PLEASE HELP !!! Twin engine help.... esm dc3 arf...cant takeoff !!
03-20-2014, 09:57 AM
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PLEASE HELP !!! Twin engine help.... esm dc3 arf...cant takeoff !!
I just built an esm dc-3 arf. what a beautiful plane... twin dle20's.
ok the instructions say to mount the left motor with 3 degrees out !!The LEFT motor !! and the right motor 4 degrees out (which I understand)... I ended up mounting the left engine at 0 degrees...oh and it said to make both engines 3 degrees down (which I did)... Ok so I have my left engine pointed straight forward with 3 degrees down.... my right engine 4 degrees out and 3 degrees down.
maiden flight.... I almost wrecked it !! it yawed left on me real bad.... second and third flight the same. I can only get lucky so many times. Now Im wondering if I should make the left engine 3 degrees out like the manual says ?? I just don't understand it though...wouldn't making it left even more make it worse ? can someone please explain and give me your opinion on what to do about this ?? It flies awesome and lands like a dream.. Please help....
ok the instructions say to mount the left motor with 3 degrees out !!The LEFT motor !! and the right motor 4 degrees out (which I understand)... I ended up mounting the left engine at 0 degrees...oh and it said to make both engines 3 degrees down (which I did)... Ok so I have my left engine pointed straight forward with 3 degrees down.... my right engine 4 degrees out and 3 degrees down.
maiden flight.... I almost wrecked it !! it yawed left on me real bad.... second and third flight the same. I can only get lucky so many times. Now Im wondering if I should make the left engine 3 degrees out like the manual says ?? I just don't understand it though...wouldn't making it left even more make it worse ? can someone please explain and give me your opinion on what to do about this ?? It flies awesome and lands like a dream.. Please help....
03-21-2014, 11:03 AM
#2
On a single you have 2-3 deg right thrust to counter the P effect. On a twin you increase the right thrust on the right engine counter both the P effect and assymetric effect with left engine out.
The left engine will have less left thrust as the P effect will help assymetric but still need left thrust in the engine out case.
Typical is 3-5 deg out on right engine and 2-4 deg out on left engine.
Try to sync engines at mid range and full throttle.
On take off open the throttle slowly part way, control swing and direction and as speed increases feed in more throttle.Lift off low and level to increase speed with a shallow high speed climb.
Speed is your saviour with a engine out.
Flying a radio twin is a little different to flying a fullsize twin as you are not sitting inside. The first indication of an engine failure in a model is a uncommanded yaw with roll. Your normal reaction will be to put in aileron for the seen roll.
Which direction you put the aileron in, once your realize a engine is out (change of noise), put full rudder in the same direction and let the aileron go back to neutral.
Keep full power on and the nose level, keep speed up and wings level.
Now balance power with rudder, power on- rudder on, power off - rudder off.
All the above should happen in 2-3 seconds.
Most twin engine out crashes happen because it takes too long to figure out "Oh I've got an engine out, I wonder which one, what do I do" , it needs to be a reaction responce.
The left engine will have less left thrust as the P effect will help assymetric but still need left thrust in the engine out case.
Typical is 3-5 deg out on right engine and 2-4 deg out on left engine.
Try to sync engines at mid range and full throttle.
On take off open the throttle slowly part way, control swing and direction and as speed increases feed in more throttle.Lift off low and level to increase speed with a shallow high speed climb.
Speed is your saviour with a engine out.
Flying a radio twin is a little different to flying a fullsize twin as you are not sitting inside. The first indication of an engine failure in a model is a uncommanded yaw with roll. Your normal reaction will be to put in aileron for the seen roll.
Which direction you put the aileron in, once your realize a engine is out (change of noise), put full rudder in the same direction and let the aileron go back to neutral.
Keep full power on and the nose level, keep speed up and wings level.
Now balance power with rudder, power on- rudder on, power off - rudder off.
All the above should happen in 2-3 seconds.
Most twin engine out crashes happen because it takes too long to figure out "Oh I've got an engine out, I wonder which one, what do I do" , it needs to be a reaction responce.
03-21-2014, 11:13 AM
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On a single you have 2-3 deg right thrust to counter the P effect. On a twin you increase the right thrust on the right engine counter both the P effect and assymetric effect with left engine out.
The left engine will have less left thrust as the P effect will help assymetric but still need left thrust in the engine out case.
Typical is 3-5 deg out on right engine and 2-4 deg out on left engine.
Try to sync engines at mid range and full throttle.
On take off open the throttle slowly part way, control swing and direction and as speed increases feed in more throttle.Lift off low and level to increase speed with a shallow high speed climb.
Speed is your saviour with a engine out.
Flying a radio twin is a little different to flying a fullsize twin as you are not sitting inside. The first indication of an engine failure in a model is a uncommanded yaw with roll. Your normal reaction will be to put in aileron for the seen roll.
Which direction you put the aileron in, once your realize a engine is out (change of noise), put full rudder in the same direction and let the aileron go back to neutral.
Keep full power on and the nose level, keep speed up and wings level.
Now balance power with rudder, power on- rudder on, power off - rudder off.
All the above should happen in 2-3 seconds.
Most twin engine out crashes happen because it takes too long to figure out "Oh I've got an engine out, I wonder which one, what do I do" , it needs to be a reaction responce.
The left engine will have less left thrust as the P effect will help assymetric but still need left thrust in the engine out case.
Typical is 3-5 deg out on right engine and 2-4 deg out on left engine.
Try to sync engines at mid range and full throttle.
On take off open the throttle slowly part way, control swing and direction and as speed increases feed in more throttle.Lift off low and level to increase speed with a shallow high speed climb.
Speed is your saviour with a engine out.
Flying a radio twin is a little different to flying a fullsize twin as you are not sitting inside. The first indication of an engine failure in a model is a uncommanded yaw with roll. Your normal reaction will be to put in aileron for the seen roll.
Which direction you put the aileron in, once your realize a engine is out (change of noise), put full rudder in the same direction and let the aileron go back to neutral.
Keep full power on and the nose level, keep speed up and wings level.
Now balance power with rudder, power on- rudder on, power off - rudder off.
All the above should happen in 2-3 seconds.
Most twin engine out crashes happen because it takes too long to figure out "Oh I've got an engine out, I wonder which one, what do I do" , it needs to be a reaction responce.
thank you. A lot of info to take in. I think I found the problem!!!
Dc3 roll to left problem....
I THINK I FOUND THE PROBLEM!!
hopefully (wishful thinking).
Tell me if this makes sense, your thoughts please....
ok, so I didn't like the tailwheel setup when I put the kit together so I ended
up putting the tailwheel on its own servo. Problem I think is ... I used that
sullivan flex rod(yellow..which is soft..all I had at the time)
i cannot even taxi the plane, the tailwheel is not effective because the rod
flexes too easy. I always said I'll get to it and change it out with stiff 4-40
rod but wanted to take care of this takeoff problem first....but I think the
tailwheel IS the problem! Let me explain
because I cannot taxi I ALWAYS end up giving more throttle than I should at
takeoff to lift the tail and hoping to control with rudder... Problem is, I
think because I don't have enough ground speed it lifts and IMMEDIATLEY will
roll. I believe if I had a working tailwheel I can ease throttle up because id
be able to control on the ground while gaining speed .
what are your thoughts ?
03-21-2014, 11:19 AM
#4
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Dc3 roll to left problem.
I THINK I FOUND THE PROBLEM!!
hopefully (wishful thinking).
Tell me if this makes sense, your thoughts please....
ok, so I didn't like the tailwheel setup when I put the kit together so I ended
up putting the tailwheel on its own servo. Problem I think is ... I used that
sullivan flex rod(yellow..which is soft..all I had at the time)
i cannot even taxi the plane, the tailwheel is not effective because the rod
flexes too easy. I always said I'll get to it and change it out with stiff 4-40
rod but wanted to take care of this takeoff problem first....but I think the
tailwheel IS the problem! Let me explain
because I cannot taxi I ALWAYS end up giving more throttle than I should at
takeoff to lift the tail and hoping to control with rudder... Problem is, I
think because I don't have enough ground speed it lifts and IMMEDIATLEY will
roll. I believe if I had a working tailwheel I can ease throttle up because id
be able to control on the ground while gaining speed .
I THINK I FOUND THE PROBLEM!!
hopefully (wishful thinking).
Tell me if this makes sense, your thoughts please....
ok, so I didn't like the tailwheel setup when I put the kit together so I ended
up putting the tailwheel on its own servo. Problem I think is ... I used that
sullivan flex rod(yellow..which is soft..all I had at the time)
i cannot even taxi the plane, the tailwheel is not effective because the rod
flexes too easy. I always said I'll get to it and change it out with stiff 4-40
rod but wanted to take care of this takeoff problem first....but I think the
tailwheel IS the problem! Let me explain
because I cannot taxi I ALWAYS end up giving more throttle than I should at
takeoff to lift the tail and hoping to control with rudder... Problem is, I
think because I don't have enough ground speed it lifts and IMMEDIATLEY will
roll. I believe if I had a working tailwheel I can ease throttle up because id
be able to control on the ground while gaining speed .
03-21-2014, 12:14 PM
#5
You need good yaw control on takeoff. The tailwheel only provides limited control with the rudder doing most of the work.
Full size A/C use a tailwheel lock with low speed control via brakes until you lift the tail then rudder.
If your pushrod will not hold a good wheel position then this may be your problem.
Full size A/C use a tailwheel lock with low speed control via brakes until you lift the tail then rudder.
If your pushrod will not hold a good wheel position then this may be your problem.
03-22-2014, 05:41 PM
#8
First twin?
Always best to start on twins with tricycle gear.
After 20 years on twins, tail-draggin' twins still give me fits
I witnessed one of the world's best RC pilots destroy a $20,000 Mosquito with a ground loop.
I've heard a rudder gyro can help by reacting faster than you can, but I have no experience with it.
What kind of runway surface? Moving off the slick onto grass can make a big difference. The tail seems to slide sideways into a ground loop a lot easier on hard surface. Need to get the tailwheel authority issues fixed first, of course. And yes, a human tendency when you're having trouble keeping the tail straight on the ground is to takeoff too soon, and then you're REALLY in trouble
Always best to start on twins with tricycle gear.
After 20 years on twins, tail-draggin' twins still give me fits
I witnessed one of the world's best RC pilots destroy a $20,000 Mosquito with a ground loop.
I've heard a rudder gyro can help by reacting faster than you can, but I have no experience with it.
What kind of runway surface? Moving off the slick onto grass can make a big difference. The tail seems to slide sideways into a ground loop a lot easier on hard surface. Need to get the tailwheel authority issues fixed first, of course. And yes, a human tendency when you're having trouble keeping the tail straight on the ground is to takeoff too soon, and then you're REALLY in trouble
Last edited by kram; 03-22-2014 at 05:49 PM.
03-22-2014, 06:49 PM
#10
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Flies ABSOLUTLEY perfect... I only needed a few clicks aeileron and ele. Lands like a trainer. I know my prob is the tailwheel for sure. I can't gain ground speed because of it.
03-23-2014, 08:06 AM
#11
OK, I'm glad to hear it flies perfect
That means it's almost certainly a ground control problem.
But that can be complicated and difficult to resolve, as I said above
I don't think fixing the tailwheel linkage alone is gonna make it all better.
Looping around on the ground with a taildraggin' twin is primarily due to: A) the inherent tendency of ANY taildragger to loop, and B) relatively minor differences in engine rpm and thrust during takeoff. Even twin powerplants synced at 8 or more points along the throttle curve can vary during takeoff due to momentary differences of carburation and spool-up speeds.
So if it still gives you fits after fixing the tailwheel, I suggest:
1) make sure your main gear is toed in a little, not OUT
2) takeoff on grass
3) consider a rudder gyro
4) have a helper hold the tail before take-off as you run your engines all the way up. If they're the same speed at top throttle, this will solve your thrust differential problem, but it could make the P-factor worse and things will happen really fast, esp. on the elevator, so if things go badly, they will go REALLY badly!
Years ago, my buddy built a Ziroli C-47 and there's a video on youtube of his maiden. Things went very badly for him because he hooked the ailerons up backwards, but his takeoff roll was PERFECT, thus perhaps educational to your topic here. His engines were G-38's
http://www.youtube.com/watch?v=yV0ZcVbM82k
That means it's almost certainly a ground control problem.
But that can be complicated and difficult to resolve, as I said above
I don't think fixing the tailwheel linkage alone is gonna make it all better.
Looping around on the ground with a taildraggin' twin is primarily due to: A) the inherent tendency of ANY taildragger to loop, and B) relatively minor differences in engine rpm and thrust during takeoff. Even twin powerplants synced at 8 or more points along the throttle curve can vary during takeoff due to momentary differences of carburation and spool-up speeds.
So if it still gives you fits after fixing the tailwheel, I suggest:
1) make sure your main gear is toed in a little, not OUT
2) takeoff on grass
3) consider a rudder gyro
4) have a helper hold the tail before take-off as you run your engines all the way up. If they're the same speed at top throttle, this will solve your thrust differential problem, but it could make the P-factor worse and things will happen really fast, esp. on the elevator, so if things go badly, they will go REALLY badly!
Years ago, my buddy built a Ziroli C-47 and there's a video on youtube of his maiden. Things went very badly for him because he hooked the ailerons up backwards, but his takeoff roll was PERFECT, thus perhaps educational to your topic here. His engines were G-38's
http://www.youtube.com/watch?v=yV0ZcVbM82k
Last edited by kram; 03-23-2014 at 08:18 AM.
03-23-2014, 11:31 AM
#12
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We shall see... I watched the video... Such a shame... My plane literally, as I'm taxiing would go left instantly.. Not even 1/4 throttle, so I just hit the throttle hoping thrvreludder will correct it . Not enough ground speed... I literally lift off by the time... On the video you just posted, says "maiden flight".. Watch it again, that's how much runway I was using because I goosed it up and she rolled on me... I def need more runway and fixing my tailwheel "should" help!
07-27-2015, 03:05 PM
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My cg was at recommended location. If you are new to twins... Please be aware it will have left torque. Easy into throttle to gain speed. It will lift off. Get it on video !!
How much nose weight did you use ?
I had twin 20cc engibes
How much nose weight did you use ?
I had twin 20cc engibes
08-11-2015, 08:24 AM
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My Marutaka DC-3 goes straight as an arrow on grass at take off (powered by two OS .26 fourstrokes swinging 3-blade carbon fiber 10x4,5 props) but is a little twichy on tarmack so there you have to hold the tail and release it at full Power, then it goes straight..
I have the engines mounted as per full size 0 degrees both sideways and up/down.
