Electric Grumpy Tigercub

[Ron Gray]

I don't think that it will make any difference! For example I have a Deuces Wild twin with left running clockwise and right running anti-clock, flies fine. My ESM TC has both running anti-clock (Laser 160v twins) if flew fine, well until one engine ran out of fuel (see thread noted in above post).

[chris larkins]

So....I had to resort to Google.

The propellers on most conventional twin-engined aircraft spin clockwise (as viewed from behind the engine). Counter-rotating propellers generally spin clockwise on the left engine and counter-clockwise on the right. The advantage of such designs is that counter-rotating propellers balance the effects of torque and P-factor, meaning that such aircraft do not have a critical engine in the case of engine failure.

Here is the full description

LINK

[Peter Miller]

I did find that with my ic version losing an engine made very little difference and in fact it was quite hard to be sure whcih engine had stopped.

[Chris Walby]

Having read a bit more, it was my mistake. I was getting confused with the P38!

Interestingly, the "prototye" P-38, the XP-38, had inwardly-rotating engines (before it crashed). However, all subsequent P-38's (including the first batch of YP-38's) had outwardly rotating propellers; Warren M. Bodie, in his book The Lockheed P-38 Lightning: The Definitive Story Of Lockheed's P-38 Fighter, states that, "Engine rotation was changed so that the propellers rotated outboard (at the top), thereby eliminating or at least reducing the downwash onto the wing centersection/fuselage juncture. There was, by then, no doubt that the disturbed airflow, trapped between the two booms, was having an adverse effect on the horizontal stabilizer. No problem was encountered in reversing propeller rotation direction; they merely had to interchange the left and right engines."

[Chris Walby]

Back to some balsa bashing with more work on the wings and fuselage U/C location fixings

I think I know the answer, but I'll just ask before giving it some welly with the sanding block

Question

Does the tip follow the red line on the drawing, as in slight radius up and a bit more from the top of the wing down? It makes sense and most drawing show a view that depicts it, but just a case of me over thinking it.

I have shaped tips to the profile of the rib and now just need to sand to a point with of course the plan view radius.

I did have a question regarding the underside of the nose, however a web photo of Rob's shows it nicely.

More photos tomorrow after waling the pup.

[Peter Miller]

The tip is shaped until it looks about right.

A big thing with a lot of my designs....it looks about right!!! The old TLAR rule.

[Chris Walby]

Thanks Peter and with that this morning with Permagrit block in hand I profiled the tips to TLAR. To be honest they are quite a chunky wingtip and I was over thinking it as a couple of lines to sand made it quite therapeutic.

Permission granted to use the kitchen worktop!

Next was the tail to epoxy in place where I discovered a bit of a bend in the fuselage just behind the LE of the horizontal stabiliser. Now this does not impact the horizontal stabiliser, but screws up the position of the rudder. A bit of fiddling and its glued up ok.

After that I bent up the U/C and had a think about the wiring a bit more. As the wing is going to come off for transport I am going to use a Maxloc with everything separated out (port aileron and throttle, starboard aileron and throttle).

One of the reasons for the build is to practice loss of engine and as I have had nearly as many electric's quit on me compared to IC I would quite like the flick of the switch option just in case recovery is not forthcoming.

Edited By Chris Walby on 31/01/2021 19:46:01

[Chris Walby]

There was some interesting commentary from a test pilot on Tigercats, the gist is that he was doing spin testing and did a two turn spin, but it felt unbalanced + its nose up tendency. Engineers checked the aircraft and suggested he look at the NACA spin tunnel model report. The navy pilots hand book was amended to state "All spins and snap rolls are prohibited in 7F7 aircraft". A military test pilot tried and on the forth it went flat for another 20 unrecoverable turns until it hit the ground, killing the pilot instantly.

Hopefully the GTC has less mass in the nacelles and won't exhibit the same characteristic, but worth a reminder for those with Tigercats

Wiring diagram on its way, soon

[Peter Miller]

As I said, the Tigercub is extrememoy forgiving on one engine. I have had others which were a bit iffy on one but not this one.

Obviously one treats it with care but mine could safely be turned in either direction on one engine if one was gentle.

I never tried spins or flick rolls on one though...that would really have been tempting providence.

Of course the real Tigercat had much more tapered wings which never helps

[Chris Walby]

Time to have a think about the wiring and my line was to have all the functionality available hence:

• Independent throttle control
• Independent aileron control
• Rudder and elevator control

On this basis I would need a 6 channel RX with a Maxloc connector for the servos and an XT90 connector for the ESC’s. This lot would plug into the fuselage wiring which would include the RX, UBEC and rudder/elevator servos.

With this lot all made up and tested, plus a conversation with a fellow club member who is building one at the same time there was an even simpler approach.

The result is one less pair of XT90 connectors as you just thread the cables over F4 and into the battery bay and the UBEC now lives in the wing.

Now is a good time to mention a couple of issues encountered with this build with first being the power and servo wiring exiting the wing behind the main spar. While this is not an issue in itself as the servo wires drop straight down into the fuselage between F4 and F5 it doe mean the hole in F4 is too small for the XT90 connector and power cables. The other issue is with the supplied servos for the rudder/elevator and the space available.

Perhaps I am missing something, but there does not seem enough room to get them in as it’s a bit tight between F3 and F4. I ended up opening a servo outer hole and making a support block for the rudder snake. If I was doing it again I would move F4 back a bit just to give a little more room, plus it would allow the power leads a bit more room between F4 and the underside of the wing.

[Chris Walby]

Hi,

 

Apologies for the delay in posting, but I was experiencing difficulty with the new "App" in part by using an old "App" to view it....So if anyone is left to follow this thread I'll do a quick update. I can't see the number of views so either let me know how to or post a emoji so I know its worth continuing? 

 

Couple of plastic spoon air scoops for the motors and ESC's

 

 

Grumpy sizing up his office

 

 

 

[dan h]

Hi Chris.

Please do carry on I have been quietly following from the beginning.

This will be a very helpful thread to us newish builders looking to build a more difficult model. Yours is looking great !!!

Dan

[EarlyBird]

Hi Chris,

Yes all views were reset to zero, something I miss. To see your current total views

Vintage Kits, Semi-Kits and Plan Projects - RCM&E Home of Model Flying Forums

 

Now 81.

 

[Bob Cotsford]

? still here Chris

[Steven S]

I'm interested and still following

[Chris Walby]

Thanks guys and with 173 views (probably mostly me!) I'll press on, but to be honest I don't think there is a lot left to do. 

 

So the todo list consists of:

• Sanding and filling, then more sanding
• Cut the hinges in
• Cover
• Install control horns and clevis's
• Fit the decals (stripes and name)
• Screw clamp for the UC
• Fix the canopy, with pilot Grumpy
• Set control throws and check C of G
• I have a check sheet that I use on all of the models developed with the idea of no surprises for the club inspector or me come the maiden (I'll share it later on)

OK so there is a bit left to do hence I have been sitting at the kitchen table cutting stripes and being distracted by another unfinished project (TN C47 from 2015).

 

I have looked at various photos of previous GTC and can't tell if its meant to have stripes on the underside? What do you think yes or now

 

And with that its off to the workshop and all the best.

 

 

 

 

 

 

[Ron Gray]

Stripes on the underside - good for orientation!

[Chris Walby]

You sure about that Ron....It will have stripes on the upper wing...so the underside will be the same? I find especially in the winter months the underside of the wing just appears dark anyway. Oh I think I have talked myself into stripes top and underside, but for a different reason!

 

I was tempted to have white or very light yellow on the underside of the ailerons and elevator, but they are quite small control surfaces so might not make that much difference.

 

Decision, orange everywhere, black stripes top and underside and if anything needs changing it can be Solartrim.

[Ron Gray]

Sorry Chris I didn’t realise it had stripes on top! But nowt wrong with stripes after all it is a tiger. 

Edited February 20, 2021 by Ron Gray

[Nigel R]

Still here!

[Chris Walby]

The C47 is driving me a bit nuts...TE wing to fuselage balsa block infill which looked simple and after much sanding has ended up not looking quite right....gave in and left it on the bench.

Cut the hinge slots in, gave it a little final sand plus a rub down with the tacky cloth.

Warmed up with control surfaces.....They appear to be very ORANGE, suits me  ?

 

[Chris Walby]

I am really not sure about this covering business although it is more enjoyable than sanding my C47 TE to fuselage fillets ?

Although it seems you have to do all the really awkward bits like nacelles and cowls first before moving on to the enjoyer underside and topside wings. More photos to follow, but as I have a couple of days holiday and I am on a roll its going to be more covering and stripes.

 

  

 

A bit more to do with Grumpy's office and the canopy fixings,

 

[Nigel R]

1 hour ago, Chris Walby said:

Although it seems you have to do all the really awkward bits like nacelles and cowls first before moving on to the enjoyer underside and topside wings.

 

I found much the same with the twin I covered with film 18 months back... There are lots of fiddly inside corners around the nacelles. Not much else to do but have at it and accept it will be a bit of a slog. I made paper templates before cutting out the film shapes for the wing surfaces, which made life a bit easier.

[Chris Walby]

Thanks Nigel, I'll bear it in mind for next time.

 

One question for anyone, when say ironing the under fuselage covering which normally has a narrow strip of film dressed onto the sides, how you you trim a nice smooth width of film? I an okay if its the razor blade guided by the edge and made a tool up, but it did not work well.

 

A bit more progress

[Ron Gray]

Chris that look excellent!

 

I'm no expert at covering but I use the edge of the object I'm covering to guide a new (important) razor blade or scalpel blade, it works for me and I can get a fairly straight line an even width from the edge. But it is very important to have a sharp blade and film blunts them very quickly.