Nigel R

January 31

You could switch to veneer for wing sheeting... it might need some sort of semi-solid substrate... maybe lightweight bead foam...

(reinventing the wheel department)

balsa cabin are listing poplar veneer for under £8 a sheet of decent size - 15" x 60"... that's heaps cheaper than balsa

January 31

When I was small, I wanted to do the "RM Flight Training Course"... although I ended up learning on a Precedent Flyboy, Junior 60 and then an aerobatic trainer I cannot remember the name of.

Many moons later I finally built the pair...

Part 1... RM Trainer (and sheep):

Part 2... RM Aerobat:

Both electrified on 4S 2200, 300W and 400W respectively.

The Aerobat is lightly modified (mainly style - I made the deck a little more rounded, and moved the tailplane upwards a couple of inches).

January 31

11 hours ago, Fly Boy 3 said:

If it’s built up it will be a lighter model.

If it's built up, it might be a lighter model... 😈

January 31

2 hours ago, Christopher Wolfe said:

the control surfaces were often a lightweight structure and fabric covered.

Just pulling a random WW2 example, Hurricane, the elevator was an appropriately sized metal torque tube - able by itself to resist the twisting forces it would experience when the elevator was moved, and tapered metal ribs, which I believe were capped (which would then form an I beam structure, and also aid in resisting racking and warping) were attached. I'd imagine this had some degree of analysis applied. Note, there are loads on an elevator, just like every other part of an airframe, your statement that it is not a load bearing structure is not true.

A slab of balsa is an easy route to making something that works for us. It is, "good enough". Is there better for a particular application? Sure.

January 30

6 hours ago, Simon Chaddock said:

Balsa like any wood has a grain. Works well in simple tension and compression as in a spar but it is not so good when used as a thin skin to resist torsion. You need a grain free homogenous material for that to achieve the most efficient use.

Wings are quite long and thin, so maybe the skin having a grain oriented in the direction of the longest measurement is quite useful. We wouldn't run the grain fore and aft, for instance, as it would leave all the spanwise strength to the spar structure. With the skin grain spanwise, it can contribute more usefully to the whole structure.

January 30

Required twist resistance will be linked to, I think -

* Maximum speed (where flutter might be an issue)

* Aileron deflection (3d? regular sport aerobat? stooging-around-scale-like-performance?)

Horses for courses, as usual. Some models want lots of torsional rigidity, some not so much.

January 30

A few more shots of where I am up to with the business end of the inner tailplane workings.

Snake entry into pocket...

...and the other side of the tailplane...

...and a different angle, now with sheeting on both sides (well, except for the ply insert) ...

...with that (nearly) done, time to put the tailplane itself down and make some fins and rudders.

The above process actually took quite a long time - the few working prototypes I made didn't come for free (sadly). I also spent a bit of time playing with the dimensions of the tailplane to find out what the widest curve I could get for the snakes was. This was a case of balancing off the span and chord of the tailplane, and a bit of suck-it-and-see to find out what curve would fit. In the end, I think I wound up with about a 6" radius in the snake, and the tailplane itself is about 20" in span. As I'm shooting for ~150 sq in on the total tailplane/elevator area, that gives 7-1/2" average chord, of which around 1-1/2" will be elevator, leaving 6" chord on the tailplane... Hence the "about 6" radius" on the snake itself...

January 29

Ugly stik was originally designed in times of doped silk?

This provides a hefty dose of resistance to twist, when finished. Shrink film plastic, less so.

But if you want to build open frame wings, go ahead. They'll simply be less strong than fully sheeted.

Ps gliders guys are probably interested in accuracy of wing section and would probably prefer a fully sheeted wing of some description...?

January 29

Here I've sheeted the tailplane.

This is a closeup of the trailing edge of the tip of the tailplane, along the hinge line with the elevator. You can see the snake now embedded in the structure.

The snake emerges into this rectangular pocket (which I haven't sheeted, for reasons). The clevis will live inside the pocket, as will the rudder horn. Hopefully this will be better illustrated a bit later on.

The sheeting over the pocket is done using a 1/32 ply insert. I figured that would give me just a touch more space inside the pocket.

This shot is from the sheeted side of the above structure, with the ply insert on the bench.

More soon.

January 29

This is the tailplane internal structure. It will be sheeted with 1/16 later on.

The quarter circle I carved out to accept the snake is (I hope) obvious 🙂

At the tip of the tailplane, toward the rear of the structure, is the pocket I am building to hide the rudder horn. More on that soon.

January 29

I've now taken the plunge, doubled my mortgage, and ordered some balsa from SLEC, as I'm reasonably certain of most of my construction details - given that I've already made a very similarly sized twin with the same fuselage shape / nacelles.

However, I have already started some work on the model using some wood I had "spare". I figured I would try and work the part of the model that I was least sure about - which at this point is the twin tails.

Wishlist:

* Two independent rudders on two servos

* Able to move a full 45 degrees for useful airbrake function

* No weak control links

* No messy external hardware

I figured I had a few options for controlling the rudders:

* Something with bellcranks and pushrods

* Snakes of some sort

* Closed loop being routed, somehow, from fuselage through the tailplane itself then on to the rudder

* a torque rod, going from inside the fuselage, to right out near the rudder, with a short link rod to the rudder itself.

* burying some servos in a tailplane or fin

I ruled out bellcranks quite quickly, although they'd probably be functionally ok, they were quite large and I'd not be able to hide them inside the structure. The structure would need to be quite deep - much deeper than I'd hoped.

I made a test piece with closed loop, but I wasn't very happy with the very tight curves I found were needed in the guide tubes.

I very nearly used torque rods - I got as far as making a pair of double ended rods up from 3/32. This was promising, but, after making them I tested how rigid the rod was, and with the (quite long) lengths involved, I found they were too flexible for my liking. I didn't want any issues with flutter in flight, or for the torque rods to be too weak to sustain a knife edge type situation.

I ruled out using individual servos - the really flat servos are too pricey for me.

This pretty much only left snakes. To check viability of these, I worked out what the largest, shallowest curve I could use whilst still containing one snake in each half of the tailplane. Short version, this appeared to be viable. And I also figured, if I was a touch crafty and with some careful building, I could also hide the rudder horns safely inside the tailplane structure.

I'll put up some pictures soon - they'll explain more than my words have!

January 29

Flew her for a second time yesterday. Aside from a blown OS#8 plug (argh! £££!) and the loss of an M4 exhaust header bolt during flight, it was all good. She definitely needs a little CG adjustment but a promising airframe for sure. Quite docile near stall with current CG, yet the spin is lovely and flat on rudder/elevator alone.

The only fly in the ointment, so to speak, is down to how sleek she is - she is fast, the glide slope is quite flat, and slowing her down on finals takes up a fair amount of sky - she could really use something (flaps or breaks or whatever) to dirty up the airframe a bit. Maybe I've just forgotten what "proper" classic pattern airframes are like! It's no particular big deal at the field I'm flying these days at but it would be very tight on a short strip.

January 27

Challenger has finally flown!

Very smooth maiden with no problems. Really pleased. OS performed flawlessly and provides endless vertical. The pipe length is set about right, although i need a longer header than the current one.

Rolls are axial, loops smooth, snaps are sharp and precise. I still need to trim the cg, it is a little forward. I also have some adjustment to do in the throttle to get a slower idle, but, all things considered, I am a happy chappie. It also looks pretty darn good in knife edge.

Photos were taken after returning to terror firmer.

January 26

Overlander use rebadged Hobbywing. Or at least they have done historically. Just FYI.

January 26

Some more background.

I've built several twins. The first was a conventional layout (build log - Double Trouble) and the second was a double fuselage layout (build log - Doppleganger).

The twin fuselage is the one with the rudder airbrakes.

Aesthetically, I was quite pleased with the fuselage shape on Double Trouble...

...so I'm going to base Orthus on Double Trouble. Not a rehash mind, more an evolution.

Double Trouble had a constant chord wing and was very mild mannered. This time around, being happier with twins in general, I'm going to use a slightly spicier tapered wing for better aerobatics. I found the overall size of the airframe made transport easy enough (62" span) with a single piece wing. Obviously it will look a bit different with the twin fins.

As an aside, I was very tempted to do a kit bash from the Galaxy Warlock...

...but, it's a big bigger than I wanted, it is 74" span.

January 25

RCG can be very "anti".

2 hours ago, Peter Jenkins said:

When I passed my FW B, I was able to look back and see that I had flown 80 flights with almost always 2 B schedules per flight so a total of 160 Bs flown to get to the consistency I needed to feel sure I would pass.

I guess at around ten minutes a pop, that's 800 minutes of air time, (round up) call it 15 hours of stick time.

Doesn't seem unreasonable to learn enough skill to consistently pilot something to B standard.

.

January 25

Definitely not Vega, they were all machined from solid (IIRC) and looked very, very different.

What are those bits on the back of cam box? Something to do with adjusting the cam timing? My other bet is that the odd bits are a gear fuel pump - the other photos seem to show a fuel nipple on the far side of it.

January 23

My flight log is one page of a larger spreadsheet where I also work out motor setups and record a bunch of other "useful info" like servo torque and fuel cost and lipo cost and some of that can then get used to work out cost per flight of each airframe, and so on. I also do some rough figuring out of build times and build costs in other tabs.

January 23

Yes. Takes but mere moments after a session...

Helps figure out what I'm actually really getting value from. Amongst other things.

January 23

The mythical Orthus had several distinguishing features; for starters he clearly had two heads. But he was also depicted with a tail that had a sting like a scorpion or even a snakes head on the end of the tail. A bit of a beast.

Orthus is a project I've had on my wishlist for a while. What will my Orthus be?

Orthus will be a twin engined airframe - like his mythical counterpart with two heads. I'm currently undecided between using a pair of Irvine 39, OS 46 SF, or OS 56alpha.

But what to do about his other feature, the tail that ends with a sting? Something different is called for. Here I decided a little while back that I would have a go at making this airframe with a 'tail end feature' - twin fins. Why twin fins? Simple - I have had good experience on another project with twin fins providing an airbrake option, by pulling both rudders inboard by 45 deg, allowing for a steeper descent into shorter strips. It's like having a parachute hung out the back. Most airframes would use flaps for a similar function; twin rudders provide an alternative option.

January 23

Orthus

Mythical two headed dog.

The brother of Cerberus; the guard dog of the Cyclops.

More soon...

January 19

Doesn't look very red. Must be fake.

January 19

1 hour ago, toto said:

Once a models engine is " set up ", is there any benefit in having a digital tachometer fitted onboard that can be visible sya .... in the cockpit or any other appropriate siting ?

I am thinking specifically of with my two Stinger petrol two strokes which are destined for my Flybaby and my Valiant.

My reasoning is that once you fire up the model, you would get a reasonable indication of its idling speed etc just by looking at the onboard tachometer if made visible.

Toto

And what will you do with this information?

Learn to walk before running, etc.

January 19

2 hours ago, MattyB said:

You can tell a lot about the demographics of this forum (and the hobby in general) from this thread. Those asking why a smartphone and social media are a necessary part of everyday life cannot have attempted to get a well paid job in the last 10 years or so. I can assure you an actively maintained LinkedIn profile and the ability to respond very quickly to hirers and recruiters is absolutely key (some companies will actively screen out applicants who do not have a social media footprint they can use to review and research them).

Yes, no, maybe. Depends on the particular nature of the job. Some actively prefer a somewhat lower social media profile.

January 17

All the thread reply buttons have ceased working for me, if I used Chrome on my PC. As have anything like "edit" or the reaction buttons, or quote - all gone.

The same is true on my mobile using the phone's browser.

I'm on a different pc for now, using the microsoft browser, but, I can't use that on my main PC, so I'm effectively now unable to post...

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