Official Freewing MiG-29 Fulcrum Twin 80mm Thread

[Lcacing]

Little bit of black paint and some spare led’s.crxmanpat gave me the idea. I just need some of them decals and I’ll be golden.

[Capt G]

a new bird added to the nest. Maidened today!

https://www.youtube.com/watch?v=aLmNmt9ZnJ0

[janmb]

Just maidened mine......upgraded servos installed. Overall, I'm pretty happy with it. It flies well and is easy to land.
2 things though: I was hoping to get a little longer run time (4 minutes MAX on RT 5500 mah....I'm pretty hard on EDFs though) and my CG is 5mm aft of the marks and I still needed 5mm of up elevator. The plane does not fly nose heavy to me, but that seems like a lot of up trim (and alot of drag)

Congrats!

And yes, that much up trim clearly explains why you are not seeing better flight times.

[Lcacing]

Just maidened mine......upgraded servos installed. Overall, I'm pretty happy with it. It flies well and is easy to land.
2 things though: I was hoping to get a little longer run time (4 minutes MAX on RT 5500 mah....I'm pretty hard on EDFs though) and my CG is 5mm aft of the marks and I still needed 5mm of up elevator. The plane does not fly nose heavy to me, but that seems like a lot of up trim (and alot of drag)

5mm of up trim is a lot. Here is where mine is and I like the way it handles. I’m near 15mm back from stock CG.

[Lcacing]

This is how I store the pitot tube after each flight and during transport. The nose cone can be put on by just making a small indentation on the bulk head.

[mshagg]

okay....i keep seeing various batteries on the middle position. i just cant seem to get the aircraft to cg there.

Spektrum Smart 5000mAh 50c, which are spec'd at 660g each. I have to move the rear battery forward, and the front bay battery against the rear most wall to balance out.

in that configuration, gear down, it will just teeter nose down when lifted at CG marks, then gently settle level. (indoors, not wind impacted)

Anyone video their cg configuration and balancing?

Thats probably about right. Those packs test at fairly low C ratings (25C), which is consistent with their very light weight for the size of the pack. I am balancing in the middle position with 900g 5000mah batteries, and so almost have another Spektrum 5000 worth of weight onboard.

Dont sweat other people's battery placement - CG is CG. Of course there will be scope to adjust to your liking but for your maiden flight, if its balancing on the CG marks you're good to go :)

[janmb]

5mm of up trim is a lot. Here is where mine is and I like the way it handles. I’m near 15mm back from stock CG.

That looks far better indeed.

[Jdcrow]

[QUOTE=mshagg;n276014]

[Jdcrow]

Thats probably about right. Those packs test at fairly low C ratings (25C), which is consistent with their very light weight for the size of the pack. I am balancing in the middle position with 900g 5000mah batteries, and so almost have another Spektrum 5000 worth of weight onboard.

Dont sweat other people's battery placement - CG is CG. Of course there will be scope to adjust to your liking but for your maiden flight, if its balancing on the CG marks you're good to go :)

Thanks. from specs, these 5000's weigh in line with the Admiral Pro 4000s set up middle and rear. So that had me scratching my head how tail heavy those locations were giving me. Correct CG is were CG is. And im happy to be at it. LOL. I was just curious as to why such disparity across various locations

[janmb]

Dont sweat other people's battery placement - CG is CG. Of course there will be scope to adjust to your liking but for your maiden flight, if its balancing on the CG marks you're good to go :)

Big +1

It is important to measure your own CG and not go by other people's battery positions. There are so many factors that can and will affect what battery positions YOU need to end up with the same/correct CG.

Batteries from the same manufacturer, with exactly the same spec may vary a fair bit in weight from one batch to another, so even within what ought to be exactly the same, you can not depend on it. And obviously your other installed components, while much lighter, still affects CG a bit as well. Things such as afterburners, heavier taileron servos/linkages, sound systems etc etc all affect CG and may explain why YOU need your batteries slightly different compared to others.

[Jdcrow]

Spektrum smart batteries tend to be on the light side. I've always felt that with these smart batteries, we aren't getting a true mah and "C" rating as stamped on the label. The typical 5000mah, 6s batteries in my collection each weight between 750g to well over 800g - Gens Ace, ChinaHobbyLine, Turnigy HD, Admiral, Revolectrix.

Thanks, i picked them up because they were close (660g) to the weight of the Admiral Pro 4000 (642g). So I was surprised it CG'd tail heavy in those locations.

[mshagg]

Heck even the few coats of poly i put on all my planes tends to see the battery move a couple of mm for a given CG.

The spektrum packs are a bit light on performance IMO BUT the beauty of a twim 80mm setup is it is actually pretty forgiving on amps when flown in mixed throttle conditions, unlike single 90mms which give a 6S system a pretty hard time no matter how much sympathy you show the battery. Shaving 600g relative to a pair of heavier packs will likely be noticeable through the sticks in this bird!

[Airguardian]

Thanks, i picked them up because they were close (660g) to the weight of the Admiral Pro 4000 (642g). So I was surprised it CG'd tail heavy in those locations.

Let me be a bit nitpicky here. I see the word 'tail heavy' being used way too often and too lightly and it can misdirect people.
If the plane CGs behind factory markings, that DOES NOT make the plane 'tail heavy' (unstable). You can say 'tail heavier' which is correct.
Factory CG is mostly always a notably 'nose heavy' (stable) starting position. Neutral CG is often several centimetres behind that mark.
A plane only becomes tail heavy when your CG exceeds that neutral point, not when the CG falls slightly behind factory reccommendations. ;)
Again, you can say I am nitpicky but it's an important remark in my mind.

I am NOT trying to be confrontational here (I know the internet can make some comments sound the bad way), I'm just trying to help with 'best practices' and rigorous wording, so that the community eventually gravitates towards better manners and less ambiguity.

Just maidened mine......upgraded servos installed. Overall, I'm pretty happy with it. It flies well and is easy to land.
2 things though: I was hoping to get a little longer run time (4 minutes MAX on RT 5500 mah....I'm pretty hard on EDFs though) and my CG is 5mm aft of the marks and I still needed 5mm of up elevator. The plane does not fly nose heavy to me, but that seems like a lot of up trim (and alot of drag)

Yep, factory reccomendation is evidently overly nose heavy, as it always is... time to slowly and carefully explore the flight envelope on our own, slowly moving CG back a few millimetres at a time. I wish manufacturers actually included the position of the neutral point on the manual but I take it that it would be a liability and 'unwise' customers may crash their jets because of that... but it is annoying having to work it out when supposedly someone else already has and could tell you to avoid potential problems. Example: The F-18 can't achieve a neutral CG position because lateral stability degrades much sooner than longitudinal stability. I would have 'loved' to know about that before starting my quest on aft CGs with this bird. Haven't crashed because of that, but almost.

Since he worded it much better than I ever can, let me quote what Kallend wrote on rcgroups:

"I agree with janmb: a safety margin that can be overcome my moving a pushrod by one hole is an insufficient safety margin on a 4kg 150kph model."

This is simply all there is to it. Servos that fail with a slightly worse geometry than intended are too marginal.

Totally agree with this.

We have to remember that there are people who post in these threads that don’t have or haven’t flown the specific model. In some cases they never intend to buy it...

It is not the case here.

On the flip side there are those that are on here just to discuss the model and don’t care about the full scale plane or physics.

Do as you please, but remember, just like you apparently don't care there are also those of us that DO care, both signs of the coin being perfectly valid.
Not like we are trying to force anything to anyone, so don't mind us talking about it!
Don't expect us to shut up either.

We're not training for Top Gun. It's a model. Cheese and Rice.

A poor argument. Models are used to design the fullscale jets.
People should not underestimate them ;)

Of course we do this for fun, but taking it seriously can be a lot of fun too. Whatever makes you happy! ;)

[janmb]

BUT the beauty of a twim 80mm setup is it is actually pretty forgiving on amps when flown in mixed throttle conditions, unlike single 90mms which give a 6S system a pretty hard time no matter how much sympathy you show the battery.

Very true. Not to mention twin 70 setups on a single 6S battery... yikes

The SU-35 is an amazing model, but that config is just a royal killer for flight times. Same goes for the competing SU-30 too.

[Bushong572]

5mm of up trim is a lot. Here is where mine is and I like the way it handles. I’m near 15mm back from stock CG.

Are you flying with any kind of gyro? I'm not ( I just wanted to make sure a gyro wasn't masking something with your rearward CG).
I guess the next time I fly it, I will move the batteries back and try to get another 5-10mm.

Thanks

[Lcacing]

Are you flying with any kind of gyro? I'm not ( I just wanted to make sure a gyro wasn't masking something with your rearward CG).
I guess the next time I fly it, I will move the batteries back and try to get another 5-10mm.

Thanks

Not using a gyro.

[mshagg]

Very true. Not to mention twin 70 setups on a single 6S battery... yikes

The SU-35 is an amazing model, but that config is just a royal killer for flight times. Same goes for the competing SU-30 too.

Ive not flown the su-35 but have observed it in operation. She looks and sounds like she needs a lot of throttle to do her thing.

In contrast I have the Me262, AL37 and the FMS A10. All of which are capable of making light work of a high C pack (FMS A-10 calls out 140A via telemetry on takeoff!) BUT being straight-ish wing configurations are really happy conducting their business at half throttle and can deliver a great balance of flight time and performance being flown as such.

But yeah, nothing comes close to the F-14 and the Mig 29, with 10000+mah on board and relatively low amp power systems even when punching out. The twin 80mm A-10 must be capable of some remarkable flight times; if it's anything like the FMS it will happily fly around at near idle throttle.

[janmb]

Ive not flown the su-35 but have observed it in operation. She looks and sounds like she needs a lot of throttle to do her thing.

In contrast I have the Me262, AL37 and the FMS A10. All of which are capable of making light work of a high C pack (FMS A-10 calls out 140A via telemetry on takeoff!) BUT being straight-ish wing configurations are really happy conducting their business at half throttle and can deliver a great balance of flight time and performance being flown as such.

But yeah, nothing comes close to the F-14 and the Mig 29, with 10000+mah on board and relatively low amp power systems even when punching out. The twin 80mm A-10 must be capable of some remarkable flight times; if it's anything like the FMS it will happily fly around at near idle throttle.

Yeah, the SU certainly pulls a lot more juice than any of those other options you list. Obviously has a lot to do with flight style too though. The SU typically encourages/pulls people into a quite more demanding flight style in terms of power.

[John Bergsmith]

GliderGuy Great write up and explanation of your experience with the Mig, enjoyed reading it. It's nice to get some education on the model. Sailplane guys are always the best!

Your story reminds me of a sport model that Top Flite released back in the 70's called a Freshman Trainer. It had a nasty habit of getting itself into a flat spin during certain maneuvers, most of the time not recoverable. Still the strangest flat spin I've seen with a model Ive ever seen.

[Airguardian]

FWIW, I have achieved 7min flight time on the Su-35 with my setup when doing formation flight instead of acro. And that's improvable as formation flight requires a lot of throttle up-down, whereas for a pure cruise flight you can leave constant rpms and consume less power ;)

But yeah, you are comparing a short aspect ratio tailed delta to high aspect ratio straight wing jets... not really fair!