Advice and links for my first twin engine build

[Vimana89]

So I can fly a trainer, and my crazy RET delta planes work, and I'm looking to expand my horizons. There were multiple directions I wanted to possibly try for my next big project, so I chose some of my favorite ideas and had a poll. Bombardier Dash 8 twin engine turbo prop airliner won. It's a plane I've been interested in possibly building for a while now, I really like its simple elegance and how the features go together. This one will stretch my skillset and require some learning, as it will be my first twin engine build, but I think it will be worth it.

I plan to build in simple FT style out of foam board, what would be considered a mid sized model. It might be a little less rounded and scale in some areas but the profile will be faithful(for example, it will look as much like a scale Dash 8 as the FT Viggen looks like a scale Viggen jet, If I do it right). I plan to use two 250 size motors, 2205 or equivalent, possibly Graupner 2806 ultra 1900 KV motors, or FT radials, mounted on FT swappable sized firewalls, and use these 5040 6 blade props https://www.amazon.com/dp/B01L25DCP6/?tag=lstir-20 for the best scale look. I can see no reason why I'd absolutely need rudder action to fly this, especially if I do thrust differential, so this will likely be a 4 channel AET yank n' bank, but if somebody more experienced knows better and thinks a rudder would add a lot of performance and be worth the extra channel, let me know!

I have read the FT quick guide on twin engine planes, and plan to review the video and Josh Bixler's podcast about twin engines again. I think I have a pretty good idea about the electronics part of wiring a twin engine plane. I also plan to research guides on setting up thrust differential with the FS/Turingy I6 transmitter. I know this topic is frequently addressed here, and I plan to do my own research and look at some of those threads, but in the mean time, if anyone swears by a certain guide or instructional video that helps me learn to configure my twin engine planes, I'd really appreciate if you linked it here. Also, if anyone has any advice on the subject to share from their own experience, I'd be grateful for your help.

 

[Vimana89]

Two of my main questions are what thrust angle, if any, do I need with twin tractor engines, and how big a battery would be reasonable to run two 2205 or equivalent motors? Should 3s be fine for this one, or should I go 4s? I have a 1300 MAH 3s laying around but not sure if that's enough juice.

 

[Grifflyer]

Two of my main questions are what thrust angle, if any, do I need with twin tractor engines, and how big a battery would be reasonable to run two 2205 or equivalent motors? Should 3s be fine for this one, or should I go 4s? I have a 1300 MAH 3s laying around but not sure if that's enough juice.

Thrust angle shouldn't be much different from your conventional plane unless the plane has some unique incidence angles. I ran my mini guinea on a 3s 1300mah with two 2205 and it was fine.

 

[Vimana89]

Thrust angle shouldn't be much different from your conventional plane unless the plane has some unique incidence angles. I ran my mini guinea on a 3s 1300mah with two 2205 and it was fine.

Not much different from a conventional plane, as in both of my engines are tractors running CCW, so both should be a bit down and to the right in terms of thrust angle?

 

[Grifflyer]

Not much different from a conventional plane, as in both of my engines are tractors running CCW, so both should be a bit down and to the right in terms of thrust angle?

No, you want them to point straight ahead, and then add up or down thrust angle depending on how it reacts when you apply throttle.
So if it climbs with throttle you want a bit of down thrust and if it dives with power you'll want to add in a bit of upthrust.

If your funds allow it, you'll be better off running a counter rotating setup.

 

[whackflyer]

I agree with @Grifflyer, you’ll be better off with a contra-rotating setup. Just reverse 2 ESC leads and put a dab of hot glue on the motor shaft to keep the nut from unscrewing itself, or just use a nylock nut.

 

[Vimana89]

No, you want them to point straight ahead, and then add up or down thrust angle depending on how it reacts when you apply throttle.
So if it climbs with throttle you want a bit of down thrust and if it dives with power you'll want to add in a bit of upthrust.

If your funds allow it, you'll be better off running a counter rotating setup.

Alright, thanks, thrust angle issue solved. How would I do a counter-rotating setup? I have no idea where to start. I'll start reading up, but do I need special motors or some extra part or an expensive TX?

 

[Vimana89]

I can get graupner motors which I described above and they specifically come in either CW or CCW for the twist of the cap nut, which sounds like it could help. I'm just all bungled on how I'd reverse which one to keep them from unscrewing, and how exactly to mount the props.

 

[Grifflyer]

Alright, thanks, thrust angle issue solved. How would I do a counter-rotating setup? I have no idea where to start. I'll start reading up, but do I need special motors or some extra part or an expensive TX?

A counter-rotating setup is when on a multiple engine plane, the motors are spinning opposite directions to reduce the effects of P factor. All you have to do is get CW and CCW props of the same make and model and mount one on each motor. If one or both of the motors are propelling air in the wrong direction, then you just have to switch around two of the leads going from the ESC to the motor.

I can get graupner motors which I described above and they specifically come in either CW or CCW for the twist of the cap nut, which sounds like it could help. I'm just all bungled on how I'd reverse which one to keep them from unscrewing, and how exactly to mount the props.

If they come with a lock nut then it wouldn't really matter which way the thread on the motor spun as long as you tighten down the nut.

 

[Merv]

How would I do a counter-rotating setup?.... do I need special motors or some extra part or an expensive TX?

Motors are easily reversed, just switch any two of the three wires from the ESC. You will need CW and CCW props.
Expensive Tx? No. Any hobby grade Tx will work, provided you have a spare channel.

 

[Vimana89]

Motors are easily reversed, just switch any two of the three wires from the ESC.
Expensive Tx? No. Any hobby grade Tx will work, provided you have a spare channel.

Alright, thanks. My FS I6 should be more than adequate, and provided I need nothing else to make the setup work, reversing the wires is an easy thing I'm already proficient in. I can use motors with the proper thread for each side to avoid the problem @whackflyer mentioned and having to glue anything. I'll get a little adapter for my 1300 MAH battery(It's XT60, I need XT30). Thanks everyone for the help so far, this is shaping up to be a fun project.

 

[Merv]

Should 3s be fine for this one, or should I go 4s? I have a 1300 MAH 3s laying around but not sure if that's enough juice.

As stated above a 1300 mAh 3S will work for 1 motor, I'm not sure if it will work for 2.

The amp supply formula is: mAh / 1000 x C. If your battery is 35C, then you can draw 45 amps (1,300/1000 x 35). If your motors draw less than 22.5 amps each, you will be fine.

 

[skymaster]

hello yu all . so lets say he wants to put 2 x 2212/6 2000kv motors with 2x30c esc would a 3000 mAh 40c lipo would it fine or not?

 

[basslord1124]

For counter rotating, first figure out which direction you want them to turn. Once you got that, you'll swap 2 wires on one of the ESCs. And then you'll probably to get an opposite prop for the other side (ex: 1 would be a CCW prop and the other would be a CW prop). It's not too bad once you look at it. Did it on my Seaduck.

 

[Headbang]

As stated above a 1300 mAh 3S will work for 1 motor, I'm not sure if it will work for 2.

The amp supply formula is: mAh / 1000 x C. If your battery is 35C, then you can draw 45 amps (1,300/1000 x 35). If your motors draw less than 22.5 amps each, you will be fine.

Making an assumption ratings are accurate. Most of the time real life performance is less then half of the battery rating. Even pulling 20amps on a 35c 1300mAh battery is pushing it in practise. Good choice of battery would be a 2200mAh 50c 3s for this project. Which would lend it's self well to any B or C pack sized projects in the future. I assume this is going to be in the 1000 to 1200mm range for wing span, so that is a good choice for that size wing wieght wise as well.

 

[Vimana89]

So my electronics/power loadout is looking like:

*1x 2200 mAh 50c 3s battery
*1x Graupner 2806 Ultra 1900KV 250 sized motor CWW
*1x Graupner 2806 Utlra 1900KV 250 sized motor CW
*2x ESC(Would there be any noticeable difference in performance between 12A or 20A ESC's here?)
*2x Gemfan 5x4 six bladed props
*1x FSIA6 receiver(the good version that binds instantly and doesn't have a flimsy casing with exposed prongs sticking up)
*3x servos(probably basic 9g cheapos), and whatever extension cables they might require
*1x Y harness cable

 

[Merv]

hello yu all . so lets say he wants to put 2 x 2212/6 2000kv motors with 2x30c esc would a 3000 mAh 40c lipo would it fine or not?

Yes, that would work. A 3,000 mAh 40C battery will supply 120amps (3000/1000 x 40).

@Headbang makes a good point, make sure you are using the continus C rating not the burst rating. A burst rating is ONLY for a few seconds. It's always a good idea to leave yourself a bit of headroom, we don't live in a perfect world.

I use Turngey/Zippy brand batteries, their ratings seem to be about right. I routinely draw 45 amps from a 2200 mAh 25C battery. I cannot speak to other brands, if their C rating is inflated.

 

[Merv]

Would there be any noticeable difference in performance between 12A or 20A ESC's here?

I have not looked up the amp draw for your motors. If your motors will not draw more than 12 amps, then their should not be any difference in preformance. That is no difference due to the amp rating.

Think of the amp rating on an ESC as a number not to exceed. Like the rating on a fuse or breaker, if you exceed it you will blow it. Also if your ESC has a BEC, you need to include the servo draw.

 

[FastCrash45]

I wouldn't go lower than an 1800mah battery if the c rating is 40c or higher. As above a 2200mah would be best. I also would stsrt with 1-2 degrees of down thrust angle. Since the motors are closest to the bottom of the fuselage downward thrust angles are the most common.

 

[Merv]

Regarding care and feeding of Lipos.
- Never charge faster than 1 C.
- After use, always give your battery a cool down period before charging or balancing.
- After charging, always give your battery a cool down period before use.
- The cool down period should be at least 15 minutes, 60 minutes is best.
- Don't exceed the amp draw your battery can supply. mAh/1000 x C
- Don't store them fully charged for more than a week.

With batterie's, there is no correlation between cost and quality.
I buy Turnigy/Zippy and will get 3 years out of them, some last longer.