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Rob's Grumpy Tigercub build

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Rob Ashley25/01/2018 19:37:05
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256 forum posts
86 photos

I have followed other MB Grumpy builds whilst my own has sat there waiting. No more excuses to get it done.

The story so far:

I started Christmas 17 and was hoping to complete in 4 weeks but things happened. Thankfully the MB 18 gifted me hope and I can now join in.

I enlarged the plan to 63" span to accommodate x2 OS 32 motors with fixed U/C.

Blew the plans up to size and drew the parts in CAD. I then CNC'd a kit to build and started over a year ago and made some progress.

Started with the nacelles which were simple to do followed by the wing.

Oh yeah this is my first thread so please be patient.

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Rob Ashley25/01/2018 19:39:17
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256 forum posts
86 photos

I decided to use spruce for the spars but other wise all as per the plan. Although I did cut lightening holes into the outer ribs.

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Peter Miller25/01/2018 19:39:20
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11093 forum posts
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looks good

Rob Ashley25/01/2018 20:12:27
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256 forum posts
86 photos

Thanks Peter.

I now have both wing panels built.

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And joined..

john stones 125/01/2018 21:09:33
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11522 forum posts
1517 photos

Good start Rob, 2 nice motors your using there, be like a rat up a drainpipe. face 1

Peter Miller26/01/2018 08:09:39
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Yes, with two OS 32s you will need your Pampers on!!

Rob Ashley28/01/2018 16:34:43
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256 forum posts
86 photos

​Thanks chaps - I had better go get some.

I appreciate I am one of a number of builders of this model so I know there will be much repetition. Anyhow I'm finding that doing this thread is keeping my motivation going, so hopefully I will finish this build. Tail feathers are ready for final sand and covering. When I cnc'd my kit a milled a tongue on the fin that slots into the horiz stab to ensure everything remains square.

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Also fitted the nacelles which didn't really need too much fettling.

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I think like most others who have scaled up I have opted for 1 servo per wing to allow for flaperons if required. Otherwise this will be as per Peter's plan.

 

Edited By Rob Ashley on 28/01/2018 16:35:01

Edited By Rob Ashley on 28/01/2018 16:35:46

Tim Ballinger28/01/2018 19:28:14
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791 forum posts
287 photos

Looking good Rob, all very neat. I went for separate flaps on mine with the servo in the aft nacelle. Still got the option of mixing the whole lot together if the brain could stand it.

Tim

Tim Ballinger28/01/2018 19:28:15
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791 forum posts
287 photos

Looking good Rob, all very neat. I went for separate flaps on mine with the servo in the aft nacelle. Still got the option of mixing the whole lot together if the brain could stand it.

Tim

Rob Ashley29/01/2018 09:20:00
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256 forum posts
86 photos

Hi Tim,

I did consider the split flaps/ailerons and also retracts having looked at yours, but in the end I decided to keep as close to the original as possible - save the size increase.

I started by using PVA for the sheeting, but having discovered aliphatic (Titebond) I am a total convert. I love the stuff. I found on cold nights the PVA just wouldn't cure properly and left a white residue. My workshop was not then permanently heated only with a calor gas heater when I was in it.

Also I think the Titebond grabs well and is much easier to sand.

Had an 'oh bugger' moment last night after I dropped a sanding block onto the wing - it's made a dent so there's my first ding.....

Rob

Rob Ashley29/01/2018 09:21:59
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256 forum posts
86 photos

I have also realised my photographic skills leave a lot to be desired!

Tim Ballinger29/01/2018 09:55:09
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791 forum posts
287 photos

Rob, I’m a fan of aliphatic too both the ‘ordinary ‘ and the super aliphatic which is nearly as good as wicking into joints as thin cyano. I like that a lot for fixing things in place that are difficult to hold/clamp. I even resorted to using thin cyano to stick some covering film into the cooling vent I had left in the cowl. Sadly I had not thought ahead enough and could find no way of getting the iron in the gap. Could easily have made it a cm wider as well.

Tim

Peter Miller29/01/2018 10:34:44
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11093 forum posts
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Rob, Nothing wrong with your photographs. They show what you want to show clearly and sharply and that is what matters.

Ace29/01/2018 13:43:21
322 forum posts
23 photos

Rob, put a drop of water on or better in with a syringe and then dry with your covering iron - should lift the ding out.

Rob Ashley29/01/2018 14:37:49
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256 forum posts
86 photos

Ace,

I've not heard of that before so will try it when I get the chance - thanks. Sadly in this instance the sanding block (a Great Planes aluminium jobby) pierced the skin so I needed to apply some glue. With a light coat of filler I don't think it will show.

Tim,

Not sure if I can be of help for your cooling vent - I know there are others who have made suitable tips from soldering irons and there are smaller proprietary shoes but I guess if glue works then go for it. Alas not needed for IC as the cylinder head is in the airflow.

Thanks for the vote of confidence Peter.

Edited By Rob Ashley on 29/01/2018 14:45:33

Tim Ballinger29/01/2018 16:23:10
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791 forum posts
287 photos

Rob,I’ll probably end up buying the small trim iron just need to remembe before the next tricky covering job and not during it like this time .

Tim

Rob Ashley29/01/2018 19:53:55
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256 forum posts
86 photos

Well I think the phrase I am looking for rhymes with clucking bell.

One of the OS 32 engines I had intended to go in to my GTC has stripped the chrome piston liner and won't run. Oddly enough as it is out of production getting another is unlikely. It was fitted to another model (a scaled-up Tequila Sunrise another PM design) and it has struggled to start and didn't develop full power - then gave up the ghost. This is the second one of these that has done that. This leaves me with just one left.

So...right in the middle of carving the cowls to fit OS 32s I now have to change tack - I'm starting to think electric but while I ponder and give the problem a huge dose of chin sctraching I will give the fuselage some attention.

Tim, I always find I need something I 'should have bought ages ago' in every project. Only if I buy it I seldom need it again. Your GTC is looking great btw.

Tim Ballinger29/01/2018 22:10:45
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791 forum posts
287 photos

sad. Sure you'll come up with something. smiley

Tim

Peter Miller30/01/2018 08:20:45
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11093 forum posts
1309 photos
10 articles

SC 32s are much more reliable and cheaper. Never had a problem with them and I have used a lot.

Rob Ashley30/01/2018 08:41:54
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256 forum posts
86 photos

That's not a bad shout Peter - I've not used SC engines before so they are certainly in the mix.

My other current thought is electric with the batteries in the nacelles - this would keep the wiring easier with less modification required. Have to admit I'm 60 elec / 40 IC which is a little scary as I consider myself an IC man.

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