Big Bobber

JIS?
Is it the 42" Cub you've gone for?

Larger Spans
I'm abit nervous of "designing" or even building a six-foot-plus-er.

Looking on OuterZone for Vee-Tails I came across this.
outerzone.co.uk/plan_details.asp?ID=10644
Plan for a 50" span kit for a diesel but it would be easy to fit an electric motor. It says it can be flown at very low speeds which is a very desirable characteristic.
Its built like a tank, would anybody like to hazard a guess at its weight?

Wing tubes?
The 1/8th barbeque skewers on my little Lysander gave a very rigid result but fitting tubes at the centre dihedral will be abit awkward. Could the centre dihedral joint be as per the usual and the tubes used to extend the wings part way up. This would also give the option of a larger span by using different wing extenders.

Sorry, Magpie,  it's not that easy!
If you enlarge the wing, you have to enlarge the tail feathers to suit! That in turn affects the balance, so you have to alter the fuselage.
So you may as well design your own beastie in the first place!
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Most larger models have the wing in two or three pieces, for transport and storage. Joining is done by - these days - carbon tubes built in to the structure, so the bending stresses are spread out.
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My Filip wing is in two sections, the Tango model has a three piece wing, but the 12 footer is a four piece.

 

Drat Drat and Double Drat

Hi Jon, you may not have noticed it but there was an S28 Savage Bobber on my bench while you were here.
 
It's available from Banggood
 
I am absolutely gobsmacked at the way prices have shot up, obviously I can't afford the postage any more.
If you can keep the weight down to 600gm the loading is 30gm/dm almost exactly the same as the FunCub so it would fly almost the same.
This project got shelved when I had difficulty gluing the rectangular carbon fibre longerons with Cyano and had to re-glue with Araldite, then I ran out of Araldite and moved on to something else.
The box contains a 1:1 plan and an illustrated construction manual. Pictures if you want them

Having seen the image just now I can kind of wind back the grey cells...  and yes there is a memory of the Bobber on your table. And I would like to get to that later after I have some skills in place...

After looking over their site and videos I have put in an order for Balsa Basics Super Cub | 42" 4-Ch RC Kit.  (plus the CA glues they recommend and some other bits). It comes with covering material so that to learn as well. I will pull motor, esc, servos and wiring from my stock.  I will have some questions to fine tune the selections in later posts.  

The vintagemodelcompany.com seem to love the idea of building in balsa and they seem to be a small company trying hard - the kind of folk I would like to support vs some back-room-operation in China.

Yes RC kit prices are unreal.  And then so many of the prices for just about anything are unreal these days.  Look when I came to the UK a pint was a quid.  That made perfect sense.  The cost of a pint today makes no sense.

When I started my apprenticeship (engineering not drinking) a pint of Federation Bitter was 1s 10d hapenny.

Jon put - will pull motor, esc, servos and wiring from my stock.
That's backwards! Find your stock FIRST, then you can adjust things so they fit, on the drawing and in the airframe, without having to butcher bits that you can't get at - later!
Prop -  motor - speed controller - they are all interactive! Changing one affects the others.
Start by deciding what prop diameter you can use, then find a motor that can turn it, and look at how many volts, for the battery cell count, and what blade pitch it can handle. Then look how many AMPS the motor draws to turn it. That takes you to the speed controller - however many amps the motor wants PLUS at least 25%. (we call it headroom).
Too small a speed controller is a bit like replacing a truck engine with one from a motorbike!
Radio receivers are all pretty much the same size, but servos are variable, both in size, power, and quality, as are batteries.

I have been using this site to check on various configurations.
rcplanes.online/calc_motor.htm

Good comment on the order of things.  My intial comment would be better stated as...
Look at what they recommend, what others have used with that weight and span and then see what options are 'close' to what I already have and what needs to be sourced.
And ensure the electrics work early in the process.

I will look at that suggested site for calculating the kit.

jon
There is a simple "order of magnitude" check you can do if you know the plane's intended all up flying weight.
For something like a Super Cub a figure of 60W/lb should be adequate. 100W/lb would give it a sparkling performance. 150W/lb would give it a vertical climb ability!
Don't automatically assume more power is better. High power itself can create handling problems than might not be evident at more modest power levels.   
A Watts/lb is more of a "check" than a calculation method so once you have selected a motor & prop it is worth checking if Watt figures are available for that particular motor/prop combination.

Like just about all the kits I've looked at, it doesn't give the built-up weight. However if you follow the link to their Standard Electronics Pack which has the specification for the ESC, motor etc you can compare it with others & also put their numbers into the rcplanes calculator to get thrust etc.

Something in the post for you Jon, it should arrive Friday. You've made an excellent choice. I think you should also look around your area for suitable ridge or hill soaring sites. Even a small lay by with a retaining wall. If the breeze is straight on you'll be able to fly left and right all day if necessary, NEVER turn towards the ridge or hill. Landing is easy, just drop it in the farmers field, he won't mind.

The basic balsa model arrived.  So here is an unboxing...

 

And inside, nicely wrapped packets and wood...  Minor scorching on the ply.  Tyres are nice and chunky.

 

 

And about 15 page guide and some sheets showing layout

 

And the covering material.  German source - any one used this before?  I now have a 'mini' iron for attaching it.

 

I got the CA recommended and some filer....

 

And they have recommendations for the electrics.  Note they have stock electrics that work with several models.  This might be at the powerful side for this model. I have watched Tony take-off with his Fun Cub like a bat-out-of-hell.  I wouldn't mind a more gentle life for this cub.

FEEDBACK PLEASE on their list please (given that we don't yet have a weight). And the 9 x 4.5 for the prop is suggested.

 

So I have some tools etc to bring across before I can get going on this one.  I will have questions no doubt.



 

If you weigh all the balsa & say if there's 50% offcuts then this will give you a starting point for the weight.

On the glue front I've been using SuperPhatic for the Cadet which is what I've tended to use on the small rubber kits & mostly its been fine but now I've started to sand the wings of the Cadet the wing tips have come away from the spar end formers - on both wings. I've a suspicion that the charring prevents the glue from wicking into the ends of the formers. I'm wary of sanding too much in case I make things undersize or make the former ends the wrong angle.
The charring on the VMC kits is nothing compared to the Dumas.

 

Oracover is rather like solarfilm, but thicker and heavier.
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As I have always said - if you have too much power, you can throttle back - but if you need 120%, you are stuffed!