HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Mar 07, 2014, 08:59 AM
ET
eteet's Avatar
United States, DE, Hockessin
Joined Apr 2006
700 Posts
Hey Daryl,

Thanks for the link. I promise not to post anything absurd. I can't promise not to say anything, um, shall we say, not too intelligent.

Eric
eteet is online now Find More Posts by eteet
Last edited by eteet; Mar 07, 2014 at 09:46 PM.
Reply With Quote
Sign up now
to remove ads between posts
Old Mar 07, 2014, 09:24 AM
Daryl Perkins's Avatar
United States, VA, Falls Church
Joined Mar 2007
1,372 Posts
Quote:
Originally Posted by eteet View Post
Hey Daryl,

Thanks for the link. I promise not to post anything absurd. I can't promise not to say anything, um, shall we say, not to intelligent.

Eric
LOL...That's not actually what I meant. I was getting some heat within the thread for even starting it and that it had gone on too long. Soooo.... I took my ball and I went home.

There is some REALLY good info in there.

Differential is not the enemy, adverse yaw is. Use the tools in your programming to help the model to track well. Don't get hung up on numbers, or "zero diff". The easier my model is to fly, the more efficiently I can fly it.
Daryl Perkins is offline Find More Posts by Daryl Perkins
Reply With Quote
Old Mar 07, 2014, 12:06 PM
RIP MC
fnnwizard's Avatar
United States, CA, Midway City
Joined Dec 2003
3,380 Posts
All I will say is if one can fly coordinated with rudder, it is more efficient overall than with differential. How easy this will be is dependent on vertical/rudder being sized (volume) correctly.

One important criteria to consider is the rolling rate/ail deflection. For the high speed case and small ail movements, differential and nondiff has little overall wing drag differences.

For cases where high deflection is needed, differential has more overall wing drag over the plane's speed range.

In very light thermal situations your inside panel is at high alpha and if at min sink speed for the bank angle and if you try to maneuver/tighten the turn using a lot of diff (also dependent on amount of camber usage) most likely the wing drops and down you go. In this situation it might be better to use just the outside ail = reverse diff.

I think at high speed, the inertia of the plane probably masks most adverse/proverse yaw = easier to keep an F3B plane tacking true at high speed with no diff usage due to the heavier parts wanting to continue in a straight line. Just my guess, haven't flown much F3B events. Would it be incorrect to think lighter tipped F3B planes would still need to counter some adverse yaw at higher speeds albeit less than at slower speeds?

Anyhow, I've ran countless simulations on XFLR and XFOIL to try and see what the rolling moment is and what the yawing moment is due to roll rate, but it depends a bit on the inertia of the extremities which I found with the Blaine Rawdon’s technique of measuring the radii of gyration in yaw. My conclusions came out to be that any adverse yaw created by the rolling motion should be correctable with moderate rudder provided the rudder is sized sufficiently.

Real world testing needs to have a yaw indicator mounted right at the front of the wing LE and lots and lots of hand tosses flying at min sink at low levels. There’s three distinct parts of the flying that can mask what the indicator is truly revealing.
1. The initial roll in.
2. The steady turn.
3. The roll out.

For 1, what I find predominately among a lot of videos is that what looks coordinated is actually proverse yaw into the turn. If it is a small amount, this is actually not that bad as it usually is just for an instant. Most of the time there is more than adequate air speed (unless in light thermals as written above) so nothing bad will happen as it gets the nose around quickly to point in the right direction again.

Once that is done, during 2 there usually is slip in the videos and is due to pilots not holding enough “in rudder” to keep coordinated. During 2, there may be a need for some opposite ail to keep the bank angle consistent where ail diff is non optimal.

During 3, is usually where severe adverse yaw occurs. This is usually the result of the pilot still holding some in rudder while ail are deflected the opposite way. However there is also the radii gyration of roll and while the lift vectors are still tilted, takes some time for the plane to roll upright so in the video it could look like the plane is “sliding” opposite of roll command.

With modern planes and building methods resulting in better mass distribution, it sure is easier to fly the plane closer to optimally than in years past. However it still comes down to what the pilots’ thumbs are able to do= setup your plane to meet your thumbs’ ability. Having said that, I am always trying to better my thumbs.
fnnwizard is offline Find More Posts by fnnwizard
Last edited by fnnwizard; Mar 07, 2014 at 12:16 PM.
Reply With Quote
Old Mar 07, 2014, 12:41 PM
Eggcellent...
tewatson's Avatar
United States, CA, Orange
Joined Oct 2006
2,461 Posts
Here we go...

Tom
tewatson is offline Find More Posts by tewatson
Reply With Quote
Old Mar 07, 2014, 01:04 PM
Daryl Perkins's Avatar
United States, VA, Falls Church
Joined Mar 2007
1,372 Posts
Quote:
Originally Posted by tewatson View Post
Here we go...

Tom
Daryl Perkins is offline Find More Posts by Daryl Perkins
Reply With Quote
Old Mar 07, 2014, 01:28 PM
Detail Freak
target's Avatar
Harbor City, CA
Joined Oct 2003
21,858 Posts
But, primarily, if one can fly in LIFT, it is remarkably more efficient than flying coordinated IN SINK, no matter how screwed up your setup is.
I'm just sayin'!

Best Regards,
Target
target is offline Find More Posts by target
Reply With Quote
Old Mar 07, 2014, 01:33 PM
-----
Woodstock 1's Avatar
Ireland, County Kerry, Kerry
Joined Dec 2005
6,994 Posts
Quote:
Originally Posted by fnnwizard View Post
All I will say is if one can fly coordinated with rudder, it is more efficient overall than with differential. How easy this will be is dependent on vertical/rudder being sized (volume) correctly.

One important criteria to consider is the rolling rate/ail deflection. For the high speed case and small ail movements, differential and nondiff has little overall wing drag differences.

For cases where high deflection is needed, differential has more overall wing drag over the plane's speed range.

In very light thermal situations your inside panel is at high alpha and if at min sink speed for the bank angle and if you try to maneuver/tighten the turn using a lot of diff (also dependent on amount of camber usage) most likely the wing drops and down you go. In this situation it might be better to use just the outside ail = reverse diff.

I think at high speed, the inertia of the plane probably masks most adverse/proverse yaw = easier to keep an F3B plane tacking true at high speed with no diff usage due to the heavier parts wanting to continue in a straight line. Just my guess, haven't flown much F3B events. Would it be incorrect to think lighter tipped F3B planes would still need to counter some adverse yaw at higher speeds albeit less than at slower speeds?

Anyhow, I've ran countless simulations on XFLR and XFOIL to try and see what the rolling moment is and what the yawing moment is due to roll rate, but it depends a bit on the inertia of the extremities which I found with the Blaine Rawdon’s technique of measuring the radii of gyration in yaw. My conclusions came out to be that any adverse yaw created by the rolling motion should be correctable with moderate rudder provided the rudder is sized sufficiently.

Real world testing needs to have a yaw indicator mounted right at the front of the wing LE and lots and lots of hand tosses flying at min sink at low levels. There’s three distinct parts of the flying that can mask what the indicator is truly revealing.
1. The initial roll in.
2. The steady turn.
3. The roll out.

For 1, what I find predominately among a lot of videos is that what looks coordinated is actually proverse yaw into the turn. If it is a small amount, this is actually not that bad as it usually is just for an instant. Most of the time there is more than adequate air speed (unless in light thermals as written above) so nothing bad will happen as it gets the nose around quickly to point in the right direction again.

Once that is done, during 2 there usually is slip in the videos and is due to pilots not holding enough “in rudder” to keep coordinated. During 2, there may be a need for some opposite ail to keep the bank angle consistent where ail diff is non optimal.

During 3, is usually where severe adverse yaw occurs. This is usually the result of the pilot still holding some in rudder while ail are deflected the opposite way. However there is also the radii gyration of roll and while the lift vectors are still tilted, takes some time for the plane to roll upright so in the video it could look like the plane is “sliding” opposite of roll command.

With modern planes and building methods resulting in better mass distribution, it sure is easier to fly the plane closer to optimally than in years past. However it still comes down to what the pilots’ thumbs are able to do= setup your plane to meet your thumbs’ ability. Having said that, I am always trying to better my thumbs.
Say what??
Woodstock 1 is online now Find More Posts by Woodstock 1
Reply With Quote
Old Mar 07, 2014, 03:33 PM
Eggcellent...
tewatson's Avatar
United States, CA, Orange
Joined Oct 2006
2,461 Posts
Need some of this

Tom
tewatson is offline Find More Posts by tewatson
Reply With Quote
Old Mar 07, 2014, 06:08 PM
PaulG
Newcastle, NSW Australia
Joined Dec 2004
321 Posts
Angels on a pin head

In the middle ages it is said that philosophers would argue day and night about how many angels could stand on the head of a pin. This thread is threatening to go the same way. The fact is that sitting in a full sized glider you have the yaw string in front of you and can make adjustments to the rudder accordingly but most instructors recommended not chasing the yaw string because all the rudder movements are slewing the fuse around and producing more drag. Aileron differential in full sized gliders is, of course, fixed but to my knowledge is always used.
In our case we cannot see the aircraft well enough to tell within a fairly wide margin whether it is slipping or skidding and so my point is that the best we can do is to make the aircraft comfortable to fly and for it to "appear" to be flying in a coordinated fashion. My own yaw string experiments showed the yaw string making fairly wide excursions despite flying in fairly calm air. I have tried all the variations and always come back to about 2:1 diff with appropriate ail/rudder mix to get the tail moving round cleanly. I reduce my diff as the speed goes up. I can fly with the left thumb controlling the rudder but when I am really concentrating I just like the simplicity of flying with my right thumb (mode 2)
pigly is offline Find More Posts by pigly
Reply With Quote
Old Mar 07, 2014, 08:02 PM
LSF - IV
Hostage-46's Avatar
United States, TX, Highland Village
Joined Jan 2003
3,206 Posts
Oh good another thread on mental masturbation... I'm going out to practice landings.
Hostage-46 is online now Find More Posts by Hostage-46
Reply With Quote
Old Mar 07, 2014, 10:21 PM
Registered User
so. cal.
Joined Jan 2006
2,777 Posts
We need Tuan to weigh in again...
s2000 is online now Find More Posts by s2000
Reply With Quote
Old Mar 08, 2014, 04:58 AM
Thermal Wrangler
DrFragnasty's Avatar
Launceston Tasmania
Joined Mar 2004
2,145 Posts
Mode 2 Paul! Hallelujah!
We can fly each other's gliders ;0)
Everyone down here in Tas. flies mode one.
As for differential I just like to be different.
DrFragnasty is offline Find More Posts by DrFragnasty
Reply With Quote
Old Mar 08, 2014, 09:30 AM
Sink Stinks
Silent-AV8R's Avatar
Orange County, CA
Joined Aug 2004
4,533 Posts
My least favorite part of math was differential equations, so this topic is difficult for me.
Silent-AV8R is offline Find More Posts by Silent-AV8R
Reply With Quote
Old Mar 08, 2014, 09:50 AM
Daryl Perkins's Avatar
United States, VA, Falls Church
Joined Mar 2007
1,372 Posts
Now do you see why I closed the thread?

I've got a gorgeous day here, and a Vixen to go beat up. Have fun kids.

D
Daryl Perkins is offline Find More Posts by Daryl Perkins
Reply With Quote
Old Mar 08, 2014, 01:43 PM
PaulG
Newcastle, NSW Australia
Joined Dec 2004
321 Posts
Tassie

Well, I think I'd better move to Tassie then. We are stuck with a 400' height limit until The RAAF deems to meet with us. Our field is in a restricted zone and they have only just noticed we are here (despite flying at this field since the 70's, having a permit to 1000' and being marked on the approach map into Williamtown AFB).
Don't be mysterious about your diff, people will think you know something the rest of us don't.
Sorry to post a bit off topic but humour an old man
pigly is offline Find More Posts by pigly
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Differential phobia Daryl Perkins Multi Task F3X 247 Dec 10, 2011 11:38 AM
Discussion Anxiety/panic/phobia in children bildo baggins Life, The Universe, and Politics 25 Jan 13, 2011 06:22 AM
Help! Developed a rc flying phobia! Laggard Beginner Training Area (Aircraft-Electric) 21 Jun 11, 2007 08:09 AM
First major crash and I think I've developed a phobia tridim Parkflyers 9 Jul 24, 2005 11:04 PM