Twin Piper Comanche

[shanemarsh28 11]

As some of you might know, in the next stage of my flying I'm looking to find something scale and I have an idea. 

I want to build something that's a bit special - a proper build if you like and something I'm considering a twin engined passenger scale plane. I have the Twin Piper Comanche in mind because it's available as ARTF by several manufactures including Seagull so parts "should" be easy to get. 

Over the past few days I've scoured the internet for issues with twins and predictably it's always the engines that appear to be the issue. Engine reliability is key. Worryingly, it seems common practice to match the engine RPMS by richening the faster engine. Leaning out the slower engine would be  big no no - unless your a pilot that enjoys deadstick landings. I feel unhappy about using mixture to match the the engines because it always leaves you with engines that are not tuned optimally - one engine will always be rich. Also engines that don't power up evenly will cause takeoff issues.  

So this is what I have in mind:

• A scale airframe build with nav & landing lights /flaps / retracts
• Two electrical systems - independant flight battery / aux battery (for retracts/lights/fuel pumps etc..)
• EITHER  suitably sized petrol  or glow (4 stroke). I hate the sound of a two stroke twin!! eerrge ... Before you ask,  I'm not interested in an electric twin
• Twinsync to balance the engines: http://www.wolfmodels.net/wrctwinsync_manual.pdf. This system controls the throttle servos with magnet based RPM sensors. Twinsync also has a safety feature that during a deadstick, it brings the running engine to idle until you do something. The idea is that it prevents uncontrolled flat spins, yaw or roll and allows you to control the aircraft in a similar way to any other deadstick landing (provided you keep the engine at idle).
• **geek alert** Two double throw RC switches that interrupt the servo signals from Twinsync linked to a three way switch on the transmitter. This idea would allow for easy engine tuning on the ground (with both engines running) but would require at least 5 channels to setup (Engine port, Engine starboard, Engine Main (with throttle curve for Twinsync), Twinsync AUX(on/off) and finally a channel connected to the double throw switches that allows either Twinsync output or direct transmitter output for each engine. With some mixing, in theory it would then be possible to switch the throttle between the port side engine (while the other is running at idle), starboard engine (while the other is at idle) and both engines synced together from the transmitter. This in my mind resolves ever having engines that are not properly tuned.

Now .. if all that makes your head hurt I'm sorry.

Regarding the field - we have a short ish runway and twins obviously have a high wing loading, a bit more weight and therefore need more space to land. I'm concerned about the length of the runway for this type of aircraft. Has anyone flown a twin out of Fickleshole before? Basically I want to ask if there anything I need to consider outside the usual site rules (weight/noise etc)? Speaking of which .. Is it likely I can get a 4 stroke twin to run within our sites noise limits?

Like I said - I want to build something special and although I might be flying into the deep end it sounds like one of those "Ultimate" type of aircraft to me IF I can get it right. I found a video of what I'd hope the finished plane to look like: https://www.youtube.com/watch?v=2x7htUmEG1I

 

Please let me know your thoughts (don't be too brutal haha)

Edited August 29, 2017 by shanemarsh28

[Bravedan 106]

Moi, Brutal?   

Pretty sure engine power sport twins have flown Fickleshole, memory says Oily (Peter) or Roger?  Dunno about twins at scale model weight though in the available space, every TO and landing would need to be perfect.

Noise very likely an issue, suspect much more of a problem with petrol than four stroke glow.

A while back i did a couple of electric twins (both still extant) and used "throttle" to "rudder" mixing for differential thrust, both with stick to act as rudder and trim to synchronise throttle. This only used two channels and was effective, so effective apart from the sync that I could fly smooth "bomber" circuits on "rudder" and "throttle" using only the LH stick (Mode 2). With OpenTX virtually anything is possible, and it keeps it simple. Your solution is tech heavy and the more you have, the more there is to not work as expected under stress, fail or not be set right in the first place!

Two Channels, one feeds throttle servo 1 as master, slave to throttle servo 2, the other channel fed to throttle servo 2 as master, slave to throttle servo 1.

Yours is nice idea but "KISS" and some attentive piloting is always best.................................

 

 

[shanemarsh28 11]

KISS is the way most people do it and it might be OK. 

I see so many horror stories online where they have the simple two channel setup for the engines but no matter how accurate you are, the engines will almost never be in sync. So you either have to put up with the sound of the engines running out of sync (and the associated thrust differences) or you have to detune one of the engines to try and get them to match. For me, in a plane where it's critial for the engines to keep running the last thing I'd want to do is detune an engine. Some have used throttle curves but that sounds really hit and miss. One thing is for sure - if I do decide to build a plane like this I won't do it lightly. Test - test - test. and then test the test

Weight looks like it would be OK and it has flaps so that might help a bit with takeoff and landings. Segaull say it should be around 4.8-5kg + fuel and they recommend 46-55 sized two stroke Glo.

I will ponder some more ...

[Bravedan 106]

Differential thrust management does not "detune" an engine! You do not tune an engine with throttle.

Keep in mind than most manufacturer recommendations are based on American site standards and NOT draggy short grass strips (no insult to the now good grass cutter intended!)

[shanemarsh28 11]

1 hour ago, Bravedan said:

Differential thrust management does not "detune" an engine! You do not tune an engine with throttle.

I have a feeling I've not explained what I mean properly - sometimes getting what's in my head out into words I find difficult ..

What I mean is - Assuming that you have two identical engines, idential throttle setups and the barrels are opening and closing exactly the same distance, no two engines will run exactly the same. It's my understanding that manufactuign tolerances ensure that even identically setup engines will run differently. 

This must mean that when it comes to fitting them in a plane together, there will always be an engine that runs faster than the other. In other words, one engine will be stronger. 

In my research, I discoveved that the most common way to combat this is to RICHEN the stronger engine and theirby reduce peak RPM so that at peak power, the RPM's are more or less the same. In my mind, if you richen an engine from it's peak you have intentionally de-tuned it, hence the term. This is the part that I don't like and wish to avoid. I'm sure it would introduce other problems - a rich engine can be slower to pick up from Idle (as an example).

So - the idea of using Twin sync is that the contol board will make independant and slight throttle (not mixture) adjustments via the servos. This way it wouldn't matter if the peaks or performaces are different, the control board will match the RPM's of both engines together and as each engine will have the same sized prop, the thrust of each engine will be (in theory) more or less eqal throughout the entire throttle range.

I hope that makes more sense.

 

Edited August 30, 2017 by shanemarsh28

[Bravedan 106]

Shane, It made sense before, but:-

1. I question the validity of the "adjust the mixture to synchronise twins" advice you found out there, not your interpretation of it.

2. I don't think it's necessary to have automatic throttle compensation in the same way I do not mix elevator to flap or mix up a knife edge mix.

3. I think the "Twin Sync" is possibly an application seeking a need rather than the other way round, in the same way that people fit in flight adjustable mixture to RC Helicopters, which in effect is either admitting they can't set an engine up for toffee or that fiddling is more important than flying. 

However, if I was up for a scale twin I'd be going electric with a sound system, a result as "real" as is possible and considerably more issue free in use. 

I hope to be able to see the result if you go for it, Good Luck, and keep reporting here please!

[shanemarsh28 11]

Okay thanks for clarifying. If I do decide to build it, I'll be sure to post my progress here

Thanks for your help!

[Pilot Ben 28]

Surely you could set it up so that the rudder is synced with the throttle? That way regular up/down is thrust and left/right is differential thrust so in flight you just trim it and takeoff just use rudder as normal. All it would need is 2 Y-leads and a bit of mixing?

This might have been suggested already but I didn't really get all of that KISS stuff

 

B

 

 

[shanemarsh28 11]

On 31/08/2017 at 6:41 PM, Pilot Ben said:

Surely you could set it up so that the rudder is synced with the throttle? That way regular up/down is thrust and left/right is differential thrust so in flight you just trim it and takeoff just use rudder as normal. All it would need is 2 Y-leads and a bit of mixing?

This might have been suggested already but I didn't really get all of that KISS stuff

 

B

 

 

That could be an option I'm really not sure. I've heard of people mixing the rudder with the trottle on twins so that manuverbility in the air and ground handling is improved.

After a play with Ians twin on Sunday, and chat with Rob at Avicraft who has flown the Piper Commanche before, I have decided to go ahead with the build. I've also ordered the optional retracts and twinsync. Not 100% sure if I will use Twinsync in the final build but I do think it's worth the time to see how viable/reliable it is. If I decide not to use it and go for the Keep It Simple Stupid (KISS) approach, I should be able to return it or re-sell it on ebay.

I'll keep you posted on the build

[Emma 47]

On 31/08/2017 at 5:58 PM, shanemarsh28 said:

Okay thanks for clarifying. If I do decide to build it, I'll be sure to post my progress here

You've had the kit for 2 days now, is it ready yet i'd love to see you maiden it on Sunday.

Em x

[shanemarsh28 11]

1 hour ago, ChasePlane said:

You've had the kit for 2 days now, is it ready yet i'd love to see you maiden it on Sunday.

Em x

Wish it was! Twin Sync has arrived from the Netherlands today - very happy about that. I always get a little worried when ordering expensive things from abroad - never quite know if it's going to arrive so I'm delighted it did. 

So .. it's turning into a MEGA build and this evening I was in need of some retail therapy so I went a bit mad with the credit card!

I ordered:

• 11 servos (RC Model World) (Might be one short - not 100% sure)
• Two Smart on-board glow drivers (Hobby King)
• Navigation & Landing light set (Hobby King)
• Fuel Tubing (Hobby King)
• Two FrSky X8R receivers (One to bind with channels 1-8+telemetry and a second to bind to channels 9-16) (T9 Hobby)
  Richard assured me this dual receiver setup is best - I did ask him about all the  SBUS options available before deciding on this)
• Altimeter (Variometer) (T9 Hobby)
• Servo tester (T9 Hobby)
• 30 Min epoxy (T9 Hobby)
• Male & Female servo plugs (T9 Hobby)
• Two ASP 61 FS four stroke engines with baffled silencers (Just Engines)
• Rubbing Alcohol (Amazon)
• Gorilla 5 min epoxy (Amazon)

So I think I've got most of it now. This will be a semi scale with all the trimmings  

Will need to think about batteries but I'll wait until I start the build and I see how much space there is in the fuselage etc pick the right shaped/sized batteries then. I'm sure I'll need at least two - flight pack and a second for onboard glow/navigation lights etc.

With some luck - all will arrive this week and I can start the build after the weekend! #excited!

 

PS: I won't maiden this plane - I'd prefer someone with far experience than me to take it for it's first flight.

Oh I nearly forgot.. 

Two 12x6 props.

Edited September 11, 2017 by shanemarsh28

[Pilot Ben 28]

Wow Shane looks like when I get hold of my savings book

And now I know where all the X6R receivers that T9 have gone!!!!!

 

[Emma 47]

10 hours ago, shanemarsh28 said:

I ordered:

• 11 servos (RC Model World) (Might be one short - not 100% sure)
• Two Smart on-board glow drivers (Hobby King)
• Navigation & Landing light set (Hobby King)
• Fuel Tubing (Hobby King)
• Two FrSky X8R receivers (One to bind with channels 1-8+telemetry and a second to bind to channels 9-16) (T9 Hobby)
  Richard assured me this dual receiver setup is best - I did ask him about all the  SBUS options available before deciding on this)
• Altimeter (Variometer) (T9 Hobby)
• Servo tester (T9 Hobby)
• 30 Min epoxy (T9 Hobby)
• Male & Female servo plugs (T9 Hobby)
• Two ASP 61 FS four stroke engines with baffled silencers (Just Engines)
• Rubbing Alcohol (Amazon)
• Gorilla 5 min epoxy (Amazon)

So I think I've got most of it now. This will be a semi scale with all the trimmings  

I can see i'm going to have to teach you how to shop but at least if it doesn't work we can blame Richard.

10 hours ago, shanemarsh28 said:

PS: I won't maiden this plane - I'd prefer someone with far experience than me to take it for it's first flight.

So you have until the first Sunday of the month to complete it then. is it a job for Funfly James by any chance

it's going to be some model when its finished though x

[shanemarsh28 11]

I think I can get it done. If I start after the weekend it gives me a two week build! (well actually less than that because mother in law will shout at me if I leave a model plane on her glossed dining room table for any longer than it has to be!)

May pop up on the Saturday before (all being well) on the 30th September to run the engines in. 

6 hours ago, ChasePlane said:

So you have until the first Sunday of the month to complete it then. is it a job for Funfly James by any chance

Yes I hope so, if he's happy to

9 hours ago, Pilot Ben said:

Wow Shane looks like when I get hold of my savings book

And now I know where all the X6R receivers that T9 have gone!!!!!

 

I've spent a LOT of money - seveal hundreds of pounds more than I planned to but I think almost everyone has a special plane in their feet and this will be my special plane I guess. It wont be an everyday flier but hopefully one I bring out on the calmer days and use at the odd display (when I finally work out my B cert).

I only got two receivers? Richard must be running low on stock! haha

Edited September 12, 2017 by shanemarsh28

[Emma 47]

17 minutes ago, shanemarsh28 said:

 I think almost everyone has a special plane in their feet and this will be my special plane I guess.

I dread to think what mine will be or how many 000's it will cost.

Don't want to duplicate what other club members have so is going to need a lot of thought.

However as I have time on my side as I'm currently Orville the duck lol x

[shanemarsh28 11]

12 minutes ago, ChasePlane said:

Don't want to duplicate what other club members have so is going to need a lot of thought.

Needs to be something unusual. So not a p51, Spitfire, Cub or anthing like that. 

Heres an idea - Lockheed P-38G?  https://www.motionrc.com/products/flightlinerc-p-38l-lightning-pacific-silver-pnp

Edited September 12, 2017 by shanemarsh28

[Emma 47]

That's nice.

I'm thinking 1/10 scale.

Quite like this one

https://centuryjet.com/shop/airplane-kits/prop-aircraft/boeing-b-17/

 

[shanemarsh28 11]

Oh wow! That is a beauty

[Pilot Ben 28]

I like the F22 next to it  

[shanemarsh28 11]

It feels like Christmas has arrived

[Pilot Ben 28]

One of the best things to see on Wednesday! I'd be careful with hobbyking extension leads though I've had lots of problems with them so now don't use them. The best ones are from T9 they are twisted servo leads. Brilliant and strong and yet fairly cheap to buy.

I think I'm going to have to wait till Christmas now before I buy my next plane.

Due to some reasons I won't be getting the Tucano but I will say it'll be as quick but yet much much cheaper!

 

Are you going up on Sunday?

 

B

 

 

[shanemarsh28 11]

2 hours ago, Pilot Ben said:

One of the best things to see on Wednesday! I'd be careful with hobbyking extension leads though I've had lots of problems with them so now don't use them. The best ones are from T9 they are twisted servo leads. Brilliant and strong and yet fairly cheap to buy.

I think I'm going to have to wait till Christmas now before I buy my next plane.

Due to some reasons I won't be getting the Tucano but I will say it'll be as quick but yet much much cheaper!

 

Are you going up on Sunday?

 

B

The door has been going all day! Just the servos left to arrive.

Thanks for the tip on the hobby king leads. I wasn't planning to use them. I got a few extension cable but I'm expecting to have to make some of the wiring myself. Time to dust off the soldering iron

Aww I was going to ask if you were too build the Tucano.. I will look forward to see your next project whatever that turns out to be!

Yes! I'll be there Sunday all being well. Early weather forecasts look fantastic

 

 

 

[Pilot Ben 28]

It's not that I don't want it. I do! It's a brilliant model but to be brutally honest Shane it would genuinely cost at least £900 as the kit is £300, engine is £300, servos £120, retracts £100 plus the stuff like rx battery switch etc etc... And that's just too much for a 5kg model let alone what my budget can afford.

I've decided to combine my need for speed and a new heavy winter plane by getting either an Acro Wot XL or Wot 4 XL and putting a mahusive engine in the front  

Come New Year time watch this space!

You are remembering its 3rd Sunday?

 

B

 

Edited September 13, 2017 by Pilot Ben

[shanemarsh28 11]

Ahh Yes.. my credit card company is feeling the strain! The current bill for the twin is near as makes no difference £1000. I won't be building another model like this for a while that's for sure  Lol sounds like you make a better account than I do though. I totally forgot about the servos thinking .. Ahh there just 10 quid a pop. As you say.. £120 later!

In some ways, building Artfs like this I think is the eaaiest but by far the most expensive way of doing it. 

I think you'll have bags of fun with an AcroWot. The covering is a bit pants (decals fly off in the breeze) but other than that.. well built. Did consider one and may still get one if anything ever happens to the Bullet.

 

 

[Pilot Ben 28]

And as the Tucano is meant to be so fast it calls for HS645MG's all round at £30 a pop!!!

The only problem I have about flying is that at the end of the day I am a kid playing an adults game but that won't stop me

 

see you on suday

b