Aerodynamics Discuss the concepts of aerodynamics here

Aileron set-up

Old 04-07-2016, 07:14 PM
  #26  
solentlife
Super Contributor
 
solentlife's Avatar
 
Join Date: Oct 2010
Location: Ex UK Brit now in Latvia west coast - Ventspils
Posts: 12,522
Default

Originally Posted by Konrad View Post
.................NOT like with most entry level computer radio at the end of the control movement, as is done with servo end points. This might be why some folks don't notice much effect in their efforts to trim for rolling.

All the best,

Konrad
Sorry that doesn't make sense. What you write there suggests that when a person reduces end point that the servo will still move exactly same movement as the full movement servo but stops at earlier End point.

That is not true. Well certainly not on my radios and none of my older ones either.

If you set control movement on one servo at say 60% ... the amount of movement of that servo compared to other servo will be 60% at all points ... not just at the end. So at any point measuring one surface against other will show the difference.

Nigel
solentlife is offline  
Old 04-07-2016, 07:33 PM
  #27  
JetPlaneFlyer
Super Contributor
 
JetPlaneFlyer's Avatar
 
Join Date: Mar 2009
Location: Aberdeen, Scotland
Posts: 6,121
Default

That's my experience too nigel. Differential in all the Tx's I've used works more like the rate function, it simply reduces the rate that the servo moves on the aileron downstroke, not just where it stops.

Possibly there are Tx's around that dont work this way but i've yet to experience one.
JetPlaneFlyer is offline  
Old 04-07-2016, 07:45 PM
  #28  
JetPlaneFlyer
Super Contributor
 
JetPlaneFlyer's Avatar
 
Join Date: Mar 2009
Location: Aberdeen, Scotland
Posts: 6,121
Default

Originally Posted by Konrad View Post
This I don't understand.
"...caused by a fore/aft rotation of lift forces due to roll rate,.." More of less vortices coming off the tips as a result of the lift changes? And that this changes the effective lift vector?

I had thought that his description was showing that the lift vector (center of pressure) moved as a result of the corresponding tilt in the cord line (camber change).
Konrad,

It's nothing to do with vortices.

It's simply that when a plane is rolling the wings have a rotational velocity. This rotational velocity causes the resultant relative wind direction that approaches each wing to be angled upward on the downgoing wing and downward on the upgoing wing.

Lift by definition is the force that acts perpendicular to the relative wind direction. Because the relative wind is no longer horizontal then the lift vector is no longer vertical. The lift vector actually tilts forward on the downgoing wing (pulling the wing forward) and tilts backward on the upgoing wing (pulling the wing backward).. This tilting of the lift vectors yaws the plane opposite to its roll direction, even though there is no difference in wing drag between one wing and the other.

In a nutshell it's lift that creates most of the adverse yaw effect, not drag*

You can offset this yaw by deliberately creating drag on the downgoing wing, which is what differential does. Of course deliberately creating drag is bad in a sailplane so Mark will prefer to use rudder to counter the yaw. Personally i doubt the difference in performance between using a bit of differential and using rudder could be noticed in any practical way but i guess in top level competitive sailplanes every fraction of a second counts.

*PS.. what Mark only hints at is that there is an exception. When a wing is operating near stall, and/or the aileron deflections are large then the downgoing aileron may experience separation (stall) creating lots of drag. This causes a very extreme adverse yaw which most certainly is due to drag. Also when this occurs you probably will get either little or no roll, or maybe a even roll opposite aileron input.
JetPlaneFlyer is offline  
Old 04-07-2016, 08:28 PM
  #29  
Konrad
E-Flight Enthusiast
 
Konrad's Avatar
 
Join Date: Jan 2007
Location: San Francisco CA USA
Posts: 102
Default

Originally Posted by JetPlaneFlyer View Post
Konrad,

It's nothing to do with vortices.

It's simply that when a plane is rolling the wings have a rotational velocity. This rotational velocity causes the resultant relative wind direction that approaches each wing to be angled upward on the downgoing wing and downward on the upgoing wing.

Lift by definition is the force that acts perpendicular to the relative wind direction. Because the relative wind is no longer horizontal then the lift vector is no longer vertical. The lift vector actually tilts forward on the downgoing wing (pulling the wing forward) and tilts backward on the upgoing wing (pulling the wing backward).. This tilting of the lift vectors yaws the plane opposite to its roll direction, even though there is no difference in wing drag between one wing and the other.

In a nutshell it's lift that creates most of the adverse yaw effect, not drag*

You can offset this yaw by deliberately creating drag on the downgoing wing, which is what differential does. Of course deliberately creating drag is bad in a sailplane so Mark will prefer to use rudder to counter the yaw. Personally i doubt the difference in performance between using a bit of differential and using rudder could be noticed in any practical way but i guess in top level competitive sailplanes every fraction of a second counts.

*PS.. what Mark only hints at is that there is an exception. When a wing is operating near stall, and/or the aileron deflections are large then the downgoing aileron may experience separation (stall) creating lots of drag. This causes a very extreme adverse yaw which most certainly is due to drag. Also when this occurs you probably will get either little or no roll, or maybe a even roll opposite aileron input.
I got this from the Dr. post
"In a nutshell it's lift that creates most of the adverse yaw effect, not drag*"

As I was taught years ago that lift produces drag I had no problem with the idea adverse yaw was predominately a result of drag. I'm also comfortable with the idea put forward by Dr. Drela that the drag actually stays close to constant and that it actually is the lift vector that is changing directions rather than the lift vector amplitude (with resultant drag change)

I didn't think the relative motion of the wing changed much as a function of the added angular velocity of the roll. We have seen adverse yaw even when the wing does not roll much at all, like with the Champs and Cubs

Here are some cartoons I drew of what I thought the Dr. Drela was trying to show.

JPF,
Thank you for forcing me to think harder on the subject. I truly appreciate it!

In a glider comp. you will see how much higher the plane in proper trim (control) is as opposed to one that is not trimmed or being flown properly. The longer both ships are in the thermal the more drastic the elevation difference. I can see this even in the lower classes I fly in!
Attached Images
File Type: jpg
Lift Tilt.jpg (279.8 KB, 192 views)

Last edited by Konrad; 04-07-2016 at 11:07 PM.
Konrad is offline  
Old 04-07-2016, 08:37 PM
  #30  
Konrad
E-Flight Enthusiast
 
Konrad's Avatar
 
Join Date: Jan 2007
Location: San Francisco CA USA
Posts: 102
Default

Originally Posted by solentlife View Post
Sorry that doesn't make sense. What you write there suggests that when a person reduces end point that the servo will still move exactly same movement as the full movement servo but stops at earlier End point.

That is not true. Well certainly not on my radios and none of my older ones either.

If you set control movement on one servo at say 60% ... the amount of movement of that servo compared to other servo will be 60% at all points ... not just at the end. So at any point measuring one surface against other will show the difference.

Nigel
You are correct, it doesn't make since. Its been years since I had an entry level radio in my hands. But to check for this add extreme dif. to your radio. If the lower going surface is still moving at the end of the TX stick movement you have a rate type set up for dif.( this is good) If the upward surface is moving and the downward surface is not then you have a radio that is using the dif function to set the end point of the servo travel (this is bad).
Konrad is offline  
Old 04-07-2016, 09:26 PM
  #31  
silent flyer
New Member
Thread Starter
 
Join Date: Feb 2010
Location: Lincolnshire
Posts: 9
Default

Konrad
I'm using a DX6i, although I can't find the post that asked that now.
All this was just an experiment and I'll probably never need it as 'solentlife' says. All Chris Foss designs are inherently good, I've had them all. Love them.
Seems to have started quite an interesting thread though.
silent flyer is offline  
Old 04-07-2016, 09:35 PM
  #32  
silent flyer
New Member
Thread Starter
 
Join Date: Feb 2010
Location: Lincolnshire
Posts: 9
Default

Originally Posted by solentlife View Post
....................

But lets be honest ... the sort of model that needs Aileron Differential .... and the Wots Wot is definitely NOT in that class, as all of Chris Foss designs are fine without - the models that need it - are not usually good candidates for steady inverted flight.

Being honest - I cannot see any point of differential on a Wots Wot ... or any other Wot design ...

A modification I can see for any Wot model though is increased control surfaces to push it into 3D work. Chris's designs are excellent aerobatic machines .....................................

Nigel
Definitely agree with this statement Nigel, although I never want to get to the 'extreme' behaviour. I like everything smooth and steady, but with a thrill level that I can take, not to take pills to calm my nerves!

This was all an experiment, which I can't fly to check out yet.

It has certainly started some very interesting chat about all this though.

Cheers

Geoff
silent flyer is offline  
Old 04-07-2016, 09:55 PM
  #33  
Konrad
E-Flight Enthusiast
 
Konrad's Avatar
 
Join Date: Jan 2007
Location: San Francisco CA USA
Posts: 102
Default

The exchange of ideas is how we learn. Please use the chart I linked to earlier. Regardless of the designer the proof is in the flying.

For my part I was trying to show you how to achieve differential throw using the cartoons I drew (I saw nobody had done or linked to similar data).

The rest of the discussion was my attempt to understand the true mechanism of adverse yaw. While I was well aware or Dr Drela work and even read the RCGoofs post years ago. It appears that the nuances of the discussion are still lost on me. I truly appreciate JPF efforts to lift the veils of ignorance from my eyes.

All the best,

Konrad
Konrad is offline  
Old 04-08-2016, 12:17 AM
  #34  
fhhuber
Super Contributor
 
fhhuber's Avatar
 
Join Date: Mar 2013
Posts: 4,786
Default

Sometimes I like to play with the extremes...

I had a plane that I could turn left by applying full right aileron and full right rudder due to its extreme adverse yaw.
fhhuber is offline  
Old 04-08-2016, 12:36 AM
  #35  
Konrad
E-Flight Enthusiast
 
Konrad's Avatar
 
Join Date: Jan 2007
Location: San Francisco CA USA
Posts: 102
Default

Originally Posted by fhhuber View Post
Sometimes I like to play with the extremes...

I had a plane that I could turn left by applying full right aileron and full right rudder due to its extreme adverse yaw.
Wow, the rudder couldn't overcome the adverse yaw? Where did it crash or were the controls reversed?
Konrad is offline  
Old 04-08-2016, 07:48 AM
  #36  
solentlife
Super Contributor
 
solentlife's Avatar
 
Join Date: Oct 2010
Location: Ex UK Brit now in Latvia west coast - Ventspils
Posts: 12,522
Default

One last point - when setting up any servo ... its best to not limit travel by end points. 'Wargo' makes a big point of this in his 3D videos.
Why ? The reason is resolution.

Keeping full servo movement keeps maximum travel resolution. Altering surface deflection at the servo arm / horn is better.

This includes preferably not using Dual rate to reduce max as well.

Nigel
solentlife is offline  
Old 04-08-2016, 08:05 AM
  #37  
fhhuber
Super Contributor
 
fhhuber's Avatar
 
Join Date: Mar 2013
Posts: 4,786
Default

I prefer dual expos over dual rates. With dual expo you can get the lessened sensitivity near center but still have full travel range without having to remember to throw a switch.
fhhuber is offline  
Old 04-08-2016, 08:52 AM
  #38  
JetPlaneFlyer
Super Contributor
 
JetPlaneFlyer's Avatar
 
Join Date: Mar 2009
Location: Aberdeen, Scotland
Posts: 6,121
Default

Dual rates does have it's place. On sports/scale models I dont use dual rates but on 3D models you really have to.

Where you have huge control surfaces and 45 degree plus throws it's impossible even with bags of expo to get a plane that flies smooth precision type maneuvers unless you use rates to reduce travel. Fair enough if you want to just fly stick banging 3D all the time just have one rate, but if you want to fly smooth sometimes you need dual rates./
JetPlaneFlyer is offline  
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
rcers
Beginners
28
01-29-2020 01:21 PM
Flysohigh
General Electric Discussions
7
09-09-2015 04:59 PM
FlyingBrick50
Heads UP RC discussion
5
11-21-2011 10:18 AM
AirmanAirhead
RC Radios, Transmitters, Receivers, Servos, gyros
3
06-19-2011 08:31 PM

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
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


Quick Reply: Aileron set-up


Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.

Page generated in 0.08376 seconds with 14 queries