Official Freewing MiG-29 Fulcrum Twin 80mm Thread

[Airguardian]

Approx 10 cm aft of the marks is what I can get too - barely. Would love another 10 though.

Wow... you daredevil! That would make for an interesting flight, rofl.

Airguardian - please re-read Firebird’s posts. He states the setup conditions for each test clearly.

Yep, my bad, I missed the part where he mentioned the wires.

Aside - I watched some of your YouTube videos. Nice flying, man!

Thanks! :D
Su-35, F-18 or Eurofighter?

[GliderGuy]

SU-35

[Airguardian]

[ColtPilot]

All you enigneers see my post on RCG I know all you folks with degrees like to over think everything just for fun and thats OK but in my 37yrs of working full scale airplanes I never saw that approach work when trouble shooting malfunctions. I think Evan has the best idea of all. please support him. Yes I do have and fly the Mig (15 flts so far) It is stock except for upgraded servos and 4/40 rod,it is a great flying A/C. I had to stop flying due to the weather here in MI ( to cold for my 83 yr old bones) Good luck to all of you that fly this A/C.

R. Driftmyer CNSgt USAF Retired

Where in Michigan? I'm in Saint Clair Shores.

[RC Rich]

Hi there RC Rich, actually in my case it didn't result in a crash! (I posted the full story some time ago). I was flying across the field maybe 100 feet up, and it was just flying straight in a very slight dive just above idle power, when both elevators suddenly stopped working for a few seconds. I only had enough time to think "oh SH** its happening" with that horrible feeling in my stomach - just helpIess with the plane not responding. I cut the throttle just by instinct before it went in and at that moment, control returned and I pulled it up. Everything was working again. Then I lowered the gear, came around, put the flaps down and landed completely normally. And then... I decided to quit for the day while I settled back down!

(Yes its possible that other controls weren't working either, but I don't know. For certain that the elevators weren't working because I was trying to pull up and that was the first thing I noticed.)

Afterwards I was inspecting the model on the bench and I removed the receiver and the plug fell out of the satellite, making me think that it may not have been plugged in all the way. So it could have been a radio glitch. But I have no idea. It happened very fast and the elevators are what got my attention.

I'm sorry, when I read earlier today "but look, both of my elevators simply stopped working while I was flying straight and at low power, just cruising by and then I tried to pull up. I want to know why both elevators stopped working while they were essentially idle.", I assumed you ended up crashing.

That's an amazing story and had to have been nerve-racking! Glad you were able to land it!

[janmb]

Wow... you daredevil! That would make for an interesting flight, rofl.

Everyone needs a little excitement in their lives lol

[Edwin-0]

Edwin your "pimp" looks really great, I love the extra detail you added!! Is the color on the wingtips and fin tips correct to scale? I really like the way it looks.

Nothing scale, i just follow my feelings, and what i like. 😎

[Drifty]

Where in Michigan? I'm in Saint Clair Shores.

Temperance, down by Toledo OH I belong to the week signals We have 400 ft of paved runway so if you`ed like to come down and fly in the spring Pm me

[kallend]

So many posts about measuring the force on the servo under various conditions, and that the servo might stall under aerodynamic load (or because of a voltage drop under load). Maybe overloading the servos due to the geometry (wrong hole)... Its a great discussion, and it could make sense if the failures happened while pulling out of a high-speed dive, or with the flaps down, or in a high-G pull in a turn. And perhaps that did happen in some cases, but look, both of my elevators simply stopped working while I was flying straight and at low power, just cruising by and then I tried to pull up. I want to know why both elevators stopped working while they were essentially idle.

I'm using the MRC-supplied replacement servos and Y-harness plugged directly into the receiver. (and I've done all the other mods, such as balancing the stabs, 4-40 rods, chokes, balance, etc)

Even in S&L flight the servos are still working when you have a FFS, just to maintain trim. The further forward the CG, the harder they have to work. In this MiG the pivot point on the FFS is very far forward, which means they would have to work even harder.

It's interesting to compare the location of the pivots in this MiG with other FFS models such as the SU35, F-35V3, etc. In each case those models have the pivots farther back on the control surface leading to better aerodynamic balance (mass balancing isn't going to help much if at all).

[Mizer67]

Does anyone know how the upgrade servos behave when they get overheated?

It would be interesting information to me if the failure mode was to shut down. What I've seen in terms of the crashes doesn't point to a singular maneuver exceeding the ability of the servos to perform, given most have started from either a shallow dive or level flight. What does make more sense speculating on in my mind is higher loads for a longer duration.

[Drifty]

Even in S&L flight the servos are still working when you have a FFS, just to maintain trim. The further forward the CG, the harder they have to work. In this MiG the pivot point on the FFS is very far forward, which means they would have to work even harder.

It's interesting to compare the location of the pivots in this MiG with other FFS models such as the SU35, F-35V3, etc. In each case those models have the pivots farther back on the control surface leading to better aerodynamic balance (mass balancing isn't going to help much if at all).

If you could scale down the air it flys in that might make sense but you can`t therefore the surfaces don`t see the kind of loads seen on full size A/C since they are much smaller in area.

[kallend]

If you could scale down the air it flys in that might make sense but you can`t therefore the surfaces don`t see the kind of loads seen on full size A/C since they are much smaller in area.

How is that relevant? The servos are smaller and the pushrods are smaller too.

And you haven't addressed the trim issue, the location of the pivot with respect to the CP, or shown any reasoning whatsoever for your opinion other than you used to be a mechanic back in the day.

The point I'm making is that the geometry of the FFS and its pivot location pretty much guarantee that the servos will be loaded even in straight and level flight on account of trim forces.

If you have a reasoned rebuttal to that then please let us have it.

[kallend]

Here is a photo from Henrik comparing the MiG FFS with the SU35 FFS, with their pivot axes aligned.

It is very clear that the MiG has a lot more area, and moment of area, behind the axis, for much the same area and moment of area ahead of the axis.

[themudduck]

Here is a photo from Henrik comparing the MiG FFS with the SU35 FFS, with their pivot axes aligned.

It is very clear that the MiG has a lot more area, and moment of area, behind the axis, for much the same area and moment of area ahead of the axis.

OK of course, we can agree that the area of the stab is larger and that the pivot point is further forward - I mass-balanced mine but you're correct that there will be a larger aerodynamic force on the servo if you compare it to a typical elevator, due to the location of the pivot point. However - as Drifty pointed out, the amount of force on the servo may not be very significant. I mean the servo may not be affected. Well I agree that whatever force there is would be making the servo work a little harder when travelling at high speed and using a lot of deflection. I really don't think that the aerodynamic forces would be making the servo work particularly hard in level flight. That kind of work is exactly what the servo is designed to do. But let's not get into an argument - we can agree that the forces are definitely higher than they would be on an aerodynamically balanced surface!

So what I would like to know is: when the servo is put under load, I am guessing it will heat/draw more amps and could that extra work cause it to simply shut down - either from overheating or from voltage drop? When mine stopped working it was towards the end of a very normal 3-minute flight, they weren't working very hard (I wasn't flying at full throttle, no high-speed dives, no flying fast with flaps down, in fact I hadn't used the flaps yet). I would like to know if the elevator servos will shut down after a time, if they get worked a little hard.

I'm not convinced this is what's happening - since if that were true, they would have failed earlier during more rigorous flights - for me and for others. There have been many posts here reporting that the servos have performed normally flight after flight. If these servos were being overloaded by aerodynamic forces as Kelllend suggests, wouldn't we see a lot more failures? For me it happened once in about 2 dozen flights.

[kallend]

When you run the numbers the MiG has its FFS pivot point 25% of MAC ahead of the center of pressure (CP). That means very large moments are going to be needed to move it against the airflow,

In contrast, the FW Sukhoi 35 has its FFS pivot almost exactly on the CP, meaning that the FFS can be moved very easily.

I don't recall a rash of loss of elevator authority crashes being reported on the Sukhoi in its 8 years of existence.

[kallend]

. If these servos were being overloaded by aerodynamic forces as Kelllend suggests, wouldn't we see a lot more failures? For me it happened once in about 2 dozen flights.

No, and I'm not sure that one crash in 2 dozen flights is a record I aspire to.

[Drifty]

How is that relevant? The servos are smaller and the pushrods are smaller too.

And you haven't addressed the trim issue, the location of the pivot with respect to the CP, or shown any reasoning whatsoever for your opinion other than you used to be a mechanic back in the day.

The point I'm making is that the geometry of the FFS and its pivot location pretty much guarantee that the servos will be loaded even in straight and level flight on account of trim forces.

If you have a reasoned rebuttal to that then please let us have it.

I have a rebuttal I think, I can easily stall a 50 in/oz torque servo using just a finger 50in/oz = 3.1 in/lbs the upgraded servos in this A/C are around that torque, therefore all your high load load on the servos is pure theory otherwise we would have many A/C in pieces all over the place, as it is we only have a few, thank goodness. As for your snide comment on my being only an A/C mechanic back in the day I would rather be that than an egotistical engineer who can`t stand to have his almighty knowledge questioned. By the way I was working on full sized A/C before you were a gleam in your daddys eye, and I don`t appreciate your buddys comment on experience, I could give you many instances where I and my fellow mechanics have proved engineers wrong in the field actually working on the A/c in combat conditions. I probably won`t comment any more on this forum, so be happy you have effectively silenced me.

Richard Driftmyer CMSgt USAF Retired .

[Eric D]

Hi Guys I just measured the wing incidence on the Mig . At 0 degrees on the wing the stab is at 6 degrees negative. To my thinking the CG is way off or this plane does not have enough wing area to support it's weight. I can see why the servos are possibly overheating.

[janmb]

Hi Guys I just measured the wing incidence on the Mig . At 0 degrees on the wing the stab is at 6 degrees negative. To my thinking the CG is way off or this plane does not have enough wing area to support it's weight. I can see why the servos are possibly overheating.

Spot on. Loading is certainly not a real issue, but the CG is.

We're used to manual recommendations for CG being conservative, but this model sets a new record I think

You don't really even have to work the math on this either - anyone can throw a quick glance at this model and immediately see how little lift is generated forward of the recommended CG

[Eric D]

Hi Guys I just measured the wing incidence on the Mig . At 0 degrees on the wing the stab is at 6 degrees negative. To my thinking the CG is way off or this plane does not have enough wing area to support it's weight. I can see why the servos are possibly overheating.