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Simon's Grumpy Tigercub


Simon Feather
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Bench has been cleared down:

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I'm enlarging mine, so rather than building sheet tail surfaces, I'm building them with some internal structure hoping to save weight in the tail. Traced and doubled the horizontal stab, and added structure; and laid the keel (as it were) - that's the formal start!

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and a little while later, we have the first components! Well, almost, there is still a lot of sanding to do as I'll taper this lot down to the TE, but it's a start.

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I've done the fin and rudder in a similar fashion too, I won't upload pictures of every stage as there's nothing here that hasn't been seen before.

I plan (hope) to do retracts so next stage is to look closely at the nacelles and see how to work those around the fuel tanks, maybe work up a prototype. The Tigercat's nacelles are a little larger than Peter's GTC versions (they extend behind the trailing edge), so some application of a bit of semi-scalishness may help.

We're on the way! it'll take me a while, as I have other projects on the go and only limited time available to work on build projects, but we'll get there.

Simon

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Thanks all for your interest.

Trebor - yes, I suppose it is an unusual room... it's one of my cellars. Three of the four have a vaulted roof like this, including the one I use as my office - bit like working in a tube station. It's a reasonable size - about 16' x 8' though the vaulted roof does make headroom a bit limited, and you can't stack stuff up the walls very well! Here's a broader shot if you're interested ('scuse the messy workshop)

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Ron - this is the supersize, go large version. I'm aiming for 130% which gives a wingspan of around 70". AUW should hopefully be around the 10-11lb mark if I build carefully. The rationale there was around the engines - I don't have or plan to have anything as small as the ones so far discussed, either powering the originals or the so-far enlarged ones, and on the pessimistic assumption that the engines will outlast the airframe, I'd want them to be reusable in another model. So I'm planning on using a pair of 52FS, and perhaps temper them down a bit with three bladers. An OS52 Surpass is perfect in my Skywriter, it performs just right, and that model came out at somewhere round the 5lb 6oz mark, so this feels about right.

But it won't be a quick build! too much else going on!

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  • 2 weeks later...

short update: some progress has been made. I looked at the nacelles after doing the tail surfaces. My original plan was for retracts, and I got as far as redrawing the nacelle plans to allow for these, extending them out behind the wing as per the Tigercat. But then I decided that actually, I'll do this as per Peter's plan because a) I don't have a lot of spare time for building, b) my model is bigger so needs heavy duty (=expensive) retracts, c) and most importantly, Peter knows best! His plan is well proven, so I'll build it pretty much as is, with only minor changes to suit my building style and the enlargement (I shall go with two dowels to hold the wing on, for example, to spread the load of the heavier model)

So the nacelle parts have now all been cut, and yesterday I traced and cut all the ribs - I used my usual technique of tracing the ribs onto tracing paper (I've tried proper artists' tracing paper, but although it's very nice, it's also very brittle. So now I use Co-op baking parchment, which is more flexible, cheap, and has the advantage of a non-stick coating which resists glue a bit), then sticking the tracings onto sheet using a spray mount adhesive and cutting out on the bandsaw (if you use proper tracing paper at this point, it shatters!). Doesn't take long

More later

Simon

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So, here's a short update - no pictures yet I'm afraid, I'll do some at some point, but there's nothing really new here.

Nacelles have been built, in outline, as the frames were necessary in order to do the wings... I'll come back to these later and do the internal fixings and cowls... My cowls will be removable, and I'll use my usual technique for that and provide pictures at the time.

One minor mistake I made is not reading ahead far enough in the plan: I've built the nacelles all nice and square as per the plan, but as soon as you then try to fit them against the wing you realise of course that this is a TAPERED wing and consequently the two sides of the nacelles need to be slightly different to get a good fit... I'll come back to that, a bit of fettling needed.

I've built the port wing, nearly, just really the skinning and the wingtip to do. Since my model is the go-large version, I think flaps will be essential, so those will be going on. I'm thinking that if I split the aileron somewhere around R6, and extend the flaps inwards as far as they'll go with out fouling the fuselage, hopefully that will do the necessary.

I've used spruce spars rather than balsa, to give the additional strength for this larger model.

Here's a tip on building the wing that I found worked out well: this is a tapered wing, and the thickness also decreases towards the wingtip, and the ribs don't have flat bottoms or building tabs. So in order to get all the ribs lined up right, I did this:

- pinned the bottom spar flat to the building board;

- made a support for the rib trailing edges from scrap balsa: this runs the entire length of the wing's TE, and has the correct taper, calculated by working out the vertical distance from the bottom of R1 (well, I actually used R2 and extrapolated) to its TE, doing the same for R11, then measuring the horizontal distance from R1 (R2) to R11 then cutting the long piece with exactly that taper over that length. Pin that bit of balsa along the TE on the board, and then make sure all the ribs touch at the bottom spar and at the TE support.

- if you think about it, since there is a taper in thickness towards the wingtip, that means the ribs are not perpendicular to either spar. I worked out the angle, and if my schoolboy trigonometry gave me the correct answer, the ribs are only 0.6 of a degree off. So, I thought, that's not enough to worry about, I'm overthinking this, and just fixed them all perpendicular to the bottom spar except for R4 and R5, where I've made an allowance for the dihedral so that I get the nacelles perpendicular to the ground (I thought tilted nacelles would look a little odd...)

more later...

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Sounds awfully complicated to me.

I just pin down the lower LE sheet and the trailing edge sheet, Add the lower main spar.

Then stick the ribs down at roughly 90 degrees to the building board measured with a pair of Mark one calibrated eyeballs (One with an over due cataract)

The two pieces of sheet allow for any slight curvature (There should be none) on the bottom of the rib.

Still all that extra precision might make it fly better.

My TLAR version flies beautifully

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Ha! you're right, Peter, my explanation does sound complicated, that's why I decided I was overthinking it. The tapered support for the TEs only took moments to make, and "perpendicular" was really more of a "stick it on, stick something vaguely square next to it for a quick check and move on" activity.

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Well Simon,

I must admit that indeed you "explanation does sound complicated". Well, 'a tiny bit' that is. frown

So, I'm really hoping not to get into much need of 'schoolboy trig' when I'll build the Vicomte...

Well done anyhow and looking forward to see some pics of your 0,6° angled ribs. wink

Cheers

Chris

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Some small amount of progress: the wing is now almost complete, just the centre sheeting, wingtips, and flaps/ailerons to do really.

Here's a poor picture of the whole thing - struggled to get a decent picture with my phone I'm afraid.

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To give you an idea of scale, that's a 24" steel rule on the bench.

Here's a slightly better picture of the centre section showing how I have two wing dowels.

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Next stage will be to fettle the nacelles into place then add the centre sheeting and other missing bits.

The paper tube extends into what will be come the aileron servo bay, as I shall have two wing servos

More later, though I probably now won't get chance to do any more until Sunday.

ps - this last picture also shows one of the downsides of "go large" when building - the D-box sheeting now can't be done with standard 4" sheet, and you can see I had to splice a bit on the width...

pps - I seem to have accidentally sealed a bit of balsa trimming - or possibly a T-pin! - into one of the D-box sections.  Oops.  I'm not going to open it up though!

Edited By Simon Feather on 01/02/2018 09:53:19

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  • 3 weeks later...

I've been ill, it seems for ages, so I've not done anything much recently. Power pills from the doc have meant I'm now much better, so been having a look to see where I got to. Prolonged absence from my subterranean workshop seems to have introduced a wonderful S-bend into the trailing edge of my unfinished wing, so I've stripped and re-made the TE.

I've just started now on the ailerons and flaps; one disadvantage of making GT bigger is that the standard aileron stock that I had was completely the wrong size (not wide enough, but also a little too tall at the thick end), and in any case I want to try to save weight where I can, so I've made a start on built-up flaps and ailerons. 1/16" sheet top and bottom, and simple triangular ribs, should be lighter than the TE stock. So progress has resumed, but it's half term here this week so although I can do a bit tonight that is probably that now until Sunday!

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here we go, pics of the flaps under construction: using the same technique I used for the ailerons on my KF3 which worked well - control horns are shaped from glass fibre sheet sandwiched between two of the simple triangular ribs. Ailerons ditto.

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TE is tapered down so that when the top sheet goes on, it ends up just a fraction more than 1/16" thick.

Edited By Simon Feather on 22/02/2018 09:46:43

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  • 2 years later...

Well, wasn't it a long time ago I last posted on here...

I hit a snag with the fit of the nacelles to the wing, so the build stalled, and then... other priorities happened as they do.

The recent lockdown prompted me to get the GTC back on the bench again, and things have progressed. Not as quickly as I'd like, because I'm neither retired nor furloughed, and work has actually been busier, so time is limited. But some progress has been made as can be seen from the pictures below.

As a reminder, this is Peter's Grumpy Tiger Cub, but enlarged to 70" wingspan.

I have put aileron servos in the wings as I always do, and added flaps. Power is 2x OS 52 Surpass - I have acquired two new-in-box never seen fuel engines for this. What a treat to fire those up for running in! Both started on the first turn of the starter.

Ignition uses a Hobbyking glow starter in the central wing section (the type that fires up the plug for 15s after you press the button), with a three way switch to control which engine the electons get sent to. 500mAh 2s Lipo provides a huge number of starts on a charge!

Covering is a mix of Hobbyking and Easycoat. Not so impressed by the Easycoat personally, I found it too easy for the glue layer to delaminate from the film, and the glue is coloured and stains the wood. Markings are vinyl cut on a Silhoutte cutter, more to be added yet...

Not done the canopy yet - once I've test flown it, I'll make a plug and vacform one.

Engines are run in, hopefully doing engine matching and ground tests later this week or sometime next week and maiden.

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Edited By Simon Feather on 01/07/2020 18:21:13

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