108" PBY

[daviator]

 I started a PBY  from plans by Robert Sweitzer 3 years ago.  I went as far as I could without a decision on the landing gear and power system.   
It is back on the bench now and the landing gear is installed and operating.
Electric power is my latest decision and Temac membership is obviously the next decision! 
I met Frank Van B through the Bramalea club a few years ago and he had some power system suggestions.  I must admit , I didn't know what I was getting into!
At the time I was just getting back into glow power models and had never considered electric for this plane. I'm now convinced that this is the way to go and I need some advice on what to use.
I've mocked this model up too estimate the finished weight.  With 650 gm X 2 for the motors, 750gms X 2, 6 cell lipo  ,6 servos and batteries for the receiver ,floats and landing gear it weighed in <18 lbs. I want it to be amphibious.  Some say, I will need more power to get off of the water.   
The Motocalc program gave me some interesting numbers. I had originally worked with the 100w per pound theory but the Motocalc says otherwise.
The problem with this model is the maximum propeller diameter of 12". Finding a motor that will fly this beast with that propeller are few and far between.

[Wingnutz]

Dave,
This sounds like a fabulous build! Can't wait to see it. You are brave building it as an amphib with working retracts!
Beyond doing the normal amps, volts watts kv calculations and suggesting three blade props (did the real PBYs use 3 bladed props?) I can't offer much help but Andre Laurent who is a TEMAC member flys a 30 lb model of a Grumman Tiger Cat with electric power and three bladed props. His props are significantly bigger than 12" but he's knowledgeable about heavier multi-engine electric powered models...might have something to offer.

[Michael]

3 or 4 blade propellers would work.

That is an amazing airplane.

[Papa]

A couple of E-Flite Power 60, 400kv on 6s  with two 50A ESc's might do the job. 3 bladed 12x7 would be pretty powerful.


Jack.

[piker]

Wow!  Nice build, Dave!  Welcome to the forum.

That's my winter build plan for NEXT winter, 2015/16.  The Cat at 108" with retracts.  It'll be fantastic to see yours finished off and joining us at our regular float fly's.  As the local seaplane fanatic, I'm glad to see another big flying boat joining the rest of our builds for this year.  Wow again!

If you're estimating <18lbs then a couple of motors on 6 cells each will probably be fine.  Let's see...  6 cells x 4.0v/cell = 20V x 40A (conservative) = 960W x 2 motors =1920W.  1920/18lbs = 106 W/lb.  That's almost the same power loading as my Sandringham, which weighs 16lbs on 3cells per motor (four motors) at about 37A.  A respectable power loading and will probably be perfect for this plane.  However, if you think the plane may come out over 18lbs you may want to consider 8 cells per motor.  You probably won't need the extra power, but it'll be nice to have it if things change as you finish off the plane.

Re. needing more power to take off from water vs land... My opinion has always been... Nah!  You may need a bit more power to carry heavier floats when converting from wheel, or you may need more power if the plane isn't set-up well, but generally, no.  When the plane is hydroplaning, the resistance of the water is minimal... probably less than a grass runway on wheels.

Please keep this build thread active.  We'd really like to see this plane evolve!

Robert

[piker]

The Motocalc program gave me some interesting numbers. I had originally worked with the 100w per pound theory but the Motocalc says otherwise.

What is Motocalc telling you?

[daviator]

 Thank-you all for your comments.  The Pigboat will always have a special place in our family. Its a long story, but this model started off as a tribute to my late father in law and our families aviation roots. The plans and plastic package were a gift and they said make it fly..... It will fly!  I  had the pleasure of working on the PBY for 5 years, early in my career. I know the machine and am proud to say that very aircraft is still airworthy and undergoing another restoration in England.

Meanwhile ,back in the workshop.......... Here are some answers to some of the questions!
  Motocalc based the calculations on the finished weight without motors,lipos and speed controls. I went a bit high and used 15 Ibs. I selected  Trainer performance with 1450 sq in wing. 12x10 props, direct drive brushless,  400' asl and thick semi symmetrical wing. Desired flight time 10-13 minutes.

The top 5 motors based on 98-100% efficiency include Scorpion HKIII-4020-1350 , SII-3026-1190.  Kontronik Tango 45-13  12V  and 2 Hyperion motors of similar performance. These motors are between 1600 & 1900W each!!
These things are appear to be top of the line and not cheap!  Suggested batteries are 2 X 3200SHD 6P and 5p for the Tango and Hyperion.  For scale appearance I would like to use 3 blade props.

My initial concern is the high KV on these motors with 6 cells. The poor propellers are going to be supersonic!  My electric heli friends tell me the ratings are no load numbers and the props will make them do there job nicely.

I got into float flying 2 summers ago and I've learned a lot. I love It! I agree with Robert on the power requirements on water. Once we're on step it should be fine.         

[Papa]

Where did you get that landing gear?


Jack.

[daviator]

Hello Jack.
I purchased the gear from Century Jet.  I went with the electric version. It is built specifically for this model, but I've got a few issues with the quality. Nothing that can't be fixed, but for that kind of money, I shouldn't have to deal with it.
The nose gear doors have been a challenge, but I think I have it fiqured out now. 
If you are interested, or know of anyone looking for a pnematic version, let me know.  A fellow club member in Beeton has a set and I believe it is for sale!     Dave

[piker]

Hello Jack.
If you are interested, or know of anyone looking for a pnematic version, let me know.  A fellow club member in Beeton has a set and I believe it is for sale!     Dave

Ummm... YA!   I am VERY interested in a set of that gear, especially pneumatic!  Where do I send the money?!!

So, I was thinking more about my power recommendations last night and feel that, especially if you're looking for scale type performance, 6 cells per side will be plenty.  8 cells would almost certainly be overkill.  For example, my Sandringhham is powered at just over 100w/lb and will climb out quite aggressively and will take-off from grass, from it's belly, and from water at half throttle.  If you went to 8 cells per side, and a typical loading of 40-50A, you would have closer to unlimited vertical, aerobatic type performance.  Not necessary and not attractive    My CL-215 Water Bomber, and Colin's CL-415 enjoy over 150w/lb, which is fun, but certainly not necessary or "scale"...

Where do you fly from water, Dave?  What planes have you been flying?

We will be float flying this weekend (see Other Events for my post... in a bit when I get it up there).  You should join us and bring a plane or two... although we only fly electric there   

[daviator]

Re : Piker     
I think 6 cells will be fine. Scale performance is the main objective. A previous post suggest the Eflite 60's but their minimum prop size is about 14". Don't know if 12" would be OK?
I started float flying with the Niagra club. Haven't seen them since they moved to the new location. 
The Beeton Pond is a favorite, also a member.  Also flew with the Burlington guys at the conservation area this spring. Nice location.
My trusty Goldberg Eagle with a Saito 56 is on floats wheels and skiis.  My electrics are the Formosa II with the R/C timer pylon motor. Also fly it on floats. For a little plane, it gets a lot of attention!! The Cap232 is  my intro to 3D electric.   My daily driver this summer is a Goldberg Chipmunk with the DLE 20.  Last summer the DLE was in a  Ultimate 60.
Quiet summer for the gliders. 1- 2m electric and a 3m  for aero tow.
I'll see if I can track down the owner of the gear later this week ..   

[piker]

It's been a while since I worked with props for an E-Flite 60.  You'll probably have to go to 3 blade and deepen the pitch a lot.

I (we... the other float flyers in TEMAC) need to make a point of getting out to more local float flying events next year.  They sound like fun.

Your fleets sounds very nice... but you need more seaplanes  (I tell that to everyone)

Thanks for looking into the retracts for me.  They do look great.

[wollins]

I started a PBY  from plans by Robert Sweitzer 3 years ago.  I went as far as I could without a decision on the landing gear and power system.   
It is back on the bench now and the landing gear is installed and operating.
Electric power is my latest decision and Temac membership is obviously the next decision! 
I met Frank Van B through the Bramalea club a few years ago and he had some power system suggestions.  I must admit , I didn't know what I was getting into!
At the time I was just getting back into glow power models and had never considered electric for this plane. I'm now convinced that this is the way to go and I need some advice on what to use.
I've mocked this model up too estimate the finished weight.  With 650 gm X 2 for the motors, 750gms X 2, 6 cell lipo  ,6 servos and batteries for the receiver ,floats and landing gear it weighed in <18 lbs. I want it to be amphibious.  Some say, I will need more power to get off of the water.   
The Motocalc program gave me some interesting numbers. I had originally worked with the 100w per pound theory but the Motocalc says otherwise.
The problem with this model is the maximum propeller diameter of 12". Finding a motor that will fly this beast with that propeller are few and far between.

Ok, Dave ... I've been working on some numbers for my winter project and the process has been beating me up. (so I understand your frustration! lol!) However I found a solution to my needs and so thought I'll try to see if I can find a solution for your needs. (since I was doing the research anyway!)

Here's what I've come up with.

The common motors in the size I think are needed for your plane are the .60 size equivalent sizes. Examples are Eflite 60 (as some have already mentioned), and as you have already pointed out the Scorpions, Hyperions (I'm a big fan of these!) Kontroniks etc etc.

As you have also pointed out these are relatively expensive motors and since you mentioned that,  I started looking for the "second tier" (but good) motors in this size. The G-Force 60, Tacon Big Foots, The Turnigy G60, Monster Power 60 (which btw is made by the same folks who make the Tacon motors. lol!) etc etc.

Anyways, to make a long story short. I've done my research on the Turnigy G60's for you (just cause I was researching G25's for mine) and I came up with the following numbers specifically for the 500KV version.

12X6 MAS 3 blader
43A
22V (6S pack)
950W

Times 2 is 1900w.  This puts you at about 105watts a pound.  Now IMHO this would be sufficient (and I'm sure Robert would agree with me even though it seems a bit low) however as Robert pointed out my waterbomber (and his) run at quite a bit more than that. But this is because we like to take off from grass as well.  You don't have that problem because you have wheels! (We do not. )

Having said that, we can still do a little better than that. These numbers are based on your AUW estimate of 18lbs, part of which was based on your motors being 46.5ounces and your batteries weighing 53.5ounces. (you mentioned 650 gm X 2 for the motors, 750gms X 2, 6 cell lipo)

Well, the two Turnigy G60's I suggest weigh in at about 27 ounces (total of both) and the 6S 4000mah batteries I used in my calculations weigh in at about 40ozs. (total of both)  So based on my suggestions, compared to your weight estimates I've just saved us 33ozs or a smidge over two pounds. This now puts us at a very respectable 120w per pound, and a nice 11 mins of scale flight time. (you did mention 10 to 13 as desirable right? )

Just my two cents.

Ok, I'm gonna go take a nap now, my brain is hurting.

Colin   

 

[piker]

Nice work, Colin!

[frajolex]

faaack!!! PBY with retracts!!! simply..


A-W-E-S-O-M-E-!