Official Freewing MiG-29 Fulcrum Twin 80mm Thread

[paulrkytek]

I checked with Motion RC about the voltage limits they told me no higher than 5 volts for the blue box or the standard servo.

I would double check that if I were you the servo and retract servo specs I have read say 4.8to 6v operating range, my understanding about the blue box is it is restricted to 5v mainly because of the feed to the led lighting part of the system. Check the mrc website go to servos and it gives you the voltage range.

[fredmdbud]

I would double check that if I were you the servo and retract servo specs I have read say 4.8to 6v operating range, my understanding about the blue box is it is restricted to 5v mainly because of the feed to the led lighting part of the system. Check the mrc website go to servos and it gives you the voltage range.

Direct-fed LEDs would gave a current-limiting resistor, needing only to be in the hundreds of ohms to keep the current in the rated hundreds of milliamps. They are unlikely to be cause of the max voltage spec.

[paulrkytek]

Direct-fed LEDs would gave a current-limiting resistor, needing only to be in the hundreds of ohms to keep the current in the rated hundreds of milliamps. They are unlikely to be cause of the max voltage spec.

err pass !!! maybe there is a resistor in the circuit of the blue box that does not like a higher voltage or amperage input relative to the ability/rating of the leds to deal with ? i DONT KNOW SO i JUST ERR ON THE SIDE OF CAUTION.. FW servos on the MRC website are definitely stated as 4.8 to 6v.

[fredmdbud]

err pass !!! maybe there is a resistor in the circuit of the blue box that does not like a higher voltage or amperage input relative to the ability/rating of the leds to deal with ? i DONT KNOW SO i JUST ERR ON THE SIDE OF CAUTION.. FW servos on the MRC website are definitely stated as 4.8 to 6v.

From what I understand, it's the servoless retracts, not the servos and the LEDs, that cannot operate above 5V, and are thus the weak link.

[mshagg]

Sorry, but thrust line is a terribly poor way to solve trim issues. It is (obviously) highly throttle dependent, and you don't want your model's trim to be dependent on neither speed nor throttle setting.

The model needing lots of elevator trim needs to be solved as much as possible with CG (and can be somewhat helped with a little reflex).

For my part, VT nozzle neutral position will be somewhat lower than the stock nozzles. Fixing that thrust line issue is half of the point with installing VT at all for me.

Appreciate the insights. So you'll be looking at running the TV nozzles effectively neutral and addressing any excessive aerodynamic trim with reflex (if we accept that there are limits to CG, both from flight characteristics and room in the battery bay)?

If you join the dots of this model, you might be left with the impression that limited space under the canopy to adjust battery position lead them to specify a nose heavy CG with some thrust line baked in to the stock nozzles to keep elevator pitch trim within the realms of the reasonable.

[janmb]

Appreciate the insights. So you'll be looking at running the TV nozzles effectively neutral and addressing any excessive aerodynamic trim with reflex (if we accept that there are limits to CG, both from flight characteristics and room in the battery bay)?

If you join the dots of this model, you might be left with the impression that limited space under the canopy to adjust battery position lead them to specify a nose heavy CG with some thrust line baked in to the stock nozzles to keep elevator pitch trim within the realms of the reasonable.

Pretty much yes to all.


First of all, I'll seek to get CG as close to horribly tail heavy as possible. Because that's where the model thrives and flies with as little loads as possible, it's where it feels the lightest to the pilot, and it's where the aerodynamic capabilities of the model are at their best. If absolutely necessary, I will add tail weight to achieve that, but might not have to after beefy servos, links, and VT installed.

Secondly, like in most of my jets, I will use a gyro for stabilization (and tolerating an even more aggressive CG than would otherwise be comfortable). Might possibly also combine with IAS for automatic gyro gain compensation. Will be testing that on my Gripen, and might do the same on the MiG.

Third, a little reflex is warranted, especially on the ailerons. Will do both, but adding washout is more important to me than solving trim aspects, but again will do both.

Four, adjust thrust line to not affect the model what so ever. After being balanced and trimmed properly, gliding vs slamming the throttle should make zero difference in pitch.

[mshagg]

That's an awesome idea. I've actually got an airspeed sensor on this one, it would be trivial to map gains to airspeed in opentx.

Are you not concerned that the extreme CG configuration could make it difficult to exit a so-called falling leaf condition?

(Thanks again for the insightful posts)

[janmb]

That's an awesome idea. I've actually got an airspeed sensor on this one, it would be trivial to map gains to airspeed in opentx.

Are you not concerned that the extreme CG configuration could make it difficult to exit a so-called falling leaf condition?

(Thanks again for the insightful posts)

Yes, using that telemetry to affect gain to whatever degree you want should be piece of cake in opentx for sure. For my part will be doing a three point switch, gyro off, moderate fixed gain, and moderate gain + an inverse variable based on IAS. Especially on my deltas, the gain setting suffers a lot of forced to run same gains during slow, high alpha vs fast passes. The fast passes forces gain much lower than what you want for slow flight.


Yes, a neutral CG will certainly make the model less willing to get the nose down. Will need to ensure I have the necessary nozzle range to achieve what I want.

No thanks required, I'm just sharing my thoughts as best I can.

[GliderGuy]

Your discussion regarding behavior with aft CG reminds me of a story told to me by the test pilot of the first FAA certified, composite power plane market entry attempt....Windecker Eagle (https://en.wikipedia.org/wiki/Windecker_Eagle) I will attempt to retell his story as best as I remember.

The certification test program at this point was the determination of the aft CG location for spin recovery characteristics. A spin recovery chute was installed on the prototype. A trip wire was installed about shoulder height to deploy the chute and another trip wire to jettison the chute was installed about thigh high/seat cushion level.

A chase plane followed for observation. The Eagle got into a flat spin and became non-responsive...time to deploy the spin recovery chute. However, the "G" loads caused the pilot to miss the top "deploy" trip wire. He hit the "jettison" trip wire and the chase plane pilot gasped, "You lost your chute!" Time to depart the plane.

Stepping aside a bit...the test pilot explained that the prototype's pilot exit hatch had a rotating latch at the front, back, top and bottom of the hatch.

So, he unlatched the top, front and back latches at which point the hatch sucked open at about a 30 degree angle and wedged itself on the bottom latch. He could not push the exit hatch open nor rotate the bottom latch. All the while the chase plane was admonishing, "Bail out, Bail out!" The pilot unbuckled his harness, moved to the right side of the cockpit, and lunged at the stuck exit hatch. Well, when he hit the hatch, there was now little resistance....and the hatch flew away with ease...not slowing his momentum as he had anticipated.

The rapid exit (more rapidly than the pilot expected), left him hanging upside down over the lead edge of the wing (low wing and his back was against the wing) with his shoe caught/wedged under the pilot's seat as the Eagle continued its flat-spin toward the ground. The pilot said, "I kept my cool and was able to fight the "G" forces, bend up and untied my shoe laces and slip out of my shoe.'

The rest of the story is the uneventful chute ride to the ground. The prototype's demise did provide additional information on the composite's ability to withstand a belly flop impact.

Postmortem - The Eagle received FAA certification (notably the first composite power plane to achieve this in the US), but it was not accepted by the market. Only eight Eagles were produced before production ended when the company ran out of money. Hats off to Dr. Leo Windecker, DDS who is among the visionary pioneers of today's composite and stealth aircraft industry.

https://www.statesman.com/article/20...NEWS/309001503


-GG

Aside: We used to fly our composite sailplanes near the Eagle so the radar signatures could be compared.

[skybolt]

I would double check that if I were you the servo and retract servo specs I have read say 4.8to 6v operating range, my understanding about the blue box is it is restricted to 5v mainly because of the feed to the led lighting part of the system. Check the mrc website go to servos and it gives you the voltage range.

You are right in what you say I have just checked. They did tell me 5volts only for both. I Will rethink my setup when put it together next spring.

[janmb]

You are right in what you say I have just checked. They did tell me 5volts only for both. I Will rethink my setup when put it together next spring.

Yeah I think that is the sensible idea

I will run HV on elevator servos and 5V on everything else.

[Evan D]

As I said they use the MCBe in planes with the ESCs that contain internal BECs that produce 5.5V (I can send you pictures of the voltage readings) so it's not the MCBe, or LEDs that would have a problem. The servos are also the same as in many planes running 5.5V so they are also not the problem. The retracts in this are different than any others but doubt it can't handle 5.5V.

I'll just say the "rep" was saying what he thought is right or what he was told to say.

[Gringotuerto]

I finally got decals on the ordnance, and so Laughing Kim Jong Un went in search of enemies today (my flights up until now had been without missiles). However, when I got to the field, a friend told me that when he added missiles, the plane experienced a huge upward change in trim, and took off dangerously steeply. He had an adventure clicking in enough down trim to stabilize it. So I chickened out and removed the ordnance before flight. But I'm curious, did anybody else have this experience? I had not seen it mentioned on this forum, but maybe missed it.

I think I have flown the A-10 with and without missiles and didn't notice a difference. But I also notice, some of the foam missiles can be a little warped. So I wonder if it depends on the particular set you have. If there is a missile with a large tail surface and it curves upward or downward at the back end, perhaps that could change the plane trim...? I don't know. Another possibility is that he just did something different that particular flight (like battery placement inadvertently off) and the missiles had nothing do to with it. Anyway, maybe next time I'll try adding missiles 2 at a time on each flight. Today I didn't fly with them at all.

[GliderGuy]

I But I'm curious, did anybody else have this experience? I had not seen it mentioned on this forum, but maybe missed it.

I've always flown with all the missiles. I suggest checking the CG with and without the missiles and anticipate any trim changes accordingly. With a full missile loadout plus reflex flaps...and some small amount of weight added to the underside of the rear fuselage area, I balance 15 mm aft of the CG mark (gear down) and carry about 1 to 2 mm of trim below the fuselage line vs the manual 4 mm below.

If you intend to leave the missiles on, you may want to consider making the large forward fins more stiff as videos have shown they bend and flex a lot. Several methods have been discussed in prior posts. I glued a wire to the bottom of each fin (not visible) that was bent to follow the fin's outer edge and then painted the wire. My concern was cracking/plastic fatigue from all the bending after a period of time.

-GG

[GliderGuy]

deleted...duplicate

[mshagg]

I dont notice any perceivable impact on trim but the air to ground loadout sure puts the brakes on. Perhaps your colleague experienced a higher takeoff distance than usual and horsed it off the ground? Once this thing gets its nose pointed up it stays there on climb out.

[GliderGuy]

Once this thing gets its nose pointed up it stays there on climb out.

To help with this, once I get about 20 ft high, I roll into about a 45 degree bank. Doing so, helps hold a reasonable pitch attitude without touching the elevator/stick while the gear and flaps are being retracted. With a little experimentation, you can pick a bank angle that perfectly counters any pitch-up tendency, and it looks good, too.

-GG

[Gringotuerto]

I dont notice any perceivable impact on trim but the air to ground loadout sure puts the brakes on. Perhaps your colleague experienced a higher takeoff distance than usual and horsed it off the ground? Once this thing gets its nose pointed up it stays there on climb out.

Doubtful - he said he had to put a lot of down trim to fly straight and level throughout the flight. Anyway, it seems this is not a universal experience with this plane. So I'll probably just add two at a time and see how it goes.

[Sky Wolf]

Is the statement, “Better late than Never”, a legitimate way to get out of being late to the party? Received my MiG-29 on the first run, second day of arrivals. But just now putting out the unboxing video. Lots and lots of unboxing vids out there, so this one is just an overview of what’s inside, with a little fun twist to getting it out of the box.

https://youtu.be/06Bqml_cNzk

[RC30Flyer]

[QUOTE=GliderGuy;n291644]

I've always flown with all the missiles. I suggest checking the CG with and without the missiles and anticipate any trim changes accordingly. With a full missile loadout plus reflex flaps...and some small amount of weight added to the underside of the rear fuselage area, I balance 15 mm aft of the CG mark (gear down) and carry about 1 to 2 mm of trim below the fuselage line vs the manual 4 mm below.

Glider... you are now the 3rd or 4th guy that has said the manual elevator neutral is 4mm below the bottom edge. Do you guys have a different manual????