Notices
Electric Pattern Aircraft Discuss epowered pattern aircraft in this forum

Prop drag

Old 08-11-2016, 12:13 PM
  #1  
JerMilosek
Thread Starter
 
Join Date: Jul 2011
Location: , NY
Posts: 71
Likes: 0
Received 0 Likes on 0 Posts
Default Prop drag

I've read that a prop spinning at a low rpm creates more drag than one that's free wheeling.


My question is at what rpm is the greatest drag created?


This comes about because I want to slow down the aircraft more and sooner during a landing.
E-power has the luxury to preset the "idle" rpm anywhere from 0 to 2000 rpm, where in that
range will I get the greatest drag/thrust ratio? I haven't gotten into fixed end points and braking
yet but looking at the logged data from my Castle ESC, I can see a long spool down. Its in the
10-12 second range from the time I hit low throttle until the rpm as reported by the ESC bottoms
out at around 450 rpm. Its under no wind, a long gentle glide with the rpm around 2100 when
low throttle is applied and its using an outrunner.

Thanks, J e r

MHRCS member
50th consecutive Rhinebeck Jamboree Sept. 9-11
http://mhrcs.com/pages/Jamboree.htm
Old 08-11-2016, 04:20 PM
  #2  
J Lachowski
My Feedback: (46)
 
Join Date: Sep 2003
Location: Bridgewater, NJ
Posts: 948
Likes: 0
Received 0 Likes on 0 Posts
Default

Just use ESC braking function and the appropriate time.
Old 08-11-2016, 10:24 PM
  #3  
bem
My Feedback: (1)
 
Join Date: Feb 2009
Location: SWEDEN
Posts: 1,688
Likes: 0
Received 1 Like on 1 Post
Default

Hi,
I think it is hard to tell an effiecient low RPM that will break more optimal.
But as I understand it:
The (slow)spinning prop act as a "disc" so when You dive You have a large disc helping slow down the plane.
Free wheeling prop will give more braking effect then a stopped prop. But a free wheeling prop will, as far as I know, increase in RPM some as You dive making it less effective as brake as RPM increase.
With ESC brake activated the prop will spinn but not increase in RPM when You are in (vertical) dive.
With most modern ECS that has brake one can set % how hard the brake is going to be. One have to experiment some how many % will give most brake effect. It is usually good to start at maybe 20% brake and work up from there to see by trail and error in flight when the brake seems to be most optimal.
I use brake in my ESC's on my F3A planes. I use Jeti/Hacker Master Mezon ESC and I use 56% brake power.

If You do not want to use ESC brake You have to experiment with various low RPM and see if You can notice any difference in how the plane might be slower at some specific low RPM on Your electric motor.
But if You have ESC brake I suggest You try that also and compare.
ESC with brake activated (at optimal brake setting) should give best braking effect on the plane.
When I land my F3A planes, that has ESC with brake and plane is on final I take the trottle fully down (so brake is activated) I can then see with my eyes that the plane slown down a little and the plane also get an increased sink rate so I must give just tiny up elevator and then flare for a touch down.

/Bo

Last edited by bem; 08-12-2016 at 04:00 AM.
Old 08-12-2016, 07:37 AM
  #4  
nonstoprc
My Feedback: (90)
 
nonstoprc's Avatar
 
Join Date: Sep 2003
Location: Central, TX
Posts: 2,466
Likes: 0
Received 1 Like on 1 Post
Default

I found that I can achieve a perfect landing by pulling pack the throttle stick to the low end (about 1000rpm) during the final landing approach.

You may need to set the low end timing to the ESC so that the low end RPM is fixed and repeatable.

If I apply the break during the landing approach, the plane will slow down very fast and sink quickly. I rarely do so unless it is a very windy day.
Old 08-12-2016, 10:03 AM
  #5  
n233w
 
Join Date: Apr 2010
Location: Richmond, CA
Posts: 169
Likes: 0
Received 0 Likes on 0 Posts
Default

My sense is the answer to your question is undefined. An aeronautical engineer might be able to give you a theoritical figure but...

Pattern pilots use the ESC brake function for slowing the aircraft.

Originally Posted by JerMilosek View Post
I've read that a prop spinning at a low rpm creates more drag than one that's free wheeling.


My question is at what rpm is the greatest drag created?


This comes about because I want to slow down the aircraft more and sooner during a landing.
E-power has the luxury to preset the "idle" rpm anywhere from 0 to 2000 rpm, where in that
range will I get the greatest drag/thrust ratio? I haven't gotten into fixed end points and braking
yet but looking at the logged data from my Castle ESC, I can see a long spool down. Its in the
10-12 second range from the time I hit low throttle until the rpm as reported by the ESC bottoms
out at around 450 rpm. Its under no wind, a long gentle glide with the rpm around 2100 when
low throttle is applied and its using an outrunner.

Thanks, J e r

MHRCS member
50th consecutive Rhinebeck Jamboree Sept. 9-11
http://mhrcs.com/pages/Jamboree.htm
Old 08-13-2016, 01:08 PM
  #6  
OhD
 
Join Date: Oct 2002
Location: west hills, CA
Posts: 1,159
Received 8 Likes on 5 Posts
Default

Originally Posted by J Lachowski View Post
Just use ESC braking function and the appropriate time.
ESC braking during landing can be a problem depending on how far you must advance the throttle stick to come out of braking. If it is a lot you will speed up too much if you need to stretch the landing. My solution is to land with my normal idle setting of about 600 rpm and pulse the brake with a push button switch on top of the throttle stick on my Jeti transmitter. Short pulses are very effective and of course the amount of braking can be controlled by the on to off time of the brake.

Jim O
Old 08-14-2016, 12:03 AM
  #7  
bem
My Feedback: (1)
 
Join Date: Feb 2009
Location: SWEDEN
Posts: 1,688
Likes: 0
Received 1 Like on 1 Post
Default

Hi,
It is also easy to hear (at least on my planes) when the brake kicks in (for example at landing), there is a noticable change in the sound and I can see the plane actually slown down. On my planes that has brake it is not difficult to come out of bake, just add a little throttle. One can also "pulse" some with the throttle to pull the plane forward during landing. Experiment some and see what works best. It is just a matter to get used to the brake at landing approach. I do not think about it anymore.

/Bo
Old 08-18-2016, 05:04 AM
  #8  
JerMilosek
Thread Starter
 
Join Date: Jul 2011
Location: , NY
Posts: 71
Likes: 0
Received 0 Likes on 0 Posts
Default

Thank you all for your replies.

Apologies for my delayed response. I haven't been able to fly due to rain every day since my original post and more today (Thursday).

Jim's idea of a pb switch on the throttle stick was enough to get me over the edge so I ordered one.

The end points I arrived at on my Jeti using a Castle ESC on a 6330 Himax are 1.286 ms and 1.806 that occur at -60% and 61% respectively. My throttle curve to get a linear rpm increase for each clik looks like a perfect exponential curve, it looks like what you get if you graphed 2 raised to the Xth.

Jim, what do you think of my end points? Could/should they be expanded?


I'll keep you all posted on this, J e r
Old 08-18-2016, 09:17 AM
  #9  
OhD
 
Join Date: Oct 2002
Location: west hills, CA
Posts: 1,159
Received 8 Likes on 5 Posts
Default

Jer, does the Castle ESC let you set the fixed endpoints or are they preset at the factory? It sounds as though you have set your transmitter to work with their preset values. I prefer to use a larger range. I set my Jeti Mezon ESC endpoints at 1.1 and 2.0 msec. I then set my transmitter up as follows:

(The High and Low refers to the throttle stick position)

Brake switch off - High 2.000, Low 1.159 The low throttle stick position results in an idle of about 550 RPM

Brake switch on - High 2.000, Low 1.087 This (less than the 1.1 arming point) applies the brake at full low throttle stick or with the push button (Logic switch). Depending on the Brake settings the motor will not stop as long as there is some forward motion of the plane.

Throttle cut switch on - 1.000 Throttle stick has no effect and motor is stopped.

Start Procedure:
Motor battery connected.
Transmitter on Throttle stick Low
Brake and throttle cut switches off.
Switch on receiver. ESC not armed as pulse width is greater than 1.1 msec.
Check control surfaces
Switch throttle cut on. ESC arms as PW is below 1.1
Switch throttle cut off. Motor starts at idle
Taxi to take off position

As far as the curve. I don't believe you will be happy with a linear rpm vs. stick position. Here is what mine looks like:



Jim O
Attached Images
File Type: bmp
Screen125.bmp (9.4 KB, 163 views)
Old 08-24-2016, 08:01 PM
  #10  
JerMilosek
Thread Starter
 
Join Date: Jul 2011
Location: , NY
Posts: 71
Likes: 0
Received 0 Likes on 0 Posts
Default

Jim,
Thanks for pointing out I wouldn't like my original throttle curve, it lasted 1 circuit around the field and I immediately landed. It was all in the very high end of the throttle stick position. My curve now looks more like your screen shot.

My comments thus far have been about a Castle Phoenix HV ESC w/10S that's over a year old. It does appear the fixed end points are preset at time of manufacture. Since I was setting end points and the weather was bad I set up a Phoenix Edge Lite 34v 75 and managed to set its end points at 1.135 - 1.903. I bring this up because I had to use the Castle Field Programmer with my PC to get the ESC to link up. To do this required me to also update the Castle program in the PC. I don't need the Field Programmer to download log data from my HV ESC.

Pilots not fortunate enough to have a xmttr that displays throttle pulse width in milliseconds can get it by down loading the ESC log data.

I'm still playing with the brake, looking for a way the log data will tell me how well its working by checking how fast the rpm's drop.

 
J e r
MHRCS member
50th consecutive Rhinebeck Jamboree Sept. 9-11

http://mhrcs.com/pages/Jamboree.htm
Old 08-24-2016, 08:40 PM
  #11  
OhD
 
Join Date: Oct 2002
Location: west hills, CA
Posts: 1,159
Received 8 Likes on 5 Posts
Default

Originally Posted by JerMilosek View Post
Jim,
…….
I'm still playing with the brake, looking for a way the log data will tell me how well its working by checking how fast the rpm's drop.

 
J e r
MHRCS member
50th consecutive Rhinebeck Jamboree Sept. 9-11

http://mhrcs.com/pages/Jamboree.htm
Don't know about Castle, but the Mezon does not readout rpm when the brake is engaged. I was hoping to get the same data. We'd need an independent tach setup but I've never pursued one.

Jim O
Old 09-10-2016, 04:19 PM
  #12  
DaveL322
 
DaveL322's Avatar
 
Join Date: Jul 2004
Location: Medford, NJ
Posts: 557
Likes: 0
Received 0 Likes on 0 Posts
Default

Originally Posted by OhD View Post
Don't know about Castle, but the Mezon does not readout rpm when the brake is engaged. I was hoping to get the same data. We'd need an independent tach setup but I've never pursued one.

Jim O
I don't think any of the sensorless ESCs can record RPM when the brake is engaged. Most radio brands (and Eagletree) make a variety of RPM sensors...it would need to be of the optical or magnetic variety, and not electrical.
Old 01-04-2017, 10:17 AM
  #13  
jnhiller
Junior Member
 
Join Date: Jul 2003
Location: Spokane, WA
Posts: 28
Likes: 0
Received 0 Likes on 0 Posts
Default

Maybe I should stay out of this but what the h. First select a prop that allows near full stick in an up line. E-power allows us to use more prop / more power than needed, which increases peak A and Mah / flight. Match the prop to the requirement (pattern class and flying style) with a minimum pitch. Diameter makes thrust and isn't as critical to a point. When I first started flying 10S (245Kv) pattern I over propped the requirement with a 20-11. Reducing to a 19-10 dropped the peak A draw 12A and reduced the re-charge Mah. Now I occasionally bump full stick on an up line. When flying glow prop selection was important, it still is.
Old 01-04-2017, 10:25 AM
  #14  
ltc
My Feedback: (3)
 
Join Date: Mar 2010
Location: Mendon, MA
Posts: 1,404
Likes: 0
Received 11 Likes on 11 Posts
Default

Originally Posted by OhD View Post
Don't know about Castle, but the Mezon does not readout rpm when the brake is engaged. I was hoping to get the same data. We'd need an independent tach setup but I've never pursued one.

Jim O
This one should work
http://www.espritmodel.com/jeti-tele...o-mrpm-ex.aspx
Old 01-05-2017, 01:00 PM
  #15  
apereira
 
apereira's Avatar
 
Join Date: Jun 2002
Posts: 1,705
Received 1 Like on 1 Post
Default

I fly both YS and electric,

Electric Oxai Amethyst Hacker C50 21x13 Mezlick Jeti/Hacker Especial Edition ESC
YS 185 Oxai Acuracy Bipe and Axiome + APC 20.5x10

I found the YS at around 1000RPM had a better brake than a very slow turning Mezlick electric prop (around 50 RPM I guess), so I adjusted the brake to ramp at a "medium" ramp to a little faster prop RPM and the brake effect improved a lot, I think it is about 600RPM, but really slow or stopped proved not to reduce the speed as desired.

Regards

Alejandro

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 - Do Not Sell My Personal Information -

Copyright 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.