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Electric Grumpy Tigercub

Peter Miller's classic design converted to electric

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Chris Walby10/01/2021 07:53:45
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1455 forum posts
386 photos

gtc flying.jpg

Well folks as the club mass Ohmen build edged towards completion last year a couple of us thought about the next build. If you don’t know already then it will soon become apparent that I have a preference for ic twins and although this build will be electric it is at least a twin.

There are already a few build logs here for ic versions (as per the original design) and electric plus scaled up with retracts and flaps, but for me it will be a straight as possible standard build.

Chris Walby10/01/2021 07:55:01
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1455 forum posts
386 photos

Boring for the experienced builders out there although I would like it to be helpful to those like me who don’t have decades of building under their belt and want a proven good flyer

Cheat 1 – Kit purchased from Sarik last year

Cheat 2 – Electrical bits purchased from 4-Max last year

Cheat 3 – Read through all of the build logs here to gleam any information I could

For those that aren’t familiar with Peter Miller’s Grumpy Tiger Cub its vital statistics are:

Wingspan: 53in (2125 mm)

Weight: 4 lb 11 oz( 2.126 Kg),
Wing area: 500sqin( dm
2
)
Wing loading: 21oz/sq ft ( g/dm
2
)
Servos: 4max 2x 10g and 2x 45g)

Retracts: Fixed
Motor: 4-Max 3035 870Kv

ESC: 30A x 2 + 5A UBEC

Prop: 9x6 tractor and pusher

Battery: 4 S 3700mAh (I have 4S3300 so will use those)

Calculated thrust (4max) 4.6 lbs (weighs 4.68 lbs) 2068g

Calculated speed 62 mph

Chris Walby10/01/2021 07:56:58
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1455 forum posts
386 photos

Lets start the build and hope I can keep the building work with the pace of posting updates

Things to consider pre-build

  • Canopy from Steve at Vortex, big thanks as there was so waiting due to COVID 19 but no rush and good job
  • Modification of the cowls/nacelles to suit the electric set up
  • Modification to the fuselage for the battery access

Nothing major and looking at the drawings it has Peter's signature design/construction style throughout which is reassuring from the experience gained from the Ohmen build and limited overall experience.

I will be using the plasterboard and plastic sheet method of bas board and dusting down the SLEC board for the fuselage once I have cleared enough bench space. I thought I would get clever and attach the drawings on both sides of the plaster board which does limit the “I just need a peek to check that” if there is balsa and pins stuck in.

20210101_133915.jpg

McG 696910/01/2021 09:42:50
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3522 forum posts
1338 photos
Posted by Chris Walby on 10/01/2021 07:55:01:

Wingspan: 53in (2125 mm)

Hey Chris,

... it seems that the inches are quite a bit larger in the UK than they are on the Continent... surprise

... but then that's probably the reason why I'm still an apprentice modeller...

Cheers & keep the faith

Chris

Piers Bowlan11/01/2021 10:16:59
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2344 forum posts
68 photos

Chris, You say you 'purchased the kit from Sarik last year'. I can't find it on their website only the plan, was it a one off? Nice looking model, following with interest.

Levanter11/01/2021 10:31:13
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894 forum posts
439 photos
Posted by McG 6969 on 10/01/2021 09:42:50:
Posted by Chris Walby on 10/01/2021 07:55:01:

Wingspan: 53in (2125 mm)

Hey Chris,

... it seems that the inches are quite a bit larger in the UK than they are on the Continent... surprise

... but then that's probably the reason why I'm still an apprentice modeller...

Cheers & keep the faith

Chris

Hi Chris (The one from Belgium)

You forget that since 1st January 2021 we can make our inches as big as we like wink

Levanter

Chris Walby11/01/2021 11:19:09
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1455 forum posts
386 photos

Thanks for the feedback and having checked it would appear that the incorrect conversion (Trump) factor was used resulting in a wildly inaccurate wingspan, the correct size should be 1346 mm.

Piers, I have PM'ed you regarding your question.

The build continues with assembly of the nacelles and the wings.

20210104_192548.jpg

20210106_193845.jpg

Only mod to the nacelle was a large hole cut in N2 to allow the ESC control wire through as the power cables will traverse via the unused aileron pushrod/bell crank rib holes. I'll be using in wing aileron servos just in case I fancy a bit of flaperon or differential later on. Oh and I made the motor stand-off on my 1940's Myford lathe.  

Nothing to report on the wing build, all standard assembly with just the wings to join and nacelles to fix later on.

Edited By Chris Walby on 11/01/2021 11:40:18

Chris Walby14/01/2021 06:46:43
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1455 forum posts
386 photos

On with the build and having moved more static useful items (rubbish, parts, materials for other projects and tools) from the end work surface I set the SLEC building board for the fuselage assembly to start. This has the benefit of allowing work on the wings and nacelles all to be progressed at the same time!

Fuselage would be easy except as this will be electric it will need a battery hatch in the nose.

20210103_172531.jpg

I want the flexibility to move the lipo between F1 all the way back to under the LE of the C of G even to the point moving the rubber/elevator servos by a bit (deal with that later).

The plan is to make F1 and F2 out of ply and open F3 out to allow the lipo to pass through in either orientation.

20210103_171943.jpg20210110_112305.jpg

Then build the fuselage with the intension to cut the top off F2 to form a hatch from F1 to F3 as I need the length to feed the lipo in and then move it about to achieve C of G

I’ll add a photo of the fuselage shortly once I get back in the workshop.

 

 

Edited By Chris Walby on 14/01/2021 07:09:49

Chris Walby14/01/2021 07:14:14
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1455 forum posts
386 photos

On to wing joining and this went without issue, the drawing says dihedral of ½ inch under each tip although I was told that in previous thread discussions it should be an inch under each tip. I went with the drawing and the supplied brace on the basis that it was easier and generally more dihedral make it more stable right way up and less when inverted! Off topic but I have loads of fun with my foamboard Nutball (flying disk) with massive dihedral trying to fly inverted with rudder and elevator only controls! Look at supports for the aileron servos mounting plates (more of that later).

20210111_171215.jpgPS - Nacelles dry fitted as I was still working on the first LE strip, but more on that later.

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