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Old Sep 16, 2006, 05:06 AM
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Alex B's Avatar
Balaguer in Lérida - Spain
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Originally Posted by wolw
Jeezz, you got your self a handfull, Alex

//Peter
I told you not to buy the FUNTANA/KATANA....
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Old Sep 16, 2006, 05:50 AM
<- Balsa flies better ->
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Gustafs, Sweden
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Quote:
Originally Posted by Alex B
I told you not to buy the FUNTANA/KATANA....
I'm starting to think that mine might just flop around if there's some wind, projected wingload 17.49oz/sq.ft

My next is decided anyway (your fault ) Seagulls P-51

//Peter
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Old Sep 16, 2006, 08:53 AM
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Originally Posted by Alex B
Carlos thanks again...no I won't be using a huge prop on this project unless it's completelly necessary...I mean for scale looks otherwise I'm pretty sure that with the AXI 5320/18 and a 15x10 or 15x12 prop I should get away very well.

Batteries will be 2 packs of Thunder Power at 10-12C rating of 8000mAh capacity and built on 5S4P each.

Motocalc shows about 1000-1200 Watts using this configuration so should be more than enough for this bird I think.

Well I won't be reporting much progress until I get Esprit's motor supports and I figure out how to fix batteries inside and other bits like finish the landing gear wells.

Alex
Alex,

I am sure it was a typo.....you meant to type AXI 5320/28 as Model Motors does not make a 5320/18 Not yet at least....

With the use of 10S Li-POLY and trying to swing a larger propeller, MotorCalc gives some warnings about the motor temperature especially using a 16 or 17 inch diameters and different pitches....also, the airpseed deminishes.

Good to learn that you will try out the 15 incher first.....that Jug Head need airspeed
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Old Sep 16, 2006, 08:58 AM
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Originally Posted by guapoman2000
Static thrust (176.1oz) to weight (146.2oz) ratio is 1.2:1, which will result in extremely short take-off
Lets not forget the above!!! For those that Love Thrust!
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Old Sep 16, 2006, 09:11 AM
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Well, here is what E Calc says about the 15" prop vrs the 17" prop based on using the 5320/28 on 10S.
The 15x12 will fly it fine, but the 17x10 would be better :-). Model Motors own website says use an 18" prop with on this motor with 10S.
Ed
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Old Sep 16, 2006, 09:19 AM
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Without filling this Thread with all kinds of Snap Shots of MotorCalc again.....

Alex,

Using 10S2P (Kokam 3200SHD (20C); 10 series x 2 parallel cells) and using the APC 17 X 10 Prop.

Here's what MotorCalc indicates as a precautionary warnings:

The full-throttle steady-state motor temperature (323°F) is extremely high, which will likely damage the motor unless full-throttle is used sparingly and cooling is good (even then, damage is possible).


The static pitch speed (70mph) is less than 2.5 times the stall speed (33mph), which may result in reduced performance at typical flying speeds and a low maximum speed. This situation is usually acceptable for an electric sailplane or other slow-flying model.
Pitch speed can be increased by using a higher pitched and/or smaller diameter propeller, a higher cell count, or some combination of these methods.
.


Alex, it's your heavy JUG HEAD we are talking about......I would certainly measure your Propeller RPMs with both just for you to see the difference in Propeller Pitch Speed
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Old Sep 16, 2006, 09:27 AM
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Originally Posted by guapoman2000
Per Model Motors Web Site:
http://www.modelmotors.cz/index.php?...495%20-%20652g)

No. Of cells max. 32
max. 10s Li-Poly
RPM/V 249 RMP/V
Max. efficiency 92%
Max. efficiency current 10 - 36 A (>85%)
No load current / 10 V 1,4 A <--- Means @ 10 Volts constant!
Current capacity 50 A/60 s
Alex,

Recall......the above Maximum Current Draw.....as listed in Model Motors Web Site.....don't make me post those Videos of Chuck McHugh pushing his AXI 41XX series Outrunner with higher AMP draw than what that poor motor could withstand......it was a sad day at the field....

That was a wake-up experience for all of us at the Field that day and for Chuck McHugh it was time to rethink things about Maximums data posted at a Web Site.....

I rather errr on the conservative when providing recommendations!
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Old Sep 16, 2006, 09:40 AM
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Alex,

Here's one graph showing what happens when you place a large diameter propeller intended for a fast flying model....especially one that has a high wing loading.....

Already at 60 MPH the Prop efficiency and that of the motor drops off something terrible.......can you say dump your battery pack energy into heat.....
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Old Sep 16, 2006, 09:54 AM
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Alex,

One last thing......if your model will have a little over 35 oz./sq.-ft. of wing loading, I seriously doubt for one minute that the models STALL SPEED is 23MPH!!! This is more like a model that sports a wing loading in the mid 20's and not a heavy model like your P-47.

Certainly, you would need to determine for yourself, what exactly is the stall speed for your model if you don't trust either software that has been posted here.

Here's what I am trying to point out......

Your models: Wing Area: 50 sq.-m. = 538.2 sq.-in. perhaps that's the error????
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Old Sep 16, 2006, 10:01 AM
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OK ..... have it your way .
Not here to argue, just trying to provide advice.
Ed
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Old Sep 16, 2006, 10:05 AM
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What? Did someone say something to me....

Argue

More like having a discussion....what is the wing area in ENGLISH from 50dM???

Anyone?
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Old Sep 16, 2006, 10:16 AM
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Originally Posted by guapoman2000
Alex,

One last thing......if your model will have a little over 35 oz./sq.-ft. of wing loading, I seriously doubt for one minute that the models STALL SPEED is 23MPH!!! This is more like a model that sports a wing loading in the mid 20's and not a heavy model like your P-47.

Certainly, you would need to determine for yourself, what exactly is the stall speed for your model if you don't trust either software that has been posted here.

Here's what I am trying to point out......

Your models: Wing Area: 50 sq.-m. = 538.2 sq.-in. perhaps that's the error????
OH well ......
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Old Sep 16, 2006, 10:22 AM
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Then perhaps 23 MPH Stall Speed is correct as it has lots of wing area....

Thereby, a 16 or even a 17 inch propeller assuming you measure AMP draw and Propeller RPMs could be a good choice.

Thanks Ed.....I would have never known such a metric value as deci whatever?

I was using this on-line calculator and the small 'd' threw me off....

http://www.sciencemadesimple.net/area.php

Wow....with that kind of wing area......she be a pussy cat, well you can not horse her around too much...but, she be a sweet flyer!
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Old Sep 16, 2006, 10:27 AM
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Okay with the new (Correct Wing Area ) again thanks to Ed....

Using 10S2P, and the APC 17 X 10 propeller!

Here's what my Motor Calc says: (Assuming an empty dry weight of 70oz.)

The static pitch speed (70mph) is within the range of approximately 2.5 to 3 times the model's stall speed (27mph), which is considered ideal for good performance.

With a wing loading of 27.2oz/sq.ft, a model of this size will have flying characteristics suited to the intermediate pilot, for use in calm to moderate wind conditions.

The static thrust (232.4oz) to weight (146.2oz) ratio is 1.59:1, which will result in extremely short take-off runs, no difficulty taking off from grass surfaces (assuming sufficiently large wheels), and vertical climb-outs. This model will probably be able to perform a hover or torque roll.

At the best lift-to-drag ratio airspeed, the excess-thrust (148.2oz) to weight (146.2oz) ratio is 1.01:1, which will give very steep climbs and incredible acceleration.
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Old Sep 16, 2006, 10:31 AM
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Alex,

Whatever prop and combination of Battery cell count you use, make sure you measure all parameters....

Wow, can't wait to see the Video on this model...assuming your Video person can keep up with it!

Best of luck!
Carlos
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