Installing The Xpwr 3910 In A 48" EXP

Things came together so fast when I got my new Xpwr 3910 that I forgot to take installation photos.  I have transferred the motor to another plane so I could do this installation article. As always, the plane of choice for me whenever I try something new is the Extreme Flight Extra EXP. I am so familiar with this plane that is it my baseline for anything I want to experiment with.

This airframe is relatively new. It was meant to be a backup plane so it has very little time on it. This
made it ideal for this article. If you are building a new EXP or want to convert an older one to the Xpwr 3910, the process is the same.

Installation is really quite easy, but having good pictures makes telling the story much easier.

The first step was to remove the 2814 motor that I was using. The 2814  and Xpwr 3910share the same bolt hole pattern for mounting the X mount to the motor, so the X mount itself makes a perfect drill jig for mounting the Xpwr 3910. Remove the X mount from the 2814 and bolt it to the firewall. To the left is the bare firewall with the motor removed, and right is the firewall with the X mount bolted into place.

Here I have marked in red the holes we will be drilling.

 

 

Just for reference. I used a sharpie to make sure I had plenty of wood surrounding the hole I will be drilling. On the left, I am marking the holes, and on the right, I've removed the mount to check my work. You can see we have plenty of wood to work with.

 

 

 

You can either drill on the marks you made with the sharpie or put the mount back on and use it as a drill jig. I preferred to drill through the mount because it's more precise that way. Once you get them drilled, then make them larger for the 4mm bolts we will be using to mount the motor. 

 

 

OK. the hard part is done. Now it's just a matter of assembly. If you have built any of the 60" EXPs, you have some 4mm bolts left over. These are used to attach the X mount on the 60" planes, but it just happens to be the same thread as on the back of the Xpwr 3910. Put a washer on each of the bolts and run them forward through through the holes you drilled in the firewall.

 

One thing to be careful of is to use the right length bolt. 60" EXPs usually come with three different lengths of 4mm bolts. You can't use the long one because it will protrude into the motor and hit the windings, which would be real bad. The short ones are too short, so I use the middle ones. They protrude just enough into the motor that you can see them, but not enough to get close to the windings.

 

Since the 3910 is a shorter motor, you will need to space the motor away from the firewall. I used 1/4" spacers that I got at Home Depot in the fasteners section. Below, use a washer first, then the spacer, and then another washer. You may need to use one more or one less washer to get the spacing just right depending on how your cowling lines up.

 

All that is left to do now is use a long allen driver to reach through the battery compartment forward to to bolts on the back side of the firewall and screw them onto the back of the Xpwr 3910.  Work carefully and slowly to make sure you get the bolts threaded in straight and get them snug, just for now.

 

Then screw the cowling back on and check alignment with your spinner. Add or remove washers until you get the spacing to your liking. Once you have that the way you want it, go back and tighten the motor mounting bolts down for good. You can either use blue locktite or just check for tightness every so often. I don't really like Locktite, so I just try to stay on top of my maintenance.

 

You can see I used a washer on each side of the 1/4" spacer and my cowl spacing came out perfect. Yours may vary, so adjust by add/removing washers until you are happy with it. 

 

 

Here is my gap and I am actually really pleased with it. Nothing looks worse than a huge gap, unless it's the spinner rubbing on the cowling, so take your time to get it just right. I think if you start with the 1/4" spacer and a washer on each side that will get you really close. 

 

 

The Xpwr 3910 puts out 1068 watts at 73 amps.As such, we also need to change out the speed controller to an Airboss 80. Here you can see I mounted it on the bottom of the motorbox, but knowing it was heavier than the Airboss 45, I simply moved it back about 1/2 from where I normally put it, and like this my CG did not change. It's a very neat arrangement that puts the ESC right in front of the Extra's chin cooling scoop and directly in the line of incoming air. With the baffles on either side of the motor, and the ESC in direct incoming air, this keeps the whole package nice and cool.

 

Remember to set the timing on your Airboss 80 to "high." That's how mine is and it runs perfectly.

 

 

OK, as always, all of this stuff seems to be a never ending work in progress. we plan to do much, much more with the Xpwr 3910, and of course the Extra, so stay tuned to the blog for updates. We hope to shoot more video on the next clear day, so please follow my blog and tell all your friends.

 

 Video

 

Extra EXP__Faster from Doc Austin on Vimeo.

  

 

 

 

Testing the Xpwr 3910

 

This will be some installation and flying notes on the new Xpwr T3910 motor. I will fly the motor much more this week and do a complete write up, but for now people want to know about the motor installation and the performance as fast as we can get the information out, so let's get started:  

 

 

First release from the new Extreme Flight power systems company is the Xpwr T3910, intended for current and future 48" EXP series planes. I chose to put mine in my trusty red Extra EXP and with a little fiddling it fit perfectly.

 

As you can see, the motor is both bigger around and shorter than the 2814, so we have to fiddle with it a little bit to get a perfect fit, but it was actually very easy.

 

 

The main reason this motor was developed was not only to provide a lot of power, but also to swing a massive Xoar 14.8 propeller. I tested mine with a Thunder Power 4s 2700 70C magna series lipo, fully charged, and came out with 1068 watts and 73 amps.

 

That's a thousand and sixty eight watts on a 48" plane. That's kind of nuts, but then again, the whole idea is extreme power, and this is it.

 

Flying

This motor is putting out about 38% more power than a 700 watt 2814, so the difference in the air is startling. Acceleration is blinding and it's fun just to punch it and watch the plane rocket away. You can judge for yourself how much power is available for punching out of a hover, but it's considerable. The thing just climbs like a football after a solid punt. After a few seconds, it's just gone.  With this kind of power you have to watch your altitude because you can exceed 400 feet pretty quickly. Mostly, when you are at full speed and power, and pull the nose up, it just never slows down. I'm pretty sure if you had enough battery it would pull the plane all the way to the moon.

 

Top speed is definitely more.  It's hard to quantify because this motor is so quiet that mutes some of the perception of speed. This motor doesn't use energy making noise. It uses energy making power. It's a totally different sound from the Torques we are used to, but I kind of like this sound too. It's less of a "whine" and more of a "whoosh."

 

Wood props seem to make a little less noise too, so I am sure with an APC it will bark very nicely.  Right now it's very, very quiet, and it's not until you fly it fast in close that you can see it's clearly going a lot faster than with the 2814. Will will have to run some back to back radar tests with my 2814 equipped Extra top be sure.

 

What I failed to convey is that the new motor pushes the plane into the next dimension. Literally. Out of all the things we argue about making a performance difference, this is truly the quantum leap. If you want a day and night difference, just bolt a 3810 on and hold on to your butt.

With that huge 14/8 prop, there is a lot more air going over the plane at every speed. as long as you have a little power on, it's blowing enough air over all the EXP's huge surfaces to keep it afloat. Like this, it certainly seems like the plane is flying much, much lighter. It's not really lighter.....the big propeller is just producing more lift.

When you are flying around in harrier, you always have full control, simply because there is so much air going over the plane. If you get too slow or need a bit more control authority, a sharp blast of about 1/2 throttle is enough to wrench the plane the way you want it to go. As you can see in the videos, punch out is insane. Now we are bordering more on model rocketry than model aviation!

 

Dimension X

Flying the extra with the big 14/8 Xoar prop takes this plane to the next dimension. Post stall character is so much improved that it is almost a totally different plane in hovers, harrier and elevators. it feels much lighter, but that's because the big prop is providing so much more lift in post stall flight.  At high speed, while the 3910 still makes the plane much faster, it is still restricted by airframe drag. However, because of the monster prop, there is still more air going over everything and he plane locks in almost like a stability system. It's uncanny how much more solid the plane is all the way around. 

 

With the Airboss 80 ESC I've got the same smooth, linear throttle response I am used to from all my other Airboss equipped planes (which is all of them), so I had confidence in the power delivery right away. It just operates like its supposed to, except there's a lot more power available. 

 

On the first video, I left off the usual musical sound track so you could hear the new sound of the 3810, and how the plane reacts to the power. The second video is our usual musical presentation. 

 

 

Extra EXP__Testing The Xpwr 3910 from Doc Austin on Vimeo.

 

 

And for those of you who refer a musical presentation, see below.

 

Extra EXP__Testing The Xpwr 3910__A Musical from Doc Austin on Vimeo.

 

 

Installation

While this part might look a little daunting it's actually no big deal. The worst part was planning it out in my head, and that made me crazy for awhile, but now I've got it figured out.
 

The Xpwr 3910 comes with an X mount that is way too big to fit the 48" EXP series planes, so we have to mount this motor without it. Here we get lucky because the motor bolt pattern (for the bolts that hold the X mount on) is the same as the 2814. Like this, I simply bolted a 2814 X mount to the firewall and use it as a jig to drill the new holes in the firewall.  Equally lucky is that there is plenty of meat surrounding the new holes.

From there you simply find some allen bolts the right thread and length and run them from the backside of the firewall into the rear of the 3910. I used some of the 4m bolts that come with the 60" EXPs.

 

Since this motor is so much shorter than the 2814, you need to space it out, For this I went to Home Depot and found 1/4" nylon spacers in their fastener department. With a washer on both sides of the spacer mine came out just right, but yours may need more or less washers to get the spacing perfect, especially if you have already mounted your cowling and are retrofitting the plane like I did.

 

The best speed controller for this motor is the Airboss 80 ESC with the timing set to high. Here I velcroed it to the bottom of the motorbox, which is right in front of the cooling slot under the spinner, so there will be plenty of cool air flowing over the esc. One important thing to note is that you want to set the timing on your Airboss 80 ESC to "high." The Boss told me to do this and everything works perfectly.