Extra Slim Twin

[Martin Harris - Moderator]

I haven't thought your diagram through in depth but I would have retained separate channels for ailerons. My current radio is extremely flexible with channels to spare but I flew my first one on either a FF9 or FF10 with an 8 channel receiver.

[Paul Marsh]

I used a 9 channel rx and used separate channel for the ailerons. Mine's exactly the same, except that.

[Chris Walby]

Hi, Would be interested in knowing what the rational of dropping one of the other functions and having differential on the ailerons would be?

Plus what would you be doing with ailerons on different channels in the way of flight modes? Cheers

I did consider only one elevator servo, but the elevator is quite flexible so went for two and a flap servo in the middle.

[Neil R]

Here's what I went for on mine in terms of mixers - this was on a FF9 - it would have all been so much easier / more flexible on a Taranis. (Unless described as 'always active' below the mixer was on a switch).

Mixes Used:

Ail Diff always active

Elevator to Flap

Ailevator (for twin elevator servos) always active

Airbrake (crow using ailerons and flap)

Rudder to Throttle (master) for taxying

Throttle (master) to Throttle (slave) always active

Throttle Safety Cut Out

Flap to Elevator always active

Rudder to Throttle (slave) for taxying

Rudder to Throttle (master) for yaw aeros

Rudder to Throttle (slave) for yaw aeros

I think I was trying for a system where the rudder stick increased thrust on the outside engine in taxi mode, and decreased thrust on the inner engine during flight mode..

Mine is electric with 2 Lipos - I made the entire D section of the wing centre section removeable to accommodate them internally in the wing.

[Neil R]

Here it is:

[Neil R]

Here it is:

 

 

Edited By Neil R on 20/04/2020 18:43:52

[Martin Harris - Moderator]

Very ingenious battery box!  The servo locations look a lot more practical than the designer's method of hiding them in underwing bays.

My preference for separate ailerons is [a] for tuning axial rolling and [b] with the nature of this model's extreme characteristics, in order to be able to mix them as full span positive and negative flaps to increase looping ability.

My whole philosophy with this model was to try to make it as extreme as possible...

Edited By Martin Harris on 20/04/2020 18:59:56

[Neil R]

What’s the thinking please on the separate rudder channels? Driving opposite directions for an air brake effect? This was where I saved my own 9th channel. Mine needs recovering due to sun damage in a poor storage location, but I have a feeling the lockdown might provide an opportunity. If this happens I’ll also be moving to the Taranis.

[Nigel R]

Now that's some lateral thinking on the lipo box! Great idea.

Could airbrakes not be achieved with a crow type mix on the central flap channel and two aileron channels?

Just my opinion - I think I'd try and keep rudders on the Y lead rather than ailerons.

You might not need differential throttle with that much rudder. Most profile 3d types can pinwheel with the large rudder area they typically have, providing you get enough (60deg or thereabouts) movement.

[Martin Harris - Moderator]

Rudders as airbrakes? Technically unnecessary but it does add to the fun - in conjunction with crow braking leads to very slow and controllable approaches...and looks suitably silly!

Edited By Martin Harris on 21/04/2020 12:35:30

[Chris Walby]

Well as complete as it can get until I have run the unknown engine in the Nova 40 for a few flights to get it set up and the they can go in here (post COVID 19 restrictions).

PS - Big mistake not having detachable outer wings as I can only get this and a couple of foamies in the car, hay oh the price for extreme fun

[Paul Marsh]

I was going to make mine also removable wings, even have the tubes, but found that it was going to be complicated and didn't go ahead.

I have loads of engines, and luckily when on a built, have about 12 x TT GP 42's spare, both new and used.

[Paul Marsh]

Mine flew today, had 3 flights. Seemed the left engine isn't pulling the same as the right, although tuned ok. Not much, just notice it on full power vertical climb, needing right rudder. As I have several spare GP42's plus 10 in box, will swap the left engine and do tacho tests until get the close.

The Vectra car is ideal for a one-piece Extra Slim Twin... Fits in quite wel;.

Edited By Paul Marsh on 09/06/2020 15:41:33

[Chris Walby]

Good to see another EST taking to the air!

I must admit I thought I had dropped a clanger when I tried to get it in the car....and I had to take everything out, but today it was IC twin day for me ! EST, Dual Ace and the SG Mossie (later two Laser 70 powered) and they all fitted in a treat.

As an observation mine climbs vertically to the left unless I hold a bit of rudder in so got sure if a trait or I have one engine out performing the other. My OS LA46 are many hands old and from different sources hence no idea of the internal condition.

They fly very nicely and I worked up to mid rates today, but bottled out of the centre flap or rudder to throttle mix!

But it does knife edge very nicely

[Paul Marsh]

Wierd as mine does the same, either a trait, as you said (this means that both have built exactly the same by different builders) so, maybe the engine is not at fault then,,,

How come you left the cheeks off the engine bay?

Edited By Paul Marsh on 09/06/2020 21:20:12

[Martin Harris - Moderator]

Both engines are rotating in the same direction and there's no side thrust so it doesn't surprise me you're noticing this effect. I added a throttle to rudder mix on mine and adjusted it until I got vertical verticals!

Sorry this didn't occur to me when we were chatting earlier Chris - seeing it in print without the distractions at the field made it the obvious response!

Edited By Martin Harris on 09/06/2020 22:08:06

[Chris Walby]

I'll try flying vertically slower and see if that has an effect as I have a couple of degrees of side thrust set on both engines.

I won't be surprised if one engine was running faster as its well over propped (for the noise test) and both engines are from different sources.

Perhaps with Dave's engine it will head in the other way! In reality I am not too fussed as I don't think the design was intended for much straight flight in any direction!

Paul, I could not see the point of the cheeks...Plus the way these things shake I would like to keep a check on the Nyloc engine mount nuts! Embarrassingly enough having my U/C fall off, but a complete engine would get to the club newsletter.

[Paul Marsh]

I used T nuts to hold the engines, do I can take the engine out in 3 mins and although the T nuts are embedded into the fuselage, they are also held against the cheeks and also hides the crankcase. I suppose it gives a little more torsional strength to the bearers.

[Martin Harris - Moderator]

While it's not impossible that the engines are far enough out of balance to cause yaw, there's little doubt in my mind that a pull to the left in vertical flight is perfectly normal with this model and to be expected. I wasn't aware of any out of balance beating when you flew on Tuesday but I wasn't listening for it as I was busy with my model at the time.

You could try putting thrust wedges under the engine mountings to provide some right thrust but a simple throttle to rudder mix would sort things out - the mix can be done electronically or with your left thumb!

Edited By Martin Harris on 11/06/2020 21:43:04

[Nigel R]

Chris if you're going to try altering the thrust it might be worth pointing the starboard engine right for about 4 - 6 degrees total right thrust and the port pretty much dead ahead.

Although tach the engines first and see if one is lacking behind if you haven't yet. What prop do you have on the 46s?

[Martin Harris - Moderator]

I see where you're coming from Nigel but this model is very well behaved on one engine so asymmetric thrust lines aren't as much of a benefit as on a twin with more widely spaced engines - the 12 inch props on mine have minimal clearance with each other and I certainly wouldn't have been able to accommodate anything larger. These are so benign that on my first one, built a couple of years after taking the hobby up after a 25 year break and on its maiden - and my first twin flight - I lost an engine on its third circuit and after realising why the trim had gone "odd" flew another circuit and landed with little drama. Later in its life, I lost an engine either on take-off or in early stages of a few flights and simply continued for the duration of the other tank with little concession to the dead engine.

The only time they may bite is during stalled flight with one engine - my first one died after failing to recover from a flat spin where I suspected in hindsight that the inner engine had cut and my latest one is languishing in a rather deranged state after a failed take-off in stupid high wind and gusty - and partially cross wind - conditions where I suspect overconfidence and ineptitude with a switch setting may have disabled the downwind engine, causing a graceful arc into the ground nose first.

I would - and did - add a throttle to rudder mix to ensure my second version tracked vertically. I think I recall building my original one with thrust wedges but can't swear to it.