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Author Topic: Lindberg 1/32 PT109 running gear?  (Read 875 times)

plastic

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Lindberg 1/32 PT109 running gear?
« on: March 03, 2018, 01:08:37 PM »

I've just been given a new Lindberg 1/32 PT-109 kit.

I had one a few years ago with a pair of 600 motors, standard 2-blade props & shafts and brass rudders with a LiPo battery & '320A' ESC. It went pretty well but didn't have much endurance.

With better props & shafts, what would anyone recommend for motors & batteries - I'd like it to get onto the plane in a scale-type way, but I don't want a 100mph rocket ship that eats the battery in 2 minutes.

I'm thinking 3x 385 motors & 2mm shafts & 3-blade plastic props - What battery would best suit?
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Stan

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Re: Lindberg 1/32 PT109 running gear?
« Reply #1 on: March 03, 2018, 06:18:49 PM »

See my elco conversion in warships military. Three 385 motors and a 11.1 lipo battery. 2mm shafts 20mm props from prop shop.


Stan
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plastic

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Re: Lindberg 1/32 PT109 running gear?
« Reply #2 on: March 04, 2018, 12:25:22 PM »

11.1V Lipo? Won't that be a bit too juicy for the boat? I normally use 7.2 or 8.4 Nimh or NiCad racing packs and they make things shift - what capacity would give a reasonable running time without being too heavy so needing more power to get up on the plane?
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Stan

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Re: Lindberg 1/32 PT109 running gear?
« Reply #3 on: March 04, 2018, 01:09:36 PM »

The 385 motors handle the voltage no problem and give a good turn of speed.I think the capacity is 2200 or 2.2 amps. But if you happy with other types of battery then go for it.

Stan

 
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Andy M

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Re: Lindberg 1/32 PT109 running gear?
« Reply #4 on: June 14, 2019, 11:02:53 AM »

Hi, here is my PT109, when I bought it, there was no motor with it. I decided not to over power it and used the running gear it was supplied with, I used a smaller motor than I would normally have used on a model of this size.Scale speed for this size of model is only about 1mph so much more than that isnt realistic. The standard running gear is adequate for scale speeds and more. If you want to do scale speeds of 100 to 200mph, then the standard set up should be upgraded.
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JimG

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Re: Lindberg 1/32 PT109 running gear?
« Reply #5 on: June 14, 2019, 12:45:23 PM »

1mph won't get the boat onto the plane so definitely not scale speed. the correct speed is not the full size speed divided by the scale as this gives unrealistically slow speeds. Remember water does not scale down, a realistic scale speed for a PT boat is one which has the hull lifting on the plane in the same way as the full size.I believe that the calculation used in test tanks is Square root of scale times full size speed. So for 1/48 scale taking a max speed of 40 knots then scale speed is nearly 6knots. This will still probably look too slow when running.
Jim
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tr7v8

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Re: Lindberg 1/32 PT109 running gear?
« Reply #6 on: June 14, 2019, 01:08:19 PM »

Lindberg kit is 32nd scale so square root of 32  is 5.65 @40Knots is 7knots or probably 8-9MPH which is not too far off. Mine was a bit slower than that in its day.
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Jim

Andy M

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Re: Lindberg 1/32 PT109 running gear?
« Reply #7 on: June 14, 2019, 02:50:15 PM »

I have to disagree. Surely the distance covered in a certain time, times the scale of the model is the actual measurement, regardless of whether it is planing or not?
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Andy M

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Re: Lindberg 1/32 PT109 running gear?
« Reply #8 on: June 14, 2019, 03:03:34 PM »

A scalextrix car at 1/32 scale running at 8mph is doing a scale speed of about 250mph, am I wrong? Why should a boat be any different, apart from wanting it to plane? Is it only planing boats that the square root calculation applies? I have seen unrealistic speeds of battleships which I think spoils the effect. King George v battleship took 17seconds at full speed to travel its own length. It was only 10 mph or so slower than a pt boat, a planing pt boat done to same scale would look far too fast beside the battleship?
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Andy M

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Re: Lindberg 1/32 PT109 running gear?
« Reply #9 on: June 14, 2019, 03:06:14 PM »

To be honest, it doesnt matter if its doing proper scale speed or planing in a realistic manner (but too fast) as long as you are having fun doing it.
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JimG

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Re: Lindberg 1/32 PT109 running gear?
« Reply #10 on: June 14, 2019, 09:01:40 PM »

The square root calculation is used when model testing designs for full size in a linear test tank. It is intended to give the same waterline pattern as the full size would have to help in calculating the power needed to give that speed. I have seen one of these models being run in the Denny tank and it was travelling faster than you might expect it to. (This is long enough to show the curvature of the earth on the water surface, thus needing the rails on either side to be curved to keep the models the correct height for the full length.)
Jim
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Andy M

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Re: Lindberg 1/32 PT109 running gear?
« Reply #11 on: June 14, 2019, 11:55:29 PM »

Hi, I used to pass it regularly and always wanted to go in. I am sure it has featured in a few tv programmes. I know they use reynolds numbers for aerodynamic calculations, I would imagine there is a hydrodynamic version? 
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Andy M

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Re: Lindberg 1/32 PT109 running gear?
« Reply #12 on: June 15, 2019, 12:22:10 AM »

Hi, I had a search and hydrodynamics does use reynolds numbers. I didnt think it was as simple as square root of scale, it may be square root of size of hull? Even at that, hulls vary in width too, I think the reynolds system takes a lot more into the calculation. What if you decide to take the 1/32 pt 109 top off your boat and substitute it for a 1/4 scale jetski top, its still the same hull. I actually used a fibreglass mtb hull to make my jetski (in the 'your models' section of the site, andy mcgarrity) I had a flat planked top, with the hatch cut to suit the mtb, and planned to build some different tops for the same hull, I started with the jetski, pilot and girl friend, then sold it without building the mtb top. It actually went to the south of france.
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Allnightin

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Re: Lindberg 1/32 PT109 running gear?
« Reply #13 on: June 15, 2019, 09:24:32 AM »

The principle I always understood for scale speed in model boats is that the wake pattern produced when the model is travelling at a particular speed equates to a full size equivalent pattern at a different speed and the relationship between the two is approximated by the square root of the scale. For example a 1/100th scale model doing 3mph should have the same wave pattern as the real ship going at 30 mph.
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Andy M

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Re: Lindberg 1/32 PT109 running gear?
« Reply #14 on: June 15, 2019, 01:34:21 PM »

Hi, I know the realism comes from how it looks, sits in the water and particularly the wake pattern, it was just that I could get 2 different results from my same hull basing the calculation on scale?
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Andy M

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Re: Lindberg 1/32 PT109 running gear?
« Reply #15 on: June 15, 2019, 01:43:08 PM »

Here is the jetski/mtb , although I never built the mtb top, taking the jetski top off would have given me a different 'scale' hull effectively, with its top actual speed remaining the same but giving an entirely different scale speed.
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