Wing jig

[kc]

Sirio,

Did you get the instructions with your Astro Hog plan?  Does the plan show full rib details?  If you have the instructions you will see they show tabs on each rib to avoid the need for a jig and just use a flat board.  Jig should be better I reckon.  

 

You might like to know that Sig ( also Great Planes ) publish their instruction manuals online.  The link on the site for  Sig ( Sigmfg.com )is difficult to find ---Instuctions & Video tab at top-Manuals-RC Sport-,then click on the Astro Hog picture ( not words!) to download the PDF file.

 

www.sigmfg.com/cgi-bin/dpsmart.exe/MainMenuFV4.html?E+Sig   is the full detail if it gets past the Modelflying censors!

 

Also check the American equivalent to the Modelflying site  for many comments on this classic model.   Also note that Radio Modeller ( now incorporated into RCME ) published in Jan 1985 an 82 percent version at 58 inch span for a 40. Plan No RM283 by David Boddington.   If you have the engine and have a car to take a six foot wing then I would stick with the original, otherwise the 40 size seems attractive.

 

Edited By kc on 22/06/2009 11:09:14

[Sirio]

Hi kc,yes that is the plans Ive orders with the instructions but Ive still not received them,

so i downloaded the instructions for now so i could get a good read at them.

in the instructions it says about the aileron torque rod and precut parts etc,

do you think on the plans it will have this information to make them myself .

apart from that it seems pretty straight forward.

i hope lol

[kc]

A proper scratch build plan will have full component details, but many English kit makers were cunning and left some important details off so you would have to buy another kit to build again.  Also the plans were not always full size. Fortunately many American kit makers supplied full plans.  You will have to wait and see!

 

Because of this experienced modellers buying a kit will draw around every component before starting work to enable them to repair crash damage or build another one.  It is important to draw accurately around each component  with a sharp pencil onto paper noting material,balsa or ply, grade, thickness and grain direction. 

 

If the plan is full size then an experienced modeller will probably be able to deduce the component shape.

 

The most important thing is to get the aerodynamic bits right. 

[kc]

Torque rods

They are easy to make from a threaded rod set with tube or plastic bearings, avail from local model shop or from SLEC.  Important to remember 3 things

1 Put the tube or bearings on BEFORE bending.

2 Make a left and right hand pair ( make a pattern from soft wire as a guide )

3  Ensure there is correct horn rake.  That is either at 90 degrees to aileron at neutral ( no rake ) or raked back or forward to give rake according to plan ( depending on whether

 horns on top or underneath -that is either high wing or low wing model )  Raking affects whether the ailerons have differential -that is more up movement than down.  This affects the flying characteristics and you must be guided by the designer who will have experimented and got it right on such a classic design.  Get it wrong and it will fly badly!

 

Torque rods use 1 aileron servo,  now that servos are cheap and small it is common to use 2 servos mounted nearer the ailerons instead of the torque rod arrangement.  This means using a Y lead or 2 seperate channels for ailerons and modern 5 channel computer radio ( such as Futaba 6EXA series and better ).  Also it means using extension leads which have to go thro a paper tube in the wing out to the servos.  Cutting the holes for leads must be planned at an early stage.  I Ilke the way that Peter Miller sometimes uses- servo mounted on a thin ply plate which forms wing surface with a slot for servo arm.

You should study all the free plans from RCME,even if you are not building that model, to see different construction methods and to work out the 3 dimensional shapes from the plan view and side elevation.  In particular check out the conventions of triangle or arrow shapes (black or clear ) which indicate different layers superimposed ( doublers, treblers etc )

 

However I advise building exactly to the plan and using torque rods unless you have guidance from someone experienced,

 

Edited By kc on 23/06/2009 11:08:20

[kc]

Wing ribs

The wing ribs are shown with jigging tabs.  These tabs can be of different sizes along the wing to give washout on some designs.  If the tabs are all the same height there will be no washout.  You need to check whether the ribs are all the same on this design.

[Sirio]

yeh the plans came through the post at lunch time,so i took them to work with me and studied them,and all the info seems to be there.
i checked for all the pre cut parts etc they talk about in the build instructions and they are all there with sizes etc and templates for the wing ribs cock pit etc.

only prob is there is different size ribs and it gives you the templates for four of these ribs but not the other two.

iv got w1,w2.w3,w5,but don't have w4 and w6.so iv asked the seller why not told him i haven't built from plans before and the info is prob there but just don't know were.

 

it also has the torque rod sizes at the right scale so i can bend them etc to match the plan.cant wait to start just hope the rib info is all there and then ill start a build thread so i should have loads of questions for you lol thanks again sirio 

[kc]

It could be that certain ribs are the same shape as others but different thickness.  Are the ribs shown on the printed plan and numbered or just a homemade copy of the wooden parts?  Show the plan to an experienced plan builder for his opinion. Where do you fly?

If you have got the ribs with tabs you don't need a wing jig for this model!

 

Unfortunately SLEC dont list torque rods anymore, so maybe nobody else does either.  Check before starting work.  You could make them from scratch but the plastic screw fittings are easier than a soldered job.

 

Also a decision on tricycle or taildragger is needed before wing construction.  Note that 5/32 music wire is 8SWG piano wire which is about 4mm ( American wire gauge is different to SWG )  and will really need a wire bender.  Ask around at your club for someone with a wire bender to help you if you don't want to buy one . Grooved u/c block is avail from Balsa Cabin etc but you can make your own with a router,  plough plane or even a circular saw and a piece of beech (old chair leg etc )

I suggest a plastic engine mount SLEC or Radioactive is kinder to the engine in event of a crash than aluminim and won't need  a thread. tapped.  Again choose mount at this early stage and make sure it fits your engine bearer width.

[Sirio]

got it sorted out kc,the ribs are all the same size but the templates are paper and are used to be placed on the rib as there is different cuts in the ribs.
w1 w2 w5 to accommodate different parts like w1 has a 1/2"balsa filler block so its leading edge is cut shorter,

Rib W2 shows the position of W2A PLY wood doubler's undercarriage supports,with optional cuts for taildragger or trike gear installation,

w6 is just cut shorter for the wing tip bow so far everything seems to make sense now.

i have found an e bay shop that sells all the different length torque rods and the screw on fittings etc if you need the lynx yourself let me know.

what engine would you suggest id like it to be slow for training and acrobatic later.

also the landing gear set up do you think trike gear or taildragger the flying field

is a grass landing strip.(warrix air field)

[kc]

Engine size.
You should always follow the designers recommendation .  In this case with a grass landing strip a .60  2 stroke seems right,  also if you already have a 40 it gives you more choice of model in future.  A 2 stroke is likely to be cheaper if you crash and damage it!   Ask at your club if anyone has a 60 for sale because the chance is high that someone has gone on to bigger models or electric and has engines he wont need now.
Only buy engines from a known person and not from adverts until you have experience.  A club sale might be OK but ask other members for their opinion ( when you are an old hand its nice to be asked for your help or opinion ) Buying off the internet is only for collectors who don’t worry too much how it runs.  You want an engine that runs without any problems, so stick to the best makes like OS, Enya, Webra, Super Tigre etc for secondhand engines.  If buying new these makes are rather expensive ( but worth it in the long run ) so Super Custom, Thunder Tiger etc are reckoned to be a good buy.  You should note Sig’s comment on non-schneurle ported engines- they are older  designs which produce less power than Schneurle ported but are perfectly OK as you don’t need the power.  Plain bearing engines also produce less power than ball race bearing but are perfectly OK and no bearing corrosion problems.
I am assuming you might be on a strict budget like most of us now,  but if not then you just go out and buy an OS  61FX at 150 pounds or an OS 65LA at 121 and enjoy it for decades.  If on a budget read on……..

If you find an older OS, Enya, Merco or Super Tigre 61 secondhand from a known source it will be the cheapest engine to suit if in good order.  An older engine at 20 pounds or less would seem a bargain at 30 pounds worth thinking about.  Much more than 30pounds  and its getting too near the price of a cheap new one ( Thunder Tiger GP 61 is 60pounds )  Don’t forget that an OS 46LA at 65 pounds new might just have enough power if model is built light.

Shows are often the cheapest source for new engines but it is better to patronise your local shop which gives your club a discount.  Might be the same price and you will get help when you need it from a good local shop.

Eventually you will want to progress to a taildragger so you might want to do that with this model.  It will certainly look better as a taildragger with that open cockpit.  However the elevator is used in a different way on take off so get some help for the first few flights.  Also have it test flown by your clubs best pilot.  Ask him beforehand if you can phone him to make an appointment when models finished, rather than relying on any less competent pilot who happens to be there when you turn up with your new masterpiece! Don’t let the club bighead volunteer to test fly your model. (every club has one and they crash other peoples new models regularly!)

 

A tricycle will need a sprung noseleg, see if you can buy one before you decide because they are difficult to make even with a wire bender.
This was considered an aerobatic model 50 years ago but modern aerobatic models are better.  It seems a good second model once you have outgrown a trainer.  That means once you have fully mastered a trainer not when you have just crashed it beyond repair and need another model!

[Sirio]

that's great i think I'm going for taildragger with OS  61FX  or an OS 65LA .plus iv got an OS for my trainer and in the manual it lists all the parts in case of a breakdown.

 

it feels if I'm banging my head of a wall already got all the plans worked out and everything seems pretty straight forward,and now I'm getting ready to order some wood to start on the wing there seems to be know were that supplies the sizes of balsa i need.

am i right in thinking as long as the woods the right thickness i just cut them to appropriate width.

 

as for the ailerons it says 1/2" x 11/2" shaped balsa aileron stock,but trying to find it is another matter no were seems to sell it,i take it i wont be able to make these as well.

sorry

[kc]

Check out the Balsa Cabin www.zyworld.com/balsacabin/page1.htm or Inwood or balsamart.co.uk

Trailing edge stock is almost OK but it is right angle triangle not an isosceles triangle and could be used.

The crucial thing is balsa selection.  Balsa varies more than any timber- some is soft and lightweight , some is hard and heavy.  You need the right weight for particular item.  All tailplane parts need to be light but quite firm in texture.  All spars need to be very hard, never soft.  Ribs are best cut from quarter grain (ribstock ) Fuselage sides need to be light but firm.  Formers can be hard or medium.  Its a matter of experience to assess whats right for where. A good supplier will help you and the Balsa Cabin allow you to specify grade for each part.

A pair of digital kitchen scales will reveal the amazing difference in weight of some sheets and you have to feel how the balsa bends  (or not ) and crushes under your thumb to work out the proper bit to use.

 

Buy plenty extra and different grades, especially if you need to buy mailorder as the minimum order is high.  Generally you cut to width but it is not worth trying to cut wing spars at all Other .stripwood could be cut if you have a balsa stripper (SLEC used to sell them ) but it is easier to buy strip.

Rudders etc can be shaped  ( tapered in thickness )from sheet with a Razor plane or Permagrit block.

 

Obviously if you bought a kit it should have just the right grade and size.  However many complain that some kits are poor balsa selection so prefer to build from scratch.  But you will have to learn by experience.

 

 

 

Start work on a small bit first such as tailplane and fin. If it is not perfect you could afford to make again.

[kc]

I cannot really help much without seeing the plan,  but there are some odd sizes on this model.   I suppose as a balsa sawmill Sig can use the sizes that are most economical for them.  Clearly it is easier to build from a plan that was designed to be made from standard English balsa!  ( even Scottish balsa )

Lots of the parts can be cut from sheet.  The chunky but short balsa blocks could be built up from 1/4 sheet layers for 1/2 and with an 1/8 as well for 5/8.  Use cyano or aliphatic but not ordinary PVA to glue.  Ordinary PVA is rubbery and 'pulls out' when you sand it.

 

The worst item is the 3/16 by 5/16 strips for stab ribs.  This needs to be cut accurately to make a flat stabiliser  which is quite difficult.

 

Decide before you order anything whether it might be better to buy a kit, you will get all the hardware and all the tricky bits shaped.  If the price of the main bits approaches the kit price buy a kit this time and observe the grades of balsa they use for your next scratch built model.

[kc]

Having done a rough costing based on the materials list (which is very vague on size ) I reckon the materials and main hardware would cost about 76 pounds plus carriage from Balsa cabin or similar.  More from your local shop probably but no carriage.  

 

As many of the balsa sizes are unobtainable ready cut it seems worth buying a kit at 103 pounds which includes all the odd fitting, nut bolts etc.  And the balsa selection is done for you.

 

I am a great advocate of plan building but for your first one I reckon you will do better to buy the kit.

[Delta Foxtrot]

Has anyone used this 2 rod system for building wings with ailerons? I am thinking of ailerons built with ribs rather than simple inset ailerons cut out of trailing edge stock.

I can imagine that this is possible by using upper and lower spars to form a rear spar from which to hinge the aileron. Two partial ribs could be added to form the left and right hand edges of the aileron and then aileron could be sheeted at the leading and trailing edges, top and bottom. This would then allow the ailerons to be cut out, bevelled and then sheeted at the front. Sorry for the wordy description, a picture or two would make this clearer.

I am sure that someone will have cracked this and I would be grateful for clever ideas on the best way of tackling this problem.

Dave

[Bob Cotsford]

On my King altair the ailerons were built as part of the wing, once the sheeting had been completed the ailerons were cut out and facings added. What I did was prick through the lower sheet with a pin so that I'd know where to cut once the wing had been closed up. The short aileron root and tip ribs were glued to the lower trailing edge sheet before adding the top sheet. I think there may be photos in my King Altair album showing the basic structure on the jig.

[Delta Foxtrot]

Thanks Bob! Sounds like the same approach I was trying to describe.

When building flat on the board I would normally have a rear wing spar and an aileron leading edge spar, but this is not really possible with a two rod jig. I guess that the sheeting on the front of the aileron would allow the aileron to be cut out without breaking the ribs.

Cheers

Dave

[Bob Cotsford]

No reason that I can see why you couldn't have aileron spars as long as they are not full depth. IIRC on my Mustfire the aileron has 3/16" upper and lower aileron spars, check the ribs centre and left:

Once the ailerons were cut out the ribs were trimmed back to the spars and facings added.

Edited By Bob Cotsford on 19/12/2016 19:35:59

[Delta Foxtrot]

Good idea. Thanks Bob!

[Delta Foxtrot]

Built my 2 rod wing jig and it works very well. I have combined this with the magnetic building blocks I bought at LMA Cosford this year to produce a very useful and flexible building system.

[Bob Cotsford]

don't you get a crick in the neck building on the ceiling like that?

[Delta Foxtrot]

Ah that's what causes my neck problems! The knowledge on this forum never ceases to amaze me.