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Mar 16, 2013, 10:49 AM
Cut it twice, still too short
dglo's Avatar
Build Log

Ivan Pettigrew 102" PBY Catalina


Here we go! I've wanted to build one of Ivans flying boats for several years now but thought I better wait until my skills developed a little more. I'm not sure if I'm ready, but jumped into the deep end anyway. This will be a challenge. Several people have posted build threads for Ivan's Mini-Cat, at 86" span, but I searched in vain for one of the "Big Cat", Ivan sent me the construction notes and half a dozen pics of the fuse construction, but other than that, I'm on my own. This is the biggest plane I've ever built, the first with retracts (Ivan's own design), including retractable tip floats, my first water-plane, and only my second plan build.

I haven't yet decided on a color scheme, but don't want to go with the rather drab military versions. Possibly the Coast Guard colors, or maybe one of the Water Bombers.

I will need a lot of help here, so any and all advice is welcome and appreciated, and if you see me doing something stupid, tell me!

Power will be brushless with differential throttle. I have a Futaba 7c 2.4Ghz, so with two channels dedicated to throttle, and two for retracts (landing gear and tip floats) I will have to put the ailerons on one channel obviously, but will probably use two servos with a Y-connector since the wing is in 3 pieces.

Doug
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Mar 16, 2013, 11:14 AM
Which means "what" to me?
invid66's Avatar
Cool. I'll be watching. The PBY is right up there for me, along with the Goose, and the Albatross.
Mar 16, 2013, 11:23 AM
Cut it twice, still too short
dglo's Avatar
I was warned about this plan, it is one of Ivans earliest, and although it is still doable, I've found numerous problems already. Ivan told me in an e-mail that it was a little rough and said the layout was horrible. I agree. It's in 2' x 3' sheets that have to be taped together, and getting all the lines matched up is about impossible. The sheet for the front half of the fuse even had a tapered dark line running vertically through it where it looks like two pieces were put in the printer but weren't quite lined up, so I cut that sheet on the line, lined it up and taped it back together. Some dimensions on the side view don't match with the top view, etc. I won't mention every detail that's amiss, but will point out a few of the one's that could cause problems. If anyone else decides to build this plane, just be sure to check, measure, and re-check everything. I've spent a lot of time studying the fuse plan and scratching my head, but have made some progress.

The first problem I encountered was the drawings for the fuse formers. The drawings on the plan aren't symetrical. Looking at the first pic below, one of the pieces was off by 5mm left and right of the centerline that forms the bottom of the hull. That would create a lot of difficulty getting the longerons straight later on. So I got out my ruler and compass and spent a couple hours redrawing all the formers. The top two in the first pic are Ivan's, the bottom two are the re-drawn ones.

The formers were made by edge gluing the sheets to get the width needed, and using bandsaw and knife to cut out. I made several copies of the drawing and cut out patterns and spray glued to the wood.
Mar 16, 2013, 11:44 AM
Cut it twice, still too short
dglo's Avatar
One more knock on Ivans plans, then I'll give him some kudos. This build recquires you to go right to the heart of the thing from the start. Before assembling the fuse, it's necesary to install the main retract crank arm into two of the formers, it wouldn't be possible to do after assembly. The exact location of the holes through the formers is very difficult to figure out, Ivan says to leave the bearing plates loose so you can make adjustments later on. The location of the crank is even shown at different heights on the side view and the cross section, note the red arrows in the pic below. So after a LOT of study, measuring and scribbling, I figured out if I went ahead and made up the gear legs too, I should be able to locate everything correctly, so that's what I did. I've never started a build by bending wire before opening a glue bottle, and I HATE bending wire.
Mar 16, 2013, 12:06 PM
Cut it twice, still too short
dglo's Avatar
Now for the kudos. The design of this landing gear is truly brilliant. It is a huge PIA bending the wire correctly, but once done I can see how ingenious it is. Entirely mechanical, with all three legs operated by one servo. No expensive retract units to buy, no air tank, etc. Since I would much rather build than buy anything, I love it. No, it's not very scale looking. The main wheels end up horizontally inside the fuse, rather than vertically in the side, but it's still brilliant. I looked at trying to design a protoypical folding A-frame main gear, but decided it would be far too complicated, expensive and probably not very reliable. I did find a guy online that sells a set of main gear he builds, although too large at 1/8 scale, for $995 for the mains, and another $400 or so for the nose, very cool, but no thanks!
Mar 16, 2013, 12:28 PM
Slip the surly bonds...
Sopwith Mike's Avatar
Subscribed! Have a great build dglo. My MiniCat flew very well and had over 100 flights, finally deciding that my incompetence was just too much for it to bear. I agree with you that the Coast Guard scheme is much more eye-catching than the camouflage ones.

Mike
Mar 16, 2013, 12:43 PM
Cut it twice, still too short
dglo's Avatar
Now for the PIA part. I don't know if it would be possible to make this gear without a wire bender, luckily I made myself one a couple years ago. It still took some cussing, pliers, hammer, sore fingers, and more than a few pieces of wire in the trash bin. The main gear legs are 5/32 and the crank arms 1/8. The toughest part is the hairpin curve in the main leg, it's very difficult to get the inside of the bend in a u-shape, which forms the stop for the crank arm. I got it as close as I could, then finished with a file so the 1/8 rod goes all the way to the end of the bend. While in bending mode, went ahead and made up the nose gear too.

The bright side to having to start the build by bending all this wire is, obviously, now it's DONE!
Mar 16, 2013, 12:59 PM
Cut it twice, still too short
dglo's Avatar
Thanks MIke, sorry to hear about the demise of your Mini-Cat, she was a beauty.

Since I already showed you my tool, (the wire bender), I'll show you another. I just made a balsa stripper. It works very well if the wood is soft enough. I just made some perfect 1/4" square sticks. I'm using #11 exacto blades in it, but I think it would work even better if I could find some scalpel blades, I think they are a little thinner? I couldn't find any locally, may have to order some. By removing the wing nuts and spinning the blade holder around, the other end is set up to hold the blade at an angle for making planking strips, I have a feeling I'll need that on this build.
Mar 16, 2013, 01:19 PM
Cut it twice, still too short
dglo's Avatar

Fuselage


I decided to assemble the fuse upside down using a foam block with grooves cut in it to hold the formers in place. Ivan suggested this as one option and has been done before. It's easy to do if you have a table saw. It makes sense to me since the top of the ship is a straight line all the up to the front, except for the front three formers. The key is to keep the formers whole at the top where they can later be cut out for the recess where the wing pylon sits, and at the front for the removable hatch. The long lengthwise groove has a 3/16 square stick down in the bottom to keep the top in a straight line, but not glued yet.
Mar 16, 2013, 02:45 PM
71% of the world is runway . .
Bart83's Avatar
Subscribed !! ,

Good luck with the build.

Cheers,

Bart
Mar 16, 2013, 03:25 PM
Registered User
Trevorh's Avatar
Congratulations on your choice, Doug. We'll be with you all the way. It sounds like you have sussed Ivan's retract design but, if it helps, there is a short article on the lessons I learned when having a go at it on my website.

Trevor
Mar 16, 2013, 04:09 PM
a.k.a. skcope
AVGDAY's Avatar
Doug-
Great choice with the PBY! One of my all time favorites. I have been collecting pictures/info on the PBY for a while- here are a few pictures of Coast Guard PBY's to get you thinking about colors. I like Ivan's retract idea- working out the scale retract mechanism in miniature is difficult! I'm watching!
-Scott
Mar 16, 2013, 06:34 PM
Cut it twice, still too short
dglo's Avatar
Welcome to all! I'm a slow builder so hang on for the long haul. Scott, the retracts are not very scale as I said. The legs simply fold up into the fuse like a standard folding leg, so that when retracted, you see the bottom of the tire, through the hole in the fuse, not the side of the wheel. Not very pretty I know, but functional, I'm not a scale fanatic by any stretch, as long as it looks pretty much like a PBY, and flies well, I'm happy.
Mar 16, 2013, 07:44 PM
Übung macht den Meister..
Deuce's Avatar


James
Mar 17, 2013, 04:01 AM
Registered User
Argyll's Avatar
As a complete newbie to the hobby I'm delighted to come across this thread as it'll show me I'm sure the skills and technical care to produce a spectacular finished product.

Good luck, I'll be visiting often.


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