Dutch Roll    Gallery
View related threads: (in this forum | in all forums)

Logged in as Guest



Users viewing this topic: none
    Search This Thread  
 
Printable Version


Aviation Design Super Scorpion
Seller:  Modellbau USA
Details:   $6,750.00   |  5/24/2013   |  Classified Ad
We will rotate YOUR AD in this spot if you select "Forum Featured" when placing or editing your ad!

All Forums >> RC Airplanes >> Aerodynamics >> Dutch Roll
Page: [1]

Tower Hobbies Get Coupon Codes Brands  
Login
Message << Older Topic   Newer Topic >>
Dutch Roll - 5/6/2008 1:40 AM   
billf



Posts: 263
Score: 100
Joined: 2/1/2002
Last Login: 5/25/2013
From: Hudson, WI, USA
Status: offline 		Here's hoping someone can help me with remembering how to correct "dutch roll". Years ago, when flying
polyhedral aircraft such as the Zombie, there was a cure for the dutch roll. It involved making the vertical fin/rudder either
larger in area or smaller and I can't remember which!

I've converted a 44" wing span Zombie to electric with rudder and elevator for R/C, and I notice that it dutch rolls. Would
moving the CG farther forward help without fooling with the vertical fin/rudder dimensions?

Thanks in advance for any suggestions.

Bill F
Hudson, WI


Hide Signatures
       Post #: 1

RE: Dutch Roll - 5/6/2008 1:58 AM   
da Rock



Posts: 10888
Score: 265
Joined: 10/11/2005
Last Login: 5/25/2013
From: western, NC, USA
Status: offline 		http://en.wikipedia.org/wiki/Dutch_roll

_____________________________

Good flying wit ya today

Hide Signatures

(in reply to billf)
       Post #: 2

RE: Dutch Roll - 5/6/2008 1:59 AM   
gboulton



Posts: 3692
Score: 773
Joined: 5/28/2005
Last Login: 5/25/2013
From: La Vergne, TN, USA
Status: offline 		Given that the "problem" is caused by insufficient lateral area aft of the CG, and the resultant insufficient yaw dampening, I'd wager that increasing the size of the vertical fin would be the answer. That's merely an "educated guess", however.

_____________________________

¡ǝʌısuǝdxǝ sı dn puɐ dn sı uʍop ''pǝʇɹǝʌuı puɐ ʍo1 uǝɥʍ

Hide Signatures

(in reply to billf)
       Post #: 3

RE: Dutch Roll - 5/6/2008 2:05 AM   
da Rock



Posts: 10888
Score: 265
Joined: 10/11/2005
Last Login: 5/25/2013
From: western, NC, USA
Status: offline
quote:

ORIGINAL: billf

Here's hoping someone can help me with remembering how to correct "dutch roll". Years ago, when flying
polyhedral aircraft such as the Zombie, there was a cure for the dutch roll. It involved making the vertical fin/rudder either
larger in area or smaller and I can't remember which!

I've converted a 44" wing span Zombie to electric with rudder and elevator for R/C, and I notice that it dutch rolls. Would
moving the CG farther forward help without fooling with the vertical fin/rudder dimensions?

Thanks in advance for any suggestions.

Bill F
Hudson, WI




As mentioned in the article, full scale designers do things like add anhedral to big cargo high wing hulks. And some have used swept wing planforms on low wingers. More fin is what is usually suggested for our models.

_____________________________

Good flying wit ya today

Hide Signatures

(in reply to billf)
       Post #: 4

RE: Dutch Roll - 5/6/2008 11:22 AM   
pimmnz


 

Posts: 1895
Score: 148
Joined: 11/9/2005
Last Login: 5/26/2013
From: Auckland, NEW ZEALAND
Status: offline 		S'funny, I thought dutch roll was caused by too much fin area...
Evan, WB #12.

Hide Signatures

(in reply to da Rock)
       Post #: 5

RE: Dutch Roll - 5/6/2008 2:28 PM   
da Rock



Posts: 10888
Score: 265
Joined: 10/11/2005
Last Login: 5/25/2013
From: western, NC, USA
Status: offline
quote:

ORIGINAL: pimmnz

S'funny, I thought dutch roll was caused by too much fin area...
Evan, WB #12.



Actually, it's caused by an imbalance between the yaw stability and the roll stability. And truth is, it's cured by fixing or overpowering what ever is weak about the design that is causing it.

_____________________________

Good flying wit ya today

Hide Signatures

(in reply to pimmnz)
       Post #: 6

RE: Dutch Roll - 5/6/2008 2:57 PM   
B.L.E.



Posts: 1333
Score: 100
Joined: 8/27/2005
Last Login: 4/14/2010
From: Austin, TX, USA
Status: offline
quote:

ORIGINAL: pimmnz

S'funny, I thought dutch roll was caused by too much fin area...
Evan, WB #12.

Too much vertical fin causes spiral instability. Not enough causes dutch roll. Or so that is what I understand from reading the free flight articles in magazines.

Too much fin and the plane doesn't want to return to level flight on its own, instead it stays in a bank which gets steeper and steeper as the plane goes into a spiral dive.

Not enough fin and the plane doesn't just return to level flight on its own, it overshoots level flight and then re-overshoots, this is dutch roll.

Hide Signatures

(in reply to pimmnz)
       Post #: 7

RE: Dutch Roll - 5/6/2008 5:58 PM   
HalH


 

Posts: 630
Score: 100
Joined: 11/25/2002
Last Login: 3/6/2009
From: Madison, WI,
Status: offline 		I would like to suggest that all read the paragraph at http://thedutchroll.com/HomePage.html

Hide Signatures

(in reply to B.L.E.)
       Post #: 8

RE: Dutch Roll - 5/7/2008 4:57 AM   
Shoe



Posts: 335
Score: 113
Joined: 9/28/2003
Last Login: 10/21/2012
From: Stuttgart, GERMANY
Status: offline
quote:

ORIGINAL: da Rock
Actually, it's caused by an imbalance between the yaw stability and the roll stability. And truth is, it's cured by fixing or overpowering what ever is weak about the design that is causing it.


I'm not sure what you mean by roll stability. If you release a directionally stable airplane at an angle of sideslip, it will yaw to reduce the sideslip angle (or return to the trim sideslip angle if it's not zero). I think that's what you mean by yaw stability. If you put an airplane at an angle of bank with zero sideslip, there's nothing to make it roll back to the original bank angle (with zero sideslip, there is nothing to tell the airplane which direction to roll). If you allow sideslip, the aircraft might roll back toward wings level, but that's due to spiral stability, not "roll stability". I'm just trying to point out that the roll axis is fundamentally different from the pitch and yaw axes. If you apply a coordinated roll input, you will not get a second-order response like you will in pitch and yaw.


Hide Signatures

(in reply to da Rock)
       Post #: 9

RE: Dutch Roll - 5/7/2008 5:28 AM   
da Rock



Posts: 10888
Score: 265
Joined: 10/11/2005
Last Login: 5/25/2013
From: western, NC, USA
Status: offline
quote:

ORIGINAL: Shoe

quote:

ORIGINAL: da Rock
Actually, it's caused by an imbalance between the yaw stability and the roll stability. And truth is, it's cured by fixing or overpowering what ever is weak about the design that is causing it.


I'm not sure what you mean by roll stability.


What do "I" mean?
That's a direct quote from the definition of dutch roll where it mentions the cause.

_____________________________

Good flying wit ya today

Hide Signatures

(in reply to Shoe)
       Post #: 10

RE: Dutch Roll - 5/7/2008 7:54 AM   
Shoe



Posts: 335
Score: 113
Joined: 9/28/2003
Last Login: 10/21/2012
From: Stuttgart, GERMANY
Status: offline 		Must be a poor definition you are referring to

Hide Signatures

(in reply to da Rock)
       Post #: 11

RE: Dutch Roll - 5/7/2008 4:13 PM   
Strat2003


 

Posts: 1181
Score: 100
Joined: 3/10/2003
Last Login: 5/25/2013
From: Mt. Pleasant, OH, USA
Status: offline 		From experience....
In general, Dutch roll comes from too little fin area for the dihedral, or too much dihedral for the fin area.
Spiral instability comes from too much fin area for the dihedral, or too little dihedral for the fin area.

They can be fixed by changing either dihedral or fin area, which ever is more practical. That's usually adjusting the fin area, but I've done it both ways.

Hide Signatures

(in reply to Shoe)
       Post #: 12

RE: Dutch Roll - 5/7/2008 5:55 PM   
da Rock



Posts: 10888
Score: 265
Joined: 10/11/2005
Last Login: 5/25/2013
From: western, NC, USA
Status: offline 		Roll stability is demonstrated by our RC trainers coming back to level flight when they aren't level and our controls are restored to center. Yaw stability is what restores from yaw when that axis has been disturbed and the disturbance is removed.

Personally, I thought the wikipedia definition of Dutch Roll is decent enough as definitions go. And the reference was actually the link I included in Post #2 of this thread.












< Message edited by da Rock -- 5/7/2008 7:44 PM >

_____________________________

Good flying wit ya today

Hide Signatures

(in reply to Strat2003)
       Post #: 13

RE: Dutch Roll - 5/7/2008 7:04 PM   
billf



Posts: 263
Score: 100
Joined: 2/1/2002
Last Login: 5/25/2013
From: Hudson, WI, USA
Status: offline 		Thanks to all who offered suggestions to my original dilemma and confusion. Having read all the posts I am beginning to remember an article a number of years ago in Model Aviation (?) that showed a cartoon of a fellow with a big pair of scissors about to clip off part of the vertical fin on his model. The caption talked about correcting a problem. I think in this case the problem was spiral instability.

So what I plan to try is simply attaching a playing card with a clamp to the vertical fin to see what happens.

Thanks again for the responses.

BillF
Hudson, WI

Hide Signatures

(in reply to da Rock)
       Post #: 14

RE: Dutch Roll - 5/7/2008 7:22 PM   
CrateCruncher



Posts: 942
Score: 100
Joined: 10/14/2005
Last Login: 1/26/2013
From: Austin, TX, USA
Status: offline 		Billf,
I was just going to suggest this! Having tinkered with fin and rudder area myself, I learned that one needs to use something as stiff as the fin itself so the extension doesn't flop around confusing the result. I experimented with several sizes and shapes of sheet balsa covered in plastic film and attached on both sides of the fin with heavy packing tape. Good luck!
Crate.

_____________________________

"Never be seen with an ugly airplane."

Hide Signatures

(in reply to billf)
       Post #: 15

RE: Dutch Roll - 5/7/2008 7:39 PM   
da Rock



Posts: 10888
Score: 265
Joined: 10/11/2005
Last Login: 5/25/2013
From: western, NC, USA
Status: offline
quote:

ORIGINAL: billf

Thanks to all who offered suggestions to my original dilemma and confusion. Having read all the posts I am beginning to remember an article a number of years ago in Model Aviation (?) that showed a cartoon of a fellow with a big pair of scissors about to clip off part of the vertical fin on his model. The caption talked about correcting a problem. I think in this case the problem was spiral instability.

So what I plan to try is simply attaching a playing card with a clamp to the vertical fin to see what happens.

Thanks again for the responses.

BillF
Hudson, WI



Don't use a clamp.

Fold the card over and tape it. Generations and generations of modelers have done just that for years and years.

_____________________________

Good flying wit ya today

Hide Signatures

(in reply to billf)
       Post #: 16

RE: Dutch Roll - 5/7/2008 7:41 PM   
da Rock



Posts: 10888
Score: 265
Joined: 10/11/2005
Last Login: 5/25/2013
From: western, NC, USA
Status: offline 		It's also very easy to shape scrap balsa to fit and tape that. You get a lot better shape that is not apt to deform from the pressure of the airflow.

_____________________________

Good flying wit ya today

Hide Signatures

(in reply to da Rock)
       Post #: 17

RE: Dutch Roll - 5/20/2008 5:33 AM   
buzzard bait


 

Posts: 2490
Score: 115
Joined: 1/2/2003
Last Login: 5/26/2013
From: Ithaca, NY, USA
Status: offline 		In the future, you might want to reduce the dihedral when you do an RC version of an old timer like the Zombie. They don't need so much when built as RCs, and then you probably won't need more fin area.

Also, CG can affect Dutch Roll. I found this on my Goldberg Skylark, which had Dutch Roll when I moved the CG back to the rear limit, but was fine when it was moved forward. I assume it was because moving the CG back increased the side area in front of the CG and reduced it in back. The effect was very dramatic, and it worked after an attempt to add rudder area failed to solve the problem.

Jim

< Message edited by buzzard bait -- 5/20/2008 5:34 AM >

Hide Signatures

(in reply to da Rock)
       Post #: 18

RE: Dutch Roll - 1/27/2009 9:19 PM   
deothoric


 

Posts: 57
Score: 100
Joined: 7/2/2007
Last Login: 10/27/2011
From: Leesburg, VA, USA
Status: offline 		Not for nuthin' Boss but the webpage refered to is wrong in almost every statement. Starting with history "Dutch Roll" is the motion ascribed to a ship when it has wind and wave under side quarter stern. Absolutely the worst ships under these conditions were the 15th Century trading cogs the Dutch used, hence, Dutch Roll.

On the more recent statements, the statement seems to refer to "dihedral" as "tip above root" while talking about dynamic conditions. Mixed messages, since the swept wing mentioned will act dynamically as extra dyhedral. I'd go on but rather I suggest not quoting this page as a definition would be better. Thanks.


quote:

ORIGINAL: da Rock


quote:

ORIGINAL: Shoe

quote:

ORIGINAL: da Rock
Actually, it's caused by an imbalance between the yaw stability and the roll stability. And truth is, it's cured by fixing or overpowering what ever is weak about the design that is causing it.


I'm not sure what you mean by roll stability.


What do "I" mean?
That's a direct quote from the definition of dutch roll where it mentions the cause.



Hide Signatures

(in reply to da Rock)
       Post #: 19

RE: Dutch Roll - 1/27/2009 9:48 PM   
rmh



Posts: 12307
Score: 252
Joined: 12/12/2001
Last Login: 5/25/2013
From: , UT, USA
Status: offline 		On and on and on we go ( Da Rock got itright.)
This is like the ground effect stuff which became a farce in 3 acts.
some of the " aerodynamic"explanations were horribly off target
Dutch roll - is simply a "balancing/ rebalancing of forces" which is has just enough energy to allow an oscillation to set in

Simply taping a cup to the fuselage at some point FORWARD the CP will typically setup the problem -or at least a rudder lwagging at a fixed frequency
Old Buicks would do a "Dutch Roll which was deadly. On those old "ships of the boulevard" the combo of castor angle/ steering geometry , soft springing etc., would let the steering wheel, if moved sharply -then released , allow the car to roll in response - then the steering would self correct and the resulting lock to lock oscillation, rapidly set in. Shimmey in other cars was also a problem but nothing like the Buick issue.
same problem on ships, same on aircraft , same on control surfaces of aircraft
if the "self correcting force is "just right" a oscillation or flutter -or Dutch Roll -call it what you will , occurs.

_____________________________

Libby is still watching you

Hide Signatures

(in reply to deothoric)
       Post #: 20

RE: Dutch Roll - 1/27/2009 11:30 PM   
Taurus Flyer



Posts: 2371
Score: 123
Joined: 1/9/2004
Last Login: 5/25/2013
From: Almelo, NETHERLANDS
Status: offline 		Gents,

I did make a picture for you,

quote:

ORIGINAL: dick Hanson

On and on and on we go ( Da Rock got itright.)
This is like the ground effect stuff which became a farce in 3 acts.
some of the " aerodynamic"explanations were horribly off target
Dutch roll - is simply a "balancing/ rebalancing of forces" which is has just enough energy to allow an oscillation to set in

Simply taping a cup to the fuselage at some point FORWARD the CP will typically setup the problem -or at least a rudder lwagging at a fixed frequency
Old Buicks would do a "Dutch Roll which was deadly. On those old "ships of the boulevard" the combo of castor angle/ steering geometry , soft springing etc., would let the steering wheel, if moved sharply -then released , allow the car to roll in response - then the steering would self correct and the resulting lock to lock oscillation, rapidly set in. Shimmey in other cars was also a problem but nothing like the Buick issue.
same problem on ships, same on aircraft , same on control surfaces of aircraft
if the "self correcting force is "just right" a oscillation or flutter -or Dutch Roll -call it what you will , occurs.




Dutch Roll, continuous oscillation after horizontal piano impact in the tail, around two axles with phase shift so not to compare with flutter.

Cees (Dutchman)


Attachments
Click to see fullsize image.
Click for fullsize


< Message edited by Taurus Flyer -- 1/27/2009 11:38 PM >

Hide Signatures

(in reply to billf)
       Post #: 21

RE: Dutch Roll - 1/27/2009 11:43 PM   
rmh



Posts: 12307
Score: 252
Joined: 12/12/2001
Last Login: 5/25/2013
From: , UT, USA
Status: offline 		For what it's worth.
I used both occillation and flutter to clarify the idea that these cases are really the same.
It's all about motion becoming self perpetuating.
That's also why I mentioned the old Buick.
The car would roll wildly from side to side and the steering wheel would spin left to right. It was "rock n rollat it's finest -sorry I have no pictures or graphs but then -the "Galloping Gertie" bridge which failed and fell in the 1940's(?) also falls into this catagory and the wild twisting and swaying was well documented .
It's all related -


< Message edited by dick Hanson -- 1/27/2009 11:55 PM >

_____________________________

Libby is still watching you

Hide Signatures

(in reply to Taurus Flyer)
       Post #: 22

RE: Dutch Roll - 1/28/2009 7:23 PM   
Bax


 

Posts: 17300
Score: 169
Joined: 4/26/2002
Last Login: 5/24/2013
From: Champaign, IL, USA
Status: offline
quote:

ORIGINAL: dick Hanson

then -the "Galloping Gertie" bridge which failed and fell in the 1940's(?) also falls into this catagory and the wild twisting and swaying was well documented .
It's all related -



Ahh....the Tacoma Narrows Bridge. I remember seeing the film in physics class when I attended university. A classic demonstration of resonance once the threshold was reached. As long as the wind was blowing, the bridge kept twisting. I'd not be surprised if it wasn't on YouTube somewhere.

http://en.wikipedia.org/wiki/Tacoma_Narrows_Bridge



< Message edited by Bax -- 1/28/2009 7:26 PM >

_____________________________

Bill Baxter, Manager Hobby Services/Futaba Service/North America
3002 N. Apollo Dr. Ste. 1 Champaign, IL 61822 USA
Service Phone: 217 398-0007
Email: hobbyservices@hobbico.com

Hide Signatures

(in reply to rmh)
       Post #: 23

RE: Dutch Roll - 1/28/2009 9:28 PM   
Tall Paul



Posts: 5210
Score: 134
Joined: 6/23/2002
Last Login: 4/23/2013
From: Palmdale, CA, USA
Status: offline 		The videos from this plane as a twin were pretty awful until I increased the vertical area.
OTOH, on this Evans Slo-Mo-Shun, I had to reduce the vertical to eliminate a high-speed wiggle in yaw.
Dutch Roll in airplanes generally is said to look like this.. From the motion of the -shoulders- of the skater on the ice.

Attachments
Click to see fullsize image.
Click for fullsize 		Click to see fullsize image.
Click for fullsize 		Click to see fullsize image.
Click for fullsize 		Click to see fullsize image.
Click for fullsize


_____________________________

Sparky Paul
http://www.angelfire.com/indie/aerostuff

Hide Signatures

(in reply to Bax)
       Post #: 24

RE: Dutch Roll - 1/28/2009 10:40 PM   
rmh



Posts: 12307
Score: 252
Joined: 12/12/2001
Last Login: 5/25/2013
From: , UT, USA
Status: offline 		A lot of the rythmic rocking n rolling is due to the weight and/or weight arrangement of the craft.
The problem can often be cured by simply moving SOMETHING or removing weight
Just as in curing a flutter or a noise .

< Message edited by dick Hanson -- 1/28/2009 10:41 PM >

_____________________________

Libby is still watching you

Hide Signatures

(in reply to Tall Paul)
       Post #: 25

Page:   [1]
All Forums >> RC Airplanes >> Aerodynamics >> Dutch Roll
Page: [1]





Jump to:


 
Google 



Search | Marketplace | Event Calendar | Local Clubs | Magazine | Product Ratings | New Products | Discussion Forums

Photo Gallery | Instructor Search | Field|Track|Marina Search

Advertisers | Hobby Vendor Resources | Rate Manufacturers | Sign In/Sign Up

SITE MAP!   : :   FORUM RULES

RC Universe is a service of Internet Brands, Inc. Copyright © 2001-2013.

Charities we support that also need your help
Yorkie Rescue | Humane Society | ASPCA | Crohn's-Colitis America


1.266RCU1