Official Freewing MiG-29 Fulcrum Twin 80mm Thread

[mshagg]

Please note the anhedral configuration of the horizontal stabs. I’m convinced that this is contributing to the loss of elevator control. My advice, please do not fly your MiG with flaps deployed at higher throttle settings

Are the flaps relevant to the force being imparted on the horizontal stab?

Or could it be that the entire mounting system is flexing under the loads of the plane, regardless of flap condition, resulting in loss of effectiveness - or even binding up against the fuselage.

[e4dragongunner]

Hi everyone,
Here is my remedy for elevator issue.

The Promodeler DS150CLHV servos arrived today. They are a direct drop in. No modding required. Except they use 4 screws instead of two. 115 oz/in on 4.8V

In regards to the rods, I found a tube I had purchased for 3D printer years ago. Turned out the internal diameter and OD are exact match for the stock carbon tubes and rods. Will prevent the rod from deforming inside the carbon tube.

I removed the super long 60cm elevator extensions and installed super short 13" ones. Was enough considering the length of the servo wire and the aft position of the receiver in the hull.

I have an alarm setup in my radio when flaps are extended AND landing gear is retracted. Prevents flying with flaps extended.

I feel quite comfortable flying it in this configuration.

These are going in my Tomcat!! :-)
Great share!

[Airguardian]

Are the flaps relevant to the force being imparted on the horizontal stab?

Or could it be that the entire mounting system is flexing under the loads of the plane, regardless of flap condition, resulting in loss of effectiveness - or even binding up against the fuselage.

Yes to both IMO.

Flaps deflect wing airflow wake, causing the stabs to have more effective angle of attack (AKA, they produce more lift force). This is in fact the reason that deploying flaps on this bird requires little to no pitch compensation on the stabs, kinda like the Su-35.

But unlike maneuvering through a looping or a turn where airflow mostly aligns with stabs and causes a small load, deploying flaps causes a static load condition. More so if flying fast and diving.

[GliderGuy]

Here is a capture from the MRC video on their website. I waited for a high speed, no flap pass. No anhedral is apparent. Seems like the flaps being down at high speed may indeed induce the anhedral due to air loads.

-GG

[mshagg]

Flaps deflect wing airflow wake, causing the stabs to have more effective angle of attack (AKA, they produce more lift force). This is in fact the reason that deploying flaps on this bird requires little to no pitch compensation on the stabs, kinda like the Su-35.

But unlike maneuvering through a looping or a turn where airflow mostly aligns with stabs and causes a small load, deploying flaps causes a static load condition. More so if flying fast and diving.

So it's more about the air 'coming over the top of the wing' (notwithstanding that it's actually the wing moving through the air lol), essentially being deflected straight into the path of the stab?

EDIT: just trawled my footage folder and have about 2 minutes of flying from my maiden day, with the camera pointed straight at the horizontal stab. I'll upload it to youtube and you guys can go crazy with the analysis lol (dont worry it's not a monetised channel). Unfortunately no footage of high energy/flaps down configuration because, well, i generally dont do that.

Here's a teaser. Got flex? This is particularly noticeable when she's settling in for a fast pass along the flight line.

[mshagg]

[Airguardian]

There seems to be a bit of flex but nothing crazy. I guess the failures happen on just the few airframes that may have some glue problems and/or under the most taxing conditions (dive at full throttle with flaps down and nose heavy).

[fredmdbud]

Think the tail tip could be catching the rod?

[janmb]

But....Considering that high speed/high throttle condition with flaps down is not a normal nor advisable realm of flight, it appears the MiG is being pushed beyond its design limits.

Well... yes, but at the same time no. Sure, it is something we normally shouldn't do. But at the same time, it does tell a story about a design that is very marginal.

[janmb]

Are the flaps relevant to the force being imparted on the horizontal stab?

Or could it be that the entire mounting system is flexing under the loads of the plane, regardless of flap condition, resulting in loss of effectiveness - or even binding up against the fuselage.

I think it kinda have to be flap induced, or at least they make it worse.

I maidened mine with a rear facing cam, which unfortunately cut out halfway through the flight, but I did get a fair bit of footage of both half flaps and no flaps. Flew to the first couple laps with takeoff flaps to get that flight mode trimmed out first. Don't see any unusual amount of flexing at all, but that was typically around 50% throttle too, maybe a touch more, but nowhere near wot.

[kallend]

There seems to be a bit of flex but nothing crazy. I guess the failures happen on just the few airframes that may have some glue problems and/or under the most taxing conditions (dive at full throttle with flaps down and nose heavy).

That amount of flex indicates the downforce that has to be opposed by the servos, given that the CP is way behind the pivot axis.

[janmb]

Looking at this flexing makes me feel like stressing an aspect that has somewhat been tuned out of the discussion: CG CG CG CG!

If we can conclude that the elevator setup in general is marginal (regardless of why really), good CG becomes more important than ever. This is a heavy bird, far more so than most foamies most of the customers have operated before. The loads on FFS elevators in this weight class are quite a lot higher than we are used to with foamies. A good CG not only makes the model feel a lot lighter and more willing to accept pilot commands, but also greatly reduces stress on the whole elevator setup.

Get your CG right!

I would go so far as to claim flying this model on any CG less than 15 mm aft of the CG marks should be considered unsafe. The model is perfectly stable and benign at +15

[PieterO]

Are the flaps relevant to the force being imparted on the horizontal stab?

In my case, the plane dives a bit when applying full flaps. So more elevator is needed to keep it level. So more force on the stab. And I already noticed this when flying not fast at all. So I can imagine that full flaps at higher speed will mean even more force on the stabs.

In case someone wonders: my CG is 10 mm aft of the factory mark. (Maybe I should consider to move it further back)

[Bushong572]

image_63992.jpgimage_63992.jpg

OK, is this what you are showing as an Axle size for your brakes. The main axle is 4mm on my SU30 and I wasn't able to use it and it looks like the same wheels?

Yes, the front axles are 4mm the rears are 5mm
The JP brakes with 5mm axles takes a lot of work to install. The back of the wheel does not fit the Freewing strut. The 4mm brakes mount flush on the backside of the wheel. When you move up to the 5mm, they have a flange on the backside. I had to do some work to the strut to get it to work. The JP brakes with 4mm axle would fit much easier but you would have to sleeve it somehow to make it fit the 5mm hole in the strut. I think an easier alternative would be the HSD replacement brake set for their F-16. They should bolt right up.

[GliderGuy]

Get your CG right!

I would go so far as to claim flying this model on any CG less than 15 mm aft of the CG marks should be considered unsafe. The model is perfectly stable and benign at +15

Me too! Moving my CG back ASAP. The photo and video are quite telling.

-GG

[skybolt]

Hi everyone,
Here is my remedy for elevator issue.

The Promodeler DS150CLHV servos arrived today. They are a direct drop in. No modding required. Except they use 4 screws instead of two. 115 oz/in on 4.8V

In regards to the rods, I found a tube I had purchased for 3D printer years ago. Turned out the internal diameter and OD are exact match for the stock carbon tubes and rods. Will prevent the rod from deforming inside the carbon tube.

I removed the super long 60cm elevator extensions and installed super short 13" ones. Was enough considering the length of the servo wire and the aft position of the receiver in the hull.

I have an alarm setup in my radio when flaps are extended AND landing gear is retracted. Prevents flying with flaps extended.

I feel quite comfortable flying it in this configuration.

That PTF tube will not stop the flex in the wire.

[Firebird]

A short update on the status of my mig. I opened the rear fuselage to install one of the receivers, the battery management system for the receiver batteries (2x 2s 1800mAh) and a battery tray for one of 4 flight batteries (6s 3800 35c).
To counterbalance for the increased take-off mass, and in order to keep the AOA and speed during landing in a reasonable envelope - i started to install leading edge flaps.

[HK111]

I have a picture, moments before impact, that demonstrates a structural problem with this plane. See below. Please note the anhedral configuration of the horizontal stabs. I’m convinced that this is contributing to the loss of elevator control.

When the rudders aren't screwed in properly (easy to miss, as the screws need a lot of force), the tails carrying the elevators are very weak and could bend. The tails need the support of the rudders. I am considering to glue them in for extra stability.

The interesting question is, what is the main source of the bend? The elevator itself or the tails with the metal axes?

And BIG THANKS to our chief airborne experimentator Borat for, in the end, sacrificing his plane!

[kallend]

Looking at this flexing makes me feel like stressing an aspect that has somewhat been tuned out of the discussion: CG CG CG CG!

CG has been mentioned plenty of times with respect to the trim force needed on the FFS and the resulting servo loads. Also mentioned with respect to aeroelasticity.

Maybe you tuned it out after you mentioned it yourself in post #2679. I certainly mentioned it a bunch of times.

[DForbes]

I mentioned about a week ago about a problem with the MiG. During flight condition with flaps deployed and higher throttle settings, with nose down attitude, the MiG loses elevator control. Please see my previous posts. I was able to reproduce the pitch control instability multiple times. Last Sunday, I had someone take close up burst photos during this maneuver. Unfortunately during my last try, I was not able to pull out of the shallow dive with up elevator input on my transmitter. The MiG was destroyed on impact. I have a picture, moments before impact, that demonstrates a structural problem with this plane. See below. Please note the anhedral configuration of the horizontal stabs. I’m convinced that this is contributing to the loss of elevator control. My advice, please do not fly your MiG with flaps deployed at higher throttle settings

Is it possible the structural foam itself is flexing?