UltraFly SU-27, 3800kv motor

[Wingman77]

Hello all,

I was kindly re-direced from another thread where I posted this question in error.
I’m a new comer to electric flight....
It was only in its infancy when I left the sport some 10 years ago.
Now the things go like a cat with it :censored: on fire!!

I’m in the process of returning and have on order an UltraFly SU-27 without motor/gearbox, this was done on recommendation from someone who had already build two of these little ships.

They suggested that I build the model with a 'Direct Drive' Brushless and around a 3800Kv rated motor swinging a 5' prop. Of course a matching ESP and battery would complete the package.

My question is:
Does anybody have any experience with similar configurations and can point out a way ahead? I’m after guidance on hardware considerations, performance/expected flight times, and any first-hand experience people may have with similar set-ups.

Any assistance would be greatly appreciated.

[GOK]

Welcome back to the hobby wingman77,

I have no experience with the Ultrafly SU27 other than having seen it flown by others (From what I have seen it is an excellent intro model for pusher jets). However, I have been flying pusher parkjets for almost three years now. The ships I build are more or less the same size and weight with the UF SU27.

I am sure more experienced moddelers will chime in here but I personally prefer outrunners on these models as opposed to geared or DD inrunners. If you choose to go with an outrunner you would need something in the range of 2000-24000kv on 3s spinning 5-6 inch props.

With the pusher jets, ideally you want at least 1 to 1 thrust ratio. Having said that, these pushers will fly wine from anywhere between .75 to 1 thrust ratio and up. Once you go over 1 to 1 thrust ratio the fun starts multiplying ;)

Among many others, the two motors that people on the pusher forum are having great success with are the little screamers parkjet motor (I think from hobby lobby) and welgard 2212-06 from Graysonhobby. These little outrunners spin 6x4 props on 3s and provide very good thrust and pitch speed.

Do a search on the pusher prop jets forum on these two motors and you'll see what I mean.

Oh BTW, these motors are relatively cheap too. The grayson hobby one is 17 bucks I think and the LSPJ shoud be around 40-50 dollars.

Don't get me wrong I am not trying to market anything just trying to offer some pointers to help out :)

Hope this helps,

GOK

[RobinBennett]

3800 does seem rather high, and a 5" prop rather small. That's pylon racer territory and a scale jet really needs more thrust and less rpm - bigger props are more efficient.

[Dr Kiwi]

3800Kv and a 5" prop is going to draw around 50A!

My Lightflight 28-37-2 (3700Kv) drew 41.60A/444W with just a 4.5x4.1.

I'd second GOK's suggestion - a Suppo 2212/6 or a Super Mega Jet motor from Grayson would be far better.

[Au_Arbiter]

I have a MiG-29 about the same size. Its powered by the himark 2815/2000 on a 3s 2150mah pack on a 6x4 prop. Pretty fast but still easy to handlaunch. Not sure on the amps but the 37A controller is warm if that.

- Arbiter -

[T3chDad]

I LOVE THAT PLANE. It was my first and favorite...(God rest its soul). You want to get one of the Grayson/Welgard/BP/Suppo 2212-06 motor and ESC combos for this plane. That combo will run you about $35 from lightflightRC. Grayson Hobbies (http://www.rcgroups.com/forums/showthread.php?t=665974) also has a decent deal on this combo and Lt. Smash (the owner) is a really stand-up guy.

You can check my blog (http://www.rcgroups.com/forums/member.php?u=150509) for a bunch of info on this model. Also, here a video of mine with this power setup.

http://www.youtube.com/watch?v=dpi8MhRmaOI

I hope I've helped. By the way, where did you find theses for sale? They've been discontinued. I wouldn't mind owning one again! :D

[Wingman77]

I found them on www.ohyesrc.com
They have the whole range with and without motors.
They are coming in from Taiwan without motors (i.e., a pack of foam and other assorted bits)

Thankyou all for your wonderful guidance, It’s given me a lot more to think about.
Once I have all this together I'll be sure to post some pics and eventually vids.

[Joe 1320]

I've got the Ultrafly Jets and perhaps the best average performance will come from a 2700-3200 kV motor and a 4.1-4.5" prop. Higher kV and larger prop will result in a large amp draw and subsequent heavier lipo packs to supply the current. The end result is the weight starts to climb and offsets any power increases. I might suggest a KDH 450 2700 kV outrunner, 4.5x4.1 prop, 30A esc and a 1800mAh lipo. if you want even more performance, go with 4s and drop the prop to a 4.1x4.1....it will scream.

[T3chDad]

I found them on www.ohyesrc.com
They have the whole range with and without motors.
They are coming in from Taiwan without motors (i.e., a pack of foam and other assorted bits)

Thankyou all for your wonderful guidance, It’s given me a lot more to think about.
Once I have all this together I'll be sure to post some pics and eventually vids.
You got the last one. :(

Glad to help!

[Wingman77]

Oh dear, sorry, now I feel guilty... :o

Well you can be sure seeing as its possible one of the last ones available I'll do it justice and post some pics of its construction.

I’m already thinking of using a different camouflage scheme instead of the one supplied in the pack. On doing some research on www.airliners.net I've come across a scheme I’m fond of, pic below hopefully.

Thanks to everyone for posting personal experiences and opinions in this thread for me, I’m researching every motor mentioned to see how they all perform and I really appreciate all your efforts.
In my travels on the net I have come across one name that has not cropped up as yet in any thead, Top Racing, I can across this one whilst on EBay. They seem to have a fairly large range of Kv's and in some cases even sell 'combo packs' with ESC.

[T3chDad]

I love that paint scheme. I used it on my X-41 Deltastorm (http://www.rcgroups.com/forums/showthread.php?t=779331). Attached are the images for the markings.

[Dr Kiwi]

I've got the Ultrafly Jets and perhaps the best average performance will come from a 2700-3200 kV motor and a 4.1-4.5" prop. Higher kV and larger prop will result in a large amp draw and subsequent heavier lipo packs to supply the current. The end result is the weight starts to climb and offsets any power increases. I might suggest a KDH 450 2700 kV outrunner, 4.5x4.1 prop, 30A esc and a 1800mAh lipo. if you want even more performance, go with 4s and drop the prop to a 4.1x4.1....it will scream.

A Don's Wicked 2700 (actually ~ 3190Kv) with a 4.5x4.1 gets you this:

10.9v, 26.80A, 290W, 26970rpm, 104.7mph, 625g, 22.01oz, 2.16g/W

You'd better have a good 20C 1800mAh pack to cope with that.

[Wingman77]

Hey thanks for the decals!!
Thats going to save me alot of time in 'Paint-Shop' drawing them up.
Now I just have to find a sign writer who can print them off on vinyl for me.

Thanks again T3chDad.

[T3chDad]

I just print them out on CD/DVD labels with my inkjet, then cut them out and stick them on. I do this before I clear-coat the model with minwax polycrylic spray.

[Wingman77]

As always a better solution presents itself....
This is why I love this sport. It attracts ‘thinkers’ and people who see difficulties as just another opportunity to develop a new technique or process to overcome it.

It also seems I've been always from the sport a little too long.
All these new techniques have been developed in the past 10 or so years from what I’m seeing.

I was only just reading in another thread about using inkjet printers with photo paper but your process with CD/DVD labels is far better.....Cheers,

[Wingman77]

Well after only 7 days of holding my breath my new toy has arrived! :)

Although, as you can see from the photos its been partly painted (be it fairly poorly) in the factory!
I’m sure they didn’t come this way the last time I searched on the net.
Didn’t they come with stickers that looked like Cam pattern that you could ellect to discard or use?!?

None the less it just provides a undercoat for the funky blue/grey Ukraine pattern I'll be using.

More pics to follow as it all progresses.

[T3chDad]

Yeah, that's weird. Mine was all white with vinyl blue and grey camo stickers. I look forward to your pictures.

[MrFlash]

Mine was unpainted as well with huge sheet of camo decals .

With some great advice from T3chDad and a few of the guys on RCG its a great introduction to pusher "jets" . ..very moddable !!!

This is my sport colourscheme job from last year. ...great plane for the money, and a hoot to fly !