Classic RC Pattern Flying Discuss here all pre 1996 RC Pattern Flying in this forum.

Electric power f/60 size classic pattern planes

Reply

Old 03-26-2012, 07:33 PM
  #26  
doxilia
My Feedback: (3)
 
doxilia's Avatar
 
Join Date: Apr 2008
Location: Montreal, QC, CANADA
Posts: 5,191
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Electric power f/60 size classic pattern planes

Good point and a good ESC is better than a big ESC.

David
doxilia is offline  
Reply With Quote
Old 03-30-2019, 09:00 AM
  #27  
barchiola
My Feedback: (6)
 
Join Date: Mar 2004
Location: milford, NJ
Posts: 170
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default

Old thread but has anybody found that a prop on the end of a high revving motor designed for a helicopter is causing the front bearings to go to hell very quickly? Being mounted in a helicopter as part of a fixed gear train is very different from the gyroscopic loads of a high RPM mass like an airplane prop.

Thanks!
barchiola is offline  
Reply With Quote
Old 09-15-2019, 10:59 AM
  #28  
stickman/vic
My Feedback: (85)
 
Join Date: Jan 2002
Location: Johnson City, TN
Posts: 48
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default

I'm one of the current SPA pilots who build from scratch and I have some motor suggestions if you are still not sure what motor to choose. I build two planes, a Dirty Bird-E at 6.5 pouds and a Bootlegger at 7 pounds. I can use the same motor for both but use different props. The actual prop/motoer/kv/ESC/battery combo is critical.
stickman/vic is offline  
Reply With Quote
Old 09-16-2019, 10:02 PM
  #29  
bjr_93tz
 
Join Date: Dec 2006
Location: ToowoombaQLD, AUSTRALIA
Posts: 940
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default

I ran a Scorpion HK-4035-400KV (8mm shaft heli motor) on 10S in my Curare once. It was either an 11x9 or 11x10 apc at about 13,000 rpm static.

It was a proof-of-concept, where I pulled the OS .75AX ad chucked that motor in the front and duct taped 2 x 5s 5000mAh batteries and Phoenix 85HV ESC in where the fuel tank was. I had to leave the canopy off.

Full power was good but 3/4 thottle the motor had horrible vibrations, very un-electric like, but ignoring the vibes it had plenty of grunt. I think there was too much flex in the motor to handle the gyroscopic force of the prop compared to a pinion that would normally be mounted in a heli. Maybe with a longer shaft and and a rear bearing support would help?

Also the weight was shocking, so while the power and speed were there I'd have to build a whole new airframe to make it work properly as my old glow airframe was too heavy.
bjr_93tz is offline  
Reply With Quote
Old 09-17-2019, 04:41 AM
  #30  
doxilia
My Feedback: (3)
 
doxilia's Avatar
 
Join Date: Apr 2008
Location: Montreal, QC, CANADA
Posts: 5,191
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default

Depending on whether one wishes to use 6s or 8s packs (and this choice is dependent on airframe size and weight primarily), the closest approximation to running a piped high RPM 60 such as a Rossi, OPS or YS is to use a motor with the right KV. Assuming 11” props, an outrunner with ~700 KV on 6s (22. 2 V nominal) will yield the desired results. This can be easily computed noting that:

700 KV x 22.2 V x 0.85 EFF = ~13.2K RPM

Similarly,

800 KV x 22.2 x 0.85 EFF = ~15.1K RPM

Conversely, for 8s (29.6 V nominal) setups:

550 KV x 29.6 x 0.85 EFF = ~13.8K RPM

and

600 KV x 29.6 V x 0.85 EFF = ~15.1K RPM

A 0.85 system efficiency is a good base line for power output calculations like these. Also noting that a motor wind difference of 100 KV results in a ~2K RPM difference on 6s and a 50 KV difference results in ~1.3K RPM difference on 8s. These four examples illustrate the lower and upper motor KV values desired to turn 11” props in the RPM range typical of high powered piped 60’s.

Of course, the high torque available from electric motors is such that the use of a larger prop is desirable if the airframe can accommodate this. Even trike retract classic pattern models will often clear a 12” prop so the same power setup can be used regardless of airframe by either “pitching up” on 11” props or “pitching down” on 12” props to keep the motor within its capabilities (current and hence power).

as far as power is concerned, a good piped 60 can output about 2-2.5 BHP or 1500-1850 W. Knowing this, one can choose the appropriate prop (or use the manufacturers prop test results) to get the motor in the desired power band.

On 6s, 1500 W would require:

1500 W / 22.2 V = ~67.5 A

On 8s, 1850 W would require:

1850 W / 29.6 V = ~62.5 A

As we know, power systems are more efficient running at high voltages and lower current draw so these two examples show that if higher power is needed, it’s best to dial the system in for an 8s setup. Running lower currents (i.e., ~60A rather than ~90A) is beneficial for battery, ESC and motor longevity.

Electric power systems are really less “dark magic” than IC engines IMO. Understanding what the numbers mean and how to use them helps to choose the right motor, ESC, battery and prop for the model in question.

David

Last edited by doxilia; 09-17-2019 at 04:51 AM.
doxilia is offline  
Reply With Quote
Old 09-18-2019, 02:48 PM
  #31  
bjr_93tz
 
Join Date: Dec 2006
Location: ToowoombaQLD, AUSTRALIA
Posts: 940
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default

Yes, people tend to forget that thrust at speed requires power.

Simple case is 6lbs of thrust @ 100MPH requires close to 1200W at 100% efficiency, 1400W at your 85% efficiency.

Only 6lbs of thrust in an 8lb plane at 100mph means you're going to slow down very quickly in an upline.
bjr_93tz is offline  
Reply With Quote
Old 09-19-2019, 04:11 AM
  #32  
UStik
 
Join Date: Oct 2006
Location: Augsburg, GERMANY
Posts: 979
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default

Another good point, but that 85% assumed efficiency kind of sacres me. I think it's way too high, especially in the latter example.

Thrust power is important in modern aerobatics with "unlimited verticals". Overall efficiency - from battery to thrust produced - includes battery, ESC, cables and connectors, and motor as well as the propeller (aerodynamically). From my experience, a good rule-of-thumb is 50% overall efficiency maximum ( a tad more, or over some airspeed range, respectively). Another rule-of-thumb is 45% (give or take) at lower speeds, from zero to climb speed. Fortunately, thrust and rpm don't vary much in this speed range so (mechanical as well as electric) motor power is about constant.

Now as we are talking about full-power setting, efficiency in climb is lower than the specified maximum, which is achieved only at high rpm (at dive speed). David, I like your simplification but prefer a different rule-of-thumb: rpm in climb (and static) is about 75% of ideal rpm (Kv times voltage). That would mean even higher Kv motors are needed if the prop rpm you specified is required.

Then I'd subtract 5% from the specified max. motor eff. (for battery, ESC, and cables/connectors) and 10% for running it at maximum-power rpm. That would mean 85-5-10=70% in your example - maybe even a bit pessimistic. Anyway, estimating the required motor power (analogous to an assumed mechanical engine/propeller power) would give even more required power and amperage.

I just mean to show that electric power is still critical for pattern planes if they are flown the modern way (with a lot of power instead of momentum), even if prop, motor, and battery are well chosen. By the way, a lower-pitch prop may be good for a constant-speed, unlimited-vertical flying style, which requires a lot of power as you said above. But maybe counterintuitively, a "ballistic" pattern style, with momentum and varying speed, might "feel" better with a higher-pitch prop and require less power.
UStik is offline  
Reply With Quote
Old 09-19-2019, 01:26 PM
  #33  
bjr_93tz
 
Join Date: Dec 2006
Location: ToowoombaQLD, AUSTRALIA
Posts: 940
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default

I was just throwing out a very simplified example tarred with a very wide brush, to illustrate that thrust at speed needs power, no if's no but's.
Unlike some of the lightweight aerobatic floaters running 3D props that accelerate like a rocket until they hit a brick wall at 50mph.

Just as an aside, I originally flew my Curare with a ASP .75 for a long time with both an APC 12x6 and APC 11x9 and while I had 2 more pounds of static thrust with the 12x6 (it'd knife edge loop with the 12x6), the plane flew nicer with the 11x9, although it was more work on the throttle stick.
bjr_93tz is offline  
Reply With Quote

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service