Grumpy Tiger Cub Increased Size

[Nigel R]

16 hours ago, Andy Joyce said:

SLEC 9oz

 

😲

 

You'll not need more than 6oz for a pair of 25s.

 

I'm only using 6oz on a pair of 40s! Reliably use about 2/3 to 3/4 tank per flight.

[Jon H]

I recommend a 9oz for a laser 100. I hope you enjoy long flights 😉 

[Andy J]

Well at least it will give me some margin if one engine is reluctant to start!

 

Did ponder if I should interconnect the two tanks to level things up, anybody got any thoughts on this aspect?

[Nigel R]

Don't bother, is my take.

 

Do two good individual installs. 

[Andy J]

Been making a bit of progress the last few days with this build and will be installing the engine mounts next. The query I have is should I include a small amount of right thrust on a twin? Assuming little or no down thrust is required given the thrust line is below the wing.

[Tom Gaskin 1]

In days gone by, you used to build-in a couple of degrees of out thrust, to help with any engine-out situation.

 

Tom

[Engine Doctor]

So whats the bigger Tiger Cub going to be called , Tiger 90 or Speed Twin perhaps ?

[Andy J]

Tom, like the concept of some outboard thrust in the event of an engine failure so will try that set up.

 

Model is I think a 12.5% increase on the original but as for a name yet to come up with anything.  Power is going to be a couple of Enya 25's.

[Andy J]

Total disaster today, was convinced I had two Enya 25SS but could only find one. Reluctant to start building the engine cowls until I at least have a matched pair.

 

Do have two OS 20's but from previous posts this is not going to be enough for a 60inch model.

[Andy J]

Seems to be plenty of SC25's available so how do these compare to the Enya 25's.

[jeff2wings]

I have a couple of low time sc 25's if interested, or I may have a ss 25 somewhere in my collection 🤔 

[Andy J]

PM sent Jeff

[Chris Walby]

11 hours ago, Andy J said:

Been making a bit of progress the last few days with this build and will be installing the engine mounts next. The query I have is should I include a small amount of right thrust on a twin? Assuming little or no down thrust is required given the thrust line is below the wing.

 

Perhaps see what the plans says as they are for the IC version or await a comment from Peter himself.

 

I asked Peter regarding my electric standard size GTC and the guidance was no down or side required and very politely suggested that is what the rudder is used for when taking off. As for in flight he mentioned that the GTC  was very benign to the point IIRC he flew an entire flight on one engine as he other quit shortly after take off.

 

I don't think either my Dual Ace, Mosquito, Tiger Cat (all IC) and foam P38 have any down/side thrust(although the P38 does have counter rotating props in the "wrong direction to convention, but scale to the full size).

 

PPS adding side thrust might produce a weird effect in flight as you increase power and engine speed is slightly different..a bit like Dutch roll and the model yaws and pitch changes. Don't fancy that myself!

 

 

[Chris Walby]

Sort of on topic for a GTC

 

Somewhere on the forums I remember a GTC modeller adjusting the rudder/tail fin shape to reduce the pitch/yaw /roll effect and was wondering if anyone can pinpoint said thread? Its a great model and flies superb on elevator and ailerons, but mine is quite feral in flight when using a lot of rudder!

[Tom Gaskin 1]

Back last century I used to fly a 'Doublet' twin by Denis Tapsfield. It was a 62" model for two 19's that could fly quite well on one engine. The plan is still available from Sarik!

 

Tom

[Andy J]

Having now acquired a second Enya 25 now need to think about how to build the engine cowls. With the engine mounted on its side and the exhaust on the bottom it struck me that this layout would result in an untidy cowl appearance and quite a complicated structure if I constructed it from balsa.  So decided to invert the engine resulting in what will be a cleaner installation and visually more appealing with the protruding cylinder head now on the bottom.

What I now need to resolve is how the construct the cowl. If I go for a balsa format with a ply front ring I cant see how I can make it removable and thus any engine removal would be impossible. Thus the other option is to go for a fiberglass of plastic cowl.  However I have never made a fiberglass cowl before and the steps of making a mould seem very difficult. Therefore a moulded plastic type is likely a better option as I do have a Heath Robinson vacuum mould jig which I used to form a canopy for another model. 

Assume I need to make the cowl plug from wood but a little lost as to what type of plastic sheet to buy that will hold its shape and be able to be drawn onto the mould using only the suction from a domestic vacuum cleaner. 

[Ron Gray]

Have a look at alloy cake tins, I bought these for my enlarged Grumpy build (not started yet!)

 

https://www.amazon.co.uk/gp/product/B00F8PB9V6/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

[Martin Harris - Moderator]

On 20/06/2023 at 09:57, Engine Doctor said:

So whats the bigger Tiger Cub going to be called , Tiger 90 or Speed Twin perhaps ?

Easier to rename a downsized version as Terrier would fit the bill nicely but logically, it would be the Trophy 250 - although I like the sound of Speed Twin for it - picking the right name is always a Triumph…

[Andy J]

4 hours ago, Ron Gray said:

Have a look at alloy cake tins, I bought these for my enlarged Grumpy build (not started yet!)

 

https://www.amazon.co.uk/gp/product/B00F8PB9V6/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Good idea Ron but that's not going to work as would need a ramakin 2.25inches diam at the base increasing to about 3.5 inches and 4 inches in depth.

 

Still think a vacuumed moulded cowl will be the better option but don't know what opaque plastic type I should be using. is it PET-G?

[jeff2wings]

I would use the lost foam method, abit more effort maybe but a much more robust 

[Caveman]

Jeff, if it's a radial cowl how about this - it's a two piece cowl, fixed to the fuselage by round-headed screws and keyhole slots and held together with external straps. With a bit more effort I could have hidden the holding straps internally so that only one screw head per strap showed externally. Made from light-ply and balsa as a whole piece and then, carefully, cut into two.

 

 

 

 

 

 

GDB

 

[Andy J]

Made a start on a wooden plug for the cowl but then I looked at the price of A3 1.5mm Styrene sheets I was surprised at its cost so have reverted to a balsa construction which will be non removable.

 

Lost foam could have been an alternative method but given I need two cowls then this would have used up  a significant amount of my remaining stock of blue foam.