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Bob's PushyCat build

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Bob Cotsford21/02/2014 09:57:56
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time to get the ball rolling, so here we go. I doubt there will be much that's not already been covered in the excellent builds that have gone before, but anyway:

I'm starting with the wings, first I extend the outlines on the plan so that I can lay the wood on top and transfer the shape

enhance the plan.jpg

Next carve up some light 1/4" balsa and tape it together, I've aligned the grain of the front sheet with the leading edge as I think it helps with warp resistance and avoids having exposed end grain the length of the wing

strap the wing together.jpg

Fold back the panels and apply some aliphatic, not to much though as most will be squeezed out in when the wing is flattened out.

fold back and gob on some glue.jpg

Leave it a minute to let the glue soak into the wood before flattening the wing, wiping off the expelled glue and taping over the joints - don't want the panels sticking to each other!

two wing panels ready to press.jpg

Next I laid the panels on top of each other on a flat surface and weighed them down overnight to dry.

I have two motors to hand, a noname 2212/06 2200kv 250W at 28A from my ex-Funjet, or a Keda 2837/08 1800kv rated up to 500W at 45A. I'm thinking of using the Keda if for no other reason than it already has a cruciform mount fitted. I don't HAVE to use all 500W after all.

The 3/16" sheet I have is a bit heavier than I'd like so there will be no need for the spruce strip on the bottom, while the 1/8" stock for the fuselage sides is pretty light, I may need to move the battery forward.

Colin Leighfield21/02/2014 11:13:30
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I don't think that this will take you very long Bob, I'm going to enjoy following this build.

Bob Cotsford21/02/2014 12:28:34
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Colin, unless there's a break in the weather this will be a very quick and dirty build - the booms and fins are currently sat on the kitchen worktop with half a dozen cans of soup holding them flat while they dry.

Points to ponder - I'm wondering about the light 1/8" sheet sides with next to no doublers, I would have liked to see something to brace the sides along the hatch so is it worth adding 1/32 ply strips along the edge? Motor mount bulkhead - ok, it's a pusher but would it be worth adding a local doubler to spread the bulkhead to side join loads? Am I thinking too much IC type building?

Colin Leighfield21/02/2014 12:42:36
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Bob, I think the design doesn't have much "ding resistance". so laminated the sides from 3mm balsa and 1/64" ply, if you go back in the thread you might see it in my early photos. I also used 1/2" triangular in the corners. I saved some weight by shortening the fus at both ends and it has come out at 26ozs, pretty much the same as everyone elses'. The triangular helps to give a reasonable shape when sanding without leaving you with hardly any joint surface, which I think is a risk with the design.

The full side area doublers solve all the problems and give tough but flexible sides which glue up into a strong and light fus without taking much time. I also reinforced the motor bulkhead join with some triangular fillets. I too am influenced by i/c experience, but in this case I think these are worthwhile improvements with no down-side. Personally, I think it looks better when shortened as well as saving weight, but that's only my opinion.

ken anderson.21/02/2014 13:41:10
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bob......I'll be following your build here.........the AUW will be around 24 oz so I would worry too much about breaking it....they do tend to break where the booms fasten on to the wing if you land and hit the booms on the ground first...but the laminated nose is pretty strong.....a lot of these pushycats will need to be scrutinised at the green acre's do...as they have been heavily modded......... devil ...

ken Anderson ne...1 .....scrutinising dept.

Colin Leighfield21/02/2014 14:36:37
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Ken's right of course. I could be banned as the builder of a pseudo "non-Pushy Cat", have the model jumped on and then be burned (me that is) on the top of Barr Beacon. (It's only a mile away).

However, I will turn up, that is if the model survives that long in the first place! Like Captain Custer, I will accept my fate.

Colin Leighfield, ne zero, counterfeit PC dept.

Bob Cotsford21/02/2014 17:02:30
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The wood I used for the booms is pretty hard so I hope I'll be safe from tailstrike damage Ken. I put some doublers in anyway - a couple of grams worth of 1/32" ply?

doublers.jpg

So on day 2 I've got this lot, just need to cut some formers and make torque rods next

a very short kit.jpg

john stones 121/02/2014 17:32:17
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I put a ply doubler full depth in battery area Bob

weighs 24 1/2 oz mine. don't worry about the scrutineer

I hear he's partial to firewater wink

Erfolg21/02/2014 17:33:10
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I was wondering about the comment with respect the booms having an apparent weakness with respect to the booms being susceptible to braking on landing.

I would expect it is the top of the boom that is crumbling. A fix that would not increase the weight by very much, is to incorporate a spruce spar as is included on the bottom. Then the crushing/crippling forces would be principally taken by the spruce members, the balsa just being the separator, seeing very little of the forces, as we all know spruce is far stronger than balsa.

It is a pity that this bit of info was not made earlier, still, better late than never.

Steve Hargreaves - Moderator21/02/2014 17:33:56
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Just adding a post so I can follow along Bob......the PC has quite taken my interest...yet ANOTHER to add to the list!!!

I guess the original PC was built light as it used SC cells....the version on the Traplet site said ir weighed 2.2kg......can that be true??? sad

ken anderson.21/02/2014 17:58:12
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Posted by john stones 1 on 21/02/2014 17:32:17:

I put a ply doubler full depth in battery area Bob

weighs 24 1/2 oz mine. don't worry about the scrutineer

I hear he's partial to firewater wink

 

..............................................................................................................................

first class job there bob...................I'm just off to have a brisk walk around our estate then out with the pipe and slippers before a drop of the good stuff(firewater).....I may even have one or two with the commoner's etc... teeth 2

 

ken Anderson ne..1 .......pc inspection dept.

 

Steve-ignore the 2.2kg...I also read that...the pc would be lucky to fly at that weight.....

 

Edited By ken anderson. on 21/02/2014 17:59:36

Erfolg21/02/2014 18:03:02
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I am not sure that it would have been 2.2kg would it? That would be +70oz.

My 26 oz model would look positively anaemic, rather than a rather lardy 2 oz over weight, from Ken's Mode value of 24 oz. Either way my version flies very well, not being as tuby as I thought.

On the basis that the original was not just lardy, using Nicads, it was probably low powered, on a brushed motor, possibly 80 watts?

Adding a little more weight to the boom would be pretty trivial, and probably very much worth while.

It does always surprise me how fast some builders are and apparently produce work of high standard, well done Bob.

Edited By Erfolg on 21/02/2014 18:03:27

Bob Cotsford21/02/2014 18:12:26
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Posted by Erfolg on 21/02/2014 18:03:02:

It does always surprise me how fast some builders are and apparently produce work of high standard, well done Bob.

Edited By Erfolg on 21/02/2014 18:03:27

the 'apparently' applies here! When I say it's a quick and dirty build, I mean exactly that!

Steve Hargreaves - Moderator21/02/2014 19:55:07
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Posted by Erfolg on 21/02/2014 18:03:02:

I am not sure that it would have been 2.2kg would it? That would be +70oz.

Edited By Erfolg on 21/02/2014 18:03:27

See here Erf......2.2kg......bloomin' heavy

John Privett21/02/2014 20:29:07
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2.2kg is clearly a mistake. The original article gives a flying weight of 28oz in the summary table at the end.

brfc721/02/2014 21:00:37
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Looking like a bald PC so far yes bookmarked 

baz

Edited By brfc7 on 21/02/2014 21:01:20

PatMc21/02/2014 21:30:22
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Posted by Erfolg on 21/02/2014 18:03:02:

On the basis that the original was not just lardy, using Nicads, it was probably low powered, on a brushed motor, possibly 80 watts?

The original used 10 RC1200 nicads (probably about 12oz) & a brushless Mega 16/15/4 (2.7oz) giving 300W dropping to 235W after 30secs. Dunno what motors & lipos people are using but a typical 3s 2200 weighs about 6.5oz.

Colin Leighfield21/02/2014 22:16:06
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I don't have it with me, but I think the QEFI build article said that the original weighed 28ozs. I did not like the design of the booms, thinking they were asking for trouble. I slimmed them down, left off the spruce skids and inserted full length 3/16" spruce stiffeners (longerons)?, positioned so that they formed the glue face directly onto the bottom of the wing. There's a photo in the thread, but for some reason I can't get it to transfer onto this post.

Colin Leighfield21/02/2014 22:18:03
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image.jpg

Colin Leighfield21/02/2014 22:18:51
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Just managed to do it, previous posting.

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