SMALL - espritmodel.com SMALL - Telemetry SMALL - Radio
Reply
Thread Tools
Old Nov 30, 2005, 12:14 PM
Warbird crazy!
new2rc's Avatar
United States, CA, San Mateo
Joined Sep 2004
3,732 Posts
Quote:
Originally Posted by Culver10
It looked a little large, but there is not really enough information on the listing. Which AXI motor would it be similar to?? They do not show the BM2915 on the Ebay Store, but that does not mean they do not have it I guess. I will send them an email and see if they have it.
Thanks for the help!!
Phil
Sure Phil

Not sure if you can find specs on the brushless motor they list on the company site, but it is
Power System: Our runner brushless motor DT-37xx (copied from their site complete with type o )

John and Christo
new2rc is online now Find More Posts by new2rc
Reply With Quote
Sign up now
to remove ads between posts
Old Nov 30, 2005, 01:43 PM
a really nice guy, really
Ralph Brekan's Avatar
Phoenix Intl, Arizona, United States
Joined Jul 2004
3,200 Posts
Yeah I ordered the 300w TowPro one a couple weeks back. Shoule arrive soon. Planning on using it in my Sureflite P40 Warhawk (foam .40 conversion). Theres a thread on these motors somewhere. Shoud be a great deal if they live up to the advertising!


John & Christo, thats EXCATLY what I had in mind for my Rippy. Thanks a bunch...


Quote:
Originally Posted by Culver10
The Hong Kong Ebay dealer World Hobby also has a nice looking outrunner motor http://cgi.ebay.ca/MASSIVE-Brushless...QQcmdZViewItem
Is this too big for this Spitfire? I have an airline pilot friend who is going to pick one up in Hong Kong for me and I may as well try an inexpensive motor and speed control also!
Ralph Brekan is offline Find More Posts by Ralph Brekan
Reply With Quote
Old Nov 30, 2005, 06:04 PM
Registered User
oldpilot's Avatar
Australia, NSW, Katoomba
Joined May 2002
5,430 Posts
Freebird et Al.

As you saw at Doonside my RM Spit flys perfectly as is.

SOooo--I cleared my work table of most of the junk and set up my Great Planes CG machine to 75mm. I plonked the Spit on it and it balanced perfectly without any further adjustment.

So there you have it, 75mm from the LE at the sides of the Fuse.
I don't see why the World_ Hobbies Spit woud be any different as all its vital dimensions are exactly the same as the RM one.

Cheers. Paddy.
oldpilot is offline Find More Posts by oldpilot
Reply With Quote
Old Nov 30, 2005, 06:30 PM
a really nice guy, really
Ralph Brekan's Avatar
Phoenix Intl, Arizona, United States
Joined Jul 2004
3,200 Posts
No doubt. I'd go with 75mm.
Ralph Brekan is offline Find More Posts by Ralph Brekan
Reply With Quote
Old Nov 30, 2005, 07:57 PM
Registered User
Bradbury, Australia
Joined Mar 2002
159 Posts
Hey Paddy,sounds like your almost ready to maiden.Good luck.

I set my CG at 75mm but Spitfire always wanted to climb,its now at 65mm and after 30+ flights i love the feel of this plane.My landings are getting better to. Im sure the CG issue is a personal preference to how one likes to fly model.
How did you go fitting the 10cell GP3300mah pack?The 8 cell 3700mah,
shotgun configuration pack i am using doesnt leave much clearance from motor.I reckon the 10 cell pack would be very tight fit.

Also Paddy, what where the Ripmax Spit specs on downthrust,sidethrust?
The World_Hobbies Spitfire had nil info.
freebird is offline Find More Posts by freebird
Reply With Quote
Old Dec 01, 2005, 10:04 AM
a really nice guy, really
Ralph Brekan's Avatar
Phoenix Intl, Arizona, United States
Joined Jul 2004
3,200 Posts
Maybe I'll start with 70mm.... I agree; I like a little nose heavy (versus ballooning while powered up).
Ralph Brekan is offline Find More Posts by Ralph Brekan
Reply With Quote
Old Dec 02, 2005, 01:23 PM
Warbird crazy!
new2rc's Avatar
United States, CA, San Mateo
Joined Sep 2004
3,732 Posts
Quote:
Originally Posted by freebird
Hey Paddy,sounds like your almost ready to maiden.Good luck.
I set my CG at 75mm but Spitfire always wanted to climb,its now at 65mm and after 30+ flights i love the feel of this plane.My landings are getting better to. Im sure the CG issue is a personal preference to how one likes to fly model.
How did you go fitting the 10cell GP3300mah pack?The 8 cell 3700mah,
shotgun configuration pack i am using doesnt leave much clearance from motor.I reckon the 10 cell pack would be very tight fit.
Also Paddy, what where the Ripmax Spit specs on downthrust,sidethrust?
The World_Hobbies Spitfire had nil info.
Freebird
I think if you look at the IC mount, you will notice side thrust built into the angle of the side wood that the glo would be fit too. I ended up using this as the brushless mount would not fit my motor gear box. I really had to more or less make a custom mount using this one as a base. I will be installing our set up using the side thrust angle. Also, I noticed if the cowl is fit exactly even side to side on the fuse, the prop openning has a side thrust built in to match the mount. Not sure on down thrust though.

Sounds like your Spit is doing very well with your DD Axi set up you are running. When checked out on P-calc using your 8 cell 3700's, it shows 52.5 oz static thrust and 255 W in. AT 52 oz AUW, you are just at 1:1 thrust. How is the climb and roll rate? It looks like mine may tip the scales at 55 oz with retracts and 7 cells, so I am trying to get an idea of how to gear my Endo to get enough thrust but not go over 40 A if possible .

John and Christo
new2rc is online now Find More Posts by new2rc
Reply With Quote
Old Dec 02, 2005, 03:37 PM
Registered User
Boston, MA
Joined Aug 2004
103 Posts
Hmm - I just plugged the same numbers into Motocalc, assuming Axi 2820/10, 8 cell GP3700 and 10x8 APC prop (even though Freebird's prop may be a graupner).

Motocalc predicted 229 watts, not too different than P-Calc but it predicted 31 oz static thrust, way different than 55 predicted by P-calc!

I adjusted the motor parameters in Motocalc to be the same as the ones assumed by P-calc so that isn't the issue.

Doesn't give you a whole lot of confidence in the mathematics!

DP
dpaul is offline Find More Posts by dpaul
Reply With Quote
Old Dec 02, 2005, 04:43 PM
Warbird crazy!
new2rc's Avatar
United States, CA, San Mateo
Joined Sep 2004
3,732 Posts
Quote:
Originally Posted by dpaul
Hmm - I just plugged the same numbers into Motocalc, assuming Axi 2820/10, 8 cell GP3700 and 10x8 APC prop (even though Freebird's prop may be a graupner).
Motocalc predicted 229 watts, not too different than P-Calc but it predicted 31 oz static thrust, way different than 55 predicted by P-calc!
I adjusted the motor parameters in Motocalc to be the same as the ones assumed by P-calc so that isn't the issue.
Doesn't give you a whole lot of confidence in the mathematics!
DP
Wow DP, surprised they are that far off . It seems the 52.5 would be correct given the way freebird describes the flight characteristics. Very strange.

John and Christo
new2rc is online now Find More Posts by new2rc
Reply With Quote
Old Dec 02, 2005, 05:35 PM
Registered User
Boston, MA
Joined Aug 2004
103 Posts
John and Christo:
Another mystery - maybe a bug in MotoCalc? Maybe Freebird has measured the current draw. However, from my admittedly limited experience, 52 oz sounds like a lot of thrust to get from only 250 watts and a 10" prop. Maybe its not really a 10" prop: I guess that with the folders, the effective diameter is a function of the length of the middlepart yoke and of the blades. So if the effective diameter was 11, the Moto-Calc figures correspond more reasonably with the reported flight characteristics. Still doesn't explain the difference between MotoCalc and P-calc.

On another note - I'm dying to see how your retracts come out. That is just too cool. Haven't had much opportunity to fly lately, just enough to burn out another ESC, this time the el cheapo BP40 from Balsa Products. Darn lucky it happened during a prop test at the work bench with the wings off. Out poured thick black nasty smelling smoke and I could actually see the glow from the device through the balsa and covering. Probably would have torched the model if I hadn't been able to get at it very quickly and yank it out. Very little damage as it was.

No more bargains electronics for me. Bought a CC Phoenix 35 which should do the trick.



DP
dpaul is offline Find More Posts by dpaul
Last edited by dpaul; Dec 02, 2005 at 05:41 PM.
Reply With Quote
Old Dec 03, 2005, 09:41 AM
Registered User
the Swamp Fox's Avatar
Wadmalaw Island ,SC
Joined Dec 2003
2,349 Posts
hey all,

After much head banging I got the prop /spinner balanced . Weird ,,,the TY spinner I have doesn't fit APC props ... Had some aeronaut carbon props on hand .

the 9.5x6 drew too much for my esc tried out a MAS 9x6 glow prop ,,,too much draw too little thrust . looks like a 8.5 x 6 aeronaut will be maiden prop .

mega 22/20/3E DD , CC45 , Tanic 4300 3s2p , 8.5x6 aeronaut .

wouldn't mind the 4 turn or a different dd motor but I have this motor in hand though and it'll work ... on wattmeter it's ...

400 watts+ , pulls like a mule , ran this combo in a heavier AT-6 and it had plenty of ooomph this one's 2 lbs 5oz , or the size of a nice trout ,,,less landing gear which will add a few oz .. as mentioned the tailwheel assembly is a bit beefy so I'll use a smaller unit . Going with Stock mains ,,,oh well , Those 603's are for the Tempest II ,right John and Christo ?

just need to loctite the motor mount screws and motor bolts ...

should be able to maiden after this weekend .

good luck all ,
Henry
the Swamp Fox is offline Find More Posts by the Swamp Fox
Last edited by the Swamp Fox; Dec 03, 2005 at 09:49 AM.
Reply With Quote
Old Dec 04, 2005, 06:01 AM
Registered User
DougC's Avatar
New Hampshire, USA
Joined Sep 2004
506 Posts
First, let me clearly state that I don't know the answer regarding the difference between P-calc and Motocal predictions. But I do have a thought.

The next time you run a P-calc determination, plug your numbers in and look at the static thrust. Now change just the prop pitch to something foolishly high, like a 25 pitch prop. You'll notice that the thrust will go up along with the prop pitch. Plug in a 30 pitch; the thrust in the static condition goes up......

To me, logically, at some point the prop pitch will become so great that the thrust can not be as high a show on p-calc. Without the plane moving forward (static condition), the prop will be "stalled", not able to bite enough air (just paddling the air), and can't possibly be producing the static thrusts indicated in the calculation. This corrolates to slow initial take-off speeds with high pitched props.

Also, the pitch speed in p-calc is a calculated pitch speed. It is directly calculated by the converting the pitch of the prop, at the given rpm's, into mph. You'll notice that with a 20 pitch prop, the pitch speed is 200mph or something. It's purely a conversion of prop pitch to mph; not considering the effect of the planes drag, or the ineffectiveness of a stalled prop.

I suspect that Moto-Calc considers the effect of high pitched props stalling when run static, therefore the actual/effective thrust applied to the plane is shown as much less, with high pitched props.

I'm hestitant to post this, as I'm not an expert by any means. But seems logical to me.

Just a thought.
DougC is offline Find More Posts by DougC
Reply With Quote
Old Dec 04, 2005, 06:17 PM
Warbird crazy!
new2rc's Avatar
United States, CA, San Mateo
Joined Sep 2004
3,732 Posts
Quote:
Originally Posted by Culver10
It looked a little large, but there is not really enough information on the listing. Which AXI motor would it be similar to?? They do not show the BM2915 on the Ebay Store, but that does not mean they do not have it I guess. I will send them an email and see if they have it.
Thanks for the help!!
Phil
Sorry Culver10, got caught up and forgot to post dimensions .

The brushless mount has mounting holes 1" center to center distance. That is top to bottom and side to side. The compartment width is 1.5" at its front just at the mount and widens out to 1.75" before the top former. A 600 motor will bolt right up to it so I am sure many brushless motors too will be a bolt in.

John and Christo
new2rc is online now Find More Posts by new2rc
Reply With Quote
Old Dec 04, 2005, 06:43 PM
Warbird crazy!
new2rc's Avatar
United States, CA, San Mateo
Joined Sep 2004
3,732 Posts
Quote:
Originally Posted by DougC
To me, logically, at some point the prop pitch will become so great that the thrust can not be as high a show on p-calc. Without the plane moving forward (static condition), the prop will be "stalled", not able to bite enough air (just paddling the air), and can't possibly be producing the static thrusts indicated in the calculation. This corrolates to slow initial take-off speeds with high pitched props.
Also, the pitch speed in p-calc is a calculated pitch speed. It is directly calculated by the converting the pitch of the prop, at the given rpm's, into mph. You'll notice that with a 20 pitch prop, the pitch speed is 200mph or something. It's purely a conversion of prop pitch to mph; not considering the effect of the planes drag, or the ineffectiveness of a stalled prop.
I suspect that Moto-Calc considers the effect of high pitched props stalling when run static, therefore the actual/effective thrust applied to the plane is shown as much less, with high pitched props.
I'm hestitant to post this, as I'm not an expert by any means. But seems logical to me.
Just a thought.
Hi Doug

What you say makes very good sense as Motocalc looks to be an actual interactive program using the model in its calculations. So entering the same motor, gearing, prop, and battery for say a Cub and Spitfire should yield different static thrust numbers. Since the very simple P-calc does not know what air frame is being used, the numbers produced are more an ideal number with no variables to adjust it.

John and Christo
new2rc is online now Find More Posts by new2rc
Reply With Quote
Old Dec 04, 2005, 07:27 PM
Registered User
Boston, MA
Joined Aug 2004
103 Posts
Quote:
Originally Posted by new2rc
Hi Doug

What you say makes very good sense as Motocalc looks to be an actual interactive program using the model in its calculations. So entering the same motor, gearing, prop, and battery for say a Cub and Spitfire should yield different static thrust numbers. Since the very simple P-calc does not know what air frame is being used, the numbers produced are more an ideal number with no variables to adjust it.

John and Christo
Actually, entering the same motor, gearing etc for a Cub and Spit do not yield different static thrust numbers. Differences in other characteristics relating to flight, yes. But the airframe itself does not influence static thrust at zero airspeed.

MotoCalc, but not P-Calc, indicates whether the prop will be stalled at zero airspeed, which you'd think would reduce the static thrust. In fact, MotoCalc predicts that a 10x8, as used by Freebird, would be stalled at zero airspeed. However, the differences in thrust between a 10x8, were stall is predicted at zero airspeed and a 10x6 where stall is not predicted, are only a few percent and therefore unlikely to be the basis of the difference between MotoCalc and P-calc predictions in this case.

DP
dpaul is offline Find More Posts by dpaul
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion what do ya think about this video? furyflyer2 Foamies (Kits) 2 May 05, 2006 05:19 PM
Discussion What do ya think, JR 10x heli or JR 9303? Bunyan Radios 2 Apr 24, 2006 04:20 PM
Discussion brushless pcw, going lipo 1stimer, what do ya think? snowcrash75 Flying Wings 1 Dec 31, 2005 02:36 AM
What do ya think about that? dad57c Engines 2 Dec 15, 2005 09:15 AM
Mini-Falcon,..What do ya think?,. wackyd Slope 19 Jan 29, 2005 09:41 PM