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Electric power system questions for a large PBY-5a

Old 02-12-2006, 02:14 AM
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yankeecanuck
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Default Electric power system questions for a large PBY-5a

Hello to all. If you can take a few minutes and suggest a few a starting points for motors, ESC and lipo cells on a project I have started I would be very grateful.

I have on the building board a PBY-5a. This is a Precision Cut Kit of a Fred Novak design. Precision Cut Kits does a great job to cut many model aircraft designer’s plans into kits. The plans are from Vintage RC Plans.

This kit has a 108” wing span and I would estimate the airframe will weigh around 10 pounds. I also want to use 13x8 three bladed props on the electric motors.

Many thanks for any suggestions!
Old 02-12-2006, 02:14 PM
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Matt Kirsch
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Default RE: Electric power system questions for a large PBY-5a

First thing is, don't get too hung up on the exact prop size. If you end up with that exact prop, you just made a lucky guess, but the final prop size will depend on quite a few factors, the most important of which is how much clearance you have on that PBY. Because the engine nacelles are so close together and right over the fuselage, you're limited as to how big a prop you can turn. Is 13" the maximum? If not, what is? With electric, you want to spin the largest diameter prop you can to get the best efficiency out of the power system.

If the airframe is going to weight 10lbs, then the whole plane is probably going to weight close to 20lbs. What do the plans say about final weight? What have other builders of this plane said about how much theirs weigh?

Going with the 20lb target weight, and typical warbird-heavy wing loading, I would recommend a minimum of 2000 Watts split equally between the two motors.

Going with my favorite go-to motor brand, AXi, it looks like your 13x8 3-bladed guess was pretty darned close to right-on. Using a 7S LiPoly pack and drawing 41 Amps, the AXi 4130/16 will spin a 14x8 2-bladed prop at about 8500 RPM for an input of just over 1000 Watts. The rule of thumb to go from 2-blade to 3-blade is to reduce the diameter by an inch, so the motor should perform similarly on a 13x8 3-blader! If you need more power, you can always go to a 13x10.

The Horizon Eflite Power 60 motor will produce similar results, as it is uncannily similar in design and specifications to the AXi 4130/16.

One pack of 20C rated LiPolys of around 3000-3500mAh capacity per motor, and you're set.

Sounds like this plane was designed around a pair of .91 4-strokes?
Old 02-12-2006, 02:55 PM
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yankeecanuck
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Default RE: Electric power system questions for a large PBY-5a

Many thanks Matt, this really helps me out!
Steve..
Old 05-12-2006, 05:18 AM
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bythebay
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Default RE: Electric power system questions for a large PBY-5a

Hi,take a visit to this site and check out the float plane specs http://www.geocities.com/ivansplans/.I`m building his minicat ,83
' span , 4lbs ,dual geared 400s driving 3 blade 9x7 props
Geoff
Old 05-15-2006, 12:42 PM
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Friesel
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Default RE: Electric power system questions for a large PBY-5a

Sorry, I haven't fihured out how to post the pictures yet.

Hi all,

I thought I'd share my experiences at Top Gun with a large scale electric plane, a 103 " wing span, 21 lb Martin Mariner PBM-5A , my first non-gas/glow powered twin effort. The plane was made from Keith Sparks plans and modified to have flaps, retractable landing gear and landing lights, nav and strobe lights, and electric power.

The plane flies with AXI 4130/16 motors powerd by FMA (Kokam) 3P6S batteries (3.2 Ahr, 20C cells) with a total cabacity of 9.6 Ahr. The system uses the FMA Balance Pro charge and discharge system which has proven to be flawless and extremely reproducible in performance from flight to flight. This power system is extremely well designed and has eliminated all high power problems I initially experience with less sophysticated systems on this plane. I also use a digital Power monitor system to record current and voltage usage during the flight. This system swings Variprop 4 blade 13 inch diameter props adjusted to 9.5 pitch, producing 16 lbs of static thrust (both motors) at 6800 rpm drawing a peak of 90 amps. See pictures below.

The batteries weigh 3.25 lbs and are needed in the nose to balance the plane for flight. This plane first flew off water 2 years ago (same motors, different batteries), and later off of our local grass field after conversion to the retractable landing gear varient (-5A). The main landing gear rotates 180 degrees from pointing straight down to recessing in the fuselage sides pointing straight up. The gear his home made, since no one makes this commercially.

My son and I are shown with the PBM in the pictures below at TOP GUN 2006 in Florida. It flew3 rounds of Pro Am flights in 10 to 18 mph 45 to 90 degree cross winds (no joke, it was the worst winds I'd flown in with a scale plane) and placed 14th. The narrow landing gear was a liability, and I could have flown better, but then, I didn't. The plane flies with authoriy, accelerates and climbs as good as any glow powered twin I've had, much faster than scale. A plot of the battery usage during the 3rd round is shown below. In this flight, the plane flew 8 maneuvers and used only the twin engine feature as an option. This flight lasted 7 minutes and consumed 4.05 Ahr out of the 9.6 Ahr capacity. Hence, I'd guess that 14 minute flights like this are reasonable to expect with this plane/power combination. Battery temperature after landing varied between 95 and 113 F. There are small cooling holes in the front and rear gun blisters immediately below the guns which are hard to see.

For a non-aerobatic plane, it is quite fun to fly with all the scale options. Low fly bys are pretty neat. Take offs and landings can be pretty scale in less the hurricane winds. I converted the plane to an amphibian because I wanted to compete with it at sport scale events, but once I get my latest scale effort done (F4F wildcat), I plane to put it back to the sea plane version. I live on a lake, and love flying off of water as well as land, which is why I built the plane in the first place. It started as a simple sea plane project and got blown completely out of proportion. Ah, but that's the fun of Flying RC, no limits but the imagination (and maybe budget)

Denny Friesel


[img][/img]

Old 05-24-2006, 03:52 AM
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aeajr
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Default RE: Electric power system questions for a large PBY-5a


ORIGINAL: yankeecanuck

Hello to all. If you can take a few minutes and suggest a few a starting points for motors, ESC and lipo cells on a project I have started I would be very grateful.

I have on the building board a PBY-5a. This is a Precision Cut Kit of a Fred Novak design. Precision Cut Kits does a great job to cut many model aircraft designer’s plans into kits. The plans are from Vintage RC Plans.

This kit has a 108” wing span and I would estimate the airframe will weigh around 10 pounds. I also want to use 13x8 three bladed props on the electric motors.

Many thanks for any suggestions!
If you have completed the project, let us know how it went.

If you are still looking for help, perhaps the info posted at this thread might be helpful.

Sizing Electric Power Systems - Starts at post 2
http://www.rcuniverse.com/forum/m_43...tm.htm#4310056

Old 10-02-2006, 10:45 PM
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LaxLife72
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Default RE: Electric power system questions for a large PBY-5a

I'm selling my HVP PBY Catalina ARC new in box
http://www.rcuniverse.com/market/item.cfm?itemId=227365
Old 03-06-2012, 06:08 AM
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untel56
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Default RE: Electric power system questions for a large PBY-5a



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