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Old Feb 17, 2013, 04:29 PM
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Originally Posted by pardshaw View Post
Anyone recommend a prop size for the E-power BL2220/07 motor suggested in Tom's PDF?

I'll test with a wattmeter, but I'd like to get as close as possible beforehand.

Dave
I had fitted a 10 X 5E APC which was pulling 12 Amps at 11,5V. After reading Guru's recommendation I fitted a 9 X 5E APC (theoretically the same as an 8 X 6 but a bit more thrust and lower forwards speed). The 9 X 5E was tested and drew 10.2 Amps.
In flight this prop gave LOADS of thrust, plenty to pull this model around however towards the end of the flight as the voltage dropped I had to use more throttle to ‘cruse’ around but that is normal. I just measured the Amps that I put back into the 2 packs and it works out at around 230-240 mAh per minute. This should give just over 6 minutes with an 1800 mAh pack (discharging to 80%).
I think that an 8 X 6, a 9 X 5 or even a 10 X 5 will all be fine.

Remember, bigger diameter, lower pitch gives more thrust but a lower top speed, small diameter more pitch give high speed, low thrust and one inch in diameter is around one inch in pitch. For this model we are looking for high thrust, low speed (this is not a pylon racer and has lots of drag), so, Guru is happy on an 8 X 6, I flew today on a 9 X 5, you pays your money you takes your chance )

10,5 Amp draw (9 X 5) gives a 6 minute flight time and everything is working well below it’s limit. A 9 X 5 equates to an 8 X 6 or a 10 X 4 (rule of thumb).

Are your blades the right way around??? If yes, don’t worry just go out, fly and enjoy.
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Old Feb 18, 2013, 03:45 AM
Flying one day at a time....
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Thanks Paul. Thats a really useful reply. Very helpful in fact as I'm just about to order the motor, ESC and battery as per Tom's PDF. So I'll order some 9 x 5 props. The power consumption figure (230-240 mAh/min) is extremely useful to know as it guides my battery sizing decision.

My blades......Haven't even started the blades yet! I began making my Crane Flies according to the order that stuff arrived in the post. The balsa only arrived the day before yesterday, so I'm still working on the fuselages. I must say I'm really enjoying the build - its a delight and so simple even I can manage it.

The weather here is superb today and tomorrow so I'll just have to go and fly my Nutball!

Dave
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Old Feb 18, 2013, 04:56 AM
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When you do your blades, remember that the blunt bit goes left, not right!!!!!!!!!

I flew with 1800 mAh packs yesterday, landed at 5:45 on one flight and 5:20 on the other but taxied back to the pits slowly so it was 7:15 when I shut down. The 5:45 flight took 1351 mAh and the 7:15 took 1404 however as the model is new I was probably using more throttle than needed (safety in speed and height) and I did do some serious throttle slams to see if I needed any side thrust. All in all I think that Guru Tom’s choice of 1800 packs is a good one for 6 minutes of fun with props in the 8-9 inch range. I was lucky in so much as I had just purchased 2 GensAce 3 Cell 1800 packs for a Depron Grppen which was my last project and they seem to be ideal for the Crane as well but I also have 2200 and 2500s lying around so when the weather improves I may try them out for those long summer evening flights.

Off topic, I did the Nutball thing last year with 24” and 12” versions great fun and if you do the calculation
F / (C*E*T)
where F is Fun, C is Cost, E is Effort and T is Time the Nutball must come out right at the top.
I am also thinking or organising a Club Combat competition in summer where the models will be 3 mm Depron and the suggestion will be the Nutball or the Piza Box Flier (PBF). Super simple low cost/ effort planes flying combat (cutting a paper streamer tied to the tail of your opponent’s model with your prop), great fun!!
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Old Feb 18, 2013, 06:36 AM
Flying one day at a time....
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Hi Paul

Just ordered up motor,ESC,1800mAh bat and a bag full of props. Your advice was very timely indeed - especially as I was dithering on bat size.

You are dead right with your formula! I taught myself to fly on Nutballs. Talk about cheap as chips! A 24 inch Nutball is superbly suited to a Blue Wonder and an 8 x 3.8 prop, coming in at 3.3 OPSF and all for under £20 (including ESC, motor & bat)!!! I think your formula says it all - I can't conceive of a cheaper, quicker-to-build and more fun foamie for a noob to learn on.
Bit off topic, though........sorry!

Dave
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Old Feb 18, 2013, 07:36 AM
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Paul and Dave.

While on the subject of lipo sizes ,Pete another CF builder over here , flew a 2.8 A yesterday with no problem at all .It's amazing how much lift the C - 30 blades will produce when correctly set up .

Will do a Watt test on my Blog SFH later as the figures in the previous posts sound on the low side .

Tom.
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Old Feb 18, 2013, 08:28 AM
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Following on from above, It's worth noting that the BL 222O is available with different KV ratings that are not indicated on the motor label.
From memory my Blog model has a 1350 KV version and the Watt meter test I have just done indicates 230 W with an 8x6 prop .
The readings Paul is getting suggests a lower KV and surprisingly good flight performance with less than 100 W per pound .....interesting!

Tom.
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Old Feb 18, 2013, 08:58 AM
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Tom, thats useful to know. I didn't realise the motor had different kV specs - I've ordered it now so its pot-luck what turns up. On the subject of rotor blades I was planning to build one set with the +5mm chord increase for enhanced slow speed performance. I imagine this give a bit more lift and a bit more drag which perhaps balance out so that the slower rotation speed ends up producing roughly the same lift as the original chord - would you think?

Dave
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Old Feb 18, 2013, 09:11 AM
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Hi Tom,

I just clicked the link on your .PDF and then pressed order to purchase the motor, didn’t even read the description, blind faith !!
Having just checked the Giant Shark site that motor is a 1200 kV. The label says 10” – 11” prop, could it be that I am under propping my motor with a 9 X 5 and thus drawing far less current?? At 230 watts you must be up in the 18-20 Amp range which makes my 10-12 look tame. I will re-check my readings tonight and do RPM as well as V/ A/ W. Interesting….
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Old Feb 18, 2013, 11:15 AM
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Hi Tom,

just measured my current draw again, the APC 9 X 5E is operating at 146 Watts @ 12 Amps turning at 10 200 RPM.

On an APC 10 X 5E she is running at 151 Watts @ 13,1 Amps, 9 210 RPM.

Do not know why the current draw seems to have gone up by 2 Amps but I did use a pack discharged to storage last time but fully charged it this time, as I did not note the Watt value I may have misread the voltage.

Even so at 151 Watts on a 10 X 5 I am still well shy of your 230 Watts.

Checked the weight and I am still tipping the scales at 780 Grams (nearly 28 Oz) which when you consider that I used ‘normal’ plywood and added paint accounts for the Oz or so more than yours and sounds about right.

Please bear in mind that I was impressed and delighted by the performance of my Crane but this is only my 3rd AG. The first was a DB Sport and Scale, which I am sure that you know well, with a .28 Invine 15-20 years ago and the second was Al Foot’s Monotwirl which although I have got it flying neither of these models are a real yard stick to compare Auto Gyro performance to. Could be that if you flew my version of the SHF that you would think that it was a bit of an underpowered overweight pig
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Old Feb 18, 2013, 02:37 PM
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Unnecessary solution for a problem which does not exist!!

Ok, so we know that Toms bearing configuration works fine and we also now know that a radial bearing can take an axial load so there is absolutely no need for a thrust bearing, right???

But, what if you lie in bed at night still trying to figure out how to prevent the trust bearing which you are not going to fit from rubbing on the inner ring of the flanged bearing (may need a solution for the next design)???

I thought about all sorts of ways to make a stepped washer with simple hand tools (one day I will buy a lathe) and the answer for me was there in the head, G10 sheet!!

Cut 2 squares and drill a hole 1,6 mm in the centre. Screw both squares onto a Dremel mandrel and turn them so that you can cut the corners off (just makes the next step a bit easier). Sand the squares (hexagons) down so that they are both the same diameter as the OD of the flanged bearing. Remove from mandrel and glue both disks to a scrap of Depron (can’t hold little disks safely in you fingers and drill them, danger of the drill biting and slashing your fingers!!) using Por contact glue. Drill one disk out to 3 mm and the other to whatever size clears the bearing inner ring (I used 4.8 mm in this case). Remove the disks from the Depron and clean off the glue, sand one face of both disks and smear with Epoxy (works best if you mix it first ) stick the disks together using the outer diameter and the mark 1 eyeball to line up and Robert is your Dad’s brother.

PS, this took longer to write than it took to do!!!
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Old Feb 18, 2013, 03:46 PM
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Paul,
It sounds straight forward but I dont understand how it all fits together - any chance of a rough sketch?

malcolm
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Old Feb 18, 2013, 05:09 PM
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Paul .
You can buy 3mm ID thrust washers as spare parts for rebuilding out-runners.

I find a good power reserve is like a sports car ... handy for getting out of bother ,but if incorrectly used it can also get some into bother.

Tom.
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Old Feb 18, 2013, 09:37 PM
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i have a problem

i have look every where for 2mm nylon bolts in my town and all the hardware stores here have stop selling them so can somebody point me in the right direction . thanks
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Old Feb 19, 2013, 01:29 AM
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I had the same problem so I just used 3 mm 'cos I had them. still seems to be enough 'meat' around the hole.

Thoughts Tom????
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Old Feb 19, 2013, 02:34 AM
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Dohhhh, I checked several hardware suppliers and searched in various helicopter spare parts lists to no avail, didn’t think of inrunner motor parts, thanks for the tip.

As a 53 year old MX5 (original NA) driver who has also spent years shoe-horning the biggest engine into the cowl that I could get in I know what you mean.

Ok, so now we also know that your design is so good that it
a) Flies with the blades on the wrong way around and
b) Flies at 88 W/ Lb.

it just keeps getting better and better

I have just done some Googleing about the 1200 kV Emax (E-Power) 2220/07 and all of the Specs that I can find come up with numbers matching what you are finding and not what I am getting, so, duff motor, packs not up to the job (new GensAce) or is my Watt meter out of calibration?

3-4 Inches of snow this morning and back down to minus temperatures so the packs are back at storage voltage and my Baby is sitting next to the rest of the fleet before I take her out again. I do hope to get a video at some point, it might be interesting for you to see the performance as you have a far better (more experienced) eye for how an AG should ‘sit’ in the air.
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