K40 Laser

[Ray Wood 3Participant @raywood3]

Hi All,

Maybe if we asked Colin B to add a topic heading for "Related Hobbies" as the Model Engineer forum contains we can keep up with our other stuff, because there is much cross fertilisation between all the modelling disciplines, especially with Paul's laser cutter & other 3d printing technologies.

Anyway just a suggestion, although I post on the Model Flying & ME forums, I consider this one's best 😀I

Paul the PBY will need 2 more engines 😄

Regards Ray

[Paul TParticipant @pault84577]

Ashley

I want to keep this thread broadly within the realms of model boating and whilst the laser cutter is interesting its value to model boat builders soon runs out after 50 wing ribs.

The PBY Catalina has been a favourite ever since I built the Airfix kit when I was young, in fact the only large scale favourite planes that I don't have (at the moment) are a Short Sunderland and Mosquito.

Ray

Yes but what type of engine as I could easily use two brushless motors especially as they don't have any exhausts to spoil those high wing cowlings, or do I go for a pair of 15cc nitro engines and hide the mufflers in the wing.

Dear all.

I am like a kid in a sweet shop with all of these models to build, which will be ideal if we are locked down for the next few months.

Paul

[Ray Wood 3Participant @raywood3]

Hi Paul,

The Catalina is a lovely subject, these days electric is the more reliable option, I built a 73" cat in 1996 with a pair of .15's it flew well, I think your 108" span was designed for . 60 2 strokes. My little version was the 5A with the bigger fin & rudder the undercarriage is a challenging arrangement as the wheels are double jointed into the fuselage, be a sod to make !

Regards Ray

[Paul TParticipant @pault84577]

Hi Ray

The peculiar undercarriage is something that I am looking forward to building.

[Dave MilbournParticipant @davemilbourn48782]

Sooner you than me, Doc! I managed to make one simple davit from brass rods today and thought I was very clever! Now I have to make three more identical ones.

My abiding memory of the PBY was the opening scene from the film of "South Pacific", with Ray Walston as Luther Billis (why do I remember such arcane stuff?). I'd never seen such an exotic aeroplane before.

Dave M

[ashley needhamParticipant @ashleyneedham69188]

I am with you there, DM, I don’t mind fiddling for one complicated item..but making several more..all identical!

Paul. Berengar always wanted me to make a Catalina, but there are more than a few difficulties with this design than the others. For instance the high wing with the relatively high c of g, and how to arrange good access inside.

Ashley

[Paul TParticipant @pault84577]

Hi Dave

At this scale I am hoping to use suspension parts from RC cars for the fiddly bits of the undercarriage.

You are not the only one influenced by a certain film

The PBY has a certain grace and looks good both in the air and on the water, not so hot on land though.

Have a look at this link and then something sad link

Or for something really impressive link

Hi Ashley

As its a kit I'm hoping that someone else has worked out the c of g and access problems but the links (above) show the instability problems especially around changeable gusts and thermals.

Paul

[Paul TParticipant @pault84577]

Going back to a much smaller model.

I thought that you might like to see the brushless motor that I have for the Sopwith Pup.

Its a sweet little compact 400w unit with a built in 45a esc, it replaces a 30-35 glow engine. Sadly I cant find anymore and the french companies website is no longer open.

The I.C. units are potential contenders for the PBY.

Paul

[Ray Wood 3Participant @raywood3]

Hi Paul,

Great shame about the cat crash ! Too low & too slow with the gear down ! He ran out of flying speed in my opinion?

This is my cat drawing, and is proven 😀 balanced dry, tanks full would put it forward to the main spar.

I have American plans for 108" PBY  by Fred Novak, but guess what no mention of the C of G 😕

regards Ray

Edited By Ray Wood 2 on 30/04/2020 11:47:10

[Paul TParticipant @pault84577]

Hi Ray

I would also question his choice of flying location being so close to those hills he must have encountered changing wind sheer.

Thank you for the c of g information as this might well save me hours of work, the 108in drawings that I am getting are by Sid Morgan but as the scale is the same I would imagine that the basic mathematics will also be very similar.

With full tanks did the aircraft become nose heavy and, if so, could the effect be countered by adjusting the trim. Given the choice would you position the tanks further astern?

Paul

[Ray Wood 3Participant @raywood3]

Hi Paul,

The Nacelles are really quite small so there's only one place the tanks can go really behind the engine bulkheads,

I would always fly slightly nose heavy from as you can pull up,but rearward c of g and you in deep doo doo 😮

They also don't like too much angle of bank, as they fall out of the sky sideways unless your doing mach 2 .

Many B52 bombers did the same thing but only once !! Truly terrifying on YouTube 😕

Regards Ray

[Paul TParticipant @pault84577]

Hi Ray

In your opinion is there any advantage in moving the tanks down into the main fuselage to get some of the weight lower down, I realise this would mean using a positive pressure fuel supply but it might be worth it to improve the flying characteristics.

I've seen the YouTube disasters involving large wingspan / multi engined planes and they make for very sobering viewing, so different from the large scale single engine models.

With the PBY I will probably do a Howard Hughes when he flew the Spruce Goose and do a short flight at a height of 6ft over a flat calm stretch of shallow water.

Paul

[Ray Wood 3Participant @raywood3]

Hi Paul,

It's really just a parasol wing aeroplane with no problematic flying characteristics fuel weight & C of G not an issue, using normal exhaust back pressure works with the tanks in the nacelles.

The engines are close enough together on the cat for you to survive an engine out, of course electric twins have a massive advantage of lasting a lot longer 😀

Regards Ray

[Tim RoweParticipant @timrowe83142]

Tapered wings, downwind leg, big input of up elevator perhaps to stop height loss instead of increasing power = classic tips stall syndrome. Nasty crash but not in the same league as this one. Click here
I was only a couple of miles away at the time.

With Ray about keeping the tanks in the nacelles.

The expression goes:

CG too far forward, plane flies badly
CG too far aft, planes flies once!

The risk of a too nose heavy planes is that you can run out of elevator particularly when flaring for landing.

I would practice fast taxying on the step before going to the next stage or airborne.

Must get some pictures up of My Sig Sealane

Tim R

[Dave MilbournParticipant @davemilbourn48782]

I used to design R/C model aeroplanes about a hundred years ago, although nothing as big and exotic as a PBY. My rule-of-thumb was always to put the CG at 1/3 back across the chord from the leading edge. It was a good place to start and I never needed to move it much in either direction to optimise performance.

There were hard-and-fast rules about the position of the fuel tank relative to the carby, especially for competition aerobatic models. Yamada somewhat blew them out of the water with their pumped YS60 glow-engine but I've never strayed from putting the tank level with the carby and as close behind the motor as possible. If you start to experiment with pumped fuel systems then you introduce a problem area that you could really do without, especially when there are two large and expensive engines and several hundred quid's worth of radio gear hanging in there. Then there's the potential for accidents (I still carry the scars….don't ask!).

Anyroad, isn't this a model boats forum?? Nowt like owd geezers to wander off the subject, eh?

Dave M – More Old Boy than Hi-Boy these days…

[Ray Wood 3Participant @raywood3]

Hi Dave,

I'd agree, but there only seems to be a handful of us actually posting boat builds on here, shame really 😢

Still think we might have a month more before we can go and play boats …… & fly 😀

Regards Ray

[Paul TParticipant @pault84577]

Hi Tim

Thank you for your advice which is noted and will help during the build and subsequent 1st flight.

Hi Dave

I used to design R/C model aeroplanes about a hundred years ago

Yes I saw your name on the Wright Brothers original plans.

I take your point about pressurised fuel systems and bow to the combined knowledge of my fellow, and more experienced model builders about keeping the tanks behind the engines.

The fact that this is a model boat forum continues to bother me every time I post something about my aircraft, I don't want to push my luck with Colins good nature.

Hi Ray

Whilst the rest of the world staggers out of this catastrophe and slowly resumes normal life I fear that the elderly and infirm will be in isolation for a long time.

Paul

[Tim RoweParticipant @timrowe83142]

Paul – Suggestion

You could post in Soapbox in which anything goes except if it breaks the rules.

Maybe Colin would be happy with the concept that you are making a flying boat as supposed to a sea or float plane. I am building a Sealane from a SIG kit and it very definitely has a hull, rudder in the water and it will have to get on the plane before it goes flying and it behaves like a boat until it makes that transition.

If Ashley was brave enough to put some decent power in his "not so flying boat" and fit some elevators he would soon be airborne.

There are lots of cross-overs in the modelling disciplines and without wishing to stretch or bend the rules here, I think there is considerable benefit in introducing aero build techniques especially if reaching for high speeds or high stability.

This is a nice sedate forum and easy to follow al the threads (I do) whereas in the other place it is very busy and easy for threads to get drowned. My vote says that if it has a hull it's a boat. If it has wings as well or anything else for that matter it's still a boat.

And you haven't been told off yet

Tim R (Got the bits for a CL415 Fire Fighting aircraft – oops Boat!)

[ashley needhamParticipant @ashleyneedham69188]

Tim, the power is there, just need elevators…but would then need a licence and insurance and a place to fly other than Bushy! (And I am not that brave!)

My take on it is that these things have to be built differently if they are to spend their time floating, bit more robust and so on.

Ashley

[Paul TParticipant @pault84577]

Hi Tim,

Your Airboat is more qualified than my Cat because, just like a ship, it takes on water ballast!

Hi Ash,

In all these years I never thought that I would say this but we need you with both feet on the ground to maintain a level of sanity and responsibility.

Paul

[Bob Abell 2Participant @bobabell2]

Never mind all this chit chat!

Let`s see what you have done up to now, Paul

Bob

[Paul TParticipant @pault84577]

Hello Captain Bob

Let me introduce you to the Twins

Don't know yet if these 20cc units will fit in the PBY but I couldn't resist them, the bulkhead end of the mounts are 115mm dia and those exhaust outlets will make some noise.

Paul

[Bob Abell 2Participant @bobabell2]

Hi Paul

What make are they and…..

Have tested them yet?

What size of prop will you use?

Rather you than me, old Boy

Bob

[Paul TParticipant @pault84577]

Hello Bob

They were sold as 20cc units but they are Supertigre 2000s and are actually 25cc each.

No not bench tested them but both have very good compression and will make great spares for the two units that I already have for the Typhoon and ME109, at £50 for the pair it would have been rude not to buy them.

A 17in twin blade prop is a good guide to the recommended size for these motors but for the Typhoon and ME109 I will be keeping to scale and use either 3 or 4 blade units.

Its taking me back to my younger days when I used to fit big 2 & 4 stroke engines into boats and planes, of course back then we didn't have elf and safety (and I could run a lot faster) but for the moment I am enjoying myself.

Paul

Edited By Paul T on 01/05/2020 17:38:58

[Bob Abell 2Participant @bobabell2]

Hi Paul

I'm very pleased that you are enjoying life again

I suppose the Lazer cutter is nice to play with

You really are a candidate for a quality 3D Printer now?

just up your street

Bob

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