Helis & Planes Compared

[Gabe]

Mar 10, 2010 20:23:48 GMT -6 akent said:

I sure wish there was a calculator that would say, "Humm, you want that foamie to go 220 mph? Ok, use this motor, this ESC, this battery, and that helmet."

I think there is: the boys on the Darkside Stryker threads use MotorCalc or something like that. I've been told there is a cubic relationship between speed and watts. It takes approximately 600watts to go 100mph. Lemmie see if I can find the data.

[19000rpm]

Now that Gabe mentions it I recall seeing that calculator a long time ago. I might have it in my favs. I'll look.

motocalc.com/

[dubehigh]

that would be interesting.

[19000rpm]

Mar 11, 2010 10:30:00 GMT -6 dubehigh said:

that would be interesting.

I never bought the software. I thought it would be a good idea to have though if you were building something where you had no coat tails to hang on to from someone elses build. ;D

[BTCat]

Bought a 10x7 APC electric prop today and did a static check to see what the amp draw would be. At 100% throttle, amp draw was steady at 30.2 with voltage at 11.2 roughly 320 watts ?? I don't have a 40 amp esc, just a 30 amp Exceed. I know I won't be pushing 100% throttle for a while, but I think I will either have to prop down or go to a 40 amp. I was going to buy a 10x6 but they were out. I looked again for a 9x7.5 nope. Out of those also.

I have an aluminum spinner on the front of my brushless now, so I need the larger shaft bore. APC Electric fits great.

[Solitaire]

I wonder how a 10x4.7 would work on that
Certainly less strain on the motor.

I'm still learning about props/motors/amps and speed.

[BTCat]

Mar 12, 2010 21:12:22 GMT -6 Solitaire said:

I wonder how a 10x4.7 would work on that
Certainly less strain on the motor.

I'm still learning about props/motors/amps and speed.

I certainly don't need all the speed and power right now. Not with my lack of experience. Where did you get the 10x4.7 idea?

[Solitaire]

To be honest, I have no idea if it's even suitable. You might find the 10x6 or 10x5 is a better match for your power and flying syle.
I got a few of these as replacements for the GWS on the Pitts and they look great (haven't tried 'em yet). Not as brittle as the APC style, but very well made and include adaptors. Weighs only 13 grams and they're inexpensive.

www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=7158&Product_Name=TGY_Slow_Fly_Prop_10*4.7SF_w/_shaft_adapters

I'll send you one and a 10x5 APC style...easy way to determine the right one.

[BTCat]

Appreciate the offer, Sol. Let me check my other LHS first. They may have it in stock. They carry some GWS stuff. Oh, and I just thought of another old LHS that had a pile of props last time I was there.

[19000rpm]

Mar 12, 2010 18:46:04 GMT -6 BTCat said:

Bought a 10x7 APC electric prop today and did a static check to see what the amp draw would be. At 100% throttle, amp draw was steady at 30.2 with voltage at 11.2 roughly 320 watts ?? I don't have a 40 amp esc, just a 30 amp Exceed. I know I won't be pushing 100% throttle for a while, but I think I will either have to prop down or go to a 40 amp. I was going to buy a 10x6 but they were out. I looked again for a 9x7.5 nope. Out of those also.

I have an aluminum spinner on the front of my brushless now, so I need the larger shaft bore. APC Electric fits great.

I think the 10X7 should work very well.

If it's pulling 30A on the bench, that 30A is good to go unless, possibly, you run it WOT all the time; which I'm sure you won't be doing. The 30A Exceed is good for 38A bursts if I remember correctly.

I'm guessing 320Watts is probably the maximum you'll be able to constructively use with that airframe, in any form, unless you cut the wing in about half. Then you have a "Stub Cub" a completely different animal. ;D

[BTCat]

Thanks 19

[akent]

That is huge power, BT!
If it were mine, I would drop down an inch of prop or an inch of pitch. That will reduce your current draw.

I'm pulling right at 10 amps with a 1300kv HC motor, 8" 4p prop, on 3s. It pulls all of these foamies vertical at around half throttle. I do run a 1500kv on the F22, but it's the same draw for some reason. So you have about triple the power!!

You are going to have a rocket!
Kent

[scarface26]

You better get a bigger amp esc soon, BT. Read NoFlyZone's blog on ESC's at the RC Group Ultimate SC thread. If I read it correctly, you will be pulling 30.2 amps at any throttle setting. It just shows on a watt meter, the average amps for any throttle setting. The pulses of 30.2 amps are just further apart at lower throttle settings.

www.rcgroups.com/forums/showthread.php?t=865319#post9873236

[BTCat]

Mar 13, 2010 10:56:32 GMT -6 scarface26 said:

You better get a bigger amp esc soon, BT. Read NoFlyZone's blog on ESC's at the RC Group Ultimate SC thread. If I read it correctly, you will be pulling 30.2 amps at any throttle setting. It just shows on a watt meter, the average amps for any throttle setting. The pulses of 30.2 amps are just further apart at lower throttle settings.

www.rcgroups.com/forums/showthread.php?t=865319#post9873236

Well..... I never thought of it being a duty cycle. The ESC is only going to deliver the amperage the Motor requires. The question in my mind is. does the motor require large amp bursts at different duty cycles to produce different speeds, or does it vary dependent upon the load?

Kent, my electronically savvy friend, what say you?

I have an extra 40 amp esc. I just have to fix a wire or two.

[19000rpm]

What does your motor specs say on amps? But, if it's pulling 30A on the bench that's kind of the acid test. I like acid tests better than specs any day. ;D

The bottom line is you can use the bigger ESC. It doesn't hurt anything. You can always drop the prop size, but I think what you have is a good place to start.

I doubt if you'll feel comfortable for awhile at anything over 50% throttle except in bursts.

Now let's hear what el engineero has to say. ;D