Twin ic throttle mixing

[gillyg1]

I fly futaba, using a 8J s-fhss protocol, I want to be able to program 2 channels to operate twin throttles on my tx. Ie , channel 3 master Throttle, with a slave channel operating the other throttle, twin ic BF110, having scand the manual this would appear as not an option. So thinking I will have to set it up manually and use a y lead.

If anyone knows different? Please could you advise me. If not which futaba tx would give me the option to allow tx setting up for twin throttle operation ?

And please I'm not swapping out to any other brand of radio, as have 11x s-fhss recievers.

[Alan Gorham_]

I think it is perfectly possible on the 8J transmitter. You use one of the 6 programmable mixers and assign channel 3 as the master and whichever free slot on the Receiver you wish to use as the slave. You then make the throws and end points of the slave channel exactly match the master channel.

[Jon H]

I have the same radio and it should be possible on a simple mix but i will need to check.

My real question is why do you want to do it? i fly/have flown about 6 different twins plus a 4 engine Hercules and have always just used y leads for the throttles. With identical servos, and the carbs/linkages set up as close to identical as possible its not normally an issue getting everything working well together

[Peter Miller]

Quite frankly I see no need to use mixers. Over the years I have done a few twins. I set the throttles as close as possible and then just go for it.

My Grumpy Skylark was great, it was quite hard to tell which engine had stopped. Slight variations between engines has never been a problem, even when I was using small Cox engine without throttles.

Of course if you like adding complications go for it. I usually find that the added complication causes more problems that they help

Edited By Peter Miller on 14/05/2019 14:06:07

[gillyg1]

Cheers Guys for the speedy reply. Really only wanted to know if it was feasible on an 8J. Being my first twin, thought it might be a better option rather then fiddling manually. Obviously I will be using the same servos, matching the linkages /travels etc.

And it would seem a slight variation in rpm is not critical then. As said why complicate the issue. And shell out on an expensive transmitter with all the " bells and whistles" when it's not required.

Do you guys use a tacho? Or just set up by ear/ sound, for balancing the engines?

[Jon H]

Mechanical setup is the most important thing. Get that right and its likely the engines will perform pretty closely anyway.

When it comes to tuning, start one engine and tune it for max power. Make sure you warm the engine up thoroughly before you tune it by holding it at 70-80% throttle for a while before winding it up. Engine tuning changes with temperature (more on this later) so dont shoot yourself in the foot by doing a 3 second run up.

Anyway once its set on both the main and slow run needles turn it off and do the same with its best mate.

Refill the tanks and start both. Bring them to half throttle and hold for a good 30 seconds before opening up.

You may now find that one engine dies, if so restart it and dont touch anything. You already tuned it for its normal running temperature so leave it alone. Just do a longer run up to make sure the engine is up to full temperature. A friend had a pair of enya 46 4 strokes in a twin and we found that we needed a solid minute of over half throttle running before the left engine would tolerate full power. If we ran it richer, it ran like a donkey in the air which is why its important to warm up the engines before you tune them.

Once tuned just get on and fly it. If possible, adjust linkages to give as close to identical power at half throttle, and its nice if the idles are close. Dont tune with a tacho, just use your ears and use the tacho as a relaity check. The most important thing is to keep them both running, and if one stops dont panic! Open up the remaining engine, control the yaw with rudder (not aileron), and do a normal circuit to land. Dont be tempted to cut and glide as twins are normally heavy and glide like bricks so you will end up short, try to open up the power and it will spin. Keep it flying fast and you will be fine.

 

Oh i forgot, use 80% throttle for takeoff and not full power as an engine cut is less likely, and refrain from slapping the throttles about. Use the throttle smoothly, counting 1, 2, 3 from idle to full power especially on a go around. Once you find a happy throttle setting just leave it alone! 

Once used to the model you can throw out some of the above, but it has to survive the maiden first so take it easy and work up to it. 

Edited By Jon - Laser Engines on 14/05/2019 15:14:51

[Martin Harris - Moderator]

Starting is where I find the ability to control the engines separately has some particular advantages. I have a 3 position switch which is set to idle starboard, idle port or full control on both.

I start the port one first, check it for full throttle running and then switch control to the starboard engine, locking the port one to idle. I then start and check the starboard engine and then activate both throttles for a full power check. Having the running engine locked at idle means I can manipulate the throttle on the one I'm starting with no sudden surprises!

I can also practice engine outs with the switch selecting either engine to idle.

Having the ability to throttle back an engine can also add to the repertoire of an aerobatic twin...

I'm afraid I don't know whether your transmitter is capable of this level of sophistication.

I balance by ear - but I'm more concerned with reliable operation than getting the RPM to any particular figure and I can't remember the last time my tacho came out of my modelling box.

Edited By Martin Harris on 14/05/2019 16:00:45

[gillyg1]

Cheers for that Jon 🖒. Hope the business is doing well and all now back in production. I do visit your website periodically to abreast of your situation. Keep up the good work.

[Jon H]

Yes! the planets have aligned, hell has frozen over and a pig somewhere is gaining altitude...at least i assume so, as all of my singles are in stock. Time for a lie down.

Back on topic, Martin's starting method is a reasonable excuse for a mix. Certainly its the best argument i ever heard but i will stick with y leads myself as i dont think the 8j will wear it

What engines are you using the in 110 by the way?

[cymaz]

I’ve done it !!

On a Seagull Dual Ace twin. With an 8ch Frsky fasst Rx and Futaba 9cap.

- took most of a Saturday to figure out

 

Edited By cymaz on 14/05/2019 17:14:32

[gillyg1]

Cymaz- sounds intriguing, but I won't be purchasing another transmitter.

Jon, using RCV 58 CDs. In a Richard Wills 72 " BF110. Super little engines, never had one cut, run them inverted, and actually have to use throttle cut to stop them. Actually have 4x off them, so 2x spares. Was thinking of the Tony Nijhuis Beaufighter maybe sometime in the future, yes I know " pie in the sky " however he doesn't list it in his collection for some reason, so don't know if there's a laser cut parts kit , nacelles, spinners etc available anywhere. I have read the thread on here I think? Same as BT did one in the early years, and that's not listed anywhere either. So open to options for another twin to accommodate 2x 60 size four strokes.

[Alan Gorham_]

I don't think there is any need to contemplate buying a new transmitter. Cymaz has given you a viable method to copy in my opinion. Futaba transmitter software has a common functional core between models.

After your original post I read the 8j manual and recognised that the mix would be possible as I stated in my reply to you.

You've been a bit dismissive of some genuine help there in my opinion.

Edited By Alan Gorham_ on 14/05/2019 19:33:11

[cymaz]

Just thought I would mention my Tx and Rx set up, just to give some idea that there are several mixes involved

[CARPERFECT]

It`s easy with the 8 and 10 j.

set up a mix . master is throttle, slave is gear so channel 3 and 5. in the mix you set rate to +100 mix to on. Plug your second engine into channel 5 . in screen 1 select Aux-chan it shows channels 5 to 10. against ch5 change the control to dt5 or dt6 this will give you your trim for the second engine.

[Jon H]

mixing the channels is easy, having the setup detailed by martin is a little more complex and (without looking) i think is beyond the capability of the 8j. I would need to investigate it on my own set to be sure but i think its a bridge too far.

I have never used an rcv 58 and have only heard stories. Some swear by them, some at them. without direct experience i cant really offer much more than the posts above.

For twin No2 be careful with a beaufighter. I would love one myself but its not an easy aircraft to model as more or less all of it is behind the c/g. Not a problem with a pair of Bristol Hercules bolted to the front of the wing but a bit of a challenge for us.

If you fancy a bit of DIY stuff you could always take a single engine model and modify it into a twin. I did it with a Pulse 125 and there is another thread on the go about designing a sport twin. If you have or can get hold of a sacrificial airframe you could let you inner aircraft designer run wild!

[Former Member]

[This posting has been removed]

[Chris Walby]

Speaking from my very limited experience of my two twins, SG Dual Ace Laser 70's and SG Mosquito Laser 70's is:

Dual Ace is Y lead, access to the throttle servos is very easy and any "on the day tuning" is a piece of cake!. I can get to both needles as they are still running in, but keeping it simple works.

Mosquito engines are behind the cowls from hell! So I set them up on separate channels with a mix....well a mix to get the throttles, then another mix to get throttle cut and a bunch of re-binding to get the fail safe to work on both.

To say its a pain is slightly unfair as its the installation of cowls that is the problem and to be fair the mix makes it much easier to set up from the TX...as long as you can remember how you got there last time + and this is the big one. That messing around with the TX at the field does not change something else to the detriment and surprise of the pilot.. Its a long walk with a bin liner, but only the once!

Separate note, I upgraded from DX8g1 to DX8g2 and all of the sub trims etc are messed up, I'll need to take the cowls off and reset the throttle and U/C servos up again (easier to get Al's to service the TX),

[Peter Miller]

While reading al these posts I am reminded of the big sign that I once saw in a RAF model club. It says "KISS."

IT is a great piece of advice which I personally adhere to.

[Denis Watkins]

I have to agree with Peter Miller, that our steeds are complex enough without too many features where we may overlook something during our routine to fly.

4 sticks to take care of is enough most of the time

[Chris Bott - Moderator]

Don't forget to set and test failsafes. I've no idea about Futaba but some other receivers have different failsafe outcomes for throttle channel to all other channels.

[Jon H]

Couldnt agree more. Get the mechanicals right then used the software we now have available to ice the cake and add the cherry. If you try and bake the cake with the software..well, good luck with that.

[gillyg1]

I agree chaps.mind made up, set up the mechanics correctly, and shouldn't have a problem, thanks for everyone's input though. Much appreciated.

[Chris Walby]

I don't have a issue with the technology per se as with the retracts it allows individual setting up that would take 10 time longer mechanically.

Its the human element (me!) that spent quite a lot of time getting the system to do what I wanted it to do and now + 6 months down the line I can't remember quite what I did. There lies the risk of me doing something and inadvertently changing something else....In the quite corner of the workshop I would probably twig what I had done, but at the field....not so sure.

So not an issue (for me) if its done and dusted, but is if I have to go back and work out all the sub trim, mixes etc later on..

[Charles Smitheman]

I manged to mix the throttles on my Ripmax Harmony using my Futaba T14SG. The only thing I have failed to get to work is engine cut on the second engine. I did write down how I did it. It was a pretty agonising process for one who prefers carving balsa.

One reason for bothering with a twin i.c. is surely the challenge of being ridiculously complicated. We could just stay home and watch the telly after all. But each to their own.

I had a goal with mine, after watching a video on you tube of a Pica Duellist doing a 540 degree "stall turn"

I think that most of my clubmates thought me mad and probably dangerous, but I have managed the manouver on a few occasions, and the model still survives!

I enjoyed the challenge, yes it was worth it

[Chris Walby]

I have tried throttle mixing on a small electric twin as it has no rudder servo, from memory it produced some very non scale yaw/pitch effect which was most unpleasant and fly. Not needed as it was a land launch so no benefit to taxiing either!