Negative diehdral stabilizer  
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Negative diehdral stabilizer - 6/23/2008 5:11:23 PM   
windcosmic


 

Posts: 62
Joined: 2/1/2008
From: Vicenza, ITALY
Status: offline 		Hi! I noted than some pattern planes of the 70's had this feature. I am interested to know if it was only a fashion or if it has a stabilizing effect
       Post #: 1

RE: Negative diehdral stabilizer - 6/23/2008 9:44:43 PM   
js3



Posts: 1142
Joined: 1/30/2002
From: Arvada, CO, USA
Status: offline 		It's called anhedral.

I believe it was thought that it helped in knife-edge flight.

These guys will be able to tell you a lot more about it than I.

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I feel a lot more like I do now than I did earlier!

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       Post #: 2

RE: Negative diehdral stabilizer - 6/23/2008 10:40:51 PM   
PatternPilot



Posts: 528
Joined: 11/17/2002
From: Knoxville, TN, USA
Status: offline 		Here is some info by Dave Brown !!!

http://www.seniorpattern.com/Junk/Dave_Brown_on_anhedral_stab.pdf


Scott Anderson
SPA 239
www.rcfoamy.com & yes we have SPA planes !

(in reply to windcosmic)
       Post #: 3

RE: Negative diehdral stabilizer - 6/24/2008 5:39:21 AM   
Ed Cregger



Posts: 7745
Joined: 1/31/2002
From: Ringgold, GA, USA
Status: offline 		Boy, does that article bring back memories. As does the sliding tray mixer for the elevator/rudder servos. Yes, I well remember trying things like that sliding tray in order to obtain control surface mixing before the computerized radios were introduced. They worked just fine, but a CG change could be noticed when in use.

I like the looks of an anhedral stab on some models, but there are so many variables when using that feature that getting it right is mostly a matter of luck, or of building one heck of a lot of variations for testing.


Ed Cregger


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"Flying models since the Fifties - I'll get the hang of this yet!!!"

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RE: Negative diehdral stabilizer - 6/25/2008 12:01:19 PM   
RCDENT



Posts: 114
Joined: 5/6/2003
From: SAN ANTONIO, TX, USA
Status: offline 		Hanno Prettner's Curare was so successful in the late 70's that everyone started adding anhedral to the stabs. Many designs and kits incorporated anhedral and many flyers added it during construction because it was the "latest thing". In essence, it did become a "style" thing. I never heard of it having a detrimental effect on any particular design. I think the eventual conscences was that it solved roll/yaw coupling issues on certain planes (Curare and Tipo), but did nothing for others. I remember asking the designer of a popular pattern kit in that day what effect the anhedral stab had on his particular ship. The answer was "nothing, but we were worried it wouldn't sell without an anhedral stab".

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RE: Negative diehdral stabilizer - 6/25/2008 1:55:54 PM   
TFF


 

Posts: 742
Joined: 10/30/2006
From: Memphis, TN, USA
Status: online 		I thought that it helped both inside and outside manouvers. I read this somewhere; inside by slowing response for small corrections for a smoother look. Outside needed a bit more crisp control; no matter how good the plane flies upside down it still flies better right side up, and the extra bit of control balanced out the instability. One thing I think that is important is that Prettner designed his planes for himself like a custom set of golf clubs. He must have learned what helped his problems to gain perfection.

(in reply to RCDENT)
       Post #: 6

RE: Negative diehdral stabilizer - 6/25/2008 2:12:06 PM   
WEDJ



Posts: 1008
Joined: 2/21/2007
From: East Haddam, CT, USA
Status: offline 		The anhedral stab did several things, not all of which were good.

In KE flight, the lower stab half added effective "up" elevator, thereby eliminating the pitch down due to half the stab being blanketed by the fuselage (think angle of attack). Because most stabs provide up force in level flight, loosing stab meant pitch to the belly, which the anhedral cured.

An alternative to anhedral would be to slant the rudder hinge line, so that it has an up component in KE.

The bad part is that in crosswind gusts, the anhedral would cause a pitch up in level flight, creating a deviation from level.

The fact that it made pattern planes look like an F4 Phantom was cool factor, pure and simple.

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       Post #: 7

RE: Negative diehdral stabilizer - 6/25/2008 7:33:57 PM   
flywilly


 

Posts: 861
Joined: 2/3/2002
From: glen allen, VA,
Status: offline 		After a long absence (like 2 decades) the anhedral stab has emerged on a few current designs (from Japan - Naruke seems to be experimenting with it). Prettner used it on his Curare and Magic designs then eliminated it from his 'basic' Calypso model. I think the anhedral stab was as much a fad as a 'factor'. I'm sure Hanno had good reason for using it, but many appeared on designs which orginally had flat stabs. Getting the correct placement and correct anhedral angle requires some sophisticated math or a lot of cut and try.
I wonder if anybody built a Curare with a flat stab and how it flew? I have my own theories...
-Will

(in reply to WEDJ)
       Post #: 8

RE: Negative diehdral stabilizer - 6/25/2008 8:01:29 PM   
rainedave



Posts: 5190
Joined: 7/21/2005
From: Greensboro, NC, USA
Status: online 		I have a short kit for Prettner's Super Sicroly II that I plan to build someday. It is the design that preceded the Curare and has a straight stab. I have no earthly idea how it compares to the Curare.

David

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(in reply to flywilly)
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RE: Negative diehdral stabilizer - 6/25/2008 8:48:46 PM   
Ed Cregger



Posts: 7745
Joined: 1/31/2002
From: Ringgold, GA, USA
Status: offline 		To me, it was just a fad.

A show on the Military Channel a few days ago said that anhedral was used to correct some severe problems with the F-4 Phantom II's handling. A bandaid, in other words. I always liked the appearance, but always doubted its utility.

Now that we are flying models that do not resemble jets in their handling, airspeed or maneuvers, the day of anhedral stabs has ended as far as current FAI pattern is concerned. Perhaps some of we OF's (Old Folks) will use it to make our models period correct, but, like others have voiced, I wonder just how some of the older pattern ships would handle with the anhedral stab replaced with a standard flat stab.

Ed Cregger


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RE: Negative diehdral stabilizer - 6/25/2008 9:00:40 PM   
windcosmic


 

Posts: 62
Joined: 2/1/2008
From: Vicenza, ITALY
Status: offline 		Thank you, guys!

(in reply to Ed Cregger)
       Post #: 11

RE: Negative diehdral stabilizer - 6/25/2008 9:07:24 PM   
UStik


 

Posts: 146
Joined: 10/28/2006
From: Augsburg, GERMANY
Status: offline 		Just to contribute to the confusion, here's an excerpt from Hanno's own build article that still comes with the FMT plans (blame me for bad / too literal translation):

For Curare, completely new wing and stab airfoils were employed as well as a new setup - compared to the Super Sicroly. The most burning question I was always asked was: Why and for what benefit an anhedral stab? My answer is that it was the most crucial development, which should be used only together with the especially matched airfoils, though, because otherwise the exact opposite may be readily achieved. It has been found in the wind tunnel that optimum steady flight of the model is achieved in all weather effects and besides landings are more steady, too, meaning the model flies perfectly at high as well as at low speed.

What airfoils, which wind tunnel test he might refer to? Only slogans? Is here an expert who could clarify?

(in reply to rainedave)
       Post #: 12

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