Thread Tools
Feb 13, 2016, 03:36 PM
What could possibly go wrong?
Thread OP
Tom, yes I do plan to continue on with another section, I had in mind the fuselage as I have material for that. Was considering a slightly modified, lighter version but I think I'll stick to the original design. I could try some alterations later, but they would be most useful with an original design to compare to, I think.

It's going to happen again for the fuselage stringers - 1/4" x 3/8". I can rip these when on Monday, but this may be available at my LHS, I'll check tomorrow. I could always strip them off a 1/4" sheet. I was also thinking, just use 1/4" or 3/8" square stringers, it'd be quicker.

There are points for and against that centre-mount clevis and horn... I'm inclined now towards keeping it. I see no problem adjustmenting the other end, and agree a straight rod is better. The alternative would exit beside the fin. I'm kind of against using Kwik-Links so I'd use a clevis on a threaded rod... you'd be limited to half-turns of the clevis for adjustment. What do you guys think of that, and is that fine enough elevator adjustment, counting transmitter trim? 2michaely's suggestion of angling the fuse end would work too.

IMO you don't want threaded clevises at both ends as the rod can possibly turn. I'd prefer something fixed at one end - how about a z-bend at the servo and threaded clevis at the elevator? Or vice versa? LHS suggested carbon rods with a clevis epoxied on at one end and a threaded coupler and clevis for adjustability at the other, the rod's very light and stiff. I'd some offer options for this build.

Sorry there's been more talkin' and less model-buildin', but it's after 4am and I've just got in from work to post this so I better wrap it up. Might be working again tomorrow night (in fact I hope so) but that still leaves a goodly portion of tomorrow for the massed legions of my undead balsa-warrior slave-army - we'll try to get a good bit done tomorrow ("YES MASTER").

Getting this bonus work means that on Monday I can get my own RC set- I've been borrowing an old one, now I'll own a Hitec Aurora 9X, complete. Against all trends this one comes with 4 decent standard servos, HS-5485B, Optima 9 Rx, batteries, charger, switch, wiring, everything.. I know you're supposed to buy the exact servos for each job but this build is meant to help new builders and I think a lot of them will be looking for a similar kit. I'll need a 5th servo for throttle, something smaller/lighter.

I'm going to post plans for that test bench anyway, but later. I kinda like the latest version I've come up with (with much advice from wiser modellers than I). Sorry for rambling but I warn you now, I always do, and I am not fast to do things. You guys can build a model in a day, I can't do that. Bear with me, the idea is this is a build by a beginner scratch-builder for other beginners, and I doubt too many of those are much faster.
Last edited by BernardW; Feb 13, 2016 at 03:55 PM.
Sign up now
to remove ads between posts
Feb 13, 2016, 04:27 PM
Registered User
Quote:
Originally Posted by BernardW
.......... but you may not realise that in starting this build and reading my thread you automatically fall under my telepathic control and are effectively my personal war-zombies, bound to do my bidding at my beck and call. .......
LOL........Bernard, the relationship between an original poster and others on a thread may very well be asymmetrical, but some of us are prepared to impose correction and disciple upon a comparative novice (smiley)

To wit,

Don't wimp out on doing straight, with the grain cuts in 3/8" thick balsa with an Xacto #11 blade for the wing spars.... just don't try to slash thru the whole thickness in one cut; use repetitive cuts and even if each stroke deepened the cut only by 1/16"th of an inch, six cuts will take how long, perhaps a minute.... even without a balsa stripper, you can do the cut, using a thin metal yardstick rule against which to make the first couple of sequential strokes, after which the kerf will be sufficiently established that subsequent cuts can be done without the blade popping out of the kerf.... just take the time to hone the Xacto #11 blade to an uber sharp point; use some fine sandpaper for honing if you don't have a water or ceramic honing stone.

Your way of using bracketing rib templates to fashion the wing ribs is ok but can be more efficient.... using 1/4" marine plywood for the templates is overkill; I've used 1/16" ply and the plastic laminate - called Formica around here - that is used on kitchen counters, etc. just about anything as long as it is significantly more wear resistant to sandpaper that the balsa rib blanks.... use two machine bolts , perhaps 1/4"x20, to make ONE template/balsa rib blanks/template sandwich instead of several smaller clipped together efforts.... for the spar cutouts use a thin kerf saw to make the two vertical cuts in the balsa blanks for each spar while everything is in the sandwich; you then either gouge out the balsa in between the saw cuts with a file or when you take apart the sandwich, pop out the spar cutouts in each rib with an Xacto knife....
...... save the money you are thinking spending on a laser cutting service the next time you need wing ribs, etc. and buy that used scroll saw sooner

let's see more post-colonial grit and economy,

God save the Queen,

Michael in Ontario, Canada
Feb 13, 2016, 05:48 PM
What could possibly go wrong?
Thread OP
Michael, I whole-heartedly agree re. the ply but I have a supply on hand that's been sitting around doing nothing for a few years. I'd never psi-command the legions to spend money on it for that task and I should have made that clear. As you say, any hard material will do and would be a heap easier to work. I wanted to use aluminium sheet and tin-snip and file it, but baulked at the new price and haven't found the right free scrap yet. I deserved that smiley... there is another asymmetry in this thread as I haven't actually seen any new builders pop their heads up (or those tin-foil hats really work).

Re. making sticks out of that 3/8" sheet, I was wondering about that, I had in mind using a trued square wood block and mounting a blade on that, with a screw through the hole and another to set it at an angle and therefore the depth, and run that along a straight edge, I'd only need to alter the blade setting once or twice. But I had thought a knife in hand would wander and I wouldn't get a nice square cut. I could sand/razor-plane it to true of course, must give it a try. I do happen to own some decent water stones and a hardware-store oil stone (which I think is actually pretty good for the price though a tad coarse for those blades... wet & dry would do fine).

I really want that scroller, but in the meantime I do pretty well with a cheap coping saw, that thing keeps surprising me with its versatility. I got it years ago when teaching myself to make dove-tail joints - for those spar slots, I'd only have to saw the two vertical cuts with a razor or tenon saw (again, my "big" saws are fine for even soft balsa) then with the coping saw make a diagonal cut from top to opposite bottom, then across the bottom edge and the bulk is released and ready to sand. Haven't tried it on a stack of balsa, I suspect the teeth are a little coarse but that's done no harm with my other hand saws on balsa. They've all done a better job than I expected.

There's an ulterior motive to the laser game, I'm trying to get work with the guy that referred me to the laser cutter so it gives me a great excuse to chat with him about stuff he enjoys, and soon he has to decide who he's giving some cool gigs to... heh, heh... But yes, I do want a scroll saw, I want it a lot. It's just for this thread I need to assume readers don't have such things. That's easy, I don't either!
Feb 13, 2016, 05:52 PM
Registered User
I have a useless comment to make. If I were determined to use a Saito 82 on this, and I expected beginners to fly it, I would be going to the copy center to make plans for an RCM Trainer 66 at least, maybe a 70 inch. I would not lengthen the wings of the existing design, I would enlarge the whole thing so that all proportions would stay the same. I'd probably keep the same wood sizes too...those things were way overbuilt, maybe not for the radios of the time, but certainly for today's radios. I'd add shear webs on the spars, and maybe even reduce them, just because it's so much more efficient to use them. Why use outmoded construction?

Sorry, I know it's no help, but I just had to write it.

Jim
Feb 13, 2016, 06:04 PM
What could possibly go wrong?
Thread OP
I thought of all these and suggested them and got persuaded right back to the original design. But secretly I'm planning to show 'em all and make a 2nd version that way just to see the difference, except I hadn't thought of a scaled up fuselage with the longer engine and tail moments... a good point.
But I did agree with 'em that the Saito in particular is so light for what it is that it's probably right as it stands.
Am devastated to learn that many of the Saito engines I wanted to buy are going out of production effective immediately.
Feb 13, 2016, 06:11 PM
Registered User
DustBen's Avatar
This design is robust that you can get away with murder and other sins and the plane will still fly well (It's a Bridi design!). I've seen dozens and dozens of 'em. Some were crooked as can be and they still worked. I've seen 'em with anemic .40's in the nose and some with small block Chevys for power.

It's a simple plane to build and can be framed in a couple days... sanded on a Friday night, and flown on Sunday. Don't spend a moment re-inventing the wheel with this one. It's meant to be flown!
Feb 13, 2016, 09:47 PM
Registered User
My Trainer 60 has the wing extended by one rib bay on either side and has dual aileron servos. It was originally powered by a K&B .61 which was more power than I needed, so it was replaced by a K&B .40. It still has ample power and flies like a dream. The finished weight is 5 lb 12 oz.

The rib template was made of thin cardboard with the edge hardened with thin ca. The ribs were cut out by tracing around the template with an exacto knife and the jig holes were cut with a sharpened brass tubing. One thing I didn't notice until after the first panel was framed up was the jig holes weren't exactly symmetrical with the top and bottom of the ribs and the top of some ribs were higher than others. On the next panel the top was marked on all ribs before assembly - problem solved.

The elevator pushrod comes out the end of the fuselage and the clevis is easily accessible by moving the elevator to full up.
Feb 14, 2016, 07:03 AM
What could possibly go wrong?
Thread OP
Fuselage sides and wing saddle (see edit 2 below). As most people will have letter-sized printers, here's what works for me to print larger pieces at full size. Use Adobe Reader, I've found it's the best of the .PDF utilities I've tried at printing accurately to scale. I copied these sections from the plan with GIMP, but I wouldn't advise trying to print them with it as it has scaling issues. Adobe Reader can print them in Poster mode and keep the size accurate to a few pixels. Load the file, select the Print icon or menu choice. From the Print page, select Actual Size first of all, then the Poster button. Ensure the Tile Scale is 100%, I'd recommend monochrome printing (these files are grey-scale anyway) which can be selected from the Properties button at the top of this same window, but when you return from that, double check those scale settings. You want Cut Marks selected, don't worry about overlap as there's enough provided with the cut marks. Also under More Options, make sure Current View is NOT selected or what prints and the scale depends where you left the view window. I prefer borderless printing under Properties too, no point wasting limited print space.

Taking it to a printing service will give a good result, for a price and some of your time, but I never bother. Neither do I print the whole plan usually, just the section I'm working on. You'll then need double-sided tape and a straight edge. You'll need to trim all the pages the same, I prefer to use a hobby knife to remove the bottom and right edges, but in this case, it's only one page in height so you needn't remove the bottom edge, or the right edge from the right-most page.

Stick them together carefully using the alignment marks, then cut around the outline to get a paper template for the fuselage sides. Yes, the line thickness varies, especially along the bottom edge, you'll just have judge it. The bottom curve is less critical than a straight top edge.

You'll be sticking this to balsa sheets with spray glue as before, then trimming out two to shape. This isn't the immediate next step but it's needed soon enough. I'm going to make more progress first then post the results rather than post baby steps for now.

EDIT - Andy K's thread for a smaller version of this model included weighing and matching pairs of wing ribs. That's good to do but you need scales that work to .1 or .01 grams.Those drug-dealer scales from pawn shops and late-night convenience stores (round here anyway) are good as they're cheap and do the job, I don't know of anything else affordable. You should go in there wearing dirty, torn jeans, checked shirt and wind-breaker, maybe an old wool beanie, so you don't stand out and say, "I need those drug scales, but I'm not a dealer or addict, no way man, not me!" Very fast and loud and repeat it many times with variations so you get your point across. Don't want to look suspicious. Best if there are cops there to observe your sincerity, and if there's a pharmacy nearby grab some syringes first for your glue, so you can say, "it's, uh, for a, um, model aeroplane, yeah, that's it! See? That's why I got these too!" so your story is consistent.

EDIT 2 - I've posted the file "Fuselage Sides - Cropped Nose" in addition to the older file. This is the file I'll be referencing in the build from now on. Again, sorry if this causes problems. If you've already made fuselage sides from the old file, I suggest you print this new one, overlay it on your fuse sides and trim as shown, but leave extra material in front of the firewall (bulkhead 1) because later I'll be including 2 degrees downthrust by angling the firewall. As the original plans used fixed wooden beams and I will assume we're using commercial engine mounts, the easiest way is to build the downthrust in at the firewall.

Just to be clear, use Fuselage Sides - Cropped Nose.pdf and not Fuselage Sides.pdf if you are following this thread and building from the plan and these files. Sorry but I made a late design decision.

Feb 27 - found I made a HUGE error, don't use the fuselage side - cropped.pdf file! it's WRONG! See posts after today's date later in the thread, I'll have to come back and fix this later. Really sorry guys and I hope I haven't messed anybody up, it's a big worry. I'm probably going to have to make all new sides and doublers.
Last edited by BernardW; Feb 26, 2016 at 04:30 PM.
Feb 14, 2016, 08:02 AM
Registered User
If you can get a good quality old fashioned two pan balance you can just compare one piece directly to another. That's how I do it.
Feb 14, 2016, 09:31 AM
It's gonna be YUGE!!!
LVsoaring's Avatar
Beautiful looking model, DStone! Bernard, you better get to work! That's a tough act to follow!
Feb 14, 2016, 02:08 PM
Registered User
Here is a link to a build thread by "tomclark" in the next door builders workshop category of a 102" wingspan blowup of the Bridi/RCM Trainer 60:

https://www.rcgroups.com/forums/show....php?t=2259151

I'm not suggesting any enlargement in the stock 58" wingspan - although xxxx's post above shows how expanding the wing by one rib bay, presumeably while not changing any other dimensions, appears to be fine.

What is interesting about Tom Clark's builds is his significant lightening of construction techniques, reasonably able to be comprehended from the photos in the linked thread.

The all up weight of his 102" span blow up is an amazing 10.4 pounds, with an OS 160 two stroke, at 1836 sq.in. wing area and 13 oz/sq.ft. wing loading.

If you click on hyperlinked 'tomclark' in the thread and scroll thru his blog, you can find more of his builds, with many more photos, using his lightened build techniques.

A cheap digital scale: the standard kitchen digital scale with a capacity of 11 pounds/5kg. and a resolution of 1gram is made under many brand/house names and is fairly cheap when on sale - the Starfrit brand was on sale in Canada last week by Canadian Tire for $10.66 Cdn.
This resolution is plenty fine to discriminate between the weights of 36" sheets of any thickness of balsa.
If, by chance, one is confronted with using sheets of balsa of significantly different densities/weights - especially for a wing - the important thing is not to use all of the heavier balsa in one wing half and the lighter balsa in the other wing half.

Michael in Ontario, Canada
Feb 14, 2016, 02:33 PM
What could possibly go wrong?
Thread OP
OK but my facetiousness with the scales was because I thought Andy K's log was comparing individual ribs and matching them up to be used paired in opposite wing panels - at that scale a single rib wouldn't weigh much.

Have patience, oh ye of little faith, I am building stuff as we speak, at a better rate than I've done in quite a while too so there will be something to see soon.
Feb 14, 2016, 06:28 PM
AndyKunz's Avatar
I weigh every sheet of balsa in my inventory. Weight also factors into laser cutter use. You weigh wood to match sheets and assume ribs cut from the same part will be closer in weight. It will affect roll rate.

Andy
Feb 14, 2016, 08:54 PM
Scratch Builder
tomclark's Avatar
I built a Trainer 60 maybe 30 years ago, so my memory may be a bit rusty, but it was a fun airplane and the symmetrical airfoil was a blast to fly.

I seem to remember that it was a bit nose heavy with the OS 60, so if was building one today I would use the lighter OS 55. You could also use dual ailerons and since you are using an even heavier engine, you could mount the elevator and rudder servos in the rear to help balance the plane.

I scratch built another in 2014 using my original plans as a guide. However, as scratch builders often do, I made a few minor changes. Flaps and air brakes really shorten the takeoff and landing distance.

This airplane is a dream to fly, far more aerobatic than my Kadet, and far more relaxing than the usual rockets.

You'll love your Trainer.

Oh yeah, I think the build was just a bit off on the plan sizes.
Feb 15, 2016, 07:28 AM
What could possibly go wrong?
Thread OP
OK Here's something to go on with. First to say though, I've read the article for the RCM Trainer Jr. and it's very similar to this model, so it would be well worth reading and keeping handy for anyone wanting to build this model. I'll link it this post.

Due to some delays coming up with alternatives for certain parts that are hard to source I've started with the horizontal stabiliser. Unlike the Trainer Jr. plans this is a built up surface, I couldn't find 1/4" x 3/8" stock anywhere in my city off the shelf so I just bought a 1/4" sheet, marked it and used a straight edge to cut sticks with a hobby knife. No real problem but if you do this, watch for the knife wanting to wander away from the edge and give you a non-straight surface.

I had printed out the plans on separate A4 sheets, if you poster-print the plan on small sheets this way don't bother assembling the whole plan, it's actually quite convenient assembling only the section you want. There are 4 sheets that go together for the tail section, lay this on your building board (something you can stick T-pins into, I use MDF). Get your sticks of 1/4" x 3/8" stock and start cutting to length to fit the pieces on the plan. Remember that the piece at the very rear of the stabiliser should be one long single piece so it at least has some long-ways strength, don't glue two halves together. I found a really useful tool for this was blades to fit a #1 hobby knife with fine saw teeth cut in it, useful for cutting softer balsa sticks with a good surface. Use sanding blocks to sand the ends nice and square (there are sanding jigs posted elsewhere, search for them if you need them or let me know).

The construction article says to use aliphatic resin, aka carpenter's glue, and that's my preference anyway. I know CA (cyano-acrylate) is very popular for model building these days but I've never liked it, I only use it in certain places when necessary. Use double-gluing (see article), and as you glue each piece put a pin in each end. For the longer pieces, use pins next to every place another piece butts up to it. As every, always sand every surface, but if you really can't be bothered with this at least sand the ends of pieces to be glued. It's also easiest to cut your pieces just a fraction too long then sand down to the exact length - if you cut them too short you'll have to make them again!

The plans say this stab. will be sheeted with 1/16" balsa. Single sheets aren't wide enough to sheet the whole thing, so I edge-glued two pieces first for this, see photo. How to do this has been better documented than I could do and I always write my posts far too long as it is, so see
http://www.airfieldmodels.com/inform...a_sheet_skins/
When the sheets are glued to the stab we'll be trimming them to size, then sanding a rounded leading edge to the whole layered construction. I've got something on the board now for a later post with glue curing, once that's out the way I'll sheet the stabiliser and get you some photos of that. Photos show the stages so far and in one you can see the main tools required.

I know there was a link to it within another thread but to make it easier, I'm re-posting that article here too.


Quick Reply
Message:

Thread Tools