Official Freewing MiG-29 Fulcrum Twin 80mm Thread

[Eric D]

I was playing with CG points and found that at 160 mm I needed 60 g with gear up and 90 g gear down. This is with 760 g batteries as far back as they can go. I already have heavier HT 5245 servos with 4/40 rods. Testing was done drilling holes at the wing root and suspending. Weight was added on top of the air brake. Food for thought.

[kallend]

Here is some data to support my theory that the micro full flying stab (FFS) servos are not up to the task on this model.

I’m no engineer, I flunked higher engineering math in the first year college and switched majors to something I could do. But I’ve flown RC airplanes for 55 years, turbines jets for 20 years and have built and flown several scratch built turbine jets. Nothing special about that, but I have used the AMA Large Model Aircraft (LMA) guidelines for years with good success.

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I am an engineer, I have a PhD in physics, been flying RC for 56 years, and I agree with you.

I did the calculations. The stabilizer axle is too far forward of the center of pressure.

Problem could be fixed with surgery to make the axle parallel to the leading edge of the stab instead of perpendicular to the fuselage. Would remove the need for the super heavy duty servos some people are installing.

[JohnVH]

Yet alot of them are flying, even on the original servos with no problems.... Wonder why

[sfcfury]

Boom. Problem solved. (thought I would throw in a lil infantry fix)

[killickb]

sfcfury -- in my day it was baling wire and duct tape, what's with this modern nylon cord stuff ? Certainly seem to be some serious issues with the Mig, will surely make many very wary of being first in the air for future releases.

[bandetx]

Yet alot of them are flying, even on the original servos with no problems.... Wonder why

Probably for the same reasons the ones that did crash didn't crash on their maiden flight.

The original FMS futura had issues with the ESC's burning up, so they changed the motor in it. Mine lasted like 2 years before the esc went.

[kallend]

Yet alot of them are flying, even on the original servos with no problems.... Wonder why

Because. . . .

[Waconut]

Wow, I love my Freewing jets but I am removing this one from my bucket list. Looks like I will go with the 90mm F-104 for my winter project.

[Evan D]

A prefab airplane, pnp, is a winter project? What are you planning?

[Evan D]

Dupe, sorry

[janmb]

But is the flexing the cause of the crashes, or just another symptom of the excessive loads on the stab that the servos can't handle over an extended period of time?

If the flexing causes the loss of control then putting in stronger servos is not going to cure that. Stiffening the structure would be the solution.

No amount of servo or pushrods would solve that, no. In fact, the elevators bending to pressure like that alleviates some of the stress seen by the servo (without that being a good thing obviously)

[GliderGuy]

Tomorrow is forecast to be light winds and good weather. I’ll be trying out the MiG’s new configuration which consists of:

- 20 AWG (0.5mm) twisted tail servo drive wires
- MRC supplied Y
- FFS servo control rod on inner servo arm hole
— 4-40 threaded rod with heavy duty DuBro ball link and Kwik-Link safety lock ends driving the FFS
- CG 15 mm aft of wing mark / wheels down
— Since I am using Admiral Pro 6000, this required adding some weight to the tail area (not a lot)
- MRC upgrade servos (they have served me well so far)
- 4 mm of FFS trim removed / We’ll see where the trim ends up after the first flight
- 5 RF chokes (each ESC, each rear servo in the tail and one by the green ferrite ring)

Thanks for everyone’s inputs.

Until I upgrade TX/RX, this is about as far as I can “improve”.

Stay tuned.

-GG

[janmb]

I did the calculations. The stabilizer axle is too far forward of the center of pressure.

Don't really even need any calculations to see that. It is so obvious/pronounced that anyone can eyeball that fact.

[Waconut]

A prefab airplane, pnp, is a winter project? What are you planning?

Upgrade the cockpit and cover the fuse and tail with Flite-Metal.
May not be smart but should look good.

[Lcacing]

I was playing with CG points and found that at 160 mm I needed 60 g with gear up and 90 g gear down. This is with 760 g batteries as far back as they can go. I already have heavier HT 5245 servos with 4/40 rods. Testing was done drilling holes at the wing root and suspending. Weight was added on top of the air brake. Food for thought.

I’m flying my MiG at 160mm with RT 5500 45c (770gr) with ordinance. Batteries as far aft as they can go.
I did statically balanced the stabs, about 2oz in total. I think balancing them helps, so if you need to add weight, might as well use that weight for something good.

[leithalweapon]

Tomorrow is forecast to be light winds and good weather. I’ll be trying out the MiG’s new configuration which consists of:

- 20 AWG (0.5mm) twisted tail servo drive wires
- MRC supplied Y
- FFS servo control rod on inner servo arm hole
- CG 15 mm aft of wing mark / wheels down
— Since I am using Admiral Pro 6000, this required adding some weight to the tail area (not a lot)
- MRC upgrade servos (they have served me well so far)
- 4 mm of FFS trim removed / We’ll see where the trim ends up after the first flight.

Thanks for everyone’s inputs. Until I upgrade TX/RX, this is about as far as I can improve.

Stay tuned.

-GG

I'm going to predict that you don't have a loss of control event.

[GliderGuy]

I'm going to predict that you don't have a loss of control event.

Man....If I do, I would have gone backwards with the changes made!

My intent is to push the loss of control event as far away as possible with my current rig.

And I have been slowing to 1/2 throttle then flaps then gear. I am changing to 1/2 throttle then gear then flaps only after slowing.

[xviper]

Had a chance to fly the MiG again this morning. These were flights number 5 and 6. Flight 5 was with a Firefly 8SE as a "hatcam" and a new Runcam 2 mounted upside down on a missile pylon pointed aft, looking at the right elevator and wing trailing edge (flap). Both videos are cued up to start at more or less the same time (at the beginning of take off roll). The Runcam is new and I can't connect to my phone via WiFi so I wasn't able to flip the video. You'll have to stand on your head or turn your computer upside down if you want to see the video right side up. It also cut out just prior to landing but it did catch all of the important runs. Flight 6 was not recorded and I just flew it around doing circuits and a couple of Cuban 8's. At no time was there loss of elevator authority. An inverted pass resulted in very little down pressure on the elevator to keep it level.

Elevator servos were the upgraded ones provided by Motion.
Elevator servo arm used the proper hole as directed in the manual.
Elevators were "Y'd" together using the provided Y and BB bypassed.
Elevator pushrods were stock BUT the CF tube was pushed onto the control horn end as far as it will go. The other end was epoxied using epoxy steel to secure it solidly to the servo arm keeper (white thing). Essentially, it's the CF tube that is the solid connection between the servo and the ball link. The wire inside the tube is pretty much going along for the ride and has no force on it.
AIL and flaps bypassed BB, with one servo reverser on one flap.
Batteries -- Gens Ace 5000mah, 6s, 45C and 60C. Rear one as far back as possible to the rear bulkhead, front one on top tray butted up against the BB. Balanced near perfectly at ~ 10mm behind the marks.
HobbyEagle A3-L in use during the whole flight.
DX9 G2, AR8000 with satellite in the front battery compartment.
One choke employed and installed on the ESC lines at the rear of the battery compartment.
Range test passed.
Ambient temp 0C.

I did 4 circuits. 1st was for trimming to make sure everything was straight and level. All trim tabs were almost at center. Elevator manually set with about few mm of UP which you can see in the video at the start. On the passes from left to right, 2nd circuit when straight and level, no flaps, went to full throttle and as soon as max speed was reached, pulled firmly and briskly UP at about 45+ degrees, then levelled off. 3rd pass, applied 1/2 flaps and went full throttle, pulled up like the previous pass. 4th pass, applied full flaps, went full throttle and pulled UP again. Then did a circuit to prepare to land with 1/2 flaps. None of my passes were done in a dive. I wasn't willing to take that chance just to see what would happen.
If you can do a split screen and start both videos at the same time, you can see things evolve between the 2 cameras at about the same time. The hat cam video was with the plane fairly high up as again, I wasn't willing to do this close up and low to the ground just in case. Also, the plane wasn't in frame some of the time (for the take off and landing) because I was concentrating on flying and not on pointing my head in the correct direction.

Hatcam video:

Pylon cam:

EDIT: I managed to rotate the pylon video so it's easier to view.

[RedAlert]

Wow, I love my Freewing jets but I am removing this one from my bucket list. Looks like I will go with the 90mm F-104 for my winter project.

why? Are you planning to do a lot of flying at full throttle with the flaps extended?!

[Waconut]

why? Are you planning to do a lot of flying at full throttle with the flaps extended?!

No but I can see me forgetting to raise them. If they correct the issue down the road I will revisit it.
JMO