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How to start twin turbines, individually.

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How to start twin turbines, individually.

Old 08-09-2020, 10:07 PM
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Ragz
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Default How to start twin turbines, individually.

Currently I start my A10 with Jet Central Cheetahs with a single trim/throttle stick combination and they both start together. At times they fail to start together. It maybe a better idea to start them individually. What is the best method for this?

thanks in advance.
Old 08-09-2020, 11:04 PM
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sysiek
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Just unplug one cable wait until the one turbine starts plug it back and do the stick up and back and the second turbine will do the start sequence separately, I do the all the time with my twin turbine setup specially with propane starts
Old 08-10-2020, 04:37 AM
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I recall a post on here describing a mix through a 3 position switch which would hold one engine at idle throttle, allowing the other to see the throttle full/ idle command to initiate start. Once that engine had started, you could toggle to the opposite side of the 3 position switch to hold that engine at idle allowing you to start the second engine. 3 position switch in the middle would give throttle control to both engines. Before start, just sending an idle throttle command to the engine will not initiate a start, and once started, holding idle will not affect the running engine. Also a good way to simulate a flame-out in flight.

Position 1 - L Engine Idle/ R Engine Active
Position 2 - Both engines active
Position 3 - L Engine Active/ R Engine Idle

A single throttle kill switch would shut down both engines irrespective of the 3-position switch setting.


I'm considering the same for my current build project, but I haven't implemented it yet.


Paul
Old 08-10-2020, 05:27 AM
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You can use 2 switches to enable the 2 engines and one as kill switch to both. Don't use trims for engine control, it's lame and error prone.
Old 08-10-2020, 07:34 AM
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Auburn02
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Originally Posted by mauryr View Post
Don't use trims for engine control, it's lame and error prone.
Can you expand on this theory? It's much harder to accidentally hit down trim 3 or 4 times than it is to hit a switch while flying. Not that I have a habit of accidentally flipping any switches, but using trim rules out nearly any chance of it entirely.
Old 08-10-2020, 07:44 AM
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Trims take a long time to actuate and if you miss one or 2 clicks by mistake, you may set your engine to a different idle point. The engine may start anyways, but shutdown in flight due to a bogus idle signal.
Switches positively set a very specific idle signal which never changes.
Moreover, if you accidentally flip a switch (never happened to me in 10 years honestly, just choose a switch that's far from reach when actuating your flight controls) - the engine will not shut down immediately: you can use throttle cut functions which have some hysteresis and will not just send the 'off' signal, unless your throttle is also at near idle. Finally, you can also set a sound to play when flipping the switch, to ensure you're aware of what you're doing, something like "Engine shut down" etc.

Obviously this is just my opinion on the matter, but I'd never recommend using trim over a switch, it's just that much more immediate.
Old 08-10-2020, 07:49 AM
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I got two on/off switches connected to red wires of turbine throttle ch.

One on, start -> after engine runs switch another on and throttle up and down. Another starts easily..

Later I was lazy and started both at the same time...
Old 08-10-2020, 07:50 AM
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Dansy
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It all depends on the System JR, Futaba, Jeti ect....... some have locking switch (that’s what I used) some you can change the trim value so one or 2 click brings you to full trim..... so it really depends on what TX you have......
Old 08-10-2020, 09:10 AM
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Originally Posted by Auburn02 View Post
Can you expand on this theory? It's much harder to accidentally hit down trim 3 or 4 times than it is to hit a switch while flying. Not that I have a habit of accidentally flipping any switches, but using trim rules out nearly any chance of it entirely.
If using a kill switch I think a locking switch is the only way to go to do away with accidentally hitting the switch.
Old 08-10-2020, 09:16 AM
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Auburn02
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Makes sense. I fly with a Futaba 18SZ so no locking switches, I like the trim option myself - but I do adjust trim increment so that it's just 2 or 3 clicks from min to max value.
Old 08-10-2020, 01:44 PM
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I have a Skymaster small A10 and used a Futaba 18mz. IF you’re using Futaba I can send you the file, that allows you to use a 3 position switch to start one at a time.
only limitation I recall was you couldn’t shut down one engine at a time.
if you’re going down this route I’d ensure there was some foolproof way to ensure you move the switch back to give you command over both engines before you takeoff. it’s funny how an A10 can fly around on one engine and just feel a bit “funny”
Old 08-11-2020, 04:44 AM
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ravill
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I put throttle trim on a knob and that works for me!
Old 08-11-2020, 09:51 PM
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Originally Posted by bidrseed2 View Post
I have a Skymaster small A10 and used a Futaba 18mz. IF you’re using Futaba I can send you the file, that allows you to use a 3 position switch to start one at a time.
only limitation I recall was you couldn’t shut down one engine at a time.
if you’re going down this route I’d ensure there was some foolproof way to ensure you move the switch back to give you command over both engines before you takeoff. it’s funny how an A10 can fly around on one engine and just feel a bit “funny”
Yes I do use a Futaba 18mz... I will send you my email on PM. thank you .
Old 08-12-2020, 02:53 AM
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Originally Posted by Ragz View Post
Currently I start my A10 with Jet Central Cheetahs with a single trim/throttle stick combination and they both start together. At times they fail to start together. It maybe a better idea to start them individually. What is the best method for this?

thanks in advance.
I remember in the ductedfan era there was a British company making a small device where you could connect a single RX throttle channel and second channel input (ie Flaps) and two throttle output channels. This way you could lock one engine to idle while working on the other, for example flaps 120% down or another free channel.

Would be relative easy to design and make by some electronic company's in rc modelling?

I would be interested!

Rgds,
Gerald

Old 08-12-2020, 03:05 AM
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You can do that with a simple programmable mix assigned to a switch.
Old 08-12-2020, 03:21 AM
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CraigG
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Originally Posted by Gerald Rutten View Post
I remember in the ductedfan era there was a British company making a small device where you could connect a single RX throttle channel and second channel input (ie Flaps) and two throttle output channels. This way you could lock one engine to idle while working on the other, for example flaps 120% down or another free channel.

Would be relative easy to design and make by some electronic company's in rc modelling?

I would be interested!

Rgds,
Gerald
You may be referring to a product called the Mini Hobby Twin sold by Atlanta Mini Hobby, which works pretty much as you described:Mini Hobby ATL, Inc.

If you happen to have JetCats, they can be programmed to start individually by setting one to "Immediate" start and one to "Sequence". The manual explains how.

It's also good to be able to disconnect battery power individually to the turbines. That allows you to reset them, one at a time if you get a bad start.
Old 08-12-2020, 03:31 AM
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Originally Posted by Gerald Rutten View Post
I remember in the ductedfan era there was a British company making a small device where you could connect a single RX throttle channel and second channel input (ie Flaps) and two throttle output channels. This way you could lock one engine to idle while working on the other, for example flaps 120% down or another free channel.

Would be relative easy to design and make by some electronic company's in rc modelling?

I would be interested!

Rgds,
Gerald
Easily done with modern TX programming.....
Old 08-12-2020, 08:49 AM
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Originally Posted by Dansy View Post
Easily done with modern TX programming.....
Sorry, I might be a bit old school , I might need a new transmitter for that..., maybe the time for that is there when I start building the twin.

Cheers,
Gerald
Old 08-12-2020, 08:50 AM
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Originally Posted by CraigG View Post
You may be referring to a product called the Mini Hobby Twin sold by Atlanta Mini Hobby, which works pretty much as you described:Mini Hobby ATL, Inc.
That's the one!
Old 08-12-2020, 11:09 AM
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Dansy
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Originally Posted by Gerald Rutten View Post
Sorry, I might be a bit old school , I might need a new transmitter for that..., maybe the time for that is there when I start building the twin.

Cheers,
Gerald
Not what I was implying at all, If you have a 3 position switch and can do a few mixes.....it should be able to do this....
Old 08-13-2020, 04:56 AM
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Edgar Perez
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Attached is how I did it on a Jeti DS-24 soem time ago. It worked very well. It was somewhat complex due to a complication on how Jeti produces the servo values when using mixes.
I have since done it in the Powerbox CORE with similar techniques and it was much more straightforward.

Hope that helps.
Old 08-13-2020, 05:08 AM
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Ragz
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Hello Edgar, thanks for the jeti instructions. Do you have the Core instructions written down as well? I use a Core as well.

thanks
Anurag
Old 08-13-2020, 05:15 AM
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Edgar Perez
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Originally Posted by Ragz View Post
Hello Edgar, thanks for the jeti instructions. Do you have the Core instructions written down as well? I use a Core as well.

thanks
Anurag
Not in such nice documentation... lol

I will take some screen images tonight that should take you there.
Basic concepts are the same;
- one switch/button to select individual turbine control or not
- one 3 POS switch to select which turbine(s) to control when in independent control mode
- Two mixes per turbine to send the right values to it based on stick position and mode of control (send either an idle signal or send the throttle stick position)
- use of throttle cut or equivalent to manage the trim. You don't want to share the single trim button in the radio for two turbines.

Old 08-13-2020, 06:23 AM
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Ragz
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Thank you Edgar... look forward to it.
Old 08-13-2020, 07:49 AM
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I just recreated something similar to Edgar's method on my DS-24, using 2 physical switches, 6 free mixes and only 2 Logical switches.

Physical Switches
3 position for selecting 'Left Idle - Right Active'/ 'Both Active'/ 'Left Active - Right Idle'
2 position for Throttle Cut
You need to create the following functions first;
Throttle (default assigned function)
Throttle - L (do not assign a control to it)
Throttle - R (do not assign a control to it)
Throttle Cut (assign to your normal Throttle Cut switch)
Do not assign the System Throttle Cut - it will not work.

Create Logical Switches
L1 - Left Active/ Right Idle - 3 position switch AND Throttle Cut False(Set 3 position switch true for Middle and one end position)
L2 - Left Idle/ Right Active - 3 position switch AND Throttle Cut False (Set 3 position switch true for Middle and other end position)
Create Mixes
Mix 1 - Throttle to Throttle - L based on L1 Logical Switch True - Simple Linear Curve (-100 to +100)
Mix 2 - Throttle to Throttle - L based on L1 Logical Switch False - Constant at -100% (to hold at idle)
Mix 3 - Throttle Cut to Throttle - L - Based on Throttle Cut Switch position - Constant at -125%
Mix 4 - Throttle to Throttle - R based on L2 Logical Switch True - Simple Linear Curve (-100 to +100)
Mix 5 - Throttle to Throttle - R based on L2 Logical Switch False - Constant at -100% (to hold at idle)
Mix 6 - Throttle Cut to Throttle - R - Based on Throttle Cut Switch position - Constant at -125%



Paul

Last edited by JSF-TC; 08-13-2020 at 08:00 AM.

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