Official Freewing MiG-29 Fulcrum Twin 80mm Thread

[HK111]

Thrust to weight: 1+ @ 12S

Aloha,

I am crossposting this from RCG: Here is a video from one of the first 12S Tests. The batteries were already quite empty during the video recording (at the end with 20% remaining capacity, Voltage was at 43V and less), but the machine can still hold itself in the air. With full batteries it goes up without any problems.

It is of course unclear whether this will also be the case with the vector nozzles. The additional weight shouldn't be the problem, but the vortex losses in the "balls", i.e. the transitions between the thrust tubes and the movable nozzle, will certainly eat up a lot of power.

A lot of smaller optimizations have not been done yet. E.g. there are no additional air feeds / cheater holes, the electrical wiring has two contact points which it wouldn't strictly need and so on.

• AUW: 5,715g
• Maximum current in this video, to be confirmed: ~120+ Ampere at 43-44V, ~5.25+kW
• Maximum current with full batteries, not in this video, T/W > 1: ~134A, ~6.5kW
• 22° Celsius, 550 AMSL
• Batteries and wires and plugs became a bit more than handwarm, but not hot

Cheers,
Henrik

PS: Ceterum censeo that we have to enable this MiG to go straight up. Hehehe...

[Edwin-0]

https://www.facebook.com/groups/1419132551675959/permalink/2919490994973433/

I wanted to show you the second day with the MIG, this plane flies on rails.
Sorry about my other planes in the movie, it was hard to cut them out but hey these are jets too. 😊

[t33jetman]

bump

[t33jetman]

[HK111]

Fred from RCG posted his video - take a look at 2:35! The elevators bend down very much once the flaps are partially deployed. Even the distance between the two rudder upper tips increases by about 5% simultaneously, so the bending of the elevators apparently is transmitted to the airframe.

Brrrrr!!! But we are getting closer to a solution!

What a tremendously useful video, thanks to Fred!

[GliderGuy]

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

I watched the video posted on RCGroups by fredmdbud (also he's uploading it to YouTube). It is quite demonstrative! Judge for yourselves but you may want to strongly consider the following;

1. Strengthen the FFS support structure back there as much as possible by the method you decide upon. Do as many of the other upgrades discussed on prior posts as you see fit. Note: Making the rear less bendy isn't going to solve the air load issue. It just makes common sense.
2. Get the flaps up ASAP after take-off....do not forget to raise the flaps, or program your TX so you cannot possibly forget.
3. I intend to maintain strict pattern discipline toward the end of each flight...a) SLOW DOWN b) drop landing gear...and wait for additional slowing....then and ONLY then...lower the flaps and continue reducing throttle and slowing to set up for landing. This has served me well for many, many MiG flights, and I intend to stick to this practice.
4. And...get the CG back behind the factory mark (read prior posts for details) to reduce servo loading.

For whatever the reason (alignment, airflow deflection, flap vortex, etc.) the video shows that the FFS is being subjected to large downward pressure. As others have pointed out, the CP being behind the FFS pivot point is causing the servos to be loaded beyond their capability to move the FFS....stalling them, no doubt.

Thanks to Fred for doing this. Very useful video...and a sad ending in the name of knowledge gained.

My father was an instructor in WWII. One of the most valuable lessons he taught me as I was learning to fly is, "You either THINK in an airplane, or you DIE in an airplane." This bird needs some THINKING as we are flying it. Rule #1...Don't fly it fast with flaps down.

-GG

[mshagg]

That video is a smoking gun for my 2c. Not clear how a manufacturer could look at that and continue to attribute hull losses in similar circumstances to user error.

Plane is grounded until I come up with a way to strengthen the tail section.

[HK111]

Wouldn't the assist in control from the soon to be released TV nozzles remove a great deal of the stress on the elevators?

Sure, or at least the stress wouldn't matter that much, because even if the elevators were less effective, the TVs would work on their own. I only bought the plane because TV units had been announced :-).

TV nozzles will also allow to steer out of the MiG's "happy ass mode", where it is stuck in high alpha and just decends over its tail, and where I learned from other posters that the current "way to get out" is to cut thrust.

[fredmdbud]

Enjoy ...

[janmb]

Fred from RCG posted his video - take a look at 2:35! The elevators bend down very much once the flaps are partially deployed. Even the distance between the two rudder upper tips increases by about 5% simultaneously, so the bending of the elevators apparently is transmitted to the airframe.

Brrrrr!!! But we are getting closer to a solution!

What a tremendously useful video, thanks to Fred!

Yeah, big thanks is definitely in order. This confirms what has been the strongest theory the last few days 100%

[GliderGuy]

That video is a smoking gun for my 2c. Not clear how a manufacturer could look at that and continue to attribute hull losses in similar circumstances to user error.

Plane is grounded until I come up with a way to strengthen the tail section.

Consider that it is a FFS loading problem...mainly. See my post #2926. Good idea to make the tail less bendy....but it won't fix the air load/loss of control issue which appears to be servo overload cause by air loads.

-GG

[Airguardian]

Sorry Fred, that's terrible, I'm so sorry... If this doesn't kick Motion into action, I don't know what will.

At least this totally puts to rest any sort of doubt anyone may still harbor as to what's causing the crashes.

[janmb]

Sure, or at least the stress wouldn't matter that much, because even if the elevators were less effective, the TVs would work on their own. I only bought the plane because TV units had been announced :-).

TV nozzles will also allow to steer out of the MiG's "happy ass mode", where it is stuck in high alpha and just decends over its tail, and where I learned from other posters that the current "way to get out" is to cut thrust.

On the first part, keep in mind that VT doesn't have a ton of authority at high speeds. Sure, it would help some, but not quite as much as some would possibly think.

On the happy ass mode, yes VT will kill that problem 100%. So not too bummed out about not being able to push proper high alpha yet - I'll happily wait with that until I get VT installed.

The elevator problem needs to be addressed regardless of VT though imo

[mshagg]

Consider that it is a FFS loading problem...mainly. See my post #2926. Good idea to make the tail less bendy....but it won't fix the air load/loss of control issue which appears to be servo overload cause by air loads.

-GG

Indeed, a good demonstration of the forces at play - a 17g servo never really stood a chance did it...

Ive got 8kg/cm servos running the show the back there, hopefully the material removed to fit them in hasn't compounded any weakness - but as noted, I won't be flying it until I've done some work to strengthen it anyway.

3DP is my preferred medium, just need to finish another project before the Mig gets back on the workstand.

[Borat]

I just saw the crash video from fredmdbud. I feel compelled to clarify something here. Some are asking: why would anybody fly with flaps down at full throttle? If you go back to my very first post on Oct 29, I did mention that this is not something that is routinely done. But these Migs are crashing and there seems to be no explanation until more recently. After reviewing some of the videos on YouTube from people who crashed their planes several weeks ago, I suspected that there was a problem with at least three of those crashes where the flaps deployed, whether the pilot knew it or not. So I set out to find out if that was the case. The first day I tried it, I could clearly demonstrate that instability with flaps deployed. All I would do is to deploy flaps at low speeds and advance the throttle. I noticed that elevator control became very mushy. At shallow dive angles, the problem was much more dramatic and no elevator control. Last Sunday I was able to capture with a photo what I shared with you right before the crash. Please do not misinterpret that I was going full throttle then deployed the flaps and the MiG went in. So why is this important? There are several instances where you will have your flaps deployed and you will need to advance your throttle. On take off, we have flaps deployed and we go to full throttle. Now imagine and unsuspecting pilot, on a maiden, has flaps deployed and goes to full throttle. Goes up on a nice climb and makes a turn and perhaps starts to descend because he needs to trim the plane. If he is too distracted with trimming the airplane and trying to get a feel for it, he may not be raising the flaps immediately after gaining some altitude. This may have happened to the pilot in Asia, one of the first videos we saw of the MiG crash where it goes right into the runway after doing one circuit. Another scenario would be during touch and go, flaps deployed, throttle up to climb again. What if you were trying to land but noticed someone on the runway and now you have to throttle up and go around again. So flaps down, throttle up is not something unusual and we do this all the time. By the way, when I was doing my experiments, it wasn’t like I was jamming the throttle all the way up with flaps down the whole time. Just for a second or so and I could see that pitch became unstable. So did MRC and FW know about this problem? If yes it would have been nice to let everyone know. Will they take our concerns seriously and address this issue? Remains to be seen. In the meantime, you have two pilots who lost their Migs and I suspect that fredmdbud like myself was only trying to figure out why these planes were/are crashing.

[HK111]

Why not cutting off 2cms of the trailing edge of the elevators, or even its tip

Hello,

I just looked at the elevators and wondered how to move the pivot axis backward, but it is not an easy operation. Well, here is another idea: Why not simply cut a ~2cm wide strip from the complete rear of the elevator, parallel to its trailing edge? And possibly even a bit of the tip, because it has the longest leverage?

The elevator would be immediately more aerodynamically balanced, meaning less servo load. And as the current recommendation seems to be to use reflex in ailerons and flaps and to move the CG 10+mms to the rear, there is less load on the elevator anyway, it does not have to hold up the hanging nose all the time.

Yes, it will look less scale. But it will also crash less. And elevators are replacement parts, so if we don't like the look of the cut elevator, we can buy new ones. Or even MRC will ship a more balanced elevator one day.

Opinions?

Cheers,
Henrik

PS: This of course on top of strengthening the two tails of the airframe that carry the elevators.
PS2: I include the already known picture of the Su-35 and MiG-29 overlaid elevators. Just cut off some of the protruding grey from the MiG :)?

[GliderGuy]

Good point...Borat. I did a go-around just yesterday and, thankfully, had full elevator control response. But, I'm seriously considering a go around will be initiated with flaps up first...then throttle. Or...at least a fast action of fingers getting the flaps up after throttle application (more likely)..

Thanks for the additional details and sorry for your loss.

-GG

[leithalweapon]

Anyone ever heard of VFE? I see on MRC website they have some info on VNE which everyone on here should read.
If you exceed VFE expect parts of the plane to start coming off and a crash.
We don't know the VFE or have an airspeed imdicator. Doing it on accident is one thing, but doimg it on purpose you've become a test pilot and the aircraft doen't have an emergency parachute.
If it were a full scale plane this would be pilot error for exceeding VFE.
The video makes me feel better about the plane. Now I know when it happened to me, i screwed up and most likely didn't put the flaps up after takeoff. If it happens again the first thing I'm gonna do is check the flap switch.
Sorry about your plane, but I think we all owe you a few bucks to get a new one! This video is like the Patterson video. Definitive proof!

[mshagg]

VFE usually denotes when damage can occur to the flap surfaces.

Again, flaps in this example are being used to demonstrate a structural weakness in the airframe. There's nothing to say this can't happen in a clean configuration - particularly if there are variances in manufacturing or assembly.

[Lcacing]

Why not cutting off 2cms of the trailing edge of the elevators, or even its tip
?

A while back I posted about statically balancing the stabs and the “powers to be” in this thread basically dismissed my idea as not helpful. I’ve been pushing the limits on my MiG with just upgraded servos (HS 5085), stock pushrods, CG @ 160mm, and CC bec running at 5.8v. I need to film me doing walls, they are so aggressive that you can actually hear the airframe pushing the air vertically, this occurs when trying to do the cobra maneuver, not enough power to push the nose down, so I just add power and do a flip into a falling leaf, looks pretty cool.