Official Freewing MiG-29 Fulcrum Twin 80mm Thread

[janmb]

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

I typically do something similar, but primarily with rudder, not aileron.

[GliderGuy]

RC30Flyer - LOL thanks for the correction.

Initially a lot of us discovered that flying with CG on the mark required 3-4 mm of trim vs the 1 mm shown in the manual. So I think “that” number became stuck in our heads as the “standard”. Oops!

Sorry for the confusion. I stand corrected and shall restate - “I balance 15 mm aft of the mark which reduced the trim amount from 3-4 mm to 1-2 mm which is CLOSER TO THE 1 mm shown in the manual.”

-GG

[GliderGuy]

I typically do something similar, but primarily with rudder, not aileron.

Yep - Either method works. The goal is to manage the lift and thrust <and other> vectors with bank angle <after pitching up> so as to establish a nice balance at which point the MiG settles into a stable condition under full thrust that doesn’t require any pitch adjustments with elevator (other than the initial pitch up and roll) by the pilot. It simply feels good (and looks good (IMO).

Once established....If the nose starts to pitch up....increase bank angle (aileron or rudder) and if the nose begins to pitch down....decrease bank angle. The balance point speed is just right...not slow and not fast and seems to be constant or only slightly accelerating.

Thinking about this a bit more....I initiate the bank more like 10 ft vs 20 ft high. In other words, soon right after lift off.

-GG

The numbers of vectors (lift, thrust, weight, drag, centripetal force) being managed by tweaking bank angle with a positive pitch/climb angle is quite amazingly simple. The MiG does this so nicely.

[paulrkytek]

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.

AH, take your point when I asked about the 5v/5.5v at MRC the model I was talking about at the time did not have servoless retracts

[paulrkytek]

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.

Ah, fair comment Evan

[paulrkytek]

r.c. Castle website shows freewing servoless retracts 4.8 to 6v so maybe its the circuit in the blue box which takes the operating gear and feeds all other circuits that does not like more than 5v ? but if some of the freewing becs are rated at 5.5v then this does not make sense either ? any thoughts anybody ? https://www.rcgroups.com/forums/show...oless-retracts

[janmb]

MRC have been very clear on several occasions that the BB (MCBe) is prone to failure if running above stock voltage - which in most FW models is 5V, not 5.5

People who have asked directly about running 6V have been discouraged from doing so. One could obviously always argue that this has more to do with covering backs than the likelihood if it actually being a problem, but I for one will not be taking that chance.

Remember, these are CHEAP electronics. Have realistic expectations and play it safe imo.

[Evan D]

Well, you posted in a thread dedicated to the Mig 29 that you talked to a Motion rep that told you this. So what plane were you asking about when they said only 5V? There is no plane that uses the MCBe blue box and doesn't have retracts.

And you still are pursuing that the MCBe can't take 5.5V, why?

AH, take your point when I asked about the 5v/5.5v at MRC the model I was talking about at the time did not have servoless retracts

[kallend]

Sometimes it's the corporate lawyers writing the script.

[paulrkytek]

Well, you posted in a thread dedicated to the Mig 29 that you talked to a Motion rep that told you this. So what plane were you asking about when they said only 5V? There is no plane that uses the MCBe blue box and doesn't have retracts.

And you still are pursuing that the MCBe can't take 5.5V, why?

sorry Evan my train of thought wandered from the mig29 to my 70mm F16 model where I am considering adding leds via a new spare blue box but I currently run 5.5v separate bec which works fine with existing servos and retracts which are rated at 4.8 to 6v but if leds are voltage sensitive then the circuit dedicated to leds in the blue box may not work if it was designed to have 5v input as opposed to 5.5v ( e.g blow the leds) which is why I also said in one of the posts that I err on the side of caution. I resolved the led issue on my F86 using leds rated at 5 to 7v range to add landing lights so my questions are basically information gathering exercises . The question is in the Mig 29 thread because I read different threads for my various models as some of the info is transferable to other planes I have in the Freewing range. Also I have not yet bought the Mig 29 so I am reading as much info as I can and asking as many questions as I can before deciding if to buy. Though I am beginning to think that the more I search and the more information I gather the less certain I become !!!

[Evan D]

The low voltage LEDs will be fine on 5.5 through the MCBe or other blue boxes that have LED outputs. be careful with landing light out puts since they may blow regular LEDs.

I caution you with asking Motion (or other resellers) reps. So many people come on here saying they've been told things that are so very wrong.

[paulrkytek]

The low voltage LEDs will be fine on 5.5 through the MCBe or other blue boxes that have LED outputs. be careful with landing light out puts since they may blow regular LEDs.

I caution you with asking Motion (or other resellers) reps. So many people come on here saying they've been told things that are so very wrong.

Thanks Evan, I understand what you are saying about the landing lights I would have been better off saying front position lights as the leds I have for my F86 are basic 5mm dia leds with a 5 to 7 volt operating range run off 5.5v rx power supply so I have kept at the lower end of the tolerance range and they come on with the rx and consume less than 5mah per 4 minute flight, also these are the only leds I have on that model. The lights are there to assist my eyes on poor light condition days and grey skies, of which we get a lot here in the UK. I have posted pictures of the lights on the F86 sabre thread. Of course as you know here is no blue box in the F86. Part of my convoluted logic on the 5 or 5.5v was because I noticed the Mig 29 BEC had 5v output and I was thinking that swapping this for a 5.5v output BEC may help address the voltage drop concerns on the rear stab servos and as long as it did not affect the blue box and the leds then this might be a good idea ? I cannot find the voltage range of the retract servos however so this question would still have to be answered /confirmed, preferably by the retract suppliers direct.

[Evan D]

When I put lights in my F-86 (when they first came out and before any blue boxes) I used a lighting board that came with the 90mm V1 F-18E. Now there are a lot of choices for controlling lights.

[kallend]

<nerd alert>

The active part of a LED is a semiconductor junction that typically needs between 2.5 and 3.5 volts to operate depending on wavelength (blue or white needs a higher voltage than red). This is a property of the semiconductor itself. It does not obey Ohm's law - a small increase in voltage leads to a LARGE increase in current which can easily blow the device. Brighter LEDs need, and can tolerate, higher currents but the voltage at the junction itself still depends on wavelength (Planck's law). For this reason some means of current limiting needs to be in the circuit. This can either be embedded in the lamp itself or in a separate controller. The cheapest way of doing this is with a resistor (which does obey Ohm's law) which is fine for operating from a very restricted voltage range (say 5 - 7 volts, or 12 - 15 volts for a LED strip). For operating from a larger voltage range, such as a 9 - 28 volt brake lamp bulb for cars and trucks, an active constant current source is used.

I have not taken a Blue Box apart but my guess is that in order to be cheap it simply uses resistors for current limiting which is why a restricted voltage range is specified. Since landing lights need higher currents in order to achieve the necessary brightness, the current limiting resistors will be lower in value. That is why you need to be careful which LED outputs you use for NAV lights as opposed to landing lights.

If you are adding non-stock LEDs to your model it is important to know whether they have built in current limiting, or need it in the driver circuit (controller/blue box).

</nerd alert>

[Airguardian]

On the not-so-nerdy note:
I've blown LEDs myself by subjecting them to higher voltages than intended. They are out in a matter of seconds.

[Evan D]

They use a small SMT, surface mount technology, 100ohm (from memory) resistor.

[kallend]

On the not-so-nerdy note:
I've blown LEDs myself by subjecting them to higher voltages than intended. They are out in a matter of seconds.

Yes, the current goes up exponentially with voltage, so a 1 volt increase (without a current limiting resistor) can cause the current to increase by 10 times, which will rapidly blow it.

[kallend]

The low voltage LEDs will be fine on 5.5 through the MCBe or other blue boxes that have LED outputs. be careful with landing light out puts since they may blow regular LEDs.

I caution you with asking Motion (or other resellers) reps. So many people come on here saying they've been told things that are so very wrong.

I doubt that many qualified engineers or physicists are answering the phones for Motion.

[Evan D]

With some of the answers they've given they might just be.

[kallend]

They use a small SMT, surface mount technology, 100ohm (from memory) resistor.

Seems reasonable. Taking 3.5V at the LED itself as typical, with a 5.5V supply the 100 ohm resistor needs to drop (5.5 - 3.5) 2 volts, which implies (Ohm's Law) a current of 20mA. The power dissipated will be 40mW, about right for a small SMT device. Raise that to 6V and the current goes to 25mA and the power to 62.5mW, an increase of 56% in the power dissipated (and heat generated) in the resistor which may well damage it.