Prop'r 3-Blade Prop size
11-30-2011, 02:31 PM
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Prop'r 3-Blade Prop size
I'm putting together a Seagull T6-A Texan II with an E-90 brushless electric motor and matching 90 amp ESCI was thinking about ganging up two 11.1v 3200 mahlipos, but still haven't quite figured that one out....anyway, the question is this: What size 3-bladed prop would be appropriate (if any), the full scale aircraft sports four blades, but Im pretty sure that isn't do-able at this scale. Common sense RC has the following chart for the motor, but it seems to be only for standard props. Can anyone help me out? I'm more of a glow guy and I don't want to screw this up! Thanks!! http://www.commonsenserc.com/product_info.php?products_id=422<-Link to the chart***
11-30-2011, 03:00 PM
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RE: Prop'r 3-Blade Prop size
If you hook up your batteries in parallel...which is postive to positive and negative to negative then you have 11.1V and 6400 mAh available.....but if you hook up your batteries in series which is positive to negative then you'll have 22.2V and 3200 mAh available....I doubt that is what you want as voltage is the issue....
For glow and gas engines going form a 2 blade to a 3 blade...go down one size in diameter but up one size in pitch...so a 12X6 two blade becomes an 11X7 3 blade
For glow and gas engines going form a 2 blade to a 3 blade...go down one size in diameter but up one size in pitch...so a 12X6 two blade becomes an 11X7 3 blade
12-01-2011, 05:36 AM
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RE: Prop'r 3-Blade Prop size
I rarely disagree with Jetmech, but he missed it this time. If you want to go from a 2-blade to a 3-blade, drop down one inch on the diameter, but keep the pitch the same.
The method Jetmech described is for dropping a 2-blade down to a smaller 2-blade
The method Jetmech described is for dropping a 2-blade down to a smaller 2-blade
12-01-2011, 11:40 AM
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RE: Prop'r 3-Blade Prop size
558th:
This is by no means a rigorous answer, and I think you're going to find some amount of experimentation may be required to get one. Jetmech mentioned series/parallel connection of your batteries, and if you're using two 11.1 LiPo's together, they'll have to be in series to get a nominal voltage of 22.2V. You'll need at least that much voltage, because the E90 is rated at 325Kv, or 325rpm/Volt. Which means you can get a maximum rpm around 7800, given that the LiPo's will charge up to about 12V each.
H9 says your Texan's flying weight is around 9.3lb, which works out to 149 oz. My guess is that between the motor/esc/battery combo, you won't end up saving a large amount of weight over glow power. Commonsense RC's chart for that weight aircraft shows them running a 17x10E prop on 22V for sport performance, or a 15x10E on 29V. The problem running a 17" prop on the Texan is going to be ground clearance. It's built for a .75-.91 2S, which generally means a prop between 13 and 15".
As Mike mentioned, the rule of thumb on 3 blades is to drop 1" in diameter for the same pitch. I don't know if that will hold with electric props, but it's a place to start. So what I'd first try would be something like a 15x8 3 blade with the two 11.1V LiPo's. You'll need to find somebody with a wattmeter to check that this draws an acceptable amount of amperage so you don't end up burning out the motor or the ESC. Gut feel says you'll probably be able to get the plane off the ground, but performance may be so-so. The glow motors would probably be turning around 9500 rpm, so the electric is giving up around 2000 rpm, which means less thrust and lower airspeeds.
Ultimately I think you're going to end up with something like a couple of 4000/5000Mah 14.1V packs hooked in series with a 14x6 to 8 3-blade. I just looked over at the APC website, and they don't make electric props bigger than a 13" 2-blade. Perhaps someone with more experience can talk about the pro's/con's of running glow props on an electric motor.
FWIW, I'm flying a 60 sized Kaos with a 50-55/400KV motor on a pair of 4000mah 11.V packs hooked in series. With a 13x7 electric prop pulling around 735 watts, the performance is decent (meaning it'll go vertical, but not straight up forever
). Decent airspeed, but it's not a blur!
You might also try this question over in the Wattflyer forums... there's a bunch more electric experience over there than I've got. Hope this helps.
This is by no means a rigorous answer, and I think you're going to find some amount of experimentation may be required to get one. Jetmech mentioned series/parallel connection of your batteries, and if you're using two 11.1 LiPo's together, they'll have to be in series to get a nominal voltage of 22.2V. You'll need at least that much voltage, because the E90 is rated at 325Kv, or 325rpm/Volt. Which means you can get a maximum rpm around 7800, given that the LiPo's will charge up to about 12V each.
H9 says your Texan's flying weight is around 9.3lb, which works out to 149 oz. My guess is that between the motor/esc/battery combo, you won't end up saving a large amount of weight over glow power. Commonsense RC's chart for that weight aircraft shows them running a 17x10E prop on 22V for sport performance, or a 15x10E on 29V. The problem running a 17" prop on the Texan is going to be ground clearance. It's built for a .75-.91 2S, which generally means a prop between 13 and 15".
As Mike mentioned, the rule of thumb on 3 blades is to drop 1" in diameter for the same pitch. I don't know if that will hold with electric props, but it's a place to start. So what I'd first try would be something like a 15x8 3 blade with the two 11.1V LiPo's. You'll need to find somebody with a wattmeter to check that this draws an acceptable amount of amperage so you don't end up burning out the motor or the ESC. Gut feel says you'll probably be able to get the plane off the ground, but performance may be so-so. The glow motors would probably be turning around 9500 rpm, so the electric is giving up around 2000 rpm, which means less thrust and lower airspeeds.
Ultimately I think you're going to end up with something like a couple of 4000/5000Mah 14.1V packs hooked in series with a 14x6 to 8 3-blade. I just looked over at the APC website, and they don't make electric props bigger than a 13" 2-blade. Perhaps someone with more experience can talk about the pro's/con's of running glow props on an electric motor.
FWIW, I'm flying a 60 sized Kaos with a 50-55/400KV motor on a pair of 4000mah 11.V packs hooked in series. With a 13x7 electric prop pulling around 735 watts, the performance is decent (meaning it'll go vertical, but not straight up forever
). Decent airspeed, but it's not a blur!You might also try this question over in the Wattflyer forums... there's a bunch more electric experience over there than I've got. Hope this helps.
12-01-2011, 01:50 PM
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RE: Prop'r 3-Blade Prop size
I'd probably put a two blade on it first and get a good feel for what the entire combination actually likes before moving to a three or four blade.
Zinger http://www.zingerpropeller.com/_2_blade_.htm says
18x10 two blade can be replaced with
16x10 three blade
16x8 four blade
They sell modular props (fairly expensive) with swappable blades so you can get just about any size three or four blade. If you're looking at APC, Graupner, etc; you take whatever size they have and hope it works.
Zinger http://www.zingerpropeller.com/_2_blade_.htm says
18x10 two blade can be replaced with
16x10 three blade
16x8 four blade
They sell modular props (fairly expensive) with swappable blades so you can get just about any size three or four blade. If you're looking at APC, Graupner, etc; you take whatever size they have and hope it works.
