Jun 18, 2010, 03:23 PM
Registered User
Joined Apr 2008
326 Posts
Quote:
 Originally Posted by Robert Youens I have attached a jpg of the formula I use to calculate the maximum theoretical speed. This does does not take into effect prop drag, fuselage drag, turbulence, impact on adjacent fuselage , etc., in fact the true speed will be much slower on 3D aircraft. Interestingly enough, according to my friend George Parks, on the fastest hot liners they are getting closer and closer to maximum theoretical speed as I have calculated. On a 3D aircraft it appears that the faster you try to get it to go, the more all the variables push back on an exponential curve. I liked Ben's comment, "the motor will let you know ..." Robert

Ok, now I see your results.
The way you found the pitch speed is if the motor was running at 100% efficiency. In this case where the motor is using a prop that is at it's max use an efficiency of about 65% to get closer.

What I did here is was measure the actual rpm of the prop so all there is to figure in is the drag on the airframe which is minimal at 60 mph.

Ken
Jun 18, 2010, 03:30 PM
Fly Low-Crash-Rebuild-Repeat !
Jackson, MO
Joined May 2009
3,231 Posts
Quote:
 Originally Posted by Subsonic Ken Ok, now I see your results. The way you found the pitch speed is if the motor was running at 100% efficiency. In this case where the motor is using a prop that is at it's max use an efficiency of about 65% to get closer. What I did here is was measure the actual rpm of the prop so all there is to figure in is the drag on the airframe which is minimal at 60 mph. Ken
Ken,

When will you have more 380's in stock?

Fred
Jun 18, 2010, 03:32 PM
Just "hanging" Around
Richmond, VA
Joined Oct 2009
1,589 Posts
Quote:
 Originally Posted by Robert Youens Mike, I bet you are getting some kick ass all around 3D performance.
Yes, I am

Everything seems kind of effortless and very floaty. What I sacrifice though is prop flexibility. I can't really prop down without getting a new ESC to handle higher voltage and bumping up to 9S or 10S. It will hover and do everything with a 19x10 fine but everything is a lot more sluggish. I lose 500 watts dropping to the 19x10.

--Mike
 Jun 18, 2010, 03:53 PM Barefoot Birkinsomething United States, CA, Hayward Joined Aug 2004 9,473 Posts try a xoar 19x10. i think they will give you a bit more power, or even try an apc if you want more. the apc will definately draw more power
 Jun 18, 2010, 05:02 PM Just "hanging" Around Richmond, VA Joined Oct 2009 1,589 Posts It's no problem, I love the 20x10. I was just letting people know tradeoffs if they select the same motor as me. Your right the APC 19x10 would pull more.
 Jun 18, 2010, 05:08 PM OOPS USA, GA, Cochran Joined Jun 2008 20,180 Posts Mike,the 250kv I bet is pretty nice on 8s.No doubt that will keep amps low and torque high.WOOT! Ken can do lower than 380 kv on the motroflys as well for 8s and bigger props.The recommended biggest prop for the 4325 380 is 19x10.If ya go much bigger you are pushing the motor a good bit.I have plenty of power in my 70 slick with that setup.It is uber crazy and i can prop down in the 65 vyper.I think 140deg is good as far as summer thrashing 3d.Ken says the magnets are raed higher than that so we have headroom.Headroom =longer life..Ken at Subsonic Planes has been really working hard to get us some kick azz motors for these size planes..I believe he has done it.More to come
Jun 18, 2010, 08:21 PM
Hovering my 85" Katana
Austin, Texas
Joined Mar 2006
943 Posts
Ken,

I appreciate the information, it is interesting.

Irregardless of the effect airframe has on speed calculations. My interest is to determine actual air speed (tested by flying past a radar gun in level flight) as compared to a constant. This way I can get an idea of total system effect on speed relative to a constant.

Robert

Quote:
 Originally Posted by Subsonic Ken Ok, now I see your results. The way you found the pitch speed is if the motor was running at 100% efficiency. In this case where the motor is using a prop that is at it's max use an efficiency of about 65% to get closer. What I did here is was measure the actual rpm of the prop so all there is to figure in is the drag on the airframe which is minimal at 60 mph. Ken
Jun 18, 2010, 09:05 PM
Registered User
United States, TX, Austin
Joined Dec 2006
13,752 Posts
Quote:
 Originally Posted by G.P. Hey guys, wondering if anyone has seen this before. Tonight my motor instantly ground to a halt. Luckily I had just pulled out of a harrier and had lots of altitude for a nice deadstick landing. 5 seconds earlier and I would have lots of repairs! After inspection I found that my Hacker A50-14L had the large inner bearing move forward and make contact with the windings. This caused the windings to melt and actually spray out of the cooling holes and around the cowling. Not sure if I should get another Hacker for the Slick or not? I was running an Xoar 18x8 on 8s, for approx 2000 watts. My motor was coming down around 130 deg, and I just installed cooling baffles to make it run even cooler. This was only the 8th flight on it. I had the circlip and the wheel collar installed on the shaft behind the motor, so nothing should have been able to contribute to the bearing moving. What do you guys think? Is it worth notifying Hacker? Was it a freak accident? Hope it didn't fry my X80 too....
You've had it for less than 2 years GP ? That's the warranty for Hacker.
Jun 18, 2010, 09:06 PM
Hovering my 85" Katana
Austin, Texas
Joined Mar 2006
943 Posts
Mike,

Wow, that is awesome

Further evidence that lower prop speed and larger prop size optimizes thrust on this airframe.

Maybe we will see more people trying a range of power on lower KV motors on this plane to improve performance. With enough power, people that want to experiment with the trade off of speed vs static thrust can adjust 20" or larger props within a range around 8000 rpm, maybe lower.

Robert

Quote:
 Originally Posted by 3D-Dabbler "hover for a 2.2 to 1 thrust to weight ratio." -Mike
Jun 18, 2010, 09:07 PM
lazy 3D specialist
United States, OH, Canal Winchester
Joined May 2007
2,140 Posts
Quote:
 Originally Posted by Manta1 Ken at Subsonic Planes has been really working hard to get us some kick azz motors for these size planes..I believe he has done it.More to come

+1 on that!!
 Jun 18, 2010, 09:25 PM Registered User United States, TX, Austin Joined Dec 2006 13,752 Posts Previous prop Minor correction Robert. I had the 19x10 on the last flight (cell dropped below voltage---which led to deadstick elevator landing). Ken, gotta say I'm thrilled with my 4325-380 ! Hope you re-stock soon 'cause Fred (rotorjockey) is on the PROWL ! Manta, you 'enabled' (when I read you comments) me into getting this excellent motor, so THX brutha ! Hoping to get some REAL time with it tomorrow (have only flown it 4 times)
Jun 18, 2010, 09:26 PM
Fly Low-Crash-Rebuild-Repeat !
Jackson, MO
Joined May 2009
3,231 Posts
Quote:
 Originally Posted by lonelasso Minor correction Robert. I had the 19x10 on the last flight (cell dropped below voltage---which led to deadstick elevator landing). Ken, gotta say I'm thrilled with my 4325-380 ! Hope you re-stock soon 'cause Fred (rotorjockey) is on the PROWL ! Manta, you 'enabled' (when I read you comments) me into getting this excellent motor, so THX brutha ! Hoping to get some REAL time with it tomorrow (have only flown it 4 times)
Yep,

Been a hardcore Scorpion guy so far, but I'd buy&try one if I could find it!

Fred
Jun 18, 2010, 09:28 PM
Registered User
United States, TX, Austin
Joined Dec 2006
13,752 Posts
Quote:
 Originally Posted by RotorJockey Yep, Been a hardcore Scorpion guy so far, but I'd buy&try one if I could find it! Fred
Pretty sure I read that Ben has one
 Jun 18, 2010, 09:31 PM OOPS USA, GA, Cochran Joined Jun 2008 20,180 Posts [QUOTE=lonelasso;15351988]Minor correction Robert. I had the 19x10 on the last flight (cell dropped below voltage---which led to deadstick elevator landing). Ken, gotta say I'm thrilled with my 4325-380 ! Hope you re-stock soon 'cause Fred (rotorjockey) is on the PROWL ! Manta, you 'enabled' (when I read you comments) me into getting this excellent motor, so THX brutha ! Hoping to get some REAL time with it tomorrow (have only flown it 4 times) [/QUOTE i'm glad you like it!I love mine.Both of them. Also liking he new one on my vyper as well.The 4320. Im hoping to get some more flights on it tomorrow depending on how i feel.The minor surgery I had on monday has me still a good bit sore.Some systems that get shut down during anestesia have been coming back online today lol..Still kinda dragging.I gotta replace a wheel on my slick then its thrash time again..I didnt know Ken was out of those motors...Theres more comin..
Jun 19, 2010, 06:35 AM
Registered User
Ireland, Kildare, Leixlip
Joined May 2002
6,441 Posts
Quote:
 Originally Posted by Robert Youens Actually you are right on with what I am gleaning. I am turning approximately 8400 rpms on my system. You should be turning around 8000 rpms.....
Robert,

I'm not following you.
He's got a 250kV motor running on 8s.
Theoretical unloaded RPM or 100% efficiency RPM is 250 x 8 x cell voltage.
Say we're assuming cell voltage of 3.5V then thats 250 x 8 x 3.5 = 7000RPM.
In reality RPM is going to be far below this. So where's the 8000RPM figure coming from?