

[HK111]

One more down, from Fred@RCG... He'll post details and footage later :-/.