** Blu-Baby Primary Trainer ** Plans, Pics and Fun! - Page 1367 - RC Groups
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Sep 02, 2017, 09:27 AM
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JohnsPop's Avatar
Quote:
Originally Posted by scruffy1
as a consequence i upgraded the spinner to this chunky monkey i bought ages ago for a now long-dead spitfire
weight 39 grams but it's the easiest way to pull the cg further forward for experimenting on how it helps the trim
That's how I like to add balance weight when I *have* to add it. On my fuel planes I use those Higley Heavy Hub type spinners. You hate to add the weight, but if you absolutely have to, getting it out front as far as possible just means you will only have to add the bare minimum to get it to balance.

I can't remember it's been so long ago, I think I learned the tip from Jackerbes, to be aware of your weight the entire build and try to balance as you go. It's a pain when you get through with a beautiful build only to find out the balance point has gone horribly wrong at some point. LOL Not implying that's what you did Scruffy, just wanted to point that out to someone new.

Edit: Ah, Mike beat me to the heavy hub perspective!
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Sep 02, 2017, 10:01 AM
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scruffy1's Avatar
it's a fair cop, johnspop

i cleverly placed the battery bay under the defined cg, so i could change battery choices without affecting balance... only to discover that it would have been better a centimetre or so forward of that spot

i have the opposite problem in my electric glider - the spinner on the folding prop makes it hard to put a bigger capacity battery in the front (only place a battery will fit) because i thought the tail was heavier than it turned out

hmmm... best of 3 maybe ?
Sep 03, 2017, 11:46 AM
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JohnsPop's Avatar
Yeah, sometimes thing just don't go as planned. LOL
Sep 12, 2017, 08:53 AM
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scruffy1's Avatar
the weather was finally favourable, and i received a clutch of 1047 props today - the signs were promising

with the additional nose weight of the spinner, it flies very nicely on the 2s 750mah battery, and i suspect will do beautifully on the 610mah for almost 1/2 oz. lighter

the controls are really nice with the cg pulled further forward, and it flies like a scale model of the genre - needs a take off run and some rudder compensation, and managed a loop and some barrel rolls (of sorts) trading height for a bit of speed for the manoeuvres

the 1047 measured in at 5.43amps peak, producing ~35 watts of power; i'm impressed by the size of prop that little motor can push, for the measured current

it seems to need a fair bit of throttle to maintain altitude, but the climb is rather majestically scale-like and will be good for beginners i think; i expect the combination of big prop and lots of undercamber aren't conducive to speed

as planned, i finished rigging the lights, and it looked great in the late dusk

only one battery worth of testing in this layout, but i'm very pleased


less fortunate was the two gouges taken from the rudder and elevator by a marauding magpie - it's coming up to nesting season, and they are very inclined to defend their air space

the baby isn't anywhere near as capable of evasive action as the 900mm discus launch glider i usually annoy them with

5.5 minutes flying left 3.72v residual per cell


next project will be to figure out getting the taranis to act as master to the dx8 as slave, to simplify tuition


all in all, a recommended plane for the purpose i built it, for sure
Sep 12, 2017, 05:33 PM
Registered User
Great to hear your flight was a success.
You might do better with a 3s battery?
I use an 800mah 3s and get 10 minutes to half battery capacity.
Mine flies level at half throttle.

Yeah - those magpies can be very vicious this time of year. Had one put a peck mark in the wing one day.
Sep 12, 2017, 07:02 PM
looking up, down under
scruffy1's Avatar
yeah, i expect it will do very well on 3s, but as a trainer 2s teaches some respect for having to fly a bit gently

the previous sortie with a 9047 used a 3s and it's much punchier, but the tables for power show that it will be pushing my luck on that prop as it pulls 7.6amps in a motor rated for 7.5amps

i might do my own testing on that; the readings on line from others suggest (amps/thrust) :

2S
8040= 3.3 / 8.2
9050= 4.9 / 10.8
9047= 5.3 / 10.9
1047= 6.5 / 11.5
3s
7035= 4.2 / 9.5
8040= 5 / 13
7060= 6.3 / 11.3
9050= 6.6 / 14.6
9047= 7.6 / 15

my reading on 2s / 1047 were 5.43amps, but that might be a reflection of the rhino lipo rather than the more performance lipo possibilities

3s looks to be a win for the 8040 (or the 9050) but i have an 8038 to try too
good to have a selection of props and the watts up meter for sure

i also discovered an unused styrene cut foam wing with full length ailerons from antiquity, that is slightly narrower chord and slightly longer span, which will do great as an intermediate trainer option, but will add 63 grams to the load compared with the undercambered version , and then a bit more for the servo and linkages

tempting to use 2x 5gm servos and mix them for flaperons...

ah, more distractions...
Last edited by scruffy1; Sep 12, 2017 at 08:01 PM.
Sep 13, 2017, 11:41 PM
Mark Harrison
Quote:
Originally Posted by scruffy1
yeah, i expect it will do very well on 3s, but as a trainer 2s teaches some respect for having to fly a bit gently

the previous sortie with a 9047 used a 3s and it's much punchier, but the tables for power show that it will be pushing my luck on that prop as it pulls 7.6amps in a motor rated for 7.5amps

i might do my own testing on that; the readings on line from others suggest (amps/thrust) :

2S
8040= 3.3 / 8.2
9050= 4.9 / 10.8
9047= 5.3 / 10.9
1047= 6.5 / 11.5
3s
7035= 4.2 / 9.5
8040= 5 / 13
7060= 6.3 / 11.3
9050= 6.6 / 14.6
9047= 7.6 / 15

my reading on 2s / 1047 were 5.43amps, but that might be a reflection of the rhino lipo rather than the more performance lipo possibilities

3s looks to be a win for the 8040 (or the 9050) but i have an 8038 to try too
good to have a selection of props and the watts up meter for sure

i also discovered an unused styrene cut foam wing with full length ailerons from antiquity, that is slightly narrower chord and slightly longer span, which will do great as an intermediate trainer option, but will add 63 grams to the load compared with the undercambered version , and then a bit more for the servo and linkages

tempting to use 2x 5gm servos and mix them for flaperons...

ah, more distractions...
Very nice! FWIW I'm happy with my 3S 500mAh an 8040 prop.
Sep 14, 2017, 06:14 AM
Registered User
Agreed, mine is flying with blue wonder 1500 kv motor, 7x5 prop and 3s battery.
Sep 14, 2017, 06:31 AM
Jack
jackerbes's Avatar
Quote:
scruffy1 worte:f

"..the previous sortie with a 9047 used a 3s and it's much punchier, but the tables for power show that it will be pushing my luck on that prop as it pulls 7.6amps in a motor rated for 7.5amps

i might do my own testing on that; the readings on line from others suggest (amps/thrust) :..."
That is probably a result from static testing and also a full throttle value for current. What you really want to look at is the input power in Watts because the value in Amps is meaningless unless you know the input voltage. Look at the power in Watts and compare it to the 3W per gram rule of thumb, that is a meaningful value.

And in flight the prop will unload and the input power drop, you won't normally be flying at continuous full throttle, the motor will have better cooling and it will all be OK.

If you have a plane that has to be flown at continuous full throttle look for a motor that is a little heavier. I always used the 59 game or so Tower Prop TP24xx motors on my Blu Baby builds and they could handle the higher winds that prevail here as they cruised about with bigger, slower turning prop and seldom over half or two thirds throttle...

Jack
Sep 14, 2017, 06:46 AM
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scruffy1's Avatar
mine's using the HexTronik 24gram Brushless Outrunner 1300kv

@jackerbes : i get continuous readings from the watts up
the 1047 on 2s peaked at over 40watts, but was consistently 35 after the initial peak discharge

but bear in mind i'm only using 2s and that my iteration of the baby is 36.5" span, so has ~ 20% more wing area than the 33" version

the motor is recommended to use 3s, and i suspect that 8040 or 8038 will be the best prop at that voltage

on 2s it is slow to accelerate, but flies handsomely (and quite slowly) at ~ 2/3 throttle, but only if you are conservative with the controls - which is good for a trainer

thanks for your comments; food for thought
Sep 14, 2017, 08:54 AM
Jack
jackerbes's Avatar
With the 1300 Kv and 2S your no load RPM would be about 1300 x 8.2 or 10,600 RPM. If you are using the thin plastic 10 x 4.7 like the GWS it still start fluttering at about 5,000 RPM and is in danger of folding or failure at full toot. The APC slow fly 10 x 4.7 will handle 6,000 or even 7,000 RPM with no problems at all but needs about 100W on the input power to get up to that.

Look at this GWS 11 x 4.7 slow fly and you'll see what I mean, that starting fluttering and moaning at around 5,000 or so:

Slow Fly Prop High RPM Testing.mp4 (2 min 9 sec)


That would put your Blue Wonder at about 4W per gram and warm it up pretting good. But if not at too much time at full throttle, the motor might handle it OK. You can see the numbers on that prop here:

APC SF 10x4.7 - www.flybrushless.com/prop/view/39

On 3S your no load RPM moves up to over 13,000 RPM and that will demand a smaller prop and probably a non slow fly type. For the the GWS HD/EP type prop might work for you. Here is the info on the GWS HD 8 x 6 and that gets 100W up around 8,000 RPM and gives you about
500g of thrust at that speed. Much more RPM than that (to get more thrust) will start threatening your motor though.

GWS HD 8x6 - www.flybrushless.com/prop/view/12

Jack
Sep 14, 2017, 09:16 AM
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scruffy1's Avatar
the prop is sold as "gws style", but it's not as flexible as the gws ones i have; it's listed as OR001-00310B

the 8038 of the same style manages 152 watts on a D2822/14 Brushless Outrunner 1450kv and flies without the noise demonstrated - and they seem indestructible into the bargain - and believe me, i've tried to prove them mortal

all good info though, so thanks again

now that i have a reasonable grasp of motor ratings, it's sensible to consider whether the prop will handle it too
Sep 16, 2017, 10:10 PM
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scruffy1's Avatar

almost "finished"


added some windows and a tail emblem, and now it looks much more seriously like a light aircraft
Sep 17, 2017, 08:41 AM
Jack
jackerbes's Avatar
That's looking good Scruff, and that slow fly style prop will both fly it nicely and suit it's character well too.

Jack
Sep 17, 2017, 08:27 PM
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scruffy1's Avatar
thanks jack

sadly, it's been windy here forever recently, so no opportunity to fly

the lights are now mounted in sawn off terumo needle sheaths (perks of access to medical stuff), so they are "fixed" but demountable in the fuselage at the top between the windows, and light up most of the bottom of each wing, and all the rear fuselage with a white strobe

at dusk it looks really impressive


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