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Old Aug 23, 2011, 10:35 AM
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Multiplex Twinjet: Any motor suggestions for Mach 1-ish performance?


Ok... so a kind forum member has sold his MPX Twinjet to me, which I will be picking up in person at the NEAT Fair in a few weeks. I'm psyched.

In the mean time, I am in motor-shopping mode and I'm looking for a high performance set up that will really make this plane shine.

I gather than 28mm inrunners are a good match for the stock motor mounts and there seem to be some great options for silly power levels in small-prop pusher configurations.

I'd like to run 4s/3000 or 5s/3000 power (since I already have some packs).

Any ideas for high quality motors that would do the job?

Secondly, when buying TWO motors and TWO speed controllers, the price goes up...well, by a factor of two. So if someone knows of a high speed/budget setup, I would be interested in this as well.

EDIT:
Does this airframe hold up the stresses of high speed like its little brother, the Funjet? Or...does it need reinforcement?


Thanks for any suggestions or advice, guys!!
-Mike
Last edited by MRGTX; Aug 23, 2011 at 10:42 AM.
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Old Aug 23, 2011, 11:29 AM
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It's definitely going to need a lot of reinforcement. And something tells me that mach 1 won't be easy on 3 or 4s
Old Aug 23, 2011, 01:34 PM
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Yeah... that's why 5s is on the table.

Honestly, if it outruns my stock Stryker Q, (by a good margin) I would be happy.
Old Aug 23, 2011, 02:17 PM
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Originally Posted by MRGTX View Post

Secondly, when buying TWO motors and TWO speed controllers, the price goes up...well, by a factor of two. So if someone knows of a high speed/budget setup, I would be interested in this as well.
There have been some conversions to a single larger motor for that very reason.
Old Aug 23, 2011, 02:27 PM
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There have been some conversions to a single larger motor for that very reason.
yeah, I have seen some of those conversions on Youtube, etc.

Are the two motors really an impediment to performance? I guess I'm not sure why they would be...other than cost.

It seems that weight and amp draw can be managed through motor size and kv selection...so long as there is ~120mph pitch speed on tap and sufficient combined wattage, two smaller motors should be able to produce enough grunt to break the 100mph barrier.

Do I have this wrong?
Old Aug 23, 2011, 02:46 PM
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I think the fastest versions have been powered with twin motors.

https://www.rcgroups.com/forums/show...hlight=twinjet

It's a great airframe, one that I wish Multiplex still offered. I'd love a 48" or 60" span version.
Old Aug 23, 2011, 09:35 PM
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I cut the twin motor mounts off mine and went with a single Ammo inrunner. Used one of the cut off mounts as the basis for the fuse mount. I also put the esc outside the fuse so that it doesn't get too hot. I can run a small prop (6x6) to get it literally screaming, or throw a big (10x4) slowflyer prop on when I need to be slow and quiet in the park. Have to be a little careful with the throttle with the big prop or I can overamp it. I do find that when I am in screamer mode it is really easy to get behind the plane and I have lost it a couple of times doing that.

I really wish that Multiplex had kept it in production, it's a great airframe. Much easier to see and fly than the minijet.

Jeff
Old Aug 23, 2011, 11:33 PM
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Originally Posted by jhspring View Post
I cut the twin motor mounts off mine and went with a single Ammo inrunner. Used one of the cut off mounts as the basis for the fuse mount. I also put the esc outside the fuse so that it doesn't get too hot. I can run a small prop (6x6) to get it literally screaming, or throw a big (10x4) slowflyer prop on when I need to be slow and quiet in the park. Have to be a little careful with the throttle with the big prop or I can overamp it. I do find that when I am in screamer mode it is really easy to get behind the plane and I have lost it a couple of times doing that.

I really wish that Multiplex had kept it in production, it's a great airframe. Much easier to see and fly than the minijet.

Jeff
And its larger size is also better for alternative batteries that weigh more than LIPOs.
Old Aug 24, 2011, 01:34 AM
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I think the fastest versions have been powered with twin motors.

https://www.rcgroups.com/forums/show...hlight=twinjet

It's a great airframe, one that I wish Multiplex still offered. I'd love a 48" or 60" span version.
That would be sweet!!
Old Aug 24, 2011, 09:49 AM
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I converted it to one motor. But let you tell, this plane is not for high speeds, the wings are to thick. 2 motors is better to start. 1 motor you need a gyro/stab.
Old Aug 24, 2011, 04:34 PM
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I use twin 1700kv outrunners running APC 7x5E and fed by 3S 4000mah. I'll tell you what, level flight performance is exhilarating, and vertical is absolutely ballistic with unlimited vertical. as others have already mentioned, the speed is limited by the airframe drag, so for a power system, there is a point of diminishing gains. That's why I stuck with a fairly lightweight , proven 3S/1700kv setup, This combination gives excellent level speed and tremendous thrust for sparkling vertical missile-like performance.
Last edited by Doubletap; Aug 24, 2011 at 11:45 PM.
Old Aug 31, 2011, 12:45 PM
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I use twin 1700kv outrunners running APC 7x5E and fed by 3S 4000mah. I'll tell you what, level flight performance is exhilarating, and vertical is absolutely ballistic with unlimited vertical. as others have already mentioned, the speed is limited by the airframe drag, so for a power system, there is a point of diminishing gains. That's why I stuck with a fairly lightweight , proven 3S/1700kv setup, This combination gives excellent level speed and tremendous thrust for sparkling vertical missile-like performance.

Cool...were you able to mount these in the stock mounts?
Old Aug 31, 2011, 03:04 PM
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Cool...were you able to mount these in the stock mounts?

No, I used a different mounting system and fashioned my own, but it's not too difficult. Look at my blog, there is a picture that shows my motor setup for my Twin Jet. If you want to use the stock motor mounting setup, which essentially is gluing inrunner/Speed 480 cans to the inside of the molded foam housings, then you would need to choose a couple of inrunner type motors, whereas, I used a couple of cheap outrunners, so I had to fashion my own mounting system.
Old Aug 31, 2011, 03:58 PM
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No, I used a different mounting system and fashioned my own, but it's not too difficult. Look at my blog, there is a picture that shows my motor setup for my Twin Jet. If you want to use the stock motor mounting setup, which essentially is gluing inrunner/Speed 480 cans to the inside of the molded foam housings, then you would need to choose a couple of inrunner type motors, whereas, I used a couple of cheap outrunners, so I had to fashion my own mounting system.
Wow... nice planes you have there...
The mount looks clean from that angle. It looks like 7" is as big as you can go! Are those counter-rotating props?
Are those 28mm outrunners? It seems like a typical size motor for these planes.
Old Aug 31, 2011, 08:15 PM
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Wow... nice planes you have there...
The mount looks clean from that angle. It looks like 7" is as big as you can go! Are those counter-rotating props?
Are those 28mm outrunners? It seems like a typical size motor for these planes.
Yes, those APC7x5e are counter rotators , although it's not really necessary to use them, you can use a couple of standard tractor 7x5e. 7" is the biggest diameter you can fit on the back end of the Twin Jet before you start clipping the fuselage and yes the motors are inexpensive common 28mm diameter outrunners of 1700kv.


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