View Full Version : outrunner vs inrunner

10-05-2005, 02:32 AM
Can anyone tell me if there is any advantage a brushless outrunner has over a brushless inrunner as a Mega or Hacker? I wish to convert an Osprey X-28 G seaplane from .019 glow to a brushless setup.The plane has a 44" wing span & would weigh in about 36 oz. w/ a std. 400 can motor & a 6-7 cell nicad as its' cousin the X-28 "A" model. The plane & specs can be seen at www.hacker-model.com (http://www.hacker-model.com)., or at www.quicktechhobby.com (http://www.quicktechhobby.com) My winter project will be converting the Ace Seamaster, 60" wingspan w/ a weight around 7 lbs. sporting a .40-.46 glow engine, & can be seen at www.towerhobbies.com (http://www.towerhobbies.com). The motors sit in a pod above the main wing, & will have very little ventilation, so I'm looking for any advice any one can give me so nothing burns up. The ESC will be in a water tight fuselage, but I think if I up the amp rating to the next size above the motors rating I should be able to keep that cool. I think the same for lipo batteries, i.e., if I up the mah rating, the battery should not overheat. Am I correct on this? Thanks in advance for any info out there.

10-05-2005, 03:21 PM
Mega and Hacker also produce outrunners :)

10-05-2005, 03:43 PM
Can anyone tell me if there is any advantage a brushless outrunner has over a brushless inrunner as a Mega or Hacker?
Here is my take, and I use both so......

Pros - No gearbox, high torque; ability to spin large props, ease of setup, silent!
Cons - Limited on prop selection (2 or 3) for "best" efficiency and amp draw, can be difficult to mount, a tad less efficient

Pros - gearbox offers nearly unlimited propeller combos, i like the gearbox noise, mounting is easier (sometimes) cooler running motors (yes this is right as the windings are near the case), usually allow much higher power outputs, more efficient (generally)
Cons - gearbox noise, gearbox maintenance and cost, slipping gears, bearing failures etc.

Both are good and have their uses!


Dr Kiwi
10-05-2005, 07:00 PM
An outrunner with sufficient power to fly the Osprey might need to spin a fairly large prop - I wonder whether one can fit a large enough prop [?10"] into the Osprey configuration.

10-06-2005, 01:16 AM
Dr. Kiwi---your reply kind of surprised me. A member of RC Universe forum left a link for me a while back w/ a video of him flying The Osprey X-28 A that he insists was equiped w/ the stock 400 can motor. That thing shot across the water like a jet, in fact it was bouncing so much I thought for sure he was gonna dunk it, but did get control & got it into the air, & in not a lot of distance either. With that I thought a brushless, even a small light one, would be more than enough needed to get it off the water. However, the 2 sites showing the specs for the X-28 A (electric) & the X-28 G (glow I want to convert), do not recommend a prop size, probably a lawyer advice thing. It just says " prop to match motor." Don't you really think a 10" prop wouldn't be a little over-kill? Larger props draw more amperage, resulting in more heat, which is exactly what I'm trying to avoid. Keep in mind the 2 planes are exactly the same size & would weigh the same if equiped the same. The X-28 G w/ the .019 glow is about 7-8 oz. lighter but would weigh the same w/ a 400 in it, & the hefty 7 cell nicad.

10-12-2005, 12:44 AM
Another gearbox pro: Protection for the motor in a crash. I just had my Tribute go in from 40ft. Ejected the battery and lost the radio. Airplane went straight into the asphalt runway. Shattered the GWS gearbox frame, but the motor survived without a scratch.


Matt Kirsch
10-12-2005, 12:57 AM
Much as I love my outrunners with their affordability and simplicity, they can't quite match the efficiency of a well-designed geared setup, or the flexibility.

I personally think that as we go along, outrunners and inrunners are going to find specific niches where they're most commonly used. Inrunners will find their homes at the extreme ends of the spectrum, including high-speed applications due to the fact that an inrunner can spin a small prop at tremendously high RPMS, or in top-end 3D setups because of the ability to use extreme gear ratios and large props. Outrunners will find their home in small 3D and park flyers, up through larger conversions of sport, and scale planes where cost is a major factor and/or getting the absolute most out of the setup is not.

Still, outrunners and inrunners will remain interchangeable for the most part throughout the spectrum. It all boils down to a matter of personal preference.

Unbalanced prop
10-12-2005, 01:53 PM
Matt..............I agree completely. A very good explanation! Both types of motors have their strong points.


10-12-2005, 03:13 PM
For the outrunner, you can choose the prop size that will physically fit your application and then select the outrunner with the windings(kv) necessary to give you the thrust needed.

For instance, you could use an A30-22S Hacker with a 7x6 prop or an A30-10XL with a 13x8 prop. (Or maybe an A20-XX series)

So with the Outrunners, you are pushed into a limited prop size per motor situation but you can find the outrunner that you need. With the inrunner, like they have said, you can use one motor and change the gear ratio to change prop sizes.

I like the simplicity of the outrunners.:)

10-13-2005, 11:55 AM
36 oz. plane with a 400 can motor and 7 cells? Has this been tried? Reason I ask is that usually, anything over 18 ounces a speed 400 has difficulty moving even if your using 8 cell packs. Sure, depends on the plane too but I had a 400 6 volt on a T-52 trainer weighing in at 23 oz. and the plane barely kept up in the air at full throttle. Even if the 400 is geared, its gonna have trouble moving a 36 oz. plane.
Conversion of .19 glow is roughly speed 550 motor from what I've seen other club members use.
If your planning on converting 40-ish sized glow over to 'lectric, be prepared for sticker shock. Brushless motor is gonna be over $100, over 100 for the esc and if you plan on using lipos, one pack is gonna run ya
well over 100 bux. And your gonna want at least 2 lipo packs. The system to power the model, you'll have $500 or more into it if you have two lipo packs. I'm sure others will disagree but my opinion is to spend that much $$$ to convert this size over to electric is a pretty hefty price tag.


Dr Kiwi
10-13-2005, 01:10 PM
36 oz. plane with a 400 can motor and 7 cells? Has this been tried? Reason I ask is that usually, anything over 18 ounces a speed 400 has difficulty moving even if your using 8 cell packs. Sure, depends on the plane too but I had a 400 6 volt on a T-52 trainer weighing in at 23 oz. and the plane barely kept up in the air at full throttle. Even if the 400 is geared, its gonna have trouble moving a 36 oz. plane.

My thoughts exactly, Dave. That's why I have trouble with the "stock 400 video" mentioned in Post #5. I would have thought at least 80W/lb and about 1:1 thrust/wt would be needed (that's 180W for a 36oz plane).

My comment on prop size ("can you fit 9"-10") was because I figured that one would need an outrunner running a prop perhaps that big to get sufficient thrust, without excessive pitch speed. I just looked at some numbers and only one of the Hacker A20 series (20L) can get you 36oz thrust (at >200W-in), and then only with at least a 10"-11" prop. Depending on the motor, a smaller prop might be spinning at enormous rpm and get you lots of speed, but insufficient thrust.

Cheers, Phil

10-13-2005, 03:57 PM
What would work out okay would be a mega 16\15\2 turn and couple that with a good gearbox. Then, you could perhaps get enough oomph to propel it. Or, get an AXI with sufficient thrust #'s. Another way would be to gear a 480 or 550 motor.
I have a himax 2025-4200 geared at 6:1. According to one of the hobby websites, a 12x6 prop gives you 36 oz. of thrust using 3S lipo pack.
However, that would be running at near full throttle which would put a burden on the motor/gearbox and batts. I have that setup in my mini funtana which goes AUW about 21 to 22 oz.


10-13-2005, 05:45 PM
Here's a quote from one owner-
"I flew mine last night! I flew it with a speed 480, 8 cell kan1050's, and a 7x3 prop. Great fun, especially tooling it around the harbor!"

From the looks, I don't think too large a prop would fit on htis model.

Matt Kirsch
10-13-2005, 06:55 PM
Beware of making calls based on thrust numbers alone... To maintain flight, you don't need anywhere near a 1:1 thrust to weight ratio. The only way you'd need to barrell around at full throttle just to stay in the air with a 1:1 thrust to weight ratio is if you go to the extreme end of the spectrum and gear the motor strictly for maximum thrust at minimum pitch speed. That's tough to do by accident, though.

Jeez, I can't believe I totally overlooked the fact that there was an actual technical question in this discussion! Sorry about that.

For a 36oz plane, 200 Watts is a good figure to start with. It's not quite 100 Watts per pound, so performance should be pretty close to the stock glow configuration with the right motor/prop combination.

Do we have any limitations on prop size? I'm not familiar with the Osprey design that's in discussion here. It's not the V-22 tilt-rotor, and that's as far as I go...

Given its weight, and assuming generic sport plane performance, my first recommendation would be a 3S LiPoly around 2000mAh in size, and an AXi 2808/24 propped to draw about 20 Amps.

10-13-2005, 07:50 PM
Not much room for a gear drive or large prop.


10-14-2005, 01:24 AM
Thank you, Hoppy for posting the pics, something I was having problems with. I also appreciate all the responses, but my main question seemed to have gotten lost in the world of technical stuff. My original question was putting a brushless motor in the goldish plane , which is the one I have, which Hacker recommends an .019 engine, & keeping the brushless motor cool. The red plane comes w/ the std. 400 can motor. Both planes are identical in size & weight if both were equiped w/ the same motors. Also, is there a specific reason why Hacker went w/ a pusher prop setup over the usual front prop on the red X-28 "A" plane?

10-14-2005, 02:28 AM
The rear motor in the electric would provide protection from spray. Perhaps the battery weight requires the motor to be farther back for balancing???

I don't know didilly about this but i think the thrust angle would be different.... must be needed for some reason.

Motor - look at the A30-22S with 3 lipo's.